71 research outputs found
Temperature monitoring during radiofrequency ablation of liver: In vivo trials
No full textRadiofrequency 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. © 2016 IEEE
Temperature monitoring during Laser Ablation by FBG sensors encapsulated within a metallic needle: Experiments on healthy swine tissue
No full textMonitoring of local temperature in tissue undergoing Laser Ablation (LA) could be particularly beneficial to optimize treatment outcomes. A number of both invasive and non-invasive thermometric techniques may be employed to perform this task. Among others, Fiber Bragg Grating (FBG) sensors show the following valuable characteristics for temperature monitoring during LA: good sensitivity and accuracy, and immunity from electromagnetic interferences. The main drawbacks are their intrinsic invasiveness and the sensitivity to strain, which can entail measurement error for respiratory and patient movements. © 2015 IEEE
Monitoring of thermal treatment by linearly chirped fiber Bragg grating sensors: Feasibility assessment during laser ablation on ex vivo liver
No full textIn 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. © 2016 IEEE
Assessment of a linearly chirped fiber Bragg grating sensor under linear and non-linear temperature gradient
No full textAmong several innovative procedures used in the fight against cancers, thermal treatments are gaining acceptance in clinical settings. In these approaches, heat is used to damage cancer cells. Therefore, it is useful to monitor the temperature reached in the tissue undergoing the treatment, in order to improve the outcome of the procedure. Despite the variety of available techniques investigated for temperature monitoring during thermal treatments, Linearly Chirped Fiber Bragg Grating (LCFBG) sensors can be seen as a good choice thanks to their small size, the flexibility of the fiber optic, as well as the immunity to electromagnetic interferences and the Magnetic Resonance-(MR-) compatibility. In this work a commercial LCFBG has been tested under different thermal gradients that typically occur during the thermal treatments (up to 30 °C). The sensor's response has been analysed under linear and non-linear thermal gradients. The shift and the width of the LCFBG's spectrum have been related to both the average temperature (Tmean) applied on its active area, and to the temperature difference (ΔT) experienced by the sensor between its two extremities. The analysis has showed promising results: actually with the sensor under test is possible to find a linear relationship between the spectrum shift and Tmean (with a sensitivity of about 10 pm°·C-1), and also between the spectrum width and the ΔT (5 pm°·C-1). These findings may allow extrapolating temperature information from the LCFBG spectrum, in order to monitor in real-time the effects of thermal treatment on biological tissue. Because the effects of thermal ablation depend on temperature, the knowledge of temperature may improve the treatments outcome, thus patient safety. © 2017 IEEE
Design and preliminary assessment of a smart textile for respiratory monitoring based on an array of Fiber Bragg Gratings
No full textComfortable 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. © 2016 IEEE
Influence of fiber Bragg grating length on temperature measurements in laser-irradiated organs
No full textThe present study investigates the influence of uniform FBG length on temperature measurement under substantial temperature gradient. This analysis is particularly relevant in the scenario of laser ablation (LA), where the temperature gradient close to the optical applicator is significant (e.g., up to 50 °C/mm). Aiming to assess how the sensor length affects the measurement process in LA, both bench and ex vivo experiments were carried out by applying temperature gradient in the range 5 °C/cm-30 °C/cm on 1 mm-length FBG and 10 mm-length FBG. Results showed that the use of small-sized FBGs is recommended in LA for two main reasons: i) the spectrum reflected by shorter sensors has not shown significant alterations with the gradient. Alterations of the spectrum shape could compromise peak detection algorithms, and, therefore, the estimation of the actual temperature; ii) Arrays of shorter sensors can provide multipoint temperature measurements, with quiet good spatial resolution (e.g., 3 mm), by inserting a single fiber in the tissue. © 2016 IEEE
Development and characterization of a fibre Bragg grating temperature probe for medical laser ablation therapy
No full textTemperature monitoring in tissue undergoing Laser Ablation (LA) is particularly beneficial to optimize therapy outcomes. During last decades several approaches have been proposed to perform thermometry during thermal ablation. Among others, Fiber Bragg Grating (FBG) sensors show valuable characteristics for such measurement, but their sensitivity to strain entails measurement error for patient respiratory movements. In this work two needle-like probes were developed using two different procedures to encapsulate an FBG into a surgical needle, aiming to allow safe insertion into the patient tissue and to neglect mechanical disturbance due to tissue movements occurring during breathing. The static calibration of the two probes has been carried out in a wide range of temperature (i.e., from 18 °C up to 100 °C), and their response time has been estimated. The calibration curves of the two probes show good linearity and a different sensitivity, and their response time is fast enough to meet the criteria set for temperature monitoring during LA. Since the metallic needle entails a measurement error, called artifact, due to the direct absorption of the laser radiation, the two abovementioned probes have been employed during LA on ex vivo liver. Then, their measurements have been compared to the measurement provided by an FBG without needle, which does not experience artifacts. The good results in terms of both static and dynamic properties of the two probes encourage to perform further analysis regarding the amplitude of the artifacts due to the direct absorption of the metallic needle and regarding the capability of the probes to neglect mechanical disturbance. © 2014 IEEE
Error of a temperature probe for cancer ablation monitoring caused by respiratory movements: Ex vivo and in vivo analysis
No full textHyperthermal techniques are spreading as an alternative to conventional surgery for cancer removal. A real-time temperature feedback can be used to adjust the treatment settings, in order to improve the clinical outcomes. In this paper, we experimentally assessed the feasibility for distributed temperature monitoring of a custom probe, which consists of a needle embedding six fiber Bragg gratings (FBGs). Since FBGs are also sensitive to strain, we focused on the analysis of the measurement error (artifact) caused by respiratory movements. We assessed the artifact both on ex vivo pig liver and lung (by mimicking the movement of these organs caused by respiration) and on in vivo trial on pig liver. Lastly, we proposed an algorithm to detect and minimize the artifact during ex vivo liver laser ablation. During both ex vivo and in vivo trials, the probe insertion within the organ was easy and safe. The artifact was significant (up to 3 °C), but the correction algorithm allows minimizing the error. The main advantages of the proposed probe are: 1) spatially resolved temperature monitoring (in six points of the tissue by inserting a single needle) and 2) the needle is magnetic resonance (MR)-compatible, hence can be used during MR-guided procedure. Even if the model is close to humans, further trials are required to investigate the feasibility of the probe for clinical applications. © 2001-2012 IEEE
Smart textile based on fiber bragg grating sensors for respiratory monitoring: Design and preliminary trials
No full textContinuous respiratory monitoring is important to assess adequate ventilation. We present a fiber optic-based smart textile for respiratory monitoring able to work during Magnetic Resonance (MR) examinations. The system is based on the conversion of chest wall movements into strain of two fiber Bragg grating (FBG) sensors, placed on the upper thorax (UT). FBGs are glued on the textile by an adhesive silicon rubber. To increase the system sensitivity, the FBGs positioning was led by preliminary experiments performed using an optoelectronic system: FBGs placed on the chest surface experienced the largest strain during breathing. System performances, in terms of respiratory period (TR), duration of inspiratory (TI) and expiratory (TE) phases, as well as left and right UT volumes, were assessed on four healthy volunteers. The comparison of results obtained by the proposed system and an optoelectronic plethysmography highlights the high accuracy in the estimation of TR, TI, and TE: Bland-Altman analysis shows mean of difference values lower than 0.045 s, 0.33 s, and 0.35 s for TR, TI, and TE, respectively. The mean difference of UT volumes between the two systems is about 8.3%. The promising results foster further development of the system to allow routine use during MR examinations
Influence of FBG sensors length on temperature measures in laser-irradiated pancreas: Theoretical and experimental evaluation
No full textTemperature distribution T(x,y,z,t) in tissue undergoing Laser-induced Interstitial Thermotherapy (LITT) plays a crucial role on treatment outcome. Theoretical and experimental assessment of temperature on ex vivo laser-irradiated pancreas is presented. The aim of this work is to assess the influence of thermometers dimensions on temperature measures during LITT. T(x,y,z,t) inside tissue is monitored by optical sensors, i.e., Fiber Bragg Gratings (FBGs): three FBGs with lengths of 10 mm and nine FBGs of 1 mm, at different distances (2 mm, 5 mm and 10 mm) and different quotes (0 mm, 2 mm and 4 mm) from the laser fiber tip are used. Theoretical punctual T(x,y,z,t) is averaged out on both 10 mm and 1 mm in order to compare numerical predictions with experimental data. Results demonstrate the influence of FBG length on T(x,y,z,t) measures. This phenomenon depends on the distance between sensor and applicator: it is particularly significant close to the applicator tip (2 mm) because of the high spatial T(x,y,z,t) gradient within the tissue. Both theoretical results and experimental ones show that just at a distance of 10 mm from the tip, differences between T(x,y,z,t) provided by FBGs of 10 mm and 1 mm are negligible. © 2013 IEEE
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