Multi-Channel-Based Differential Pathlength Factor Estimation for Continuous-Wave fNIRS

Abstract

Functional near-infrared spectroscopy (fNIRS) in brain imaging needs to be robust to subjectwise variability. The use of a fixed differential pathlength factor (DPF) per wavelength for the entire brain will degrade the accuracy of hemodynamic responses. Since the tissue composition varies within the brain, correct DPF values should be used for various emitter-detector distances and brain regions. In this paper, a DPF estimation method combining a state-space model of the modified Beer-Lambert law (mBLL), a parameter model for estimating the reduced scattering coefficients, and dual square-root cubature Kalman filters (SCKFs) is proposed. To validate the proposed method, known light intensities (six channels, two wavelengths) and reference DPFs are generated using NIRFAST (a Matlab toolbox) using a presumed paradigm, known tissue properties, a Balloon model, and a finite element head model consisting of 58,818 mesh elements. Then, the DPF values are estimated using a Jacobian matrix from the head model and the mBLL. The results show that the estimated concentration changes correlate well with the reference data. Also, the estimated DPFs showed relative errors less than 1.33% maximum and 0.75% on average. A onetailed t-test revealed that the estimated DPFs matched the reference DPFs with more than 99.9% confidence. The developed method can efficiently access the actual DPFs even if emitter-detector distances vary significantly and the tissue properties are not uniform. With the developed state-space models for dual SCKFs, real-time estimation of the DPFs from one experiment to another has become plausible.INDEX TERMS Differential pathlength factor (DPF), functional near-infrared spectroscopy (fNIRS), Kalman filter, state-space method, finite element method (FEM)

Faster Walking Speeds Require Greater Activity from the Primary Motor Cortex in Older Adults Compared to Younger Adults

“…However, using such a system is limited to treadmill walking (as in the present study) or moving the system with the participant during the walking trials. Furthermore, equations used for estimating the path length vector corrected for age are only valid for adults aged ≤60 years and are fixed across the entire brain, which must be considered in light of the present findings [ 99 ].…”

Physiological Noise Filtering in Functional Near-Infrared Spectroscopy Signals Using Wavelet Transform and Long-Short Term Memory Networks

“…However, these methods rely heavily on the desired hemodynamic function as a reference signal ( Table 3 ). The hemodynamic signal is designed by gamma functions [ 64 ], the balloon model [ 65 ], the finite element method [ 66 ], the state-space method [ 67 , 68 ], etc. These hemodynamic signals are not suitable for use in unknown areas because they depend on the brain region or task being measured.…”

Self-calibrated pulse oximetry algorithm based on photon pathlength change and the application in human freedivers

“…This approach adjusts for ΔDPF without gauging its absolute value. For the absolute estimation, Huang and Hong 22 introduced dual square-root cubature Kalman filters with a multichannel probe. However, this requires an initial phantom experiment calibration, and their method was only applied on simulated data.…”