metastases can be hypovascular (in gastric, colonic, pancreatic or ovarian adenocarcinomas) with hypoechoic pattern during arterial phase, and similar during portal venous and late phases, respectively hypervascular (neuroendocrine tumors, malignant melanoma, sarcomas, renal, breast or thyroid tumors) with hyperechoic appearance during arterial phase, with washout during the portal venous phase and hypoechoic pattern 30 seconds after injection. using ceus examination to detect metastases a sensitivity of 80–95% is obtained, similar to that of contrast ct and mri . intraoperative use of the procedure increases its performance even if it does not have a decisive contribution to change the therapeutic behavior . limitations of the method are those related to us penetration (pronounced fatty liver disease, deep lesion, excessive obesity) and to the experience of the examiner. to this the risk of confusion between hypervascular metastases, hepatocellular carcinoma and hemangioma and the confusion between hypovascular metastases and small liver cysts is added. routine use of ceus examination to detect liver metastases is recommended when conventional us examination is not conclusive, when precise information on some injuries (number, location) is necessary in conjunction with contrast ct/mri and to assess the effectiveness of treatment when using an antiangiogenic therapy for hypervascular metastases . the method cannot replace ct/mri examinations which have well established indications in oncology. pseudotumors and inflammatory masses of the liver besides the entities listed above inflammatory masses or even pseudo-masses can occur. their diagnosis is quite difficult and the criteria used for differentiation are often insufficient, requiring morphologic diagnostic procedures, use of other diagnostic imaging methods or patient reevaluation from time to time. this includes lesions developed on liver parenchyma reconstruction, as occurs in cirrhosis, steatosis accumulation or in case of acute or chronic inflammatory diseases. focal steatosis it consists of localized accumulation of fat-rich liver cells. in some cases this accumulation can mimic a liver tumor. sometimes the opposite phenomenon can be seen, that is an "island" of normal parenchyma in a “shining” liver. in both cases ultrasound examination identifies a well defined, un-encapsulated area, with echostructure and vasculature similar to those of normal liver parenchyma. the lesion can have different forms, most cases being oval and located in the ivth segment, anterior from the hepatic hilum. it occurs in dyslipidemic or alcohol intake patients with normal physical and biological status. benign diagnosis confirmation is made using ceus examination which proves a normal circulatory bed similar to adjacent liver parenchyma in all three phases of investigation. liver abscess liver abscess (2d and ceus). 2d examination reveals the fluid nature of the mass and imprecise delineation. ceus examination shows congestion in the surrounding liver parenchyma and excludes a vascular tumor. liver abscess have heteromorphic ultrasound appearance, the most typical being that of a mass with irregular shapes, fringed, with fluid or semifluid content, with or without air inside. doppler examination shows the lack of vessels within the lesion. ceus exploration shows hyperenhancement during arterial phase close to the lesion, this being suggestive of a liver parenchymal hyperemia. during venous and sinusoidal phase the pattern is hypoechoic, and the central fluid is contrast enhanced. ceus examination is useful because it confirms the clinical suspicion of abscess. in addition, it allows for an accurate measurement of the collection size and an indication regarding its topography inside the liver (lobe, segment). preneoplastic status. cirrhotic liver monitoring cirrhotic liver is characterized by the occurrence of nodules with different sizes and evolution degrees, so that regenerative nodules, dysplastic nodules and even early hepatocellular carcinoma can coexist at some moment during disease progression. there are studies showing that between 59–94% of newly diagnosed liver nodules in cirrhotic patients have malignant histology and up to 50% of hyperechoic lesions, with ultrasound appearance of hemangioma, ultimately prove to be hepatocellular carcinoma. therefore, current practice in many centers considers that any new lesion revealed in a cirrhotic patient should be regarded as malignant until otherwise proven. there are three categories of cirrhotic liver nodules: regenerative, dysplastic (considered as premalignant conditions) and tumoral (hcc). regenerative nodules (rn) regenerative nodule (ceus). one can see the hypovascular pattern of the solid nodule, with a size <10 mm. these lesions are well defined, with isoechoic or hypoechoic appearance and sizes less than 1 cm. they are high in numbers and have a more or less uniform distribution, involving all liver segments. they can crowd resulting in large pseudo tumors. at doppler examination, these nodules have no circulatory signal. ceus exploration is indicated when a nodule is different against the general pattern of restructured liver either by different echogenity or by a different size than the majority of nodules. during the arterial phase, the signal is weak or absent. during the portal venous and late phase, the appearance is persistently isoechoic. generally, rn is not distinct from the surrounding parenchyma. ceus examination is useful to exclude an active lesion at the moment of exploration but does not have absolute prognostic value; therefore the patient should be periodically examined at short intervals. correlation with clinical status and afp measurements is required. dysplastic nodules (dn) dysplastic nodule (2d, cfm, ceus). the nodule is well-defined with a size between 10– 20 mm, lacks vessels in cfm and ceus exploration. these lesions have various patterns (hypo or hyperechoic) with at least 1 cm diameter. they are hepatocytes with dysplastic changes, but without clear histological criteria for malignancy. they are divided into low-grade dysplastic nodules, where cellular atypia are mild and high-grade dysplastic nodules with moderate or severe cellular atypia, but without any established signs of malignancy. occasionally, well-differentiated hcc foci can be identified in high-grade dysplastic nodules (appearance called "nodule in nodule") . most authors accept the carcinogenesis process as a progressive transformation of dn from low-grade to high-grade and into hcc. the nodule's vasculature changes progressively, correlated with the degree of malignancy, and it is characterized by decrease until absence of portal venous input and by increase of arterial intratumoral input. neoformation vessels occur with increasing degree of dysplasia. arterial neovascularization is enhanced in a chaotic and explosive way, while normal, arterial and portal vasculature continues to decline. high-grade dysplastic nodules are hypovascularized both arterial and portal phases, while early hcc nodules may have similar arterial pattern with the surrounding parenchyma or exacerbated, and portal hypovascularization. in moderate or poorly differentiated hcc (classic hcc) tumor nutrition is performed only by neoformation vessels (abundant), the normal arterial and portal vasculature completely disappearing. this behavior of intratumoral vascularization is typical for hcc and is the key to imaging diagnosis. b-mode ultrasonography is unable to distinguish between regenerative nodules and borderline lesions such as dysplastic nodules and even early hcc. doppler examination also has a low sensitivity in differentiating dysplastic nodules from early hcc. doppler signal may be absent in both regenerative and dysplastic nodules. some authors indicate the presence of venous type doppler flow which reflects the portal venous nutrition of the nodule as a characteristic feature of dysplastic nodules and early hcc (minami & kudo, 2010). other authors noticed the presence of an arterial flow with small frequency variations and a normal resistivity index. on ceus examination both rn and dn may have quite a variable enhancement pattern. generally, both nodules enhances identically with the surrounding liver parenchyma after ucas injection. dysplastic nodules are hypovascular in the arterial phase. in case of highgrade dysplastic nodule sometimes a hypervascularization can be detected, but without associating "wash out" during portal and late ceus phases. in these cases, biopsy may clarify the diagnosis. early hepatocellular carcinoma (early hcc) the suggestive appearance of early hcc on 2d ultrasound examination is that of hypoechoic nodule, with distinct pattern, developed on cirrhotic liver. hypoechoic appearance is characteristic of moderate/poorly differentiated hcc, with low or absent fatty changes. rarely, hcc may appear isoechoic, consist of a tumor type with a higher degree of differentiation and therefore with slower development. another common aspect is "bright loop" or "nodule-in-nodule" appearance, hypoechoic nodules in a hyperechoic tumor. spectral doppler characteristics of early hcc overlap those of the dysplastic nodule, as they are represented by the presence of portal venous signal type or arterial type with normal ri (well differentiated hcc) or increased ri (moderately or poorly differentiated hcc). the cfm exploration identifies a chaotic vessels pattern. on ceus examination, early hcc has an iso- or hypervascular appearance during the arterial phase followed by wash out during portal venous and late phase. there are studies showing that the wash out process is directly correlated with the size and features of neoplastic circulatory bed. thus, highly differentiated hcc illustrates the phenomenon of late or even very late "wash out" while poorly differentiated hcc has an accelerated wash out at the end of arterial phase. it is therefore mandatory to analyze all these three phases of ceus examination for a proper characterization of liver nodules. tumor wash out at the end of the arterial phase allows the hcc diagnosis with a predictability of 89.5%. some authors consider that early pronounced contrast enhancement of a nodule within 1–2 cm developed on a cirrhotic liver is sufficient for hcc diagnosis. these results prove that for a correct characterization of the lesions it is necessary to extend the examination time to 5 minutes or even longer. fig. 11. early hepatocellular carcinoma (2d, cfm). the 2d examination reveals a solid, hypoechoic nodule in ivth liver segment, without encapsulation. cfm shows a central vessel with ramifications to the periphery. the underlying liver is cirrhotic. fig. 12. early hepatocellular carcinoma (2d, cfm). “nodule in nodule” image: small hypoechoic early hcc inside monitored dysplastic nodule. the ultrasound value in hcc "screening" baseline 2d ultrasound has an important role in surveillance programs for patients at risk to develop hcc. the examination has an acceptable sensitivity which increases with the tumor size. sensitivity varies between 42% for lesions <1 cm and 95% for tumors larger than 1 cm, and specificity can reach 90%. optimal time interval for ultrasound screening of “at risk” population is 6 months as it results from clinical trials that investigated the tumor size doubling time (bruix, 2005; maruyama et al., 2008). for a recently developed nodule the dimensional criteria will be taken into account. thus, for a nodule with a size of less than 10 mm the patient will be reevaluated by ultrasound every 3 months, as the growth trend is an indication for completion of investigations with other diagnostic procedures; at a size between 10 – 20 mm two concordant imaging procedures are necessary, supplemented if necessary by an ultrasound guided biopsy; at a size over 20 mm one single dynamic imaging technique with characteristic appearance is enough for positive diagnostic. in uncertain cases complementary dynamic imaging techniques or biopsy should be performed. when doppler exploration is not enough, ceus examination will be performed. one should always keep in mind the risk of false positive results for hcc in case of cholangiocarcinomas so complementary diagnostic procedures should be considered. the effectiveness of screening programs is proved by an increase in detection rate of hcc <2 cm (from <5% in the 90s in europe to > 30% today in japan) with curative therapy options. the main problem of ultrasound screening is that, in order to be cost-effective, it should be applied to the general population and not in tertiary hospitals. this raises the importance of the operator and equipment dependent part of the ultrasound examination. the efficiency of such a program is linked to the functional liver parenchyma of the cirrhotic patient. therefore, some authors argue that screening should be excluded in patients with etiologies that prevent curative treatment or in patients with advanced liver disease (child-pugh class c). after curative therapies (surgical resection, local ablative therapies) continuing ultrasound screening is recommended first at 1 month then at 3 months intervals after the therapy to assess the effectiveness of therapy and to detect other nodules. antitumor therapies ultrasound exploration can be an effective procedure for the assessment of liver tumors response to treatment. over the years, different criteria for assessing the effectiveness of curative or palliative therapies have been considered. now it has been proved that the degree of tumor necrosis is not correlated with tumor diameter, therefore simple measurement of the tumor diameter (recist criteria) is not enough for therapy assessment. currently, local response to treatment is focused on tumor necrosis diagnosed by