Evaluation of light scattering and absorption properties ofin vivorat liver using a single-reflectance fiber probe during preischemia, ischemia–reperfusion, and postmortem

Abstract

Diffuse reflectance spectroscopy (DRS) has been extensively used for characterization of biological tissues as a noninvasive optical technique to evaluate the optical properties of tissue. We investigated a method for evaluating the reduced scattering coefficient μ(s)', the absorption coefficient μ(a), the tissue oxygen saturation StO₂, and the reduction of heme aa3 in cytochrome c oxidase CcO of in vivo liver tissue using a single-reflectance fiber probe with two source-collector geometries. We performed in vivo recordings of diffuse reflectance spectra for exposed rat liver during the ischemia-reperfusion induced by the hepatic portal (hepatic artery, portal vein, and bile duct) occlusion. The time courses of μ a at 500, 530, 570, and 584 nm indicated the hemodynamic change in liver tissue as well as StO₂. Significant increase in μ(a)(605)/μ(a)(620) during ischemia and after euthanasia induced by nitrogen breathing was observed, which indicates the reduction of heme aa3, representing a sign of mitochondrial energy failure. The time courses of μ(s)' at 500, 530, 570, and 584 nm were well correlated with those of μ(a), which also reflect the scattering by red blood cells. On the other hand, at 700 and 800 nm, a temporary increase in μ(s)' and an irreversible decrease in μ(s)' were observed during ischemia-reperfusion and after euthanasia induced by nitrogen breathing, respectively. The change in μ(s)' in the near-infrared wavelength region during ischemia is indicative of the morphological changes in the cellular and subcellular structures induced by the ischemia, whereas that after euthanasia implies the hepatocyte vacuolation. The results of the present study indicate the potential application of the current DRS system for evaluating the pathophysiological conditions of in vivo liver tissue.

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

“…C HbO , C HbR , C HbT , and StO 2 of the normal liver tissue (oxygen breathing and air breathing state) revealed high levels of oxyhemoglobin and tissue oxygen saturation. The large increase in C HbR and decreases in C HbO and StO 2 typically observed in ischemia are consistent with the changes in time courses in StO 2 reported in our previous studies [12,24]. Successive images recorded at 5-min after the onset of reperfusion (t = 25-min) show the spatial changes in C HbO and StO 2 that are indicated by a white arrow on the less perfused portion of the imaged area, which is accompanied with scattered hepatic lobular perfusion.…”

“…The results of spatial and temporal changes in C HbO, C HbR , C HbT , StO 2 , and b following ischemia and reperfusion demonstrated that our method is reliable and reproducible for evaluating hepatic hemodynamic parameters and tissue morphology. A notable association is found between the tissue oxygen saturation StO 2 measured using the RGB imaging technique and that measured using a reflectance fiber probe based diffuse reflectance spectroscopy [12,24], which supports the value of the RGB imaging technique in monitoring hepatic tissue perfusion and oxygenation.…”

“…The reduced scattering coefficient spectrum μ s ' (λ) of biological tissues is considered to be the product of the combination of μ s ' (λ) for cellular and subcellular structures of different sizes [9]. The changes in scattering during ischemia are thought to originate from ischemia-induced changes in cellular and subcellular structures, whereas post-anoxia alterations indicate hepatocyte vacuolation [10][11][12]. Thus, it is important to measure the b to evaluate morphological changes in liver tissue resulting from ischemia, reperfusion and anoxia.…”

“…In our previous studies we used reflectance fiber probe based diffuse reflectance spectroscopy (DRS) to evaluate the optical properties (such as reduced scattering coefficient (μ s ' ), absorption coefficient (μ a ), StO 2 and the oxidation of heme aa 3 in CcO) of in vivo liver tissue during ischemia and reperfusion evoked by portal triad occlusion [12,24]. The reflectance fiber probe-based spectroscopic technique provides spatially averaged information of the optical properties of biological tissues obtained from the measurement point.…”

Medical applications of reflectance spectroscopy in the diffusive and sub-diffusive regimes

“…Diffusely reflected light collected by the central fiber of the fiber probe is delivered to one multichannel spectrometer (USB4000, Ocean Optics Inc.) via another lead of the bifurcated fiber, whereas that collected by the six surrounding fibers of fiber probe is delivered to another multichannel spectrometer (USB4000, Ocean Optics Inc.). Figure 1 depicts a schematic illustration of the optical fiber system developed and utilized by Nishidate et al 34 and Akter et al 35,36 Instrumentation for clinical applications of DRS are presented by Jayanthi et al 37 for detecting oral cancer and Hsu et al 38 for detecting therapeutic response in keloid scar. Jayanthi et al 37 constructed their DRS system (shown in Figure 2) using a tungsten halogen lamp (Model LSI-LL, Ocean Optics, Dunedin, Florida) for tissue illumination and a fiber-optic spectrometer (Ocean Optics; Model: USB 2000FL VIS-NIR) connected to the USB port of a laptop for recording diffuse reflectance spectra from tissues.…”