The detection of small amounts of indocyanine green (ICG) in small volumes would suggest its potential use in the detection of early breast tumors. While phased array has already shown its ability to sharply localize small amounts of ICG in the picomole region, the question has arisen, what would be the comparable sensitivity of continous light systems for the same purpose? If this were a comparable sensitivity, the advantages of the simplest of opto- electronic systems and the use of light intensity not limited to those available under FDA regulations for laser diodes could be realized. In this research work, we investigate two methods of enhancing the contrast agent between diseased and healthy tissue using low frequency amplitude modulated light sources. The first method exploits the symmetry between the left and right breast and the second exploits the cylindrical symmetry of the breast. Both effect are enhanced by the use of an injected contrast agent (ICG). Based on the theory and model study, several human subjects cases were studied in the Hospital of the University of Pennsylvania. The results show that the peak signal can get about 60 seconds after ICG injection through the vein and then will take few minutes to get back to the baseline. The half decay time and maximum (Delta) OD are dependent of the characteristics of the breast tissue.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.