Fiber-Optic Temperature and Pressure Sensors Applied to Radiofrequency Thermal Ablation in Liver Phantom: Methodology and Experimental Measurements

Abstract

Radiofrequency thermal ablation (RFA) is a procedure aimed at interventional cancer care and is applied to the treatment of small- and midsize tumors in lung, kidney, liver, and other tissues. RFA generates a selective high-temperature field in the tissue; temperature values and their persistency are directly related to the mortality rate of tumor cells. Temperature measurement in up to 3–5 points, using electrical thermocouples, belongs to the present clinical practice of RFA and is the foundation of a physical model of the ablation process. Fiber-optic sensors allow extending the detection of biophysical parameters to a vast plurality of sensing points, using miniature and noninvasive technologies that do not alter the RFA pattern. This work addresses the methodology for optical measurement of temperature distribution and pressure using four different fiber-optic technologies: fiber Bragg gratings (FBGs), linearly chirped FBGs (LCFBGs), Rayleigh scattering-based distributed temperature system (DTS), and extrinsic Fabry-Perot interferometry (EFPI). For each instrument, methodology forex vivosensing, as well as experimental results, is reported, leading to the application of fiber-optic technologiesin vivo. The possibility of using a fiber-optic sensor network, in conjunction with a suitable ablation device, can enable smart ablation procedure whereas ablation parameters are dynamically changed.

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

“…40 Even if this referenced model does not completely fit our setup due to its being drawn for one electrode and 15-to 30-W RF power, when we used a different applicator with four electrodes and high power with a very short pulse, 40 the temperature pattern obtained during our experiments was found to be compatible with the work in Ref. 29. Figure 5(b) contains a photo of the liver during an insertion.…”

“…[24][25][26] Moreover, FBG technology has been used in experiments for thermal measurements during RF and/or laser ablation therapy. 8,27,28 Tosi et al 29 conducted experiments on thermal monitoring during RFA of liver tumors using an array of five draw-tower FBGs fabricated on an ormoceramic bend-insentive fiber as well as on a distributed FOS using chirped FBGs. 27,30,31 However, to the best of our knowledge, thermal monitoring based on FOSs has only been applied to hepatic and pancreatic tissues based upon a single-step RFA, laser, and microwave ablation.…”

Error of a Temperature Probe for Cancer Ablation Monitoring Caused by Respiratory Movements: <italic>Ex Vivo</italic> and <italic>In Vivo</italic> Analysis

“…FBGs sensor are a valid alternative to non-invasive procedure because by inserting only one fiber optic they are able to perform distributed measurements. Several studies have been monitored the effects of thermal treatments by FBGs either on ex vivo organs and phantoms or on small animals [12,13,15,17,28,29,30]. All these experiments do not take into account the effect of the respiratory movements on the FBGs' output.…”

“…They can be split in two main categories [9]: i) invasive methods, which need the transducer to be in contact with the tissue. The most popular sensors used in this field are thermocouples [10,11], and fiber optic sensors [12,13]; ii) non-invasive methods based on the analysis of diagnostic imaging techniques, such as, Magnetic Resonance (MR) [14,15], Computed Tomography [16,17], and Ultrasound [18].…”

“…Among invasive techniques, Fiber Bragg Grating (FBG) sensors have several valuable features, such as the immunity from electromagnetic interferences, good metrological properties (i.e., short response time, good accuracy and high thermal sensitivity), small size, and the possibility to perform spatially resolved measurements: it is possible to measure the tissue temperature in different points by inserting only one fiber optic which embeds several FBGs [12,13,19]. The two main risks of using FBGs during LA are: i) they are fragile (their typical diameter is ~200μm), hence their rupture within the organ must be avoided; and ii) the sensitivity to both temperature and strain, so the output change caused by strain can be related to a temperature variation.…”