Muscle Phantom Research Articles

Performance characteristics of a helical microwave interstitial antenna for local hyperthermia.

A helical microwave antenna has been designed to improve heat deposition by interstitial applicators used for clinical hyperthermia. Iso-specific-absorption-rate (SAR) curves of the helical antenna as well as a conventional monopole antenna were measured and compared in both muscle and brain tissue phantoms. The heating pattern of the helical antenna is more uniform along the length of the antenna which has important implications for multiarray implant configurations.

Field penetration of arrays of compact applicators in localized hyperthermia.

The three-dimensional analysis of a range of new compact applicators indicates that there is an optimum operating frequency for maximum depth of field penetration and a given applicator size. The prospect of obtaining increased penetration depth by deploying more than one applicator is considered and assessed for an equi-phase array of compact applicators arranged symmetrically around a cylindrical shaped volume of uniform muscle phantom material; field penetration curves enable the maximum cross-section that can be heated to be assessed. Experiments at 200 MHz and results from a three-dimensional analysis demonstrate the usefulness of the assessment and establish that in multi-applicator configurations the field penetration decreases markedly for cross-sectional diameters in excess of 10 cm. However, the three-dimensional analysis for four applicators also shows that more uniform fields are obtained in the muscle phantom when it is surrounded by a low loss bolus region. In conclusion the clinical implications of the investigations are briefly discussed.

Identification of periodic, specular, and diffusely scattering structures in skeletal muscle and tissue-mimicking phantoms via generalized Rician statistics

Identification of periodic, specular, and diffusely scattering structures in skeletal muscle and tissue-mimicking phantoms via generalized Rician statistics

Absorption of microwave energy by muscle models and by birds of differing mass and geometry.

Spheres composed of phantom muscle of radius 1.5, 2, 3, 4, 6 and 8 cm, as well as birds (parakeets, quail, pigeons, chickens, turkeys) were exposed to far-field plane waves at power densities of incident radiation between 182 and 560 mW/cm2 and at frequencies of 775, 915 and 2450 MHz. Specific absorption rate (SAR) patterns were determined by thermographic techniques for both spheres and birds. The measured SAR patterns in spheres were comparable to those from theoretical predictions. The SAR patterns in birds, however, varied markedly from those obtained from spheres of comparable mass. The results indicate that the geometrically complex animal is not represented by simple geometric models for making absorption studies. Thermograms of birds exposed in the flying position indicated that the SAR is high in the wings. The behavioral response of the birds to the exposure was variable. Threshold power densities for biological or behavioral reactions were determined for each bird at all three frequencies. The lowest power density associated with reactivity by the chicken was 5.8 mW/cm2 (corresponding to SARs of 3.1 W/kg in the head and 3.9 W/kg in the neck) at 775 MHz.

Microstrip Loop Radiators for Medical Applications

Three microstrip loop radiators designed to operate at frequencies of 433, 915, and 1300 MHz are described. Empirical design methods and experimental results obtained with phantoms and human tissues are presented. The radiators are relatively well matched when applied to water boluses followed by muscle phantoms or human tissues. When used with the boluses, the radiators have circular surface-temperature distribution while the in-depth heating patterns are similar to those of the aperture-type radiators.

The Performance of a New Direct Contact Applicator for Microwave Diathermy

A direct contact applicator, specifically designed for microwave diathermy at the Industrial, Scientific Medical (ISM) frequency of 2.45 GHz was evaluated by studying near-field patterns in free space, thermographic heating patterns in phantoms of simulated fat and muscle tissue, and associated leakage radiation. The main features are a circular waveguide with a short conical flare horn output section surrounded by an annular choke and two sets of dual posts to generate far-field circular polarization. The significant near field components of the therapeutic beam are in a transverse plane, parallel to the aperture. Heating patterns on the exposed surface of muscle phantoms and inside fat-muscle phantoms are spatially similar and relatively uniform. The leakage level is 0.8 mW/cm/sup 2/ per 100 W of forward power for direct contact and 4 mW/cm/sup 2/ per 100 W of forward power for a 1-cm air gap between aperture and planar phantoms. The uncertainty of these leakage measurements is /spl plusmn/2 dB. This investigation demonstrates the technical feasibility of a safe and effective direct contact microwave diathermy applicator operating at 2.45 GHz. The applicator is a viable candidate for hyperthermia appllications.