FREQUENCY-DOMAIN OPTICAL-IMAGE RECONSTRUCTION IN TURBID MEDIA - AN EXPERIMENTAL-STUDY OF SINGLE-TARGET DETECTABILITY

An experimental study of the detectability of an object embedded in op tically tissue-equivalent media by frequency-domain image reconstructi on is presented. The experiments were performed in an 86-mm-diameter c ylindrical phantom containing an optically homogeneous cylindrical tar get whose absorption and scattering properties presented a 2:1 contras t with the background medium. The parameter space explored during expe rimentation involved object size (15-, 8-, and 4-mm targets) and locat ion (centered, 20-mm off-centered, and 35-mm off-centered) variations. Image reconstruction was achieved with a previously reported regulari zed least-squares approach that incorporates finite-element solutions of the diffusion equation and Newton's method solutions of the nonline ar minimization problem. Also included during image formation were ima ge enhancement schemes-(1) total variation minimization, (2) dual mesh ing, and (3) spatial low-pass filtering-which have recently been added . Quantitative measures of image quality including the size, location, and shape of the heterogeneity along with errors in its recovered opt ical property values are used to quantify the image reconstructions. T he results show that a near 22:1 ratio of tissue thickness relative to detectable object size has been achieved with this approach in the la boratory conditions and parameter space that have been investigated. ( C) 1997 Optical Society of America