Spatiofrequency Filter in Turbid Medium Enhanced by Background Scattered Light Subtraction from a Deviated Laser Source

Angular Domain Imaging is an optical tomography technique that filters out scattered light by accepting only photons with small deviation angles from their original trajectories. Previously, angular filters of linear collimating array (0.29 degrees acceptance) or spatiofrequency filter of a +50mm lens with a 214um aperture (0.25 degrees acceptance) were used. In the linear collimating array system, using a wedge prism to deviate the light source by 2-3x the acceptance angle creates a second image of only the scattered components which can then be subtracted from the filtered image to enhance detectability. We now apply this technique to the spatiofrequency filter system at an angle 2x the acceptance. Utilizing several wavelengths of laser sources with different beam symmetries, test phantoms are placed in a 5cm thick sample of diluted intralipid solution, with a maximum SR of 1.64x10(6):1 (mu(s)' = 1.8cm(-1)). By digitally subtracting the background scattered light, test phantoms previously unobservable are now distinguishable. Using background subtraction, the SR limitation of the SFF system improves 3x under full illumination and similar to 40x under line of light illumination. The improvement under partial illumination is similar to the result using the collimator array, but with resolution limited by the optics used in the system.