Thermometry System Research Articles

Radiofrequency-induced Heating near Fixed Orthodontic Appliances in High Field MRI Systems at 3.0 Tesla

To assess radiofrequency (RF)-induced heating of fixed orthodontic appliances during acquisition of three different sequences in magnetic resonance imaging (MRI) at 3 Tesla. Ten commonly used fixed orthodontic appliances were investigated utilizing a phantom head and simulating the in vivo intraoral situation. A 3 Tesla MRI system (Intera, Philips Medical Systems, Best, The Netherlands) was used to acquire T1w spin-echo (T1 SE), T1w turbo spin-echo (T1 TSE) and T1w gradient-echo (T1 GRE) sequences in axial orientation. Continuous temperature measurement was performed with a dedicated four channel fluoroptic thermometry system. For each orthodontic appliance temperature probes were placed at three predefined sites in order to perform temperature measurements during MR imaging. The fourth temperature probe was fixed to the neck of the phantom head and served as the reference. Mean temperature alterations were determined for all appliances. Temperature elevations ranged from -0.3 degrees C to 0.2 degrees C and were negligible for all orthodontic appliances investigated. There was no difference in mean temperature alteration for any of the three imaging sequences. Based on the data of our experimental study the radiofrequency-induced heating of orthodontic brackets during high field MRI at 3 Tesla can be categorized as negligibly low. Even the clinical routine examination of the head at 3 Tesla using high-energetic pulse sequences can be applied without hesitation in patients with fixed orthodontic appliances.

Quench-Limited SRF Cavities: Failure at the Heat-Affected Zone

With the recent progress in surface cleaning, the performance of superconducting RF cavities is mostly limited by a quench. It is important to understand the nature of the quench origin. In a common SRF cavity design the RF magnetic field is concentrated near the equatorial weld of the cavity. This weld has long been the major suspect in forming a surface defect, either as an impurity or in an increased surface roughness, that eventually gives rise to a quench. We used surface mounted thermometers to obtain a temperature map of the cavity in the quench region. A high temperature, temporal, and spatial resolution of the thermometry system allows us to pinpoint the quench origin with an accuracy of a few millimeters. We found that the hot-spot precursor forms in the weld heat-affected area rather than in the melted zone. The high resolution optical inspection found surface defects in exactly the same locations as the temperature mapping system. We will describe the measurement techniques and discuss possible scenarios of formation of these defects.

Feasibility of Real-Time MRI With a Novel Carbon Catheter for Interventional Electrophysiology

Background— Cardiac MRI offers 3D real-time imaging with unsurpassed soft tissue contrast without x-ray exposure. To minimize safety concerns and imaging artifacts in MR-guided interventional electrophysiology (EP), we aimed at developing a setup including catheters for ablation therapy based on carbon technology. Methods and Results— The setup, including a steerable carbon catheter, was tested for safety, image distortion, and feasibility of diagnostic EP studies and radiofrequency ablation at 1.5 T. MRI was performed in 3 different 1.5-T whole-body scanners using various receive coils and pulse sequences. To assess unintentional heating of the catheters by radiofrequency pulses of the MR scanner in vitro, a fluoroptic thermometry system was used to record heating at the catheter tip. Programmed stimulation and ablation therapy was performed in 8 pigs. There was no significant heating of the carbon catheters while using short, repetitive radiofrequency pulses from the MR system. Because there was no image distortion when using the carbon catheters, exact targeting of the lesion sites was possible. Both atrial and ventricular radiofrequency ablation procedures including atrioventricular node modulation were performed successfully in the scanner. Potential complications such as pericardial effusion after intentional perforation of the right ventricular free wall during ablation could be monitored in real time as well. Conclusion— We describe a newly developed EP technology for interventional electrophysiology based on carbon catheters. The feasibility of this approach was demonstrated by safety testing and performing EP studies and ablation therapy with carbon catheters in the MRI environment.

Improvements in the NIST Johnson Noise Thermometry System

We have developed a Johnson noise thermometry (JNT) system that is calibrated by precision waveforms synthesized with a quantized voltage noise source (QVNS). Improvements to the QVNS and the cross-correlation measurement electronics have significantly reduced systematic errors and measurement uncertainty. We describe in detail a number of these improvements, such as amplifier performance and frequency response. We also show details of recent measurements that characterize the nonlinearities and distortion properties of the measurement electronics. Finally, we present an uncertainty analysis and discuss the potential for the QVNS-JNT technique to contribute to the redefinition of Boltzmann's constant.

Abstract 2245: Interventional Electrophysiology Studies And Ablation Therapy Under Real Time MRI Guidance - Early Detection Of Complications

Background: Cardiac magnetic resonance imaging (MRI) offers 3D real time imaging with unsurpassed soft tissue contrast without X-ray exposure. However, electrophysiological (EP) examinations of patients with rhythm disorders and ablation procedures are still not possible in the MRI environment. To minimize safety concerns and imaging artifacts, we aimed at developing a setup including catheters for interventional EP based on carbon technology. Methods and Results: The setup, which includes a steerable carbon catheter, was tested for safety, image distortion, pacing and sensing properties, and feasibility of ablation at 1.5 Tesla. MR imaging was performed in two different 1.5-T whole-body scanners. To assess unintentional heating of the catheters by radio frequency (RF) pulses of the MR scanner in vitro , a fluoroptic thermometry system was used to record heating at the catheter tip. In vivo tests for pacing and sensing properties and ablation therapy were performed in eight pigs. There was no significant heating of the carbon catheters while using short, repetitive RF pulses from the MR system. Since there was no image distortion when using the carbon catheters, exact targeting of the lesion sites was possible. During imaging, pacing of in vivo pig hearts and sensing the intra cardiac electrogram was possible without any artifacts. Several RF-ablation procedures, including AV node modulation were performed successfully in the scanner. Potential complications during ablation such as perforation of the RV free wall could be monitored in real time as well. Conclusion: Here we describe a newly developed EP technology for interventional electrophysiology based on carbon catheters. These catheters are suitable for electrophysiological diagnostic and ablation procedures. Their feasibility was demonstrated by performing safety EP studies and ablation therapy with carbon catheters in the MRI environment.

Characterization of a digital microwave radiometry system for noninvasive thermometry using a temperature-controlled homogeneous test load

Microwave radiometry has been proposed as a viable noninvasive thermometry approach for monitoring subsurface tissue temperatures and potentially controlling power levels of multielement heat applicators during clinical hyperthermia treatments. With the evolution of technology, several analog microwave radiometry devices have been developed for biomedical applications. In this paper, we describe a digital microwave radiometer with built-in electronics for signal processing and automatic self-calibration. The performance of the radiometer with an Archimedean spiral receive antenna is evaluated over a bandwidth of 3.7–4.2 GHz in homogeneous and layered water test loads. Controlled laboratory experiments over the range of 30–50 °C characterize measurement accuracy, stability, repeatability and penetration depth sensitivity. The ability to sense load temperature through an intervening water coupling bolus of 6 mm thickness is also investigated. To assess the clinical utility and sensitivity to electromagnetic interference (EMI), experiments are conducted inside standard clinical hyperthermia treatment rooms with no EM shielding. The digital radiometer provided repeatable measurements with 0.075 °C resolution and standard deviation of 0.217 °C for homogeneous and layered tissue loads at temperatures between 32–45 °C. Within the 3.7–4.2 GHz band, EM noise rejection was good other than some interference from overhead fluorescent lights in the same room as the radiometer. The system response obtained for ideal water loads suggests that this digital radiometer should be useful for estimating subcutaneous tissue temperatures under a 6 mm waterbolus used during clinical hyperthermia treatments. The accuracy and stability data obtained in water test loads of several configurations support our expectation that single band radiometry should be sufficient for sub-surface temperature monitoring and power control of large multielement array superficial hyperthermia applicators.

PROBING GRAVITY IN NEO'S WITH HIGH-ACCURACY LASER-RANGED TEST MASSES

Gravity can be studied in detail in near Earth orbits NEO's using laser-ranged test masses tracked with few-mm accuracy by ILRS. The two LAGEOS satellites have been used to measure frame dragging (a truly rotational effect predicted by GR) with a 10% error. A new mission and an optimized, second generation satellite, LARES (I. Ciufolini PI), is in preparation to reach an accuracy of 1% or less on frame dragging, to measure some PPN parameters, to test the 1/r2 law in a very weak field and, possibly, to test select models of unified theories (using the perigee). This requires a full thermal analysis of the test mass and an accurate knowledge of the asymmetric thermal thursts due to the radiation emitted by the Sun and Earth. A Space Climatic Facility (SCF) has been built at INFN-LNF (Frascati, Italy) to perform this experimental program on LAGEOS and LARES prototypes. It consists of a 2 m × 1 m cryostat, simulators of the Sun and Earth radiations and a versatile thermometry system made of discrete probes and an infrared digital camera. The SCF commissioning is well underway. A test of all its subsystems has been successfully completed on August 4, 2006, using a LAGEOS 3 × 3 retroreflector array built at LNF. This prototype has been thermally modeled in detail with a commercial simulation software. We expect to demonstrate the full functionality of the SCF with the thermal characterization of this LAGEOS array by the beginning of September 2006.

Full-field and real-time surface plasmon resonance imaging thermometry

The feasibility of surface plasmon resonance (SPR) imaging thermometry is tested as a potential tool for full-field and real-time temperature field mapping for thermally transient liquid mediums. Using the well-known Kretschmann's analysis [Physik 241, 313 (1971)]. parametric examinations are performed to delineate the effects of important optical properties, including seven different prism materials with different refractive index values and seven different measured dielectric constants for thin gold (Au) films (approximately 47.5 nm in thickness), on the temperature dependence of SPR reflectance intensity variations. Furthermore, a laboratory-implemented real-time SPR thermometry system demonstrates the full-field mapping capabilities for transient temperature field developments in the near-wall region when a hot water droplet (80 degrees C) contacts the Au metal surface (20 degrees C) and spreads either in an air- or in a water-surrounded environment.

Evaluation of sapphire substrate heating behaviour using GaN band-gap thermometry

The recent development of a commercial band-gap thermometry system for wide band-gap materials such as GaN (the k-Space Associates’ “ BandiT TM ”) has allowed a systematic study of the relationship between pyrometric or thermocouple temperature-monitoring methods and the directly determined layer temperature. The wide band gap of GaN gives a weak and sample-dependent coupling to radiant heat sources, and it is common in molecular beam epitaxy (MBE) to use a sputtered Mo coating on the rear of the sapphire substrate to improve the efficiency and consistency of heat transfer. We have investigated the role of this backing layer and the use of a PBN diffuser in an MBE chamber, but similar results are expected to be obtained from band-gap thermometry in a metal-organic vapour phase epitaxy (MOVPE) system. The wide range spectrometer used for the band-edge determination can also be employed in a pyrometric mode, at wavelengths both within the band gap of GaN and above it. The latter is insensitive to thickness oscillations, and is less affected by the presence or absence of a Mo backing layer. Results are presented comparing all these measurement techniques, and analysed to show that the Mo backing does not significantly increase the power coupling into the epitaxial layer, although it does improve the accuracy of pyrometric measurements.

A combustion temperature and species standard for the calibration of laser diagnostic techniques

Optical diagnostic thermometry techniques are not generally traceable to temperature standards and due to their complexity it is often difficult to assess their absolute accuracy. This work aims to address this by calibrating a McKenna premixed flat-flame burner with a high-accuracy Rayleigh scattering thermometry system. By applying corrections for the temperature dependence of the scattering cross section, it has been possible to determine the temperature of a premixed propane/air flame with an uncertainty of less than 1%. The temperature dependence of the differential Rayleigh scattering cross section arises from changes in the mean molecular polarizability and mean molecular anisotropy. Changes in the cross section of up to 2% between room and flame temperatures have been found. The burner and associated gas mixing system are described here as a combustion temperature and species standard allowing the calibration of optical diagnostic techniques.

Re-setting the biologic rationale for thermal therapy

This review takes a retrospective look at how hyperthermia biology, as defined from studies emergingfrom the late 1970s and into the 1980s, mis-directed the clinical field of hyperthermia, by placing toomuch emphasis on the necessity of killing cells with hyperthermia in order to define success.The requirement that cell killing be achieved led to sub-optimal hyperthermia fractionation goalsfor combinations with radiotherapy, inappropriate sequencing between radiation and hyperthermiaand goals for hyperthermia equipment performance that were neither achievable nor necessary.The review then considers the importance of the biologic effects of hyperthermia that occur in thetemperature range that lies between that necessary to kill substantial proportions of cells andnormothermia (e.g. 39–42°C for 1 h). The effects that occur in this temperature range are compellingincluding—inhibition of radiation-induced damage repair, changes in perfusion, re-oxygenation,effects on macromolecular and nanoparticle delivery, induction of the heat shock response andimmunological stimulation, all of which can be exploited to improve tumour response to radiationand chemotherapy. This new knowledge about the biology of hyperthermia compels one to continueto move the field forward, but with thermal goals that are eminently achievable and tolerable bypatients. The fact that lower temperatures are incorporated into thermal goals does not lessen theneed for non-invasive thermometry or more sophisticated hyperthermia delivery systems, however.If anything, it further compels one to move the field forward on an integrated biological, engineeringand clinical level.

Noncontact transient temperature mapping of active electronic devices using the thermoreflectance method

This work presents a demonstration of the applicability and efficacy of an experimental system capable of noninvasively and nondestructively scanning the transient surface temperature of pulsed microelectronic devices with submicron spatial and sub-microsecond temporal resolutions. The article describes the features of the experimental setup, provides details of the calibration process used to map the changes in the measured surface reflectivity to absolute temperature values, and explains the data acquisition procedure used to measure the transient temperature over a given active region. This thermoreflectance thermometry system is shown to be particularly suited for directly measuring the surface temperature field of devices undergoing the fast transients that are typical of next generation microelectronic devices. To illustrate the experimental approach, both quasisteady and transient temperature measurement results are presented for standard MOSFET devices.

Progress on Johnson Noise Thermometry Using a Quantum Voltage Noise Source for Calibration

We describe our progress toward a high-precision measurement of temperature using Johnson noise. Using a quantized voltage noise source (QVNS) based on the Josephson effect as a calculable noise source, we have been able to measure the ratio of the gallium and water triple-point temperatures to within an accuracy better than 100 /spl mu/K/K. We also describe the operation of our Johnson noise thermometry system that could be used as a primary thermometer and possible sources of error that limit our absolute temperature measurements to /spl sim/150 /spl mu/K/K.

A thermometry system for quality assurance and documentation of whole body hyperthermia procedures

Since December 2001, the Department of Oncology and Medical Physics, Haukeland University Hospital, Norway has been conducting whole body hyperthermia (WBH) studies, treating patients with either ovarian carcinoma or non-Hodgkin lymphomas. Accurate and reliable thermometry instrumentation is important in all types of hyperthermia procedures, particularly in WBH, where the target patient body temperature is 41.8°C. Reliable documentation of side-effects in clinical studies is also dependent on precise temperature monitoring, since in this temperature range even small, but systematic, inaccuracies (0.1–0.2°C) in the temperature monitoring is expected to affect the amount of side effects. Readily available heating and temperature data from previous treatment sessions of the same patient is also valuable for precise temperature control in future treatment sessions. The WBH thermometry system implemented at Haukeland University Hospital is described. It is based on commercially available components, including standard medical thermistor probes, and includes a temperature calibration and verification facility. The thermometry system is accurate, reliable, easy to use, comfortable for the patient and relatively inexpensive. By implementing the Steinhart-Hart polynomial fit to standard medical thermistor probe data, it is shown that the WBH treatment thermometers used can measure the patient body temperatures with a short- and long-term accuracy of ± 0.01°C.

Application of mineral thermometers and barometers to granitoid igneous rocks: the Etive Complex, W Scotland

The Etive complex, one of the Caledonian ‘Newer Granites’ of Scotland, is a ring complex of Devonian age, ranging in composition from pyroxene-diorite to leucogranite. Six samples, representing the major rock units in the southern parts of the Etive complex were chosen for mineral chemical studies and for estimation of the pressure and temperature conditions of magmatic crystallisation. Application of Al- in-hornblende barometry and crossite contents of amphiboles indicates a pressure <3 kbar for the intrusion, in good agreement with published independent pressure estimates of ∼2 kbar from mineral equilibria in metasedimentary hornfelses in the Etive thermal aureole. Thermometry, using ternary and binary feldspar systems, yields low temperatures, which probably reflect late-stage, post-magmatic re-equilibration of these minerals. Several geothermometers have been applied to the Quarry Diorite, the outermost intrusion of the complex. The highest temperature for the rocks comes from orthopyroxene–clinopyroxene solvus thermometry, and is ∼1000 °C; this is interpreted to reflect the initial crystallisation of the diorite magma immediately after its emplacement. The maximum temperature from hornblende-plagioclase thermometer is ∼816 °C, which probably reflects late-stage crystallisation of the magma.

Some considerations for a method that simultaneously measures the temperature and emissivity of a metal in a high temperature furnace

This article describes some considerations for designing a practical radiation thermometry system for a glossy metal moving through a high temperature furnace, such as a continuous annealing furnace. In order to accomplish this task, two problems must be solved. The emissivity compensation of an object must be calculated and the furnace’s background radiation noise must be eliminated. The authors have proposed a method that uses the radiance’s polarized directional properties to simultaneously measure the emissivity and temperature to solve the first problem and a technique using a pseudo-blackbody installed in the furnace to solve the second problem. During heating, there is a one-to-one correspondence between the emissivity and the ratio of p- and s-polarized radiances for metals. This characteristic has successfully led to the development of a method for simultaneously measuring the emissivity and temperature of metals regardless of a potential large change in emissivity. Introducing a pseudo-blackbody radiator into a furnace removes the background radiation noise. Moreover, the blackbody radiator supplies a constant reference radiance. This reference plays an important role in maintaining the principle of emissivity-compensated radiation thermometry inside the furnace. Experimental results have simultaneously measured the emissivity and temperature of stainless steel at 1300 K with errors of 12% and 0.96%, respectively. These values were attained even though the s-polarized emissivities change from 0.25 to 0.75 at a wavelength of 0.9 μm. These errors can be achieved by designing the apparatus to have a solid angle, the aperture of the pseudo-blackbody subtended by a measuring point of the specimen, of more than 0.02π steradians. The accuracy of this method is heavily dependent upon the specimen’s surface roughness. The maximum surface roughness that allows for the successful utilization of this method is Ra=0.12 μm.

Magnetic resonance safety testing of a newly-developed fiber-optic cardiac pacing lead.

To assess magnetic resonance (MR) safety for a newly developed, fiber-optic cardiac pacing lead. MR safety was assessed for the fiber-optic cardiac pacing lead by evaluating magnetic field interactions and heating. Translational attraction and torque were evaluated using a 1.5-Tesla MR system and previously described, standardized techniques. MR imaging-related heating was assessed using a 1.5-Tesla MR system and a transmit/receive, body radiofrequency (RF) coil with the fiber-optic lead positioned to simulate an in vivo condition in a saline-filled phantom. The phantom had dimensions similar to a human subject's torso and head. A fluoroptic thermometry system was used to record temperatures on and near the electrodes of the fiber-optic pacing lead at five-second intervals immediately before and during 20 minutes of MR imaging performed at a whole-body-averaged specific absorption rate (SAR) of 1.5 W/kg. Temperatures were also recorded from a reference site during this experiment. Magnetic field interactions for the fiber-optic lead were minimal (deflection angle, 23 degrees; torque, +2). The highest temperature change recorded for the fiber-optic cardiac pacing lead and reference site was +0.8 degrees C. The minor magnetic field interactions and relative lack of heating for the fiber-optic pacing lead indicate that it should be safe for patients with this device to undergo MR imaging procedures using MR systems operating at 1.5-T or less and at a whole-body-averaged SARs up to 1.5 W/kg.

Radiofrequency energy induced heating of bovine capsular tissue: in vitro assessment of newly developed, temperature-controlled monopolar and bipolar radiofrequency electrodes.

This in vitro investigation characterized temperature changes associated with radiofrequency (RF) energy induced heating of bovine capsular tissue using newly developed, temperature-controlled monopolar (Vulcan RF system and Vulcan, TAC-S Electrothermal Probe) and bipolar (VAPR II RF system and VAPR TC RF electrode) RF systems and electrodes. Bovine capsular tissue samples were placed in a saline bath maintained at room temperature. Both RF generators were used at settings of 75 degrees C and 40 W. The RF electrodes were placed in stationary positions on the tissue samples and activated for 1- to 10-s. A fluoroptic thermometry system was utilized to record temperatures at the RF electrode-tissue interface at 1-s intervals. The results indicated that the mean tissue temperatures for the monopolar RF electrode tended to be higher than those produced by the bipolar RF electrode, especially during the 2- to 10-s RF delivery time intervals (P<0.05). Notably, during the 2- to 10-s time intervals the monopolar RF electrode produced mean tissue temperatures that exceeded the set temperature of 75 degrees C (range of differences +1.2 to +15.7 degrees C highest mean temperature 90.7 degrees C). By comparison, the bipolar RF electrode maintained tissue temperatures relatively close to the set temperature(range of differences -3.2 to +2.7 degrees C; highest mean temperature 77.7 degrees C). These findings provide basic temperature profiles for the two new temperature-controlled RF devices.

Automated unit for physical research on quantum crystals at millikelvin temperatures

A cryogenic unit designed for physical research on quantum crystals at ultralow temperatures is described. The unit includes a dilution refrigerator with a hybrid 3He circulation system, an antivibration protection system, and a system of automated control and data acquisition and processing. The construction of the basic units, the thermometry system, the algorithms for measurements, and the software for conducting research on quantum crystals by the method of precision pressure measurements are described. The unit may be used for performing a wide range of tasks in research on various condensed systems at millikelvin temperatures.

Development and evaluation of a 27 MHz multielectrode current‐source interstitial hyperthermia system

Hyperthermia is a cancer therapy, which is mostly applied in combination with radiotherapy. The aim of hyperthermia is to increase tumor temperatures to 40 °C−45 °C. One of the heating techniques that has been developed to be combined with afterloading interstitial radiotherapy (IRT) is 27 MHz current‐source interstitial hyperthermia (IHT). A four‐channel version of a current‐source IHT system had been developed to study the effectiveness of interstitial hyperthermia in combination with IRT in tumors growing in the flank of a rat. Temperatures up to 46 °C at the edges of various solid tumors with volumes in the range 1500–2000 are easily reached within 4–10 min. Furthermore, in a collaboration between the University Hospital Utrecht and the Daniel den Hoed Cancer Center in Rotterdam, a multielectrode current‐source (MECS) IHT‐system for clinical use has been developed. Basically, this system consists of three units. First, the actual heating system, including a 27 MHz electromagnetic power unit and multielectrode applicators. Second, a 196‐channel thermometry system with manganin–constantan thermcouple thermometers. Third, a computer plus treatment control software that provides the connection between the first two units and the operator. The power unit has 2 groups of 32 channels with opposite phase. The power can be controlled separately for each channel. Temperatures are measured with seven‐point thermocouple probes inside applicators or inside extra nonheating catheters. The performance of the MECS‐IHT system was examined, focusing on the efficiency of the power deposition in tissue, the homogeneity of the temperature distribution, and on thermometry accuracy.