Feature Of The Week 10/20/13: Multiparametric, Longitudinal Optical Coherence Tomography Imaging Reveals Acute Injury and Chronic Recovery in Experimental Ischemic Stroke
To better understand pathophysiology during brain injuries such as stroke, we combined a number of OCT imaging techniques. Namely, we employed Doppler methods to map blood flow, angiography methods to measure capillary-level perfusion and vessel diameter, and scattering quantification methods to determine cell viability. This multi-parametric approach was used to perform imaging in the acute and recovery stages in experimental ischemic stroke, with the goal of determining the fate of the penumbra using imaging biomarkers. The penumbra is an area of brain tissue which is compromised during stroke but could be salvaged through thrombolysis or other treatment methods.
Multi-parametric imaging was performed using a 1310 nm spectral/Fourier domain OCT system with either a 5x or a 10x long-working distance infrared objective on C57BL/6 mice through thinned-skull, glass coverslip-reinforced cranial windows. Two models of experimental ischemic stroke were used: a transient filament middle cerebral artery occlusion (fMCAO) model and a permanent distal middle cerebral artery occlusion (dMCAO) model.
In the acute fMCAO model, a region devoid of perfused capillaries during occlusion correlated spatially with the eventual development of altered cellular scattering properties, despite reperfusion of the capillaries following filament withdrawal. Histological correlations showed that the altered scattering properties may result from aberrant cellular morphology that is characteristic of infarcted tissue. Vessel dilation and increased blood flow were also noted in the middle cerebral artery (MCA) region following reperfusion. This “luxury perfusion” may at first appear paradoxical, but can potentially be explained by failure of autoregulation in the region destined for infarction. In the permanent occliusion model, one week after occlusion, there was a reduction in blood flow in the MCA region compared to the anterior cerebral artery (ACA) region, where flow was maintained. High resolution angiograms revealed collateral growth in the border zone between the MCA and ACA.
Our imaging results suggest candidate biomarkers for eventual tissue infraction, namely, capillary non-perfusion and flow deficits during occlusion, as well as altered cellular scattering and impaired flow autoregulation. This study shows the capability of multi-parametric OCT to independently map both hemodynamics and cell viability simultaneously using dynamic and static intrinsic optical scattering. Thus multi-parametric OCT represents a novel and robust in vivo imaging platform to identify biomarkers for cerebrovascular disease during both injury and recovery.
For more information see recent Article. Courtesy of Vivek J. Srinivasan from University of California at Davis, USA. For more information see recent Article. Courtesy of Vivek Srinivasan from University of California at Davis.