Characterization of fiber optic distributed temperature sensors for tissue laser ablation

Fiber optics is the most promising technology for distributed temperature sensing. The paper investigates the characterization of probes based on single or multiplexed fiber Bragg gratings, specifically conceived to evaluate the temperature distribution in applications that imply large temperature gradients, such as in laser induced thermal treatments of solid tumors. A setup for the characterization of fiber Bragg grating sensors in non uniform temperature conditions is described and examples of applications in case that mimic actual working conditions are reported

A Fiber Optic Probe for Tumor Laser Ablation with Integrated Temperature Measurement Capability

The paper presents the characterization results of a new all-optical applicator for improved tumor laser ablation treatments that features customized irradiation pattern and builtin temperature sensors. The probe exploits a double cladding optical fiber to integrate some Bragg gratings acting as temperature sensing elements in the core, while guiding the high power beam used for the ablation in the inner cladding. The assessment of the probe behavior has been conducted in two steps: first, with an agar gel phantom to characterize the irradiation pattern and to validate the Bragg grating based measurement setup in comparison with a thermographic camera; then, simulating actual treatments using an ex-vivo animal liver

Linearly chirped fiber Bragg grating response to thermal gradient: from bench tests to the real-time assessment during in vivo laser ablations of biological tissue

The response of a fiber optic sensor [linearly chirped fiber Bragg grating (LCFBG)] to a linear thermal gradient applied on its sensing length (i.e., 1.5 cm) has been investigated. After these bench tests, we assessed their feasibility for temperature monitoring during thermal tumor treatment. In particular, we performed experi- ments during ex vivo laser ablation (LA) in pig liver and in vivo thermal ablation in animal models (pigs). We investigated the following: (i) the relationship between the full width at half maximum of the LCFBG spectrum and the temperature difference among the extremities of the LCFBG and (ii) the relationship between the mean spectrum wavelength and the mean temperature acting on the LCFBG sensing area. These relationships showed a linear trend during both bench tests and LA in animal models. Thermal sensitivity was significant although different values were found with regards to bench tests and animal experiments. The linear trend and significant sensitivity allow hypothesizing a future use of this kind of sensor to monitor both temperature gradient and mean temperature within a tissue undergoing thermal treatment

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

[EN] 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 cu). 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.The research has been supported by ORAU program at Nazarbayev University (grants LIFESTART 2017-2019 and FOSTHER2018-2020), by ANR project Nice-DREAM (grant ANR-14-CE07-0016-03), and by project DIMENSION TEC2017 88029-R funded by the Spanish Ministry of Economy and Competitiveness. This work was partly supported by the SIRASI project - Sistema Robotico a supporto della Riabilitazione di Arto Superiore e Inferiore (Bando INTESE - CUP: F86D15000050002).Beisenova, A.; Issatayeva, A.; Sovetov, S.; Korganbayev, S.; Jelbuldina, M.; Ashikbayeva, Z.; Blanc, W.... (2019). Multi-fiber distributed thermal profiling of minimally invasive thermal ablation with scattering-level multiplexing in MgO-doped fibers. 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Towards inline spatially resolved temperature sensing in thermal ablation with chirped fiber Bragg grating

We investigate the theory and feasibility of an in-line spatially resolved temperature sensor, suitable for thermal ablation monitoring. The sensor is based o a chirped fiber Bragg grating (CFBG). The CFBG is modelled as a chain of Bragg gratings, each sensitive to local temperature variations. By using a combination of iterative and statistical optimization techniques, it is possible to use demodulate the CFBG, in case of a Gaussian-like spatial temperature profile. A feasibility test based on CFBG simulation shows that the CFBG returns error <1 mm on cells damage threshold spatial estimation and good noise resilience

Characterization of susceptibility artifacts in magnetic resonance thermometry images during laser interstitial thermal therapy: dimension analysis and temperature error estimation

Objective: Laser interstitial thermal therapy (LITT) is a minimally invasive procedure used to treat a lesion through light irradiation and consequent temperature increase. Magnetic Resonance Thermometry Imaging (MRTI) provides a multidimensional measurement of the temperature inside the target thus enabling accurate monitoring of the zone of damage during the procedure. In proton resonance frequency shift-based thermometry, artifacts in the images may strongly interfere with the estimated temperature maps. In our work, after noticing the formation of the dipolar-behavior artifact linkable to magnetic susceptibility changes during in vivo LITT, an investigation of susceptibility artifacts in tissue-mimicking phantoms was implemented. Approach: The artifact was characterized: (i) by measuring the area and total volume of error regions and their evolution during the treatment; and (ii) by comparison with temperature reference provided by three temperature sensing needles. Lastly, a strategy to avoid artifacts formation was devised by using the temperature-sensing needles to implement a temperature-controlled LITT. Main results: The artifact appearance was associated with gas bubble formation and with unwanted treatment effects producing magnetic susceptibility changes when 2 W laser power was set. The analysis of the artifact's dimension demonstrated that in the sagittal plane the dipolar-shape artifact may consistently spread following the temperature trend until reaching a volume 8 times bigger than the ablated one. Also, the artifact shape is quite symmetric with respect to the laser tip. An absolute temperature error showing a negative Gaussian profile in the area of susceptibility artifact with values up to 64.4 °C was estimated. Conversely, a maximum error of 2.8 °C is measured in the area not-affected by artifacts and far from the applicator tip. Finally, by regulating laser power, susceptibility artifacts formation was avoided, and appreciable thermal damage was induced. Significance: Such findings may help in improving the MRTI-based guidance of thermal therapies

Distributed 2D temperature sensing during nanoparticles assisted laser ablation by means of high-scattering fiber sensors

The high demand in effective and minimally invasive cancer treatments, namely thermal ablation, leads to the demand for real-time multi-dimensional thermometry to evaluate the treatment effectiveness, which can be also assisted by the use of nanoparticles. We report the results of 20-nm gold and magnetic iron oxide nanoparticles-assisted laser ablation on a porcine liver phantom. The experimental set-up consisting of high-scattering nanoparticle-doped fibers was operated by means of a scattering–level multiplexing arrangement and interrogated via optical backscattered reflectometry, together with a solid-state laser diode operating at 980 nm. The multiplexed 2-dimensional fiber arrangement based on nanoparticle-doped fibers allowed an accurate superficial thermal map detected in real-time

Recent advances in biomedical photonic sensors: a focus on optical-fibre-based sensing

In this invited review, we provide an overview of the recent advances in biomedical pho tonic sensors within the last five years. This review is focused on works using optical-fibre technology, employing diverse optical fibres, sensing techniques, and configurations applied in several medical fields. We identified technical innovations and advancements with increased implementations of optical-fibre sensors, multiparameter sensors, and control systems in real applications. Examples of outstanding optical-fibre sensor performances for physical and biochemical parameters are covered, including diverse sensing strategies and fibre-optical probes for integration into medical instruments such as catheters, needles, or endoscopes.This work was supported by Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-107270RB-C21/AEI/10.13039/501100011033), and TeDFeS Project (RTC-2017- 6321-1) co-funded by European FEDER funds. M.O. and J.F.A. received funding from Ministerio de Ciencia, Innovación y Universidades of Spain under Juan de la Cierva-Formación and Juan de la Cierva-Incorporación grants, respectively. P.R-V. received funding from Ministerio de Educación, Cultura y Deporte of Spain under PhD grant FPU2018/02797

Temperature profile of ex-vivo organs during radio frequency thermal ablation by fiber Bragg gratings.

We report on the integration of fiber optic sensors with commercial medical instrumentation for temperature monitoring during radio frequency ablation for tumor treatment. A suitable configuration with five fiber Bragg grating sensors bonded to a bipolar radio frequency (RF) probe has been developed to monitor the area under treatment. A series of experiments were conducted on ex-vivo animal kidney and liver and the results confirm that we were able to make a multipoint measurement and to develop a real-time temperature profile of the area, with a temperature resolution of 0.1°C and a spatial resolution of 5 mm during a series of different and consecutive RF discharges