The initial diagnostic test to evaluate a thyroid nodule is a high resolution ultrasound of the thyroid. The ultrasound will show the characteristics of the nodule including smoothness of the edges of the nodule, whether the nodule has calcifications, whether there are multiple nodules or a single nodule, and whether the nodule(s) has benign characteristics suspicious for malignancy.
An ultrasound uses cyclic sound pressure, higher than the upper limit of human hearing (approximately 20 kilohertz or 20,000 hertz) to illuminate details about the inner structure of organs or tissues. For a thyroid ultrasound, a transducer (like a small microphone) is placed at the neck, from which sound waves pass into the skin. As the transducer converts the echoes into electronic signals, images of the neck appear on a television monitor for physician review. An ultrasound of the neck is a painless procedure that takes about 10 minutes.