Photon migration theory is employed to calculate the line spread function of time-resolved photons as they cross different planes inside a finite slab. Results are used to determine the spatial resolution for objects imbedded at each depth, shown to be proportional to the square root of the excess transit time (Delta) t. However, the light intensities available at small excess transit times, required to obtain finer resolutions, are severely reduced as tissue thickness is increased. Optical parameters of breast tissues are used in our theoretical findings in order to analyze the feasibility of breast screening. For 5- cm-thick tissues that mimic targets of interest in clinical mammography, were predict vanishingly small detectable intensity at the small values of (Delta) t needed in order to achieve 2-mm resolution. Additionally, because normal breast is a spatially heterogeneous mixture of glandular and adipose tissues, which have significantly different optical scattering parameters, the analysis indicates large-amplitude background variations, particularly at short delay times.