Abstract
Variations of hemoglobin (Hb) oxygenation in tissue provide important indications concerning the physiological conditions of tissue, and the data related to these variations are of intense interest in medical research as well as in clinical care. In this study, we derived a new algorithm to estimate Hb oxygenation from diffuse reflectance spectra. The algorithm was developed based on the unique spectral profile differences between the extinction coefficient spectra of oxy-Hb and deoxy-Hb within the visible wavelength region. Using differential wavelet transformation, these differences were quantified using the locations of certain spectral features, and, then, they were related to the oxygenation saturation level of Hb. The applicability of the algorithm was evaluated using a set of diffuse reflectance spectra produced by a Monte Carlo simulation model of photon migration and by tissue phantoms experimentally. The algorithm was further applied to the diffuse reflectance spectra acquired from in vivo experiments to demonstrate its clinical utility. The validation and evaluation results concluded that the algorithm is applicable to various tissue types (i.e., scattering properties) and can be easily used in conjunction with a diverse range of probe geometries for real-time monitoring of Hb oxygenation.
Highlights
The microcirculation is that part of the vascular tree that comprises blood vessels smaller than 100 μm in diameter, including arterioles, capillaries, and venules
The main oxygen carrier within the circulatory system is red blood cells (RBCs), and the oxygen transport rate in various organs is controlled by microvascular geometry, hemodynamics, and RBC hemoglobin (Hb) oxygen saturation
Since diseases and injuries can lead to certain local modifications in microvasculature, and microvascular oxygen transport, local tissue may be hypoxic despite normal global Hb oxygenation
Summary
The microcirculation is that part of the vascular tree that comprises blood vessels smaller than 100 μm in diameter, including arterioles, capillaries, and venules. Sepsis leads to the termination of flow in a significant number of capillaries, such that the microcirculation fails to compensate for decreased functional capillary density [1] This change elevates the likelihood of local organ failure. Understanding and assessing Hb oxygenation in the microcirculation provides valuable insights into a given patient’s level of health. It is not surprising, that local Hb oxygenation is highly-sought information in medical research, as well as in clinical care [2,3,4,5,6,7]
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