Preclinical evaluation of an MRI-compatible pneumatic robot for angulated needle placement in transperineal prostate interventions

Abstract

Purpose: To evaluate the targeting accuracy of a small profile MRI-compatible pneumatic robot for needle placement that can angulate a needle insertion path into a large accessible target volume.

Methods: We extended our MRI-compatible pneumatic robot for needle placement to utilize its four degrees-of-freedom (4-DOF) mechanism with two parallel triangular structures and support transperineal prostate biopsies in a closed-bore magnetic resonance imaging (MRI) scanner. The robot is designed to guide a needle toward a lesion so that a radiologist can manually insert it in the bore. The robot is integrated with navigation software that allows an operator to plan angulated needle insertion by selecting a target and an entry point. The targeting error was evaluated while the angle between the needle insertion path and the static magnetic field was between -5.7° and 5.7° horizontally and between -5.7° and 4.3° vertically in the MRI scanner after sterilizing and draping the device.

Results: The robot positioned the needle for angulated insertion as specified on the navigation software with overall targeting error of 0.8 ± 0.5mm along the horizontal axis and 0.8 ± 0.8mm along the vertical axis. The two-dimensional root-mean-square targeting error on the axial slices as containing the targets was 1.4mm.

Conclusions: Our preclinical evaluation demonstrated that the MRI-compatible pneumatic robot for needle placement with the capability to angulate the needle insertion path provides targeting accuracy feasible for clinical MRI-guided prostate interventions. The clinical feasibility has to be established in a clinical study.

Fig. 1

(A) The photo shows an overview of the 4-DOF MRI-compatible pneumatic needle placement robot and the agar phantom placed on the patient table of the MRI scanner. The phantom was removed from the scanner during the needle placement in the experiment. (B) The robot with 4-DOF parallel kinematic structure has two identical triangular planar positioning mechanisms that move within the x-y plane (axial in patient coordinate system) and are connected by a linkage as a needle insertion platform. The needle is manually inserted into the prostate through the perineum after the robot positions and orients the needle insertion platform.

Fig. 2

The configuration of the robot system for MRI-guided prostate interventions. Robot controller for low-level servo control of the robot is placed in the scanner room, while the navigation workstation is placed next to the host workstation of the MRI scanner system in the control room. Optical fiber Ethernet is used for network communication between the robot controller and navigation workstation to shut off electromagnetic (EM) noise from outside the EM shielded scanner room.

Fig. 3

The screenshot of the navigation software based on 3D Slicer shows the 3D models representing reachable target range and motion range of the front and back triangular-shaped links.

Fig. 4

The robot was draped with a transparent plastic cover for sterilization of the interventional workspace. Only the base of the robot, which is not sterilizable, is draped. The linkage that connects the two triangular mechanisms and the ball joints that hold the needle were sterilized before the procedure and attached to the base part of the robot. The four links of the front and back triangular mechanisms penetrate the cover.

Fig. 5

The tip of the needle was covered by an MRI-visible marker (upper left) so that the tip of the needle can be identified as an artifact on an MR image acquired from a plane perpendicular to the needle (upper right). The bottom photo shows the needle with the marker placed at the target by the robot.

Fig. 6

The plots show the error of needle placement in the x-axis (horizontal: right-left axis of the patient) and y-axis (vertical: anterior-posterior axis of the patient) with respect to the needle angle from the static field.