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PubMed1994

Hydralazine at thermoradiotherapy: tumor size and blood flow effects.

PURPOSE: This study was aimed to assess the dependence on tumor size and blood flow of the efficacy of a vasoactive drug hydralazine with thermoradiotherapy. METHODS AND MATERIALS: Experiments were performed on mice bearing SCC-VII tumors with volumes of about 85 and 340 mm3 (7-8 or 11-12 days after transplantation, respectively). Local hyperthermia (water bath, 43 degrees C, 0.5 h) was started 3 h after irradiation of tumors. Hydralazine (2.5 mg/kg, IP) was given 0.5 h before heating. Tumor blood flow was evaluated by laser Doppler flowmetry before, during and up to 2 days after the treatments. RESULTS: It was shown that hydralazine and hyperthermia, even in combination with each other, had very weak anti-tumor effect, especially for 85 mm tumors. The agents also insignificantly enhanced the efficacy of radiotherapy excluding the case of polyradiomodification for 340 mm3 tumors when a dose modifying factor of about 2.0 was achieved. Thermometry showed only a small improvement by HDZ in heating patterns of tumors of both sizes. Meanwhile, the therapeutic efficacy of hydralazine and heat was correlated with the changes in tumor blood flow, first of all with the delayed effects. The radiomodifiers induced only minor and transient suppression of perfusion in the smaller tumors, and more markedly and for longer time decreased blood flow in the larger tumors. In the latter case, the inhibiting effect of the drug plus hyperthermia remained for at least 48 h after the treatment. CONCLUSION: (a) The combined use of hydralazine and heat seems to be advisable only at radiotherapy of rather large advanced tumors; (b) the efficacy of such radiomodification is correlated with prolonged inhibition of tumor blood flow by these agents; and (c) hydralazine and hyperthermia are likely to kill selectively both acutely and chronically hypoxic radioresistant cancer cells.

Animals↗
PubMed1996

Effects of intraoperative irradiation and intraoperative hyperthermia on canine sciatic nerve: neurologic and electrophysiologic study.

PURPOSE: Late radiation injury to peripheral nerve may be the limiting factor in the clinical application of intraoperative radiation therapy (IORT). The combination of IORT with intraoperative hyperthermia (IOHT) raises specific concerns regarding the effects on certain normal tissues such as peripheral nerve, which might be included in the treatment field. The objective of this study was to compare the effect of IORT alone to the effect of IORT combined with IOHT on peripheral nerve in normal beagle dogs. METHODS AND MATERIALS: Young adult beagle dogs were randomized into five groups of three to five dogs each to receive IORT doses of 16, 20, 24, 28, or 32 Gy to 5 cm of surgically exposed right sciatic nerve using 6 MeV electrons and six groups of four to five dogs each received IORT doses of 0, 12,16, 20, 24, or 28 Gy simultaneously with 44 degrees C of IOHT for 60 min. IOHT was performed using a water circulating hyperthermia device with a multichannel thermometry system on the surgically exposed sciatic nerve. Neurologic and electrophysiologic examinations were done before and monthly after treatment for 24 months. Electrophysiologic studies included electromyographic (EMG) examinations of motor function, as well as motor nerve conduction velocities studies. RESULTS: Two years after treatment, the effective dose for 50% complication (ED50) for limb paresis in dogs exposed to IORT only was 22 Gy. The ED50 for paresis in dogs exposed to IORT combined with IOHT was 15 Gy. The thermal enhancement ratio (TER) was 1.5. Electrophysiologic studies showed more prominent changes such as EMG abnormalities, decrease in conduction velocity and amplitude of the action potential, and complete conduction block in dogs that received the combination of IORT and IOHT. The latency to development of peripheral neuropathies was shorter for dogs exposed to the combined treatment. CONCLUSION: The probability of developing peripheral neuropathies in a large animal model was higher for IORT combined with IOHT, than for IORT alone. The dose required to produce the same level of late radiation injury to the sciatic nerve was reduced by a factor of 1.5 (TER) if IORT was combined with 44 degrees C of IOHT for 60 min.

Animals↗
PubMed1996

Local hyperthermia of N2/N3 cervical lymph node metastases: correlationof technical/thermal parameters and response.

PURPOSE: Patients with advanced head and neck carcinomas, primarily nonresectable as well as recurrent cases, were treated in multimodality regimens with radiotherapy, chemotherapy, and local hyperthermia. Commercially available microwave and radiowave applicators were used in 50 patients with N2/N3 cervical lymph node metastases during more than 250 heat treatments. To assess technical suitability, the achieved power densities and thermal parameters were tested for correlation with anatomical and geometrical factors. To assess effectiveness, the response was compared with derived parameters of the achieved temperature distributions. METHODS AND MATERIALS: The temperature measurement points (in thermometry catheters) documented by computerized tomography are labeled according to tissue depth, shielding by osseous structures, and location in relation to the external applicators. Relative and absolute specific absorption rates (SAR) and cooling coefficients are extracted from the temperature-time curves. Time-averaged temperature-position curves are evaluated to obtain index temperatures (T90, T50, T20), minimum/maximum tumor temperatures, cumulative minutes T90 > or = 43 degrees C, and 43 degrees C-equivalent min T90. Radiation dose, treatment time, and chemotherapy regiment are also considered. A response parameter is defined using the pre- and posttherapeutic tumor volumes. A multivariate variance analysis is performed for the dependent variables power density, thermal parameters, and response. RESULTS: A significant correlation exists between power density and absorption, presence of a fat layer, and applicator illumination. The maximum depth is 5 cm, where SAR of >= 10 mW/g are registered. Achieved temperatures at individual measurement points are dependent on the SAR, and to a lesser extent, the perfusion-dependent cooling coefficients, but the index temperature T90 is only significantly related to intratumorally achieved SAR. The thermal gradient (T20-T50) and temperature peak (T20) are significantly influenced by the tumor volume. The response is directly related to the index temperature T90, equivalent minute T90 43 degrees C, and cumulative minutes T90 > or = 40.5 degrees C, and inversely related to the tumor volume. CONCLUSIONS: Local hyperthermia using microwave and radiowave applicators in the head and neck region is a tolerable and clinically practical supplementary therapy used as part of multimodal regimens, and has already been proven to be effective. However, the analyses also demonstrated the limits of currently available technology, and confirm the need for continued methodical research.

Adult↗
PubMed1996

Abdomino-pelvic hyperthermia and intraperitoneal carboplatin in epithelial ovarian cancer: feasibility, tolerance and pharmacology.

PURPOSE: To investigate the feasibility, toxicity, and pharmacokinetics of intraperitoneal (i.p.) carboplatin (CB) with concomitant abdomino-pelvic hyperthermia (HT) in advanced ovarian cancer patients. METHODS AND MATERIALS: Patients with residual disease mainly confined to the peritoneal cavity after platinum based chemotherapy received an initial course of i.p. CB for baseline pharmacokinetics followed by three cycles of i.p. CB with concomitant regional hyperthermia. The goal of HT was to achieve at least 45 min of intraperitoneal temperature > 42 degrees but < 50 degrees C while maintaining normal tissue temperatures < 43 degrees C and systemic body temperatures < 38 degrees C. No analgesic premedication was used. Thermometry was recorded by multisensor fiberoptic probes placed within the peritoneal cavity, bladder, vagina, and oral cavity. RESULTS: Thirteen patients received a total of 31 sessions. Our intraperitoneal temperature goal could not be achieved because of patient intolerance. At best, we could maintain intraperitoneal temperatures > 40 degrees C, for more than 40 min in 7 of 31 sessions. The average values of thermal variables were T90 = 40 degrees C, TAVE = 41 degrees C, TMIN = 38.2 degrees C, and TMAX = 42.9 degrees C. The mean maximum systemic temperature was 38 degrees C. Acute thermal toxicities requiring early interruption of hyperthermia were systemic temperature exceeding 38 degrees C (11 of 31), abdominal pain or generalized distress (20 of 31), and vomiting (2 of 31). Hematological toxicities were not increased by hyperthermia. Pharmacokinetics were consistent with enhanced clearance of CB by HT. Lower radio frequencies (< 75 MHz) achieved better heat deposition in the peritoneal cavity than higher frequencies (> 75 MHz). Two of the 13 patients (a Stage III and a Stage IV patient) are alive with no evidence of disease at 40 and 43 months from treatment. CONCLUSIONS: Intraperitoneal temperatures in the range of 40 degrees C maintained for approximately 40 min can be achieved within the described setting. The probability of successful induction of therapeutic intraperitoneal temperatures appears to be higher when frequencies below 75 MHz are used. Patients who are potentially platinum sensitive and have minimal residual disease could potentially benefit from the combined treatment under the conditions studied. However, this temperature-time range appears inadequate against platinum resistant disease, and/or bulky residual pelvic disease. Alternative approaches such as whole body hyperthermia and carboplatin are warranted to overcome some of the obstacles observed.

Adult↗
PubMed1994

Myoglobin signal as an NMR tissue thermometer: implication for hyperthermia treatment of tumors.

Measuring local tissue temperature is critical in establishing a rational approach for hyperthermia treatment of tumors. We have found that the heme signals of myoglobin provide a unique basis for NMR thermometry in vivo. In particular the 5-methyl heme signal of MbCN exhibits a sharp, temperature-dependent resonance that is distinguishable in the tissue spectrum. Its calibrated chemical shift can then reflect the local tissue temperature in vivo.

Animals↗
PubMed1996

Comparison of esophageal, tympanic, and forehead skin temperatures in adult patients.

STUDY OBJECTIVE: To compare esophageal, tympanic membrane, and forehead skin temperatures in patients undergoing elective surgeries. DESIGN: Prospective clinical study. SETTING: Operating room and postanesthesia care unit of a tertiary care teaching hospital. PATIENTS: 40 adult ASA status I, II and III patients requiring anesthesia and surgery. INTERVENTION: Application of crystalline thermometry strips to the forehead of patients. MEASUREMENTS AND MAIN RESULTS: Concurrent forehead skin, tympanic membrane, and lower esophageal temperatures were measured and compared. The overall bias between esophageal and skin temperatures was 0.3 degrees C, between tympanic membrane and skin was 0.5 degrees C, and between esophageal and tympanic membrane was -0.1 degrees C The limits of agreement (precision) between esophageal and skin temperatures were: -1.64 degrees C to +2.32 degrees C, between esophageal and tympanic membrane were: -1.02 degrees C to +0.74, and between tympanic membrane and skin were: -1.48 degrees C to +2.52 degrees C. There was no significant relation between the change in skin temperature and change in esophageal temperature, whereas there was a weak linear relation between change in skin temperature and change in tympanic membrane temperature (y = -0.03 + 0.09, r = 0.12). CONCLUSION: There was a lack of precision between the clinically accepted measurements (lower esophageal and tympanic membranes and the skin temperature measurement. The data suggest that forehead skin temperature is not interchangeable with standard core temperature measurements, and that sole reliance on the forehead skin measurement in the perioperative setting could adversely affect patient care.

Adult↗
PubMed2005

Effect of simulated shoulder thermal capsulorrhaphy using radiofrequency energy on glenohumeral fluid temperature.

PURPOSE: To determine joint fluid temperatures at different time intervals during treatment with radiofrequency energy (RFE) applied in intermittent and continuous treatment manners under flow or no-flow conditions using a simulated shoulder joint model. TYPE OF STUDY: In vitro measurement of simulated joint fluid temperature during RFE treatment. METHODS: A custom-built jig with a chamber (volume size, 25 mL) was used to mimic the adult human shoulder. Three RFE systems: Vulcan EAS plus TAC-S probe (Smith & Nephew Endoscopy, Andover, MA); VAPR II plus End-Effect Electrode (Mitek, Westwood, MA); and ArthroCare 2000 plus TurboVac 90 degrees probe (ArthroCare, Sunnyvale, CA) were tested in the chamber with saline solution initially set at 23 degrees C. Each RFE probe was applied in a paintbrush pattern on the capsular tissue in the chamber and a fluoroptic thermometry probe was placed 1 cm above the RFE treatment probe to record the fluid temperature. Both intermittent and the continuous treatment manners were tested under flow and no-flow conditions. For each probe/manner/flow combination, 6 bovine capsular tissue specimens were tested (n = 6). All data were recorded using a HyperTerminal software program (Hilgraeve Inc, Monroe, MI) into a personal computer. RESULTS: When using intermittent and continuous treatment manners with flow, all recorded chamber fluid temperatures for all tested RFE probes at each time interval were below 40 degrees C. Under no-flow conditions, with intermittent treatment, the ArthroCare probe caused joint fluid temperatures to exceed 50 degrees C after 70 seconds of RFE treatment. With the continuous treatment, the ArthroCare caused chamber fluid temperatures to exceed 65 degrees C after 2 minutes of treatment. The highest mean recorded chamber fluid temperature was caused by ArthroCare probe, which reached 80 degrees C at 3 minutes. For all probes, continuous treatment caused significantly higher chamber fluid temperatures than intermittent treatment. CONCLUSIONS: The results of this study indicate that using flow during thermal capsulorrhaphy could lower joint fluid temperature to prevent heated joint fluid from killing chondrocytes of articular cartilage, and the intermittent treatment manner caused lower fluid temperature compared with continuous treatment within the RFE-treated shoulder joint. CLINICAL RELEVANCE: Articular cartilage of the humeral head may suffer potential thermal injury from heating of joint fluid during RFE thermal capsulorrhaphy.

Animals↗
PubMed2004

Joule heating and determination of temperature in capillary electrophoresis and capillary electrochromatography columns.

This article reviews the progress that has taken place in the past decade on the topic of estimation of Joule heating and temperature inside an open or packed capillary in electro-driven separation techniques of capillary electrophoresis (CE) and capillary electrochromatography (CEC), respectively. Developments in theoretical modeling of the heat transfer in the capillary systems have focused on attempts to apply the existing models on newer techniques such as CEC and chip-based CE. However, the advent of novel analytical tools such as pulsed magnetic field gradient nuclear magnetic resonance (NMR), NMR thermometry, and Raman spectroscopy, have led to a revolution in the area of experimental estimation of Joule heating and temperature inside the capillary via the various noninvasive techniques. This review attempts to capture the major findings that have been reported in the past decade.

Chromatography↗
PubMed2005

Predictive value of symptom level measurements for complex regional pain syndrome type I.

The validity with respect to presence or absence of CRPS I according to Veldman's criteria was assessed for measured pain, temperature, volume differences and limitations in range of motion. Evaluated were 155 assessments of 66 outpatients, initially diagnosed with CRPS I, but many of them not so on follow up visits. Pain was measured with VAS and McGill, temperature by infrared thermometry, volume differences by water displacement volumeters and limitations in range of motion by universal goniometers. Sensitivity, specificity, positive and negative predictive value of the measurement instruments at different cut-off points was calculated. Combined symptom scores were evaluated in a similar fashion. High sensitivity was found for the VAS, McGill, and range of motion. The specificity was overall lower, but highest values were obtained for volume differences. The positive predictive value was good for all measurement instruments. Negative predictive value was lower, especially for measurement of temperature and volume asymmetries. If sensitivity and specificity are equally important, VAS>3 cm, McGill>6 words, temperature difference>or=0.4 degrees C, volume difference>6.5% and ROM limitation>15% provide the best results. Using these cut off values, the highest value of sensitivity and of sensitivity and specificity combined, was found for a combination of VAS, McGill and ROM. The highest value of specificity was found for different combinations of 3, 4 and 5 instruments, all containing the VAS. We conclude that the measured pain, temperature, volume and range of motion can be used as diagnostic indicators for establishing presence or absence of CRPS I.

Adult↗
PubMed2006

Pre-clinical testing of a phased array ultrasound system for MRI-guided noninvasive surgery of the brain--a primate study.

MRI-guided and monitored focused ultrasound thermal surgery of brain through intact skull was tested in three rhesus monkeys. The aim of this study was to determine the amount of skull heating in an animal model with a head shape similar to that of a human. The ultrasound beam was generated by a 512 channel phased array system (Exablate 3000, InSightec, Haifa, Israel) that was integrated within a 1.5-T MR-scanner. The skin was pre-cooled by degassed temperature controlled water circulating between the array surface and the skin. Skull surface temperature was measured with invasive thermocouple probes. The results showed that by applying surface cooling the skin and skull surface can be protected, and that the brain surface temperature becomes the limiting factor. The MRI thermometry was shown to be useful in detecting the tissue temperature distribution next to the bone, and it should be used to monitor the brain surface temperature. The acoustic intensity values during the 20 s sonications were adequate for thermal ablation in the human brain provided that surface cooling is used.

Animals↗
PubMed2006

Thermotherapy of prostate cancer using magnetic nanoparticles: feasibility, imaging, and three-dimensional temperature distribution.

OBJECTIVES: To investigate the feasibility of thermotherapy using biocompatible superparamagnetic nanoparticles in patients with locally recurrent prostate cancer and to evaluate an imaging-based approach for noninvasive calculations of the three-dimensional temperature distribution. METHODS: Ten patients with locally recurrent prostate cancer following primary therapy with curative intent were entered into a prospective phase 1 trial. The magnetic fluid was injected transperineally into the prostates according to a preplan. Patients received six thermal therapies of 60-min duration at weekly intervals using an alternating magnetic field applicator. A method of three-dimensional thermal analysis based on computed tomography (CT) of the prostates was developed and correlated with invasive and intraluminal temperature measurements. The sensitivity of nanoparticle detection by means of CT was investigated in phantoms. RESULTS: The median detection rate of iron oxide nanoparticles in tissue specimens using CT was 89.5% (range: 70-98%). Maximum temperatures up to 55 degrees C were achieved in the prostates. Median temperatures in 20%, 50%, and 90% of the prostates were 41.1 degrees C (range: 40.0-47.4 degrees C), 40.8 degrees C (range: 39.5-45.4 degrees C), and 40.1 degrees C (range: 38.8-43.4 degrees C), respectively. Median urethral and rectal temperatures were 40.5 degrees C (range: 38.4-43.6 degrees C) and 39.8 degrees C (range: 38.2-43.4 degrees C). The median thermal dose was 7.8 (range: 3.5-136.4) cumulative equivalent minutes at 43 degrees C in 90% of the prostates. CONCLUSION: The heating technique using magnetic nanoparticles was feasible. Hyperthermic to thermoablative temperatures were achieved in the prostates at 25% of the available magnetic field strength, indicating a significant potential for higher temperatures. A noninvasive thermometry method specific for this approach could be developed, which may be used for thermal dosimetry in future studies.

Humans↗
PubMed2005

Microbubbles during radiofrequency catheter ablation: composition and formation.

OBJECTIVES: The purpose of this study was to measure tissue temperatures associated with microbubble formation during radiofrequency (RF) ablation. BACKGROUND: Microbubble formation visualized by echocardiography has been used to indicate excessive tissue heating during RF pulmonary vein isolation. However, little is known about the tissue temperatures associated with microbubble formation. METHODS: Optical fluorometric thermometry probes were used to record tissue temperatures in isolated porcine atrium overlying either lung or esophageal tissue in a saline bath. RF energy was delivered through an irrigated ablation electrode during echocardiographic monitoring for microbubble formation. RESULTS: The maximal recorded tissue temperatures were 81.0 +/- 5.0 degrees C and 88.3 +/- 8.1 degrees C at the time of intermittent (type 1) microbubble formation for lung and esophageal preparations, respectively. During continuous (type 2) microbubble formation, the temperatures were 91.4 +/- 8.2 degrees C and 99.2 +/- 7.8 degrees C, respectively (both P < .001 vs type 1). Tissue temperatures averaged >100 degrees C at the time of "pops." The maximal recorded temperature occurred up to 4 mm deep in the tissues and frequently occurred external to the atrial tissue. The total RF lesion volumes for lung and esophageal preparations were related to the pattern of microbubble formation but not to total power delivered. After generation of type 1 bubbles, up to 60% reductions in RF energy were needed to restore target tissue temperatures of 65 degrees C. Gas chromatographic analysis of the microbubbles was consistent with steam formation. CONCLUSIONS: Microbubble formation during RF ablation represents excessive tissue heating to the point of steam formation. Maximal tissue heating may occur in the adjacent lung and esophagus during cooled ablation.

Animals↗
PubMed2005

Regional hyperthermia combined with radiotherapy for uterine cervical cancers: a multi-institutional prospective randomized trial of the international atomic energy agency.

PURPOSE: Hyperthermia can be used to enhance the effects of radiation, and a combined treatment may, in some circumstances, be an advantage. Uterine cervical cancer is very common in developing countries. The control of locally advanced pelvic tumors is difficult with conventional treatment modalities. Based upon the biologic rationale and in view of the recent advances in heating and thermometry techniques, radiotherapy in combination with hyperthermia was investigated in a multi-institutional prospective randomized trial sponsored by the International Atomic Energy Agency. The primary purpose was to clarify whether the combination of hyperthermia and radiotherapy improves the rate of local control, compared with radiotherapy alone. METHODS AND MATERIALS: A total of 110 patients with biopsy-proven, locally advanced carcinoma of the uterine cervix were randomized to treatment by radiotherapy with or without hyperthermia. The patients were stratified by institution, stage, and histologic type. Each patient received external beam radiation therapy and brachytherapy. For the patients randomized to receive hyperthermia, a minimum of five sessions (60 min each, once per week) were administered, employing a radiofrequency (RF) capacitive heating device. Intratumoral temperature was measured at the first hyperthermic treatment, and at least once more during the course of treatment. The equipment and the policies and procedures at each participating institution except one (Pusan) were personally inspected at least once by the corresponding author, to ensure that quality assurance procedures were in place and were followed for treatment according to the protocol guidelines. The median follow-up period was 466 days for all the patients and 512 days for the surviving patients. RESULTS: The two arms were well balanced with regard to the patient factors, tumor factors, and treatment factors. The overall survival rate at 3 years was 73.2%, and the local control rate was 68.5%. There were no significant differences between the patients treated with or without hyperthermia, either with regard to the survival (p = 0.1893) or the rate of local control (p = 0.58). The survival was significantly worse among the patients with Stage IIb disease who received hyperthermia (p = 0.0162) although there was no difference in their rate of local control (p = 0.7988). Further analysis is necessary to determine if the difference in survival is due to a greater incidence of distant metastases or some other cause. Acute Grade 2-3 toxicity was seen in 10/55 patients (18%) treated by hyperthermia and in 2/55 of the patients (4%) treated without hyperthermia (p = 0.01). There was no significant difference in the late toxicity observed in the two arms. CONCLUSION: This prospective randomized study failed to show any benefit from the addition of hyperthermia to radiotherapy in the treatment of locally advanced carcinoma of the uterine cervix. The acute toxicity was significantly greater among the patients receiving hyperthermia, and the survival was significantly worse among the Stage IIb patients receiving hyperthermia even though there was no difference in the local control rate.

Adult↗
PubMed2005

A practical approach to thermography in a hyperthermia/magnetic resonance hybrid system: validation in a heterogeneous phantom.

PURPOSE: This study investigates the feasibility and accuracy of noninvasive magnetic resonance (MR) monitoring for a system that includes a multiantenna applicator for part-body hyperthermia (SIGMA-Eye applicator, BSD-2000/3D) and a 1.5 Tesla MR tomograph (Siemens Magnetom Symphony). METHODS: A careful electrical decoupling enabled simultaneous operation of both systems, the hyperthermia system (100 MHz, up to 1600 W) and the MR tomograph (63.9 MHz). We used the phase data sets of a gradient echo sequence (long echo time TE = 20 ms) according to the proton frequency shift (PFS) method to determine MR temperature changes. Data postprocessing and visualization was conducted in the software platform AMIRA-HyperPlan. Heating was evaluated in an elliptical Lucite cylinder of 50 cm length filled with tissue-equivalent agarose and a skeleton made from low-dielectric material to simulate the heterogeneity of a real patient. Multiple catheters were included longitudinally for direct thermometry (using Bowman high-impedance thermistors). The phantom was positioned in the 24-antenna applicator SIGMA-Eye employing the integrated water bolus (filled with deionized water) both for coupling the radiated power into the lossy medium and to enable a correction procedure based on direct temperature measurements. RESULTS: In eight phantom experiments we monitored the heating in the applicator not only by repetitive acquisition of three-dimensional MR datasets, but also by measuring temperature-time curves directly at selected spatial positions. For the correction, we specified regions in the bolus. Direct bolus temperatures at fixed positions were taken to aim at best possible agreement between MR temperatures and these direct temperature-time curves. Then we compared additional direct temperature-position scans (thermal maps) for each experiment with the MR temperatures along these probes, which agreed satisfactorily (averaged accuracy of +/- 0.4-0.5 degrees C). The deviations decreased with decreasing observation time, temperature increase, and thermal load to the surroundings (corresponding to bolus heating)-estimating a resolution of, at best, +/- 0.2-0.3 degrees C. The acquired MR temperature distributions give also insight into limitations and control possibilities of regional hyperthermia (annular phased array technology) for various tumor sites. CONCLUSIONS: On-line MR monitoring of regional hyperthermia by using the PFS method is feasible in a phantom setup and can be further developed for clinical applications.

Feasibility Studies↗
PubMed2006

Validity of infrared thermal measurements of segmental paraspinal skin surface temperature.

OBJECTIVE: The purpose of this study was to evaluate the validity of thermal measurements by infrared camera thermometry. METHODS: Seventeen subjects underwent a 30-minute acclimatizing period in a controlled environment room. Thermal recordings were executed at the levels of C4 and L4. Fifteen recordings per segment were acquired in an alternating mode that always started at L4. Each subject was required to participate on 5 occasions. The exclusion criteria for the subjects included the following: no inflammatory disease or fever, no consumption of beverages containing caffeine, and no participation in physical activity 2 hours before the recording session; female subjects could not be menstruating on a day of recording. RESULTS: A total of 2550 recordings for the cervical area and the lumbar area was recorded. Strong significant correlations were found for the left (r = .77) and right (r = .71) lumbar sections (P < .0001) whereas weaker significant correlations were observed for the left (r = .56) and right (r = .63) cervical areas (P < .0001). The limits of agreement (Bland-Altman) showed good relationships but poor interchangeability. CONCLUSIONS: In this study, the infrared cameras showed that they were valid tools in a controlled environment; however, the technique for the cervical measurements needs to be reassessed.

Adult↗
PubMed2004

Quantitative measurement of temperature by proton resonance frequency shift at low field: a general method to correct non-linear spatial and temporal phase deformations.

MRI thermometry methods are usually based on the temperature dependence of the proton resonance frequency. Unfortunately, these methods are very sensitive to the phase drift induced by the instability of the scanner which prevents any temperature mapping over long periods of time. A general method based on 3D spatial modelling of the phase drift as a function of time is presented. The MRI temperature measurements were validated on gel samples with uniform and constant temperature and with a linear temperature gradient. In the case of uniform temperature conditions, correction of the phase drift proved to be essential when long periods of acquisition were required, as bias could reach values of up to 200 degrees C in its absence. The temperature uncertainty measured by MRI was 1.2 degrees C in average over 290 min. This accuracy is coherent with the requirements for food applications especially when thermocouples are useless.

Journal Article↗
PubMed2005

Effects of coil dimensions and field polarization on RF heating inside a head phantom.

Deterioration of radiofrequency (RF) inhomogeneity with increasing static magnetic field in magnetic resonance imaging (MRI) is one of the fundamental challenges preventing their clinical rendition and posing safety hazards. Variation in RF coil designs could help redistribute RF energy absorption over the imaged object. This work is intended to determine experimentally the difference in RF heating produced within a human head phantom by in situ measurement of RF inhomogeneity as a function of coil design utilized at 8 T. The heating patterns of 1/4 wavelength (long) and 1/8 wavelength 11-cm (short) transverse electromagnetic (TEM) coils loaded with a homogeneous human head phantom at 340 MHz were evaluated. In addition, different transmit/receive (T/R) configurations were used in search for the possibility of "hot-spot" formation. Fluoroptic thermometry was used to measure temperatures in multiple positions in a head phantom made of ground turkey breast for RF powers corresponding to a specific absorption rate (SAR) of 4.0 W/kg for 10 min. Numerical simulations were performed to study the general RF power deposition patterns in phantoms at 340 MHz including the effects of field polarization. The temperature increases varied from 0 to 0.8 degrees C for the long RF coil, while the short RF coil produced a maximum temperature change of 0.5 degrees C. Similar to ultra high-field electromagnetic simulations, these measurements revealed low peripheral and high deep-tissue heating at 8 T. The findings indicated that the largest temperature changes for both cases were less than 1 degrees C. While these results showed an increase in localized heating due to RF pulses at 8 T, they highlight that RF inhomogeneity could be redistributed using different RF coil designs through which the hot spots could be made cooler.

Equipment Safety↗
PubMed2005

Functional MRI and NMR spectroscopy of an operating gas-liquid-solid catalytic reactor.

A dynamic in situ study of alpha-methylstyrene catalytic hydrogenation on a single catalyst pellet or in a granular bed is performed using 1H MRI and spatially resolved 1H NMR spectroscopy. Owing to reaction exothermicity, a reciprocating motion of the liquid front within the pellet accompanied by pellet temperature oscillations has been observed. Spatially resolved information on the reactant to product conversion within the catalyst bed has been obtained for a steady-state regime. Two-dimensional 27Al NMR images of alumina catalyst supports and other alumina-containing materials have been detected using moderate magnetic field gradients (80 G/cm) and a two-pulse spin-echo sequence. Temperature dependence of signal intensity and 27Al T1 time of alumina are considered as possible temperature sensors for NMR thermometry applications.

Aluminum↗