A diffusion model of noninvasive absorption spectroscopy was used to determine how the change in signal resulting from a point absorber depends on the position of that absorber relative to the source and detector. This is equivalent to calculating the relative probability that a photon will visit a certain location in tissue before its detection. Experimental mapping of the point-target response in tissue-simulating materials confirmed the accuracy of the model. For steady-state spectroscopy a simple relation was derived between the mean depth visited by detected photons, the source–detector separation, and the optical penetration depth. It was also demonstrated theoretically that combining a pulsed source with time-gated detection provides additional control over the spatial distribution of the photon-visit probability.
© 1995 Optical Society of America
Original Manuscript: September 23, 1993
Revised Manuscript: July 15, 1994
Published: January 1, 1995
Michael S. Patterson, Stefan Andersson-Engels, Brian C. Wilson, and Ernest K. Osei, "Absorption spectroscopy in tissue-simulating materials: a theoretical and experimental study of photon paths," Appl. Opt. 34, 22-30 (1995)