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With the development of clinical diagnostic techniques to investigate the coronary circulation in conscious humans, the in vitro validation of such newly developed techniques is of major importance. The aim of this study was to develop an in vitro model that is able to mimic the coronary circulation in such a way that coronary pressure and flow signals under baseline as well as hyperaemic conditions are approximated as realistically as possible and are in accordance with recently gained insights into such signals in conscious man. In the present in vitro model the heart, the systemic and coronary circulation are modelled on the basis of the elements of a lumped parameter mathematical model only consisting of elements that can be represented by segments in an experimental set-up. A collapsible tube, collapsed by the ventricular pressure, represents the variable resistance and volume behaviour of the endocardial part of the myocardium. The pressure and flow signals obtained are similar to physiological human coronary pressure and flow, both for baseline and hyperaemic conditions. The model allows for in vitro evaluation of clinical diagnostic techniques.

An efficient iterative method for solving quasi-static electromagnetic field problems is presented. A relaxation function is introduced in the quasi-static field equations. Then, the resulting equations can be solved by iteration. The method is similar to the one of solving a Laplace equation by computing the stationary state of a diffusion equation. Next, for a radially layered configuration the numerical results are compared with the results from an existing integral equation method. Subsequently, for a realistic three-dimensional model of a human knee numerical results are arrived at.

The energy deposition pattern within a radially layered fat-muscle phantom, diameter 135 mm, heated by a novel ring capacitor applicator has been determined experimentally as well as theoretically. Good to excellent agreement is found between measured and predicted energy distributions. For the specific absorption rate in the muscle tissue the differences are in general smaller than 6%. When the ring electrodes are placed directly on the phantom surface both measured and predicted energy distributions show the presence of superficial hot spots located within the fat layer at the site of the ring electrodes. The theoretical distributions showed that the radial component of the E-field contributes for more than 90% to the energy absorption at the hot spot in the fatty tissue in front of the ring electrodes. Introducing a small air gap (10 mm) between the phantom surface and the ring electrode results in a decrease of the energy absorption within the fatty tissue at the hot spot location by 30%. Further theoretical analysis of the energy distribution within the inhomogeneous model showed that the intensity of the hot spots at the ring electrodes can be controlled by adjustment of the applicator configuration. Independent of the size of the electrode to phantom gap the specific absorption rate values predicted in the fat-muscle model show a more favorable distribution at a frequency of 27.12 MHz than at 13.56 MHz. For a similar electrode to phantom gap the specific absorption rate within the fatty tissue is approximately two times lower at 27.12 than at 13.56 MHz. For the model calculations performed the best ratio of fat to muscle SAR (0.2) is obtained with distilled water as bolus medium in the gap.