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

Abstract

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.

The Solus Instrument: Optical Characterization of the First Hand-Held Probe for Multimodal Imaging (Ultrasound and Multi-Wavelength Time-Resolved Diffuse Optical Tomography)

“…In this case, the solution adopted was the use of a tailored 3D printed "IRF box" (black PLA filament, 3DiTALY, shown in Fig. 4) [33]. The probe is placed into a housing, whose back end is provided with a mask that reproduces the probe optodes arrangement.…”

Translation of a diffuse optical system for monitoring neurocritical patients

“…Regardless of the analysis algorithm employed, to accurately recover the optical properties of the tissue we need to account for the additional time-delay and broadening caused by the detector and pulse-width of the source. To that end, we can measure the instrument response function (IRF) by directly coupling the light-source and the detector [114]. For example, for non-linear fitting algorithms, we can account for the IRF by convolving the theoretical fluence from Equation 2.6 with the measured IRF.…”

“…Just prior to removing the patient from the procedure table, data collection was stopped, and the optical probes were removed from the patient's head. The TD-DOS IRF measurement was then carried out in a manner described elsewhere [114,115]. MAP data was recorded once every minute and were retrospectively retrieved from the anesthesia record and time-synced with optical data.…”