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| Over their lifetimes, American women face a 12.5% risk of developing breast cancer— the leading form of cancer in women today. Although X-ray mammography is effective at detecting cancer in women over the age of 50, false-negative rates can be as high as 22% in younger women owing to denser breast tissue associated with age and hormonal influences. For these women, a highly sensitive detection method does not yet exist.
Highly effective alternatives to mammography have been slow in coming. Magnetic resonance imaging and ultrasound are increasingly used but are hampered by high cost and low sensitivity, respectively. Recently, however, biomedical engineers at the Beckman Laser Institute and Medical Clinic at the University of California, Irvine, devised a detection method that is both noninvasive and reliable for women, regardless of their age, hormonal status, and breast tissue density. A handheld probe uses a near-infrared optical method known as frequency domain photon migration and takes advantage of the turbidity or heterogeneity of a sample or tissue. The probe launches a series of light signals into the breast tissue at different frequencies, measuring how the light is absorbed and scattered by the deoxyhemoglobin, oxyhemoglobin, water, and adipose contents of the breast tissue. “You need to find contrast to find tumors,” says Bruce Tromberg, the team’s principal investigator. “We’re trying to discover what the main contrast features will be.” By varying the modulating frequencies and using different wavelengths, Tromberg’s team can measure the phase and amplitude of the wave and calculate the absorption and scattering spectra of tissue (Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 4420–4425). In a preliminary study, the technique was sensitive enough to detect small, palpable breast lesions and subtle physiological changes influenced by age, menopausal status, and menstrual cycle phase. “I don’t think this technique will replace mammography, but there will be a population of women this will be best for,” Tromberg adds. “In pre- and perimenopausal women, there are problems with mammography, [and] this is a population where the disease can be quite aggressive. This technology will be most useful for radiographically dense tissue.” The technique can also be used for tracking the effects of chemotherapy before and after biopsy or surgery. Furthermore, it can be used to establish a connection between the changes associated with age and risk of disease. |
