title: Reduced k-space acquisition to accelerate MR imaging of moving interventional instruments: a phantom study.
abstract: OBJECTIVE
  The goal of this study was to investigate the impact of reduced k-space sampling rates on the visualization of a moving MR-compatible puncture needle and to demonstrate the feasibility of keyhole imaging in interventional magnetic resonance imaging (MRI).
  
  
  METHODS
  All experiments were performed in an open 1.0 Tesla MRI. MR images of a moving puncture needle were taken with different keyhole sampling rates from 15-100%, in 10% increments. The needle was submerged in a water-filled basin and was imaged in motion with a T1-weighted gradient-echo sequence with an initial acquisition rate of 1.4 s per image. An apparatus operated by a compressor unit enabled needle rotation and ensured reproducible needle movements. The median forward velocity of the needle tip was 2 cm/s. To evaluate the depiction of the needle, artifact diameter of the needle, contrast-to-noise ratio (CNR), and needle tip profiles (delineation) were measured.
  
  
  RESULTS
  The needle position was determined with an longitudinal error of 3 mm and a transverse error of 0.8 mm with respect to the needle's orientation and the theoretically calculated trajectory. No significant correlation was found between the CNR and velocity. A reduction of k-space update rates caused neither a significant reduction of CNR nor a significant increase in artifact diameter or blurring of the needle profile.
  
  
  CONCLUSIONS
  The application of keyhole imaging with update rates of greater than 15% is sufficient for the MR guidance of interventions with an signal-to-noise ratio >9 of the surrounding tissue and a target accuracy of >1 mm. Keyhole imaging can increase temporal resolution while ensuring unimpaired spatial resolution and image quality of the depicted instrument.
authors.affiliation: Charité University Medicine, Berlin, Germany. jens.rump@charite.de
authors.forename: Jens Christian
authors.initials: JC
authors.lastname: Rump
authors.forename: Martin
authors.initials: M
authors.lastname: Jonczyk
authors.forename: Christian Jürgen
authors.initials: CJ
authors.lastname: Seebauer
authors.forename: Florian
authors.initials: F
authors.lastname: Streitparth
authors.forename: Felix Victor
authors.initials: FV
authors.lastname: Güttler
authors.forename: Ulf Karl-Martin
authors.initials: UK
authors.lastname: Teichgräber
authors.forename: Bernd
authors.initials: B
authors.lastname: Hamm
mesh_terms: D000054:Acceleration; D000465:Algorithms; D004867:Equipment Design; D006801:Humans; D053783:Magnetic Resonance Imaging, Interventional / Q000295:instrumentation* / Q000379:methods; D009339:Needles; D019047:Phantoms, Imaging; D011786:Quality Control; D011856:Radiographic Image Enhancement / Q000295:instrumentation / Q000379:methods*; D012680:Sensitivity and Specificity