Ultrasound Thyroid Elastography as a Pre-FNA Screening Tool: Algorithms and Clinical Evaluation

Abstract

Thyroid nodules are a common medical problem, with studies reporting as high as 50% of the population having a thyroid nodule at autopsy. Although the majority of thyroid nodules are benign, it is clinically important to diagnose the small malignant population from the rest of the asymptomatic benign nodules. A fine needle aspiration (FNA) biopsy is used to evaluate a thyroid nodule's malignancy and determine whether a surgical removal is warranted. It is estimated that somewhere between 250,000 and 300,000 thyroid FNA biopsies are performed annually in the United States. However, a large percentage (approximately 70%) of these biopsies turn out to be benign. Thus, considering the increasing number of thyroid nodules being detected and the vast number of benign nodules undergoing FNA biopsies, the challenge lies in judiciously deciding which nodules should be aspirated. Ultrasound (US) elastography measures the deformation of tissue in response to stress and derives and displays its stiffness. Recent studies demonstrated the potential of applying elastography to the thyroid gland in noninvasively differentiating benign and malignant thyroid nodules. However, lack of reproducibility in data acquisition and scoring has been a major limitation for US elastography using external compression. In this dissertation, we have utilized the carotid artery pulsation as an intrinsic compression source and developed quantitative scoring methods to reduce the variability due to the externally-applied compression and subjective assessment of elastography images. We have performed studies with human subjects to evaluate the clinical usability (i.e., interobserver agreement and intraobserver reproducibility, and influence of a nodule's parameters on the diagnostic performance) of the developed elastography technique. We have also demonstrated the good diagnostic performance of our elastography method in differentiating benign and malignant thyroid nodules in clinical settings. The elastography technique described in this dissertation has been implemented and available in commercial ultrasound machines. We believe that our work would be of use to clinicians in deciding whether a thyroid nodule should be referred for an FNA biopsy or follow-up with a higher level of confidence, and providing better care at a lower cost for patients with thyroid nodules.