The reproducibility of cerebral time-domain near-infrared spectroscopy (TD-NIRS) has not been investigated so far. Besides, reference intervals of cerebral optical properties, of absolute concentrations of deoxygenated-hemoglobin (HbR), oxygenated-hemoglobin (HbO), total hemoglobin (HbT) and tissue oxygen saturation (StO) and their variability have not been reported. We have addressed these issues on a sample of 88 adult healthy subjects. TD-NIRS measurements at 690, 785, 830 nm were fitted with the diffusion model for semi-infinite homogenous media. Reproducibility, performed on 3 measurements at 5 minutes intervals, ranges from 1.8 to 6.9% for each of the hemoglobin species. The mean ± SD global values of HbR, HbO, HbT, StO are respectively 24 ± 7 μM, 33.3 ± 9.5 μM, 57.4 ± 15.8 μM, 58 ± 4.2%. StO displays the narrowest range of variability across brain regions.

Abstract:We present the recipe and characterization for preparing liquid phantoms that are suitable for both near-infrared spectroscopy and diffuse correlation spectroscopy. The phantoms have well-defined and tunable optical and dynamic properties, and consist of a solution of water and glycerol with fat emulsion as the scattering element. The recipe takes into account the effect of bulk refractive index changes due to the addition of glycerol, which is commonly used to alter the sample viscosity. M. Carrol, F. J. Combs, T. Strömberg, A.G. Yodth, and B. Tromberg, "Mapping breast cancer blood flow index, composition, and metabolism in a human subject using combined diffuse optical spectroscopic imaging and diffuse correlation spectroscopy," J. Biomed. Opt. 22(4), 045003 (2017) 21.

Background COVID-19 is primarily a respiratory disease; however, there is also evidence that it causes endothelial damage in the microvasculature of several organs. The aim of the present study is to characterize in vivo the microvascular reactivity in peripheral skeletal muscle of severe COVID-19 patients. Methods This is a prospective observational study carried out in Spain, Mexico and Brazil. Healthy subjects and severe COVID-19 patients admitted to the intermediate respiratory (IRCU) and intensive care units (ICU) due to hypoxemia were studied. Local tissue/blood oxygen saturation (StO2) and local hemoglobin concentration (THC) were non-invasively measured on the forearm by near-infrared spectroscopy (NIRS). A vascular occlusion test (VOT), a three-minute induced ischemia, was performed in order to obtain dynamic StO2 parameters: deoxygenation rate (DeO2), reoxygenation rate (ReO2), and hyperemic response (HAUC). In COVID-19 patients, the severity of ARDS was evaluated by the ratio between peripheral arterial oxygen saturation (SpO2) and the fraction of inspired oxygen (FiO2) (SF ratio). Results Healthy controls (32) and COVID-19 patients (73) were studied. Baseline StO2 and THC did not differ between the two groups. Dynamic VOT-derived parameters were significantly impaired in COVID-19 patients showing lower metabolic rate (DeO2) and diminished endothelial reactivity. At enrollment, most COVID-19 patients were receiving invasive mechanical ventilation (MV) (53%) or high-flow nasal cannula support (32%). Patients on MV were also receiving sedative agents (100%) and vasopressors (29%). Baseline StO2 and DeO2 negatively correlated with SF ratio, while ReO2 showed a positive correlation with SF ratio. There were significant differences in baseline StO2 and ReO2 among the different ARDS groups according to SF ratio, but not among different respiratory support therapies. Conclusion Patients with severe COVID-19 show systemic microcirculatory alterations suggestive of endothelial dysfunction, and these alterations are associated with the severity of ARDS. Further evaluation is needed to determine whether these observations have prognostic implications. These results represent interim findings of the ongoing HEMOCOVID-19 trial. Trial registration ClinicalTrials.gov NCT04689477. Retrospectively registered 30 December 2020.

. Significance : Multi-laboratory initiatives are essential in performance assessment and standardization—crucial for bringing biophotonics to mature clinical use—to establish protocols and develop reference tissue phantoms that all will allow universal instrument comparison. Aim : The largest multi-laboratory comparison of performance assessment in near-infrared diffuse optics is presented, involving 28 instruments and 12 institutions on a total of eight experiments based on three consolidated protocols (BIP, MEDPHOT, and NEUROPT) as implemented on three kits of tissue phantoms. A total of 20 synthetic indicators were extracted from the dataset, some of them defined here anew. Approach : The exercise stems from the Innovative Training Network BitMap funded by the European Commission and expanded to include other European laboratories. A large variety of diffuse optics instruments were considered, based on different approaches (time domain/frequency domain/continuous wave), at various stages of maturity and designed for different applications (e.g., oximetry, spectroscopy, and imaging). Results : This study highlights a substantial difference in hardware performances (e.g., nine decades in responsivity, four decades in dark count rate, and one decade in temporal resolution). Agreement in the estimates of homogeneous optical properties was within 12% of the median value for half of the systems, with a temporal stability of over 1 h, and day-to-day reproducibility of . Other tests encompassed linearity, crosstalk, uncertainty, and detection of optical inhomogeneities. Conclusions : This extensive multi-laboratory exercise provides a detailed assessment of near-infrared Diffuse optical instruments and can be used for reference grading. The dataset—available soon in an open data repository—can be evaluated in multiple ways, for instance, to compare different analysis tools or study the impact of hardware implementations.

Background: cerebral microcirculation might reveal important prognostic information for acute ischemic stroke. Time-Domain Near-Infrared Spectroscopy (TD-NIRS) is an advanced optical technique that estimates quantitatively and non-invasively the oxygenation in microcirculation of cerebral outer layers at the bedside of the patient. We aimed to measure hemoglobin species and tissue oxygen saturation in acute ischemic stroke patients comparing them to controls according to brain areas and large vessel recanalization status. Methods: TD-NIRS measurements within 24 h of stroke onset (1 st time point) and after 24 h (2 nd time point) were performed on anterior circulation stroke patients classified as lacunar and recanalized or non-recanalized partial/total anterior circulation syndrome. Fiducial markers categorized the brain region below each TD-NIRS probe as ischemic or non-stroke areas. We evaluated the concentration of deoxyhemoglobin (HbR), oxyhemoglobin (HbO), total hemoglobin (HbT) and tissue oxygen saturation (StO 2 ) and assessed differences compared to control subjects and according to large vessel occlusion. Results: TD-NIRS measurements were performed on 47 acute ischemic stroke patients. At 1 st time point the ischemic area had higher HbR and HbT compared to controls in both recanalized (p=8.2·10 -4 ; p=0.03) and non-recanalized patients (p=4.9·10 -3 , p=0.03), but lower StO 2 only in recanalized patients (p=0.015). The ischemic area of recanalized patients had higher concentration of HbR, HbO, HbT compared to the ipsilateral non-stroke area (p=0.01; p=3.6·10 -3 ; p=2.0·10 -3 ). The same pattern was observed at 2 nd time point. Recanalized patients had lower mean StO 2 in the ipsilateral hemisphere compared to non-recanalized patients at both time points (p=0.016, p=0.011). Conclusions: TD-NIRS can be performed during routine Stroke Unit activity and it is able to detect significant differences in hemoglobin species in large vessels ischemic stroke patients compared to controls. Data suggest that StO 2 could serve as surrogate functional marker of the metabolic activity of the rescued brain tissue.