Chapman,” Angular domain imaging of phantom objects within highly scattering mediums

Most optical tomography work within highly scattering media has employed coherence domain and time domain methodologies, both detecting the shortest path photons over the dominant randomly scattered background. Angular domain imaging instead uses micromachined collimators to observe only those photons within a small angle of the aligned laser light source, which simulations show are the shortest path photons, while rejecting heavily scattered light. These angular filters consist of micromachined silicon collimator channels 51 micron wide by 10 mm or 20 mm long on 102 micron spacing giving acceptance angles of 0.29 or 0.15 degrees respectively on a CCD detector. Phantom test objects were observed in mediums ranging from 1 to 5 cm thick at scattered to ballistic ratios of 500,000:1 to 10,000,000:1 depending on the illumination pattern. Object detection was retained at the same scattering levels for either 1 cm or 5cm thick mediums, demonstrating little dependence on medium thickness. Detection was also independent of the object size: phantoms ranging from thin structures of 100 micron wide lines and spaces to 4 mm spheres were detected at approximately the same scattering ratios. Minimum size resolution depends on CCD pixel size, not the collimator characteristics. Furthermore, detection was a function of the scattering ratio produced after the phantom's position, not of the whole medium’s scattering ratio. This means objects nearer the detector are much more observable. Longer collimators significantly increase the scattered light rejection as expected. Monte-Carlo simulations with angular tracking demonstrate the object size independence and are undertaken to verify the other behaviors