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ANATOMY FOR DIAGNOSTIC IMAGING
Ultrasound (Fig. 9.5) Ultrasound of the breast may be performed by direct contact scanning using a high-resolution linear probe. Linear reflections of Cooper's ligaments may be seen traversing the fat. In young women with glandular breasts the parenchyma is of homogeneously high echogenicity. With increasing age the pattern is less homogeneous, with increasing deposits of fat showing as hypoechoic lobules separated by echogenic fibrous strands. The lactiferous ducts may be seen as small tubular anechoic structures radiating from the nipple. Deep to the breast, an anechoic area of retromammary fat is seen anterior to the echogenic pectoralis muscle. Magnetic resonance imaging (Fig. 9.6 a and b) This technique is performed with the patient prone and the breasts suspended in a surface coil. With MRI the breast and chest wall may be demonstrated; skin, subcutaneous fat, connective tissue, parenchyma and vessels are also shown. Connective tissue is of low signal intensity and fat is of high signal intensity. Parenchymal tissue varies in appearance, as with mammography, according to the subject's age and hormonal status. Fat can be suppressed and contrast can be given to highlight abnormal areas. Sentinel node mapping (Fig. 9.7) This technique is performed by injecting a technetium colloid into the region of abnormality of the breast. Imaging after 2 hours demonstrates the 'sentinel node or nodes' - that is, the first 'port of call' for the lymphatic drainage. These nodes can also be identified intraoperatively by a special probe which can detect the higher concentration of radioactivity. If this node is normal, the likelihood is that the disease process has not spread from the breast.
Fig. 9.3
Lobular structure of breast
RADIOLOGY OF THE BREAST Mammography (Fig. 9.4 a and b) This technique uses a low-energy X-ray beam to maximize differences in soft tissue density and demonstrate the internal architecture of the breast. Compression of the breast, a short exposure time and the use of high-quality screen-film equipment improve image quality.
Mammographic patterns (see Fig. 9.4 a and b) Depending on the parenchymal pattern, that is, the relative composition of ductal, fatty and fibrotic or glandular tissue, the following may be seen on the mammogram. The ducts radiate out from the nipple, and may be seen centrally if dilated. When fat predominates the ducts may be seen. When fibrotic and glandular tissue predominate, the ducts are difficult to see. Blood vessels may be distinguished from ducts as they run more haphazardly through the breast and have a more uniform calibre, whereas ducts increase in calibre as they converge on to the nipple.
