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.
The effect of hemoglobin spectra on quantification of concentrations of oxy-, deoxyhemoglobin, and oxygen saturation were studied using multi-wavelength time-domain NIRS measurements performed on a series of blood-lipid phantoms.
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.
Time-domain fNIRS facilitates the elimination of the influence of extracerebral, systemic effects on measured signals since it contains time-of-flight information that is related to the penetration depth. Employing perturbation and MonteCarlo simulations, we quantitatively characterized and compared the performance of measurands based on moments and time windows of time-of-flight distributions. We extend our analysis to investigate whether higher moments and MellinLaplace (ML) moments promise improvements in performance. The comparison is based on spatial sensitivity profiles as well as metrics for relative contrast, contrast-to-noise ratio (CNR), depth selectivity, and the product of CNR and depth selectivity for layered absorption changes. The influence of reduced scattering coefficient, thickness of the superficial layer, and source-detector distance was analyzed. The third central moment performs similarly to variance and is worth considering for data analyzes. Higher order ML moments perform similarly to time windows and they likewise provide variable depth selectivity.
Absolute concentrations of oxyhaemoglobin and deoxyhaemoglobin obtained using multi-wavelength measurements of time-resolved diffuse reflectance signals are presented. The aim was to test how accurately the concentration of oxy- and deoxyhemoglobin can be measured simultaneously at multiple wavelengths. The optical signals were collected using the system constructed by the author’s groupa , which records the distribution in time of flight of photons (DTOFs) simultaneously at 16 spectral channels ranging from 650 to 850 nm. The measurements were carried out on liquid phantoms containing intralipid solution, human blood and yeast in varying amounts. The oxygen saturation of blood covered a continuous range from 100 % to 0 % during 6 deoxygenation cycles. The estimated values of total haemoglobin (20.9, 35.7, 57.3, 45.7 μM) are close to the reference values obtained using a blood gas analyzer (21.3, 37.0, 57.3, 48.0 μM) and the estimated values of absolute concentrations of oxy-, deoxyand total haemoglobin are similar to the values obtained using a commercial frequency-domain NIRS system (OxiplexTS TM ). The phantom measurements have shown the capability to measure the absolute concentrations of chromophores in a studied media using multi-wavelength, time-resolved NIRS technique. The excess number of spectral channels can potentially be used to resolve changes in oxidation state of cytochrome-c-oxidase enzyme.
Performance assessment of instruments is a growing demand in the diffuse optics community and there is a definite need to get together to address this issue. Within the EU Network BITMAP1, we initiated a campaign for the performance evaluation of 10 diffuse optical instrumentation from 7 partner institutions adopting a set of 3 well accepted, standardized protocols. A preliminary analysis of the outcome along with future perspectives will be presented.
Open Data philosophy is becoming more popular among scientists. Open Data approach aims to transform science by making high-quality and well-documented scientific data open to everybody in order to promote collaboration and transparency. In diffuse optical and near-infrared spectroscopy community, a large measurement dataset collected with state-of-the-art instrumentation applied on well-defined phantoms is still missing. Within that context, several European labs from BitMap network1 have collected diffuse optical data on standard phantoms involving the largest set of diffuse optics instruments published until now. In this work, we present a running project on the open dataset and associated reporting tools.
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