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 <5 % over 1 h, and day-to-day reproducibility of <3 % . 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.
In this TD-fNIRS study on 98 subjects, primary open angle glaucoma patients have an involvement of the occipital (visual) cortical region; we assess the best fNIRS parameters for discriminating between glaucoma patients and healthy subjects.
KEYWORDS: 3D printing, Mass attenuation coefficient, Printing, 3D metrology, Near infrared spectroscopy, Diffuse optical imaging, 3D acquisition, Spectroscopy, Photons, Optical properties
PLA and ABS filaments, 3D printed as thin sheets were optically characterized in UV/VIS/NIR. The applicability of these materials, used as optical probes, in diffused optics applications was tested through TD-NIRS and DCS measurements.
KEYWORDS: Near infrared spectroscopy, Tissue optics, Optical properties, In vivo imaging, Scattering, Tissues, Absorption, Photons, Time metrology, Spectroscopy
We present simulation and in-vivo Time Domain NIRS studies to investigate differential pathlength factor in skeletal muscles at rest and its dependence on the subcutaneous adipose tissue thickness, tissue absorption and reduced scattering coefficients.
Neural and cerebral hemodynamic activities of 16 programmers were monitored during programming tasks by simultaneous EEG and Time-Domain fNIRS measurements aiming at identifying cognitive and emotional states during code programming.
We assess the muscular fatigue during sustained exercises with both sEMG and TD-NIRS. We found that during the “slow” phase of TD-NIRS signal, the best fatigue biomarkers are: MF, O2Hb, HHb and SO2.
We report on a preliminary longitudinal study on 21 elderly patients to non-invasively quantify rehabilitation outcomes in skeletal muscle after bed-rest by a combined approach based on TD-NIRS (for hemodynamics) and sEMG (for myoelectric recordings).
Performance assessment and standardization are indispensable for instruments of clinical relevance in general and clinical instrumentation based on photon migration/diffuse optics in particular. In this direction, a multi-laboratory exercise was initiated with the aim of assessing and comparing their performances. 29 diffuse optical instruments belonging to 11 partner institutions of a European level Marie Curie Consortium BitMap1 were considered for this exercise. The enrolled instruments covered different approaches (continuous wave, CW; frequency domain, FD; time domain, TD and spatial frequency domain imaging, SFDI) and applications (e.g. mammography, oximetry, functional imaging, tissue spectroscopy). 10 different tests from 3 well-accepted protocols, namely, the MEDPHOT2 , the BIP3 , and the nEUROPt4 protocols were chosen for the exercise and the necessary phantoms kits were circulated across labs and institutions enrolled in the study. A brief outline of the methodology of the exercise is presented here. Mainly, the design of some of the synthetic descriptors, (single numeric values used to summarize the result of a test and facilitate comparison between instruments) for some of the tests will be discussed.. Future actions of the exercise aim at deploying these measurements onto an open data repository and investigating common analysis tools for the whole dataset.
Functional near infrared spectroscopy (NIRS) is a widespread non-invasive technique to monitor skeletal muscle metabolism. However, only variation of oxygenated (HHb), deoxygenated (O2Hb), total (tHb) hemoglobin and saturation (SO2) are usually reported. In this study, Time Domain (TD) NIRS approach was exploited to perform a preliminary quantitative characterization of vastus lateralis muscle during incremental exercise. A population of 11 healthy young male subjects performed on a mechanical cycle ergometer an incremental exercise (initial work rate range = 60-96 W, increment = 12-18 W/min) until exhaustion. TD NIRS, heart rate, pulmonary ventilation (VE), O2 uptake (VO2), CO2 output (VCO2), blood lactate concentration ([La]b) and Borg scale were measured during the exercise. From TD NIRS, muscles absolute values of absorption and scattering coefficients were obtained with a homogeneous approach and hemoglobin concentrations and saturation levels were calculated. The time courses of HHb, O2Hb, tHb and SO2 were consistent with previous literature results. A high inter-subject variability was found for both optical properties and hemodynamic concentrations. Further statistical group analysis will be required in order to highlight significant behavior within the population and correlation with physiological parameters.
Glaucoma is a multifactorial optic neuropathy characterized by progressive loss of retinal ganglion cells, changes in optic disk morphology and visual field defects; its pathophysiology is still unclear. Recently it was demonstrated that glaucoma can be associated with a degenerative effect at the level of the optic nerve and the primary visual cortex. Functional near infrared spectroscopy (fNIRS) is a non-invasive optical technique, which allows the brain hemodynamic monitoring. In particular, the Time Domain fNIRS (TD-fNIRS) allows to remove from the detected signal the contribution coming from the surface (scalp, skull and cerebral fluid) in order to obtain the brain hemodynamic activation. The aim of this preliminary study is to understand if in the glaucomatous patients, the visual cortex activation during a visual stimulus is different from the one of a control group. A total of 20 subjects took part to the study. We divided them into three groups: 7 controls, 5 ocular hypertension (HYPER), and 8 glaucoma. The hemodynamic time courses of oxy- (OHB) and deoxy- (HHB) hemoglobin were compared with a hemodynamic response function (HRF) with the adaptive HRF approach. Finally, an inference test was applied (t-student) to statistically determine the visual cortex activation (simultaneous increase in OHB and decrease in HHB). The p-value threshold was set at 0.05. The 86% of the controls and the 80% of the HYPER combinations are activated; while the 81% of the glaucoma ones are not, outlining a well-defined trend. Also the OHB and HHB show drastic differences between controls and patients.
Time-resolved (TR) techniques are exploited in many biomedical applications in order to find absolute values of absorption (μa) and reduced scattering (μs’) coefficients that characterize biological tissues chemical and microstructure properties. However, the concomitant acquisition of tissue distribution time-of-flight (DTOF) and instrument response function (IRF) is necessary to perform quantitative measurements. This can be a non-trivial time consuming operation which typically requires to detach the optical fibers from the measurement probe (usually put in a reflectance configuration for in-vivo applications) in order to face them one to each other (“reference” geometry). To overcome these difficulties, a new IRF measurement method that exploit the “reflectance” geometry is here proposed. A practical 3D printed implementation has been carried out for a specific device to test the feasibility of this approach and if the IRF acquired in the “reflectance” geometry is equivalent to the “reference” one. A particular problem addressed is the determination of the temporal shift T0 that can occur between IRF and sample DTOF. Two different approaches, based respectively on the curves barycenters difference and on a calibration phantom, are proposed. Both methods are valid and indifferently applicable according to specific measurement requirements. This allows “reflectance” IRF acquisition to be eligible as standard methodology for TR measurements.
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