Biology subjects

Mogharari, N.

Publications and source records attributed to Mogharari, N..

3 recordsLinked to original sources

bioRxiv2026

Readout-dependent time-of-flight weighting of absorption and flow in interferometric diffuse optics

Joint optical measurement of hemoglobin and blood-flow dynamics could provide a compact route to richer functional monitoring of tissue physiology. However, hybrid diffuse-optical systems commonly optimize photon time-of-flight (TOF) for individual readouts, even when absorption and flow are recovered from the same acquisition. Here, we asked whether a single TOF window can optimally preserve both signals. Dual-wavelength TOF-iSCOS recovered absorption, hemoglobin and relative blood-flow index (BFI) from the same interferometrically sensed optical field, while Early, Middle and Late photon windows provided progressively greater weighting of longer and deeper photon paths. During forearm cuff occlusion in 11 adults, absorption and flow showed markedly different TOF dependence: Late-gate BFI responses were retained, whereas absorption decreased to a median Late/Early ratio of 0.18. The resulting readout-by-TOF interaction was positive in all 11 participants (median 2.61 octaves, 95% bootstrap CI 2.44-3.22; exact sign-test P = 9.8 x 10-4). Readout-specific gate selection increased held-out response retention by 24.8% (95% CI 8.8-42.5%) relative to a single common gate. We then tested the approach during prefrontal working-memory activation in seven participants using a higher-load 2-back task relative to a low-load 0-back control. Late-gate BFI increased in all seven participants (+5.07%, 95% CI 1.46-8.68%; P = 0.014) and remained positive after adjustment using an Early-TOF signal, whereas hemoglobin responses were less consistent. Layered Monte Carlo modeling showed that the same detected photon histories acquire different absorption and dynamic-scattering sensitivity across TOF, linking the experimental effects to anatomy- and geometry-conditioned tissue weighting. Within the present geometry and photon budget, the central result is therefore not that one readout is intrinsically superior, but that absorption and flow recovered from the same optical field retain physiological information differently across photon time-of-flight.

bioengineering↗

bioRxiv2026

Assessing the fractional contributions of static, slow and fast dynamic scatterer components to the flow index derived by continuous wave diffuse correlation spectroscopy

Continuous wave diffuse correlation spectroscopy (cw-DCS) is a noninvasive optical technique to monitor the tissues blood flow changes. This technique measures the tissue blood flow index (BFI) by evaluating the decay rate of the autocorrelation function. The derived BFI is proportional to mean squared displacements of the red blood cells considered as the fast-dynamic scatterer component of tissue in time. However, biological tissue contains static scatterer component and slow-dynamic scatterer component which affect the decay rate of autocorrelation function and as a result the derived BFI. In this study, we assessed the fractional contribution of static, slow-dynamic and fast-dynamic scatterer components of a medium in the flow index derived by cw-DCS. The measurements performed on Agar-based phantom with tube showed that presence of static scatterer component and slow-dynamic scatterer component led to substantial underestimation ({approx} 123%) of the flow index derived by Siegert relation, compared to effective diffusion coefficient of fast-dynamic scatterers components derived by modified Siegert relation and bi-exponential model. The less underestimation was observed for the corresponding parameters obtained from the liquid phantom measurements ({approx} 25%) as well as during the forearm occlusion test and respiratory challenges ({approx} 16% - 26%).

bioengineering↗

bioRxiv2026

Time-of-flight-resolved interferometric speckle-contrast optical spectroscopy (TOF-iSCOS) for depth-resolved blood-flow sensing

SignificanceContinuous, noninvasive, and depth-resolved monitoring of blood-flow-related tissue dynamics remains an important unmet need. Speckle-contrast optical spectroscopy (SCOS), including interferometric implementations such as iSCOS, provides a scalable optical route to blood-flow sensing, but conventional continuous-wave approaches lack intrinsic depth selectivity. Time-of-flight (TOF) gating offers a way to separate superficial and deeper dynamic contributions in layered tissues, such as skin- muscle or scalp-cortex, by resolving photon path lengths. AimWe introduce a swept-source, single-channel implementation of interferometric speckle-contrast optical spectroscopy (iSCOS) to obtain TOF-resolved temporal speckle contrast,{kappa} 2, from the measured field autocorrelation g1, and evaluate its feasibility for depth-resolved blood-flow sensing. ApproachA swept-source iNIRS system operating at 780 nm acquired interferometric signals, which were Fourier-transformed along the optical-frequency axis to recover complex TOF-resolved speckle fields. Temporal speckle contrast was then estimated at each TOF gate indirectly from g1 using the speckle-visibility relation. Diffusion-based numerical simulations were first used to compare the direct variance-based estimator and the indirect g1-based estimator under varying reduced scattering coefficient, diffusion coefficient, additive noise level, and bi-layer geometry. Because the simulations showed that the g1-derived{kappa} 2 estimator was substantially less sensitive to additive noise than the direct estimator, this estimator was used for the main phantom and in vivo analyses, while the direct estimator served as a simulation comparator. The g1-derived estimator was then applied to liquid and bi-layer phantoms, followed by proof-of-concept in vivo measurements on the human forearm during cuff occlusion and on the forehead during a Sudoku task. ResultsTOF-resolved{kappa} 2 curves recovered with the g1-derived estimator matched DWS theory across scattering coefficients, photon path lengths, and exposure times. The estimator preserved theoretical accuracy for additive noise amplitudes up to 50% of the field amplitude, whereas the direct variance estimator showed substantial noise-induced bias and required correction. Bi-layer simulations and phantom experiments reproduced the predicted direction and onset of TOF-dependent decorrelation-rate trends in layered media. In vivo, the recovered blood-flow index tracked the expected TOF-dependent cuff-occlusion and reactive-hyperemia response in the forearm. During the single-subject Sudoku task, the left-forehead recording showed a TOF-dependent relative blood-flow-index increase of +0.8 {+/-} 1.9% at TOF = 400 ps, +9.8 {+/-} 2.2% at TOF = 600 ps, and +15.2 {+/-} 5.6% at TOF = 800 ps. This pattern is consistent with increased sensitivity to deeper tissue at longer photon path lengths, but requires cohort-level validation before quantitative interpretation as cognitive activation. ConclusionsCoupling temporal speckle-contrast analysis with swept-source iNIRS yields a proof-of-concept, depth-resolved platform for blood-flow sensing. By estimating TOF-resolved speckle contrast through the g1-derived{kappa} 2 route, TOF-iSCOS suppresses additive-noise bias while preserving sensitivity to deeper dynamic tissue layers. The present single-channel results bridge continuous-wave iSCOS, interferometric NIRS and time-domain diffuse correlation spectroscopy (TD-DCS), and motivate future multi-channel and cohort studies for scalable cortical hemodynamic monitoring.

bioengineering↗