Photoacoustic tomography can detect cerebral hemodynamic alterations in a neonatal rodent model of hypoxia-ischemia.

Abstract

Hypoxic-Ischemic Encephalopathy (HIE) is one of the most recognized causes of neurological deficits in children. Cerebral blood flow (CBF) reductions, as seen with HIE, resulting in neuronal injury have not been evaluated in real-time. Photoacoustic Tomography (PAT) is a form of optical imaging which can detect cerebral hemodynamic alterations in a noninvasive, non-ionizing fashion via changes in hemoglobin optical absorption. Further, this technology has the potential to capture cerebral blood volume (CBV) fluctuations and perhaps CBF changes in real-time. We hypothesized that PAT can detect a reduction in cerebral hemoglobin optical absorption, and therefore CBF, in a neonatal model of hypoxia-ischemia. To investigate, P7 rats underwent right carotid artery ligation and exposure to 8 percent oxygen for 60 minutes while imaged with PAT every 20 minutes. Cerebral hemodynamic alterations, as measured by mean optical absorption (MOA), were calculated as a change from baseline. Global and regional MOA was analyzed using a linear mixed model. Global MOA was reduced within the right hemisphere as compared to the left during hypoxia. Regional differences in MOA were detected between the left and right sides for the middle and posterior cortical regions. Injury was confirmed using immunohistochemistry. We conclude that a reduction in global and regional MOA, and hence CBF, could be identified by PAT in a neonatal rat model of HIE. This is the first study described in the literature utilizing a neonatal rat model of HIE to demonstrate in vivo alterations in cerebral hemodynamics in a non-invasive and near real-time fashion.