Breast Ultrasound (Sonogram)

Breast ultrasound uses high frequency sound waves that cannot be heard by humans. It involves no ionizing radiation. Screening ultrasound examinations can either be performed entirely by hand by a trained technologist or radiologist (where the operator moves the detection piece, i.e. the “transducer”, by hand), or by using an “automated” or semi-automated device (operated by a motor with positioning assistance from a technologist). Hand-held screening ultrasound requires skill on the part of the person performing the test since an abnormality must be seen while scanning in order to be reported by the radiologist. It is also necessary to perform real-time adjustments of technique while performing hand-held breast ultrasound. On average, screening ultrasound takes about 15 minutes to perform, though it can take longer if there are multiple findings requiring documentation.

Automated breast ultrasound (Figs. 7, 8) typically uses a special wide (usually 15-cm) transducer to document the entire breast (usually in three overlapping sections). A semi-automated approach adapts a motorized arm to a standard 3.8- to 5-cm transducer that is moved across the breast in overlapping segments. Both approaches create hundreds of images that must be later reviewed by a radiologist. Several other approaches to whole breast ultrasound are in development, including return to use of prone positioning (with the woman lying on her stomach). Automated ultrasound is less dependent on the technologist performing the screening and it can be performed in a slightly shorter time than when screening is performed by hand. Preliminary studies show similar cancer detection rates for fully automated ultrasound compared to hand-held ultrasound [1]. When an abnormality is seen on automated ultrasound, the patient must usually return for additional testing with hand-held ultrasound in order to determine appropriate care. Results with semi-automated ultrasound showed cancer detection rates at least as high as with hand-held ultrasound, with fewer benign biopsies [2].

Ultrasound uses high-frequency sound waves to form an image (sonogram). The sound waves pass through the breast and bounce back or “echo” from various tissues to form a picture of the internal structures of the breast. Only gentle pressure is applied to the breasts and ultrasound rarely causes any discomfort. Ultrasound does not use or produce ionizing radiation. A water-soluble gel or lotion is placed on the skin of the breast. A hand-held device (transducer) directs the sound waves to the breast tissue. The transducer is moved over the skin of the breast to create a picture that can be seen on a computer screen. Cancers are usually seen as masses that are slightly darker than the normal lighter gray fat or white (fibrous) breast tissue (Figs 9, 10). Sometimes distortion of the tissue or bright (white) echogenic dots due to calcifications can be seen. Cysts are round or oval black fluid-filled sacs and are often seen with ultrasound; cysts are a normal finding (Fig 11). Some ultrasound equipment also allows assessment of tissue stiffness through use of elastography; this can be used to help determine need for biopsy of low suspicion lesions, with soft lesions more likely benign and stiff lesions more likely malignant [3, 4].

Physician-performed or technologist-performed ultrasound finds an additional 2 to 4 cancers per thousand women already screened by mammography [5-8]; or tomosynthesis (3D mammography) [9, 10]. Similarly, automated ultrasound finds 2 to 3 additional cancers per thousand women already screened by mammography [8, 11]. More than 85% of cancers seen only on ultrasound are invasive, early stage, and node negative [8, 12]. In a prospective randomized study from Japan [13], women who had screening ultrasound in addition to mammography were half as likely to have cancer detected because of a lump or other symptoms before the next screen (known as an “interval cancer”). Ultrasound is readily available and cost effective, though not all centers offer screening ultrasound due to a shortage of trained personnel.

Both the individual performing the scanning (technologist and/or radiologist) and the radiologist who interprets the images should have experience and skill in screening breast ultrasound. On average, ultrasound will show more areas which need follow-up than does mammography. Some of those “finds” will be cancer, but the vast majority will not (known as a “false positive”). In two multicenter prospective trials [5, 13], 20-30% of cancers were seen only on mammography and 29-33% of cancers were seen only on ultrasound: it is important to continue mammography in addition to ultrasound screening.