title: MR phase-contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf.
abstract: OBJECTIVE
  To evaluate the feasibility of using un-gated, real-time MRI for venous blood velocity mapping in the calf, comparing an interleaved spiral k-space sequence (ISP) against a standard segmented gradient echo sequence (GRE).
  
  
  METHODS
  A flow phantom with a variable flow-rate was scanned using both GRE and ISP sequences for an in vitro comparison. Seven subjects were scanned prone, performing metronome guided breathing, using the (externally triggered) segmented GRE and real-time ISP sequences. The segmented GRE acquisition duration was 2.5 mins (22 guided respiratory cycles) and the ISP sequence ran continuously for 35 s, 4 full guided respiratory cycles. Mean velocity from each of the deep veins was measured and peak mean velocity, peak flow rate and cumulative volume flow over a respiratory cycle compared between sequences.
  
  
  RESULTS
  The two sequences compared well both in vitro and in vivo. The real-time ISP sequence showed short-term variations in mean velocity superimposed on the respiratory induced flow, which were averaged out using the segmented GRE sequence.
  
  
  CONCLUSIONS
  Real-time ISP provides comparable time-averaged flow results to the standard sequence with additional information on real-time flow variations and so could be used for further investigation into venous blood flow in the lower leg.
authors.affiliation: CMR Unit, National Heart and Lung Institute, Imperial College London, United Kingdom. i.pierce08@imperial.ac.uk
authors.forename: Iain T
authors.initials: IT
authors.lastname: Pierce
authors.forename: Peter D
authors.initials: PD
authors.lastname: Gatehouse
authors.forename: X Yun
authors.initials: XY
authors.lastname: Xu
authors.forename: David N
authors.initials: DN
authors.lastname: Firmin
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001783:Blood Flow Velocity; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007866:Leg / Q000098:blood supply* / Q000502:physiology*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity