Evaluation of Laser Speckle Flowmetry for Imaging Cortical Perfusion in Experimental Stroke Studies: Quantitation of Perfusion and Detection of Peri-Infarct Depolarisations

Abstract

Laser speckle imaging of the exposed cerebral cortex allows detailed examination of the time course and topography of perfusion under different experimental conditions. Here we examine the quantitative capacity of the method and its sensitivity for the detection of peri-infarct depolarisations (PIDs). In four cats anaesthetised with chloralose, the right hemisphere was exposed and the right middle cerebral artery was occluded. The brain was illuminated with a laser diode, the speckle pattern was imaged, and images of inverse speckle correlation time (ICT) were derived from the calculated speckle contrast images. We examined the relationship of ICT with perfusion, as imaged quantitively using umbelliferone clearance (CBF umb ). Values of ICT and CBF umb were compared and regression parameters were calculated for each experiment. In eight cats, cortical surface direct current (DC) potential was monitored at two locations and detection of PIDs by DC potential and ICT change was compared. ICT-and CBF umb -derived values of perfusion were closely correlated, with a high degree of significance (P < 0.0001). Overall, monitoring of DC potential detected 90% of PIDs, whereas ICT detected 56%. We conclude that (1) laser speckle imaging provides an index of perfusion that has a linear relationship with the clearance rate of umbelliferone within the range of levels of perfusion examined; (2) this relationship is relatively stable between experiments; and (3) the method's ability to detect blood flow changes associated with PIDs likely depends on the noise level of the speckle measurements.

Chronic Imaging of Cortical Blood Flow using Multi-Exposure Speckle Imaging

“…The relative flow measures from each technique were obtained by normalizing to the first imaging session, akin to typical analyses of relative CBF dynamics 11,14 and to provide a normalization factor for comparison between imaging modalities. Specifically, the MESI ICTs remain within a 95% confidence interval across all ROIs with RBC tracking over the chronic period, while LSCI estimates exceed these bounds in nearly all animals ( Figure 3A).…”

“…Examples of the former include laser scanning microscopy, 5,6 as well as high-frame rate red blood cell (RBC) photography, 7,8 while the latter include Laser Doppler Flowmetry 9,10 and Laser Speckle Contrast Imaging (LSCI). Among these techniques, LSCI has recently emerged as the tool to use in rodent cortical blood flow imaging but has been largely limited to acute studies of neurovascular disease models [11][12][13][14][15] and functional activation. [16][17][18] Stroke studies in particular benefit from the intrinsic contrast obtained from imaging the effects of dynamic light scattering without introducing exogenous contrast agents into the bloodstream.…”

Distinct Spatiotemporal Patterns of Spreading Depolarizations during Early Infarct Evolution: Evidence from Real-Time Imaging

“…Methodological details have been described, and quantification aspects have been discussed (Dunn et al, 2001;Strong et al, 2006Strong et al, , 2007. In brief, the exposed cortex was illuminated through thinned skull and dura mater with a laser light (laser diode: DL7140-201, 785 nm, 70 mW, Sanyo and laser diode controller: LDC 205B, THORLABS, Newton, NJ, USA) to produce a speckle pattern that was detected with a CCD camera (A602f-2 BASLER, Ahrensburg, Germany).…”

Chronic Monitoring of Vascular Progression after Ischemic Stroke Using Multiexposure Speckle Imaging and Two-Photon Fluorescence Microscopy

“…[10][11][12][13][14] Recent advances in LSCI termed multiexposure speckle imaging (MESI) have allowed for the technique to move from primarily acute experiments to chronic studies through improvements in its quantitative accuracy of blood flow measurements. 15 By using multiple camera exposures spanning almost three decades in duration and improved mathematical models, MESI is able to more precisely sample and map the flow distributions prevalent in the rodent vasculature.…”