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.
Highlights
Tissue oximetry using near-infrared spectroscopy (NIRS) is used in a range of fields, including brain research, sports medicine, surgery, and obstetrics.[1,2] Implantable devices and devices mounted on the finger of the investigator have been developed,[3,4] and the range of tissue types that can be examined has widened
We examined the SRS sensitivity in the source–detector axis direction and depth direction and compared the difference in measurement sensitivity of SRS and continuouswave spectroscopy (CWS) at each voxel and layer
At a ρA of 30 mm, a strong positive sensitivity was noted within a narrow range in the deep layer, but a small negative sensitivity appeared at the side near the light source
Summary
Tissue oximetry using near-infrared spectroscopy (NIRS) is used in a range of fields, including brain research, sports medicine, surgery, and obstetrics.[1,2] Implantable devices and devices mounted on the finger of the investigator have been developed,[3,4] and the range of tissue types that can be examined has widened. NIRS instruments apply four basic techniques: timeresolved spectroscopy (TRS), spatially resolved spectroscopy (SRS), frequency-domain spectroscopy (FDS), and continuouswave spectroscopy (CWS).
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