LIGHT MAMMOGRAPHY WITH MODULATION TECHNIQ UE

Optical mammography is an alternative method tox-ray mammography or ca ncer detection in the female breast. In addition to high absorption a major problem arises from the scattering of light during propagation i n tissue. As a result, tissue inhomogeneities are imaged with reduced contrast and resolution. New techniques, such as phase sensitive detec tion of RF modulated laser light or time-gated detection of short-puls ed laser systems promise to overcome the limiting factors given by the use of cw light. Today, only frequency-domain techniques can be used in a clinical environment. Carl Zeiss developed a prototype based on t his technique. Two laser diodes emitting light at 690 and 825 nm are s inusoidally modulated in intensity with 110 MHz. The detector is a pho tomultiplier tube or alternatively an avalanche photodiode. Using a he terodyne technique signals are converted into low frequency components , from which changes in amplitude and phase caused by light propagatio n through tissue can be derived. The instrument operates in transmissi on mode. The breast is slightly compressed between two glass plates. S ource and detector are moved in tandem along the upper and lower plane in a raster scan. The raw data amplitude and phase are processed usin g newly developed algorithms, which perform corrections of the contras t reducing edge effects and calculate average absorption and scatterin g coefficients for a given source-detector position. These images are displayed without time delay on a computer screen and show an enhanced image contrast resulting in a greater tumor detectability.Currently, clinical data are acquired in the Robert-Roessle-Clinic of the Humbold t-University Berlin. The results obtained so far show that frequency d omain optical mammography, taking into account further technical impro vements, has the potential to reach the diagnostic quality of x-ray ma mmography and to yield complementary diagnostic results in special fie lds.