Robotically assisted focal spot scanning MRgFUS: Initial in vivo experiments

Abstract

Magnetic Resonance imaging guided Focus Ultrasound Surgery (MRgFUS) is a highly precise method to ablate tissue non-invasively. Commercial MRgFUS systems are typically integrated into the patient table of the MR scanner. The objective of this ongoing project is to establish an MRgFUS therapy unit consisting of a specially designed FUS applicator as add-on for a commercial robotic assistance system. The robot was originally designed for percutaneous needle interventions in whole-body MR scanners. The fully MR compatible robotic system Innomotion™ (Innomedic, Herxheim, Germany) offers six degrees of freedom. The developed FUS treatment applicator features a fix focus ultrasound transducer (ν = 1.7 MHz; f' = 68 mm, NA = 0.44), which is embedded in a water-filled flexible bellow. For FUS application, the therapy unit is directly connected to the head of the robotic system. The treatment region is targeted from above. The system's ability for therapeutic relevant focal spot scanning was tested in a clinical 1.5 T whole body MR scanner in animal experiments with pigs. In vivo trials proved the new add-on MRgFUS system as highly MR compatible. Focal spot scanning experiments were performed and a well-defined pattern of thermal lesions under MRI guidance and online thermometry was created. A total positioning accuracy of the US focus better than 2 mm was estimated which is comparable to existing MRgFUS systems. The combined robotic FUS approach offers accurate, highly flexible focus positioning, and thus, might enable different acoustic target access.