Imaging cortical absorption, scattering, and hemodynamic response during ischemic stroke using spatially modulated near-infrared illumination

Abstract

We describe a technique that uses spatially modulated near-infrared (NIR) illumination to detect and map changes in both optical properties (absorption and reduced scattering parameters) and tissue composition (oxy-and deoxyhemoglobin, total hemoglobin, and oxygen saturation) during acute ischemic injury in the rat barrel cortex. Cerebral ischemia is induced using an open vascular occlusion technique of the middle cerebral artery (MCA). Diffuse reflected NIR light (680 to 980 nm) from the left parietal somatosensory cortex is detected by a CCD camera before and after MCA occlusion. Monte Carlo simulations are used to analyze the spatial frequency dependence of the reflected light to predict spatiotemporal changes in the distribution of tissue absorption and scattering properties in the brain. Experimental results from seven rats show a 17±4.7% increase in tissue concentration of deoxyhemoglobin and a 45±3.1, 23±5.4, and 21±2.2% decrease in oxyhemoglobin, total hemoglobin concentration and cerebral tissue oxygen saturation levels, respectively, 45 min following induction of cerebral ischemia. An ischemic index (I isch =ctHHb/ctO 2 Hb) reveals an average of more then twofold contrast after MCAo. The wavelength-dependence of the reduced scattering (i.e., scatter power) decreased by 35±10.3% after MCA occlusion. Compared to conventional CCD-based intrinsic signal optical imaging (ISOI), the use of structured illumination and model-based analysis

Quantitative assessment of hemodynamic and structural characteristics of in vivo brain tissue using total diffuse reflectance spectrum measured in a non-contact fashion

“…This might indicate those results obtained based on this constant scattering property assumption need to be carefully reinterpreted. One obvious limitation of the proposed spectrum interpretation algorithm is that it cannot separate [Hb] The results presented for this study are consistent with those from another previously-published study [34], in which a different imaging technique and interpretation algorithm were used.…”

“…These values were lower than those reported previously [34,38,39]. With the partial pressure of oxygen in the normal cortex being 35 mm Hg [40], the standard hemoglobin dissociation curve for Sprague-Dawley rats suggests that the expected SatO 2 of the brain cortex at rest should be roughly 48% [41].…”

“…The variations observed in the scattering power B might be a result of the increase of blood flow in the studied tissue, though it requires further investigation to gain insight to the underlying mechanism. Abookasis et al [34] performed an open vascular occlusion to the middle cerebral artery of rats and observed changes in the scattering properties (both scattering amplitude A and scattering power B) of the cortex measured using the spatially modulated illumination methods. The pre-occlusion value of B reported by Abookasis (0.65 ± 0.1, mean ± standard error) is very close to the estimated B value at the resting-state (baseline) from the "old" rats in this study, which is 0.62 ± 0.02 (mean ± standard error).…”

Intraoperative video-rate hemodynamic response assessment in human cortex using snapshot hyperspectral optical imaging

“…3,4,[10][11][12][13][14] Prominent clinical applications of tissue optical spectroscopy include tissue wound healing monitoring 15,16 and brain hemodynamic assessment. 12,14,17,18 For each of these applications, a range of optical imaging techniques has been developed leading to tissue functional status information, either provided in absolute terms-i.e., by evaluating the concentration of the chromophores-or relative to a baseline value, oftentimes in terms of variations with respect to a signal detected at a specific time point. In brain hemodynamic imaging, the information is either provided topographically with the information effectively being averaged over the penetration depth of the light, 3,17,[19][20][21][22][23][24] or tomographically exploiting the penetration of visible and/or near-infrared light to provide volumetric information up to a few millimeters or centimeters underneath the surface.…”

In vivo imaging of hepatic hemodynamics and light scattering property during ischemia-reperfusion in rats based on spectrocolorimetry

“…The spectra of reduced scattering coefficient μ s ' (λ) in biological soft tissues follow a power law function [5,6] that can be approximated in the following form: …”