A perfused tissue phantom for ultrasound hyperthermia

A perfused tissue phantom, developed as a tool for analyzing the performance of ultrasound hyperthermia applicators, was investigated. The phantom, consisting of a fixed porcine kidney with thermocouples placed throughout the tissue, was perfused with degassed water by a variable flow rate pump. The phantom was insonated by an unfocused multielement ultrasound applicator and the temperatures in the phantom were recorded. The results indicate that for testing protocols where tissue phantoms are needed, the fixed kidney preparation offers an opportunity to use a more realistic phantom than has previously been available to assess the heating performance of ultrasound hyperthermia applicators.     

Optimal microwave source distributions for heating off-centertumors in spheres of high water content tissue

A surface distribution of electric dipoles can be used to represent a multielement microwave hyperthermia applicator for noninvasive heating of off-center targets within a spherical high-water-content tissue volume, such as the head. A method for finding the optimal surface distributions for delivering maximum power for arbitrarily located deep tumors in such a uniform spherical volume is presented. The resulting focused power dissipation pattern for any tumor location has a global maximum at the tumor, and also is the largest spherical volume for which no healthy tissue is overheated. The optimization uses spherical field harmonics, centered at the tumor target, summed with suitable complex weights to iteratively minimize surface power. Once the best field distributions are derived, the current sources which generate these distributions are determined. The resulting excitations represent the theoretically ideal spherical microwave hyperthermia configuration that no physical applicator system can surpass     

Induction of hyperthermia using an intracavitary multielementultrasonic applicator

In this paper, the possibility of inducing controlled hyperthermia in rectal or vaginal wall tumors using an intracavitary ultrasonic applicator was investigated. A computer model that took into account the thermal and ultrasonic properties of tissues and surface cooling was used to optimize the transducer parameters to obtain desirable temperature distributions for different perfusion situations in the tumor. Also, an applicator that consisted of a cylindrical array of five independently controllable ultrasonic transducers was developed. This array was then tested in degassed water to determine the functional characteristics. This same applicator, modified to include water cooling of the tissue surface, was tested in vivo in dogs. The temperature distributions were found to be promising and with modifications this approach will be used in clinical treatments of suitable tumors.     

Model-predictive control of hyperthermia treatments

A model-predictive controller (MPC) of the thermal dose in hyperthermia cancer treatments has been developed and evaluated using simulations with one-point and one-dimensional models of a tumor. The developed controller is the first effort in: 1) the application of feedback control to pulsed, high-temperature hyperthermia treatments; 2) the direct control of the treatment thermal dose rather than the treatment temperatures; and 3) the application of MPC to hyperthermia treatments. Simulations were performed with different blood flow rates in the tumor and constraints on temperatures in normal tissues. The results demonstrate that 1) thermal dose can be controlled in the presence of plant-model mismatch and 2) constraints on the maximum allowable temperatures in normal tissue and/or the pulsed power magnitude can be directly incorporated into MPC and met while delivering the desired thermal dose to the tumor. For relatively high blood flow rates and low transducer surface intensities--factors that limit the range of temperature variations in the tumor, the linear MPC, obtained by piece-wise linearization of the dose-temperature relationship, provides an adequate performance. For large temperature variations, the development of nonlinear MPC is necessary.     

Electric-field distribution near rectangular microstrip radiatorsfor hyperthermia heating: theory versus experiment in water

A rectangular microstrip antenna radiator is investigated for its near-zone radiation characteristics in water. Calculations of a cavity model theory are compared with the electric-field measurements of a miniature nonperturbing diode-dipole E-field probe whose 3 mm tip was positioned by an automatic three-axis scanning system. These comparisons have implications for the use of microstrip antennas in a multielement microwave hyperthermia applicator. Half-wavelength rectangular microstrip patches were designed to radiate in water at 915 MHz. Both low (epsilon r = 10) and high (epsilon r = 85) dielectric constant substrates were tested. Normal and tangential components of the near-zone radiated electric field were discriminated by appropriate orientation of the E-field probe. Low normal to transverse electric-field ratios at 3.0 cm depth indicate that the radiators may be useful for hyperthermia heating with an intervening water bolus. Electric-field pattern addition from a three-element linear array of these elements in water indicates that phase and amplitude adjustment can achieve some limited control over the distribution of radiated power.     

Simulations of MAPA and APA heating using a whole body thermalmodel

Simulations of hyperthermia treatments to the extremities and the pelvis with miniannular phased array (MAPA) and annular phased array (APA) applicators have been conducted using a whole-body thermal model of man. The model is an enhanced version of a simpler model and accounts for gross spatial variations in arterial and venous blood temperatures throughout the body during a hyperthermia treatment. Included in the modified model are constitutive relations governing the local thermoregulatory changes in skin and muscle blood flow and sweating during local heating. Results of these simulations reveal that systemic heating is not significant during extremity heating with a MAPA due to the lack of aberrant energy deposition outside of the treated area. A nonthermoregulated tumor can be preferentially heated to therapeutic levels by the MAPA if it is positioned within the central region of the applicator. Simulations of APA treatments show that systemic heating is quite significant when aberrant electromagnetic energy deposition is taken into account. Comparison of simulated results to clinical data indicates that the modified model can predict the deep body temperatures and cardiac output changes in a more realistic manner than the original model     

A patch antenna design for application in a phased-array head and neck hyperthermia applicator

In this paper, we describe a specifically designed patch antenna that can be used as the basis antenna element of a clinical phased-array head and neck hyperthermia applicator. Using electromagnetic simulations we optimized the dimensions of a probe-fed patch antenna design for operation at 433 MHz. By several optimization steps we could converge to a theoretical reflection of -38 dB and a bandwidth (-15 dB) of 20 MHz (4.6%). Theoretically, the electrical performance of the antenna was satisfactory over a temperature range of 15 degrees C-35 degrees C, and stable for patient-antenna distances to as low as 4 cm. In an experimental cylindrical setup using six elements of the final patch design, we measured the impedance characteristics of the antenna 1) to establish its performance in the applicator and 2) to validate the simulations. For this experimental setup we simulated and measured comparable values: -21 dB reflection at 433 MHz and a bandwidth of 18.5 MHz. On the basis of this study, we anticipate good central interference of the fields of multiple antennas and conclude that this patch antenna design is very suitable for the clinical antenna array. In future research we will verify the electrical performance in a prototype applicator.     

Arrays of multielement ultrasound applicators for interstitialhyperthermia

Arrays of multielement ultrasound applicators for interstitial hyperthermia have been developed and tested both in vitro and in vivo. The system includes multielement applicators, a 64 channel RF driving unit, a power measuring unit, a 112 channel multisensor temperature measuring unit, and a water cooling unit. Ninety-five arrays of single-element and nine arrays of three-element ultrasound applicators were designed, built, and characterized by measuring transducer efficiency and ultrasound field distribution. Improved uniformity in the azimuthal direction was achieved by using multiple driving frequencies. In addition, production of ultrasound in a desired sector of the transducer was possible by selecting a suitable frequency. Both in vitro and in vivo experiments showed that 92% of monitored temperature points within the target volume of 30 mm x 30 mm x 35 mm achieved a therapeutic temperature rise (above 5 degrees C) when an array of five three-element applicators were used. These results indicated that the arrays of multielement ultrasound applicators have distinct advantages over present interstitial hyperthermia modalities in terms of the capability to control the temperature distribution with a large catheter spacing. As a conclusion, the feasibility of a practical arrays of multielement ultrasound applicators for interstitial hyperthermia was demonstrated.     

Experimental investigation of an adaptive feedback algorithm forhot spot reduction in radio-frequency phased-array hyperthermia

A computer-controlled adaptive phased array radiofrequency hyperthermia system for improved therapeutic tumor heating is experimentally investigated. Adaptive array feedback techniques are used to modify the electric-field in hyperthermia experiments with a homogeneous saline phantom target. A hyperthermia phased-array antenna system has been modified to implement adaptive nulling and adaptive focusing algorithms. The hyperthermia system is a ring phased-array antenna applicator with four independently controlled RF transmitter channels operating at a CW frequency of 100 MHz. The hyperthermia phased array is made adaptive by software modifications which invoke a gradient-search feedback algorithm that controls the amplitude and phase of each transmitter channel. The gradient-search algorithm implements the method of steepest descent for adaptive nulling (power minimization) and the method of steepest ascent for adaptive focusing (power maximization). The feedback signals are measured by electric-field short-dipole probe antennas. The measured data indicate that with an adaptive hyperthermia array it may be possible to maximize the applied electric field at a tumor position in a complex scattering target body and simultaneously minimize or reduce the electric field at target positions where undesired high-temperature regions (hot spots) occur     

基于混合优化算法的神经元PID控制策略

为解决传统比例-积分-微分(PID)控制器在实际工业过程中难以满足控制要求的问题,将二次型性能指标引入到神经元的加权系数的调整中,并利用自学习功能构成了神经元自适应PID控制器.利用混沌优化算法和最速下降法结合起来的混合优化算法,对神经元自适应PID控制器的学习速率和神经元比例系数进行了优化.仿真实验和结果分析表明:该混合优化神经元自适应PID控制器具有很好的动态和静态性能,系统的稳定性和鲁棒性增强,学习参数选择的盲目性和对经验的高度依赖性降低.     

Optimal power deposition with finite-sized, planar hyperthermiaapplicator arrays

Improved hyperthermia applicator technology is allowing finer spatial power resolution within the heated tissue volume. Effective utilization of these planar applicator arrays requires an understanding of the interrelationships between the lateral dimensions of the tumor and the applicators, the power field produced by the applicators, the amount of surface cooling, the tumor tissue blood perfusion, and the normal tissue blood perfusion. These interrelationships are investigated using three-dimensional power patterns and temperature fields produced by optimizing the power amplitudes of the individual applicators located within an array of small, but finite, planar applicators. Five major conclusions are obtained. First, optimization works and is effective in determining optimal power fields. Second, for optimal treatments the lateral dimensions of a single superficial applicator need to extend beyond the tumor boundary. Third, surface cooling is needed to reduce the high normal tissue temperatures at shallow depths. Fourth, finer power resolution becomes more important as the tumor size decreases, but, little improvement in the temperature field is achieved beyond a 3 x 3 array configuration. Fifth, increasing the normal blood perfusion rate can decrease the temperature on the tumor boundary if direct power deposition on that boundary is unavailable.     

Power deposition properties of a travelling-wave applicator forinterstitial hyperthermia

An interstitial hyperthermia applicator is described that is capable of providing uniform heating over an extended range of depths. The applicator utilizes lossy two-wire transmission lines that are terminated in p-i-n diodes that may be biased on or off. A pair of these transmission lines within a single applicator allows a variety of symmetrical and asymmetrical patterns to be produced. Theoretical predictions of the applicator's performance are provided that are based on empirically determined transmission line characteristics     

Experimental Investigation of a Retro-Focusing Microwave Hyperthermia Applicator: Conjugate-Field Matching Scheme

A seven-element array of dielectric-loaded open-ended waveguides totally immersed in a water tank is tested as a possible hyperthermia applicator. Experimental results show a substantial increase in focusing ability of the array if a conjugate matching scheme is used to adjust the phase of each element excitation. This scheme could offer a practical procedure for operating a focused hyperthermia applicator in a living patient.     

The RF toroidal transformer as a heat delivery system for regionalhyperthermia

A novel working principle for a RF (radio-frequency) hyperthermia applicator, suitable for heating large cylindrical volumes of coaxial loads, is described. The system includes a toroidal inductor as an active device producing an almost uniform electric field, which is polarized along the toroidal z axis in the space inside the toroidal ring where the conductive tissue is placed. This electric field produces axial RF currents which, in turn, produce the required heating, provided that a closed loop is formed by electrically connecting the conductive load through capacitive ring (CR) electrodes to form an electric circuit closed externally to the toroidal inductor. This system behaves like a toroidal transformer (TT), the secondary circuit of which includes the dissipative load between the CR electrodes     

Thin linear thermometer arrays for use in localized cancer hyperthermia

A thin linear array of silicon diodes has been developed to measure one-dimensional temperature profiles in tissue during treatment of cancer by localized hyperthermia. The array is composed of six discrete diodes on three flexible stainless steel wires, with a maximum cross-sectional dimension of 0.5 mm, so that it can be introduced into a tumor area via a small puncture wound. Temperature data are extracted using an external electronics system under microprocessor control; the present overall accuracy of the system is 0.2°C over the range of 37-45°C. The array has been tested in ultrasound, RF, and microwave heating fields. Computer simulation shows this array to be nonperturbing of the thermal field in tissue, so that it can provide accurate temperature data. Development of a batch-fabricated array of twenty diodes on five leads is under way. A monolithic silicon diode array is shown to produce large temperature perturbations because of its high thermal conductivity, while an alternative technology using silicon micromachining and adaptations of existing techniques for lead fabrication should produce an array of low thermal conductivity which can obtain accurate measurements. The present and future arrays should also be suitable for data collection in many in-vivo situations other than hyperthermia.     

A spherical-section ultrasound phased array applicator for deeplocalized hyperthermia

Computer simulation shows that a new ultrasound phased-array with nonplanar geometry has considerable potential as an applicator for deep localized hyperthermia. The array provides precise control over the heating pattern in three dimensions. The array elements form a rectangular lattice on a section of a sphere. Therefore, the array has a natural focus at its geometric center when all its elements are driven in phase. When compared to a planar array with similar dimensions, the spherical-section array provides higher focal intensity gain which is useful for deep penetration and heat localization. Furthermore, the relative grating-lobe level (with respect to the focus) is lower for scanned foci synthesized with this array (compared to a planar array with equal center-to-center spacing and number of elements). This could be the key to the realization of phased-array applicator systems with a realistic number of elements. The spherical-section array is simulated as a spot-scanning applicator and, using the pseudo-inverse pattern synthesis method, to directly synthesize heating patterns overlaying the tumor geometry. A combination of the above two methods can be used to achieve the desired heating pattern in the rapidly varying tumor environment.     

Radiation patterns of dual concentric conductor microstrip antennasfor superficial hyperthermia

The finite difference time domain (FDTD) method has been used to calculate electromagnetic radiation patterns from 915-MHz dual concentric conductor (DCC) microwave antennas that are constructed from thin and flexible printed circuit board (PCB) materials. Radiated field distributions are calculated in homogeneous lossy muscle tissue loads located under variable thickness coupling bolus layers. This effort extends the results of previous investigations to consider more realistic applicator configurations with smaller 2 cm-square apertures and different coupling bolus materials and thicknesses, as well as various spacings of multiple-element arrays. Results are given for practical applicator designs with microstrip feedlines etched on the backside of the PCB antenna array instead of previously tested bulky coaxial-cable feedline connections to each radiating aperture. The results demonstrate that for an optimum coupling bolus thickness of 2.5-5 mm, the thin, flexible, and lightweight DCC antennas produce effective heating to the periphery of each aperture to a depth of approximately 1 cm, and may be combined into arrays for uniform heating of large area superficial tissue regions with the 50% power deposition contour conforming closely to the outer perimeter of the array     

ALFC of hybrid multi-generation power system using UC and TCPS by ANFIS control technique

ABSTRACT

This paper reveals the impact of an ultra-capacitor (UC) and thyristor control phase shifter (TCPS) on frequency stability of large hybrid interconnected power system. The impact of UC and TCPS has been studied for general purpose hybrid generated multi areas power system. Further to this, an adaptive neuro fuzzy inference system (ANFIS) is is proposed for automatic load frequency control (ALFC). Thermal and reheat thermal plants are connected in Area-1 and area-2, whereas area-3 has hydro plant and area-4, 5, 6 consists of nuclear power plant, diesel power and gas turbine plant, respectively. A micro grid based on Solar Photovoltaic (PV) system and fleet of electric vehicle (EV) system is developed and integrated with load side of area-1 for load management in interconnected grid. Effect of Small load change and large load change are discussed in separate cases. The controllers are tuned by adding sliding surface to enhance the performance. A comparison between ANFIS and PI-based control approaches with and without UC and TCPS exhibits the superiority of ANFIS controller by integrating UC and TCPS. The results of the proposed control technique are compared with already published results.     

Theoretical and experimental analysis of air cooling forintracavitary microwave hyperthermia applicators

An intracavitary microwave antenna array system has been developed and tested for the hyperthermia treatment of prostate cancer at Thayer School of Engineering and Dartmouth-Witchcock Medical Center. The antenna array consists of a choked dipole antenna inserted into the urethra and a choked dipole antenna eccentrically embedded in a Teflon obturator inserted into the rectum. To prevent unnecessary heating of the healthy tissue that surrounds each applicator, an air cooling system has been incorporated into the rectal applicator. The air cooling system was designed and modeled theoretically using a numerical solution of heat and momentum equations within the applicator, and an analytical solution of the Pennes bioheat equation in tissue surrounding the applicator. The 3D temperature distribution produced by the air-cooled rectal applicator was measured in a perfused canine prostate     

基于预测控制的Fuzzy-PID控制器算法研究

针对常规Fuzzy-PID控制器存在的问题,提出了一种基于预测控制的Fuzzy-PID控制器算法,并给出了预测部分的数学推导过程.该算法无需建立精确的数学模型,能大大改善控制器性能,使其对受控对象的适应能力加强.基于预测控制的Fuzzy-PID控制器为解决工业过程中非线性、时变、大滞后环节的控制问题提供了一个有效的方案,在热工控制领域具有较好的应用前景.