breast cancer, and is recommended to be used when mammography or other findings clearly indicate the need for a biopsy.

In a separate study comparing EIS to sestimibi scans, the T-scan had 72.2 percent sensitivity and 67 percent specificity in detecting breast cancer and sestamibi had 88.9 percent sensitivity. The T-scan detected one more breast cancer than sestamibi, at the expense of 27 additional false-positive results.34

Based on his studies of electrical impedance spectroscopy (the technology on which T-Scan is based), Keith Paulsen concluded that more work needs to be done with this technology. The placement of the electrodes on the breast, which determine the signal, depends on the operator and the impact of this on the test accuracy needs to be tested further. The technique is generally a low resolution, at best detecting tumors that are 1 cm or larger (about pea-sized). Because the technique loses sensitivity as the distance from the electrode increases, lesions deep in the breast will be harder to detect than those close to the skin surface. Finally, although the technique is potentially very high contrast, this remains somewhat controversial. Furthermore, this technology has not been evaluated by any large clinical trials and its lack of widespread acceptance might be due to the extraordinarily high reliability and accuracy of biopsy.

Microwave Imaging

Mapping the differences in the electrical properties can be accomplished by using low-energy electromagnetic waves, known as microwaves. Due to higher water content in tumors as compared with healthy tissue, differences in the electrical-conducting properties of breast tissue can be analyzed. Two to three times the amount of electrical conductivity is observed through microwave imaging of cancerous breast tissue when contrasted with surrounding normal tissue.5,23,27,48

While researchers are still years away from clinical trials, they have studied the technique using breast phantoms (test objects that simulate the radiographic characteristics of normal and cancerous breast tissue) and excised breast samples. Researchers were able to identify tumors as small as 6 mm in diameter (comparable to x-ray mammography for masses). But microcalcifications, which are often signs of early breast cancer, can be found much smaller than 6 mm with mammography.

However, breast cancers have the potential to show more contrast at microwave frequencies than at the x-ray frequencies used for mammograms.12 Also, the sometimes painful breast compression associated with x-ray mammography is not required for the conformal microwave imaging. Women can recline comfortably on their backs during the procedure. Microwaves imaging also avoids the use of radiation (see Harms of Mammography in Chapter 2).

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