Frequency domain multidistance NIRS
Definition: By capturing the change in intensity and phase at multiple source detector separations/distances, the frequency-domain (FD) multidistance NIRS technique can estimate absolute values of absorption and scattering of the medium, and subsequently chromophore concentrations. This may involve one or more modulation frequencies. The key here is that these measurements are taken at multiple source detector separations as opposed to one. Ideally, this allows one to obtain the optical properties of the medium under investigation without performing a calibration measurement on a tissue-like medium. Additionally, this allows a simpler processing method requiring linear regression only instead of non-linear optimization to get absorption and scattering of the medium. However, most practical multi-distance frequency-domain multidistance NIRS systems do utilize a phantom calibration of the coupling coefficients between the sources/detectors and media.
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References: https://doi.org/10.1117/12.183988https://dx.doi.org/10.1088/0031-9155/46/1/304
https://doi.org/10.1364/BOE.2.000552
Related terms: frequency domain, source detector separations, time domain, continuous wavelength fNIRS