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Technical aspects of thyroid ultrasound

Author
Manfred Blum, MD, FACP
Section Editor
Douglas S Ross, MD
Deputy Editor
Jean E Mulder, MD

INTRODUCTION

Current methods of ultrasonography permit "real-time" identification of structures as small as 2 mm in diameter, thereby allowing the visualization of very small tumors of the thyroid and parathyroid glands. These methods also permit estimates of overall and regional blood flow to the thyroid. This topic review will discuss the basic technology of thyroid ultrasonography. The clinical use of thyroid ultrasonography is reviewed elsewhere. (See "Overview of the clinical utility of ultrasonography in thyroid disease".)

PRINCIPLES AND METHODS

Thyroid ultrasonography is a technique that requires experience and an understanding of thyroid anatomy and pathology. It cannot be optimally performed by a technician who simply takes pictures and then submits the photographs for later interpretation. Instead, cost-effective testing requires input from both the ordering clinician and the interpreting clinician. The ordering clinician should specify the precise clinical question that must be answered.

Some endocrinologists prefer to perform the sonogram themselves, while others refer the patient to a sonographer or a radiologist. In some cases improved efficiency may be obtained when the endocrinologist or surgeon actually performs the sonogram. The endocrinologist, surgeon, or radiologist who does thyroid sonograms must master thyroid palpation, anatomy, and pathophysiology; have special training in ultrasound procedures; meticulous attention to detail; and adequate time to perform a full examination. They must be willing to invest in costly and sophisticated equipment, and perform an adequate number of studies to achieve expertise. They cannot merely examine films or digital images. No matter who does the test, results can sometimes be equivocal and misleading.

Gray-scale ultrasonography — Gray-scale ultrasonography involves the intermittent generation of a pulse of sound energy and the reception of reflected echoes to produce an image of the structures traversed by the sound. Current technology produces high-resolution thyroid images by using sound frequencies between 5 and 13 million cycles per second (megahertz [MHz]). These frequencies are well above the range audible by humans and are safe. Sound waves of this frequency pass through air poorly and, therefore, the transducer, the device that generates the sound and receives the echo, must be coupled to the skin with a medium that excludes air.

The sound waves penetrate tissues, and a portion of the energy is reflected at tissue interfaces up to a depth of 5 cm. The thyroid gland is well within this distance in most patients.

        

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Literature review current through: Nov 2016. | This topic last updated: Wed Apr 01 00:00:00 GMT+00:00 2015.
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