Conventional 2-D & 3-D Ultrasound
Breast ultrasound is becoming an important adjunct to mammography and is usually performed in cases of dense breast, or implants when mammography is not sufficiently effective in identifying breast lumps. It is also in wide use in guided biopsy, as it allows real time imaging.
Ultrasound makes images with very high frequency sound waves, far higher than can be heard or have any effect on hearing. Although sound is a kind of radiation, ultrasound beams are not the cancer-causing ionizing radiation used in X-ray mammography. Ultrasound exams are performed without the discomfort of breast compression.
During the exam, a transducer generates a very short pulse of sound focused in a narrow beam. Special gel helps this sound travel from the transducer to the skin, and the sound travels through the breast tissues. The sound can bounce off of different materials in the breast and be reflected back to the transducer. The farther from the transducer the reflection is, the longer the sound takes to return to the transducer, so that by listening to echoes coming at different times, a map of reflections inside the breast can be generated. In modern transducers, the sound beam can be steered to make a map of a slice of the breast.
Benign and malignant tissues look different under ultrasound. Not all tumors are malignant: some will stay encapsulated in a small region of the breast. If the cancer doesn’t spread, it is considered “benign”. Malignant tumors can spread through the breast. Thus, smooth, oval-shaped regions with sharp edges in an ultrasound image are a sign of benign tumor. But areas with spikes spreading into the surrounding tissues with rough edges that are not well defined are a sign of malignancy. In addition to examining the shape of a lesion, a radiologist will examine other factors. Malignant tumors are typically darker than surrounding tissues. They typically absorb more sound than surrounding tissues (creating characteristic shadows on the ultrasound image). Benign lesions are typically wider than they are tall, while malignant tumors can be oriented vertically. However, there are other more subtle factors as well. No single factor tells everything about an observed image, but rather a serious of combined factors.
One of the factors in breast ultrasound is the presence of microcalcifications, which can be a sign that a tumor is malignant. But microcalcifications are difficult, if not impossible, to observe by ultrasound due to their similarity to the white speckles of the image.
Evaluation of the ultrasound technique in distinguishing malignant from benign tumors has shown the accuracy of benign condition detection to be 99.5%. Reportedly, a combination of ultrasonography and standard X-ray mammography has yielded a sensitivity of 92% and a specificity of 98%. With recent advancements in ultrasound platforms, some earlier-stage, clinically occult tumors, that were missed by screening mammography, could be detected. Since the speed of sound in fatty and less fatty breast tissues are approximately the same, ultrasound possesses a promising role in the future screening of younger women with dense breast and high risk factors.
For more information, visit: http://www.radiologyinfo.org/en/info.cfm?pg=breastus
