Method for the discrimination of superficial and deep absorption variations by time domain fNIRS

Abstract

Abstract:A method for the discrimination of superficial and deep absorption variations by time domain functional near infrared spectroscopy is presented. The method exploits the estimate of the photon timedependent pathlength in different domains of the sampled medium and makes use of an approach based on time-gating of the photon distribution of time-of-flights. Validation of the method is performed in the two-layer geometry to focus on muscle and head applications. Numerical simulations varied the thickness of the upper layer, the interfiber distance, the shape of the instrument response function and the photon counts. Preliminary results from in vivo data are also shown.

Estimate of tissue composition in malignant and benign breast lesions by time-domain optical mammography

“…where 0 ( ) T t  and ( ) T t  are the unperturbed and perturbed time-resolved transmittance curves measured by the optical mammograph, while ( ) l t  represents the photon pathlength traveled in the inclusion in this realistic case [45] and can be derived similar to Eq. (2):…”

“…The 8 th time-window was then considered for the analysis to provide information on the absorption of the investigated medium, since it is related to late photons which are less affected by a potential scattering variation inside the inclusion. A similar binning procedure was implemented for the pathlength ( ) l t  [45] and the equivalent time-gate was considered.…”

Effect of a thin superficial layer on the estimate of hemodynamic changes in a two-layer medium by time domain NIRS

“…The total number of collected photons was set at 10 8 photons, and Poisson noise was added to the simulated curves to mimic real measurements. We did not implement repetitions since it was already demonstrated by Zucchelli et al [13] that the error introduced by repetitions is just a negligible stochastic one. In the previously mentioned paper was also already discussed the influence of different counts rates for the TRR curves.…”

“…Therefore, it is possible to qualitatively discriminate superficial and deep changes by selecting early and late time-windows in the recorded distribution of photon time-of-flights (DTOF). However, the accurate quantification of the hemodynamic changes in the different compartments of tissues is still an open issue, and different solutions were proposed [11][12][13][14]. In particular, a method, based on the refined computation of the pathlengths traveled by photons in a two-layer medium, was recently proposed by our group [13].…”

“…However, the accurate quantification of the hemodynamic changes in the different compartments of tissues is still an open issue, and different solutions were proposed [11][12][13][14]. In particular, a method, based on the refined computation of the pathlengths traveled by photons in a two-layer medium, was recently proposed by our group [13]. This method was applied for modelling the adult head, where the thickness of the upper layer was varied in the range 0.5 -2 cm in 0.5 cm steps.…”