Performance of interventions with manipulator-driven real-time MR guidance: implementation and initial in vitro tests.

The purpose of this work was to implement and assess the performance of interventions inside a cylindrical magnetic resonance imaging (MRI) scanner with an MR-compatible manipulator system and manipulator-driven real-time MR guidance. The interventional system is based on a seven degree-of-freedom MR-compatible manipulator, which offers man-in-the-loop control either with a graphical user interface or with a master/slave device. The position and the orientation of the interventional tool are sent to an MR scanner for a manipulator-driven dynamic update of the imaging plane to track, visualize and guide the motion of an end-effector. Studies on phantoms were performed with a cylindrical 1.5-T scanner using an operator-managed triggered gradient-recalled echo (GRE) or a computer-managed dynamic True Fast Imaging with Steady Precession (TrueFISP). Targets were acquired with an accuracy of 3.2 mm and with an in-plane path orientation of 2.5 degrees relative to the prescribed one. Path planning, including negotiation of obstacles and needle bending, was successfully performed. The signal-to-noise ratio (SNR) of TrueFISP was 25.3+/-2.1 when the manipulator was idle and was 18.6+/-2.4 during its operation. The SNR of triggered GRE (acquired only when the manipulator was idle) was 61.3+/-1.8. In conclusion, this study shows the feasibility of performing manually directed interventions inside cylindrical MR scanners with real-time MRI.