Something old and something new: a brief history of thyroid ultrasound technology

Abstract

Objective: To discuss both early and recent ultrasound technologic advances and to explore the role of such technology in the evaluation of the thyroid gland.

Methods: The physics of sound and the history of the use of reflected sound waves are reviewed, and the medical applications of ultrasound, with a particular focus on the thyroid gland, are presented.

Results: Since the first reports of thyroid ultrasonography were published in the late 1960s, the field has undergone remarkable evolution. Ultrasound imaging improved in parallel with growth in computing, transducer, and display technology. The transition from A-mode to B-mode to gray-scale imaging was associated with dramatic improvements in clarity and interpretability of ultrasound images. Current high-resolution ultrasound images are able to identify virtually all structural thyroid lesions of clinical significance. Although ultrasound characteristics cannot be used for accurate diagnosis of benign thyroid lesions, certain features such as irregular margins, microcalcifications, and central vascularity suggest the presence of "suspicious" thyroid nodules. Recent advances including the use of contrast agents, tissue harmonic imaging, and multiplanar reconstruction of images will further enhance the resolution and interpretability of ultrasound images. The use of Doppler flow analysis may improve the predictive value for determining the risk of a malignant thyroid lesion, but no current ultrasound technique is capable of determining benignity with an acceptable degree of accuracy. Ultrasound guidance of fine-needle aspiration biopsy has been demonstrated to improve both diagnostic yield and accuracy and will likely become the standard of care.

Conclusion: Because high-quality ultrasound systems are now available at a reasonable price, routine clinical use of ultrasonography is considered an important extension of the physical examination by many endocrinologists.