uN1 <3 malignant perirectal lymph nodes uN2 >3 malignant perirectal lymph nodes Level 4, carcinoma invading into the submucosa of the bowel wall below the stalk of the polyp. By definition, all sessile polyps with invasive adenocarcinoma are Level 4.

They studied 129 patients with pTis to pT1 colorectal tumors and noted that Level 4 invasion was a statistically significant factor (p<0.001) predicting positive nodes. Similar results were reported by Nivatvongs et al. (23) on 151 patients with pT1 colorectal tumors undergoing bowel resection in which invasion into the submucosa of the bowel wall at the base of the stalk (Level 4) was the single most significant risk factor for positive nodes. For sessile polyps the risk was 10% and for pedunculated polyps 27%. Suzuky et al. (24) determined the risk of lymph node metastases in 65 patients having Haggitt's Level 4 invasion into the submucosa. Lymph node metastasis was noted in 11 (16.9%) of the 65 patients, however the width of submucosal invasion was significantly greater in nodepositive than in node-negative patients (p=0,001). When 5mm wide submucosal invasion was used as an indicator for intestinal resection, 37 patients were found to have indications for bowel resection and 11 (29.7%) had lymph node metastases. The positive predictive value increased from 17 to 30% when the width of submucosal invasion was added to Haggitt's Level 4 as an indicator for bowel resection. Seitz et al. (25) suggested that Haggitt's classification applies well for pedunculated polyps, however it should not be used for malignant sessile polyps.

Fig. 2. Villous rectal lesion are characterized at ultrasonography by a broadening of the first hypoechoic layer and an intact hyperechoic submucosal interface

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 57

only independent risk factor for lymph node metastasis. Akasu et al. (28) recently proposed

2. SM-massive (SM-m), tumor invasion extended to the middle or lower third of the

In their series, the prevalence of lymph node metastasis in pTis, pT1-slight and pT1-massive were 0%, 0% and 22%, respectively. Thus massive submucosal invasion can be considered a risk factor for lymph node metastasis. They suggested that patients with massive submucosal invasion are best treated by radical surgery. A recent study from Mayo Clinic confirmed these data (29). Among patients with T1 carcinoma in the middle or lower third of the rectum the multivariate risk factors for long-term, cancer-free survival was invasion into the lower third of the submucosa. For lesions with SM-3 invasion, the radical surgical resection group had lower rates of distant metastasis and better survival compared with patients who underwent local excision (29, 30). Therefore a decision whether to perform radical surgery or local excision or polypectomy should be based principally on assessment

1. benign lesion (uT0): hypoechoic mass within the second hypoechoic mucosal layer. The submucosal hyperechoic layer remains intact around the entire breadth of the tumor; Carcinoma in situ (pTis) is included in this group because it cannot be differentiated

2. submucosal cancer (uT1): tumor invading the submucosal layer. These lesions are stratified into two subtypes: uT1-slight (slightly irregularity of the submucosa) (Figure 4) and uT1-massive (massive irregularity) (Figure 5). Small focal disruption of the submucosal layer but with the fourth hypoechoic muscular layer intact are also

3. lesions with distinct break of the submucosal layer and invasion of the muscular layer

Over- and under-staging of rectal tumors continues to be a problem with ERUS due to a variety of well-documented causes as reported by Adams and Wong (21) and Kim et al. (31). A source of error can be due to the compression of the rectal wall by the water-filled balloon. To prevent any distortion of the lesion or separation of the balloon from the rectal wall with the interposition of non-conductive air between the probe and the rectum, a sufficient quantity of water can be instilled to fill the entire rectum. In this case the transducer is covered with a condom that does not cause compression of the rectal wall as with the balloon. A source of errors in the evaluation of early rectal cancer by ERUS can also frequently be caused by examiner misinterpretation or a tendency to overestimate a malignant lesion because of concern for under-treatment despite clear ERUS imaging.

Sonographic diagnosis of tumor invasion of the muscularis propria is based on thickening of this layer (Figure 6). The muscularis propria is represented by a thin hypoechoic layer adjacent to the hyperechoic submucosal interface. As the tumor is also hypoechoic, early muscular invasion is difficult to detect. The surrounding hyperechoic layer corresponding to the perirectal fat interface remains intact. Lymph node metastases occur in approximately 15-20% of patients with T2 tumors. ERUS is important to distinguish uT2 and uT1 lesions,

because local therapy is not routinely recommended for uT2 rectal lesions (30).

1. SM-slight (SM-s), tumor invasion limited to the upper third of the submucosa;

Our ERUS criteria to determine the depth of tumor invasion are as follows:

from benign adenoma by ultrasound imaging alone;

a classification of the depth of submucosal cancer into two groups:

submucosa.

of submucosal invasion depth.

classified as uT1-massive tumor;

**5.3 Stage uT2: Invasion of the muscular layer**

(uT2).

Fig. 3. Very large exophytic villous adenoma may cause technical difficulties during scanning

Kudo et al. (26) were the first to differentiate three different types of early invasive cancers:

Type SM-1 tumors were further subdivided in three subtypes:

Kikuchi et al. (27) found that the risk of lymph node metastasis was 0% for SM-1 lesions, 10% for SM-2 lesions and 25% for SM-3 lesions (p<0.001). In their study the SM-3 was the

Fig. 3. Very large exophytic villous adenoma may cause technical difficulties during

1. SM-1 tumor, invading the superior third of the submucosa;

3. SM-3 tumor, invading the deep third of the submucosa. Type SM-1 tumors were further subdivided in three subtypes:

1. SM-1a: invasion is <1/4 of the submucosa; 2. SM-1b: invasion is <1/2 of the submucosa; 3. SM-1c: invasion is >1/2 of the submucosa.

2. SM-2 tumor, invading the superficial two thirds of the submucosa;

Kudo et al. (26) were the first to differentiate three different types of early invasive cancers:

Kikuchi et al. (27) found that the risk of lymph node metastasis was 0% for SM-1 lesions, 10% for SM-2 lesions and 25% for SM-3 lesions (p<0.001). In their study the SM-3 was the

scanning

only independent risk factor for lymph node metastasis. Akasu et al. (28) recently proposed a classification of the depth of submucosal cancer into two groups:

In their series, the prevalence of lymph node metastasis in pTis, pT1-slight and pT1-massive were 0%, 0% and 22%, respectively. Thus massive submucosal invasion can be considered a risk factor for lymph node metastasis. They suggested that patients with massive submucosal invasion are best treated by radical surgery. A recent study from Mayo Clinic confirmed these data (29). Among patients with T1 carcinoma in the middle or lower third of the rectum the multivariate risk factors for long-term, cancer-free survival was invasion into the lower third of the submucosa. For lesions with SM-3 invasion, the radical surgical resection group had lower rates of distant metastasis and better survival compared with patients who underwent local excision (29, 30). Therefore a decision whether to perform radical surgery or local excision or polypectomy should be based principally on assessment of submucosal invasion depth.

Our ERUS criteria to determine the depth of tumor invasion are as follows:

Over- and under-staging of rectal tumors continues to be a problem with ERUS due to a variety of well-documented causes as reported by Adams and Wong (21) and Kim et al. (31). A source of error can be due to the compression of the rectal wall by the water-filled balloon. To prevent any distortion of the lesion or separation of the balloon from the rectal wall with the interposition of non-conductive air between the probe and the rectum, a sufficient quantity of water can be instilled to fill the entire rectum. In this case the transducer is covered with a condom that does not cause compression of the rectal wall as with the balloon. A source of errors in the evaluation of early rectal cancer by ERUS can also frequently be caused by examiner misinterpretation or a tendency to overestimate a malignant lesion because of concern for under-treatment despite clear ERUS imaging.

#### **5.3 Stage uT2: Invasion of the muscular layer**

Sonographic diagnosis of tumor invasion of the muscularis propria is based on thickening of this layer (Figure 6). The muscularis propria is represented by a thin hypoechoic layer adjacent to the hyperechoic submucosal interface. As the tumor is also hypoechoic, early muscular invasion is difficult to detect. The surrounding hyperechoic layer corresponding to the perirectal fat interface remains intact. Lymph node metastases occur in approximately 15-20% of patients with T2 tumors. ERUS is important to distinguish uT2 and uT1 lesions, because local therapy is not routinely recommended for uT2 rectal lesions (30).

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 59

Fig. 6. Sonographic diagnosis of tumor invasion of the muscularis propria (uT2) is based on

Overstaging is a particular problem with T2 tumors. Among the interpretative errors, severe inflammatory infiltrate underlying a tumor, which is sonographically indistinguishable from malignant tissue, can prohibit accurate evaluation of tumor invasion and appears to cause inevitable errors (32, 33).  These findings should be associated with disruption of the hyperechoic layer corresponding to the submucosa and thickening of the hyperechoic layer representing the muscularis propria (Figure 7). Contiguous organs are not involved. About 10% of such tumors are, however, accompanied by a narrowing of the lumen or angulation that may render it difficult or impossible to advance the probe proximal to the tumor. To perform a complete staging by ERUS, a residual lumen of 2cm is necessary. Under these circumstances the study may be incomplete and the presence of enlarged lymph nodes may not be ascertained accurately

thickening of this layer

**5.4 Stage uT3: Perirectal fat invasion**

(32, 33, 34).

Fig. 4. uT1-slight cancer are characterized at ultrasonography by a broadening of the first hypoechoic layer and a slightly irregularity of the hyperechoic submucosal interface

Fig. 5. uT1-massive cancer are characterized at ultrasonography by a broadening of the first hypoechoic layer and a massive irregularity or a small focal disruption of the hyperechoic submucosal interface. The fourth hypoechoic muscular layer appears intact

Fig. 4. uT1-slight cancer are characterized at ultrasonography by a broadening of the first hypoechoic layer and a slightly irregularity of the hyperechoic submucosal interface

Fig. 5. uT1-massive cancer are characterized at ultrasonography by a broadening of the first hypoechoic layer and a massive irregularity or a small focal disruption of the hyperechoic

submucosal interface. The fourth hypoechoic muscular layer appears intact

Fig. 6. Sonographic diagnosis of tumor invasion of the muscularis propria (uT2) is based on thickening of this layer

Overstaging is a particular problem with T2 tumors. Among the interpretative errors, severe inflammatory infiltrate underlying a tumor, which is sonographically indistinguishable from malignant tissue, can prohibit accurate evaluation of tumor invasion and appears to cause inevitable errors (32, 33).  These findings should be associated with disruption of the hyperechoic layer corresponding to the submucosa and thickening of the hyperechoic layer representing the muscularis propria (Figure 7). Contiguous organs are not involved. About 10% of such tumors are, however, accompanied by a narrowing of the lumen or angulation that may render it difficult or impossible to advance the probe proximal to the tumor. To perform a complete staging by ERUS, a residual lumen of 2cm is necessary. Under these circumstances the study may be incomplete and the presence of enlarged lymph nodes may not be ascertained accurately

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 61

poor prognosis. Moreover, identification of a metastatic perirectal lymph node is important as these patients may benefit from pre-operative adjuvant radiotherapy and some of the early T1 or T2 lesions with mesorectal node involvement are not suitable for local excision. Sonographic evaluation of lymph node metastases is somewhat less accurate than depth of invasion (16, 18, 19, 34, 35). Undetectable or benign appearing lymph nodes are classified as uN0. Malignant appearing lymph nodes are classified as uN1 (<3 lymph nodes) or uN2 (>3 lymph nodes). Normal, non-enlarged perirectal nodes are not usually seen on ERUS. The criteria used to identify metastatic lymph nodes in most of the studies are echogenicity, border demarcation and node diameter. Inflamed, enlarged lymph nodes appear hypoechoic, with ill defined borders. Most of the sound energy is reflected because the lymphatic tissue has not changed. In contrast, metastatic lymph nodes that have been completely replaced by the tumor do not provide the normal tissue architecture and appear hypoechoic with an echogenicity similar to the primary tumor. Malignant lymph nodes tend to be round in shape rather than oval, have discrete borders and are most commonly found adjacent to the primary tumor or in the mesorectum proximal to the tumor (15) (Figure 9). The sonographic features of lymph nodes generally can be distinguished into four groups: 1. if lymph nodes are not visible by ultrasound, the probability of lymph node metastasis

2. hyperechoic lymph nodes are often benign and result from non-specific inflammatory

3. hypoechoic lymph nodes larger than 5mm are highly suggestive for lymph node

4. lymph nodes larger than 5mm with mixed echogenic patterns cannot be classified

On size characteristic alone, sonographically detected nodes in the mesorectum greater than 5mm in diameter have a 50-70% chance of being involved, whereas those smaller than 4mm have less than 20% chance. However, up to 20% of patients have involved nodes of less than 3mm, limiting the accuracy of the technique. Hulsmans et al (37) studied several features by correlating pathologic and sonographic findings in the lymph nodes of specimens obtained from a series of 21 consecutive patients with resected rectal cancer. These features included ratio of long axis to short axis diameter, referred as to roundness index; lobulations (multiple notches); echogenicity; not homogeneous; border delineation; presence of an echopoor rim (the outer rim being more hypoechoic than the rest of the node); presence of a peripheral halo; and presence of a hilar reflection. The authors showed that three ultrasonographic features of a node significantly correlated to it being benign or malignant at histopathologic examination are: short axis diameter, degree of inhomogeneity and the

Overstaging and understaging may occur during assessment of lymph node involvement. Edematous lymph nodes transmit more sound energy and have an echogenicity similar to metastases. The cross-sectional appearance of blood vessels in the perirectal fat may be commonly confused with positive lymph nodes. The sonographic continuity of hypoechoic vessels over a distance greater than the cross-sectional diameter is the criterion used to distinguish vessels from hypoechoic lymph nodes. With careful scanning, blood vessels appear to branch or extend longitudinally. In addition, it may be difficult to differentiate islands of tumor outside the bowel wall from involved nodes. With careful scanning, one can demonstrate continuity with the main tumor that may not have been recognised initially. Even with an improved understanding of the characteristic of malignant lymph

accurately but should be considered metastatic.

presence or absence of hilar reflection.

is low;

changes;

metastasis;

because nodes are often located proximal to the tumor. The prevalence of regional lymph node metastases in uT3 tumors is approximately 30-50%.

The recognition of perirectal fat invasion is an important determination to select appropriate patients for pre-operative combined chemotherapy and radiation therapy followed by surgery. One of the most important drawbacks in endosonographic staging is the distinction between T2 tumors invading most of the muscularis propria and T3 tumor which slightly invades the perirectal fat. Indeed most errors are understaging of small pT3 tumors or overstaging of pT2 tumors (35, 36).

Fig. 7.  These advanced lesions are clinically fixed or tethered. Sonographically there is a loss of the normal hyperechoic interface between the tumor and the adjacent organ. The inability of ERUS to distinguish between malignant infiltration or peritumoral inflammation results in a somewhat lower staging accuracy with regard to T4 cancers. Frank stenosis also precludes precise endosonographic evaluation and angulation of the probe to the tumor axis also can cause misinterpretation.

#### **5.6 Stage uN1-2: Lymph node metastases**

Metastatic involvement of the mesorectal lymph nodes is a major independent prognostic factor. It has been observed that the presence of more than three nodes is associated with a

because nodes are often located proximal to the tumor. The prevalence of regional lymph

The recognition of perirectal fat invasion is an important determination to select appropriate patients for pre-operative combined chemotherapy and radiation therapy followed by surgery. One of the most important drawbacks in endosonographic staging is the distinction between T2 tumors invading most of the muscularis propria and T3 tumor which slightly invades the perirectal fat. Indeed most errors are understaging of small pT3 tumors or

Fig. 7. Perirectal fat invasion (uT3) is diagnosed sonographically by the presence of irregularity of the outer hyperechoic layer that corresponds to the perirectal fat interface

angulation of the probe to the tumor axis also can cause misinterpretation.

uT4 lesions are locally invasive into contiguous organs such as bladder, uterus, cervix, vagina, prostate and seminal vesicles (Figure 8). These advanced lesions are clinically fixed or tethered. Sonographically there is a loss of the normal hyperechoic interface between the tumor and the adjacent organ. The inability of ERUS to distinguish between malignant infiltration or peritumoral inflammation results in a somewhat lower staging accuracy with regard to T4 cancers. Frank stenosis also precludes precise endosonographic evaluation and

Metastatic involvement of the mesorectal lymph nodes is a major independent prognostic factor. It has been observed that the presence of more than three nodes is associated with a

node metastases in uT3 tumors is approximately 30-50%.

overstaging of pT2 tumors (35, 36).

**5.5 Stage uT4: Extensive local invasion**

**5.6 Stage uN1-2: Lymph node metastases**

poor prognosis. Moreover, identification of a metastatic perirectal lymph node is important as these patients may benefit from pre-operative adjuvant radiotherapy and some of the early T1 or T2 lesions with mesorectal node involvement are not suitable for local excision.

Sonographic evaluation of lymph node metastases is somewhat less accurate than depth of invasion (16, 18, 19, 34, 35). Undetectable or benign appearing lymph nodes are classified as uN0. Malignant appearing lymph nodes are classified as uN1 (<3 lymph nodes) or uN2 (>3 lymph nodes). Normal, non-enlarged perirectal nodes are not usually seen on ERUS. The criteria used to identify metastatic lymph nodes in most of the studies are echogenicity, border demarcation and node diameter. Inflamed, enlarged lymph nodes appear hypoechoic, with ill defined borders. Most of the sound energy is reflected because the lymphatic tissue has not changed. In contrast, metastatic lymph nodes that have been completely replaced by the tumor do not provide the normal tissue architecture and appear hypoechoic with an echogenicity similar to the primary tumor. Malignant lymph nodes tend to be round in shape rather than oval, have discrete borders and are most commonly found adjacent to the primary tumor or in the mesorectum proximal to the tumor (15) (Figure 9).

The sonographic features of lymph nodes generally can be distinguished into four groups:

On size characteristic alone, sonographically detected nodes in the mesorectum greater than 5mm in diameter have a 50-70% chance of being involved, whereas those smaller than 4mm have less than 20% chance. However, up to 20% of patients have involved nodes of less than 3mm, limiting the accuracy of the technique. Hulsmans et al (37) studied several features by correlating pathologic and sonographic findings in the lymph nodes of specimens obtained from a series of 21 consecutive patients with resected rectal cancer. These features included ratio of long axis to short axis diameter, referred as to roundness index; lobulations (multiple notches); echogenicity; not homogeneous; border delineation; presence of an echopoor rim (the outer rim being more hypoechoic than the rest of the node); presence of a peripheral halo; and presence of a hilar reflection. The authors showed that three ultrasonographic features of a node significantly correlated to it being benign or malignant at histopathologic examination are: short axis diameter, degree of inhomogeneity and the presence or absence of hilar reflection.

Overstaging and understaging may occur during assessment of lymph node involvement. Edematous lymph nodes transmit more sound energy and have an echogenicity similar to metastases. The cross-sectional appearance of blood vessels in the perirectal fat may be commonly confused with positive lymph nodes. The sonographic continuity of hypoechoic vessels over a distance greater than the cross-sectional diameter is the criterion used to distinguish vessels from hypoechoic lymph nodes. With careful scanning, blood vessels appear to branch or extend longitudinally. In addition, it may be difficult to differentiate islands of tumor outside the bowel wall from involved nodes. With careful scanning, one can demonstrate continuity with the main tumor that may not have been recognised initially. Even with an improved understanding of the characteristic of malignant lymph

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 63

Fig. 9. Malignant lymph nodes appear as round hypoechoic structure, with discrete borders,

The improved understanding of rectal cancer biologic behavior mandates for a correct staging of the disease to allow tailored treatment in relation to the stage of the tumor. There is general agreement that villous adenomas with focal areas of carcinoma in situ and early T1 rectal cancers are best treated with local surgery, whereas advanced T1 and T2 rectal cancers because of the well known risk of associated nodal metastases, are best cured with radical surgery. Early T3 cancers may be safely treated with radical surgery alone or a short course of preoperative radiotherapy, while advanced T3, T3N1-2, T4N0-1-2 lesions mandate neoadjuvant chemotherapy-radiotherapy regimens to attempt to downstage the tumours

(38, 39). Furthermore, staging is linked to ultimate prognostic outcome of the patient. Systemic staging of rectal cancer is best achieved by contrast-enhanced thoraco-abdominopelvic multidetector CT scan. This is justified by the general availability of the device, the costs and the short duration time of the examination required to achieve good quality images and for the ability to reconstruct images into planes other than the axial plan alone (e.g. sagittal, frontal, oblique planes). For local staging of rectal cancer, CT accuracy is limited by the intrinsic difficulty to define the layers of rectal wall and thus the depth of penetration of the lesion. In the study of Rifkin et al. (18), 81 patients underwent CT and ERUS for staging purposes of rectal cancer; the accuracy of CT in assessing depth of rectal

adjacent to the primary tumor

**6. Discussion**

node and utilizing criteria of shape, echogenicity and border features, micrometastases and granulomatous inflammation will remain difficult, if not impossible, to differentiate by ERUS. If a whole node is replaced by tumor or the node is enlarged secondary to it, detection is more likely. However, if only a small deposit or a micrometastasis is present in a node, the characteristics of the node are unlikely to be sufficiently altered to allow detection. This explains in part the lower accuracy rate for lymph node detection with current, conventional ultrasonography. Grossly malignant lymph nodes located at a distance from the primary tumor also remain undetected if they exceed the depth of penetration of the transducer. This is particularly true for nodes in the proximal mesorectum out of the length of the probe. To obtain high sensitivity and high specificity, the combination of a small cutoff value and ERUS-guided fine needle aspiration biopsy may be helpful.

Fig. 8. uT4 lesion with invasion of the vaginal wall

Fig. 9. Malignant lymph nodes appear as round hypoechoic structure, with discrete borders, adjacent to the primary tumor

#### **6. Discussion**

62 Rectal Cancer – A Multidisciplinary Approach to Management

node and utilizing criteria of shape, echogenicity and border features, micrometastases and granulomatous inflammation will remain difficult, if not impossible, to differentiate by ERUS. If a whole node is replaced by tumor or the node is enlarged secondary to it, detection is more likely. However, if only a small deposit or a micrometastasis is present in a node, the characteristics of the node are unlikely to be sufficiently altered to allow detection. This explains in part the lower accuracy rate for lymph node detection with current, conventional ultrasonography. Grossly malignant lymph nodes located at a distance from the primary tumor also remain undetected if they exceed the depth of penetration of the transducer. This is particularly true for nodes in the proximal mesorectum out of the length of the probe. To obtain high sensitivity and high specificity, the combination of a small

cutoff value and ERUS-guided fine needle aspiration biopsy may be helpful.

Fig. 8. uT4 lesion with invasion of the vaginal wall

The improved understanding of rectal cancer biologic behavior mandates for a correct staging of the disease to allow tailored treatment in relation to the stage of the tumor. There is general agreement that villous adenomas with focal areas of carcinoma in situ and early T1 rectal cancers are best treated with local surgery, whereas advanced T1 and T2 rectal cancers because of the well known risk of associated nodal metastases, are best cured with radical surgery. Early T3 cancers may be safely treated with radical surgery alone or a short course of preoperative radiotherapy, while advanced T3, T3N1-2, T4N0-1-2 lesions mandate neoadjuvant chemotherapy-radiotherapy regimens to attempt to downstage the tumours (38, 39). Furthermore, staging is linked to ultimate prognostic outcome of the patient.

Systemic staging of rectal cancer is best achieved by contrast-enhanced thoraco-abdominopelvic multidetector CT scan. This is justified by the general availability of the device, the costs and the short duration time of the examination required to achieve good quality images and for the ability to reconstruct images into planes other than the axial plan alone (e.g. sagittal, frontal, oblique planes). For local staging of rectal cancer, CT accuracy is limited by the intrinsic difficulty to define the layers of rectal wall and thus the depth of penetration of the lesion. In the study of Rifkin et al. (18), 81 patients underwent CT and ERUS for staging purposes of rectal cancer; the accuracy of CT in assessing depth of rectal

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 65

second recent meta-analysis comprised 31 studies and reported ERUS sensitivity rate related

The sensitivity and specificity of ERUS in staging rectal cancer after polypectomy was evaluated in two papers. Garcia-Aguilar et al. (53) assessed 63 patients with malignant rectal polyps removed by snare excision at colonoscopy. ERUS accuracy in evaluating the presence of residual cancer in the rectal wall was 54%, with 39% of positive predictive value and 65% of negative predictive value. Furthermore ERUS accurately identified metastatic lymph nodes in two of three patients who had radical surgery. ERUS was more useful than polyp morphologic and histologic criteria to determine the presence of residual cancer in the rectal wall. Kruskal et al. (54) reported 18 patients who had ERUS staging before surgical resection for adenocarcinoma discovered in polypectomy specimens (5 transanal surgery, 13 endoscopic surgery). ERUS correctly predicted T stage in eight patients (44%); seven tumors (39%) were overstaged and three tumors (17%) were understaged. In this study, ERUS showed a sensitivity of 94%, specificity of 50%, accuracy of 89%, positive predictive value of 94% and negative predictive value of 50%. They concluded that ERUS facilitates surgical planning and should be considered the technique of choice in staging this patient population, always keeping in mind the limits of ERUS staging when performed after biopsy or polypectomy (edema, blood clots, and inflammatory reaction) could interfere with

A recent study (55) evaluated 142 patients to characterize slight or massive irregularity of the hyperechoic submucosal layer to differentiate uT1-slight or uT1 massive tumors. ERUS correctly detected the depth of invasion in 87.2% of patients with a concordance between ultrasonographic and histopathologic staging of kappa 0.81 (95% confidence interval). The recognition of early from massive T1 rectal cancers consequently selected the appropriate management in 95.2% of cases. Akasu et al. (28) reported the result of a study on 154 patients with early stage rectal cancer preoperatively evaluated with ERUS. Sensitivity, specificity and overall accuracy rates for detection of slight or massive submucosal invasion were 99%, 74%, 96% and 98%, 88%, 97% respectively. Pikarsky (56) from Cleveland Clinic showed that ERUS confirmed the histopathologic diagnosis of rectal villous tumor without evidence of malignancy in 26 out of 27 patients. Konishi et al. (57) reported that the overall accuracy of ERUS-based evaluation of tumor invasion depth was 60% in villous lesions and 91% in non-villous lesions. In differentiating mucosa neoplasias (M)/ submucosal cancers with slight invasion (SM-s) from non M/SM-s the accuracy of ERUS in villous and nonvillous lesions was 66% and 96%, respectively. Akahoshi et al. (58) improved the accuracy of ERUS by using a high-frequency ultrasound probe (12MHz). The depth of invasion was correctly assessed in 87% (46/53) of pT1 tumors. Stark et al. (59) reported their experience with high multifrequency probes. The sensitivity of ERUS with regard to invasion was 89% (16/18), specificity 88% (37/42), and accuracy 88% (53/60). They concluded that rectal endosonography can distinguish between benign rectal lesions and early invasive rectal cancers. Similar results were reported by Hunerbein et al. (60) with a high frequency miniprobe in the staging of colonic tumors. The infiltration depth was correctly classified in 78 of 88 patients (accuracy, 87%). We conducted a prospective study to compare accuracy of 3D-ERUS with high frequency probe to conventional 2D-ERUS in the preoperative staging of early invasive rectal cancer (61): eighty-nine consecutive patients with rectal villous lesions were examined using both 3D-ERUS and conventional 2D-ERUS. All lesions were resected either endoscopically or surgically. Malignant transformation was found in 35 rectal villous adenomas at histological examination. 2D-ERUS correctly determined the

to the stage of 76%, 75%, 88% and 87% respectively (52).

a good imaging, leading to over- or understaging the tumor.

wall invasion was 53%, compared with 72% for ERUS. Beynon et al. (40) compared ERUS to CT for the evaluation of mesorectal nodal status; they found that the accuracy of CT was only 57%, compared with 87% for ERUS. More recently Herzog et al. (41) examined 87 patients who underwent both CT and ERUS; they found accuracy of CT to be 74.7%, whereas ERUS had an accuracy of 90.,8%. In the study of Goldman et al. (42) the accuracy in defining perirectal fat invasion was 52% for CT scanning vs. 81% for ERUS; the accuracy was respectively 64% vs. 68% for lymph node metastases. The best results in rectal staging with CT scan are reported by Civelli et al. (43) with an accuracy of 86.8% for T3 stage, a sensitivity of 100% and a specificity of 78.7%. In lymph node staging, the referred accuracy was 73.6%, sensitivity was 52.6% and specificity was 85.3%. In summary, the accuracy of CT is highly variable and should not be used as a sole method of staging rectal cancer (42).

ERUS is currently the most widely used and effective staging modality in the local assessment of rectal cancer. Its accuracy in numerous trials ranges from 80 to 95% for Tstaging and 70 to 75% for N-staging, levels that are slightly higher than the respective 75 to 85% and 60 to 70% reported with MRI (44). In experienced hands, ERUS can accurately measure size, circumference and distance of the tumor from various anatomic landmarks (e.g. sphincters, prostate, vagina, seminal vesicles, mesorectal fascia, etc.) and gives indications to radiotherapists to plan irradiation fields (depth and length of infiltration). Furthermore it is capable of examining the anal sphincters for defects as well as tumor infiltration, allowing the surgeon to decide whether a sphincter-saving resection is safe or feasible (45). The accuracy of ERUS has been assessed in many studies and the main evidence emerged has been that T-staging accuracy varies relative to tumor stage. ERUS tends to be less accurate in staging T2 rectal cancers that are often overstaged (44, 46, 47). Orrom et al. (48) evaluated 59 patient who underwent ERUS and radical resection for rectal cancer. The patients were divided into three categories chronologically based on user experience. Group 1 had no standardization of the operator who performed the exam. The accuracy of this group was only 58%, with 37% of lesions that were overstaged and 4% of tumors that were understaged. Group 2 was based on a better standardization in the performance of the exam. In this group a proctoscope was used to improve localization of the rectal cancer. The accuracy increased to 77%, with 20% of cancers overstaged and 3% understaged. Group 3 adopted the widely accepted division of rectal wall into five layers. Accuracy rate increased to 95% with only 5% overstaging and no understaging. Garcia-Aguilar et al. (47) undertook a large retrospective study to assess the accuracy of ERUS on 545 patients, who underwent rectal surgery without neoadjuvant treatment. The overall accuracy of ERUS in assessing depth of penetration of the tumor into the rectal wall was 69%, with 18% of tumors overstaged and 13% understaged. Furthermore, ERUS correctly staged most villous adenomas (accuracy 87%) but less than half of T1 tumors (accuracy 47%). A selection bias of this study is represented by the exclusion from the final analysis of all patients (270 patients) who received neoadjuvant radiation/chemotherapy. A systematic literature review from Worrell et al. (49) showed that ERUS correctly established a cancer diagnosis in 81% of 62 biopsy-negative rectal adenomas which had focal carcinoma on histopathology. Beynon (50) examined 111 patients, of whom 100 undewent surgical resection; the accuracy was 93% for tumor staging, and the sensitivity for T3 and T4 stage was 98.7%. Overstaging occurred in 5% cases and understaging occurred 2% of cases. Two recent meta-analysis, based the first on 11 studies reported that the sensitivity of ERUS in correctly staging T1, T2, T3, T4 rectal cancers was 84%, 76%, 88%, 87% respectively (51). The

wall invasion was 53%, compared with 72% for ERUS. Beynon et al. (40) compared ERUS to CT for the evaluation of mesorectal nodal status; they found that the accuracy of CT was only 57%, compared with 87% for ERUS. More recently Herzog et al. (41) examined 87 patients who underwent both CT and ERUS; they found accuracy of CT to be 74.7%, whereas ERUS had an accuracy of 90.,8%. In the study of Goldman et al. (42) the accuracy in defining perirectal fat invasion was 52% for CT scanning vs. 81% for ERUS; the accuracy was respectively 64% vs. 68% for lymph node metastases. The best results in rectal staging with CT scan are reported by Civelli et al. (43) with an accuracy of 86.8% for T3 stage, a sensitivity of 100% and a specificity of 78.7%. In lymph node staging, the referred accuracy was 73.6%, sensitivity was 52.6% and specificity was 85.3%. In summary, the accuracy of CT is highly variable and should not be used as a sole method of staging rectal cancer (42). ERUS is currently the most widely used and effective staging modality in the local assessment of rectal cancer. Its accuracy in numerous trials ranges from 80 to 95% for Tstaging and 70 to 75% for N-staging, levels that are slightly higher than the respective 75 to 85% and 60 to 70% reported with MRI (44). In experienced hands, ERUS can accurately measure size, circumference and distance of the tumor from various anatomic landmarks (e.g. sphincters, prostate, vagina, seminal vesicles, mesorectal fascia, etc.) and gives indications to radiotherapists to plan irradiation fields (depth and length of infiltration). Furthermore it is capable of examining the anal sphincters for defects as well as tumor infiltration, allowing the surgeon to decide whether a sphincter-saving resection is safe or feasible (45). The accuracy of ERUS has been assessed in many studies and the main evidence emerged has been that T-staging accuracy varies relative to tumor stage. ERUS tends to be less accurate in staging T2 rectal cancers that are often overstaged (44, 46, 47). Orrom et al. (48) evaluated 59 patient who underwent ERUS and radical resection for rectal cancer. The patients were divided into three categories chronologically based on user experience. Group 1 had no standardization of the operator who performed the exam. The accuracy of this group was only 58%, with 37% of lesions that were overstaged and 4% of tumors that were understaged. Group 2 was based on a better standardization in the performance of the exam. In this group a proctoscope was used to improve localization of the rectal cancer. The accuracy increased to 77%, with 20% of cancers overstaged and 3% understaged. Group 3 adopted the widely accepted division of rectal wall into five layers. Accuracy rate increased to 95% with only 5% overstaging and no understaging. Garcia-Aguilar et al. (47) undertook a large retrospective study to assess the accuracy of ERUS on 545 patients, who underwent rectal surgery without neoadjuvant treatment. The overall accuracy of ERUS in assessing depth of penetration of the tumor into the rectal wall was 69%, with 18% of tumors overstaged and 13% understaged. Furthermore, ERUS correctly staged most villous adenomas (accuracy 87%) but less than half of T1 tumors (accuracy 47%). A selection bias of this study is represented by the exclusion from the final analysis of all patients (270 patients) who received neoadjuvant radiation/chemotherapy. A systematic literature review from Worrell et al. (49) showed that ERUS correctly established a cancer diagnosis in 81% of 62 biopsy-negative rectal adenomas which had focal carcinoma on histopathology. Beynon (50) examined 111 patients, of whom 100 undewent surgical resection; the accuracy was 93% for tumor staging, and the sensitivity for T3 and T4 stage was 98.7%. Overstaging occurred in 5% cases and understaging occurred 2% of cases. Two recent meta-analysis, based the first on 11 studies reported that the sensitivity of ERUS in correctly staging T1, T2, T3, T4 rectal cancers was 84%, 76%, 88%, 87% respectively (51). The second recent meta-analysis comprised 31 studies and reported ERUS sensitivity rate related to the stage of 76%, 75%, 88% and 87% respectively (52).

The sensitivity and specificity of ERUS in staging rectal cancer after polypectomy was evaluated in two papers. Garcia-Aguilar et al. (53) assessed 63 patients with malignant rectal polyps removed by snare excision at colonoscopy. ERUS accuracy in evaluating the presence of residual cancer in the rectal wall was 54%, with 39% of positive predictive value and 65% of negative predictive value. Furthermore ERUS accurately identified metastatic lymph nodes in two of three patients who had radical surgery. ERUS was more useful than polyp morphologic and histologic criteria to determine the presence of residual cancer in the rectal wall. Kruskal et al. (54) reported 18 patients who had ERUS staging before surgical resection for adenocarcinoma discovered in polypectomy specimens (5 transanal surgery, 13 endoscopic surgery). ERUS correctly predicted T stage in eight patients (44%); seven tumors (39%) were overstaged and three tumors (17%) were understaged. In this study, ERUS showed a sensitivity of 94%, specificity of 50%, accuracy of 89%, positive predictive value of 94% and negative predictive value of 50%. They concluded that ERUS facilitates surgical planning and should be considered the technique of choice in staging this patient population, always keeping in mind the limits of ERUS staging when performed after biopsy or polypectomy (edema, blood clots, and inflammatory reaction) could interfere with a good imaging, leading to over- or understaging the tumor.

A recent study (55) evaluated 142 patients to characterize slight or massive irregularity of the hyperechoic submucosal layer to differentiate uT1-slight or uT1 massive tumors. ERUS correctly detected the depth of invasion in 87.2% of patients with a concordance between ultrasonographic and histopathologic staging of kappa 0.81 (95% confidence interval). The recognition of early from massive T1 rectal cancers consequently selected the appropriate management in 95.2% of cases. Akasu et al. (28) reported the result of a study on 154 patients with early stage rectal cancer preoperatively evaluated with ERUS. Sensitivity, specificity and overall accuracy rates for detection of slight or massive submucosal invasion were 99%, 74%, 96% and 98%, 88%, 97% respectively. Pikarsky (56) from Cleveland Clinic showed that ERUS confirmed the histopathologic diagnosis of rectal villous tumor without evidence of malignancy in 26 out of 27 patients. Konishi et al. (57) reported that the overall accuracy of ERUS-based evaluation of tumor invasion depth was 60% in villous lesions and 91% in non-villous lesions. In differentiating mucosa neoplasias (M)/ submucosal cancers with slight invasion (SM-s) from non M/SM-s the accuracy of ERUS in villous and nonvillous lesions was 66% and 96%, respectively. Akahoshi et al. (58) improved the accuracy of ERUS by using a high-frequency ultrasound probe (12MHz). The depth of invasion was correctly assessed in 87% (46/53) of pT1 tumors. Stark et al. (59) reported their experience with high multifrequency probes. The sensitivity of ERUS with regard to invasion was 89% (16/18), specificity 88% (37/42), and accuracy 88% (53/60). They concluded that rectal endosonography can distinguish between benign rectal lesions and early invasive rectal cancers. Similar results were reported by Hunerbein et al. (60) with a high frequency miniprobe in the staging of colonic tumors. The infiltration depth was correctly classified in 78 of 88 patients (accuracy, 87%). We conducted a prospective study to compare accuracy of 3D-ERUS with high frequency probe to conventional 2D-ERUS in the preoperative staging of early invasive rectal cancer (61): eighty-nine consecutive patients with rectal villous lesions were examined using both 3D-ERUS and conventional 2D-ERUS. All lesions were resected either endoscopically or surgically. Malignant transformation was found in 35 rectal villous adenomas at histological examination. 2D-ERUS correctly determined the

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 67

There is a marked reduction in survival rate in patients with rectal cancer and nodal metastases. Ultrasonographic criteria for distinguishing malignant from inflammatory lymph nodes are a source of controversy. The criteria of echogenicity and border characteristics are subjective, although at least one study has shown that as many as 72% of nodes with hypoechoic patterns are metastatic (70). Nodal size as a criterion to consider a node to be metastatic is a matter of debate. Whilst metastatic lymph nodes tend to be larger than normal nodes, the 3 to 5mm diameter used as a cutoff is quite arbitrary. Kim et al. (51) reported that roughly 18% of nodes measuring less than 5mm in diameter harboured metastases. Akasu et al. (28) found that the incidence of metastasis in nodes with diameter around 2mm, 3 to 5mm and >6mm was 9.5%, 47% and 87%, respectively. These data suggest that ERUS can miss up to 20% of these smaller nodes. The accuracy of ERUS in assessing lymph node involvement varies from 58% to 86% (35). In a recent meta-analysis by Puli et al. (71), in which only studies confirmed by surgical histology were selected, the sensitivity of ERUS in diagnosing nodal involvement by rectal cancers was 73.2% and specificity was of 75.8%. In this meta-analysis was evaluated also the influence of fine needle aspiration (FNA) during the procedure that resulted in very low or not complications. However, there were not enough studies to draw definitive conclusions on the accuracy of FNA. The potential bias of this meta-analysis was that all the studies were either retrospective or consecutive, but no prospective studies were included. The authors concluded that sensitivity and specificity of ERUS for nodal involvement was moderate. It performs better when there is no anatomic nodal invasion than in the presence of anatomic nodal invasion. Further refinement in ERUS technologies and re-evaluation of diagnostic criteria based on prospective studies are needed to improve our diagnostic accuracy. The theoretic additional value of ERUS-guided FNA on suspicious nodes, was addressed by Siddiqui et al. (71). They found no benefits in using FNA, because all perirectal node large enough to be visualized by ERUS were confirmed to harbour metastases. In their initial experience of ultrasonographic rectal staging, Holdsworth et al. (72) used a 5.5MHz transducer. They identified lymph node metastases with a sensitivity of 57% and specificity of 64%, concluding that the technique is not reliable to identify metastases. With the growing experience of the operator, the modernization of the probes (introduction of multifrequencies probes) and with the introduction of 3D-dedicated software, Kim et al. (65) reported that lymph node metastases were accurately predicted by 3D-ERUS in 84.8% of patients, whereas 2D-ERUS predicted the disorder in 66.7%. Although their findings did not show 3D-ERUS to have a statistically significant advantage over 2D-ERUS, stereoscopic visualization provided easier and more

Accuracy of ERUS is highly dependent on operator experience. The capability to perform an accurate examination is crucial for the acquisition of high quality images and for the interpretation of the study. The presence of an uniform acoustic contact is essential for the production of good ultrasonographic images. The position of the probe in relation to the tumor is critical. Whether tumor site (in terms of height) and position (with respect to rectal circumference) has an influence on the reliability of ERUS staging is not settled as yet. Sentovich et al. (74) and Senesse at al. (75) reported significantly better result for tumors of the distal third. The reason for the less accurate staging in the lower rectum is a technical one, because it is the difficult to reach all sites of the rectum with a rigid probe. This consideration prompted us to develop a new dedicated proctoscope to allow easy passage of

complete understanding of lymph nodes.

depth of invasion of villous polyps in 6 of 7 M neoplasias (85.7%), 8 of 12 SM-s lesions (66.6%) and 12 of 16 SM-m lesions (75%), whereas the accuracy of 3D-ERUS was 85.7% for M neoplasias, 83.3% for SM-s and 87.5% for SM-m lesions. Overall accuracy of the 2D-ERUS based evaluation of villous lesions was lower than that of 3D-ERUS based evaluation (27/35, 77.1%, vs. 30/35, 85.7%), however there was no significant difference (p=0.5). In the evaluation of SM-s lesions the accuracy of 3D-ERUS was significantly superior to 2D-ERUS based evaluation (p<0.029). Tumor location and gross morphology (sessile or pedunculated did not correlate with the accuracy of the T-staging. Eight of 54 pT0 tumors (14.8%) were overstaged by 2D-ERUS, while 5 of 54 (9.2%) were overstaged by 3D-ERUS. The prevalence of lymph node metastases in M, SM-s and SM-m lesions were 0%, 0% and 12.5%, respectively. These findings showed 3D-ERUS to have a significant advantage over 2D-ERUS for the accurate evaluation of superficial submucosal cancer invasion. Stereoscopic visualization provided easier and more complete understanding of depth of submucosal invasion.

Overstaging is a particular problem with T2 tumors. Peritumoral inflammation and desmoplastic changes are commonly causes of error, as both are difficult to differentiate from actual tumor borders. Overstaging may also be the result of preoperative biopsies, that can create hematomas, edema, clots due to bleeding and disrupt sonographic anatomy. Fear of understaging is another cause that has been described as responsible of overstaging in T2 rectal cancers (63). In general, the time interval between performance of diagnostic tests and the reference test (pathology on surgical specimen) should be short. A longer period between the performance of the diagnostic test and the reference test will lead to a greater change in the disease status and decrease in the discriminatory power of the diagnostic test. Potential bias of several studies is that the time elapsed between test and surgery was not described or was longer than the ideal of one week. In a prospective study Sailer et al. (62) examined the value of ERUS in the preoperative staging of 160 rectal tumors. For T2 tumors, the sensitivity was only 41% and the specificity 92% as the majority of pT2 rectal cancers were overstaged (uT3). The authors concluded that ERUS is not helpful in the assessment of T2 carcinomas. Katsura et al (64) reported that the predictive value of positive rate in the assessment of rectal wall invasion by ERUS was 96.2% in uT1 and 87.5% in uT2.

3D-ERUS offers a significant advantage over conventional 2D-ERUS for the accurate evaluation of rectal cancer. In a preliminary study, Kim et al. (65) showed that the accuracy of 3D-ERUS was 90.9% for pT2 whereas that of 2D-ERUS was 84.8%. It is of note that the classification system is highly reproducible through the use of cut-off points that are usually straightforward histologically, such as the distinction between T2 and T3 tumor depending on the invasion of the mesorectum or not. This does not always easily transfer to staging through imaging. All imaging methods are good enough to show the bulk of the tumor, but have difficulty in predicting the microscopic invasion of an interface. It is therefore unrealistic to expect 100% accuracy from imaging technology in predicting a histologic classification (66). Glaser et al. (67) reported that the sensitivity of ERUS for detection of perirectal fat infiltration (uT3) was 97%, specificity was 90% and positive predictive value was 90%. The inability of ERUS to distinguish between fat infiltration or peritumoral inflammation results in somewhat lower staging accuracy with regard to T4 cancers. In conclusion, the overall agreement between uT-stage and pTstage in the larger studies is 63% to 69%, with 12% to 15% understaging and 18% to 24% overstaging (44, 47, 68, 69). In these series there was understaging of uT1 between 6% to 24%, and of uT2 tumor from 16% to 30%. Overstaging in uT3 occurred in 20% to 28% of cases.

depth of invasion of villous polyps in 6 of 7 M neoplasias (85.7%), 8 of 12 SM-s lesions (66.6%) and 12 of 16 SM-m lesions (75%), whereas the accuracy of 3D-ERUS was 85.7% for M neoplasias, 83.3% for SM-s and 87.5% for SM-m lesions. Overall accuracy of the 2D-ERUS based evaluation of villous lesions was lower than that of 3D-ERUS based evaluation (27/35, 77.1%, vs. 30/35, 85.7%), however there was no significant difference (p=0.5). In the evaluation of SM-s lesions the accuracy of 3D-ERUS was significantly superior to 2D-ERUS based evaluation (p<0.029). Tumor location and gross morphology (sessile or pedunculated did not correlate with the accuracy of the T-staging. Eight of 54 pT0 tumors (14.8%) were overstaged by 2D-ERUS, while 5 of 54 (9.2%) were overstaged by 3D-ERUS. The prevalence of lymph node metastases in M, SM-s and SM-m lesions were 0%, 0% and 12.5%, respectively. These findings showed 3D-ERUS to have a significant advantage over 2D-ERUS for the accurate evaluation of superficial submucosal cancer invasion. Stereoscopic visualization provided easier and more complete understanding of depth of submucosal

Overstaging is a particular problem with T2 tumors. Peritumoral inflammation and desmoplastic changes are commonly causes of error, as both are difficult to differentiate from actual tumor borders. Overstaging may also be the result of preoperative biopsies, that can create hematomas, edema, clots due to bleeding and disrupt sonographic anatomy. Fear of understaging is another cause that has been described as responsible of overstaging in T2 rectal cancers (63). In general, the time interval between performance of diagnostic tests and the reference test (pathology on surgical specimen) should be short. A longer period between the performance of the diagnostic test and the reference test will lead to a greater change in the disease status and decrease in the discriminatory power of the diagnostic test. Potential bias of several studies is that the time elapsed between test and surgery was not described or was longer than the ideal of one week. In a prospective study Sailer et al. (62) examined the value of ERUS in the preoperative staging of 160 rectal tumors. For T2 tumors, the sensitivity was only 41% and the specificity 92% as the majority of pT2 rectal cancers were overstaged (uT3). The authors concluded that ERUS is not helpful in the assessment of T2 carcinomas. Katsura et al (64) reported that the predictive value of positive rate in the

assessment of rectal wall invasion by ERUS was 96.2% in uT1 and 87.5% in uT2.

30%. Overstaging in uT3 occurred in 20% to 28% of cases.

3D-ERUS offers a significant advantage over conventional 2D-ERUS for the accurate evaluation of rectal cancer. In a preliminary study, Kim et al. (65) showed that the accuracy of 3D-ERUS was 90.9% for pT2 whereas that of 2D-ERUS was 84.8%. It is of note that the classification system is highly reproducible through the use of cut-off points that are usually straightforward histologically, such as the distinction between T2 and T3 tumor depending on the invasion of the mesorectum or not. This does not always easily transfer to staging through imaging. All imaging methods are good enough to show the bulk of the tumor, but have difficulty in predicting the microscopic invasion of an interface. It is therefore unrealistic to expect 100% accuracy from imaging technology in predicting a histologic classification (66). Glaser et al. (67) reported that the sensitivity of ERUS for detection of perirectal fat infiltration (uT3) was 97%, specificity was 90% and positive predictive value was 90%. The inability of ERUS to distinguish between fat infiltration or peritumoral inflammation results in somewhat lower staging accuracy with regard to T4 cancers. In conclusion, the overall agreement between uT-stage and pTstage in the larger studies is 63% to 69%, with 12% to 15% understaging and 18% to 24% overstaging (44, 47, 68, 69). In these series there was understaging of uT1 between 6% to 24%, and of uT2 tumor from 16% to

invasion.

There is a marked reduction in survival rate in patients with rectal cancer and nodal metastases. Ultrasonographic criteria for distinguishing malignant from inflammatory lymph nodes are a source of controversy. The criteria of echogenicity and border characteristics are subjective, although at least one study has shown that as many as 72% of nodes with hypoechoic patterns are metastatic (70). Nodal size as a criterion to consider a node to be metastatic is a matter of debate. Whilst metastatic lymph nodes tend to be larger than normal nodes, the 3 to 5mm diameter used as a cutoff is quite arbitrary. Kim et al. (51) reported that roughly 18% of nodes measuring less than 5mm in diameter harboured metastases. Akasu et al. (28) found that the incidence of metastasis in nodes with diameter around 2mm, 3 to 5mm and >6mm was 9.5%, 47% and 87%, respectively. These data suggest that ERUS can miss up to 20% of these smaller nodes. The accuracy of ERUS in assessing lymph node involvement varies from 58% to 86% (35). In a recent meta-analysis by Puli et al. (71), in which only studies confirmed by surgical histology were selected, the sensitivity of ERUS in diagnosing nodal involvement by rectal cancers was 73.2% and specificity was of 75.8%. In this meta-analysis was evaluated also the influence of fine needle aspiration (FNA) during the procedure that resulted in very low or not complications. However, there were not enough studies to draw definitive conclusions on the accuracy of FNA. The potential bias of this meta-analysis was that all the studies were either retrospective or consecutive, but no prospective studies were included. The authors concluded that sensitivity and specificity of ERUS for nodal involvement was moderate. It performs better when there is no anatomic nodal invasion than in the presence of anatomic nodal invasion. Further refinement in ERUS technologies and re-evaluation of diagnostic criteria based on prospective studies are needed to improve our diagnostic accuracy. The theoretic additional value of ERUS-guided FNA on suspicious nodes, was addressed by Siddiqui et al. (71). They found no benefits in using FNA, because all perirectal node large enough to be visualized by ERUS were confirmed to harbour metastases. In their initial experience of ultrasonographic rectal staging, Holdsworth et al. (72) used a 5.5MHz transducer. They identified lymph node metastases with a sensitivity of 57% and specificity of 64%, concluding that the technique is not reliable to identify metastases. With the growing experience of the operator, the modernization of the probes (introduction of multifrequencies probes) and with the introduction of 3D-dedicated software, Kim et al. (65) reported that lymph node metastases were accurately predicted by 3D-ERUS in 84.8% of patients, whereas 2D-ERUS predicted the disorder in 66.7%. Although their findings did not show 3D-ERUS to have a statistically significant advantage over 2D-ERUS, stereoscopic visualization provided easier and more complete understanding of lymph nodes.

Accuracy of ERUS is highly dependent on operator experience. The capability to perform an accurate examination is crucial for the acquisition of high quality images and for the interpretation of the study. The presence of an uniform acoustic contact is essential for the production of good ultrasonographic images. The position of the probe in relation to the tumor is critical. Whether tumor site (in terms of height) and position (with respect to rectal circumference) has an influence on the reliability of ERUS staging is not settled as yet. Sentovich et al. (74) and Senesse at al. (75) reported significantly better result for tumors of the distal third. The reason for the less accurate staging in the lower rectum is a technical one, because it is the difficult to reach all sites of the rectum with a rigid probe. This consideration prompted us to develop a new dedicated proctoscope to allow easy passage of

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 69

correctly identified all patients. In the preoperative identification of tumors with unfavorable prognosis, ERUS correctly identified 32 out of 39 (82%) patients and MRI correctly identified 33 out of 39 (85%) tumors. In the preoperative identification of locally advanced tumors (28 cases), only one was successfully identified using ERUS; in 12 patients, tumor could not be assessed because not reached by the probe or because of pain experienced by the patient. In 15 patients, tumor deposits involving the mesorectal fascia had not been identified. MRI successfully identified 22 out of 28 patients with locally advanced tumors. In four patients, nodes close to the mesorectal fascia had not been detected. In each of these cases, nodes were partially replaced by small tumor foci that were not resolved on MR images. In two patients tumor was thought to have breached the wall anteriorly by <1mm, but histopathologic examination showed stage pT4 peritoneal infiltration by the tumor. In a metaanalysis by Bipat et al (80), ERUS was found to be the most accurate staging modality when compared to CT and MRI imaging for evaluation of local invasion of rectal cancer. For lymph node involvement, the results were comparable, with low sensitivity values. ERUS was used to evaluate only perirectal or mesorectal lymph nodes, whereas CT and MRI were also used to evaluate iliac and mesenteric or retroperitoneal lymph nodes. In a large recent European multicenter study (81), MRI showed an agreement in T-staging of 57% with 19% overstaging and 24% understaging. It was also very accurate in predicting the extramural depth of tumor invading the mesorectum. MRI was able to identify large T3 and T4 tumors and invasion of the mesorectal fascia. Because of the accurate depiction of large tumoral mass, it is often said that with MRI "what you see is what you get" (66). Most failures of MRI occur in the differentiation between T1 and T2 lesions and between T2 and borderline T3 lesions. A T1 tumor cannot be reliably distinguished from T2 because the submucosal layer is generally not visualized on phased array MRI. Like ERUS, MRI has some difficulty in differentiating lesions on the border of T2 and T3 from a desmoplastic reaction. MRI with endorectal coils has been studied in a number of small size studies for the evaluation and staging of rectal tumors (82). With the addition of endorectal surface coils to conventional MR imaging, spatial resolution has increased and anatomic definition improved. T2-weighted turbo spin-echo sequences allow to distinguish the five layers of the rectal wall. Rectal carcinoma in T2-weighted turbo spin-echo sequences has medium-to-low signal intensity, higher than the muscular layer. MRI and ERUS demonstrate similar efficacy in the preoperative staging of rectal tumors. Overall accuracy rates of 70-90% have been reported for staging of rectal tumors using MRI with endorectal coils. However, coils are too expensive and not used worldwide. A further limitation of MRI with endoanal coils is the inability to advance the coil through a stricture caused by advanced rectal cancer. In the evaluation of lymph nodes, MRI does not offer

significant improvement in accuracy rates compared with ERUS.

guide the resection in advanced cases.

In conclusion, ERUS is currently the best modality for the preoperative staging of rectal cancer. It is not alternative, but rather complementary to high-resolution MRI. Future improvements may include the possibility to visualize the mesorectal fascia or to better evaluate lymph nodes less than 5mm in diameter. ERUS is much less expensive than MRI and it can be readily used in the office, immediately providing important information for treatment planning. MRI has the advantage, over ERUS, that the images can be more easily interpreted and evaluated by other radiologists, clinicians and oncologists. The images can also be used by radiotherapists for planning the radiotherapy fields and by surgeons to

the probe above the rectal lesion. We performed a prospective study to determine whether tumor site and tumor position would influence the accuracy of 3D-ERUS staging. (13). ERUS was performed on 173 consecutive patients with primary rectal cancer. In 65 patients the tumor was located 0.1-6cm from the anal verge (lower rectal tumor), 77 patients had tumors 7-12cm from the anal verge (middle rectal tumor) and 31 tumors were 13-18cm form the anal verge (upper rectal tumors). With regard to position, 46 tumors were situated anteriorly, 30 in the left lateral wall, 43 posteriorly and 42 in the right lateral wall. In 12 patients the tumor occupied two-thirds of the rectal circumference. All lesions were resected either endoscopically or surgically. ERUS correctly predicted the depth of invasion in 62/65 (95.3%) lower rectal tumors, 74/77 (96.1%) middle rectal tumors and 28/31 (90.3%) upper rectal tumors. With regard to position, accuracy was 93.4% for tumors located anteriorly, 90.4% for tumors in the right lateral rectal wall, 90.6% for tumors located posteriorly and 86.6% for tumors in the left lateral rectal wall. The accuracy of 3D-ERUS for lymph node metastases, assessed in 142 patients, was 44/46 (95.6%) for lower rectal tumors, 61/65 (93.8%) for middle rectal tumors and 28/31 (90.3%) for upper rectal tumors. Our analysis showed that there was no difference between the different positions, which means that all tumors are equally amenable to ERUS staging if they are within reach of the probe. Tumors situated on the haustral folds are often overstaged because of artifacts induced by tangential imaging. Air bubbles trapped from unfilled space in the rectal vault due to insufficient inflation, produce strong acoustic shadowing and prevent visualization of deeper tissues (75). The impact of tumor level on ERUS accuracy is controversial. Sailer et al. (76) have suggested impaired visualization of tumors located in both the proximal and distal rectum. In their study, 162 tumors were divided into three groups based on tumor location. Reduced accuracy in the staging of low rectal tumors has been attributed to the anatomy of the rectum, who makes it difficult to maintain uniform acoustic contact and properly orientation of the probe. Another explanation is poor definition of the five sonographic layers just above the dentate line, particularly along the posterior wall (47, 75).

A number of comparative studies have been performed to assess the efficacy of ERUS and MRI. Some studies have shown clear supremacy of ERUS, whereas other have shown little difference. MRI as with CT, is accurate in assessing spread of the tumor beyond the rectal wall, invasion of contiguous structures, spread to regional lymph nodes or distant metastases. The lateral pelvic nodes, such as the obturator nodes, are located too far from the rectum to be imaged effectively with ERUS. Therefore, possible advantages of MRI may lie with assessment of the lateral pelvic lymph nodes, pelvic wall invasion and involvement of levator ani muscle. Previously, MRI was not able to delineate the layers of the rectal wall. With high resolution techniques, thin slice MRI can be used to measure the depth of extramural spread accurately, with good correlation with corresponding pathology measurement in surgical specimens (78). Furthermore the relationship of tumor to the mesorectal fascia can be evaluated so that CRM positive status can be predicted when tumor is imaged within 1mm from the mesorectal fascia. Brown et al. (79) evaluated the effectiveness of digital examination, ERUS and MRI in staging rectal cancer in 98 patients undergoing total mesorectal excision with pathology as the gold standard. ERUS correctly identified 14 out of 31 (45%) tumors with favorable prognosis (in two cases extramural depth was overestimated; in the remaining 15 patients, failure to reach the tumor using the EUS probe resulted in inability to assess tumor depth). In this category of patients, MRI

the probe above the rectal lesion. We performed a prospective study to determine whether tumor site and tumor position would influence the accuracy of 3D-ERUS staging. (13). ERUS was performed on 173 consecutive patients with primary rectal cancer. In 65 patients the tumor was located 0.1-6cm from the anal verge (lower rectal tumor), 77 patients had tumors 7-12cm from the anal verge (middle rectal tumor) and 31 tumors were 13-18cm form the anal verge (upper rectal tumors). With regard to position, 46 tumors were situated anteriorly, 30 in the left lateral wall, 43 posteriorly and 42 in the right lateral wall. In 12 patients the tumor occupied two-thirds of the rectal circumference. All lesions were resected either endoscopically or surgically. ERUS correctly predicted the depth of invasion in 62/65 (95.3%) lower rectal tumors, 74/77 (96.1%) middle rectal tumors and 28/31 (90.3%) upper rectal tumors. With regard to position, accuracy was 93.4% for tumors located anteriorly, 90.4% for tumors in the right lateral rectal wall, 90.6% for tumors located posteriorly and 86.6% for tumors in the left lateral rectal wall. The accuracy of 3D-ERUS for lymph node metastases, assessed in 142 patients, was 44/46 (95.6%) for lower rectal tumors, 61/65 (93.8%) for middle rectal tumors and 28/31 (90.3%) for upper rectal tumors. Our analysis showed that there was no difference between the different positions, which means that all tumors are equally amenable to ERUS staging if they are within reach of the probe. Tumors situated on the haustral folds are often overstaged because of artifacts induced by tangential imaging. Air bubbles trapped from unfilled space in the rectal vault due to insufficient inflation, produce strong acoustic shadowing and prevent visualization of deeper tissues (75). The impact of tumor level on ERUS accuracy is controversial. Sailer et al. (76) have suggested impaired visualization of tumors located in both the proximal and distal rectum. In their study, 162 tumors were divided into three groups based on tumor location. Reduced accuracy in the staging of low rectal tumors has been attributed to the anatomy of the rectum, who makes it difficult to maintain uniform acoustic contact and properly orientation of the probe. Another explanation is poor definition of the five sonographic

layers just above the dentate line, particularly along the posterior wall (47, 75).

A number of comparative studies have been performed to assess the efficacy of ERUS and MRI. Some studies have shown clear supremacy of ERUS, whereas other have shown little difference. MRI as with CT, is accurate in assessing spread of the tumor beyond the rectal wall, invasion of contiguous structures, spread to regional lymph nodes or distant metastases. The lateral pelvic nodes, such as the obturator nodes, are located too far from the rectum to be imaged effectively with ERUS. Therefore, possible advantages of MRI may lie with assessment of the lateral pelvic lymph nodes, pelvic wall invasion and involvement of levator ani muscle. Previously, MRI was not able to delineate the layers of the rectal wall. With high resolution techniques, thin slice MRI can be used to measure the depth of extramural spread accurately, with good correlation with corresponding pathology measurement in surgical specimens (78). Furthermore the relationship of tumor to the mesorectal fascia can be evaluated so that CRM positive status can be predicted when tumor is imaged within 1mm from the mesorectal fascia. Brown et al. (79) evaluated the effectiveness of digital examination, ERUS and MRI in staging rectal cancer in 98 patients undergoing total mesorectal excision with pathology as the gold standard. ERUS correctly identified 14 out of 31 (45%) tumors with favorable prognosis (in two cases extramural depth was overestimated; in the remaining 15 patients, failure to reach the tumor using the EUS probe resulted in inability to assess tumor depth). In this category of patients, MRI correctly identified all patients. In the preoperative identification of tumors with unfavorable prognosis, ERUS correctly identified 32 out of 39 (82%) patients and MRI correctly identified 33 out of 39 (85%) tumors. In the preoperative identification of locally advanced tumors (28 cases), only one was successfully identified using ERUS; in 12 patients, tumor could not be assessed because not reached by the probe or because of pain experienced by the patient. In 15 patients, tumor deposits involving the mesorectal fascia had not been identified. MRI successfully identified 22 out of 28 patients with locally advanced tumors. In four patients, nodes close to the mesorectal fascia had not been detected. In each of these cases, nodes were partially replaced by small tumor foci that were not resolved on MR images. In two patients tumor was thought to have breached the wall anteriorly by <1mm, but histopathologic examination showed stage pT4 peritoneal infiltration by the tumor. In a metaanalysis by Bipat et al (80), ERUS was found to be the most accurate staging modality when compared to CT and MRI imaging for evaluation of local invasion of rectal cancer. For lymph node involvement, the results were comparable, with low sensitivity values. ERUS was used to evaluate only perirectal or mesorectal lymph nodes, whereas CT and MRI were also used to evaluate iliac and mesenteric or retroperitoneal lymph nodes. In a large recent European multicenter study (81), MRI showed an agreement in T-staging of 57% with 19% overstaging and 24% understaging. It was also very accurate in predicting the extramural depth of tumor invading the mesorectum. MRI was able to identify large T3 and T4 tumors and invasion of the mesorectal fascia. Because of the accurate depiction of large tumoral mass, it is often said that with MRI "what you see is what you get" (66). Most failures of MRI occur in the differentiation between T1 and T2 lesions and between T2 and borderline T3 lesions. A T1 tumor cannot be reliably distinguished from T2 because the submucosal layer is generally not visualized on phased array MRI. Like ERUS, MRI has some difficulty in differentiating lesions on the border of T2 and T3 from a desmoplastic reaction. MRI with endorectal coils has been studied in a number of small size studies for the evaluation and staging of rectal tumors (82). With the addition of endorectal surface coils to conventional MR imaging, spatial resolution has increased and anatomic definition improved. T2-weighted turbo spin-echo sequences allow to distinguish the five layers of the rectal wall. Rectal carcinoma in T2-weighted turbo spin-echo sequences has medium-to-low signal intensity, higher than the muscular layer. MRI and ERUS demonstrate similar efficacy in the preoperative staging of rectal tumors. Overall accuracy rates of 70-90% have been reported for staging of rectal tumors using MRI with endorectal coils. However, coils are too expensive and not used worldwide. A further limitation of MRI with endoanal coils is the inability to advance the coil through a stricture caused by advanced rectal cancer. In the evaluation of lymph nodes, MRI does not offer significant improvement in accuracy rates compared with ERUS.

In conclusion, ERUS is currently the best modality for the preoperative staging of rectal cancer. It is not alternative, but rather complementary to high-resolution MRI. Future improvements may include the possibility to visualize the mesorectal fascia or to better evaluate lymph nodes less than 5mm in diameter. ERUS is much less expensive than MRI and it can be readily used in the office, immediately providing important information for treatment planning. MRI has the advantage, over ERUS, that the images can be more easily interpreted and evaluated by other radiologists, clinicians and oncologists. The images can also be used by radiotherapists for planning the radiotherapy fields and by surgeons to guide the resection in advanced cases.

Preoperative Staging of Rectal Cancer: Role of Endorectal Ultrasound 71

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**0**

**5**

*Italy*

**Dynamic Contrast Enhanced Magnetic**

Roberta Fusco1, Mario Sansone1, Mario Petrillo2, Antonio Avallone3,

In the last few years the clinical management of rectal cancer has become very complex. A wide spectrum of therapeutic options is available. Magnetic Resonance Imaging (MRI) could play a pivotal rule in the prognostic and therapeutic assessment of rectal cancer (Chen et al.,

As known, MRI can provide information about the stage of the disease according to TNM classification focussing on the depth of mesorectal invasion and on lymph node involvement inside and outside the mesorectum (Beets-Tan & Beets, 2004; Gunderson et al., 2004). Due to its intrinsic multiparametricity and multiplanarity MRI is considered the 'gold standard' particularly in differentiating between intramural and extramural disease, and in the management of Locally Advanced Rectal Cancer (LARC) (Beets-Tan & Beets, 2004;

The common use of total mesorectal excision (TME) and the shift from a postoperative to a preoperative chemo-radiotherapy (pre-CRT) approach have substantially reduced the risk of local recurrences, increasing curative resection and the rate of anal sphincter preservation and improving local control and overall survival rates (Avallone et al., 2006; 2011; Delrio et al.,

Although morphological tumour assessment performed by MRI has been repeatedly shown to be the most accurate modality in evaluating the presence of a positive circumferential resection margin (CRM), MRI is considered not to be conclusive in pre-CRT tumor response evaluation since histopathological downstage is not always associated with tumour effective reduction (Petrillo et al., 2007). The main difficulty regarding post-chemoradiation MRI includes discrimination of active tumour and post-treatment fibrosis, particularly when differentiating stage T2 and stage T3 carcinomas, according to different recurrence and overall survival rates between Low Risk (T1/T2N0) and Intermediate Risk (T3/N0) as reported by

Previous considerations support a Dynamic Contrast Enhanced-Magnetic Resonance Imaging (DCE-MRI) approach that could gain a renewed role to MRI adding functional data to

**1. Introduction**

Petrillo et al., 2006).

Gunderson et al. (2002; 2004).

2005; 2003).

2005).

<sup>1</sup>*Department of Biomedical, Electronics and Telecommunications Engineering*

**Resonance Imaging in Rectal Cancer**

Paolo Delrio<sup>3</sup> and Antonella Petrillo<sup>3</sup>

<sup>2</sup>*Department of Radiology, Second University of Naples*

<sup>3</sup>*IRCCS National Cancer Institute, Fondazione Pascale, Naples*

*University 'Federico II' of Naples*

### **Dynamic Contrast Enhanced Magnetic Resonance Imaging in Rectal Cancer**

Roberta Fusco1, Mario Sansone1, Mario Petrillo2, Antonio Avallone3, Paolo Delrio<sup>3</sup> and Antonella Petrillo<sup>3</sup> <sup>1</sup>*Department of Biomedical, Electronics and Telecommunications Engineering University 'Federico II' of Naples* <sup>2</sup>*Department of Radiology, Second University of Naples* <sup>3</sup>*IRCCS National Cancer Institute, Fondazione Pascale, Naples Italy*

#### **1. Introduction**

74 Rectal Cancer – A Multidisciplinary Approach to Management

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In the last few years the clinical management of rectal cancer has become very complex. A wide spectrum of therapeutic options is available. Magnetic Resonance Imaging (MRI) could play a pivotal rule in the prognostic and therapeutic assessment of rectal cancer (Chen et al., 2005).

As known, MRI can provide information about the stage of the disease according to TNM classification focussing on the depth of mesorectal invasion and on lymph node involvement inside and outside the mesorectum (Beets-Tan & Beets, 2004; Gunderson et al., 2004). Due to its intrinsic multiparametricity and multiplanarity MRI is considered the 'gold standard' particularly in differentiating between intramural and extramural disease, and in the management of Locally Advanced Rectal Cancer (LARC) (Beets-Tan & Beets, 2004; Petrillo et al., 2006).

The common use of total mesorectal excision (TME) and the shift from a postoperative to a preoperative chemo-radiotherapy (pre-CRT) approach have substantially reduced the risk of local recurrences, increasing curative resection and the rate of anal sphincter preservation and improving local control and overall survival rates (Avallone et al., 2006; 2011; Delrio et al., 2005; 2003).

Although morphological tumour assessment performed by MRI has been repeatedly shown to be the most accurate modality in evaluating the presence of a positive circumferential resection margin (CRM), MRI is considered not to be conclusive in pre-CRT tumor response evaluation since histopathological downstage is not always associated with tumour effective reduction (Petrillo et al., 2007). The main difficulty regarding post-chemoradiation MRI includes discrimination of active tumour and post-treatment fibrosis, particularly when differentiating stage T2 and stage T3 carcinomas, according to different recurrence and overall survival rates between Low Risk (T1/T2N0) and Intermediate Risk (T3/N0) as reported by Gunderson et al. (2002; 2004).

Previous considerations support a Dynamic Contrast Enhanced-Magnetic Resonance Imaging (DCE-MRI) approach that could gain a renewed role to MRI adding functional data to

Fig. 1. A summary of the main phases of tumor vasculature development (angiogenesis) and

Dynamic Contrast Enhanced Magnetic Resonance Imaging in Rectal Cancer 77

Fig. 2. DCE-MRI in rectal cancer: a series of *T*1-weighted images before and after CA injection; the time-intensity curve of the selected region of interest (ROI) is also shown.

of tumour angiogenesis and in the development and trial of anti angiogenic drugs.

Angiogenic inhibitors can reduce both the number of vessels (particularly nonfunctional vessels) and their permeability. Some therapies, such as anti-vascular endothelial growth factor antibody (antiVEGF Ab), are specifically directed against a growth factor (VEGF) and are thought to regulate vascular maturation and permeability (Lichtenbeld et al., 1999). While avascular tumours are not detectable by MRI (Choyke et al., 2003), DCE-MRI can help to characterise vascularized cancers (Leach et al., 2005). After intravenous injection, the contrast agent (CA) pass through the tumor vasculature and immediately leaks through the vessels walls accumulating in the extravascular extracellular space (EES) because of the concentration gradient (wash-in phase, see fig. 2). Hereafter, CA concentration within plasma will return lower than EES and backflow will occur (wash-out phase). Using specific *T*1-weighted pulse sequences the accumulation of CA causes an increase of signal intensity (enhancement) on images (fig. 2). Malignant tumors generally show faster and higher levels of enhancement than is seen in normal tissue. DCE-MRI is currently widely used in the study

the effects that are measurable by means of DCE-MRI.

the morphological examination. DCE-MRI has been reported by many authors as a tool potentially able to permit an evaluation of pre-CRT effectiveness basing on the strict relationship between tumor growth and angiogenesis (Ceelen et al., 2006; de Lussanet et al., 2005; Kremser et al., 2007).

DCE-MRI is gaining a large consensus as a technique for diagnosis, staging and assessment of therapy response for different types of tumours, due to its capability to detect highly active angiogenesis. It is well known that angiogenesis is a key factor in the growth and dissemination of cancer; characterisation of the angiogenic status of the tumour on an individual patient basis could allow for a more targeted approach to treatment of rectal cancer (Goh et al., 2007; Kapse & Goh, 2009).

More specifically, in the case of rectal cancer, previous trials have provided the proof of principle that inhibition of angiogenesis has the potential to enhance the effectiveness of the treatment for this disease. In vivo imaging techniques capable to assess tumour perfusion have the potential to improve the management of treatment for patients with rectal cancer (Chen et al., 2005; de Vries et al., 2000; 2001; 2003; Kremser et al., 2007).

The aim of this chapter is to review the main issues concerning the assessment of the angiogenic status of rectal cancer by means of DCE-MRI. More specifically, the aim of this chapter is to present:

#### **2. DCE-MRI basis**

Cancer can develop in any tissue of the body that contains cells capable of division. The earliest detectable malignant lesions, referred to as *cancer in situ*, are often a few millimeters or less in diameter and at an early stage are commonly avascular. In avascular tumours cellular nutrition depends on diffusion of nutrients and waste materials and places a severe limitation on the size that such a tumour can achieve. The maximum diameter of an avascular solid tumour is approximately 150 − 200*μm*, and is governed effectively by the maximum diffusion distance of oxygen. Conversion of a dormant tumour in situ to a more rapidly growing invasive neoplasm, may take several years and is associated with vascularization of the tumour. The development of neo-vascularization within a tumour results from a process known as angiogenesis.

There are positive and negative regulators of angiogenesis. Release of a promoter substance stimulates the endothelial cells of the existing vasculature close to the neoplasia to initiate the formation of solid endothelial sprouts that grow toward the solid tumour (Knopp et al., 1999). Vascular endothelial growth factor (VEGF) also known as vascular permeability factor (VPF), induces angiogenesis and strongly increases microvascular permeability to plasma proteins. As vascular growth factors are released, proteases are also induced to degrade perivascular tissue, allowing the endothelial cells to proliferate and form primitive, immature, and, therefore, leaky vessels (Dor et al., 2001; Guetz et al., 2006). Figure 1 summarizes the main phases of tumor vasculature development.

Therefore, the morphology of the neo-vascular network in tumours can differ significantly from that seen in normal tissue. Tumour vasculature is often highly heterogeneous, and the capillaries are extremely coarse, irregularly constricted or dilated and distorted.

2 Will-be-set-by-IN-T-ECH

the morphological examination. DCE-MRI has been reported by many authors as a tool potentially able to permit an evaluation of pre-CRT effectiveness basing on the strict relationship between tumor growth and angiogenesis (Ceelen et al., 2006; de Lussanet et al.,

DCE-MRI is gaining a large consensus as a technique for diagnosis, staging and assessment of therapy response for different types of tumours, due to its capability to detect highly active angiogenesis. It is well known that angiogenesis is a key factor in the growth and dissemination of cancer; characterisation of the angiogenic status of the tumour on an individual patient basis could allow for a more targeted approach to treatment of rectal cancer

More specifically, in the case of rectal cancer, previous trials have provided the proof of principle that inhibition of angiogenesis has the potential to enhance the effectiveness of the treatment for this disease. In vivo imaging techniques capable to assess tumour perfusion have the potential to improve the management of treatment for patients with rectal cancer

The aim of this chapter is to review the main issues concerning the assessment of the angiogenic status of rectal cancer by means of DCE-MRI. More specifically, the aim of this

• a review of the widespread methodologies used for DCE-MRI data acquisition and

• the main findings of scientific literature concerning DCE-MRI evaluation of rectal cancer.

Cancer can develop in any tissue of the body that contains cells capable of division. The earliest detectable malignant lesions, referred to as *cancer in situ*, are often a few millimeters or less in diameter and at an early stage are commonly avascular. In avascular tumours cellular nutrition depends on diffusion of nutrients and waste materials and places a severe limitation on the size that such a tumour can achieve. The maximum diameter of an avascular solid tumour is approximately 150 − 200*μm*, and is governed effectively by the maximum diffusion distance of oxygen. Conversion of a dormant tumour in situ to a more rapidly growing invasive neoplasm, may take several years and is associated with vascularization of the tumour. The development of neo-vascularization within a tumour results from a process

There are positive and negative regulators of angiogenesis. Release of a promoter substance stimulates the endothelial cells of the existing vasculature close to the neoplasia to initiate the formation of solid endothelial sprouts that grow toward the solid tumour (Knopp et al., 1999). Vascular endothelial growth factor (VEGF) also known as vascular permeability factor (VPF), induces angiogenesis and strongly increases microvascular permeability to plasma proteins. As vascular growth factors are released, proteases are also induced to degrade perivascular tissue, allowing the endothelial cells to proliferate and form primitive, immature, and, therefore, leaky vessels (Dor et al., 2001; Guetz et al., 2006). Figure 1 summarizes the

Therefore, the morphology of the neo-vascular network in tumours can differ significantly from that seen in normal tissue. Tumour vasculature is often highly heterogeneous, and the

capillaries are extremely coarse, irregularly constricted or dilated and distorted.

(Chen et al., 2005; de Vries et al., 2000; 2001; 2003; Kremser et al., 2007).

2005; Kremser et al., 2007).

chapter is to present:

**2. DCE-MRI basis**

known as angiogenesis.

main phases of tumor vasculature development.

analysis;

(Goh et al., 2007; Kapse & Goh, 2009).

Fig. 1. A summary of the main phases of tumor vasculature development (angiogenesis) and the effects that are measurable by means of DCE-MRI.

Fig. 2. DCE-MRI in rectal cancer: a series of *T*1-weighted images before and after CA injection; the time-intensity curve of the selected region of interest (ROI) is also shown.

Angiogenic inhibitors can reduce both the number of vessels (particularly nonfunctional vessels) and their permeability. Some therapies, such as anti-vascular endothelial growth factor antibody (antiVEGF Ab), are specifically directed against a growth factor (VEGF) and are thought to regulate vascular maturation and permeability (Lichtenbeld et al., 1999). While avascular tumours are not detectable by MRI (Choyke et al., 2003), DCE-MRI can help to characterise vascularized cancers (Leach et al., 2005). After intravenous injection, the contrast agent (CA) pass through the tumor vasculature and immediately leaks through the vessels walls accumulating in the extravascular extracellular space (EES) because of the concentration gradient (wash-in phase, see fig. 2). Hereafter, CA concentration within plasma will return lower than EES and backflow will occur (wash-out phase). Using specific *T*1-weighted pulse sequences the accumulation of CA causes an increase of signal intensity (enhancement) on images (fig. 2). Malignant tumors generally show faster and higher levels of enhancement than is seen in normal tissue. DCE-MRI is currently widely used in the study of tumour angiogenesis and in the development and trial of anti angiogenic drugs.

[*Gd*] = <sup>1</sup> *r*1

*enhancement*.

intensity:

be different among several studies.

of CA is related to both *r*<sup>1</sup> and *T*1,0 of tissue.

the slope (via standard linear regression).

(de Vries et al., 2003; Kremser et al., 2007).

adopted in the wash-out phase (de Vries et al., 2000; 2003).

**3.2 Spatial and temporal resolution**

 1 *T*1 <sup>−</sup> <sup>1</sup> *T*1,0

where *S*0, *S*, *T*1,0 and *T*<sup>1</sup> are the signal intensities and spin-lattice relaxation times before and after administration of contrast agent respectively. The difference *S* − *S*<sup>0</sup> is called *signal*

Dynamic Contrast Enhanced Magnetic Resonance Imaging in Rectal Cancer 79

The difficulty in comparing different studies comes from the nature of *g*: in fact, the loading of the coil, the receiver settings at the MR console and image reconstruction parameters can

Therefore, it could be more advantageous to normalise with respect to the pre-contrast signal

The quantity (*S* − *S*0)/*S*<sup>0</sup> is called *relative signal enhancement*. Consequently, the concentration

As observed before, the relaxivity *r*<sup>1</sup> can be considered fixed for soft tissues. As far as the longitudinal relaxation time prior to contrast injection (*T*1,0) it can be easily measured before

One common method for *T*1,0 estimation is to use several gradient-echo (GRE) images with variable flip angles. In fact, rearranging eq. (2) that equation yields (Parker et al., 1997):

*Y*(*α*) = *X*(*α*) · exp(−*TR*/*T*1,0) − *ρg*(1 − exp(−*TR*/*T*1,0)) exp(−*TE*/*T*<sup>∗</sup>

where *Y*(*α*) = *Sα*/ sin *α* and *X*(*α*) = *Sα*/ tan *α*. Hence a plot of *Y*(*α*) against *X*(*α*) for several (typically three or more) flip angles will result in a straight line and *T*1,0 can be calculated from

The requirements for temporal and spatial resolution for a particular oncologic application often are in direct conflict. Both the importance for high temporal resolution to accurately characterize contrast kinetics and the need for high spatial resolution to identify distinguishing features of lesion morphology have been investigated in several studies

In general, it can be stated that for an accurate estimation of tracer kinetics parameters, a short interval between samples must be used, especially for the analysis of the wash-in phase. For example, Henderson et al. (1998) found that this interval should be approximately less than 16 s in the case of breast DCE-MRI. In the wash-out phase, this requirement could be relaxed

A high temporal resolution can be difficult to obtain because the acquisition of a single volume could require several seconds as a large part of the whole abdomen is scanned. One approach to overcome this problem is to choose a single slice containing the tumor, so that the sampling interval can be maintained below a few seconds (Blomqvist et al., 1998; Ceelen et al., 2006; de Lussanet et al., 2005). However, this approach is not able to manage with the heterogeneity of the tumour (Jackson et al., 2007). An hybrid approach could involve a rapid imaging with low spatial resolution in the wash-in phase while a slow, high-resolution imaging could be

1 *r*<sup>1</sup> · *T*1,0

. (5)

<sup>2</sup> ) (6)

[*Gd*] <sup>≈</sup> *<sup>S</sup>* <sup>−</sup> *<sup>S</sup>*<sup>0</sup> *S*0

CA administration using opportune pulse sequences (Collins & Padhani, 2004).

(Cheng, 2008; Dale et al., 2003; Evelhoch, 1999; Henderson et al., 1998).

<sup>≈</sup> *<sup>S</sup>* <sup>−</sup> *<sup>S</sup>*<sup>0</sup> *r*<sup>1</sup> · *ρ* · *g* · *TR*

(4)

#### **3. DCE-MRI data acquisition**

Several issues of data acquisition should be taken into account when developing protocols for DCE-MRI, both to facilitate the integration of results from multiple institutions and to ensure that the data reflect the underlying physiology as accurately as possible (Ashton, 2010; Evelhoch, 1999; Leach et al., 2005).

In particular, the type of data acquisition affects the data analysis procedure: while semi-quantitative model-free analysis (see section 4) can be performed without accurate measurement of CA concentration, a full model-based approach requires accurate CA quantification.

Key factors affecting DCE-MRI of rectal cancer include: type of contrast agents and the relationship between CA concentration and signal enhancement; constraints concerning spatial and temporal resolution; the impact of patient motion.

#### **3.1 Relationship between contrast agent concentration and signal enhancement**

It is generally assumed that the relaxation rate (*R*<sup>1</sup> = 1/*T*1) of soft tissues is linearly related to the mean tissue CA concentration (*CT*) via the Bloembergen and Solomon equation:

$$R\_1 = \frac{1}{T\_1} = \frac{1}{T\_{1,0}} + r\_1 C\_T = R\_{1,0} + r\_1 C\_T \tag{1}$$

where *T*1,0 and *R*1,0 are, respectively, the relaxation time and the relaxation rate of the tissue in absence of CA and the proportionality constant *r*<sup>1</sup> is called 'relaxivity'.

Main properties concerning the relaxivity include: it depends upon the macromolecular environment; it is dependent on the type of macromolecule to which the Gd ion is attached; it decreases with external magnetic field; it increases with temperature; and it is also dependent on the pH of the solution (Stanisz & Henkelman, 2000).

However, most studies assume that *r*<sup>1</sup> is constant at a given temperature and magnetic field and that it is independent on the tissue environment. The typical value used for *r*1, estimated in pure saline water, is 4.5 L/mmol/s per kg of water (Stanisz & Henkelman, 2000).

In typical DCE-MRI experiments, *T*1-weighted spoiled gradient-echo sequences are used. In this case the signal intensity *S* has the following expression (Sourbron, 2010):

$$S = \rho \cdot g \cdot \frac{\sin \alpha \cdot (1 - \exp(-T\_R/T\_1))}{1 - \cos \alpha \cdot \exp(-T\_R/T\_1)} \cdot \exp(-T\_E/T\_2^\*) \tag{2}$$

where *ρ* is the proton density, *g* is a constant determined by system receiver and image reconstruction settings, *α* is the flip angle, *TR* is the repetition time, *TE* is the echo time, *T*∗ 2 is the transverse relaxation time taking into account field inhomogeneity .

If it is assumed that Gd ions have no effect on *ρ* and that the *TE* is so short to neglect the influence of *T*<sup>2</sup> (or, more importantly, changes in *T*∗ <sup>2</sup> during the series), then the Gd ions can influence the signal intensity only by means of their effect on *T*<sup>1</sup> (decrease of *T*1). Under these assumptions, and as *α* approaches 90◦ and *TR* � *T*<sup>1</sup> the relationship between signal intensity and 1/*T*<sup>1</sup> becomes approximately linear:

$$S \approx \rho \cdot g \cdot \frac{T\_R}{T\_1} \tag{3}$$

this relationship remains approximately valid across a range of values for *TR*/*T*<sup>1</sup> and *α*. Therefore, an estimate of CA concentration can be obtained using eq. (1) and eq. (3):

4 Will-be-set-by-IN-T-ECH

Several issues of data acquisition should be taken into account when developing protocols for DCE-MRI, both to facilitate the integration of results from multiple institutions and to ensure that the data reflect the underlying physiology as accurately as possible (Ashton, 2010;

In particular, the type of data acquisition affects the data analysis procedure: while semi-quantitative model-free analysis (see section 4) can be performed without accurate measurement of CA concentration, a full model-based approach requires accurate CA

Key factors affecting DCE-MRI of rectal cancer include: type of contrast agents and the relationship between CA concentration and signal enhancement; constraints concerning

It is generally assumed that the relaxation rate (*R*<sup>1</sup> = 1/*T*1) of soft tissues is linearly related to

where *T*1,0 and *R*1,0 are, respectively, the relaxation time and the relaxation rate of the tissue

Main properties concerning the relaxivity include: it depends upon the macromolecular environment; it is dependent on the type of macromolecule to which the Gd ion is attached; it decreases with external magnetic field; it increases with temperature; and it is also dependent

However, most studies assume that *r*<sup>1</sup> is constant at a given temperature and magnetic field and that it is independent on the tissue environment. The typical value used for *r*1, estimated

In typical DCE-MRI experiments, *T*1-weighted spoiled gradient-echo sequences are used. In

where *ρ* is the proton density, *g* is a constant determined by system receiver and image reconstruction settings, *α* is the flip angle, *TR* is the repetition time, *TE* is the echo time, *T*∗

If it is assumed that Gd ions have no effect on *ρ* and that the *TE* is so short to neglect the

influence the signal intensity only by means of their effect on *T*<sup>1</sup> (decrease of *T*1). Under these assumptions, and as *α* approaches 90◦ and *TR* � *T*<sup>1</sup> the relationship between signal intensity

*S* ≈ *ρ* · *g* ·

this relationship remains approximately valid across a range of values for *TR*/*T*<sup>1</sup> and *α*. Therefore, an estimate of CA concentration can be obtained using eq. (1) and eq. (3):

<sup>1</sup> <sup>−</sup> cos *<sup>α</sup>* · exp(−*TR*/*T*1) · exp(−*TE*/*T*<sup>∗</sup>

*TR T*1

in pure saline water, is 4.5 L/mmol/s per kg of water (Stanisz & Henkelman, 2000).

sin *α* · (1 − exp(−*TR*/*T*1))

this case the signal intensity *S* has the following expression (Sourbron, 2010):

is the transverse relaxation time taking into account field inhomogeneity .

+ *r*1*CT* = *R*1,0 + *r*1*CT* (1)

<sup>2</sup> ) (2)

<sup>2</sup> during the series), then the Gd ions can

2

(3)

**3.1 Relationship between contrast agent concentration and signal enhancement**

the mean tissue CA concentration (*CT*) via the Bloembergen and Solomon equation:

<sup>=</sup> <sup>1</sup> *T*1,0

in absence of CA and the proportionality constant *r*<sup>1</sup> is called 'relaxivity'.

spatial and temporal resolution; the impact of patient motion.

*<sup>R</sup>*<sup>1</sup> <sup>=</sup> <sup>1</sup> *T*1

on the pH of the solution (Stanisz & Henkelman, 2000).

*S* = *ρ* · *g* ·

influence of *T*<sup>2</sup> (or, more importantly, changes in *T*∗

and 1/*T*<sup>1</sup> becomes approximately linear:

**3. DCE-MRI data acquisition**

Evelhoch, 1999; Leach et al., 2005).

quantification.

$$\mathbb{E}[\mathbb{G}d] = \frac{1}{r\_1} \left( \frac{1}{T\_1} - \frac{1}{T\_{1,0}} \right) \approx \frac{S - S\_0}{r\_1 \cdot \rho \cdot \mathcal{g} \cdot T\_R} \tag{4}$$

where *S*0, *S*, *T*1,0 and *T*<sup>1</sup> are the signal intensities and spin-lattice relaxation times before and after administration of contrast agent respectively. The difference *S* − *S*<sup>0</sup> is called *signal enhancement*.

The difficulty in comparing different studies comes from the nature of *g*: in fact, the loading of the coil, the receiver settings at the MR console and image reconstruction parameters can be different among several studies.

Therefore, it could be more advantageous to normalise with respect to the pre-contrast signal intensity:

$$\mathbb{E}\left[\mathbb{G}d\right] \approx \frac{\mathbb{S}-\mathbb{S}\_0}{\mathbb{S}\_0} \frac{1}{r\_1 \cdot T\_{1,0}}.\tag{5}$$

The quantity (*S* − *S*0)/*S*<sup>0</sup> is called *relative signal enhancement*. Consequently, the concentration of CA is related to both *r*<sup>1</sup> and *T*1,0 of tissue.

As observed before, the relaxivity *r*<sup>1</sup> can be considered fixed for soft tissues. As far as the longitudinal relaxation time prior to contrast injection (*T*1,0) it can be easily measured before CA administration using opportune pulse sequences (Collins & Padhani, 2004).

One common method for *T*1,0 estimation is to use several gradient-echo (GRE) images with variable flip angles. In fact, rearranging eq. (2) that equation yields (Parker et al., 1997):

$$Y(\mathfrak{a}) = X(\mathfrak{a}) \cdot \exp(-T\_{\mathbb{R}}/T\_{1,0}) - \rho \lg(1 - \exp(-T\_{\mathbb{R}}/T\_{1,0})) \cdot \exp(-T\_{\mathbb{E}}/T\_{2}^\*) \tag{6}$$

where *Y*(*α*) = *Sα*/ sin *α* and *X*(*α*) = *Sα*/ tan *α*. Hence a plot of *Y*(*α*) against *X*(*α*) for several (typically three or more) flip angles will result in a straight line and *T*1,0 can be calculated from the slope (via standard linear regression).

#### **3.2 Spatial and temporal resolution**

The requirements for temporal and spatial resolution for a particular oncologic application often are in direct conflict. Both the importance for high temporal resolution to accurately characterize contrast kinetics and the need for high spatial resolution to identify distinguishing features of lesion morphology have been investigated in several studies (Cheng, 2008; Dale et al., 2003; Evelhoch, 1999; Henderson et al., 1998).

In general, it can be stated that for an accurate estimation of tracer kinetics parameters, a short interval between samples must be used, especially for the analysis of the wash-in phase. For example, Henderson et al. (1998) found that this interval should be approximately less than 16 s in the case of breast DCE-MRI. In the wash-out phase, this requirement could be relaxed (de Vries et al., 2003; Kremser et al., 2007).

A high temporal resolution can be difficult to obtain because the acquisition of a single volume could require several seconds as a large part of the whole abdomen is scanned. One approach to overcome this problem is to choose a single slice containing the tumor, so that the sampling interval can be maintained below a few seconds (Blomqvist et al., 1998; Ceelen et al., 2006; de Lussanet et al., 2005). However, this approach is not able to manage with the heterogeneity of the tumour (Jackson et al., 2007). An hybrid approach could involve a rapid imaging with low spatial resolution in the wash-in phase while a slow, high-resolution imaging could be adopted in the wash-out phase (de Vries et al., 2000; 2003).

good diagnostic performance in differentiating malignant from benign lesions as described in

Dynamic Contrast Enhanced Magnetic Resonance Imaging in Rectal Cancer 81

As regards the rectal cancer, many papers explored the possibility to apply a semi-quantitative approach to lesion classification. Different TIC features have been used by the different

The approaches can be roughly subdivided in two classes. In a first type of approach, the classification of the TIC is performed by means of several features having, on an intuitive basis, a link with physiological characteristics (see fig. 4). As an example, Tuncbilek et al. (2004) used the maximal relative enhancement within the first minute (*MSD*1*min*), the maximal relative enhancement of the entire study (*MSD*), the steepest slope (*WISmax*). Similarly,

Another approach is to extract TIC features that are associated to tracer kinetics theory (see section 4.2). Within this framework de Lussanet et al. (2005); de Vries et al. (2000; 2001; 2003); Kremser et al. (2007) used, as a first step in quantitative assessment of tumor perfusion, the steepest slope of the TIC during contrast medium uptake (*WISmax*), and, on the base of the

> *dCtumor*/*dt*|*max Cart*|*max*

> > (7)

*Cp*(*t*)|*max*

the case of breast lesions (Daniel et al., 1998; Kuhl, 2007; Nishiura et al., 2011).

authors, the aim being to extract as much physiological information as possible.

Blomqvist et al. (1998) and Dicle et al. (1999) used *MSD* and *WISmax*.

work by Miles (1991) they evaluated the Perfusion Index (PI) as:

2010).

section 4.3, fig. 7).

*P I* <sup>=</sup> <sup>1</sup>

<sup>=</sup> <sup>1</sup>

use a unifying terminology for semi-quantitative parameters (see tab. 1):

**MSD** the maximum signal level with respect to the baseline;

maximum enhancement divided by time to peak);

**WII** intercept of the wash-in straight-line with the y-axis; **WOI** intercept of the wash-our straight-line with the y-axis; **AUCWI** area under gadolinium curve in the was-in phase; **AUCWO** are under gadolinium curve in the wash-out phase;

**TWI** time between the onset of enhancement and the maximum enhancement; **TWO** time between the maximum enhancement and the end of the acquisition;

*<sup>σ</sup>tumor*

*<sup>σ</sup>tumor WISmax*

where *σtumor* is tissue density. Although PI is an approximated parameter, it combines two important quantities: tissue perfusion and extraction fraction (Brix et al., 2010; Sourbron,

When calculated on a pixel-by-pixel basis the above parameters can be displayed graphically as pseudo-coloured maps superimposed on the corresponding morphological MR images (see

Figure 4 shows the most important parameters that have been used in several studies. The definitions of the several quantities are not always in accordance. Therefore we have tried to

**TTK** time between the beginning of dynamic acquisition and the maximum enhancement;

**WIS** slope of the wash-in phase (increase in signal intensity between enhancement onset and

**WOS** slope of the wash-out phase (decrease in signal intensity between maximum enhancement and the signal intensity at the end of acquisition divided by time TWO);

Fig. 3. Classification system for semi-quantitative of the TICs. The level of angiogenesis is supposed to increase with the number of the curve-type: (I) no enhancement; (II) slow sustained enhancement; (III) rapid initial and sustained late enhancement (persistent); (IV) rapid initial and stable late enhancement (plateau); (V) rapid initial and decreasing late enhancement (wash-out). Curves from (I) to (III) are typically associated to normal or benign tissues; type (IV) can be classified as suspicious and (V) as malignant.

#### **3.3 Patient motion**

Since the TIC is sampled over several minutes, patient motion can become a serious obstacle to an accurate evaluation of kinetic parameters. Motion correction should be applied before any tracer kinetics analysis is performed (Fei et al., 2002). However, 2D or 3D registration is difficult because the signal intensity of a pixel can change over time both because of spatial displacement and CA absorption. Therefore, DCE-MRI specific methods are currently being developed for simultaneous iterative registration and tracer kinetics analysis (Buonaccorsi et al., 2007; Melbourne et al., 2007; Xiaohua et al., 2005).

#### **4. DCE-MRI data analysis**

Different methods for DCE-MRI data analysis have been proposed, ranging from simple semi-quantitative inspection of the time-intensity curves (TICs) to more sophisticated tracer kinetics modelling (Brix et al., 2010; Sourbron, 2010). The different methods were designed to capture the biologically relevant components from the dynamic MR signal and to relate them to the underlying pathophysiological processes taking place in the tissue.

In principle, the derivation of physiological data from DCE-MRI relies on the application of appropriate tracer kinetics models to describe the distribution of contrast media following its systemic administration. However, the application of these techniques is still complex and they cold not be widely available outside specialist centres. In response to this, many semi-quantitative approaches for the classification of enhancement curve shapes have been described and are now in relatively common use in clinical settings.

Both semi-quantitative and full-quantitative data analysis can be performed on a region of interest (ROI) basis or on a pixel-by-pixel basis. We will briefly describe the two approaches.

#### **4.1 Semi-quantitative analysis**

Semi-quantitative analysis can help the radiologist in classifying the TIC shape as normal, benign, malignant (see fig. 3). Classification of TICs according to this scheme can achieve very 6 Will-be-set-by-IN-T-ECH

Fig. 3. Classification system for semi-quantitative of the TICs. The level of angiogenesis is supposed to increase with the number of the curve-type: (I) no enhancement; (II) slow sustained enhancement; (III) rapid initial and sustained late enhancement (persistent); (IV) rapid initial and stable late enhancement (plateau); (V) rapid initial and decreasing late enhancement (wash-out). Curves from (I) to (III) are typically associated to normal or benign

Since the TIC is sampled over several minutes, patient motion can become a serious obstacle to an accurate evaluation of kinetic parameters. Motion correction should be applied before any tracer kinetics analysis is performed (Fei et al., 2002). However, 2D or 3D registration is difficult because the signal intensity of a pixel can change over time both because of spatial displacement and CA absorption. Therefore, DCE-MRI specific methods are currently being developed for simultaneous iterative registration and tracer kinetics analysis