Optimizing accuracy and precision of micro-coil localization in active-MR tracking.

OBJECTIVE To examine whether a centroid peak detection algorithm and micro-transmit tracking improve the accuracy and precision of active-MR tracking when combined with previously published strategies of Hadamard Multiplexing and Phase-field Dithering. MATERIALS AND METHODS The dipole magnetic field of a solenoid tracking coil was modeled and MR spin excitation using both a uniform body coil and the tracking coil was simulated for 5329 orientations of the solenoid coil with respect to B0. A lumenless micro-coil was built onto a rotation platform and MR-tracking accuracy and precision were experimentally assessed for 576 orientations within a 1.5-T MRI scanner. Peak identification strategies (i.e. maximum pixel detection and the centroid pixel method) and transmit modes (body transmit and micro-transmit tracking) were employed and localization accuracy was assessed for each orientation in both simulation and experimentation. RESULTS The simultaneous use of the centroid pixel method, micro-transmit tracking, Phase-field Dithering, and Hadamard Multiplexing resulted in high MR tracking accuracy and precision: 0.52±0.41 mm and 0.34 mm respectively. Furthermore, all four methods combined offered a tracking error less than the size of the micro-coil, despite the lack of a signal source within the micro-coil. CONCLUSIONS Micro-transmit tracking and the centroid pixel method improve MR tracking accuracy and precision when combined with Phase-field Dithering and Hadamard Multiplexing compared to using Phase-field Dithering and Hadamard Multiplexing alone.