Comparison of Laser Speckle Flowmetry and Intrinsic Optical Signal Imaging in Gyrencephalic Swine Brain during Cortical Spreading Depolarisations
Blood flow changes that occur during the propagation of cortical spreading depolarisations (CSDs) along the gray matter of the cortex may play a major role in the development of secondary brain damage in patients with brain injuries. To investigate the underlying mechanisms of CSDs, spatiotemporal patterns of their neurovascular response are of particular interest. In the gyrencephalic brains of swine, a much larger variety of these patterns can be observed com pared to the lissencephalic
... of rodents. Due to their size, however, swine brains create more movement artefacts during imaging. We compared the use of laser speckle flowmetry (LSF) and intrinsic optical signal imaging (IOSI) to track the changes in cortical blood flow (CBF) and volume (CBV). Methods: Swine were anaesthetised and the cortices were exposed by craniotomy and removal of the dura. A pool of paraffin oil improved recording quality. After middle cerebral artery occlusion (MCAO), we simultaneously monitored CBF and CBV for up to ten hours using LSF and IOSI. Throughout the measurements 47 CSDs could be observed. Images acquired by IOSI were postprocessed and elastically registered to compensate for movement artefacts. Results: In the case of gyrencephalic swine brain, LSF was prone to movement artefacts caused by heart beat and breathing. Both signals highly correlated during CSDs, showing a close re lationship between CBF (measured by LSF) and CBV (measured by IOSI). In portions of the MCAO territory, both sig nals diverged. Conclusion: Both methods performed well in tracking the propagation of CSDs. LSF had a lower signal tonoise ratio, but allowed a better quantitative measurement of CBF, whereas IOSI was able to detect phenomena not observable in LSF.