LOCALIZATION OF ABSORBERS IN SCATTERING MEDIA BY USE OF FREQUENCY-DOMAIN MEASUREMENTS OF TIME-DEPENDENT PHOTON MIGRATION

Frequency-domain studies of time-dependent light propagation in tissue like phantoms that contain optical heterogeneities are described. Spec ifically the phase shift and amplitude modulation of reemergent light were measured when illuminated by an amplitude-modulated light source. Changes in the phase angle and the extent of modulation revealed the presence of a light-absorbing object. Furthermore the magnitude and di rection of these changes were sensitive to the absorber depth and the light modulation frequency in a manner that could be used to infer the location of the heterogeneity. These data suggest the feasibility of optical imaging by frequency-domain methods.