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ObjectivesA new device that combines, for the first time, two photonic technologies (time-resolved near-infrared spectroscopy and diffuse correlation spectroscopy) was provided and tested within the BabyLux project. Aim was to validate the expected changes in cerebral oxygenation and blood flow.MethodsA pulse oximeter and the BabyLux device were held in place (right hand/wrist and frontoparietal region, respectively) for 10 min after birth in healthy term infants delivered by elective caesarean section. Pulse oximeter saturation (SpO2), cerebral tissue oxygen saturation (StO2) and blood flow index (BFI) were measured over time. Tissue oxygen extraction (TOE) and cerebral metabolic rate of oxygen index (CMRO2I) were calculated.ResultsThirty infants were enrolled in two centres. After validity check of data, 23% of infants were excluded from TOE and CMRO2I calculation due to missing data. As expected, SpO2 (estimate 3.05 %/min; 95% CI 2.78 to 3.31 %/min) and StO2 (estimate 3.95 %/min; 95% CI 3.63 to 4.27 %/min) increased in the first 10 min after birth, whereas BFI (estimate −2.84×10−9 cm2/s/min; 95% CI −2.50×10−9 to −3.24×10−9 cm2/s/min) and TOE (estimate −0.78 %/min; 95% CI −1.12 to –0.45 %/min) decreased. Surprisingly, CMRO2I decreased (estimate −7.94×10−8/min; 95% CI −6.26×10−8 to −9.62×10−8/min).ConclusionsBrain oxygenation and BFI during transition were successfully and simultaneously obtained by the BabyLux device; no adverse effects were recorded, and the BabyLux device did not limit the standard care. The preliminary results from clinical application of the BabyLux device are encouraging in terms of safety and feasibility; they are consistent with previous reports on brain oxygenation during transition, although the interpretation of the decreasing CMRO2I remains open.Trial registration numberNCT02815618.

Diffuse correlation spectroscopy (DCS) is an emerging diffuse optical technique that quantifies microvascular blood flow. In spite of the wide range of clinical/research applications, DCS instrumentation is not yet standardized. In this study, we have analyzed the effect of experimental parameters as the measurement duration time and the number of detectors, at different photon count-rates, on the precision of a DCS experiment. This provides a recipe for finding device and experimental settings that optimize the precision while balancing cost and temporal resolution.

Over the recent years, a typical implementation of diffuse correlation spectroscopy (DCS) instrumentation has been adapted widely. However, there are no detailed and accepted recipes for designing such instrumentation to meet pre-defined signal-to-noise ratio (SNR) and precision targets. These require specific attention due to the subtleties of the DCS signals. Here, DCS experiments have been performed using liquid tissue simulating phantoms to study the effect of the detected photon count-rate, the number of parallel detection channels and the measurement duration on the precision and SNR to suggest scaling relations to be utilized for device design.

A practical assessment of the health of the palm muscle, abductor pollicis brevis (APB), is important for diagnosis of different conditions. Here we have developed a protocol and a probe to utilize diffuse correlation spectroscopy (DCS) to characterize microvascular blood flow changes in the APB during and after sustained isometric exercise, during and after thumb abduction at at 55% of maximum voluntary contraction (MVC). Blood flow in the APB decreased during exercise in the subjects (n=13) with high MVC (n=7) and stayed constant in the ones with low MVC (n=6) suggesting that the mechanical occlusion due to increased intramuscular pressure exceeded the vasodilation elicited by the higher demand. Blood flow changes during exercise negatively correlated with the absolute force applied by each subject. Muscular blood flow increased after exercise compared to the values reached during exercise. In conclusion, DCS allows the study of the response of a small muscle to static exercise.

Diffuse correlation spectroscopy (DCS) can non-invasively and continuously asses regional cerebral blood flow (rCBF) at the cot-side by measuring a blood flow index (BFI) in non-traditional units of cm(2)/s. We have validated DCS against positron emission tomography using (15)O-labeled water ((15)O-water PET) in a piglet model allowing us to derive a conversion formula for BFI to rCBF in conventional units (ml/100g/min). Neonatal piglets were continuously monitored by the BabyLux device integrating DCS and time resolved near infrared spectroscopy (TRS) while acquiring (15)O-water PET scans at baseline, after injection of acetazolamide and during induced hypoxic episodes. BFI by DCS was highly correlated with rCBF (R = 0.94, p

A practical assessment of the general health and microvascular function of the palm muscle, abductor pollicis brevis (APB), is important for the diagnosis of different conditions. In this study, we have developed a protocol and a probe to study microvascular blood flow using near-infrared diffuse correlation spectroscopy (DCS) in APB during and after thumb abduction at 55% of maximum voluntary contraction (MVC). Near-infrared time resolved spectroscopy (TRS) was also used to characterize the baseline optical and hemodynamic properties. Thirteen (n=13) subjects were enrolled and subdivided in low MVC (N=6, MVC

Neurophotonics 6(02), 025007 (2019). doi:10.1117/1.NPh.6.2.025007, Published by SPIE, Bellingham, Wash.

Diffuse correlation spectroscopy (DCS) can non-invasively and continuously asses regional cerebral blood flow (rCBF) at the cot-side by measuring a blood flow index (BFI) in non-traditional units of cm2/s. We have validated DCS against positron emission tomography using 15 O-labeled water (15O-water PET) in a piglet model allowing us to derive a conversion formula for BFI to rCBF in conventional units (ml/100g/min). Neonatal piglets were continuously monitored by the BabyLux device integrating DCS and time resolved near infrared spectroscopy (TRS) while acquiring 15 O-water PET scans at baseline, after injection of acetazolamide and during induced hypoxic episodes. BFI by DCS was highly correlated with rCBF (R = 0.94, p 9× (ml/100g/min)/(cm2/s) was used to derive baseline rCBF from baseline BFI measurements of another group of piglets and of healthy newborn infants showing an agreement with expected values. These results pave the way towards non-invasive, cot-side absolute CBF measurements by DCS on neonates.

We have investigated the accuracy and precision of "the BabyLux device", a hybrid time-resolved near-infrared (TRS) and diffuse correlation spectroscopy (DCS) neuro-monitor for the pre-term infant. Numerical data with realistic noise were simulated and analyzed using the BabyLux device as a reference system and different experimental and analysis parameters. The results describe the limits for the precision and the accuracy to be expected. The dependence of these limits on different experimental conditions and choices of the analysis method is also described. Experiments demonstrate comparable values for precision with respect to the simulation results. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Background: The BabyLux device is a prototype optical neuro-monitor of cerebral oxygenation and blood flow for neonatology integrating time-resolved reflectance spectroscopy and diffuse correlation spectroscopy. Methods: Here we report the variability of six consecutive 30 s measurements performed in 27 healthy term infants at rest. Poor data quality excluded four infants. Results: Mean cerebral oxygenation was 59.6 ± 8.0%, with intra-subject standard deviation of 3.4%, that is, coefficient of variation (CV) of 5.7%. The inter-subject CV was 13.5%. Mean blood flow index was 2.7 × 10−8 ± 1.56 × 10−8 (cm2/s), with intra-subject CV of 27% and inter-subject CV of 56%. The variability in blood flow index was not reduced by the use of individual measures of tissue scattering, nor accompanied by a parallel variability in cerebral oxygenation. Conclusion: The intra-subject variability for cerebral oxygenation variability was improved compared to spatially resolved spectroscopy devices, while for the blood flow index it was comparable to that of other modalities for estimating cerebral blood flow in newborn infants. Most importantly, the simultaneous measurement of oxygenation and flow allows for interpretation of the high inter-subject variability of cerebral blood flow as being due to error of measurement rather than to physiological instability.

Transcranial direct current stimulation (tDCS) is currently being used for research and treatment of some neurological and neuropsychiatric disorders, as well as for improvement of cognitive functions. In order to better understand cerebral response to the stimulation and to redefine protocols and dosage, its effects must be monitored. To this end, we have used functional diffuse correlation spectroscopy (fDCS) and time-resolved functional near-infrared spectroscopy (TR-fNIRS) together with electroencephalography (EEG) during and after stimulation of the frontal cortex. Twenty subjects participated in two sessions of stimulation with two different polarity montages and twelve also underwent a sham session. Cerebral blood flow and oxyhemoglobin concentration increased during and after active stimulation in the region under the stimulation electrode while deoxyhemoglobin concentration decreased. The EEG spectrum displayed statistically significant power changes across different stimulation sessions in delta (2 to 4 Hz), theta (4 to 8 Hz), and beta (12 to 18 Hz) bands. Results suggest that fDCS and TR-fNIRS can be employed as neuromonitors of the effects of transcranial electrical stimulation and can be used together with EEG.

Motivation Obstructive sleep apnea (OSA) can impair cerebral vasoreactivity and is associated with an increased risk of cerebrovascular disease. Unfortunately, an easy-to-use, non-invasive, portable monitor of cerebral vasoreactivity does not exist. Therefore, we have evaluated the use of near-infrared diffuse correlation spectroscopy to measure the microvascular cerebral blood flow (CBF) response to a mild head-of-bed position change as a biomarker for the evaluation of cerebral vasoreactivity alteration due to chronic OSA. Furthermore, we have monitored the effect of two years of continuous positive airway pressure (CPAP) treatment on the cerebral vasoreactivity. Methodology CBF was measured at different head-of-bed position changes (supine to 30 degrees to supine) in sixty-eight patients with OSA grouped according to severity (forty moderate to severe, twenty-eight mild) and in fourteen control subjects without OSA. A subgroup (n = 13) with severe OSA was measured again after two years of CPAP treatment. Results All patients and controls showed a similar CBF response after changing position from supine to 30 degrees (p = 0.819), with a median (confidence interval) change of -17.5 (-10.3, -22.9)%. However, when being tilted back to the supine position, while the control group (p = 0.091) and the mild patients with OSA (p = 0.227) recovered to the initial baseline, patients with moderate and severe OSA did not recover to the baseline (9.8 (0.8, 12.9)%, p < 0.001) suggesting altered cerebral vasoreactivity. This alteration was correlated with OSA severity defined by the apnea-hypopnea index, and with mean nocturnal arterial oxygen saturation. The CBF response was normalized after two years of CPAP treatment upon follow-up measurements. Conclusion In conclusion, microvascular CBF response to a head-of-bed challenge measured by diffuse correlation spectroscopy suggests that moderate and severe patients with OSA have altered cerebral vasoreactivity related to OSA severity. This may normalize after two years of CPAP treatment.

Supine postures are utilized to increase cerebral blood flow following ischemic stroke. We find supine cerebral blood flow is lower than sitting flow in 25% of subjects and that postural changes increase supine blood flow.

We present simultaneous diffuse correlation spectroscopy (DCS) and time resolved spectroscopy (TR NIRS) measurements on exercising and non-exercising vastus lateralis muscle. We discuss the results at two different exercise levels.

Obstructive sleep apnea (OSA) impairs cerebral vasoreactivity (CVR). CVR was evaluated in severe OSA patients and a control group before and after two years of continuous positive air pressure treatment demonstrating improvements in vasoreactivity.

Improved cerebral monitoring systems are needed to prevent preterm infants from long-term cognitive and motor restrictions. Combining advanced near-infrared diffuse spectroscopy measurement technologies, time-resolved spectroscopy (TRS) and diffuse correlation spectroscopy (DCS) will introduce novel indicators of cerebral oxygen metabolism and blood flow for neonatology. For non-invasive sensing a fiber-optical probe is used to send and receive light from the infant head. In this study we introduce a new fiber-based hybrid probe that is designed for volume production. The probe supports TRS and DCS measurements in a cross geometry, thus both technologies gain information on the same region inside the tissue. The probe is highly miniaturized to perform cerebral measurements on heads of extreme preterm infants down to head diameters of 6cm. Considerations concerning probe production focus on a reproducible accuracy in shape and precise optical alignment. In this way deviations in measurement data within a series of probes should be minimized. In addition to that, requirements for clinical use like robustness and hygiene are considered. An additional soft-touching sleeve made of FDA compatible silicone allows for a flexible attachment with respect to the individual anatomy of each patient. We present the technical concept of the hybrid probe and corresponding manufacturing methods. A prototype of the probe is shown and tested on tissue phantoms as well as in vivo to verify its operational reliability.

International audience; Ultrashort, coherent x-ray pulses of a free-electron laser are used to holographically image the magnetization dynamics within a magnetic domain pattern after creation of a localized excitation via an optical standing wave. We observe a spatially confined reduction of the magnetization within a couple of hundred femtoseconds followed by its slower recovery. Additionally, the experimental results show evidence of a spatial evolution of magnetization, which we attribute to ultrafast transport of nonequilibrium spin-polarized electrons for early times and to a fluence-dependent remagnetization rate for later times.

The influence on ultrafast demagnetization dynamics of metallic nano-structured gratings deposited on thin films of magnetic Co/Pt multilayers is investigated by the time-resolved optical Kerr effect. Depending on the polarization of the pump pulse, a pronounced enhancement of the demagnetization amplitude is found. Calculation of the inhomogeneous optical field distribution due to plasmon interaction and time-dependent solutions of the coupled electron, lattice, and spin temperatures in two dimensions show good agreement with the experimental data, as well as giving evidence of non-local demagnetization dynamics due to electron diffusion.

We present measurements of cerebral hemodynamics with diffuse optical monitor and electroencephalography (EEG) during transcranial direct current stimulation (tDCS). Cerebral blood flow (CBF), measured by Diffuse Correlation Spectroscopy (DCS), cerebral tissue oxygenation, measured by Time Resolved Near Infrared Spectroscopy (TR-NIRS), and electrical activity measured by EEG were studied in a sham-controlled, randomized cross-over study with 20 healthy adults, before during and after a 10 minute session of tDCS over the left frontal cortex.

BabyLux project is driven by the end-users working with academia and industry to develop a hybrid near-infrared diffuse correlation spectroscopy (DCS)/ time resolved spectroscopy (TRS) system to address the challenge of a user-friendly, medical grade device for neonatology.

A long-lasting (>2 months), stable liquid phantom suitable for longitudinal testing and calibration of diffuse optical and correlation spectroscopies is presented.

The precision of diffuse correlation spectroscopy (DCS) measurements was evaluated for varying instrumental and experimental parameters to provide recipes for making practical choices when designing devices.