Abstract
Detection limits of the changes in absorption and reduced scattering coefficients were investigated using a frequency-domain near-infrared system in a realistic head phantom. The results were quantified in terms of the maximum detectable depth for different activation volumes in the range of 0.8–20 microliters. The non-linear relation between the maximum detectable depth and the magnitude of changes in the absorption coefficient conform well with the Born approximation to the diffusion equation. The minimal detectable changes in the reduced scattering coefficient measured in terms of the phase signal were found to be approximately twice as large as that of the absorption coefficient using the AC signal for the same volume and at the same depth. The phase delay, which can be used to quantify the fast neuronal optical response in the human brain, showed a linear dependence on the reciprocal of the reduced scattering coefficient, as predicted by the Rytov approximation.
Highlights
Near infrared (NIR) spectroscopy and imaging methods are increasingly important measurement tools in biology, neuroscience, and medicine because of their noninvasive nature, high chemical specificity, high temporal resolution, high versatility, and portability [1,2,3,4,5,6,7,8,9,10]
NIR techniques are most often applied to measure the hemodynamic response in the brain, which peaks approximately four to six seconds after the actual neuronal response via measurement of the change in tissue absorption coefficient ( )
To address the issue of signal detectability, we investigated the relative detection limits of the AC
Summary
Near infrared (NIR) spectroscopy and imaging methods are increasingly important measurement tools in biology, neuroscience, and medicine because of their noninvasive nature, high chemical specificity, high temporal resolution, high versatility, and portability [1,2,3,4,5,6,7,8,9,10] These methods have shown great potential for human and animal functional studies when integrated with other imaging modalities such as magnetic resonance imaging, which provides structural information and enables improved signal localization and accurate image registration [11,12,13,14,15,16,17]. To the best of our knowledge, this type of data is not available in the literature, which is highly important to understand the fundamental characteristics of frequency-domain NIR methods (including spectroscopy and tomography) in human cerebral functional studies
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