Purpose: Percutaneous ablation under MRI-guidance allows treating otherwise inoperable liver tumors locally using a catheter probe. However, manually placing the probe is an error-prone and time consuming task that requires a considerable amount of training. The aim of this paper was to present a pneumatically actuated robotic instrument that can assist clinicians in MRI-guided percutaneous intervention of the liver and to assess its functionality in a clinical setting. The robot positions a needle-guide inside the MRI scanner bore and assists manual needle insertions outside the bore.
Methods: The robot supports double oblique insertions that are particularly challenging for less experienced clinicians. Additionally, the system employs only standard imaging sequences and can therefore be used on different MRI scanners without requiring prior integration. The repeatability and the accuracy of the robot were evaluated with an optical tracking system. The functionality of the robot was assessed in an initial pilot study on two patients that underwent MRI-guided laser ablation of the liver.
Results: The robot positioned the needle-guide in a repeatable manner with a mean error of 0.35 mm and a standard deviation of 0.32 mm. The mean position error corresponding to the needle tip, measured for an equivalent needle length of 195 mm over 25 fixed points, was 2.5 mm with a standard deviation of 1.2 mm. The pilot study confirmed that the robot does not interfere with the equipment used for MRI-guided laser ablation and does not visibly affect the MR images. The robot setup integrated seamlessly within the established clinical workflow. The robot-assisted procedure was successfully completed on two patients, one of which required a complex double oblique insertion. For both patients, the insertion depth and the tumor size were within the range reported for previous MRI-guided percutaneous interventions. A third patient initially enrolled in the pilot study and was considerably heavier than the others, preventing the use of the robot and requiring several freehand insertion attempts.
Conclusions: The robot repeatability and accuracy are appropriate for liver tumors normally treated with MRI-guided ablation. The results of the pilot study endorse the clinical use of the robot in its current form: the robot is fully functional and MRI-compatible in a clinical setting and is suitable for double-oblique needle insertions.