Robust binary feedback control of MR guided volumetric HIFU ablation

Volumetric High Intensity Focused Ultrasound (HIFU) ablation has several advantages as compared to the traditional point-by-point ablation, such as improved energy efficiency and homogeneous thermal lesions with sharp borders [1]. However, there is an increased risk of excessive off-focus heating, especially in the near-field [2], and the thermal lesions can also vary in shape and size due to local differences in thermal tissue parameters as is the case for any predefined sonication procedure. Nearfield heating can be monitored by multiplane volumetric MR thermometry that visualizes the heat development in the target region as well as along the beam-path and in sensitive nearand/or far-field regions. To overcome the problem of variability in size and shape of the thermal lesions, MRI thermometry can be used to dynamically adjust the local acoustic power deposition. This study presents a simple and robust binary feedback control algorithm specifically designed for the volumetric ablation method based on trajectories of concentric outwards-moving circles [1]. The proposed feedback control acts on the time while keeping the sonication power high and constant, in contrast to already published feedback methods that control the power [3]. The main benefit of this approach is that the treatment time is kept as short as possible The efficacy of the binary feedback controlled volumetric ablation is proven in-vivo by comparing the resulting thermal lesion size and the variability of the temperature of volumetric ablations with and without the proposed control method.