<title>Three-dimensional optical tomographic localization of changes in absorption coefficients in the human brain</title>

Abstract

ABSTRACT We report on the first three dimensional tomographic localization of vascular reactivity in the brain. Using a model-based iterative image reconstruction algorithm we show the spatial distribution of changes in the absorption coefficientcaused by changes in blood volume. Unlike currently available topographic reconstruction techniques, three-dimensional,volumetric reconstruction schemes promise to be capable of spatially distinguishing between signals originating in thecerebral cortex from those originating in the overlying tissues.Keywords: Diffuse optical tomography, brain imaging, three-dimensional imaging, inverse-problem. 1. INTRODUCTION In recent years there has been an increased interest in using diffuse optical tomography (DOT) for imaging the brain. 1-12 It iswell established that near-infrared light can be used to probe the brain for changes in blood oxygenation during functionalneural activation or changes in blood volume as they occur in injuries like hematomas. In most of the currently establishedprotocols, either a single source and a single detector is used to perform point measurements, or an array of sources anddetectors with a fixed geometry is employed to obtain topographic maps. Topographic maps show spatially resolved changesin the absorption coefficient during certain exercise protocols, such as finger flexes or breath holds. These maps project thecortical response together with the superficial vascular changes onto a two-dimensional surface map. The resulting surfacemaps are usually obtained by back-projecting absorption coefficients along a line between source and detector pairs.