A focus control method based on time reversal aided by numerical simulation was implemented to correct focal errors in heterogeneous media by using a 56-element phased array transducer at a frequency of 2 MHz. Two types of acrylic phantom were employed to mimic the acoustic heterogeneities in the human body. Focal errors were significantly reduced by applying the phase correction. Moreover, the effects of amplitude correction, array configuration of the transducer, and transverse wave propagation in an elastic body were examined to improve the focal quality. The results suggested that the ultrasound was effectively converged on the target by correcting the amplitude of the ultrasound, and the accuracy of the focus control was enhanced by changing the array configuration and taking into account the shear elasticity of the elastic body in the simulation.
Various catheter simulators using a computer or blood vessel biomodels have been developed for training of medical students and young physicians. Moreover, we have developed a system to simulate a guidewire in blood vessels that uses both numerical analysis and experimental observation for the quantitative analysis of treatment technique, surgical planning, intra-operative assistance, and to facilitate the design of new guidewires. However, not limited to our group, there is a lack of studies evaluating the motions of both the guidewire and catheter and their interaction in a blood vessel. Therefore, in the present study, we modified our computer-based system and experimental apparatus to evaluate the catheter motion and compared both results. First, we added a mechanism to the experimental apparatus to move and evaluate the catheter in a poly (vinyl alcohol) hydrogel blood vessel model. Second, we added a new catheter model to the calculation. We subsequently evaluated the behaviors of the medical devices (the guidewire and the catheter) by measuring the three-dimensional position and the contact force between the medical devices and the vessel wall. Comparison of the calculation and experimental results showed that the trajectories and the contact forces of both the experimental and numerically analyzed medical devices had the same tendencies. By considering the flexibility of the catheter in both the experimental and numerical analysis methods, we could reproduce the phenomena seen in clinical situations, such as movement of the catheter during the insertion or removal of the guidewire, and movement of the guidewire during the insertion of the catheter.
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