. 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 ( ), 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 times more photons and achieved an SNR gain of 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 with respect to the 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.
Objectives: Real-time noninvasive monitoring of cerebral blood flow (CBF) during surgery is key to reducing mortality rates associated with adult cardiac surgeries requiring hypothermic circulatory arrest (HCA). We explored a method to monitor cerebral blood flow during different brain protection techniques using diffuse correlation spectroscopy (DCS), a noninvasive optical technique which, combined with frequency-domain near-infrared spectroscopy (FDNIRS), also provides a measure of oxygen metabolism.Methods: We used DCS in combination with FDNIRS to simultaneously measure hemoglobin oxygen saturation (SO 2 ), an index of cerebral blood flow (CBF i ), and an index of cerebral metabolic rate of oxygen (CMRO 2i ) in 12 patients undergoing cardiac surgery with HCA.
In premature infants with an extremely low gestational age (ELGA, < 29 weeks GA), dysregulated changes in cerebral blood flow (CBF) are among the major pathogenic factors leading to germinal matrix/intraventricular hemorrhage (GM/IVH). Continuous monitoring of CBF can guide interventions to minimize the risk of brain injury, but there are no clinically standard techniques or tools for its measurement. We report the feasibility of the continuous monitoring of CBF, including measures of autoregulation, via diffuse correlation spectroscopy (DCS) in ELGA infants using CBF variability and correlation with scalp blood flow (SBF, served as a surrogate measure of systemic perturbations). In nineteen ELGA infants (with 9 cases of GM/IVH) monitored for 6–24 h between days 2–5 of life, we found a strong correlation between CBF and SBF in severe IVH (Grade III or IV) and IVH diagnosed within 72 h of life, while CBF variability alone was not associated with IVH. The proposed method is potentially useful at the bedside for the prompt assessment of cerebral autoregulation and early identification of infants vulnerable to GM/IVH.
Objective: This pilot study aims to show the feasibility of noninvasive and real-time cerebral hemodynamic monitoring during carotid endarterectomy (CEA) via diffuse correlation spectroscopy (DCS) and near-infrared spectroscopy (NIRS). Methods: Cerebral blood flow index (CBFi) was measured unilaterally in seven patients and bilaterally in seventeen patients via DCS. In fourteen patients, hemoglobin oxygenation changes were measured bilaterally and simultaneously via NIRS. Cerebral autoregulation (CAR) and cerebrovascular resistance (CVR) were estimated using CBFi and arterial blood pressure data. Further, compensatory responses to the ipsilateral hemisphere were investigated at different contralateral stenosis levels. Results: Clamping of carotid arteries caused a sharp increase of CVR (~70%) and a marked decrease of ipsilateral CBFi (57%). From the initial drop, we observed partial recovery in CBFi, an increase of blood volume, and a reduction in CVR in the ipsilateral hemisphere. There were no significant changes in compensatory responses between different contralateral stenosis levels as CAR was intact in both hemispheres throughout the CEA phase. A comparison between hemispheric CBFi showed lower ipsilateral levels during the CEA and post-CEA phases (p < 0.001, 0.03). Conclusion: DCS alone or combined with NIRS is a useful monitoring technique for real-time assessment of cerebral hemodynamic changes and allows individualized strategies to improve cerebral perfusion during CEA by identifying different hemodynamic metrics.
Hypoxic ischaemic encephalopathy (HIE), an important complication of perinatal asphyxia, remains a major health burden. Neonates are classifi ed using the Sarnat score and neonates >35 weeks with moderate/ severe HIE are treated with therapeutic hypothermia (TH). TH improves survival/ decreases disability however 30-50% of mild HIE cases (not offered TH) develop cognitive impairment. Early biomarkers are vital to redefi ne HIE and better manage these infants. Cerebral monitoring is essential to establish cerebral activity, categorise encephalopathy stages, diagnose seizures, and monitor treatment. EEG and near infrared spectroscopy (NIRS) may be used concomitantly as monitoring tools (combined cerebral activity and haemodynamics) in order to study neurovascular coupling (NVC). NVC as a biomarker may increase sensitivity and specifi city for HIE outcome prediction. Limited research exists on NVC in neonates and in HIE where lower oxygen saturation may exist, physiological patterns may be altered. Easy integration of EEG and NIRS, continuous results over long periods, different clinical settings, favors studies. NVC analysis may identify neonates at risk earlier and reduce neurodevelopmental disabilities. AIM:-Study continuous EEG and NIRS data in HIE.-Measure NVC as biomarker for asphyxia severity -Identify/establish patterns of outcome prediction -Study effects of physiological variability and medication on NVC. METHODOLOGY:-Single center retrospective cohort study -UZ Leuven, Belgium: 10-year period 2010 -2020.-Establish database and inclusions.-Inclusion: 72 hours TH, EEG and NIRS, magnetic resonance imaging (MRI) < day 10 of life.-Demographic and clinical data (REDCap system) -Statistical analysis using GraphPad Prism.-MRIs scored blinded (Weeke HIE score). Score = 0 considered normal outcome, 1-2 a mild/moderate and >2 severe HIE. Comparisons between groups were performed.
Objective: The objective of this study was to investigate neural responses during subliminal oddball tasks concerning reward-directed motivation to distinguish the P3a and P3b components of evoked P300 potentials. Methods: The subliminal oddball task included congruent/incongruent stimuli and masked prime subliminal stimuli. The task was to push the button when an incongruent stimulus appeared. Participants underwent two pre- and post-break electroencephalogram (EEG) recordings. During the break, the thirst scores of the participants were evaluated. Then, participants consumed three different salty foods in the same amount and completed the remaining two post-break EEG recordings, followed by the second thirst scores evaluation. Finally, participants physically selected lettered cards (A, B, C, and D) to receive a reward and quench their thirst. Results: Thirty participants were enrolled, 28 of whom were included for data analysis. Ten participants selected lettered cards as the given subliminal stimulus (sub(+) group), and 18 participants selected different lettered cards from the given subliminal stimulus (sub(–) group). We found a significant increase in post-P3a and post-P3b amplitudes in the sub(+) group at the Pz/Oz electrodes. Changes in P3b amplitude were significantly higher in the sub(+) group (2.83 ± 1.14 μV) than in the sub(–) group (0.62 ± 2.29 μV) at the Pz/Oz electrodes. Correlation analysis revealed that higher thirst scores resulted in higher P3b amplitudes in the sub(+) group. Conclusion: These findings suggest that reward-directed motivation increases parietal-posterior P3b amplitudes, signifying the involvement of cognitive processes to achieve a reward.
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