Minimization of thermal dose delivery time and development of an isolated kidney phantom: Applications for high intensity focused ultrasound

High intensity focused ultrasound treatments have been proven to be both safe and effective in destroying tumor cells. However, long treatment times have limited the clinical application of this therapy modality. Improved modeling techniques, in both pre-treatment and on-line applications, can help minimize the thermal dose delivery time.; It is known that inclusion of thermally significant blood vessels in bio-thermal models improves their accuracy. A methodology using magnetic resonance angiography is presented for identifying thermally significant blood vessels in perfused, isolated kidneys, specifically for use in bio-thermal model development. Improved organ preparation and refinement of pulse sequence parameters showed an improvement of the number of characterized vessel segments over baseline results. Ultrasound heating experiments showed a decrease in average temperature in the kidney with an increase in flow rate. Thermal convective effects were also seen locally around known vessel locations.; In order to reduce thermal dose delivery times, on-line adjustments must be made to heating and cooling times of the individual pulses. Two studies are presented. The first evaluates a simple exponential tissue heating and cooling model used to minimize dose delivery times. Validated with experimental data, the model proves that optimal heating and cooling times exist as a function of treatment parameters, with higher applied power densities yielding shorter dose delivery times. This exponential model has the 3 ability to be used for fast computational predictions, increasing its potential for use in on-line model predictive control.; The dose delivery time of a fully three-dimensional HIFU treatment can be minimized through the optimization of individual pulses heating and cooling times. Numerical simulations were performed using the three-dimensional Pennes' bio-heat transfer equation. Pre-defined scan paths were evaluated for a variety of treatment parameters, finding that dose delivery time decreased with increasing power density for all scan paths and power density models. In addition, parameters were estimated to simplify the three-dimensional model into simple linear and exponential formulations that could potentially be used in a model predictive controller to make the online adjustments which are necessary to minimize the overall treatment time.