A dilemma at gray scale thyroid ultrasound: microcalcification or not? Differentiation with Acoustic Radiation Force Impulse Imaging-Virtual Touch Imaging.

Aims: To evaluate the capacity of virtual touch imaging (VTI) of the acoustic radiation force impulse (ARFI) techniquein the differential diagnosis of micro-echogenicities in thyroid nodules.

Material And Methods: The study comprised 28patients. Gray scale and ARFI displacement maps were used during ultrasound examination.In the same session, fine needleaspiration biopsy (FNAB) samples were obtained from the dominant nodule hav-ing micro-echogenicities. Two radiologists blinded to the FNAB results and clinical data of the patients evaluated these images and rated ARFI echogenicities according to the degree of shining points on the displacement maps and classified them as isohypoechogenic, isohyperechogenic, and obvious hyperechogenic. To differentiate between benignancy and malignancy, "a new sign" was defined as follows: in the ARFI maps obtained by VTI, iso-echogenic or hyper-echogenic appearance of micro-echogenic foci was evaluated as benignancy and hypo-echogenic appearance of micro-echogenic foci was evaluated as malignancy.

Results: The FNAB results indicated 14 cases and benign nodules in the other 14 cases. Interobserver agreement between the two radiologists was highly significant for the classification of the micro-echogenic foci (Kappa=0.659, p<0.001). When we reclassified the hyperechoic and isohyperechoic foci as "benign" and isohypoechoic foci as "malignant", the interobserver agreement between the two radiologists increased (Kappa=0.772, p<0.001). The evaluation of the first and second radiologists were highly concordant with the gold standard pathology results (Kappa=0.786, p<0.001 and Kappa=0.714, p<0.001, respectively).

Conclusions: ARFI method with specific VTI features could be a very useful tool in the differentiation of malignant microcalcifications in thyroid nodules.