[Mammography with light--possibilities and limits].

Translucence of tissue in the spectral range 650-1000 nm suggests the use of light for medical diagnosis. Measuring light absorption at wavelengths of 760, 840, 930 and 975 nm yields information on the amounts of deoxygenated and oxygenated hemoglobin as well as of fat and water. However, because of the strong scatter the propagation of light in tissue is diffuse. For this reason details in thick tissue slices cannot be imaged sharply. It is expected that tumors will differ from surrounding tissue in their scatter and absorption properties. Recent experimental progress has led to an improved contrast of details differing in their scattering properties, and also to images with better spatial resolution. This is rendered possible either by illuminating the object to be investigated with short light pulses and analyzing the time course of the emerging light or by applying intensity modulation and measuring the phase difference between the entering and the emerging light. In this way the mean pathlength of light propagation can be determined. Attention is now returning to mammography with light after the early trials on diaphanography were not successful. Clinical tests with improved instruments are in progress.