title: Venous saturation slab causes overestimation of stenosis length in two-dimensional time-of-flight magnetic resonance angiography.
abstract: BACKGROUND
  The use of downstream saturation slabs in two-dimensional time-of-flight magnetic resonance angiography (2D TOF MRA) of the arterial system eliminates signal from regions with countercurrent flow, as seen in veins, but possibly also beyond arterial stenoses because of flow turbulence.
  
  
  OBJECTIVE
  To investigate the contribution of a downstream saturation slab to signal intensity (SI) loss beyond stenoses at 2D TOF MRA.
  
  
  METHODS
  2D TOF MRA was performed on a bifurcation phantom with a tight stenosis at 1.5T during pulsatile flow. Qualitative and quantitative evaluations of stenosis delineation were performed with different echo times (TE) (3.7 or 7.0 ms), spatial resolution (1 x 1 x 1 or 1 x 1 x 5 mm(3)), and with or without a downstream saturation slab. For reference, a high-resolution contrast-enhanced sequence without flow was obtained.
  
  
  RESULTS
  The downstream saturation slab caused severe signal loss immediately distal to the stenosis, causing overestimation of stenosis length. This region corresponded with a region of poststenotic flow jet, where turbulence is expected. With increase in TE, there was some increased SI loss at the level of maximum stenosis. A lower spatial resolution resulted in overall poorer delineation of the stenosis.
  
  
  CONCLUSIONS
  Using clinically relevant sequence parameters, the use of a downstream saturation slab at 2D TOF MRA was found to be a major contributor to signal loss in stenotic regions, which can result in an overestimation of stenosis length.
authors.affiliation: Department of Radiology, Uppsala University Hospital, Uppsala, Sweden. johan.wikstrom@radiol.uu.se
authors.forename: J
authors.initials: J
authors.lastname: Wikström
authors.forename: A
authors.initials: A
authors.lastname: Bjornerud
authors.forename: S
authors.initials: S
authors.lastname: McGill
authors.forename: L
authors.initials: L
authors.lastname: Johansson
mesh_terms: D001783:Blood Flow Velocity; D003287:Contrast Media; D007091:Image Processing, Computer-Assisted; D018810:Magnetic Resonance Angiography / Q000379:methods*; D019047:Phantoms, Imaging; D011673:Pulsatile Flow; D014689:Venous Insufficiency / Q000175:diagnosis*
chemical_list: D003287:Contrast Media