Dual-slope diffuse optical imaging with a modular source-detector array

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 (phi) 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 phi sensitivity to cerebral hemodynamics. Further, close observation of the results demonstrate the importance of considering both the Oxy-hemoglobin concentration change (Delta O) and Deoxy-hemoglobin concentration change (Delta D) during such protocols. The results indicated that if one observed only Delta O they would have mis-identified brain activation in the short SD I measurement. Other data-types and Delta D dynamics suggested that the short SD I was dominated by superficial blood-volume instead of the blood-flow dynamics associated with brain activation.