Instrument response function acquisition in reflectance geometry for time-resolved diffuse optical measurements

摘要

Time-resolved (TR) techniques are exploited in many biomedical applications in order to find absolute values of absorption (μ_a) and reduced scattering (μ_s') 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 T_0 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.