No description available.

Thesis (Doctoral)--Department of Radiation Physics, Lund University Hospital, Lund University. / Added t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (Doctoral)--Department of Radiation Physics, Lund University Hospital, Lund University. / Added t.p. with thesis statement inserted. Includes bibliographical references.

The purpose of this research was to develop three real-time adaptive temperature controllers for hyperthermia heating systems. Each scheme is made adaptive by using a transient Gaussian estimation routine to estimate the tissue blood perfusion and by then using these estimated values either in an optimizing routine, or in an observer, or in both. The optimizing routine uses a steady-state Gaussian estimation technique to optimize the power distribution until the best possible match is obtained between the steady-state temperatures predicted by a treatment model and a prespecified ideal temperature distribution. The observer uses a treatment model to control unmeasured locations. The first adaptive control scheme uses the optimizing routine alone, the second uses the observer alone and the third uses both the optimzing routine and observer. The performance of each of the adaptive control schemes is compared to a standard proportional-integral-derivative (PID) control scheme for one-dimensional simulations of typical treatments. Results comparing the deviation of the controlled temperature distribution to the ideal desired temperature distribution for all locations and all times indicate that the adaptive schemes perform better than the PID scheme. It can be concluded that adaptive control yields improved performance if good a priori knowledge of the treated region tissue and perfusion region boundaries is available. While these control schemes were designed for eventual implementation on a scanned focused ultrasound hyperthermia treatment system, the techniques are applicable to any system with the capability to vary specific power with respect to location and with an unknown distributed energy sink proportional to the temperature elevation.

The purpose of this research was to investigate the feasibility of using high temperature ultrasonic pulses to administer therapeutic hyperthermia treatments independent of changes in blood perfusion and tissue properties. The use of a computer simulation program was used to study the effects of blood perfusion, tissue properties, transducer characteristics, and treatment geometry on the temperature elevation and thermal dose delivered by short high temperature ultrasonic pulses. Experiments were conducted in vitro and in vivo to investigate the effects of blood perfusion changes. Other experiments were carried out in dog thigh muscle to determine the effects of changes in tissue properties. A final study was done where murine melanoma in mice were treated with high temperature ultrasound. Results show that shorter pulse lengths (≤ 2 s) and smaller focal diameters (≤ 3 mm) give practically perfusion independent temperature elevation and thermal dose. Normal fluctuations in tissue properties should not have a significant effect on the treatment provided that proper choice of transducer is made for each individual application. High temperature ultrasonic pulses have also been shown to induce tumor responses. Based on this research, this technique is a feasible means of administering hyperthermia for cancer therapy.

Power deposition in ferromagnetic implants of cylindrical and spherical shape from an externally applied uniform time harmonic radio-frequency magnetic field has been investigated by means of quasi-static analysis. Inductive heating efficiency is related to the relative permeability and temperature dependence of permeability can be exploited to limit the maximum temperature rise to the desired value by proper choice of Curie point of ferromagnetic material. It is found that theoretically calculated power absorption versus orientation of the cylindrical implant with the direction of magnetic field is in good agreement with the experimental results. The parametric studies are based on a two-dimensional finite difference model for calculating temperature distribution in perfused tissues due to induction heating of an array of implants. An approximate analytical model was developed for a large regular array of implants in perfused tissues. The results of the analytical model are compared with those of the numerical model. (Abstract shortened with permission of author.)

No description available.

Thesis (Ph. D.)--University of Washington, 1981. / Vita. Bibliography: leaves [233]-251.

Given the proper conditions, antennas applied in medicine can offer improved quality of life to patients. However the human body proves hostile to typical, analytical antenna design techniques as it is composed entirely of frequency- and temperature-dependent lossy media. By combining optimization techniques with numerical methods, many of these challenges may be overcome. Particle swarm optimization (PSO) models the solution process after the natural movement of groups such as swarms of bees as they search for food sources. This meta-heuristic procedure has proven adept at overcoming many challenging problems in the electromagnetics literature. Therefore, this dissertation explores PSO and some of its variants in the solution of two biomedical antenna problems. Recent advances in biosensor technology have led to miniaturized devices that are suitable for in vivo operation. While these sensors hold great promise for medical treatment, they demand a wireless installation for maximum patient benefit, which in turn demands quite specific antenna requirements. The antennas must be composed of biocompatible materials, and must be very small (no more than a few square centimeters) to minimize invasiveness. Here PSO is applied to design a 22.5 mm × 22.5 mm × 2.5 mm implantable serpentine planar inverted-F antenna for dual-band MedRadio and ISM operation. Measurements reveal the accuracy of the models. Hyperthermia is the process of elevating a patient’s temperature for therapeutic gain. Since the ancient Egyptians, physicians have employed hyperthermia in the destruction of cancerous tumors. Modern implementations typically apply electromagnetic radiation at radio and microwave frequencies to induce local or regional heating. In this dissertation PSO is used to evaluate candidate antennas for inclusion in an array of antennas with the aim of local adjuvant hyperthermia for breast cancer treatment. The nearield of the array is then optimized to induce a uniform specific absorption rate throughout the breast.

A series of hyperthermic, static, torso phantom experiments have been performed. The results are presented in comparison to a two-dimensional, theoretical, electromagnetic model. The 2-D model is assessed for potential use in clinical plannings and evaluations. Included in the assay of this model are comparisons of actual clinical patient data. Theoretically calculated electromagnetic fields and temperatures are obtained using a finite element numerical method (FEM) based on weighted residuals. Two experimental methods of extracting energy deposition data are discussed and utilized: (1) by measuring temperature differentials to calculate specific absorption rates (SAR), and (2) by measuring the square of the E-field directly which relates proportionally to the absorbed power. The employed regional heat source is an annular phased array (APA) operating at 70 MHz. The outcome of the assessment suggests that the results can be quantitative for simple heterogeneous phantom problems, but remain qualitative for clinical evaluative purposes.