Voxel-based measurement sensitivity of spatially resolved near-infrared spectroscopy in layered tissues

Abstract

We quantitatively investigated the measurement sensitivity of spatially resolved spectroscopy (SRS) across six tissue models: cerebral tissue, a small animal brain, the forehead of a fetus, an adult brain, forearm muscle, and thigh muscle. The optical path length in the voxel of the model was analyzed using Monte Carlo simulations. It was found that the measurement sensitivity can be represented as the product of the change in the absorption coefficient and the difference in optical path length in two states with different source-detector distances. The results clarified the sensitivity ratio between the surface layer and the deep layer at each source-detector distance for each model and identified changes in the deep measurement area when one of the detectors was close to the light source. A comparison was made with the results from continuous-wave spectroscopy. The study also identified measurement challenges that arise when the surface layer is inhomogeneous. Findings on the measurement sensitivity of SRS at each voxel and in each layer can support the correct interpretation of measured values when near-infrared oximetry or functional near-infrared spectroscopy is used to investigate different tissue structures.

Usefulness of a finger-mounted tissue oximeter with near-infrared spectroscopy for evaluating the intestinal oxygenation and viability in rats

“…To examine the correlation between the degree of tissue damage and rSO 2 , hourly rSO 2 and the Park/Chiu score was analyzed up to 6 h. The rSO 2 decreased over time, and the Park/Chiu score increased over time, suggesting that finger-mounted oximeter evaluates the degree of intestinal ischemia. rSO 2 was calculated by the concentrations of oxyhemoglobin [O 2 Hb] and deoxyhemoglobin [HHb] in the target tissue as rSO 2 = [O 2 Hb]/([O 2 Hb] + [HHb]) [ 6 , 11 ]. We considered the reasons for reducing rSO 2 by intestinal ischemia to be as follows: the first is the decreasing of oxyhemoglobin by consuming oxygen in the tissue when blood flow is blocked.…”

“…A finger-mounted tissue oximeter (Toccare; Astem Co., Ltd., Kawasaki, Japan) is a newly developed device for measuring rSO 2 using near-infrared spectroscopy (NIRS). This device enables iterative and quantitative rSO 2 evaluation of the target tissue/organ using a simple method and has been reported to be useful in obstetrics and gynecology, vascular surgery, and plastic surgery [6][7][8][9][10][11]. If this device can be used to evaluate intestinal ischemia, we can determine whether the intestine can be preserved, intraoperatively, using a rapid and quantitative evaluation.…”

Tissue Oximeter with Selectable Measurement Depth Using Spatially Resolved Near-Infrared Spectroscopy

“…Monte Carlo analysis [ 11 , 17 , 18 , 19 ] was performed to clarify the measurement sensitivity at each small volume in biological tissue based on radiative transfer theory [ 19 , 20 , 21 , 22 ]. First, by assuming a widely used semi-infinite homogeneous model, we analyzed how the change in the sensitivity distribution of SRS depends on the combination of detectors.…”

“…These measurements are generally interpreted as measuring information at a depth of about half the source–detector distance. On the other hand, in recent years SRS devices with source–detector distances reduced to 10 mm or less have been developed to measure surface layers [ 10 , 11 , 12 ]. The sensor can obtain information at depths of 4–5 mm.…”

Impact of optical clearing on ex vivo human skin optical properties characterized by spatially resolved multimodal spectroscopy

“…Depending on the type and stage of pathological changes, different layers of the skin and their related structural components may be affected. To serve as efficient and accurate complementary diagnostic tool, optical spectroscopy techniques thus have to be capable of providing spatial discrimination between assessed layers [21][22][23][24][25]. The depth resolution of tissue spectroscopy techniques is achieved using spatially resolved (SR) configuration featuring usually an optical probe made of (a) one (central) excitation (or source) optical fiber that guides the light source onto the tissue and (b) several light-collecting (or detection) optical fibers located at various distances from the source fiber, that is, different source-detector separations (SDS) [22].…”