title: Technical Note: MR-visualization of interventional devices using transient field alterations and balanced steady-state free precession imaging.
abstract: OBJECTIVE
  In interventional magnetic resonance imaging, instruments can be equipped with conducting wires for visualization by current application. The potential of sequence triggered application of transient direct currents in balanced steady-state free precession (bSSFP) imaging is demonstrated.
  
  
  METHODS
  A conductor and a modified catheter were examined in water phantoms and in an ex vivo porcine liver. The current was switched by a trigger pulse in the bSSFP sequence in an interval between radiofrequency pulse and signal acquisition. Magnitude and phase images were recorded. Regions with transient field alterations were evaluated by a postprocessing algorithm. A phase mask was computed and overlaid with the magnitude image.
  
  
  RESULTS
  Transient field alterations caused continuous phase shifts, which were separated by the postprocessing algorithm from phase jumps due to persistent field alterations. The overlaid images revealed the position of the conductor. The modified catheter generated visible phase offset in all orientations toward the static magnetic field and could be unambiguously localized in the ex vivo porcine liver.
  
  
  CONCLUSIONS
  The application of a sequence triggered, direct current in combination with phase imaging allows conspicuous localization of interventional devices with a bSSFP sequence.
authors.affiliation: Section on Experimental Radiology, University Hospital Tübingen, Tübingen D-72076, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Eibofner
authors.affiliation: Section on Experimental Radiology, University Hospital Tübingen, Tübingen D-72076, Germany.
authors.forename: Petros
authors.initials: P
authors.lastname: Martirosian
authors.affiliation: Section on Experimental Radiology, University Hospital Tübingen, Tübingen D-72076, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Würslin
authors.affiliation: Section on Experimental Radiology, University Hospital Tübingen, Tübingen D-72076, Germany.
authors.forename: Hansjörg
authors.initials: H
authors.lastname: Graf
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tübingen, Tübingen D-72076, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Syha
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tübingen, Tübingen D-72076, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Clasen
mesh_terms: D000465:Algorithms; D000818:Animals; D016477:Artifacts; D057785:Catheters; D003300:Copper; D004560:Electricity; D008099:Liver / Q000033:anatomy & histology / Q000601:surgery; D060526:Magnetic Fields; D053783:Magnetic Resonance Imaging, Interventional / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves; D013552:Swine; D014025:Titanium; D015032:Zinc
chemical_list: C048399:brass; D003300:Copper; D014025:Titanium; D015032:Zinc