UC Irvine

Near infrared optical imaging is emerging as a potentially important imaging modality, because it offers real time data access, portability, cost-effectiveness, and the relatively safe use of non-ionizing radiation. Reconstruction of images by optical tomography is complicated by the diffusive character of light propagation in optically heterogeneous tissue. The spatial volume element probed by the light path between the light source and optical detector is rather wide and depends on a variety of experimental and instrumental factors. We have published an optical image of the hand in air based on photon density wave distribution characteristics, using both steady-state (intensity) and frequency-domain (phase and modulation)1 experimental conditions. Since then, we have developed new instrumentation, better measurement protocols, some reconstruction algorithms and a more complete theoretical understanding of photon diffusion in both homogeneous and heterogeneous media. We have now performed frequency-domain measurements (at a modulation frequency of 160 MHz with 760 nm near infrared light) with the hand immersed in a scattering fluid (the infinite geometry arrangement). The advantages of our current approach include the spectroscopic resolution of physiologically interesting tissue regions, greater spatial resolution, the generation of absorption and reduced scattering coefficient maps of the image, rapid data acquisition, real time simultaneous display of the experimental parameters and calculated optical parameters and the possibility of obtaining some tomographic reconstruction.