Significance: The ability of diffuse correlation spectroscopy (DCS) to measure cerebral blood flow (CBF) in humans is hindered by the low signal-to-noise ratio (SNR) of the method. This limits the high acquisition rates needed to resolve dynamic flow changes and to optimally filter out large pulsatile oscillations and prevents the use of large source-detector separations (≥3 cm), which are needed to achieve adequate brain sensitivity in most adult subjects.
Aim: To substantially improve SNR, we have built a DCS device that operates at 1064 nm and uses superconducting nanowire single-photon detectors (SNSPD).
Approach: We compared the performances of the SNSPD-DCS in humans with respect to a typical DCS system operating at 850 nm and using silicon single-photon avalanche diode detectors.
Results: At a 25-mm separation, we detected 13 ± 6 times more photons and achieved an SNR gain of 16 ± 8 on the forehead of 11 subjects using the SNSPD-DCS as compared to typical DCS. At this separation, the SNSPD-DCS is able to detect a clean pulsatile flow signal at 20 Hz in all subjects. With the SNSPD-DCS, we also performed measurements at 35 mm, showing a lower scalp sensitivity of 31 ± 6 % with respect to the 48 ± 8 % scalp sensitivity at 25 mm for both the 850 and 1064 nm systems. Furthermore, we demonstrated blood flow responses to breath holding and hyperventilation tasks.
Conclusions: While current commercial SNSPDs are expensive, bulky, and loud, they may allow for more robust measures of non-invasive cerebral perfusion in an intensive care setting.
Real-time noninvasive cerebral blood flow monitoring during cardiac surgery could decrease rates of neurologic injury associated with hypothermic circulatory arrests (HCA). We used combined frequency domain near-infrared spectroscopy and diffuse correlation spectroscopy (FDNIRS-DCS) to measure cerebral oxygen saturation and an index of blood flow (CBFi) in 12 adults undergoing HCA. Our measurements revealed negligible CBFi during retrograde cerebral perfusion (RCP: CBFi 91.2%±3.3% drop; HCA-only: 95.5%±1.8% drop). There was a significant difference during antegrade cerebral perfusion (p = 0.003). We conclude that FDNIRS-DCS can be a powerful tool to optimize cerebral perfusion and that RCP’s efficacy needs to be further examined.
Carotid endarterectomy (CEA) is a prophylactic operation to remove plaques inside carotid arteries, during which the patients are at high risk of embolic stroke. CEA is performed at carotid bifurcation, where carotid arteries are cross-clamping in order to isolate from circulation. However, there has been no gold standard for monitoring blood flow during CEA. Here, we aimed to investigate changes in the blood flow index (CBFi) and hemoglobin oxygenation with a combined frequency-domain near-infrared spectroscopy (FDNIRS) and diffuse correlation spectroscopy (DCS) system in patients who underwent CEA. Our results revealed that CBFi and total hemoglobin concentration (HbT) dropped substantially (58±14% and 18±10%, respectively) when the carotid arteries were cross-clamped. We also found that overshoot in CBFi and HbT was noticeably higher respect to the baseline before clamping (22±43% and 38±23%, respectively). Oxygen saturation at carotid clamping dropped by an average of 8−5% with respect to the pre-clamp baseline. At unclamping, oxygen saturation had an average overshoot of 2±9% with respect to the baseline level. According to our results, FDNIRS-DCS could be a robust tool for observing vascular physiology changes during CEA. Furthermore, as an indicator of cerebral hemodynamic and a proper perioperative blood flow monitoring, FDNIRS-DCS could help mitigate some of the risks and complications that follow CEA procedures.
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