Toward focused ultrasound liver surgery under free breathing

Focused ultrasound surgery is an outstanding novel technique for cancer treatment because it is completely noninvasive with the potential for complete and controlled local tumor destruction. Because focused ultrasound surgery is applied from outside of the patient's body, imaging such as ultrasound or magnetic resonance imaging is required to plan and monitor the intervention. For the treatment of liver tumors, several complexities have to be taken into account, including accessibility of the target and protection of structures at risk. To allow for safe and efficient treatment under free respiration, in which the liver moves significantly, both planning and execution have to be performed specifically according to the patient's individual breathing. This article reviews the state of the art of liver applications, the tremendous challenges of this field, and approaches to overcome these challenges. This includes modeling of the patient-individual breathing cycle, detection of and adaptation to the actual breathing, and simulation and monitoring of the therapy.