Near infrared imaging of brains

Summary form only given. The authors describe a near-infrared imaging instrument capable of providing spectroscopic information over a spatially localized region of the brain. This regional imager is a frequency domain, multiwavelength (779 and 834 nm) system with multiple source (12) and detector (4) positions. The modulation frequency is selectable, ranging from 50 to over 400 MHz. The regional imager offers the possibility for reconstruction of optical properties with linear resolutions of /spl sim/1 cm, beneath an area of /spl sim/40 cm/sup 2/ in size, within a short period of time (3 min). Clinical applications include evaluation of critical care conditions such as hydrocephalus and hematoma, as well as monitoring blood oxygenation during heart surgery and cognition studies. For real-time analysis of a measurement, the authors use a backprojection algorithm to reconstruct images. In the authors´ backprojection approach, they derive an absorption coefficient /spl mu//sub s/ and scattering coefficient /spl mu//sub s/´ for each source-detector pair by numerically solving the semi-infinite solution for the values of /spl mu//sub s/ and /spl mu//sub s/´ using the measurements from the source-detector pair. These values are then back-projected using weights that are essentially the three-point Green´s function. The authors are currently investigating use of the Rytov approximation for image reconstruction in a reflectance geometry.