A multi-laboratory comparison of photon migration instruments and their performances: the BitMap exercise

Abstract

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 BitMap 1 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 MEDPHOT 2 , the BIP 3 , and the nEUROPt 4 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.

Reproducibility of identical solid phantoms

“…From the first pioneering basic studies on photon migration 3 – 6 to the more recent NIRS instrumentation involved in clinical trials, 7 – 12 it was clear that the availability of phantoms mimicking the optical properties and also the structures of biological tissues was required for reliability of the results attained. Whatever approach is exploited for NIRS—continuous wave, time domain, or frequency domain; the geometry adopted—transmittance or reflectance; the reconstruction modality utilized—tomography or topography; the instrument configuration employed—a multichannel imaging system or a single-channel monitor; the clinical application aimed for—brain, breast, or muscle, diffuse samples with reliable and invariable properties are fundamental and important tools for (1) the development of novel approaches in basic research; (2) the instrumentation assessment in laboratory environment 13 , 14 ; (3) interlaboratory comparison studies 15 – 17 ; and (4) quality check in clinics. 18 …”

“…(2) the instrumentation assessment in laboratory environment 13,14 ; (3) interlaboratory comparison studies [15][16][17] ; and (4) quality check in clinics. 18 In this framework, the possibility to have phantoms with optical properties known with few percent of uncertainty is highly advisable.…”

A practical guide for synthetic fNIRS data generation

“…Its use in research has greatly increased over the last two decades [2] and so has the diversity in methodological practices. A large heterogeneity in experimental approaches and data analysis methods inevitably poses a challenge to the comparability and replicability of studies [3], which is why the fNIRS community is currently dedicating considerable effort to the systematic validation and standardization of practices for each aspect of fNIRS research, by comparing different hardware performances [4], [5], pre-processing methods [6]- [8] and techniques for the statistical analysis [9], [10], just to name a few, with the ultimate goal of establishing common, standardized and well-reproducible practices [11].…”