Abstract
In time-domain diffuse optical spectroscopy, the simultaneous acquisition of the time-of-flight distribution (DTOF) of photons traveling in a diffusive medium and of the instrument response function (IRF) is necessary to perform quantitative measurements of optical properties (absorption and reduced scattering coefficients) while taking into account the non-idealities of a real system (e.g. temporal resolution and time delays). The IRF acquisition can be a non-trivial and time-consuming operation that requires directly facing the injection and collection fibers. Since this operation is not always possible, a new IRF measurement scheme is here proposed where the IRF is acquired in reflectance geometry from a corrugate reflective surface. Validation measurements on a set of reference homogenous phantoms have been performed, resulting in an error in the optical properties estimation lower than 10% with respect to the typical IRF configuration. Thus, the proposed method proved to be a reliable approach that after a preliminary calibration can be exploited in a laboratory and clinical set-ups, leading to faster and more accurate measurements and reducing the operator-dependent performance.
Highlights
Many applications in biomedical optics, such as functional near-infrared spectroscopy or optical mammography, exploit the theory of light propagation into highly diffusive media to non-invasively determine biological tissues optical properties
To take into account the instrument contribution to the experimental curves modifications, data has to be de-convolved with the instrument response function (IRF) or the theoretical model has to be convolved with the IRF3
The only drawback of this configuration is that it is still necessary to determine the temporal shift T0 that occurs between IRF and sample distribution of time-of-flight (DTOF) and this can not be directly achieved with a simple distance measurement as before, but it needs a specific calibration
Summary
Many applications in biomedical optics, such as functional near-infrared spectroscopy (fNIRS) or optical mammography, exploit the theory of light propagation into highly diffusive media to non-invasively determine biological tissues optical properties. Time-resolved (TR) techniques allow to retrieve absolute absorption (μa) and reduced scattering (μs’) coefficients[1]. In these methods, pulsed light at different specific wavelengths is injected into the tissue and the distribution of time-of-flight (DTOF) of photons, which have been re-emitted, is collected at a certain distance ρ. To take into account the instrument contribution to the experimental curves modifications, data has to be de-convolved with the instrument response function (IRF) or the theoretical model has to be convolved with the IRF3 This one includes information about the time resolution of the TR instrument, (due to the optical fibers, detectors, ...) causing a temporal dispersion of the DTOF. This work focuses on the aspects of practical acquisition of the IRF during a session of time-resolved diffuse optics measurements, providing an easy, general purpose and feasible methodology that can be executed by healthcare personnel in a critical environment such as clinics
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