Fig. 3: Enabled by motion correction, iNIRS quantifies TOF-resolved dynamics in human tissues.

a–d Non-contact illumination and detection geometry for phantom, mouse, and human measurements. iNIRS, like TD-NIRS, measures temporal point spread functions (TPSFs) which can be fitted with diffusion theory to extract optical properties (absorption and reduced scattering coefficients, \({\upmu}_{\mathrm{a}}\)and \({\upmu}_{s}^\prime\), respectively). e–h Exemplary TPSFs, fitting regions, diffusion theory fits, and extracted optical properties for each respective medium are shown. TOF-resolved iNIRS field autocorrelations can be fitted with a 3-parameter model (two amplitudes, one decay rate), Eq. (7), to yield amplitude distributions (i–l) and decay rates (m–p). In vivo, the phase correction procedure (Fig. 2) enhances the static component, likely scattering from extravascular tissue, and reduces the dynamic component decay rate at early TOFs, improving overall agreement with DWS theory. Importantly, the DWS fits (dashed lines) intercept closer to zero TOF: −9.8 ps (raw) to −8.8 ps (corrected) in Intralipid, −280.6 ps (raw) to 30.5 ps (corrected) in the forearm, 59.7 ps (raw) to 57.8 ps (corrected) in the mouse brain, −287.9 ps (raw) to 16.1 ps (corrected) in the human forehead. q–t TOF-dependent averaging enables measurements at longer TOFs; the inverse of the iNIRS lag time resolution (10 μs) is shown as a dotted violet line. All shaded regions and error bars represent 95% confidence intervals.