|
Functional Near-InfraRed Spectroscopy (NIRS) (fNIRS) is a powerful method for non-invasively measuring cerebral hemodynamics on human subjects. Measurement contamination from superficial tissue which do not represent the brain continues to be an issue. We have proposed the Dual-Slope (DS) approach which is less sensitive to superficial tissue compared to typical Single-Distance (SD) methods. This DS method has been applied to Diffuse Optical Imaging (DOI), designing and constructing a large source-detector array. Previous results suggested that DS phase (Φ) has intrinsically higher sensitivity to the brain compared to SD Intensity (I). To further investigate this finding, on a large population of subjects, a modular DS array is designed. Allowing for collection from different cortical locations during various protocols. These source-detector modules are hexagonal and contain 4 intra-module DS sets. Tessellation greatly expands the number of measurement sets through the creation of inter-module DS sets. In one example, we found a tessellation of 7 modules which generated 94 DS sets. The modules will be used to enable large population DS DOI studies. Here we present one example trace during a 3-back protocol. Examination of the DS traces suggest the expected higher DS Φ sensitivity to cerebral hemodynamics. Further, close observation of the results demonstrate the importance of considering both the Oxy-hemoglobin concentration change (ΔO) and Deoxy-hemoglobin concentration change (ΔD) during such protocols. The results indicated that if one observed only ΔO they would have mis-identified brain activation in the short SD I measurement. Other data-types and ΔD dynamics suggested that the short SD I was dominated by superficial blood-volume instead of the blood-flow dynamics associated with brain activation.
|
