  Purpose: This study demonstrates a proof of concept of a method for
simultaneous anatomical imaging and real-time (SMART) passive device tracking
for MR-guided interventions.
  Methods: Phase Correlation template matching was combined with a fast
undersampled radial multi-echo acquisition using the white marker phenomenon
after the first echo. In this way, the first echo provides anatomical contrast,
whereas the other echoes provide white marker contrast to allow accurate device
localization using fast simulations and template matching. This approach was
tested on tracking of five 0.5 mm steel markers in an agarose phantom and on
insertion of an MRI-compatible 20 Gauge titanium needle in ex vivo porcine
tissue. The locations of the steel markers were quantitatively compared to the
marker locations as found on a CT scan of the same phantom.
  Results: The average pairwise error between the MRI and CT locations was 0.30
mm for tracking of stationary steel spheres and 0.29 mm during motion.
Qualitative evaluation of the tracking of needle insertions showed that tracked
positions were stable throughout needle insertion and retraction.
  Conclusions: The proposed SMART tracking method provided accurate passive
tracking of devices at high framerates, inclusion of real-time anatomical
scanning, and the capability of automatic slice positioning. Furthermore, the
method does not require specialized hardware and could therefore be applied to
track any rigid metal device that causes appreciable magnetic field
distortions.
