Ultrasonography uses sound waves at very high frequency to image internal structures, including those deep within the body. Either pulsed or continuous sound waves are directed at the area of interest using a hand-held device called a transducer. The transducer also receives echoes of the sound waves in a pattern that reflects the outlines of the internal structure mass. The transducer changes electrical signals into ultrasound waves and converts the reflected sound waves back to electrical energy. Unlike radiological procedures, the ultrasound method requires no exposure to x-rays.
When ultrasound is chosen to guide a breast biopsy, one of the biopsy instruments used is a VAD. Nodules of tissue less than about an inch in size can be totally removed using this equipment. These systems use vacuum pressure to pull tissue into a needle and remove it without having to withdraw the probe after each sampling—as is necessary when the core needle method is used. Biopsies are obtained in an orderly manner by rotating the needle, ensuring that the entire region of interest will be sampled.
The core needle method is used most commonly because it is the least expensive, easy to perform and highly accurate for many lesions. An inner needle with a trough extending from it at one end is covered by a sheath and attached to a spring-loaded mechanism. When the mechanism is activated, the needle moves forward, filling the trough with breast tissue. The outer sheath instantly moves forward to cut the tissue and keep it in the trough. It takes only a fraction of a second to obtain a sample and for each sample it is necessary to withdraw the needle to collect the tissue.