A HIFU system using annular and strip-electrode arrays with a digital diagnostic array system

A system for high-intensity focused ultrasound (HIFU) has been developed that integrates a digitally controlled diagnostic array system with a multichannel therapy system. HIFU therapy transducer arrays (5 MHz; 35 mm focal lengths; 32 mm diameter) have been tested and employed with the system. The HIFU arrays have central apertures housing a phased array (48 elements; 7.5 MHz center frequency) for tissue visualization. Digital radiofrequency ultrasound echo acquisition is included for assays of induced therapeutic effects before, during, and after HIFU exposures. Simulations tested the ability of this array to induce lesions with repeated short pulses (0.2-0.3 s) designed to expose the heart during sequential periods near end-diastole when cardiac motion is minimal. The variation of lesion size with total duration (number of cardiac cycles treated) was examined using a linear propagation model. Comparison with in-vitro lesions showed that the linear model is often sufficient and particularly useful since it permits rapid evaluations of alternate strategies, which can then be examined in more detail with nonlinear simulations. While in-vitro and in-vivo studies focused on lesion induction, the digital acquisition capabilities of the system are being used to evaluate techniques for positioning HIFU beams and monitoring lesion production. Such information promises to help evaluate nonlinear propagation effects on HIFU beams.