Recently we developed the open-source FlexNIRS: a battery-operated, wireless, wearable oximeter whose self-calibrating geometry allows measurements of oxygen saturation in tissue. The first implementation of the device operating at 100 Hz has been validated and is enrolled in several measurement campaigns across different research laboratories. A recent firmware upgrade provides 266 Hz sampling rate, and hardware modifications provide improved form factor, wearability, and multi-modal acquisition. The new version is currently adopted in multiple clinical measurement campaigns focusing on pulsatile component analysis. We will present the instrument performance, its recent and future upgrades, and the applications where the device is currently in use.
SignificanceCombining near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) allows for quantifying cerebral blood volume, flow, and oxygenation changes continuously and non-invasively. As recently shown, the DCS pulsatile cerebral blood flow index (pCBFi) can be used to quantify critical closing pressure (CrCP) and cerebrovascular resistance (CVRi).AimAlthough current DCS technology allows for reliable monitoring of the slow hemodynamic changes, resolving pulsatile blood flow at large source–detector separations, which is needed to ensure cerebral sensitivity, is challenging because of its low signal-to-noise ratio (SNR). Cardiac-gated averaging of several arterial pulse cycles is required to obtain a meaningful waveform.ApproachTaking advantage of the high SNR of NIRS, we demonstrate a method that uses the NIRS photoplethysmography (NIRS-PPG) pulsatile signal to model DCS pCBFi, reducing the coefficient of variation of the recovered pulsatile waveform (pCBFi-fit) and allowing for an unprecedented temporal resolution (266 Hz) at a large source-detector separation (>3 cm).ResultsIn 10 healthy subjects, we verified the quality of the NIRS-PPG pCBFi-fit during common tasks, showing high fidelity against pCBFi (R2 0.98 ± 0.01). We recovered CrCP and CVRi at 0.25 Hz, >10 times faster than previously achieved with DCS.ConclusionsNIRS-PPG improves DCS pCBFi SNR, reducing the number of gate-averaged heartbeats required to recover CrCP and CVRi.
Transcatheter aortic valve replacement (TAVR) surgery has a risk of cognitive impairment and neurological injury. Currently, there are few options for non-invasively monitoring brain activity and perfusion, with electroencephalography, transcranial Doppler, and near-infrared spectroscopy (NIRS) all having significant drawbacks. By combining NIRS with diffuse correlation spectroscopy (DCS) we can obtain a more complete picture of cerebral hemodynamics during TAVR procedures and examine the link to neurological outcomes. We show examples of post-valve replacement hemodynamic changes that correspond with worse/better patient outcomes
We present a novel system based on a four-stage fiber delay network designed for multistate time-domain diffuse correlation spectroscopy, providing three output fibers per each delay state. The fiber delay network is coupled to a custom pulsed laser at 1064 nm and four SNSPDs, allowing to measure up to 12 independent source-detector pairs simultaneously. The system delivers 300ps optical pulses, 100 mW average optical power per fiber output, operates at 62.5 MHz and each cycle provides 4 laser pulses displaced of 4 ns. The instrument has been validated on healthy human subject during functional tasks, proving state-of-the-art performance.
Infants born at an extremely low gestational age are at an increased risk of intraventricular hemorrhaging during the first three postnatal days. We have built a standalone easy-to-use multi-wavelength multi-distance diffuse correlation spectroscopy system, which utilizes three time-multiplexed long coherence lasers at 785, 808, and 853 nm, single photon detectors, and photon time-tagging electronics to simultaneously quantify cerebral blood flow, tissue optical properties, and blood oxygen saturation. The system has been designed specifically for use on preterm infants. The device shows good agreement with a commercially available NIRS-DCS system. We are currently monitoring preterm infants and will show results.
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