Si Luo MEng, Abstract Co-Author: Nothing to Disclose

Manjiri K. Dighe MD, Abstract Co-Author: Nothing to Disclose

Dong-Jun Lim MD, Abstract Co-Author: Nothing to Disclose

Yongmin Kim PhD, Presenter: Nothing to Disclose

To objectively derive the elasticity score for differential diagnosis of thyroid nodules using ultrasound elastography.

Elastography data from 82 patients (92 nodules) referred for an FNA biopsy were used for this retrospective study. An IRB approval from the University of Washington was obtained. Elastography was performed prior to the FNA using a clinical ultrasound machine, Hitachi Hi Vision 5500. No external compression was applied since carotid artery pulsation was used as the compression source. Instead of assigning a score of 1~5 by visually inspecting the elastography images to make a diagnosis, the spatial distribution of a strain image was analyzed by calculating the occurrence rate of different combinations of strain values. A metric, called elasticity contrast index (ECI), was then computed to quantify the difference in stiffness between the nodule and its surrounding normal tissue. A larger ECI value suggests a stiffer nodule, thus indicating the increased likelihood of being malignant.

The mean nodule size was 2.1 × 1.6 × 1.9 cm (ranging from 0.5 × 0.6 × 0.6 cm to 4.1 × 2.3 × 3.5 cm). 21 out of 92 were smaller than 1 cm. The mean ECI (n=12, 6.32±2.25) of malignant nodules was significantly higher than that of benign nodules (n=80, 3.39±1.58) (p=0.0008), indicating that malignant nodules are stiffer than benign nodules compared to the surrounding normal tissue. Using a cut-off value of 3.85, all 12 malignant nodules could be detected, leading to the sensitivity, specificity, positive predictive value and negative predictive value of 100%, 73.8%, 36.4% and 100%, respectively.

We have developed an objective method to derive the ultrasound elastography score. For most US elastography studies, the stiffness of a nodule is inferred by visually inspecting the pseudo-color pattern in the strain images. This approach tends to be subjective and suffers from intra and interobserver variability. Utilizing the strain distribution information, the elasticity contrast index (ECI) was effective in quantifying the elasticity difference between a nodule and its surrounding tissue. This method is also applicable in the thyroid elastography using external compression.

The quantification of elasticity scores could be of benefit in reducing the intra and interobserver variability and the amount of training required for interpreting the ultrasound elastography images.

Luo, S, Dighe, M, Lim, D, Kim, Y, Objective Ultrasound Elastography Scoring on Thyroid Nodules.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9007118.html