We developed a combined near-infrared reflectance and transmittance approach to enable depth-selective characterization of renal hemodynamics and oxygenation in rats. Test interventions such as arterial occlusion reveal differences in the response between renal cortex and medulla.
Regulation of renal hemodynamics and oxygenation is complex and its detailed understanding is crucial to improve therapeutic procedures for kidney diseases like acute kidney injury. For the challenging task of monitoring renal hemodynamics and oxygenation in rats, we designed a continuous wave (cw) multispectral near-infrared spectroscopy setup. A fiber probe with a source fiber and eight detection fibers is placed on the ventral surface of the exposed rat kidney in vivo, and an additional source fiber is positioned on the dorsal surface. Nine wavelengths from 658 nm to 1060 nm are used to have sufficient redundancy for reliable quantification of hemoglobin concentration, oxygen saturation of hemoglobin, and tissue water content. To investigate both, the surface layer and deeper tissues, the setup alternates between reflection and transmission at a rate of 10 Hz. Our system relies on spatially resolved reflection and transmission, and multispectral analysis to differentiate absorption from scattering. Monte-Carlo Simulations for a layered tissue structure are used as a model for quantitative characterization of the renal cortex and medulla. Renal parameters are monitored during baseline conditions and during dedicated pathophysiologically relevant interventions including arterial occlusion and changes of inspiratory gas mixture. Together with invasive probes, which monitor arterial blood pressure, renal perfusion and tissue oxygenation, a detailed picture of renal hemodynamics and oxygenation in several pathophysiological conditions is acquired. This detailed information can serve as a quantitative reference to other methods such as MRI.
Spatially resolved reflectance was measured on various phantoms and in vivo to evaluate its performance in determining their optical properties. To obtain reliable results it was necessary to use the absolute values of the reflectance.
Spatially resolved reflectance is a frequently used technique to derive optical properties and physiological parameters of tissue. We have evaluated the accuracy of this method by investigations on a set of phantoms with known optical properties derived from time-resolved measurements. The recorded profiles of spatially resolved reflectance were analyzed by a Monte Carlo model of photon transport. When we took only the shape of the measured profiles into account, we got only poor estimates of the optical properties. In particular, the absorption was strongly underestimated. The main reason for failing of this approach is that the shape of the measured profiles can be well described by many combinations of absorption and reduced scattering coefficients. The separation between scattering and absorption was strongly improved when the reflectance data were calibrated by using a reference phantom. We applied both the relative and the calibration based analysis method to reflectance data obtained from in vivo investigations on the kidney of rats. Despite the limited number of only 4 detector positions the calibration based analysis method yielded reliable estimates of the tissue optical properties.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.