Objective
The goal of this research is to determine the feasibility of using a model predictive, thermal dose feedback control system for phased array HIFU treatments.

Methods
We have modified a model predictive control system previously used for a fixed focus single transducer for use in an MR compatible 256 element phased array HIFU system (IGT, Inc). Tests show that our controller is easily interfaced with the PA and can be used to overcome the effects of unknown blood flow values by directly controlling thermal dose in a fully 3D mode (3D MR temperature measurements, 3D model in the model predictive controller, 3D focal zone movement under computerized feedback control and 3D control of thermal dose). Treatment efficacy is guaranteed by the direct control of thermal dose during each heating pulse, while patient safety is similarly directly controlled by maintaining all normal tissue temperatures below user defined safety levels. This control approach is applicable to all heating strategies such as the currently used minimum heating time and minimum cooling time approaches.

Results
Our model predictive, thermal dose feedback control system has been successfully interfaced with an MR compatible phased array HIFU treatment system and tested in vivo.

Conclusions
User specified treatment volumes’ 3D thermal dose distributions can be directly controlled and specified temperature safety constraints can be monitored and maintained through the use of 3D MR temperature measurements, phased array heating and a 3D model predictive, thermal dose feedback control system.