Development and Evaluation of an Actuated MRI-Compatible Robotic System for MRI-Guided Prostate Intervention

This paper reports the design, development, and magnetic resonance imaging (MRI) compatibility evaluation of an actuated transrectal prostate robot for MRI-guided needle intervention in the prostate. The robot performs actuated needle MRI guidance with the goals of providing 1) MRI compatibility; 2) MRI-guided needle placement with accuracy sufficient for targeting clinically significant prostate cancer foci; 3) reducing interventional procedure times (thus increasing patient comfort and reducing opportunity for needle targeting error due to patient motion); 4) enabling real-time MRI monitoring of interventional procedures; and 5) reducing the opportunities for error that arise in manually actuated needle placement. The design of the robot, employing piezoceramic-motor actuated needle guide positioning and manual needle insertion, is reported. Results of an MRI compatibility study show no reduction of MRI signal-to-noise ratio (SNR) with the disabled motors. Enabling the motors reduces the SNR by 80% without radio frequency (RF) shielding, but the SNR is only reduced by 40-60% with RF shielding. The addition of RF shielding is shown to significantly reduce image SNR degradation caused by the presence of the robotic device. An accuracy study of MRI-guided biopsy needle placements in a prostate phantom is reported. The study shows an average in-plane targeting error of 2.4 mm with a maximum error of 3.7 mm. These data indicate that the system's needle targeting accuracy is similar to that obtained with a previously reported manually actuated system, and is sufficient to reliably sample clinically significant prostate cancer foci under MRI guidance.