The objective of the research is to establish the scientific basis for efficacy of diaphanography for diagnosis of tumors of the breast. Diaphanography involves transillumination of the breast by visible and near infrared light, and imaging with a video camera. It does not employ ionizing radiation. Malignant tumors have been detected by diaphanography, but the reasons for the success are not well understood, nor are the limitations of the method. It is not clear that the optimum technique has been found. The proposed research project will investigate these questions by several methods: the diffuse transmittance and optical properties of breast tisues will be measured from at least 600 nm (red) to 1100 nm (near infrared) and extended up to 2000 nm if feasible. The diffuse transmittance measurements will be made in both surgical specimens and in vivo, in the intact human breast. The contrast due to an anomaly or lesion in a matrix of tissue will be calculated and compared with measurements in phantoms, investigating the dependence of contrast on the size, depth, and optical scattering and absorption coefficients of anomaly and matrix. The anatomical or physiological basis for changes in optical properties will be investigated by a combination of optical and histological techniques. Particular attention will be paid to the role of absorption in blood in tumor and surrounding tissue, and of changes in content of watery tissue, related to the growth of the tumor. The optical experiments and histological results will be correlated with the appearance of the tumor in color as well as monochrome diaphanography.