J. Pribetich

Non-invasive microwave multifrequency radiometry used in microwave hyperthermia for bidimensional reconstruction of temperature patterns

Microwave radiometry, used routinely since 1984 for non-invasive temperature measurements during hyperthermia sessions for superficial tumours treatment has proven its efficiency for temperature control. From radiometric temperature measurements in two frequency ranges (around 1 and 3 GHz) and superficial (or cutaneous) temperature measurements achieved during hyperthermia sessions, a numerical method to obtain the two-dimensional thermal profile has been developed and implemented. This method is based on hyperthermia simulation from the bioheat equation, the absorbed microwave power calculation in the medium taking into account the radiative diagram of the applicator, and the calculation of radiometric temperatures. From these experimental measurements (radiometric and superficial temperatures, heating power, dielectric and thermal characteristics), a program to determine the bidimensional distribution of temperature during the hyperthermia session has been developed, tested and used during and after clinical treatments.

Complete three-dimensional modeling of new microstrip-microslot applicators for microwave hyperthermia using the FDTD method

Describes a complete 3D modeling using the finite difference time domain (FDTD) method of a new generation of external applicators for microwave hyperthermia used at either at 434 MHz or 915 MHz without any modifications. With this new model, it is possible to obtain theoretical results concerning the variations of the reflection coefficient as a function of frequency, the power deposition inside the heated lossy tissues and the heating patterns. Experimental electromagnetic and thermal characteristics are presented and compared with the theoretical results obtained with the 3D method. >

Complete three-dimensional modeling of new microstrip-microslot applicators for microwave hyperthermia using F.D.T.D. method

Describes a complete 3D modeling using the finite difference time domain (FDTD) method of a new generation of external applicators for microwave hyperthermia used at either at 434 MHz or 915 MHz without any modifications. With this new model, it is possible to obtain theoretical results concerning the variations of the reflection coefficient as a function of frequency, the power deposition inside the heated lossy tissues and the heating patterns. Experimental electromagnetic and thermal characteristics are presented and compared with the theoretical results obtained with the 3D method.<<ETX>>

Modeling of various kinds of applicators used for microwave hyperthermia based on the FDTD method

Interstitial and endocavitary applicators, which have been designed and developed for microwave hyperthermia treatments controlled by microwave radiometry, are modeled using the finite difference time domain (FDTD) method. For each type of applicator, the numerical results concerning the reflection coefficient S/sub 11/, the power deposition, and the heating patterns are given. These results are compared with measurements performed on phantom models of human tissues and show good agreement. Possibilities for future developments are discussed.

Coaxial antenna array for 915 MHz interstitial hyperthermia: design and modelization-power deposition and heating pattern-phased array

Coaxial antennas different in their active length have been designed for use in a complete 915-MHz hyperthermia system with temperature control by microwave radiometry. Heating patterns are reconstructed from the power deposition associated with the bioheat transfer equation. Temperature control is effected by means of microwave radiometry and used in order to determine bioheat parameters. Phased arrays are studied allowing heated volume expansion. >

New 434MHz interstitial hyperthermia system monitored by microwave radiometry: theoretical and experimental results

A new complete microwave interstitial hyperthermia system monitored automatically by microwave radiometry and working at 434MHz is described in this paper. This system, which includes a new radiometer with two internal temperature references, is detailed. All its characteristics for microwave heating and radiometry are presented. The new possibilities are shown through numerous experiments on acrylamide phantom and excised tissues, which have been carried out for different antennae implantation corresponding to the clinical situation. The clinic protocol, associate to the brachytherapy, imposes the use of semi-loop catheters. Coaxial antennae, inserted in these catheters, are not, therefore, positioned in a rectilinear manner but undergo a curve. So, models based on the FDTD formalism are developed to determine the theoretical power deposition. Owing to these models, the effects of this physical motive on radiation diagrams can be taken into account. The results of the power deposition are presented for two antennae. Thermal patterns can then be determined by the solution of the bioheat-transfer equation in the steady state. Also, the comparison of the results given by the new interstitial hyperthermia system with those obtained with the previous 915MHz one shows an improvement of the thermal performances.

Temperature Measurement by Microwave Radiometry: Application to Microwave Sintering

Temperature is a key parameter in industrial manufacturing, and its control is very often directly related to the quality of the products. Microwave-assisted processing has gained worldwide acceptance in powder technologies, in particular for the sintering of ceramic parts. High-energy efficiency, fast heating rate, and new and improved properties of the materials are typically observed. For example, fully dense bodies could be produced with improved mechanical properties due to the finer grain size. In fast-processing conditions, the system is mostly out of thermal equilibrium. A complex temperature-distribution pattern develops inside the heated parts, which can lead to localized melting or detrimental distortions if it is not under control. Today, none of the available thermometric methods (thermocouples, optical fiber, infrared, etc.) gives access to this volumetric information. We propose the use of microwave radiometry to noninvasively measure and control the temperature during the microwave sintering processes.

Modeling of planar applicators for microwave thermotherapy

In order to improve the external applicators used for microwave thermotherapy controlled by microwave radiometry in medical applications, we propose specific planar applicators developed for heating: either annular ones to be used at the frequency equal to 915 MHz or in the shape of a horseshoe (short-circuited ring) for 434 MHz. The final goal of this paper is the realization of a honeycomb network for the treatment of larger areas and greater volumes.

Radiometric sensor for temperature control of food processing

This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented.

Design and modeling of a specific microwave applicator for the treatment of snoring

One of the main objectives of using microwaves in medical applications is to make use of the therapeutic effects resulting from the interaction between electromagnetic waves and biological tissues in order to obtain a local heating. For this purpose, a large number of devices have been designed and tested for various medical applications. We present in this paper the results concerning the design and the modeling of an applicator developed for the treatment of snoring using microwaves.