title: MR imaging: influence of imaging technique and postprocessing on measurement of internal carotid artery stenosis.
abstract: OBJECTIVE
  MR angiography (MRA) is increasingly used as an alternative to digital subtraction angiography (DSA) to evaluate internal carotid artery (ICA) stenosis. Because MRA is not standardized in data acquisition and postprocessing, we sought to evaluate the effects of different acquisition techniques (time-of-flight MRA [TOF-MRA]) and contrast-enhanced MRA [CE-MRA]) and postprocessing methods (maximum intensity projection [MIP], multiplanar reformation [MPR], and volume-rendering on stenosis grading.
  
  
  METHODS
  Fifty patients (33 men, 17 women) with symptomatic ICA stenosis were examined at 1.5T. Two imaging techniques and 3 postprocessing methods resulted in 6 image datasets per patient. Two readers independently evaluated ICA stenosis according to the North American Symptomatic Carotid Endarterectomy Trial criteria. Interobserver variability was calculated with the Pearson correlation coefficient and simultaneous confidence intervals (CI). The relationship of the values of ICA stenosis between the techniques was assessed by means of simultaneous 95% Tukey CI.
  
  
  RESULTS
  Interobserver agreement was high. Higher concordance was found for postprocessing techniques with TOF- than with CE-MRA; the mean difference between TOF-MPR and TOF-MIP was 0.4% (95% CI, -2.9%-3.8%). Stenosis values for CE-MPR differed significantly from those of CE volume-rendering (7.2%; 95% CI, 3.9%-10.6%).
  
  
  CONCLUSIONS
  Stenosis grading was found to be independent of the postprocessing technique except for comparison of CE-MPR with CE volume-rendering, with the volume-rendering technique resulting in higher stenosis values. MPR seems to be best-suited for measurement of ICA stenosis. Parameter setting is critical with volume-rendering, in which stenosis values were consistently higher compared with the other methods.
authors.affiliation: Department of Radiology and Neuroradiology, Klinikum Augsburg, Augsburg, Germany. frank.runck@klinikum-augsburg.de
authors.forename: F
authors.initials: F
authors.lastname: Runck
authors.forename: R P
authors.initials: RP
authors.lastname: Steiner
authors.forename: W A
authors.initials: WA
authors.lastname: Bautz
authors.forename: M M
authors.initials: MM
authors.lastname: Lell
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002343:Carotid Artery, Internal / Q000473:pathology*; D016893:Carotid Stenosis / Q000145:classification / Q000175:diagnosis*; D002544:Cerebral Infarction / Q000145:classification / Q000175:diagnosis; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D002546:Ischemic Attack, Transient / Q000145:classification / Q000175:diagnosis; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012680:Sensitivity and Specificity