Manipulator-driven selection of semi-active MR-visible markers.

BACKGROUND: A method for the identification of semi-active fiducial magnetic resonance (MR) markers is presented based on selectively optically tuning and detuning them. METHODS: Four inductively coupled solenoid coils with photoresistors were connected to light sources. A microcontroller timed the optical tuning/detuning of coils and image collection. The markers were tested on an MR manipulator linking the microcontroller to the manipulator control to visibly select the marker subset according to the actuated joint. RESULTS: In closed-loop control, the average and maximum were 0.76° ± 0.41° and 1.18° errors for a rotational joint, and 0.87 mm ± 0.26 mm and 1.13 mm for the prismatic joint. CONCLUSIONS: This technique is suitable for MR-compatible actuated devices that use semi-active MR-compatible markers.