Optical fiber arrangement of optical topography for spatial resolution improvement

In medical instrumentation, optical topography (OT) refers to the use of near-infrared spectroscopy for measuring brain function in systems. Arrays of optical fibers are attached to the scalps of subjects; infrared light is passed through the fibers, and changes in the reflections depict blood-volume changes in the cortex. In this study, the spatial resolution and locational accuracy of topographical images obtained by three arrangements of optical fibers was analyzed through simulation. Three arrangements, a "lattice arrangement" (LA), "double-density arrangement" (DA), and "quadruple density arrangement" (QA) were investigated. The density of spatial-sapling points is higher in the DA and QA than in the LA, i.e. the distance between sampling points for these arrangements were 21, 15 and 11 mm, respectively. The efficacy of these arrangements was evaluated. An adult head-structure phantom was prepared. The absorption coefficient in the phantom was varied to simulate brain activation in the cortex, and the resulting absorbance change (ΔOD) was thus obtained. The 'activated' area in the overall measurement area was fixed and the ΔOD at each of the sampling point in each arrangement was obtained. The resulting distributions of ΔOD were spatially interpolated to obtain topographical images. The spatial resolution and locational accuracy was obtained for each of the images; the results indicated that the DA is the most efficacious of the three arrangements. An experimental DA-OT system was then built. Topographical images of motor-function activation obtained by this system and a commercial LA-based system were compared; the DA-OT system provided the higher spatial resolution.