The purpose of this study was to test the in vivo feasibility of safe automatic catheter tracking based on an optically detunable resonant marker installed on the catheter tip, and also to test the compatibility of this approach with guidewire materials. The design of the resonant marker and the integration into the real-time MR environment is described. The catheter was used for real-time MR-guided catheterization of the aorta, left ventricle, and carotid in two swine. For in-plane visualization, the marker was repeatedly detuned. For automatic slice tracking, a projection difference measurement including detuning was interleaved with the imaging sequence. In vitro experiments were conducted to investigate the RF-safety of the marker and the effect of the guidewires on the signal intensity. For all orientations the marker provided excellent in vivo contrast using a radial steady-state free-precession sequence. Flashing of the marker by repetitive tuning/detuning further improved the in-plane visualization. Automatic slice tracking during real-time imaging was successfully performed. The plastic guidewires did not interfere with the marker, and detuning by guidewires containing nitinol could be compensated. In conclusion, automatic slice tracking as well as excellent in-plane visualization can be achieved with this approach and it is safe with respect to RF transmission.
