Photon Time Of Flight Research Articles

Skin remittance kinetics in the spectral range of 550 – 790 nm

An experimental method for remitted photon time-of-flight (PTOF) estimation in human skin in vivo is developed and tested. Remitted light signals are obtained using a picosecond broadband laser and a set of narrowband interference filters centred at 550, 600, 650, 700, 750 and 790 nm. Four different distances of 8, 12, 16 and 20 mm between the source and detector fibres are used. Measurements are performed at different wavelengths and distance combinations. Direct kinetic measurements make it possible to assess the mean photon path length in skin at various spectral regions. Results generally correspond to theoretical expectations; however, no clear dependence on wavelengths in the spectral range 650–790 nm is observed. This study shows a promising opportunity to use this kind of measurement system in the future research of PTOF in human skin.

Transmission Near-Infrared (NIR) and Photon Time-of-Flight (PTOF) Spectroscopy in a Comparative Analysis of Pharmaceuticals

We present a comprehensive study of the application of photon time-of-flight spectroscopy (PTOFS) in the wavelength range 1050-1350 nm as a spectroscopic technique for the evaluation of the chemical composition and structural properties of pharmaceutical tablets. PTOFS is compared to transmission near-infrared spectroscopy (NIRS). In contrast to transmission NIRS, PTOFS is capable of directly and independently determining the absorption and reduced scattering coefficients of the medium. Chemometric models were built on the evaluated absorption spectra for predicting tablet drug concentration. Results are compared to corresponding predictions built on transmission NIRS measurements. The predictive ability of PTOFS and transmission NIRS is comparable when models are based on uniformly distributed tablet sets. For non-uniform distribution of tablets based on particle sizes, the prediction ability of PTOFS is better than that of transmission NIRS. Analysis of reduced scattering spectra shows that PTOFS is able to characterize tablet microstructure and manufacturing process parameters. In contrast to the chemometric pseudo-variables provided by transmission NIRS, PTOFS provides physically meaningful quantities such as scattering strength and slope of particle size. The ability of PTOFS to quantify the reduced scattering spectra, together with its robustness in predicting drug content, makes it suitable for such evaluations in the pharmaceutical industry.

Effects of ON and OFF subthalamic nucleus deep brain stimulation on cortical activation during finger movements tasks: a simultaneous fNIRS and EEG study

s / Brain Stimulation 8 (2015) 378e394 393 Continuous-wave (CW) fNIRS measures light attenuation through both the cortical and superficial (e.g., skin) tissues, while timedomain (TD) fNIRS directly measures the photon time-of flight that contains information about the depth probed by photons in the tissue, and in turn provides a possibility to separate the superficial from the cortical layer haemodynamic signals. Therefore, the aim of this study was to compare the changes in resting cortical haemodynamics measured by a CW and TDfNIRS system during anodal tDCS. Methods: A Startstim tDCS system (Neuroelectrics) was used to deliver a constant direct current (2mA) to the left sensorimotor cortex (SMC) via an anodal 4x1 high definition (HD)-tDCS electrode montage. During 10min of anodal HD-tDCS, changes in resting oxygenated (O2Hb) and deoxygenated (HHb) haemoglobin concentrations from the left and right SMC were monitored by a CWfNIRS system (Oxymon MK III, AMS) and in a subsequent session with a TD-fNIRS system (Politecnico di Milano). Results/Discussion: CWand TDfNIRS showed a similar time course (i.e. increase in O2Hb from baseline with no or only minimal decrease in HHb) in the stimulated left SMC (no or only minimal changes in right SMC) over the 10min of anodal HD-tDCS (Fig. a, b). The TD-fNIRS confirmed this time course in the cortical layer of the stimulated left SMC (Fig. d), but the changes were much smaller than the superficial layer changes (Fig. b). Conclusion: This preliminary study has shown that 10min of anodal HD-tDCS induces an increase in activation in the cortical layer of the stimulated left SMC.

Computationally effective solution of the inverse problem in time-of-flight spectroscopy.

Photon time-of-flight (PTOF) spectroscopy enables the estimation of absorption and reduced scattering coefficients of turbid media by measuring the propagation time of short light pulses through turbid medium. The present investigation provides a comparison of the assessed absorption and reduced scattering coefficients from PTOF measurements of intralipid 20% and India ink-based optical phantoms covering a wide range of optical properties relevant for biological tissues and dairy products. Three different models are used to obtain the optical properties by fitting to measured temporal profiles: the Liemert-Kienle model (LKM), the diffusion model (DM) and a white Monte-Carlo (WMC) simulation-based algorithm. For the infinite space geometry, a very good agreement is found between the LKM and WMC, while the results obtained by the DM differ, indicating that the LKM can provide accurate estimation of the optical parameters beyond the limits of the diffusion approximation in a computational effective and accurate manner. This result increases the potential range of applications for PTOF spectroscopy within industrial and biomedical applications.

Broadband photon time-of-flight spectroscopy of pharmaceuticals and highly scattering plastics in the VIS and close NIR spectral ranges

We present extended spectroscopic analysis of pharmaceutical tablets in the close near infrared spectral range performed using broadband photon time-of-flight (PTOF) absorption and scattering spectra measurements. We show that the absorption spectra can be used to perform evaluation of the chemical composition of pharmaceutical tablets without need for chemo-metric calibration. The spectroscopic analysis was performed using an advanced PTOF spectrometer operating in the 650 to 1400 nm spectral range. By employing temporal stabilization of the system we achieve the high precision of 0.5% required to evaluate the concentration of tablet ingredients. In order to further illustrate the performance of the system, we present the first ever reported broadband evaluation of absorption and scattering spectra from pure and doped Spectralon®.

Time Correlated Single Photon Counting System for Optical Measurements

Time Correlated Single Photon Counting System for Optical MeasurementsThe high sensitivity time correlated single photon counting system (with photomultiplier tube) for biomedical measurements was designed and tested. Photon time of flight through a parafine wax phantom was modeled by Monte Carlo simulation and next measured by the device. Mean time delay introduced by a phantom is in a good agreement with simulation results. The results presented in this paper demonstrate the feasibility of measuring the optical response with the device.

Fluorescence Lifetime and Depth Estimation of a Tumor Site for Functional Imaging Purposes

Cancerous cells have irregular environmental conditions, such as temperature and pH, which distinguish them from their surroundings. Fluorescence lifetime imaging using near-IR (NIR) fluorescent probes, whose lifetime value is sensitive to pH and temperature, enables the estimation of these values, and provides functional information about the tumor. The lifetime value, extracted from the time-resolved intensity decay curve, combines the photon time delays, caused by the photon time of flight, and the intrinsic lifetime in which we are interested. In this study, we present a model, based on the diffusion approximation of the radiation transport equation, for extracting both the depth of an NIR fluorescent probe, and its intrinsic lifetime value, from a fluorescence time decay curve. The model was validated for different inclusion depths, fluorescent lifetime values, and scattering coefficients using a time-resolved Monte Carlo simulation. Our reported results are the first step toward performing functional imaging using fluorescence lifetime in vivo measurements.