Unscented Kalman Filtering for Real Time Thermometry During Laser Ablation Interventions.

We present a data-assimilation Bayesian framework in the context of laser ablation for the treatment of cancer. For solving the nonlinear estimation of the tissue temperature evolving during the therapy, the Unscented Kalman Filter (UKF) predicts the next thermal status and controls the ablation process, based on sparse temperature information. The purpose of this paper is to study the outcome of the prediction model based on UKF and to assess the influence of different model settings on the framework performances. In particular, we analyze the effects of the time resolution of the filter and the number and the location of the observations. Clinical Relevance - The application of a data-assimilation approach based on limited temperature information allows to monitor and predict in real-time the thermal effects induced by thermal therapy for tumors.

Model-Based Thermometry for Laser Ablation Procedure Using Kalman Filters and Sparse Temperature Measurements.

OBJECTIVE: We implement a data assimilation Bayesian framework for the reconstruction of the spatiotemporal profile of the tissue temperature during laser irradiation. The predictions of a physical model simulating the heat transfer in the tissue are associated with sparse temperature measurements, using an Unscented Kalman Filter. METHODS: We compare a standard state-estimation filtering procedure with a joint-estimation (state and parameters) approach: whereas in the state-estimation only the temperature is evaluated, in the joint-estimation the filter corrects also uncertain model parameters (i.e., the medium thermal diffusivity, and laser beam properties). We have tested the method on synthetic temperature data, and on the temperature measured on agar-gel phantom and porcine liver with fiber optic sensors. RESULTS: The joint-estimation allows retrieving an accurate estimate of the temperature distribution with a maximal error 1.5 °C in both synthetic and liver 1D data, and 2 °C in phantom 2D data. Our approach allows also suggesting a strategy for optimizing the temperature estimation based on the positions of the sensors. Under the constraint of using only two sensors, optimal temperature estimation is obtained when one sensor is placed in proximity of the source, and the other one is non-symmetrical. CONCLUSION: The joint-estimation significantly improves the predictive capability of the physical model. SIGNIFICANCE: This work opens new perspectives on the benefit of data assimilation frameworks for laser therapy monitoring.

Laser ablation in biliary tree: analysis of the intraductal and superficial thermal effects during the treatment.

The treatment of choice for the unresectable cholangiocarcinoma is based on biliary decompression procedures. Despite stent placement is the standard of care, it is related to well-known complications. Hence, alternative techniques were proposed. Ideally, they should guarantee an adequate intraductal disobstruction, without injuring the surrounding tissues.This pre-clinical study aims to investigate the thermal effects of the laser ablation (LA) in the biliary tree, in terms of intraductal and surrounding tissue temperature achieved with different laser settings. The common bile ducts (in their upper and lower portions) of two pigs were ablated for 6 minutes with a diode laser at 3 W and 5 W. A custom-made laser applicator was used to obtain a circumferential ablation within the ducts. The intraductal temperature (Tid) was monitored by means of a fiber Bragg grating (FBG) sensor, while an infrared thermal camera monitored the T distribution in the surrounding tissues (Tsup). A maximum T difference of 65 °C and 57 °C was evidenced between the two power settings for the Tid measured in the upper and lower ducts, respectively. The mean difference between Tid and the averaged Tsup values was evaluated. At 5 W, a difference of 37±3 °C and 44±10 °C were obtained for the upper and lower ducts, respectively. At 3 W, a T difference of 2±1 °C was obtained for the upper biliary duct, while a difference of 8±1 °C was documented for the lower duct. Based on the results obtained in this preliminary study, the possibility to equip the laser probe with temperature sensor can improve the control and the safety of the procedure; this solution will guarantee the monitoring of the treatment while preserving the lumen and the surrounding structures.

Hyperspectral imaging for thermal effect monitoring in in vivo liver during laser ablation.

Thermal ablation is a minimally invasive technique used to induce a controlled necrosis of malignant cells by increasing the temperature in localized areas. This procedure needs an accurate and real-time monitoring of thermal effects to evaluate and control treatment outcome. In this work, a hyperspectral imaging (HSI) technique is proposed as a new and non-invasive method to monitor ablative therapy. HSI provides images of the target object in several spectral bands, hence the reflectance/absorbance spectrum for each pixel. This paper presents a preliminary and original HSI-based analysis of the thermal state in the in vivo porcine liver undergoing laser ablation. In order to compare the spectral response between treated and untreated areas of the organ, proper Regions of Interest (ROIs) were chosen on the hyperspectral images; for each ROI, the absorbance variation for the selected wavelengths (i.e., 630, 760, and 960nm, for deoxyhemoglobin, methemoglobin, and water respectively) was assessed. Results obtained during and after laser ablation show that the absorbance of the methemoglobin peaks increases up to 40% in the burned region with respect to the non-ablated one. Conversely, the relative change of deoxyhemoglobin and water peaks is less marked. Based on these results, absorbance threshold values were retrieved and used to visualize the ablation zone on the images. This preliminary analysis suggests that a combination of the absorbance information is essential to achieve a more accurate identification of the ablation region. The results encourage further studies on the correlation between thermal effects and the spectral response of biological tissues undergoing thermal ablation, for final clinical use.

Polymer-coated fiber optic probe for the monitoring of breathing pattern and respiratory rate.

In recent years, no-invasive and small size systems are meeting the demand of the new healthcare system, in which the vital signs monitoring is gaining in importance. In this context, Fiber Bragg grating (FBG) sensors are becoming very popular and FBG-based systems could be used for monitoring vital signs. At the same time, FBG could be able to sense chemical parameters by the polymer functionalization. The aim of our study was investigating the ability of a polymer-coated FBG-based probe for monitoring breathing patterns and respiratory rates. We tested the proposed FBG-based probe on 9 healthy volunteers during spirometry, the most common pulmonary function test. Results showed the high accuracy of the proposed probe to detect respiratory rate. The comparison between the respiratory rates estimated by the probe with the ones by the spirometer showed the absolute value of the percentage errors lower than 2.07% (in the 78% of cases <.91%). Lastly, a Bland Altman analysis was performed to compare the instantaneous respiratory rate values gathered by the spirometer and the FBG probe showing the feasibility of breath-by-breath monitoring by the proposed probe. Results showed a bias of 0.06± 2.90 $\mathrm{breaths}\square {\mathrm {min}}^{-1}$. Additionally, our system was able to follow the breathing activities and monitoring the breathing patterns.

Wearable textile based on silver plated knitted sensor for respiratory rate monitoring.

Wearable systems are gaining broad acceptance for monitoring physiological parameters in several medical applications. Among a number of approaches, smart textiles have attracted interest because they are comfortable and do not impair patients' movements. In this article, we aim at developing a smart textile for respiratory monitoring based on a piezoresistive sensing element. Firstly, the calibration curve of the system and its hysteresis have been investigated. Then, the proposed system has been assessed on 6 healthy subjects. The volunteers were invited to wear the system to monitor their breathing rate. The results of the calibration show a good mean sensitivity (i.e., approximately 0.11V·%-1); although the hysteresis is not negligible, the system can follow the cycles also at high rates (up to 36 cycle·min-1). The feasibility assessment on 6 volunteers (two trials for each one) shows that the proposed system can estimate with good accuracy the breathing rate. Indeed, the results obtained by the proposed system were compared with the ones collected with a spirometer, used as reference. Considering all the experiments, a mean percentage error was approximately 2%. In conclusion, the proposed system has several valuable features (e.g., the sensing element is lightweight, the sensitivity is high, and it is possible to develop comfortable smart textile); in addition, the promising performances considering both metrological properties and assessment on volunteers foster future tests focused on: i) the possibility of developing and system embedding several sensing elements, and ii) to develop a wireless acquisition system, to allow comfortable and long-term acquisition in both patients and during sport activities.

Ex vivo animal-model assessment of a non-invasive system for loss of resistance detection during epidural blockade.

During recent decades epidural analgesia has gained widespread recognition in many applications. In this complex procedure, anaesthetist uses a specific needle to inject anesthetic into the epidural space. It is crucial the appropriate insertion of the needle through inhomogeneous tissues placed between the skin and the epidural space to minimize anesthetic-related complications (e.g., nausea, headache, and dural puncture). Usually, anaesthetists perform the procedure without any supporting tools, and stop pushing the syringe when they sense a loss of resistance (LOR). This phenomenon is caused by the physical properties of the epidural space: the needle breaks the ligamentum flavum and reaches the epidural space, in this stage the anaesthetist perceives a LOR because the epidural space is much softer than the ligamentum flavum. To support the clinician in this maneuver we designed a non-invasive system able to detect the LOR by measuring the pressure exerted on the syringe plunger to push the needle up to the epidural space. In a previous work we described the system and its assessment during in vitro tests. This work aims at assessing the feasibility of the system for LOR detection on a more realistic model (ex vivo pig model). The system was assessed by analyzing: its ability to hold a constant value (saturation condition) during the insertion of the needle, and its ability to detect the entrance within the epidural space by a decrease of the system's output. Lastly, the anaesthetist was asked to assess how the ex vivo procedure mimics a clinical scenario. The system reached the saturation condition during the needle insertion; this feature is critical to avoid false positive during the procedure. However, it was not easy to detect the entrance within the epidural space due to its small volume in the animal model. Lastly, the practitioner found real the model, and performed the procedures in a conventional manner because the system did not influence his actions.

Novel carbon fiber probe for temperature monitoring during thermal therapies.

Thermal treatments are a valid clinical option in the management of several solid tumors. The difficulties to perform an accurate prediction improve the selectivity of the treatment effects represent the main hurdles in the spread of these techniques. Among other solutions, thermometric techniques are gaining acceptance in monitoring the effects of thermal treatments because they provide a clear end-point to obtain the complete removal of cancer without damaging the surrounding healthy tissue. This paper proposes a custom needle-like probe made of carbon fibers to embed seven fiber Bragg grating (FBG) sensors. This tool aims at a multiple points monitoring the tissue temperature during the thermal procedures, streamlining the FBG sensors insertion within the organ. After the description of the probe manufacturing, we reported the calibration of the seven sensors embedded within the probe, their step response, and the feasibility assessment of the probe for temperature monitoring during laser ablation on animal model (both in vivo and ex vivo). Results show that the proposed probe is easily maneuverable by the clinician, the sensors have a linear response with the temperature and a short step response; moreover, the probe allows measuring the temperature in seven points of the tissue; finally, it can be used during CTand MR-guided procedures without causing any artifact to the images. Thanks to these features the probe may be an useful solution to improve the safety and the outcomes of minimally invasive thermal ablation procedures, so to spread these procedures in the clinical field.

A wearable textile for respiratory monitoring: Feasibility assessment and analysis of sensors position on system response.

The interest on wearable textiles to monitor vital signs is growing in the research field and clinical scenario related to the increasing demands of long-term monitoring. Despite several smart textile-based solutions have been proposed for assessing the respiratory status, only a limited number of devices allow the respiratory monitoring in a harsh environment or in different positions of the human body. In this paper, we investigated the performances of a smart textile for respiratory rate monitoring characterized by 12 fiber optic sensors (i.e., fiber Bragg grating) placed on specific landmarks for compartmental analysis of the chest wall movements during quiet breathing. We focused on the analysis of the influence of sensor position on both peak-to-peak amplitude of sensors output and accuracy of respiratory rate measurements. This analysis was performed on two participants, who wore the textile in two positions (i.e., standing and supine). Bland-Altman analysis on respiratory rate showed promising results (better than 0.3 breaths per minute). Referring to the peak-to-peak output amplitude, the abdomen compartment showed the highest excursions in both the enrolled participants and positions. Our findings open up new approaches to design and develop smart textile for respiratory rate monitoring.

Tapered fiber optic applicator for laser ablation: Theoretical and experimental assessment of thermal effects on ex vivo model.

Laser Ablation (LA) is a minimally invasive technique for tumor removal. The laser light is guided into the target tissue by a fiber optic applicator; thus the physical features of the applicator tip strongly influence size and shape of the tissue lesion. This study aims to verify the geometry of the lesion achieved by a tapered-tip applicator, and to investigate the percentage of thermally damaged cells induced by the tapered-tip fiber optic applicator. A theoretical model was implemented to simulate: i) the distribution of laser light fluence rate in the tissue through Monte Carlo method, ii) the induced temperature distribution, by means of the Bio Heat Equation, iii) the tissue injury, by Arrhenius integral. The results obtained by the implementation of the theoretical model were experimentally assessed. Ex vivo porcine liver underwent LA with tapered-tip applicator, at different laser settings (laser power of 1 W and 1.7 W, deposited energy equal to 330 J and 500 J, respectively). Almost spherical volume lesions were produced. The thermal damage was assessed by measuring the diameter of the circular-shaped lesion. The comparison between experimental results and theoretical prediction shows that the thermal damage discriminated by visual inspection always corresponds to a percentage of damaged cells of 96%. A tapered-tip applicator allows obtaining localized and reproducible damage close to spherical shape, whose diameter is related to the laser settings, and the simple theoretical model described is suitable to predict the effects, in terms of thermal damage, on ex vivo liver. Further trials should be addressed to adapt the model also on in vivo tissue, aiming to develop a tool useful to support the physician in clinical application of LA.

Effects of Nd:YAG laser for the controlled and localized treatment of early gastrointestinal tumors: Preliminary in vivo study.

Endoscopic submucosal dissection (ESD) is a minimally invasive technique allowing for the removal of early gastrointestinal (GI) tumors, widely considered as a valid alternative to conventional surgery. However, ESD is technically demanding, and potentially severe complications, such as bleeding and perforation, may occur. Energy-based techniques (e.g., radiofrequency ablation) might offer a potential alternative to ESD. However, their use mandates the ability to predict the damage induced and to identify a "signature" of the complete ablation, without the need for a physical specimen. Ideally, an energy-based procedure should be tunable in order to limit the ablation to the superficial layers, namely mucosa (M) and submucosa (SM), without injuring the muscularis propria (MP), thereby minimizing GI perforation. This experimental study aims to investigate thermal damage induced by Nd:YAG laser on the gastric wall, at different laser settings such as power (P) and time (t). Laser ablation was performed on the stomach wall of 6 Wistar rats. Two powers (2.5W and 1.0W) and 3 exposure times (12s, 6s and 2s) were tested, for a total of 30 ablations. Histological analysis allowed to assess thermal damage, in terms of damage depth (DD) and identification of involved layers. The ratio (R) between DD and the total depth (TD) of target layers (M+SM) was used as an index to evaluate the effectiveness of laser settings. At P=2.5W, MP was damaged (R>1) in the majority of cases (11/15). At P=1.0W, MP was preserved in all tests (R<;1), and rarely (4/15) did the damage reach the whole SM (R=1). Histopathological analysis evidenced that tissue damage was strongly related to the variable tissue thickness. These preliminary results seem to support the fact that endoscopic tunable laser ablation is feasible with a consistent damage/power correlation. Further tests are required to optimize the settings for applications on early GI tumors.

Bronchial blockers under pressure: in vitro model and ex vivo model.

BACKGROUND: Pressures (Pe) exerted by bronchial blockers on the inner wall of the bronchi may cause mucosal ischaemia. Our aims were as follows: (i) to compare the intracuff pressure (Pi) and Pe exerted by commercially available bronchial blockers in an in vitro and an ex vivo model; (ii) to investigate the influence of both the inflated intracuff volume and cuff diameter on Pe; and (iii) to estimate the minimal sealing volume (VSmin) and the corresponding Pe for each bronchial blocker studied. METHODS: The Pe exerted by seven commercial bronchial blockers was measured at different inflation volumes using a custom-designed system using in vitro and ex vivo animal models with two internal diameters (12 and 15 mm). RESULTS: In the same conditions, Pi was significantly lower than Pe (P<0.05), and Pe was higher in the in vitro model than in the ex vivo model. The Pe increased with the inflated volume, with use of the small-diameter model (P<0.05). Ex vivo models needed a higher minimal sealing volume than the in vitro models, and this volume increased with the diameter (e.g. the VSmin at a positive pressure of 25 cm H2O required a Pe ranging from 12 to 78 mm Hg on the 15 mm ex vivo model and from 66 to 110 mm Hg on the 12 mm ex vivo model). CONCLUSIONS: The Pi cannot be used to approximate Pe. The diameter of the model, the inflated volume, and the bronchial blocker design all influence Pe. A pressure higher than the critical ischaemic threshold (i.e. 25 mm Hg) was needed to prevent air leak around the cuff in the in vitro and ex vivo models.

A cost-effective, non-invasive system for pressure monitoring during epidural needle insertion: Design, development and bench tests.

Epidural blockade procedures have gained large acceptance during last decades. However, the insertion of the needle during epidural blockade procedures is challenging, and there is an increasing alarming risk in accidental dural puncture. One of the most popular approaches to minimize the mentioned risk is to detect the epidural space on the base of the loss of resistance (LOR) during the epidural needle insertion. The aim of this paper is to illustrate an innovative and non-invasive system able to monitor the pressure exerted during the epidural blockade procedure in order to detect the LOR. The system is based on a Force Sensing Resistor (FSR) sensor arranged on the top of the syringe's plunger. Such a sensor is able to register the resistance opposed to the needle by the different tissues transducing the pressure exerted on the plunger into a change of an electrical resistance. Hence, on the base of a peculiar algorithm, the system automatically detects LOR providing visual and acoustic feedbacks to the operator improving the safety of the procedure. Experiments have been performed to characterize the measurement device and to validate the whole system. Notice that the proposed solution is able to perform an effective detection of the LOR.

Temperature monitoring during radiofrequency ablation of liver: in vivo trials.

Radiofrequency ablation (RFA) is a minimally invasive procedure used to treat tumors by means of hyperthermia, mostly through percutaneous approach. The tissue temperature plays a pivotal role in the achievement of the target volume heating, while sparing the surrounding healthy tissue from thermal damage. Several techniques for thermometry during RFA are investigated, most of them based on the use of single-point measurement system (e.g., thermocouples). The measurement of temperature map is crucial for the real-time control and fine adjustment of the treatment settings, to optimize the shape and size of the ablated volume. The recent interest about fiber optic sensors and, among them, fiber Bragg gratings (FBGs) for the monitoring of thermal effects motivated further investigation. In particular, the feature of FBGs to form an array of several elements, thus to be inscribed within the same fiber, allows the use of a single probe for the multi-points monitoring of the tissue temperature during RFA. Hence, the aim of this study is the development and characterization of a needle-like probe embedding an array of three FBGs, which was tested on pig liver during in vivo trials. The needle allows a safe and easy insertion of the fiber optic within the liver. It was inserted by ultrasound guidance into the liver, and monitored the change of tissue temperature during RFA controlled by the roll-off technique. Also the measurement error induced by breathing movements of the liver was assessed (less than 3 °C). Results encourage the use of the probe in clinical settings, as well as the improvement of some features, e.g., a higher number of FBGs for performing quasi-distributed measurement.

Multipoint temperature monitoring in liver undergoing computed tomography-guided radiofrequency ablation with fiber Bragg grating probes.

In this work, we investigated the temperature increment experienced by biological tissue during radiofrequency ablation (RFA). The measurements were performed by using two custom-made thermal probes based on fiber optic sensors (fiber Bragg gratings, FBGs). The two probes embed a total of 9 FBGs. Experiments were performed during RFA of an ex vivo healthy porcine liver. The RFA heating module was equipped with 5 thermocouples. Results show that the temperature increment close to the applicator (i.e., 0.6 cm-0.7 cm) reaches the temperature which is set as a target on the RFA module (i.e., approximately 100 °C). The distance from the applicator also has an impact on the dynamics of the heating phenomenon: at short distances the tissue temperature reaches a steady state condition after a few minutes, on the other hand the sensors placed at a distance ≥2cm did not reach the steady-state conditions during the 14-minute procedure. The multipoint temperature monitoring, which uses sensors at several distances from the applicator, can provide useful information regarding the boundary of damaged volume. This approach can be combined with the monitoring temperature system embedded in the heating equipment, to better control the damaged volume, and to improve the treatment outcomes.

A novel tool and procedure for in-situ volumetric calibration of motion capture systems for breathing analysis.

Optical motion capture systems are widely used in biomechanics although have not been significantly explored for measuring volumes and volume variations yet. The aim of this study was to propose and test a completely novel procedure for the calibration of motion capture systems for the breathing analysis in terms of volume measurements, by the use of a tool consisting in an ad-hoc designed in-situ calibration device (CD) and two algorithms for calibration. Both the calibration tool and the calibration procedure performed in the range 0-2780mL on an Optoelectronic Plethysmography (OEP) system are presented. The CD delivered known volume (ΔVCD) variations to the OEP; the two algorithms performed the calibration by the comparison between ΔVCD and OEP recorded volume (ΔVOEP), in both static and dynamic conditions. Discrimination threshold, accuracy, precision and repeatability for the volume variation measurements have been evaluated, as well as the calibration curve of the OEP. OEP volume threshold of ±8.92mL was assessed; the volume measurement accuracy was always better than 6.0% of measured volume, and a volume repeatability of ±2.7mL was found. Lastly, the calibration curve was assessed to be ΔVOEP= 0.962·ΔVCD. Results demonstrate that the proposed calibration procedure can be useful to provide an in-situ accurate calibration of motion capture systems in the volume analysis, to optimize the hardware and the software of the available system for volume measurement as well as to establish the motion capture system appropriateness, in terms of technical suitability and data quality.

Design and preliminary assessment of a smart textile for respiratory monitoring based on an array of Fiber Bragg Gratings.

Comfortable and easy to wear smart textiles have gained popularity for continuous respiratory monitoring. Among different emerging technologies, smart textiles based on fiber optic sensors (FOSs) have several advantages, like Magnetic Resonance (MR)-compatibility and good metrological properties. In this paper we report on the development and assessment of an MR-compatible smart textiles based on FOSs for respiratory monitoring. The system consists of six fiber Bragg grating (FBG) sensors glued on the textile to monitor six compartments of the chest wall (i.e., right and left upper thorax, right and left abdominal rib cage, and right and left abdomen). This solution allows monitoring both global respiratory parameters and each compartment volume change. The system converts thoracic movements into strain measured by the FBGs. The positioning of the FBGs was optimized by experiments performed using an optoelectronic system. The feasibility of the smart textile was assessed on 6 healthy volunteers. Experimental data were compared to the ones estimated by an optoelectronic plethysmography used as reference. Promising results were obtained on both breathing period (maximum percentage error is 1.14%), inspiratory and expiratory period, as well as on total volume change (mean percentage difference between the two systems was ~14%). The Bland-Altman analysis shows a satisfactory accuracy for the parameters under investigation. The proposed system is safe and non-invasive, MR-compatible, and allows monitoring compartmental volumes.

Monitoring of thermal treatment by linearly chirped fiber Bragg grating sensors: feasibility assessment during laser ablation on ex vivo liver.

In this work a spatially-resolved fiber optic temperature sensor has been characterized in a wide range of gradient applied on its active area (from -35 °C to +35 °C). Preliminary experiments to assess its feasibility for application in laser ablation have been performed. The sensor under test is a linearly chirped fiber Bragg grating (FBG), with 1.5 cm-length of active area. It can be considered as a chain of several FBGs, each able to sense local temperature. The sensor response to the gradient has been analyzed in terms of its spectrum width (full width at half maximum). There is a linear relationship between the full width at half maximum and the gradient, with a sensitivity of 0.0087 nm°C-1. The feasibility test using the linearly chirped FBG during laser ablation showed promising results: it is able to detect both the thermal gradients along is active area and the average temperature increment during the procedure.

Temperature monitoring during microwave ablation in ex vivo porcine livers.

OBJECTIVE: The aim of the present study was to assess the temperature map and its reproducibility while applying two different MWA systems (915 MHz vs 2.45 GHz) in ex vivo porcine livers. MATERIALS AND METHODS: Fifteen fresh pig livers were treated using the two antennae at three different settings: treatment time of 10 min and power of 45 W for both systems; 4 min and 100 W for the 2.45 GHz system. Trends of temperature were recorded during all procedures by means of fiber optic-based probes located at five fixed distances from the antenna, ranging between 10 mm and 30 mm. Each trial was repeated twice to assess the reproducibility of temperature distribution. RESULTS: Temperature as function of distance from the antenna can be modeled by a decreasing exponential trend. At the same settings, temperature obtained with the 2.45 GHz system was higher than that obtained with the 915 MHz thus resulting into a wider area of ablation (diameter 17 mm vs 15 mm). Both systems showed good reproducibility in terms of temperature distribution (root mean squared difference for both systems ranged between 2.8 °C and 3.4 °C). CONCLUSIONS: When both MWA systems are applied, a decreasing exponential model can predict the temperature map. The 2.45 GHz antenna causes higher temperatures as compared to the 915 MHz thus, resulting into larger areas of ablation. Both systems showed good reproducibility although better results were achieved with the 2.45 GHz antenna.

Magnetic resonance-based thermometry during laser ablation on ex-vivo swine pancreas and liver.

Laser Ablation (LA) is a minimally-invasive procedure for tumor treatment. LA outcomes depend on the heat distribution inside tissues and require accurate temperature measurement during the procedure. Magnetic resonance imaging (MRI) allows a non-invasive and three-dimensional thermometry of the organ undergoing LA. In this study, the temperature distribution within two swine pancreases and three swine livers undergoing LA (Nd:YAG, power: 2 W, treatment time: 4 min) was monitored by a 1.5-T MR scanner, utilizing two T1-weighted sequences (IRTF and SRTF). The signal intensity in four regions of interest, placed at different distances from the laser applicator, was related to temperature variations monitored in the same regions by twelve fiber Bragg grating sensors. The relationship between the signal intensity and temperature increase was calculated to obtain the calibration curve and to evaluate accuracy, sensibility and precision of each sequence. This is the first study of MR-based thermometry during LA on pancreas. More specifically, the IRTF sequence provides the highest temperature sensitivity in both liver (1.8 ± 0.2 °C(-1)) and pancreas (1.8 ± 0.5 °C(-1)) and the lowest precision and accuracy. SRTF sequence on pancreas presents the highest accuracy and precision (MODSFRT = -0.1 °C and LOASFRT = [-2.3; 2.1] °C).