WHAT IS THYROID ULTRASONOGRAPHY (THYROID ECHOGRAM, THYROID ULTRASONOGRAM) TEST?
High-frequency B-mode sonography and colour-power Doppler are used to evaluate the thyroid gland size, shape, and positions. Ultrasound creates an oscilloscopic picture from the echoes of high-frequency sound waves passing over the neck area (acoustic imaging). The time required for the ultrasonic beam to be reflected back to the transducer from differing densities of tissue is converted by a computer to an electrical impulse displayed on an oscilloscopic screen to create a three-dimensional picture of the thyroid gland. The differing tissue densities of cysts and tumours enable the ultrasonogram to be helpful in determining which is present. Cysts are clearly demarcated by smooth borders and do not demonstrate internal echoes. Adenoma appearances vary but usually demonstrate halo. Multinodular goitre may also demonstrate a halo. In thyroiditis, the gland appears enlarged, with a greater than normal amount of low-level echoes. Ultrasound is a cost-effective procedure for screening for thyroid cancer because thyroid tissue has a high echogenicity. Thyroid cancer is usually poorly defined, with low-level echoes and without a halo. Advantages of this test are that it is safe for use during pregnancy because it does not use radiation, it can visualize the entire area of the anterior neck, it can detect smaller nodules (2 mm) than a nuclear scan, it can differentiate cysts from solid nodules (which a nuclear scan cannot), and it can improve the sensitivity of fine-needle aspiration biopsy.