A non-contact fluorescence diffuse optical tomography (DOT) system capable of producing B-scan-type images of localized fluorescence regions up to depths of 15mm is presented. The B-Scan mode is analogous to ultrasound where the excitation and remission signals are delivered from the same surface of the tissue. This optical fluorescence system utilizes a 635 nm diode laser and two orthogonal galvanometers to raster scan the position of the source along the tissue surface. Using Protoporphyrin IX (PpIX) as a fluorescent agent, the amplitude of the remitted signal is separated by a 650 nm long pass filter and the fluorescence is then detected by a cooled CCD camera. Images are acquired for all source positions along the surface of the tissue, providing remission intensity images for each. This volume data set is then used in image reconstruction of the sub-surface volume, via a finite element method of modeling the fluorescence diffusion. The optimal remission imaging geometry, in terms of depth sensitivity, computation time, and image contrast-to-noise, was determined by performing sensitivity and singular-value decomposition analysis of the Jacobian for various source/detector combinations. The simulated results indicate that the fluorophore concentration and the inclusion size can not be recovered accurately in this mode; however, it is shown that the inclusion depth can accurately be predicted. Finally, by performing simulations on a mesh created from an MR image, we show that our system may prove useful in predicting the regions of local tissue fluorescence in the application of resection of residual brain tumor tissue under fluorescence guidance. This non-contact diagnostic system is being calibrated and finalized for potential use in this application of sub-surface imaging in the brain.
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