Light scattering signal as an indicator of loss of tissue viability in brains: Experiments using rat hypoxia models

Abstract

Measurement of the intrinsic optical signal (IOS) related to cellular/subcellular morphological characteristics, i.e., light scattering, is attractive for noninvasive, real-time monitoring of brain tissue viability because cellular/subcellular structural integrity is a sign of cell viability of brain tissue. We previously performed simultaneous measurement of light scattering and IOSs related to metabolic activity for blood-free rat brains after oxygen and glucose deprivation. The measurement showed that a unique triphasic change in light scattering occurred at a certain time after starting ischemia and this change preceded the reduction of CuA in cytochrome c oxidase; the reduction has been shown to correlate with cerebral ATP decrease. In the present study, we examined whether such a triphasic scattering change can be observed in the presence of blood in vivo; transcranial measurement of diffuse reflectance was performed using a broadband tungsten lamp for a rat brain during hypoxia induced by nitrogen gas inhalation. After starting nitrogen gas inhalation, reflectance intensities in the visible region (500-600 nm) showed an increase in deoxy-hemoglobin concentration. After full deoxygenation of hemoglobins, reflectance intensities in the near-infrared (NIR) region (700-850 nm) showed a triphasic change that was similar to that observed in our blood-free rat brain model described above. Spectroscopic analysis demonstrated that this triphasic reflectance change was due to change in light scattering, suggesting that light scattering signal can be used as a useful indicator of loss of brain tissue viability.