Following acute traumatic brain injury (TBI), timely transport to a hospital can significantly improve the prognosis for recovery. There is, however, a dearth of quantitative biomarkers for brain injury that can be rapidly acquired and interpreted in active, field environments in which TBIs are frequently incurred. We explored potential functional indicators for TBI that can be noninvasively obtained through portable detection modalities, namely optical and electrophysiological approaches. By combining diffuse correlation spectroscopy with colocalized electrophysiological measurements in a mouse model of TBI, we observed concomitant alterations in sensory-evoked cerebral blood flow (CBF) and electrical potentials following controlled cortical impact. Injury acutely reduced the peak amplitude of both electrophysiological and CBF responses, which mostly recovered to baseline values within 30 min, and intertrial variability for these parameters was also acutely altered. Notably, the postinjury dynamics of the CBF overshoot and undershoot amplitudes differed significantly; whereas the amplitude of the initial peak of stimulus-evoked CBF recovered relatively rapidly, the ensuing undershoot did not appear to recover within 30 min of injury. Additionally, acute injury induced apparent low-frequency oscillatory behavior in CBF (<1 Hz). Histological assessment indicated that these physiological alterations were not associated with any major, persisting anatomical changes. Several time-domain features of the blood flow and electrophysiological responses showed strong correlations in recovery kinetics. Overall, our results reveal an array of stereotyped, injury-induced alterations in electrophysiological and hemodynamic responses that can be rapidly obtained using a combination of portable detection techniques.
Standardized approaches for performance assessment of biophotonic devices have the potential to facilitate system development and intercomparison, clinical trial standardization, recalibration, manufacturing quality control and quality assurance during clinical use. Evaluation of devices based on near-infrared spectroscopy (NIRS) for detection of hemoglobin (Hb) content and oxygenation have often involved tissue-simulating phantoms incorporating artificial dyes or flow systems. Towards the development of simple, effective techniques for objective, quantitative evaluation of basic NIRS system performance, we have developed and evaluated two test methods. These methods are based on cuvette inserts in solid turbid phantoms for measuring commercially-available Hb oximetry standards and custom-formulated oxy/deoxy-Hb solutions. Both approaches incorporate solid acetal, or polyoxymethylene (POM), as a tissue-simulating matrix material. First, inverse-adding-doubling (IAD) based on measurements with a spectrophotometer and an integrating sphere was used to measure POM optical properties and their stability over time. Second, two fiberopticprobe- based NIRS systems were used to measure concentration change of oxy- and deoxy-Hb in standard Hb solutions and customized Hb solutions by adding yeast. Differences in system performance were likely due to differences in light source outputs and fiberoptic probe design. Our preliminary results indicate that simple phantom-based approaches based on commercially available polymers and inclusions containing Hb standards, or controlled oxygenation levels may be useful for benchtop assessment of NIRS device quality for a variety of biophotonic devices.