Broadband (600–1350 nm) Time-Resolved Diffuse Optical Spectrometer for Clinical Use

Abstract

We report on the design, development, and performance assessment of a portable time resolved system measuring absorption and scattering spectra of highly diffusive media over the 600-1350 nm range. In view of clinical use, two strategies were implemented; the first one equips the system with high responsivity in key tissue absorbing regions, whereas the second one makes the system immune to time drift. The MEDPHOT protocol was used for the performance assessment of the instrument. Finally, the system was enrolled into its first in vivo trial phase, measuring the broadband absorption and scattering spectra of human manubrium, abdomen fat tissues, and forehead for the in vivo quantification of key tissue constituents.

Towards the use of bioresorbable fibers in time‐domain diffuse optics

“…For the linearity measurements, we built a dedicated setup, while for the spectroscopic acquisition we used a setup similar to a state-of-the-art system [21]. Generally speaking, both the experimental setups were based on a pulsed laser as a light source, optical fibers for injecting and collecting the optical pulses to and from the sample, a free-running (i. e. not timegated) Single-Photon Avalanche Diode (SPAD) as a detector and a Time-Correlated Single-Photon Counting (TCSPC) board, as schematically depicted in Figure 2.…”

“…Details about the components of the setup are described below and summarized in Table 2. Compared to a state-of-the-art clinical prototype [21] operating with standard 1 mm core glass fibers with NA = 0.37, a theoretical loss in responsivity by a factor of 1900, 470 and 120 is ex- Figure 2 Schematics of the main building blocks composing the setup used for both experiments (linearity and spectroscopy measurements). Details about the main blocks can be found in Table 2.…”

“…Such a source allowed us to make use of high average optical power at a fixed wavelength, thus permitting to measure samples with absorption coefficients up to 0.70 cm À1 employing all the three fiber cores. For the spectroscopy measurements, we built a system close to the state-of-the-art [21], which is composed by a supercontinuum laser (SuperK Extreme, NKT Photonics, Denmark) coupled to a prism to provide optical pulses at 80 MHz with a wavelength tunable in the 500-1100 nm range. In both cases (linearity and spectroscopy measurements) the light provided by the laser source was attenuated by means of a Variable Optical Attenuator (VOA) in order to set the proper photon counting rate at the detector (i. e.~700000 counts per second) to avoid distortions in TCSPC reconstructions of the distribution of photons time of flight [28].…”

“…In both cases we obtained a low signal using the bioresorbable fiber due to high absorption. Using a different detector (i. e. the SiPM module [36] used in a state-of-the-art system [21]) with a larger area but also higher dark count rate we observed a significant discrepancy in these two spectral regions (data not shown), thus demonstrating the need of a low noise detector to cope with the limited light harvesting of the fiber.…”

“…The aim of the present work is to explore the aptness of CPG fibers to perform time-domain broadband diffuse optical spectroscopy (TD-DOS) deep into biological tissues. Since TD-DOS can provide absolute estimate of the absorption and reduced scattering spectra of the diffusive medium [19,20], it conveys information on the chemical composition (mainly water, oxy-and deoxy-hemoglobin, water, lipids, collagen), on the functional status (e. g. oxygenation) and on the scattering properties (changes in tissue microstructure, edema) [21]. Such information can then be related to the tissue regeneration, to the healing process or to a harmful evolution.…”