Closed head injury-induced changes in brain pathophysiology assessed with near-infrared structured illumination in a mouse model

Use of near-infrared (NIR) structured illumination technique has recently received great interest in biomedical research and clinical studies because of its ability to perform wide-field imaging and quantitatively map changes in tissue hemodynamic properties and morphological features in a noncontact and scan-free fashion. We report on the feasibility of using the same to quantitatively monitor and map changes in brain optical properties and physiological parameters pre-and post-closed head injury in a mouse model. Five anesthetized male mice underwent head injury by weight-drop model using a ~50-g cylindrical metal object falling from a height of 90 cm onto the intact scalp. During experiments, NIR structured illumination was projected on the mouse head at two spatial frequencies and six different NIR wavelengths. A CCD camera positioned perpendicular to the head recorded the diffuse-reflected light. Computer analysis performed off-line on the captured data reveals spatiotemporal changes in the distribution of brain tissue absorption and reduced scattering coefficients. Using Beer's law and Mie theory, hemodynamic (hemoglobin, oxygen saturation, and lipids) and morphological (scattering amplitude and power) changes up to 1-h post-trauma were observed in comparison with baseline measurements. Functional maps of different brain properties were also generated. Following injury, we found difference in both brain hemodynamic and morphologic properties with respect to baseline levels, where in some properties, this difference was considered statistically significant. Specifically, a t-test indicates a substantial decrease in oxyhemoglobin (HbO2) concentration and tissue oxygen saturation (StO2) post-injury (p < 0.01 and p < 0.001, respectively). Overall, our preliminary results demonstrate the potential application of NIR structured illumination technique to track and spatially map changes in intact mouse brain pathophysiological parameters following head injury.