Investigation of active tracking for robotic arm assisted magnetic resonance guided focused ultrasound ablation

Background: Focused ultrasound surgery (FUS) is a technique that does not need invasive access to the patient while allowing precise targeted therapy. Magnetic resonance (MR) guided FUS provides capabilities for monitoring treatments. Considering that the targeted tumours are distributed at different positions, focus repositioning becomes necessary.Methods: We used an MR compatible robot to increase the operational range of FUS application. Active tracking was developed to detect the robotic arm in regards to the MR coordinate system. The purpose of this study was to construct active tracking to allow a wide spatial range of repositioning the FUS transducer that is fast and accurate. The technique was characterised and validated by a series of positioning tests to prove its efficiency for guiding the robot.Results: In the calibration range, the tracking could achieve an accuracy of RMS=0.63 mm. Results of phantom ablation showed a focal scanning precision of Δx=0.4±0.37 mm, Δy=0.4±0.28 mm and Δz=0.7±0.66 mm.Conclusions: The active tracking localisation can be considered as a feasible approach for the MR guided FUS system positioned by a robot