title: Simultaneous 3D localization of multiple MR-visible markers in fully reconstructed MR images: proof-of-concept for subsecond position tracking.
abstract: OBJECTIVE
  To determine whether a greatly reduced spatial resolution of fully reconstructed projection MR images can be used for the simultaneous 3D localization of multiple MR-visible markers and to assess the feasibility of a subsecond position tracking for clinical purposes.
  
  
  METHODS
  Miniature, inductively coupled RF coils were imaged in three orthogonal planes with a balanced steady-state free precession (SSFP) sequence and automatically localized using a two-dimensional template fitting and a subsequent three-dimensional (3D) matching of the coordinates. Precision, accuracy, speed and robustness of 3D localization were assessed for decreasing in-plane resolutions (0.6-4.7 mm). The feasibility of marker tracking was evaluated at the lowest resolution by following a robotically driven needle on a complex 3D trajectory.
  
  
  RESULTS
  Average 3D precision and accuracy, sensitivity and specificity of localization ranged between 0.1 and 0.4 mm, 0.5 and 1.0 mm, 100% and 95%, and 100% and 96%, respectively. At the lowest resolution, imaging and localization took ≈350 ms and provided an accuracy of ≈1.0 mm. In the tracking experiment, the needle was clearly depicted on the oblique scan planes defined by the markers.
  
  
  CONCLUSIONS
  Image-based marker localization at a greatly reduced spatial resolution is considered a feasible approach to monitor reference points or rigid instruments at subsecond update rates.
authors.affiliation: Department of Diagnostic and Interventional Radiology, Leipzig University Hospital, Leipzig, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Thörmer
authors.forename: Nikita
authors.initials: N
authors.lastname: Garnov
authors.forename: Michael
authors.initials: M
authors.lastname: Moche
authors.forename: Jürgen
authors.initials: J
authors.lastname: Haase
authors.forename: Thomas
authors.initials: T
authors.lastname: Kahn
authors.forename: Harald
authors.initials: H
authors.lastname: Busse
mesh_terms: D004867:Equipment Design; D005240:Feasibility Studies; D057918:Fiducial Markers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity