Needle-Guiding Robot for Laser Ablation of Liver Tumors Under MRI Guidance

This paper presents the design, control, and experimental evaluation of a needle-guiding robot intended for use in laser ablation (LA) of liver tumors under guidance by magnetic resonance imaging (MRI). The robot provides alignment of a needle guide inside the MRI scanner bore and employs manual needle insertion. In order to minimize MR-image deterioration, the robot is actuated using plastic pneumatic cylinders and long pipes connecting to control valves located outside the MRI scanner room. A new time-delay control scheme was employed to achieve high position accuracy without requiring pressure or force measurements in the MRI scanner. The control scheme was compared with experiments to a previously developed sliding mode controller. A marker localization method based on the convolution theorem of Fourier transform was employed to register the robot in the MRI scanner coordinate system and to verify the position of the needle guide before the manual needle insertion. Experiments in a closed-bore MRI scanner showed a variation in SNR below 5%. A phantom study indicates that the targeting error in robot-assisted needle insertions is below 5 mm and suggest a potential time saving of 30 min compared to the manual MRI-guided LA procedure.