Giovanni Braschi

Fiber-optic chirped FBG for distributed thermal monitoring of ex-vivo radiofrequency ablation of liver

A linearly chirped fiber Bragg grating (LCFBG) has been used as a temperature sensor for online monitoring of radiofrequency thermal ablation (RFTA). The LCFBG acts as a distributed sensor, with spatial resolution of 75 μm. A white-light setup that records the LCFBG spectrum estimates the temperature profile in real time. Three RFTA experiments have been performed ex-vivo on porcine liver measuring the radial temperature distribution during the heating process. The analysis of thermal maps quantifies the spatial heat distribution along the measurement axis and determines the ablation efficiency.

Fiber-optic combined FPI/FBG sensors for monitoring of radiofrequency thermal ablation of liver tumors: ex vivo experiments.

We present a biocompatible, all-glass, 0.2 mm diameter, fiber-optic probe that combines an extrinsic Fabry-Perot interferometry and a proximal fiber Bragg grating sensor; the probe enables dual pressure and temperature measurement on an active 4 mm length, with 40 Pa and 0.2°C nominal accuracy. The sensing system has been applied to monitor online the radiofrequency thermal ablation of tumors in liver tissue. Preliminary experiments have been performed in a reference chamber with uniform heating; further experiments have been carried out on ex vivo porcine liver, which allowed the measurement of a steep temperature gradient and monitoring of the local pressure increase during the ablation procedure.

Optical fiber sensors-based temperature distribution measurement in ex vivo radiofrequency ablation with submillimeter resolution

Abstract. Radiofrequency thermal ablation (RFTA) induces a high-temperature field in a biological tissue having steep spatial (up to 6°C/mm) and temporal (up to 1°C/s) gradients. Applied in cancer care, RFTA produces a localized heating, cytotoxic for tumor cells, and is able to treat tumors with sizes up to 3 to 5 cm in diameter. The online measurement of temperature distribution at the RFTA point of care has been previously carried out with miniature thermocouples and optical fiber sensors, which exhibit problems of size, alteration of RFTA pattern, hysteresis, and sensor density worse than 1  sensor/cm. In this work, we apply a distributed temperature sensor (DTS) with a submillimeter spatial resolution for the monitoring of RFTA in porcine liver tissue. The DTS demodulates the chaotic Rayleigh backscattering pattern with an interferometric setup to obtain the real-time temperature distribution. A measurement chamber has been set up with the fiber crossing the tissue along different diameters. Several experiments have been carried out measuring the space-time evolution of temperature during RFTA. The present work showcases the temperature monitoring in RFTA with an unprecedented spatial resolution and is exportable to in vivo measurement; the acquired data can be particularly useful for the validation of RFTA computational models.

On the Simulation of Radio Frequency Thermal Lesions in Porcine Liver

In the present paper we present some results of our research on the RFTA (Radio Frequency Thermal Ablation) simulation: in particular the steps performed for the validation of the numerical model. We performed a series of RFTA experiments on pig liver tissue as accurate as possible, at different powers, measuring the time evolution of temperature in selected points and impedances, to be taken as a reference to compare the output of different numerical models. We present the results obtained with a basic simulation model (shortly described) assessing the need to account for the change of the tissue electrical resistivity with temperature. We then underline the need of getting a deeper insight in the phenomena that bring to the power suspension thus limiting the extension of the necrotized tissue. At the end we suggest a line for the future development of the research.

Distributed fiber-optic sensors for thermal monitoring in radiofrequency thermal ablation in porcine phantom

In this paper, we report for the first time the application of two distributed fiber-optic sensing systems in medical radiofrequency thermal ablation (RFTA). Measurement systems are based on a distributed temperature sensor based on high-speed detection of Rayleigh signature, and a linearly chirped fiber Bragg grating (LCFBG) sensor that detects temperature distribution on 1.5 cm length. Both technologies are capable of achieving sub-0.1mm spatial resolution. The sensing systems have been applied to monitor the temperature pattern induced by RFTA, measuring temperature gradients in excess of 5°C/mm. All tests have been performed on porcine liver tissue, the phantom of human liver. The results show the premises for the realization of a distributed sensor installed on a RFTA device, capable of real-time prediction and estimation of the ablation effect.

Optical fiber biocompatible sensors for monitoring selective treatment of tumors via thermal ablation

Thermal ablation (TA) is an interventional procedure for selective treatment of tumors, that results in low-invasive outpatient care. The lack of real-time control of TA is one of its main weaknesses. Miniature and biocompatible optical fiber sensors are applied to achieve a dense, multi-parameter monitoring, that can substantially improve the control of TA. Ex vivo measurements are reported performed on porcine liver tissue, to reproduce radiofrequency ablation of hepatocellular carcinoma. Our measurement campaign has a two-fold focus: (1) dual pressure-temperature measurement with a single probe; (2) distributed thermal measurement to estimate point-by-point cells mortality.

Fiber-Optic EFPI/FBG Dual Sensor for Monitoring of Radiofrequency Thermal Ablation of Liver Tumors

A dual extrinsic Fabry-Perot interferometer fibre Bragg grating (EFPI/FBG) pressure and temperature sensing architecture, biocompatible and with minimum cross-sensitivity, is presented. The system performs online monitoring of radiofrequency thermal ablation in liver tumor, detecting the physical phenomena; ex-vivo experiments are reported.

Fiber optic dual EFPI/FBG for radiofrequency ablation monitoring in liver: ex-vivo experiments

We present a miniature and biocompatible fiber-optic sensing system, for specific application in monitoring of the radiofrequency thermal ablation (RFA) process. The sensing system is based on combination of Extrinsic Fabry-Perot Interferometry (EFPI) sensor for pressure detection, and Fiber Bragg Grating (FBG) for temperature measurement. The dual pressure/temperature measurement shows an extremely low cross-sensitivity. Measurements have been performed ex-vivo on porcine liver, recording several RFA procedures in different location. Maximum values of 164°C and 162 kPa have been recorded on the ablation point.