Abstract

Potential of depth resolution of continuous-wave (CW) illumination in diffuse optical imaging is explained. It is known both experimentally and numerically that in CW measurements photons traversing a homogenous, semi-infinite, highly scattering medium between a source and a detector located on the surface of the medium follow paths that the volume interrogated resembles a banana-shape. Also is known that, sensitivity profile of photon propagation in CW measurements is non-uniformly distributed in depth, reaching a maximum at a certain value depending on geometry, source-detector separation, and optical properties of the medium. The presence of an inclusion with a higher absorption coefficient with respect to that of the background in a homogeneous medium can be estimated by increasing time-rate-of- photon-injection into the medium. The inclusion is assumed to be at a depth between the optode pair such that distances to optodes are the same. An increment in the time-rate-of-photon-injection will give different detection slopes depending on the depth of the inclusion, because the number of photons which is blocked by the inclusion is high if it resides at a depth where the sensitivity profile has a higher value. In this work, preliminary results of Monte-Simulation of light propagation show that measuring slopes of increase in detected light intensity for different interoptode distances are different for extreme case of screen between optodes blocking all photons below a certain depth. Specification of inclusion with this method may enable us to make predictions about the depth and optical properties of the inclusion to be used as a priori information to be used image reconstruction in diffuse optical tomography that may be integrated imaging systems.

© 2007 SPIE