Breast ultrasound.
In ultrasound, ultrasonic images are formed by means of echoes among tissues with different acoustic impedance. Acoustic impedance is the product of sound speed and bulk modulus. The bulk modulus expresses the elasticity of an object, and in the human body, the value is increased by conditions such as fibrosis and calcification. The sound speed is usually high in elastic tissues and low in water. In the body, it is lowest in the fatty tissue. Ultrasound echoes are strong on the surface of bones which are hard and have a high sound speed. In organs filled with air such as the lungs, the bulk modulus is low and the sound speed is extremely low at 340 m/s, which produce strong echoes (the sound speed in solid tissues is 1,530 m/s). Human tissue is constructed of units smaller than the ultrasonic beam, and it is necessary to understand back-scattering in order to understand the ultrasonic images of these tissues. When ultrasound passes through tissue, it is absorbed as thermal energy and attenuated. Fiber is a tissue with a high absorption and attenuation rate. When the rate increases, the posterior echoes are attenuated. However, in masses with a high water content such as cysts, the posterior echoes are accentuated. This phenomenon is an important, basic finding for determining the properties of tumors. Breast cancer can be classified into two types: stellate carcinoma and circumscribed carcinoma. Since stellate carcinoma is rich in fiber, the posterior echoes are attenuated or lacking. However, circumscribed carcinoma has a high cellularity and the posterior echoes are accentuated. The same tendency is also seen in benign tumors. In immature fibroadenomas, posterior echoes are accentuated, while in fibroadenomas with hyalinosis, the posterior echoes are attenuated. Therefore, if the fundamentals of this tissue characterization and the histological features are understood, reading of ultrasound becomes easy. Color Doppler has also been developed and has contributed to the diagnosis of breast cancer. Breast cancer is rich in blood vessels. The feeding arteries flow directly into the tumor and are characterized by tortuosity and flexion. Since the intraductal spread of breast cancer can easily be evaluated, ultrasound has come to play an important role in breast conserving treatment. Breast cancer with intraductal spreading causes dilation of the mammary ducts, and the resolution of ultrasound at present has been improved to the degree that this dilation is shown as a tubular hypoechoic area. With the progress made in imaging diagnosis, nonpalpable breast cancer has increased and ultrasonically-guided aspiration cytology and biopsy techniques have been developed to obtain definite diagnoses of these lesions. In cases of micro-calcification detected by mammography, ultrasonically guided biopsy is recommended when identification by ultrasound is possible. Since this is a simple technique, it should be mastered.
Ueno
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Institute of Clinical Medicine, University of Tsukuba, Japan.
D000328:Adult; D001706:Biopsy / Q000379:methods; D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000473:pathology; D002277:Carcinoma / Q000098:blood supply / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D006801:Humans; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D018615:Ultrasonography, Doppler, Color; D016217:Ultrasonography, Mammary