| A control system using a model predictive controller, MR temperature feedback, and ultrasound phased array heating has been designed, simulated, and experimentally validated. A previously developed model predictive controller has been expanded to three dimensions (3-D), where it uses a 3-D thermal model to predict the temperatures, receives 3-D temperature measurements from the MR scanner, and controls the 3-D power deposition trajectory with a 256-element phased array. The controller has also been modified to decrease the treatment time by predicting the dose to be delivered during subsequent cooling, accounting for the dose delivered during the treatment of neighboring regions, and predicting the minimum cooling time between sonications. The performance of the improvements to the control system was compared to openloop baseline treatment protocols published in the literature. In agar phantom experiments, the advanced controller decreased the treatment time by 65%, increased the dose uniformity, and maintained normal tissue safety limits. Preliminary work was also completed to develop a technique for experimental identification of the acoustic model relating the phases and amplitudes of the ultrasound phased array to the resulting power deposition pattern. This model and its inverse would enable the extra degrees of freedom of the array to be more fully utilized in complex situations involving the movement of the focal zone or changes in its shape in heterogeneous tissue. |
