Design of applicators for a 27 MHz multielectrode current source interstitial hyperthermia system; impedance matching and effective power

In interstitial heating one of the main requirements for achieving a certain elevated temperature in a tumour is that the effective power per applicator (Peff), i.e. the power which is actually deposited in the tissue, is sufficiently high. In this paper this requirement is discussed for the applicators of the 27 MHz multielectrode current source (MECS) interstitial hyperthermia (IHT) system. To minimize power reflection, the applicator impedance was matched with the generator impedance by adjusting the length of the coaxial cable in between. Transmission line losses, applicator efficiency and subsequently Peff were computed for several applicator types. The actual Peff per electrode was obtained from calorimetric measurements. Experiments with RC loads, which can be seen as perfect applicators, were performed to investigate the effect of mismatching on Peff. Applicator losses were measured for clinically used applicators, both single- and dual-electrode, utilizing saline phantoms. A simple spherical tumour model, using the effective heat conductivity (keff) to account for heat transport, was used to estimate Peff for a given tumour size, implant size and applicator density. Computations of Peff of various MECS-IHT electrodes were in close agreement with the phantom measurements. Most of the initial generator power was absorbed in the transmission line (60-65%). The efficiency of the applicators was about 65%. For both single- and dual-electrode applicators the effective electrode power was found to be about 1 W. Model calculations show that Peff of 1 W is sufficient to reach a minimum tumour temperature of 43 degrees C in well perfused tumours (keff = 3 W m-1 degree C-1), using a typical implant with 2 cm electrodes and 1.5 cm spacing. Mismatching can considerably affect Peff. Both a reduction to almost zero and a two-fold increase are possible. However, because the matching theory is well understood, mismatching is not a serious problem in clinical practice and can even be used to increase Peff if necessary. We conclude that the applicator design and the impedance matching method chosen in the MECS system allow heating to temperatures in the therapeutic range with implants used in clinical practice.     

Air-cooling of direct-coupled ultrasound applicators for interstitial hyperthermia and thermal coagulation

The feasibility of using air-cooling to improve the thermal penetration of direct-coupled interstitial ultrasound (US) applicators was investigated using biothermal simulations, bench experiments, phantom testing, and in vivo thermal dosimetry. Two applicator configurations using tubular US transducers were constructed and tested. The first design, intended for simultaneous thermobrachy-therapy, utilizes a 2.5 mm OD transducer with a central lumen to accommodate a radiation source from remote afterloaders. The second applicator consists of a 2.2 mm OD transducer designed for coagulative thermal therapy. Both designs provide cooling of the inner transducer surface by the counterflow of chilled air or CO2 gas through the annulus of the enclosed applicator. The average convective heat transfer (ha) associated with each applicator was determined empirically from curve-fits of radial steady-state temperatures measured in a tissue-mimicking phantom. High levels of convective heat transfer (ha > 500 W m-2 degrees C-1) were demonstrated in both designs at relatively low flow rates (< 5 L min-1). Transient and steady-state radial heating profiles were also measured in vivo (pig thigh muscle) with and without cooling. The therapeutic radius for hyperthermia (41-45 degrees C) was extended from 5-6 mm (without cooling) to 11-19 mm with air-cooling (4.8 L min-1, airflow 10 degrees C), effectively doubling and tripling the thermal penetration in vivo. Similar improvements were demonstrated at higher temperatures with the thermal coagulation applicator. Biothermal simulations, which modeled the physical, thermal, and acoustic parameters of the air-cooled applicator and surrounding tissue, were also used to investigate potential improvements in heating patterns. The simulated radial heating profiles with transducer cooling demonstrated significantly enhanced thermal penetration over the experimental range of convective transfer, and also agreed with in vivo results. These theoretical and experimental results clearly show air-cooling controls the transducer surface temperature, significantly increases thermal penetration, and produces a greater treatment volume for direct-coupled US applicators in hyperthermia and thermal coagulation.     

Transrectal ultrasound applicator for prostate heating monitored using MRI thermometry

PURPOSE: For potential localized hyperthermia treatment of tumors within the prostate, an ultrasound applicator consisting entirely of nonmagnetic materials for use with magnetic resonance imaging (MRI) has been developed and tested on muscle tissue ex vivo and in vivo. METHODS AND MATERIALS: A partial-cylindrical intracavitary transducer consisting of 16 elements in a 4 x 4 pattern was constructed. It produced a radially propagating acoustic pressure field. Each element of this array (1.5 x 0.75 cm), operating at 1.5 MHz, could be separately powered to produce a desired energy deposition pattern within a target volume. Spatial and temporal temperature elevations were determined using the temperature-dependent proton resonant frequency (PRF) shift and phase subtraction of MR images acquired during ultrasonic heating. Four rabbits were exposed to the ultrasound to raise the local tissue temperature to 45 degrees C for 25 minutes. Six experiments compared thermocouple temperature results to PRF shift temperature results. RESULTS: The tests showed that the multi-element ultrasound applicator was MRI-compatible and allowed imaging during sonication. The induced temperature distribution could be controlled by monitoring the RF power to each transducer element. Therapeutic temperature elevations were easily achieved in vivo at power levels that were about 16% of the maximum system power. From the six thermocouple experiments, comparison between the thermocouple temperature and the PRF temperature yielded an average error of 0.34+/-0.36 degrees C. CONCLUSIONS: The MRI-compatible intracavitary applicator and driving system was able to control the ultrasound field and temperature pattern in vivo. MRI thermometry using the PRF shift can provide adequate temperature accuracy and stability for controlling the temperature distribution.     

Pre-clinical evaluation of a microwave planar array applicator for superficial hyperthermia

Multi-element hyperthermia applicators have an advantage over single-aperture devices in that the power deposition pattern across the applicator surface may be adjusted to improve the resultant temperature distribution. This capability can be used to compensate for irregular tumour geometry as well as heterogeneity of thermal and power absorption parameters within the tissue. This paper evaluates the first commercially available microwave system of this type designed for superficial hyperthermia. The applicator (16-element planar array, 915 MHz, 15.2 x 15.2 cm footprint) was evaluated by the following: (1) measuring absolute SAR distributions in muscle-equivalent liquid phantom with an intervening 1 cm thick layer of fat phantom by scanning a calibrated E-field sensor, and (2) power output measurements using calorimetric methods. The SAR distributions measured for each individual aperture exhibited significant irregularities and differing power deposition patterns. A priori knowledge of these different power deposition characteristics was used to provide appropriate illumination schemes which could be used as initial starting points for producing clinically useful power deposition patterns. Measurements of these composite patterns demonstrate the adjustable nature and flexibility of the heating capabilities of this applicator, which includes 50% iso-SAR coverage that can be extended to the applicator perimeter. This clearly illustrates the clinical utility and potential advantages of this system over single-aperture devices for superficial hyperthermia.     

低功耗微热板ZnO甲烷传感器仿真及性能研究

随着微机电系统(MEMS)的发展,运用该技术的半导体传感器也跟着迅速发展,逐渐走向微型化、集成化和智能化。基于MEMS的微加热板(MHP)的金属氧化物甲烷传感器具有功耗小、响应快等优点,广泛应用于甲烷检测。其中,氧化锌(ZnO)甲烷敏感材料因其灵敏度高、中毒效应小、工作温度低等优点,广受关注。但是,该敏感材料制备的传感器响应性能依然受加热温度及热量分布的强烈影响。使用有限元分析(FEA)软件COMSOL中的Multiphysics模块对物理场中的温度进行仿真分析与比较,揭示了在相同工作条件下加热电极结构对温度分布的影响,优选的微加热板达到300 ℃时需要75 mW左右的功率。在商用微加热板的叉指电极上采用无遮挡全表面溅射氧化锌敏感材料构建ZnO薄膜甲烷传感器,并使用合肥微纳公司HIS9010测试了气体传感器的响应。采用静态测量的方法向1 L的气体腔内注射甲烷气体,经过测试,与现在不同形貌的ZnO相比,本课题组使用的磁控溅射制备的氧化锌薄膜气体传感器,在(1000～10000)×10?6甲烷浓度区间内响应线性度比较好,对浓度为10000×10?6的甲烷响应值达到了30。与国内外商用甲烷传感器的甲烷响应性能进行了对比,结果表明本课题组制作传感器响应更高,更具有应用优势。      

Design of an ultrasonic therapy system for breast cancer treatment

This paper describes the design of a novel ultrasonic therapy system dedicated to the breast cancer treatment and the theoretical investigation of the heating characteristics of the system. The applicator is a cylinder comprised of a stack of rings. Each ring has up to 48 transducers mounted on the inside of the ring and directed towards the centre. The transducers operate in one of two frequency bands (1.8-2.8 MHz and 4.3-40.8 MHz), arranged alternately in each ring. During treatment the patient is positioned in prone position, with the breast immersed in water and surrounded by this array. This design was modelled and optimized by 3-D simulations for a variety of treatment conditions. The simulated results demonstrate that the system has an excellent capability to achieve and maintain a temperature distribution (41.5-44 degrees C) in a quadrant to a whole breast. Initial experiments using a single ring of transducers has been performed to verify the power deposition calculation.     

Effects of magnetic resonance imaging on cardiac pacemakers and electrodes

In phantom studies we investigated the effects of magnetic resonance imaging (MRI) on pacemakers and electrodes. Twenty-five electrodes were exposed to MRI in a 1.5T scanner with continuous registration of the temperature at the electrode tip. Eleven pacemakers (five single chamber and six dual chamber) were exposed to MRI. Pacemaker output was monitored to detect malfunction in VOO/DOO and VVI/DDD modes. A temperature increase at the electrode tip of up to 63.1 degrees C was observed during 90 seconds of scanning. In seven electrodes the temperature increase exceeded 15 degrees C. Although no pacemaker malfunctions were observed in asynchronous pacing mode (VOO/DOO), inhibition and rapid pacing were observed during spin-echo imaging if the pacemakers were set to VVI or DDD mode. Pacemaker function was not impaired during scanning with gradient-echo sequences. Next to pacemaker dysfunction, electrode heating has to be considered a possible adverse effect when exposing patients with pacemakers to MRI.     

Production and manipulation of elevated temperatures in pig abdomen with a three-electrode capacitive heating device

The ability of a three-electrode capacitive heating device operating at 13.56 MHz to produce and effect spatial redistribution of hyperthermic temperatures is demonstrated through abdominal heating studies conducted with 80 kg female and 65 kg male pigs. Temperature-time profiles over the respective heating periods were obtained in anterior and posterior superficial tissue and in selected abdominal organs. At selected times during heating, spatial redistribution of elevated temperatures was effected through adjustment of power settings for one or more of the three electrodes, i.e. through manipulation of the specific absorption rate (SAR) in-vivo.     

Tumor cure and cell survival after localized radiofrequency heating

Radiofrequency electromagnetic fields at 13.56 MHz were used to heat locally EMT-6 sarcomas and KHJJ carcinomas in BALB/cKa mice. Temperature profiles obtained in tumors during treatment showed uniform temperature distribution throughout the tumor volume with no systemic hyperthermia. Temperature could be maintained at a stable level throughout treatment by adjustment of power. Tumors were treated at 43 degrees, 43-5 degrees, and 44 degrees, for 5, 10, 20, 30, and 40 min. The EMT-6 tumor was highly sensitive to cure by radiofrequency heating: a 5-min exposure at 44 degrees resulted in cure of almost 50% of the tumors. Cure rate was a function of temperature and of duration of exposure. The KHJJ carcinoma was somewhat more resistant to cure by radiofrequency heating, although most of the animals treated at 43.5 degrees or above were cured of their tumors. In an effort to explain the remarkable effectiveness of radiofrequency heating, tumor cell survival studies were done on EMT-6 tumors treated in situ. Cell inactivation by radiofrequency heating was similar to that for hot water bath heating. However, direct cell killing cannot account for the observed cures, and an additional mechanism must be responsible for tumor eradication.     

Efficacy of multiple ring and coil electrode radiofrequency ablation catheters for the creation of long linear lesions in the atria

Atrial fibrillation is an arrhythmia that may potentially be treated by creating long linear lesions in the atria to create lines of electrical conduction block. While this has been performed with success with open-heart surgery, it has been proposed that a less invasive catheter-based approach could achieve similar success. Radiofrequency energy catheter ablation was performed in vivo with two novel electrode catheters. Each was an expanding loop design: one with 3 mm ring electrodes; and one with 12.5 mm coil electrodes. Power delivery was controlled automatically with temperature (70 degrees C target) feedback from thermistors embedded in each electrode. A total of 39 lines of ablation were created in the atria of 11 normal dogs. The coil electrodes were more effective in creating lesions than the ring electrodes with a similar prevalence of transmurality (89% vs. 85%) but a higher prevalence of continuous transmurality (35% vs. 5%). Sequential electrode energy delivery was better than simultaneous multipolar delivery due to varying efficiencies of tissue heating. Inadequate heating was observed in 47% of simultaneous versus 1% of sequential multipolar deliveries, and excessive heating in 6% versus 1% of cases, respectively. It is feasible to create linear atrial lesions with an expanding loop electrode catheter. Catheters with coil electrodes are more effective than those with ring electrodes. In order to avoid coagulum formation and inefficient heating, sequential electrode energy delivery is preferable to multipolar delivery.     

方坯直轧工艺中头尾温差消除过程数值模拟

方坯直轧工艺有一个难以避免的问题，即钢坯头尾温差问题，当头尾温差过大时，会对产品长度方向上组织性能均匀性产生不利影响。针对方坯直轧工艺下钢坯“头低尾高”的温度特点，提出采用在精轧前进行“头弱尾强”的变水量冷却策略，或在粗轧前进行“头强尾弱”的变功率感应补热策略，并利用有限元法分别对上述两种过程进行数值模拟，根据计算结果对关键工艺参数进行优化设计，为实际应用提供参考。模拟计算结果表明，对于变水量冷却方式，为消除纵向上线性分布的头尾温差，所需水流密度与轧件长度基本呈抛物线关系；对于变功率感应补热方式，所需补热功率与钢坯长度基本呈线性关系。     

基于脉冲燃烧控制的退火炉热负荷分配模型

脉冲燃烧控制技术以其良好的动态响应性、较高的炉温控制精度、较低的燃气消耗及污染物排放水平等优点,广泛应用于各类加热炉.对于立式退火炉而言,常见的加热模型有3种,即比例模型、窄带钢模型、正常模型.生产中操作人员可以根据带钢在加热段跑偏、瓢曲风险选择相应的模型,但上述这3种模型均无法避免因烧嘴频繁开启和关闭导致的辐射管骤冷...     

六电极连续式石墨化电炉的数值模拟

为了了解六电极电炉在生产过程中电参数和温度场的变化规律,利用ANSYS软件实现炉内物料热电场的数值模拟。通过对六电极电炉电场和温度场的模拟,得到炉内主要发热区和温度分布规律,验证该电炉的可行性与安全性。结果表明:六电极连续式石墨化电炉的主要发热区域集中在相邻电极之间,炉内最高温度达3 093℃;高温区温度分布较为均匀,其温度均在2 360℃以上,可以保证物料的充分石墨化。炉体内壁和电极温度均在安全范围内,六电极连续式石墨化电炉可以实现安全连续生产。     

Modeling of Electromagnetic Field and Liquid Metal Pool Shape in an Electroslag Remelting Process with Two Series-Connected Electrodes

A three-dimensional finite-element model has been developed to understand the electromagnetic field and liquid metal pool shape in an electroslag remelting (ESR) process with two series-connected electrodes. The magnetic vector potential is introduced into the Maxwell’s equations, and the nodal-based method is used to solve a three-dimensional harmonic electromagnetic field. The heat transfer of the solidifying processes of ingot is modeled by a source-based enthalpy method, and the Joule heating is included in an inner source. The results show the main part of the current flows through the slag cap and a little enters into ingot in a two-series-connected electrode ESR system. As the interaction of self-induced and mutual-induced of two electrodes occurs, the skin effect is significantly suppressed by the neighbor effect. A symmetrical pattern of magnetic flux density in a two-series-connected electrode ESR system is displayed. The magnetic flux density between two electrodes is reinforced and reduced at the outside of two electrodes. The maximum Joule heat power density is located at the interface of slag and electrodes, and it decreases with an increase of the electrode immersion depth. The averaged Joule heat power density increases when slag cap thickness is reduced. With the increase of ingot height, the liquid metal pool shape changes from arc shaped to “V” shaped. When the ingot height is more than the diameter in the ESR processes, the liquid metal pool shape is constant.     

Influence of non-uniform material properties and water cooling on current density and temperature profiles in arc furnace electrodes

The influence of the simplifying assumption of constant electrical conductivity on the modelling of current density and temperature profiles in arc furnace electrodes is investigated in comparison with calculations taking into account the complete interdependence of electrical and thermal effects. With respect to the accuracy of the calculated values for UHP arc furnace electrodes it is shown that the classical theory for the skin effect using the approximation of constant electrical conductivity is inferior to an exact numerical evaluation, especially concerning the current distribution. A two-dimensional thermal analysis is performed for combination electrodes consisting of a water cooling shank and a graphite wearing part, in order to demonstrate the cooling effect for the reduction of graphite consumption. In the electrodes considered here, the cooled region in the wearing part covers an axial distance in the order of one electrode diameter.     

Symmetry of Arc Furnace Operation

The electrical asymmetry in the operation of arc furnace with an asymmetric triangular configuration of the electrodes is noted. Experimental data from the DSP-100 furnace permit analysis of how the electrical parameters affect the arc characteristics. Nonuniform power distribution over the phases of the electrofurnace decreases the component of the useful power consumed in heating the metal and slag. The power consumption by the furnace may potentially be reduced by 7.4% and the electrode consumption by 9%. The results confirm the need for research on phase-by-phase regulation of the power of ac arc furnaces.     

Improvement of tumor oxygenation status by mild temperature hyperthermia alone or in combination with carbogen

The effects of mild temperature hyperthermia (MTH) on the oxygenation and radioresponse in rodent tumors were investigated. FSall tumors grown in the legs of C3H mice and R3230 AC tumors grown in the legs of Fischer rats were heated with a water bath and the partial pressure of oxygen (pO2) was determined using the microelectrode method. In FSall tumors, the pO2 measured immediately after heating at 41.5 degrees C for 1 hour was markedly higher than that in the control tumors, whereas heating at higher temperatures for 1 hour decreased the tumor oxygenation. In R3230 AC tumors, heating at 41.5 degrees C for 1 hour caused a moderate increase in the pO2 and heating at 42.5 degrees or 43.5 degrees C for 30 minutes markedly increased the pO2. However, heating at 42.5 degrees C or higher temperatures for 1 hour decreased the pO2 in the R3230 AC tumors. The improvement of oxygenation in FSall tumors by heating at 41.5 degrees C for 1 hour increased the radiation-induced cell death in these tumors. The combination of carbogen breathing with MTH was far more potent than carbogen breathing or MTH alone in increasing tumor oxygenation and potentiating the radiation effect in FSall tumors.     

Electrode discrimination and speech recognition in postlingually deafened adult cochlear implant subjects

This study investigated the relationship between electrode discrimination and speech recognition in 11 postlingually deafened adult cochlear implant subjects who were implanted with the Nucleus/Cochlear Corporation multichannel device. The discriminability of each electrode included in a subject's clinical map was measured using adaptive and fixed-level discrimination tasks. Considerable variability in electrode discriminability was observed across subjects. Two subjects could discriminate all electrodes, and discrimination performance by the remaining nine subjects varied from near perfect to very poor. In these nine subjects, the results obtained from the discrimination tasks were used to create a map that contained only discriminable electrodes, and subjects' performance on speech recognition tasks using this experimental map was measured. Four different speech recognition tests were administered: a nine-choice closed-set medial vowel recognition task, a 14-choice closed-set medial consonant recognition task, the NU6 Monosyllabic Words Test [T. W. Tillman and T. Carhart, Tech. Rep. No. SAM-TR-66-55, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas (1966)] scored for both words and phonemes correct, and the Central Institute for the Deaf (CID) Everyday Sentences test [H. Davis and S. R. Silverman, Hearing and Deafness (Holt, Rinehart, and Winston, New York, 1978)]. Seven of the nine subjects tested with the experimental map showed significant improvement on at least one speech recognition measure, even though the experimental map contained fewer electrodes than the original map. Three subjects' scores improved significantly on the CID Everyday Sentences test, three subjects' scores improved significantly on the NU6 Monosyllabic Words test, and five subjects' scores improved significantly on the NU6 Monosyllabic Words test scored for phonemes correct. None of the subjects' scores improved significantly on either the vowel or consonant tests. No significant correlation was observed between electrode discrimination ability and speech recognition scores or between electrode discrimination ability and improvement in speech recognition scores when programmed with the experimental map. The results of this study suggest that electrode discrimination tasks may be used to improve speech recognition of some cochlear implant subjects, and that each electrode site does not necessarily provide perceptually distinct information.     

Multiphase microstructure in steel bars produced by dieless drawing

In the dieless drawing technology the drawing dies are replaced by a heating device, generally by an induction coil. Bars of different cross-sections, round or even rectangular, with varying dimensions along the length can be produced. By using a cooling box in connection with the heating device this deformation process may also be employed for a thermomechanical treatment of steels. The special cooling strategy with low cooling rates at high temperatures (during ferrite formation) and higher cooling rates at lower temperatures favours the formation of multiphase microstructures (ferrite - bainite/martensite) with a low yield strength but a strong work hardening effect. The experiments were carried out on rods with a diameter of 16 mm of a plain low carbon steel (0.1%C, 0.7%Mn). The specimens were locally heated up to the maximum temperature ?_max that initiates the dieless drawing process, and subsequently cooled with different coolants. The change in yield strength and tensile strength and the corresponding change in the ratio of both could be achieved by variation of ?_max and the cooling conditions. The multiphase microstructure with desired mechanical properties was produced at a strain of about more than 0.45 within the region of ?_max ≈ 900–1000°C and a finale cooling rate of about 20 K/s.     

Effect of skin temperature on multifrequency bioelectrical impedance analysis

This study assessed the effects of changes in skin temperature on multifrequency bioimpedance analysis (MF-BIA) and on the prediction of body water compartments. Skin temperature (baseline 29.3 +/- 2.1 degrees C) of six healthy adults was raised over 50 min to 35.8 +/- 0.6 degrees C, followed by cooling for 20 min to 26.9 +/- 1.3 degrees C, by using an external heating and cooling blanket. MF-BIA was measured at both distal (conventional) and proximal electrode placements. Both distal and proximal impedance varied inversely with a change in skin temperature across all frequencies (5-500 kHz). The change in proximal impedance per degree centigrade change in skin surface temperature was approximately 60% of distal impedance. The change in measured impedance at 50 kHz erroneously increased predicted total body water (TBW) by 2.6 +/- 0.9 liters (P < 0.001) and underpredicted fat mass by 3.3 +/- 1.3 kg (P < 0.0001). Computer modeling of the MF-BIA data indicated changes in predicted water compartments with temperature modifications; however, the ratio of extracellular water (ECW) to TBW did not significantly change (P < 0.4). This change in impedance was not due to a change in the movement of water of the ECW compartment and thus probably represents a change in cutaneous impedance of the skin. Controlled ambient and skin temperatures should be included in the standardization of BIA measurements. The error in predicted TBW is < 1% within an ambient temperature range of 22.3 to 27.7 degrees C (72.1-81.9 degrees F).