Fiber-optic Thermometer Research Articles

Heating of an Aortic Stent for Coarctation Treatment During Magnetic Particle Imaging and Magnetic Resonance Imaging\u2014A Comparative In Vitro Study

PurposeTo evaluate heating of a redilatable stent for the treatment of aortic coarctation in neonates and small children in the new imaging modality magnetic particle imaging and established magnetic resonance imaging.Materials and MethodsThe cobalt-chromium stent (BabyStent, OSYPKA AG, Rheinfelden, Germany) has a stent design which allows for redilatation and adjustment of the diameter from 6 to 16 mm for a use in aortic coarctation. The stent loses its radial integrity while opening at predetermined breaking points at a diameter of 14 mm or 16 mm, respectively. We measured the temperature increase in the stent at different diameters during 7-min magnetic particle imaging and magnetic resonance imaging scans with fiber optic thermometers under static conditions surrounded by air. In magnetic particle imaging, stents with diameters from 6 to 16 mm were tested while in magnetic resonance imaging only stents with diameters of 6 mm and 14 mm were investigated exemplarily.ResultIn magnetic particle imaging, the measured temperature differences increased up to 4.7 K with growing diameters, whereas the opened stents with discontinuous struts at 14 and 16 mm showed only minimal heating of max. 0.5 K. In contrast to magnetic particle imaging, our measurements showed no heating of the stents during magnetic resonance imaging under identical conditions.ConclusionThe BabyStent did show only slight heating in magnetic particle imaging and no detectable temperature increase in magnetic resonance imaging.

Machine learning-assited optical thermometer for continuous temperature analysis inside molten metal

This paper demonstrates a robust optical fiber thermometer (OFT) for temperature measurement under extreme environments. To date, the development of sensors for continuous temperature measurement in environments with temperatures over 1000 °C, severe electromagnetic interferences, and strong oxidizing agents has been very challenging. The proposed nano-OFT system consists of a ceramic tube, a nanorod coated sapphire fiber, and a near-infrared (NIR) spectrum analyzer for continuous measurement of molten steel temperature in furnaces. The nanorod layer functions as an effective cladding material for the sapphire fiber to sustain a reliable transmission of NIR thermal emissions. The thermal radiation from the ceramic tube's tip was coupled out of the nano-OFT probe via the sapphire fiber and measured using the NIR spectrometer. The NIR emissions were analyzed using a convolution neural network to determine the probe temperature. Our results show that the nano-OFT probe can measure furnace temperature in the temperature range from 1,000–1,650 °C, with the error percentage as low as 0.5 %. The nano-OFT system can be employed by the steel industry to monitor steel temperature continuously, and thus enhance steel production efficiency and reduce energy consumption.

Piezoelectric Implant Site Preparation: Influence of Handpiece Movements on Temperature Elevation.

Piezoelectric devices are widely used in oral surgical procedures, including implant site preparation. However, little is known about the influence of working movement on temperature elevation in bone. The aim of this study was to assess the effects of two different working cycles on temperature elevation during piezoelectric implant site preparation. Sixty osteotomies at a depth of 10 mm were performed on bone blocks of bovine ribs using a piezoelectric tip with external irrigation (IM1s, Mectron Medical Technology, Carasco, Italy). A mechanical positioning device was used to guarantee reproducible working and measuring conditions. Two different working cycles, of 4 and 6 s, respectively, were tested, including both longitudinal and rotational movements. Temperature was recorded in real time with a fiber optic thermometer and applied pressure was maintained under 150 g. For each test, the highest recorded temperature (Tmax) and the mean temperature recorded from 30 s before to 30 s after the highest recorded temperature (T±30) were extrapolated. Tests duration was also recorded. Both Tmax and T±30 were significantly higher in the ‘6 s cycles’ group than the ‘4 s cycles’ group (42.44 ± 7.3 °C vs. 37.24 ± 4.6 °C, p = 0.002; 37.24 ± 4.6 °C vs. 33.30 ± 3.3 °C, p = 0.003). Test duration was also significantly higher using 6 s cycles compared to 4 s cycles (143.17 ± 29.4 s vs. 119.80 ± 36.4 s, p = 0.002). The results of this study indicate that working cycles of 4 s effectively reduce heat generation and working time during piezoelectric implant site preparation.

Luminescence temperature sensing using thin-films of undoped Gd2O3 and doped with Ho3+, Eu3+ and Er3+ prepared by plasma electrolytic oxidation

The steady-state luminescence thermometry analysis was performed on thin-films of undoped Gd2O3 and Gd2O3 doped with Ho3+, Eu3+ and Er3+, created by the plasma electrolytic oxidation process. The experimental setup for luminescent measurements closely resembles the practical luminescent fiber-optic thermometer. The visible PL from Gd3+ was utilized for the luminescence intensity ratio method, exceling over the traditional method by using the thermally coupled levels, as it is superior by either better sensitivities, widened temperature range or improved temperature resolution. The relative uncertainty by our method is ~300 times lower @ 300 K for Gd2O3:Eu3+. The maximum relative sensitivities by the luminescence intensity ratio (LIR) of Gd2O3:Ho3+, Gd2O3:Eu3+ and Gd2O3:Er3+ are 0.12% @ 295 K, 0.44% @ 580 K and 1.1% @ 290 K, respectively. Line-shift showed a significant change solely for Eu3+ doped sample, by 0.076 cm−1 K−1. The full-width-half-maximum (FWHM) changes of undoped Gd2O3 and doped by Eu3+ at the high rate of 0.3 cm−1 K−1 @ 573 K and 0.53 cm−1 K−1 @ 300 K, respectively, but was marked impractical for other samples.

Miniature Fizeau Interferometric Thermometer

Precise measurement of temperature is vital in a variety of industries and basic sciences. Numerous techniques have been proposed for temperature measurement, such as fiber Bragg gratings and Fabry–Perot interferometers. Despite several important accomplishments, such optical thermometers are still limited in their performances. Two major limitations are the low operational temperature and the paradox between a large dynamic range and a high resolution. Here, we propose a fiber-optic thermometer based on fiber-tip microspherical Fizeau interferometer made from high temperature-resistant material. The sensor is fabricated by inserting a section of single-mode fiber into a spherical microcavity to form a Fizeau interferometer. Thanks to the thermo-optic effect and thermal expansion effect, the variation of ambient temperature modifies the refractive index and the interferometric length of the microcavity, and then a corresponding change in the interferometric spectrum can be observed. The demodulation method is based on the combination measurement of interferometric fringe shift and free spectral range variation, which is capable of providing high resolution and wide dynamic range. Experimental results show that by using a simple wavelength tracking demodulation method, a sensitivity of 22 pm/°C with a high resolution and a dynamic range over 1000 °C can be achieved. Since the sensor is of small size, it exhibits fast response and recovery time which mean it can monitor ambient temperature variation in real time. Additionally, the structure is robust and compact which makes the technology an interesting alternative to conventional thermometers for temperature measurement.

A Novel Theranostic Platform: Integration of Magnetomotive and Thermal Ultrasound Imaging With Magnetic Hyperthermia.

Nanotheranostic systems integrate therapeutic and diagnostic procedures using nanotechnology. This type of approach has enabled the development of methods for early detection and treatment of different pathologies. Magnetic hyperthermia (MH) has been proposed as an alternative or complementary method of cancer therapy. However, challenges such as delivering and localizing the magnetic nanoparticles (MNPs) within tissues and monitoring the temperature during the treatment hinder this technique to be effectively translated into a clinical routine. Therefore, in this study a theranostic platform has been proposed and examined to address two main issues, localizing MNPs and real-time temperature monitoring, for preclinical MH. The system integrates magnetomotive (MMUS) and thermal ultrasound imaging with MH. An ultrasound device was used to acquire MMUS images to detect MNPs, and ultrasound thermometry to monitor the temperature. This platform was designed such that a single coil generated the magnetic field for MMUS and MH. The feasibility of the system was examined using a tissue mimicking phantom containing an inclusion filled with zinc substituted magnetite NPs. These MNPs were effectively used as contrast agent for MMUS and to generate heat during MH. In addition to localizing MNPs, real-time two-dimensional temperature maps were obtained with substantial concordance (ρc > 0.97) with invasive measurements using fiber optic thermometer. The heating rate was proportional to the displacements in MMUS (r=0.92). Ultrasound thermometry was successfully used to monitor the temperature during MH. In addition, it was shown that acquiring MMUS images prior to MH can qualitatively predict the temperature distribution of the MNP-laden regions.

Real-time volumetric MR thermometry using 3D echo-shifted sequence under an open source reconstruction platform

PurposeThe aim of this work is to implement real-time 3D MR thermometry for high intensity focused ultrasound (HIFU) monitoring. MethodsVolumetric MR thermometry was implemented based on a 3D echo-shifted sequence with short TR to improve temperature sensitivity. The 3D acquisition was accelerated in two phase encoding directions with controlled aliasing in volumetric parallel imaging (CAIPIRINHA). Image reconstruction was run in an open source reconstruction platform (Gadgetron). ResultsPhantom experiments showed the proposed volumetric thermometry was comparable to the fiber optical thermometer. In-vivo animal experiments in rabbit thigh showed that the temperature error before and after 4× acceleration was less than 0.65 °C. Finally, real-time 3D thermometry with temporal resolution ~3 s and spatial resolution 2 × 2 × 5 mm3 (spatial coverage 192 × 192 × 80 mm3) was achieved with Gadgetron reconstruction. ConclusionReal-time temperature monitoring was achieved in-vivo by using parallel imaging accelerated 3D echo-shifted sequence with Gadgetron reconstruction.

Characteristics of temperature distribution in atmospheric pulsed surface dielectric barrier discharge for ozone production

The temperature field distribution in air SDBD (surface dielectric barrier discharge) is investigated by measuring the temperatures of reactive plasma volume (Tp), electrode (Te) and gas (Tg) using the fiber optic thermometer. Results show that Tp is almost the same as Te, while Tg is lower than Tp. Both Tp and Tg follow a first-order model. The temperature in the area between the boundary of the plexiglass surfaces and the electrodes is higher than the temperature in the center. The gas flow rate has little effect on Tp due to that air flow is in steady laminar flow state.

MR safety watchdog for active catheters: Wireless impedance control with real-time feedback.

To dynamically minimize radiofrequency (RF)-induced heating of an active catheter through an automatic change of the termination impedance. A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔTmax . The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built-in thermistor or external data from a fiber-optical thermometer. It automatically changes the catheter input impedance until the temperature rise during MRI is minimized. If ΔTmax is exceeded, RF transmission is blocked by a feedback system. The thermistor and fiber-optical thermometer provided consistent temperature data in a phantom experiment. During MRI, the MRsWD was able to reduce the maximum temperature rise by 25% when operated in real-time feedback mode. This study demonstrates the technical feasibility of an MRsWD as an alternative or complementary approach to reduce RF-induced heating of active interventional devices. The automatic MRsWD can reduce heating using direct temperature measurements at the tip of the catheter. Given that temperature measurements are intrinsically slow, for a clinical implementation, a faster feedback parameter would be required such as the RF currents along the catheter or scattered electric fields at the tip.

Validation of Noninvasive Ultrasound Temperature Measurement System Through Experiments Using Resonant Cavity Applicator.

We developed a resonant cavity applicator for noninvasive deep hyperthermia treatment of osteoarthritis. In previous studies, we confirmed its viability by heating agar phantoms and conducting computer simulations. To evaluate the heating performance of this system on human subjects, it is necessary to develop a new noninvasive temperature measurement system. In this study, we developed a new temperature measurement system utilizing ultrasound imaging techniques. After heating an agar phantom with our resonant cavity applicator, temperature measurements from both our custom-made noninvasive ultrasonic thermometer and an optical fiber thermometer were collected and compared. Both temperature distributions showed a reliable trend, with heat energy concentrated at the center of the agar phantom. Average error rates were less than 13% for temperatures. The results of this study describe the viability of the temperature measurement system and the resonant cavity applicator for clinical applications.

Ex vivo validation of microwave thermal ablation simulation using different flow coefficients in the porcine liver

The purpose of the study was to validate the simulation model for a microwave thermal ablation in ex vivo liver tissue. The study aims to show that heat transfer due to the flow of tissue water during ablation in ex vivo tissue is not negligible. Ablation experiments were performed in ex vivo porcine liver with microwave powers of 60 W to 100 W. During the procedure, the temperature was recorded in the liver sample at different distances to the applicator using a fiber-optic thermometer. The position of the probes was identified by CT imaging and transferred to the simulation. The simulation of the heat distribution in the liver tissue was carried out with the software CST Studio Suite. The results of the simulation with different flow coefficients were compared with the results of the ablation experiments using the Bland–Altman analysis. The analysis showed that the flow coefficient of 90,000 W/(K*m3) can be considered as the most suitable value for clinically used powers. The presented simulation model can be used to calculate the temperature distribution for microwave ablation in ex vivo liver tissue.

A thermometry software tool for monitoring laser-induced interstitial thermotherapy.

The purpose of this study was to develop a thermometry software tool for temperature monitoring during laser-induced interstitial thermotherapy (LITT). C++ programming language and several libraries including DICOM Toolkit, Grassroots DICOM library, Insight Segmentation and Registration Toolkit, Visualization Toolkit and Quasar Toolkit were used. The software's graphical user interface creates windows displaying the temperature map and the coagulation extent in the tissue, determined by the magnetic resonance imaging (MRI) thermometry with the echo planar imaging sequence and a numerical simulation based on the radiation and heat transfer in biological tissues, respectively. The software was evaluated applying the MRI-guided LITT to ex vivo pig liver and simultaneously measuring the temperature through a fiber-optic thermometer as reference. Using the software, the temperature distribution determined by the MRI method was compared with the coagulation extent simulation. An agreement was shown between the MRI temperature map and the simulated coagulation extent. Furthermore, the MRI-based and simulated temperatures agreed with the measured one - a correlation coefficient of 0.9993 and 0.9996 was obtained, respectively. The precision of the MRI temperature amounted to 2.4°C. In conclusion, the software tool developed in the present study can be applied for monitoring and controlling the LITT procedure in ex vivo tissues.

Single fiber temperature probe configuration using anti-Stokes luminescence from Cr:GdAlO3

Single-photon excitation of anti-Stokes-shifted emission from a thermographic phosphor allows operation of a luminescence decay-based single fiber temperature probe with negligible interference from background fiber-generated Raman scattering. While single fiber probe configurations for luminescence-based fiber optic thermometers offer advantages of simple design, compactness, and superior emission light collection efficiency, their effective use has been limited by interference from Raman scattering in the fiber probe and excitation delivery fiber that produces distortion of the luminescence decay that follows the excitation pulse. The near elimination of interference by background fiber-generated Raman scattering was demonstrated by incorporating a Cr-doped GdAlO3 (Cr:GdAlO3) thermographic phosphor as the sensing element at the end of a single fiber luminescence decay-based thermometer and detecting anti-Stokes-shifted luminescence centered at 542 or 593 nm produced by 695 nm excitation. Measurements were performed using both silica (up to 1150 °C) and single-crystal YAG (up to 1200 °C) fiber-based thermometers. Selection of emission detection centered at 542 nm greatly benefited the YAG fiber probe measurements by practically eliminating detection of otherwise significant luminescence from Cr3+ impurities in the YAG fiber. For both the silica and YAG fiber probes, the relative benefit of adopting single-photon excitation of anti-Stokes-shifted luminescence was evaluated by comparison with results obtained by conventional 532 nm excitation of Stokes-shifted luminescence.

Optical Fiber Thermometer Based on Fiber Bragg Gratings

Fiber Bragg grating has generated much interest in use as sensors to measure strain, temperature, and other physical parameters. It also the most common component used to develop this sensor with the advantages of simple, intrinsic sensing elements, electrically passive operation, EMI immunity, high sensitivity, compact size and potentially low cost [6]. This paper reports the design of an optical fiber thermometer based on fiber Bragg gratings. The system was developed for detecting temperature and strain by monitoring the shift of Bragg wavelength. The shifting of Bragg wavelength is used to indicate the temperature and strain due to the change in the surrounding temperature and strain. When the temperature and strain reach the exact wavelength level of the system, the temperature and strain value will display on the Arduino liquid crystal display (LCD). The optical fiber will provide the broadband light source and after passing the FBG the Bragg wavelength into the optical spectrum analyzer (OSA). The system is based on FBG as a physical quantity sensor. The temperatures measured is taken from the water bath and that of the strain is provided by amount of slotted mass used. The outcome of this project is to characterize the Bragg wavelength shifting from the fiber Bragg grating output. As the conclusion, this project provides an efficient optical fiber thermometer in measuring temperature and strain in order to replace the use of conventional electrical instruments.

Synthesis and Magneto–Thermal properties of NiPd nanoparticles

In this study, two NiPd magnetic alloys, i.e., Ni30Pd70 and Ni50Pd50, were synthesized for use in magnetic hyperthermia. The alloys were synthesized using the polyol method and identified using a powder X-ray diffractometer (XRD), transmission electron microscope (TEM), scanning electron microscope–energy dispersive X-ray spectrometer, and vibrating sample magnetometer. The magneto–thermal properties were determined using a fiber optic thermometer and induction heating system.The average crystal sizes of the Ni30Pd70 and Ni50Pd50 alloys were determined to be 3.48 ± 0.04 nm and 2.47 ± 0.11 nm, respectively, based on the XRD patterns. The magnetization measurements indicated that Ni30Pd70 sample exhibited paramagnetic property while the Ni50Pd50 alloy shows superparamagnetic and ferromagnetic behaviors at room temperature. The magnetization versus temperature measurements showed that the blocking temperature of the Ni30Pd70 alloy was less than 10 K and the blocking temperature of the Ni50Pd50 alloy was around 155 K. The specific absorption rate values were calculated to range between 0.2 and 7.6 W g−1 based on magneto-thermal experiments under the AC magnetic field ranging from 8.7 to 23.7 kA/m.

Improvement of Residual Stress Analysis by Prediction of Phase Transformation Behavior with an Optical Fiber Thermometer

Improvement of Residual Stress Analysis by Prediction of Phase Transformation Behavior with an Optical Fiber Thermometer

Evaluation of feasibility of 1.5 Tesla prostate MRI using body coil RF transmit in a patient with an implanted vagus nerve stimulator.

To assess risks of RF-heating of a vagus nerve stimulator (VNS) during 1.5T prostate MRI using body coil transmit and to compare these risks with those associated with MRI head exams using a transmit/receive head coil. Spatial distributions of radio-frequency (RF) B1 fields generated by transmit/receive (T/R) body and head coils were empirically assessed along the long axis of a 1.5T MRI scanner bore. Measurements were obtained along the center axis of the scanner and laterally offset by 15cm (body coil) and 7cm (head coil). RF-field measurements were supplemented with direct measurements of RF-heating of 15cm long copper wires affixed to and submerged in the "neck" region of the gelled saline-filled (sodium chloride and polyacrylic acid) "head-and-torso" phantom. Temperature elevations at the lead tips were measured using fiber-optic thermometers with the phantom positioned at systematically increased distances from the scanner isocenter. B1 field measurements demonstrated greater than 10dB reduction in RF power at distances beyond 28cm and 24cm from isocenter for body and head coil, respectively. Moreover, RF power from body coil transmit at distances greater than 32cm from isocenter was found to be lower than from the RF power from head coil transmit measured at locations adjacent to the coil array at its opening. Correspondingly, maximum temperature elevations at the tips of the copper wires decreased with increasing distance from isocenter - from 7.4°C at 0cm to no appreciable heating at locations beyond 40cm. For the particular scanner model evaluated in this study, positioning an implanted VNS farther than 32cm from isocenter (configuration achievable for prostate exams) can reduce risks of RF-heating resulting from the body coil transmit to those associated with using a T/R head coil.

Validation of a mathematical model for laser-induced thermotherapy in liver tissue.

The purpose of the study was to develop a simulation approach for laser-induced thermotherapy (LITT) that is based on mathematical models for radiation transport, heat transport, and tissue damage. The LITT ablation was applied to ex vivo pig liver tissue. Experiments were repeated with different laser powers, i.e., 22-34 W, and flow rates of the cooling water in the applicator system, i.e., 47-92 ml/min. During the procedure, the temperature was measured in the liver sample at different distances to the applicator as well as in the cooling circuit using a fiber optic thermometer. For validation, the simulation results were compared with the results of the laser ablation experiments in the ex vivo pig liver samples. The simulated and measured temperature curves presented a relatively good agreement. The Bland-Altman plot showed an average of temperature differences of -0.13 ∘C and 95%-limits-of-agreement of ±7.11 ∘C. The standard deviation amounted to ±3.63 ∘C. The accuracy of the developed simulation is comparable with the accuracy of the MR thermometry reported in other clinical studies. The simulation showed a significant potential for the application in treatment planning.

ルビー及び、スピネル結晶の育成と光ファイバー温度計への応用 : バルク成長II

ルビー及び、スピネル結晶の育成と光ファイバー温度計への応用 : バルク成長II

Comparative Study of Extracellular and Intracellular Magnetic Hyperthermia Treatments Using Magnetic Particle Imaging

The purpose of this study was to evaluate the effectiveness of intracellular magnetic hyperthermia treatment (MHT) in comparison with that of extracellular MHT using magnetic particle imaging (MPI). Colon-26 cells were implanted subcutaneously into the backs of 8-week-old male BALB/c mice. When the tumor volume reached approximately 100 mm3, the mice were divided into control (n = 10), extracellular MHT (n = 8), and intracellular MHT groups (n = 7). In the control group, MHT was not performed. In the extracellular MHT and intracellular MHT groups, the tumors were injected directly with magnetic nanoparticles (MNPs) (400 mM Resovist®) and were heated for 20 min using an alternating magnetic field. During MHT, the temperatures of the tumor and rectum were measured using optical fiber thermometers. In the extracellular MHT group, MHT was performed 15 min after the injection of MNPs, whereas MHT was performed one day after the injection of MNPs in the intracellular MHT group. In both groups, MPI images were obtained using our MPI scanner immediately before, immediately after, and 7 and 14 days after MHT. After the MPI studies, we drew a region of interest (ROI) on the tumor in the MPI image and calculated the average, maximum, and total MPI values and the number of pixels within the ROI. Transmission electron microscopic (TEM) images were also obtained from resected tumors. In all groups, tumor volume was measured every day and the relative tumor volume growth (RTVG) was calculated. The TEM images showed that almost all the MNPs were aggregated in the extracellular space in the extracellular MHT group, whereas they were contained within the intracellular space in the intracellular MHT group. Although the temperature of the tumor in the intracellular MHT group was significantly lower than that in the extracellular MHT group, the RTVG value in the intracellular MHT group was significantly lower than that in the control group 2 days or more after MHT and that in the extracellular MHT group 3, 4, and 5 days after MHT. The average MPI value normalized by that immediately before MHT in the intracellular MHT group was significantly higher than that in the extracellular MHT group immediately and 7 days after MHT. The maximum and total MPI values normalized by those immediately before MHT in the intracellular MHT group were significantly higher than those in the extracellular MHT group 7 days after MHT, suggesting that the temporal change of MNPs within the tumor in the intracellular MHT group was smaller than that in the extracellular MHT group. Our results suggest that intracellular MHT is more cytotoxic than extracellular MHT in spite of a lower temperature rise of tumors, and that MPI is useful for evaluating the difference in the temporal change of MNPs in the tumor between extracellular MHT and intracellular MHT.