Mammography equipment and the human hand are the two most widely used tools of breast cancer detection, but neither is 100 percent accurate. As noted earlier, very small cancers are difficult or impossible to detect by palpation. Although many of these cancers show up on a mammogram, others do not. In fact, 10 to 15 percent of palpable breast cancers (those detectable on manual examination) are not seen in a mammogram.
Thus there is an ongoing search for other techniques that may further improve the chances of early breast cancer detection.
- Thermography. This technique measures minute temperature variations and produces a heat map of the area photographed. Cancers are warmer than normal body tissue, because their rapid growth requires an increased blood supply. The drawback of thermography is that it misses perhaps 30 percent of cancers, especially the small, early ones not detectable by manual examination. Also, a number of benign conditions also produce “hot” areas. Therefore thermography is not accurate enough to be used in screening.
- Ultrasound. This technique uses sound waves to differentiate solid masses from ones that contain fluid. A technician uses a microphonelike probe called a transducer, pressed firmly against the patient’s skin. Very high frequency sound waves produce echoes as they bounce off body tissue. Another ultrasonic technique involves immersing the breasts in a tank of water. The technician will take a photograph of the oscilloscope screen for future reference. Ultrasound has the advantages of being painless, quick, and radiation-free. However, it is not accurate enough to be used alone in screening for breast cancer, and its main use is to determine whether a lump is a cyst.
- Diaphanography. This technique, also called transillumination, uses a strong, cold light and infrared photography. It can differentiate a solid tumor from a cyst filled with clear fluid, but it, too, cannot detect very small cancers, and has not proved useful in screening for breast cancer.
- Computerized tomography. Generally referred to as CT scanning, this technique uses multiple X-ray images and a computer to construct a series of cross-sectional views of a body part. CT scanning is being studied as a possible tool for detecting breast cancer, particularly in small, dense breasts that are difficult to examine by mammography. Tomography has drawbacks, however, that make it an unlikely candidate for routine screening: It is expensive and it requires a relatively high dose of radiation compared to mammography.
- Magnetic resonance imaging (MRI, formerly called NMR). This is still a highly experimental and very expensive technique. It involves using radiowaves and magnetism to image a biological structure. In experimental studies, MRI has detected large, palpable breast cancers, but it is not yet known whether the technique can be used to tell the difference between cancer and benign growths.