title: Comparison of pre- and postcontrast 3D time-of-flight MR angiography for the evaluation of distal intracranial branch occlusions in acute ischemic stroke.
abstract: OBJECTIVE
  Three-dimensional time-of-flight (TOF) MR angiography is used routinely in stroke workup to detect arterial occlusions, but a major drawback is its inadequate depiction of vessels with slow or in-plane flow. We hypothesized that the use of contrast-enhanced MR angiography improves delineation of vessels with diminished or absent flow on precontrast MR angiograms.
  
  
  METHODS
  Pre- and postcontrast 3D TOF MR angiograms were acquired in 55 consecutive patients with acute stroke. Patency of 480 intracranial vessels was assessed on both the pre- and postcontrast angiograms. Diffusion-weighted (DW) and perfusion-weighted (PW) imaging data were also obtained and results correlated with those of pre- and postcontrast MR angiography.
  
  
  RESULTS
  For 50 abnormal vessel segments seen on precontrast MR angiograms, postcontrast MR angiograms resulted in change in the vascular signal intensity in 70% (35 vessel segments); 94% of these changes showed a greater extent of vessel patency. Venous and soft-tissue contrast enhancement had no effect on assessment in 95% of all 480 vessels examined. Interobserver reliability was moderate, with postcontrast interpretation (kappa = 0.48) showing a slight improvement over precontrast interpretation (kappa = 0.41). Good agreement was found between the TOF results and the pooled DW and PW imaging results.
  
  
  CONCLUSIONS
  Compared with precontrast 3D TOF MR angiograms, postcontrast 3D TOF angiograms improve assessment of intracranial vessel patency in acutely ischemic vascular territories. In some patients, an improved understanding of acute ischemic stroke was obtained by viewing the pre- and postcontrast images. Postcontrast MR angiography should be included in the MR evaluation of acute stroke.
authors.affiliation: Seaman Family MR Research Centre, Foothills Medical Centre, Calgary Health Region Calgary, Alberta, Canada.
authors.forename: Janice J
authors.initials: JJ
authors.lastname: Yang
authors.forename: Michael D
authors.initials: MD
authors.lastname: Hill
authors.forename: William F
authors.initials: WF
authors.lastname: Morrish
authors.forename: Mark E
authors.initials: ME
authors.lastname: Hudon
authors.forename: Philip A
authors.initials: PA
authors.lastname: Barber
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Demchuk
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Sevick
authors.forename: Richard
authors.initials: R
authors.lastname: Frayne
mesh_terms: D000208:Acute Disease; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000175:diagnosis*; D002536:Cerebral Arteries / Q000473:pathology*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011446:Prospective Studies