Time-resolved optical mammography at four wavelengths between 680 and 975 nm

A portable prototype for optical mammography was developed and is presently applied in a clinical study. It is the first system for time-resolved transmittance imaging operating at four wavelengths in the range of 680 to 975 nm, and was designed so as to minimize the measurement time. The breast is slightly compressed between parallel plates. Four pulsed diode lasers provide light at 683, 785, 912, and 975 nm. The time distributions of transmitted photons are detected using a PC board for time-correlated single photon counting. The breast is scanned at the constant speed of 4 cm/s. Images are constructed by plotting the average absorption and reduced scattering coefficients (obtained from the Random Walk model for a homogeneous medium) and the intensity transmitted in a selected time gate. The two shorter wavelengths (683 and 785 nm) better probe the blood content (oxy- and deoxyhemoglobin) and oxygenation in tissues, while the two longer wavelengths (912 and 975 nm) are more sensitive to lipids and water, respectively. Thus, insight into tissue physiology can be obtained with potentially useful outcomes for the detection and characterization of breast lesions.