Evaluation of Spatial Variations in the Time and Frequency Dependence of Imaging Operators for Diffusion Tomography

H.L. Graber et al. (1994)


Employing the framework of a perturbation model for optical diffusion tomography, the sensitivity and selectivity attainable from optical time- and frequency-domain, including phased array, measurements, are compared and contrasted. Monte Carlo simulations were used to calculate impulseresponse functions in the interior of several homogeneous media. From the results, the impact on detected light due to small localized changes in absorption cross-section were computed. A feature unique to the frequency domain is the ability to qualitatively modify the depth profile of the weight amplitude by employing several sources in a phased array. In the case of single-source transmission measurements, a time-resolved measurement with a short integration time leads to enhanced ability to resolve deep-lying structures, by increasing the weight in deep regions relative to those near the surface. In contrast, as the source modulation frequency is increased in a frequency-domain measurement, the weight amplitude drops off most rapidly in regions farthest from the boundaries, and more slowly in more superficial regions. The significance of these findings for perturbation-based image recovery schemes is discussed.