Multiple Temperature Sensors Research Articles

Comparison of a Saline Irrigated Cooled-Tip Catheter to Large Electrode Catheters with Single and Multiple Temperature Sensors for Creation of Large Radiofrequency Lesions

Several catheter technologies for creating large radiofrequency (RF) lesions are used in clinical practice, but direct comparisons of the pathological lesions created by these technologies are unavailable. The purpose of this study was to compare the safety and efficacy of lesions created by three different large lesion RF ablation technologies. RF lesions were created in all four chambers of 15 mongrel dogs using 10 mm-tip multiple temperature sensor catheters, 10 mm tip single temperature sensor catheters, and 4 mm cooled-tip catheters. Pathological lesions were bisected, and measured after viability staining. A total of 242 (79 large-tip single sensor, 82 large-tip multiple sensor, and 81 cooled-tip) lesions were created. All atrial lesions were transmural but tended to have larger surface areas with the single thermistor large-tip catheter (73.4 +/- 24.8 mm2) compared to either the multithermistor large-tip (60.9 +/- 28.3 mm2) or the cooled-tip (61.9 +/- 28.5 mm2) catheters (p = 0.07), especially those in the IVC-TA isthmus. Depths and volumes of ventricular lesions created by the multiple-thermistor catheter (5.0 +/- 1.5 mm; 260 +/- 168 mm3) were smaller than either the single thermistor (5.7 +/- 1.5 mm; 428 +/- 290 mm3) or cooled-tip (6.1 +/- 1.8 mm; 403 +/- 217 mm3) catheters (p < 0.05). The difference in the depth and volume of lesions made by large-tip single thermistor and cooled-tip catheters was not significant. Char formation occurred during 11% of ablation with the single thermistor catheter, 6% with multithermistor and 8% of cooled-tip catheter (p = NS). There were no complications of ablation. All three catheters reliably created full thickness atrial lesions. For ventricular lesions, depths and volumes were similar for 10 mm-tip single thermistor and cooled-tip catheters. The multithermistor catheter lesions were smaller due to more precise temperature regulated power control. Safety was similar in all 3 groups.

Low-gravity propellant gauging system for accurate predictions of spacecraft end-of-life

This paper describes a low-gravity propellant gauging system (PGS) developed, tested, and patented at Hughes Aircraft Company. The PGS predicts spacecraft end of life (EOL) within ± 2 months or better at midlife for a 15-year nominal mission and is used in the Hughes HS601 geosynchronous communications satellites. The PGS is conceptually simple and strives to minimize hardware required for implementation. It incorporates high-resolution pressure transducers and interconnect valves between existing pressurant and propellant tanks. The PGS employs periodic repressurization of propellant tanks by momentary opening of the interconnect valve between the relatively higher pressure pressurant tank and the propellant tank. Measurements of pressures before and after repressurization allow the determination of gas volume in the propellant tank through gas-law calculations, which in turn yields liquid volume, and hence propellant mass within the tank. The use of the gas law also requires temperature measurements, tor accurate temperature measurement, multiple temperature sensors are employed in each tank, and to enhance further the accuracy, extremely accurate and high-resolution pressure transducers are used as gas thermometers. Prototype testing of the proposed measurement scheme has established confidence in the system's ability to predict spacecraft EOL accurately due to propellant depletion. The PGS is failure-toler ant and does not interfere with normal operation of the propulsion subsystem. The repressurizatioh capability offers an additional advantage of closely controlling the oxidizer-to-fuel-mixture ratio in a bipropellant propulsion system. This, in turn, increases the stationkeeping life by minimizing the propellant residuals associated With depletion of one propellant species before the other.

INVERSE HEAT CONDUCTION PROBLEM OF SIMULTANEOUSLY ESTIMATING SPATIALLY VARYING THERMAL CONDUCTIVITY AND HEAT CAPACITY PER UNIT VOLUME

An inverse heat conduction method for simultaneously estimating spatially varying thermal conductivity and heat capacity per unit volume under the conditions of a flash method type of experiment is developed. The unknown thermal properties are assumed to vary only in the space dimension normal to the slab sample and are modeled with piecewise linear representations. Lacking in the literature are specific requirements that must be satisfied by the number of measurements in the spatial domain in order to ensure uniqueness of the inverse solution. We prepared a series of numerical experiments to provide a better understanding of this issue. Multiple temperature sensors are shown to be necessary to determine spatially varying properties. The effectiveness of the method is illustrated through simulated experimental applications of the method.

A Predictive-Adaptive, Multipoint Feedback Controller for Local Heat Therapy of Solid Tumors

Uniform heating of tumor tissue to therapeutic temperatures without damaging surrounding normal tissue is required for optimal local heat therapy of cancer. This paper describes an algorithm for on-line computer control that will allow the therapist to minimize the standard deviation of measured intratumoral temperatures. The method is applicable to systems incorporating multiple surface and/or interstitial applicators delivering microwave, radiofrequency, or ultrasonic power and operating under control of a small computer. The essential element is a novel predictive-adaptive control algorithm that infers relevant thermal parameters from the responses of multiple temperature sensors as each of the power applicators is briefly turned off. Applied power and effective perfusion are estimated from transient slope changes of the temperature-time curves for each sensor. By substituting these values into a system of linear equations derived from the bio-heat transfer equation, the small computer can calculate the optimal allocation of power among the various applicators (knob settings) to generate most uniform intratumoral temperature distribution with the desired mean, or minimum, tumor temperature.