Amir Salehi Lashkajani

SignificanceAchieving adequate brain sensitivity remains a significant obstacle to noninvasive optical measurements of pulsatile cerebral blood flow. Increasing source-detector separation (SDS), utilizing time-of-flight (ToF) information, and/or increasing acquisition frequency can increase brain sensitivity. However, optimizing these parameters is nontrivial and must balance the need to achieve sufficient signal-to-noise ratio.AimWe aim to guide hardware optimization by evaluating the benefits of ToF gating, autocorrelation time-lag gating, and increased source-detector separation in recovering pulsatile cerebral blood flow.ApproachMonte Carlo simulations of ToF-resolved pulsatile blood flow index at 1064 nm were performed. A simulation and analysis pipeline is presented and validated against phantom and in vivo measurements.ResultsBrain sensitivity deteriorates for autocorrelation time-lags >1 to 10 μs. Continuous-wave diffuse correlation spectroscopy (CW-DCS) at 40 mm SDS achieves equivalent brain sensitivity to time-resolved measurements with a 1.2 ns ToF gate. For median adult brain depths, a 31 mm SDS (CW-DCS), 35 mm SDS (speckle contrast optical spectroscopy), or 0.9 ns ToF are needed for brain-dominated signals. For the 85th percentile of brain depth, these thresholds increase to 40 mm, 46 mm, and 1.2 ns, respectively.ConclusionsWe quantitatively compare source-detector separation, ToF gating, and acquisition frequency and identify crucial performance requirements for clinically viable optical monitors of cerebral blood flow.

SignificanceContinuous, noninvasive monitoring of cerebral blood flow (CBF) at the bedside is a critical unmet clinical need and a long-standing goal of biomedical optics. Despite extensive development, no optical measurement of CBF has achieved routine clinical use.AimWe aim to demonstrate and validate CoMind R1, a time-resolved interferometric neuromonitoring system designed to noninvasively measure CBF at pulsatile rates.ApproachCoMind R1 integrates numerous advances, including a high-power, linearly swept 1064 nm laser, multimode collection, parallelized detection, and real-time processing. Performance is evaluated with homogeneous and dynamic bi-layer phantoms and in vivo studies of adults at rest and during visual stimulation.ResultsCoMind R1 achieves an instrument response function width of 120 ps and exhibits no significant drift over 24 h. In vivo data from 25 adults show consistent pulsatile blood flow waveforms at times-of-flight averaging 1.2 ns, exceeding the prior art. Visual stimulation produces significant, time-of-flight-dependent hyperaemic responses, demonstrating brain sensitivity and selectivity.ConclusionsCoMind R1 consistently achieves time-of-flight resolved measurements of pulsatile blood flow at the late times-of-flight necessary to ensure a brain-dominated signal in the typical adult. CoMind R1 thus provides cerebral sensitivity and tissue specificity in a scalable, cost-effective architecture and advances optical monitoring of CBF toward clinical translation.