the main reasons for the widespread use of thyroid sonography are availability , low cost , limited discomfort to the patient , and absence of ionizing radiation .
sonography has many favourable features , such as detection of nonpalpable nodules , estimation of nodule size / goiter volume , and guidance for fine needle biopsy ( fnb ) .
high - resolution ultrasound is very sensitive in detection of thyroid nodules , enabling differentiation of solid and liquid lesions .
however , with introduction of sonography it became evident that thyroid nodules are very common , with prevalence ranging from 17% to as much as 67% in some cohorts .
nodular goiter does not include thyroid cancer , but one of the main aims of the clinical evaluation is to exclude the risk of overlooking thyroid cancer which is much less prevalent than benign nodules .
sonographic characteristics such as hypoechogenicity , microcalcifications , and increased nodular flow visualized by doppler are all to some extent predictive of malignancy .
microcalcifications visible on ultrasound examination are considered to be a specific feature of thyroid cancer ( 85,895% ) ; however , the sensitivity of this sign is relatively low ( 2959% ) .
presence of calcifications doubles the risk of malignancy , whereas microcalcifications increase the risk of thyroid cancer three - fold .
however , in pathologic examinations of benign thyroid nodules - inspissated colloid , fibrosis , and microcalcifications often coexist .
palpation  the earliest and most common form of tissue hardness estimation  was practiced by egyptian physicians as early as 2600 bc .
a more recent and sophisticated method of imaging of tissue hardness is the technique known as elastography .
the term  elastography  was coined by ophir et al .   to refer to an ultrasound - based imaging technique , where local axial strains were estimated by computing the gradient of axial shifts in echo arrival times along the ultrasound beam direction following quasistatic tissue deformation .
elastography , however , has now been used as a more general term to identify methods that image tissue stiffness , using different imaging modalities for example , ultrasound , magnetic resonance imaging , optical coherence tomography , different perturbation techniques to deform tissue , based on the elasticity parameter being measured or imaged .
roughly 20 years have elapsed since the first images depicting the local elastic properties of tissues were obtained .
the first decade of development produced a remarkable proliferation of techniques and optimization strategies . in the second decade
this trend continued , but with an important extension to dedicated platforms for conducting clinical trials in the hands of radiologists and skilled clinicians .
there are 3 main types of ultrasound elasticity imaging : elastography that tracks tissue movement during compression to obtain an estimate of strain ( quasi - static elastography ) , sonoelastography that uses color doppler to generate an image of tissue movement in response to external vibrations ( harmonic elastography ) , and a technique tracking shear wave propagation through tissue to obtain the elastic modulus ( transient elastography ) .
the first commercially available , clinical ultrasound scanners with option of tissue elasticity evaluation were equipped with strain elastography .
application of strain elastography to thyroid nodules examination resulted in different results of evaluation of usefulness of this technique in regard to differential diagnosis of benign and malignant thyroid nodules [ 914 ] .
diagnostic value of strain elastography is limited in evaluation of small nodules , large nodules ( with diameter approaching or exceeding the length of the probe ) , nodules with calcifications , and nodules with liquid content .
different results are obtained in different anatomical planes ( e.g. , axial versus sagittal ) , and the reproducibility is poor . finally , multinodular goiters with scarce or no normal thyroid tissue for reference are difficult to evaluate [ 9 , 1116 ] .
the new generation of elasticity imaging called supersonic shear wave elastography ( sswe ) has been introduced since 2006 to imaging of superficial organs as breast and thyroid with high - frequency linear probes [ 1721 ] .
this type of transient elastography does not require the compression of the tissues during their elasticity examination .
the obtained information is based on calculated elastic modulus ( described in kpa ) of the examined tissues .
based on multinational large - scale studies in the field of breast cancer detection and characterization , sswe proved to be highly reproducible , and it increased specificity without loss of sensitivity [ 20 , 21 ] . in the field of thyroid sswe
, it was proved that autoimmune thyroiditis does not hinder the evaluation of elasticity of thyroid nodules .
the aim of this study was to compare the usefulness of the new supersonic shear wave imaging elastography with strain elastography in evaluation of thyroid nodules .
during a few weeks trial time in 2010 , four consecutive patients with single thyroid nodule ( n = 1 ) and nodular goiter ( n = 3 ) were evaluated .
approval for this study was obtained from the ethics committee of the medical university of warsaw , and all patients provided informed consent .
the b mode and power doppler ultrasound of whole thyroid and neck lymph nodes was performed .
six dominant thyroid nodules ( in regard to b - mode and power doppler ultrasound features ) were evaluated with shear wave and strain elastography qualitatively and quantitatively as well as some with contrast - enhanced ultrasound ( sonovue ( bracco ) ) .
france)sswe , aplio xg ( toshiba , japan)strain elastography , technos ( esaote , italy)contrast - enhanced ultrasound , with linear high - resolution transducers : 154  mhz , 187  mhz , and , 83  mhz respectively . for strain elastography
, we adopted qualitative scale of rubaltelli et al . with threshold score of 2/3   and quantitative scale of cantisani et al .
with threshold thyroid tissue / nodule strain ratio of 2   measured with elasto - q ( toshiba ) .
for shear wave elastography , we adopted quantitative scale of sebag et al . with the threshold stiffness ( mean elastic modulus ) of thyroid nodule of 65  kpa .
the final diagnosis was based on clinical evaluation , multiple fnb , 1 year followup , or surgery .
final diagnosis ( pathology examination after surgery in 5 nodules , double fnb , and 1 year followup in 1 nodule ) was established : 1 papillary carcinoma ( figure 1 ) , 4 colloid nodules , and 1 benign nodule ( figure 2 ) .
shear weave elastography revealed 1 true positive and 5 true negative diagnoses in regard of thyroid cancer .
false positive diagnoses with strain elastography were found in nodules with liquid ( not evident on b - mode ultrasound ) or degenerative content of the nodules visible on contrast - enhanced ultrasound and/or pathology examination . a novel finding were
the punctate increased stiffness foci in microcalcifications seen in 4 nodules , some not visible on b - mode ultrasound as opposed to soft inspissated colloid foci visible on b - mode ultrasound in 2 nodules ( figure 3 ) .
supersonic shear weave elastography consists of the generation of remote radiation force by focused ultrasonic beams , the so - called  pushing beams ,  a patented technology called  sonic touch  . using sonic touch ,
the source is moved at a speed that is higher than the speed of the shear waves that are generated . in this supersonic regime ,
shape , which increases their amplitude and improves their propagation distance . for a fixed acoustic power at a given location ,
sonic touch increases shear wave generation efficiency by a factor of 4 to 8 compared to a nonsupersonic source .
after generation of this shear wave , an ultrafast echographic imaging sequence is performed to acquire successive raw radiofrequency dots at a very high - frame rate ( up to 20000 frames per second ) . based on young 's modulus formula ,
a color - coded image is displayed , which shows softer tissue in blue and stiffer tissue in red .
quantitative information is delivered ; elasticity is expressed in kilo - pascal ( kpa ) .
this preliminary paper based on small number of cases indicates that sswe indicated correctly thyroid nodules suspicious for cancer in contrast to strain elastography .
false positives on strain elastography could be due to liquid or degenerative content of nodules .
however , imaging with sswe , as a sensitive method of evaluation of stiffness of human tissue , the operator should be aware of physiological processes influencing the elasticity and easily apply a few rules to avoid artifacts ( figures 4 , 5 and 6 ) ( supplementary material 1-cine loop video ) . among well - known artifacts on sswe that should be mentioned is the one that can be encountered in any region when the sswe can be applied : the increased stiffness of the structures under externally applied pressure ( figures 4 and 5 ) ( supplementary material 1-cine loop video ) that can be due to nonlinear elastic effects , well explained by theory .
another artifact that can be encountered in thyroid sswe is one of increased stiffness in the isthmus of the thyroid due to trachea ( figure 6 ) .
it can be avoided with imaging in paracoronal plane of the nodule that does not incorporate the trachea .
however , it is important to state that these artifacts when properly interpreted do not hinder the accurate diagnosis .  
supersonic shear wave elastography may add a new dimension to ultrasound evaluation of thyroid nodules in several ways , for example : improve general performance in elasticity differentiation of thyroid nodules over strain elastography due to its high reproducibility , independence of examiners skill and numeral scale of elasticity measurement in kpa ; overcome the limitations of strain elastography : 
 nodules with liquid components or with degenerative changes;small nodules ( very good spatial resolution of the technique);large nodules ( possibility of subsequent determination of stiff regions even of large nodules , without the need of visualizing the whole nodule on one image);multinodular goiter with no or scarce normal thyroid tissue as a reference ; 
  nodules with liquid components or with degenerative changes ; small nodules ( very good spatial resolution of the technique ) ; large nodules ( possibility of subsequent determination of stiff regions even of large nodules , without the need of visualizing the whole nodule on one image ) ; multinodular goiter with no or scarce normal thyroid tissue as a reference ; differentiation between soft - inspissated colloid and stiff microcalcifications ; visualization of microcalcifications , even not visualized on b - mode imaging ( may increase sensitivity and decrease specificity of thyroid cancer diagnosis ) ; introduction of three - dimensional elastographic images to routine clinical practice and to national thyroid cancer databases , as this technique is already available and enables rapid acquisition of 3d ultrasound and elastographic data .
this would devoid diagnostic process and data archiving of image selection bias attributable to 2d ultrasound examination .
further multicenter large scale studies of thyroid nodules evaluating different elastographic methods are warranted , including ( a ) investigation of developmental models of diseases that link biomechanical properties ( elastography findings ) with genetic , cellular , biochemical , and gross pathological changes ; ( b ) comparison of accuracy of different elastographic methods ; ( c ) establishment of optimal diagnostic elastographic criteria ; ( d ) establishment of limitations of different elastographic methods in relation to evaluation of thyroid pathology .
 although elastography can enhance the differential diagnosis of thyroid nodules , its diagnostic performance is not ideal at present . 
 further improvements in the technique and creation of robust diagnostic criteria are necessary . 
 the purpose of this study was to compare the usefulness of strain elastography and a new generation of elasticity imaging called supersonic shear wave elastography ( sswe ) in differential evaluation of thyroid nodules . 
 six thyroid nodules in 4 patients were studied . 
 sswe yielded 1 true - positive and 5 true - negative results . 
 strain elastography yielded 5 false - positive results and 1 false - negative result . 
 a novel finding appreciated with sswe , were punctate foci of increased stiffness corresponding to microcalcifications in 4 nodules , some not visible on b - mode ultrasound , as opposed to soft , colloid - inspissated areas visible on b - mode ultrasound in 2 nodules . 
 this preliminary paper indicates that sswe may outperform strain elastography in differentiation of thyroid nodules with regard to their stiffness . 
 sswe showed the possibility of differentiation of high echogenic foci into microcalcifications and inspissated colloid , adding a new dimension to thyroid elastography . 
 further multicenter large - scale studies of thyroid nodules evaluating different elastographic methods are warranted . 
1. Introduction
2. Methods
3. Results
4. Discussion