Purpose: Ultrasound (US) elastography measures the deformation of tissue in response to stress to derive and display its stiffness. Typically, the clinicians visually inspect and categorize the pseudo-color pattern of an elastography image into one of 5-6 different scores. This scoring method could lead to sizable variability due to its subjective nature. In this paper, we introduce a new method to objectively derive an elasticity score for differential diagnosis of thyroid nodules using US elastography.
Methods: Elastography data from 106 patients (123 nodules: 103 benign and 20 malignant) referred for a fine needle aspiration (FNA) biopsy were used for this retrospective study. No external compression was applied since carotid artery pulsation was used as the compression source. Elasticity contrast index (ECI), which was derived using spatiotemporal strain information, was computed to quantify the local stiffness contrast within a nodule. A larger ECI value suggests a stiffer nodule, thus indicating an increased likelihood of being malignant.
Results: The mean ECI value of malignant nodules (0.83 ± 0.23) was significantly higher than that of benign nodules (0.53 ± 0.18) (p = 0.00002). Using a cut-off value of 0.60, 19 malignant nodules and 76 benign nodules were detected correctly, leading to the sensitivity, specificity, positive predictive value and negative predictive value of 95%, 73.8%, 41.3%, and 98.7%, respectively.
Conclusions: The objective determination of an elasticity score by our method could reduce variability in scoring, leading to more reliable elastography results. With further clinical validation, we believe that ultrasound elastography could be used as an FNA triage tool in managing thyroid nodules.