Multi-fiber distributed thermal profiling of minimally invasive thermal ablation with scattering-level multiplexing in MgO-doped fibers

Abstract

We propose a setup for multiplexed distributed optical fiber sensors capable of resolving temperature distribution in thermo-therapies, with a spatial resolution of 2.5 mm over multiple fibers interrogated simultaneously. The setup is based on optical backscatter reflectometry (OBR) applied to optical fibers having backscattered power significantly larger than standard fibers (36.5 dB), obtained through MgO doping. The setup is based on a scattering-level multiplexing, which allows interrogating all the sensing fibers simultaneously, thanks to the fact that the backscattered power can be unambiguously associated to each fiber. The setup has been validated for the planar measurement of temperature profiles in ex vivo radiofrequency ablation, obtaining the measurement of temperature over a surface of 96 total points (4 fibers, 8 sensing points per cm 2). The spatial resolution obtained for the planar measurement allows extending distributed sensing to surface, or even three-dimensional, geometries performing temperature sensing in the tissue with millimeter resolution in multiple dimensions.

Fiber Bragg Grating (FBG) Sensors in a High-Scattering Optical Fiber Doped with MgO Nanoparticles for Polarization-Dependent Temperature Sensing

“…In sensing, this is important as the FBG allows "tagging" a specific sensing point where the FBG is located, and referencing the remainder of the fiber to the valued measured in this location, enabling solutions that mix optical frequency domain reflectometry of fiber scattering and FBG interrogation [24,25]. The main application for the MgO-NP fiber is in scattering-level multiplexing, which requires a fiber with high Rayleigh scattering in order to simultaneously detect multiple channels on the OBR device [16,17]. The addition of FBGs to this sensing system can be used to extend the sensing length of each channel, by using the additional reflectivity of the FBG in addition to the scattering level, compensating for the relative inline high losses of the fiber.…”

“…Parent et al [14] have obtained similar results, with a scattering increment of 37 dB, by means of exposure to intense ultraviolet light; this method has also been used to generate random gratings [15]. More recently, Beisenova et al [16] have obtained a 36.5 dB scattering increment by using a MgO-nanoparticle-doped (MgO-NP) fiber as sensing medium. This setup has also been used to design a scattering-level multiplexing [16,17], a new domain of multiplexing where the diversity is given by the scattering level at each sensing point.…”

“…More recently, Beisenova et al [16] have obtained a 36.5 dB scattering increment by using a MgO-nanoparticle-doped (MgO-NP) fiber as sensing medium. This setup has also been used to design a scattering-level multiplexing [16,17], a new domain of multiplexing where the diversity is given by the scattering level at each sensing point. While the first two methods are characterized by a specific fabrication at one specific sensing point, the third method provides an optical fiber that can be spooled and spliced directly to a SMF, making the operation of building a multi-fiber sensing network much simpler.…”

“…The possibility to increase the scattering of a fiber is intriguing in distributed sensing, particularly using optical backscatter reflectometry (OBR) [18], whereas the analyzer detects the distributed Rayleigh scattering backreflection occurring in each region of the fiber. In such system, by increasing the Rayleigh scattering a larger signal at the analyzer can be obtained [13][14][15][16][17], over 3-4 orders of magnitude larger when properly tuning scattering properties.…”

Nano-Structured Optical Fibers Made of Glass-Ceramics, and Phase Separated and Metallic Particle-Containing Glasses

“…A fiber-optic refractive index sensor was demonstrated by simply etching a high-scattering nanoparticle-doped fiber in hydrofluoric acid [195,196]. A setup for multiplexed distributed optical fiber sensors, which are capable to measure temperature in the range of up to 140 • C (of interest for biomedical applications such as thermo-therapy) with a spatial resolution of 2.5 mm over the several fibers simultaneously, has been reported in [197]. Finally, this approach is also applicable for strain measurements and 3D shape sensing [198,199].…”