Abstract
A complete methodology has been developed to integrate simultaneous diffuse optical tomography (DOT) and functional magnetic resonance imaging (MRI) measurements. This includes development of an MRI-compatible optical probe and a method for accurate estimation of the positions of the source and detector optodes in the presence of subject-specific geometric deformations of the optical probe. Subject-specific head models are generated by segmentation of structural MR images. DOT image reconstruction involves solution of the forward problem of light transport in the head using Monte Carlo simulations, and inversion of the linearized problem for small perturbations of the absorption coefficient. Initial results show good co-localization between the DOT images of changes in oxy- and deoxyhemoglobin concentration and functional MRI data.
Highlights
The first traceable attempt to use light to image biological tissues was made as early as the 1920's [1], but at that time the problem of high scattering was not resolved
Practical achievements in three-dimensional tomography of adult human brain [6,7,8,9,10,11], i.e. the spatial localization of optical properties and their changes, have been significantly more modest than the results of purely spectroscopic [8,12,13,14,15,16,17] and two-dimensional mapping [18,19,20,21] studies. The latter have exploited the ability of near infrared (NIR) spectroscopy to provide direct measurement of oxy- and deoxy-hemoglobin concentrations, as well as detection of the fast neuronal responses with millisecond time resolution [17]
The diffusion approximation [2,23] has been shown to be adequate for most tissues, providing a very efficient approach to solving the forward problem, a wellknown obstacle to applying the diffusion or higher order deterministic approximations [2] in the adult brain imaging is the presence of low-scattering cerebro-spinal fluid (CSF) [24]
Summary
The first traceable attempt to use light to image biological tissues was made as early as the 1920's [1], but at that time the problem of high scattering was not resolved. The diffusion approximation [2,23] has been shown to be adequate for most tissues, providing a very efficient approach to solving the forward problem, a wellknown obstacle to applying the diffusion or higher order deterministic approximations [2] in the adult brain imaging is the presence of low-scattering cerebro-spinal fluid (CSF) [24] For this reason approaches based on a direct Monte Carlo (MC) simulation of photon migration have been developed by a number of groups [4,25]. In this context the simultaneous measurement of optical and MRI data allows highly accurate and reproducible image co-registration, as well as providing a high-resolution subject-specific structural model for Monte Carlo simulations of photon migration paths
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