title: Autocorrection of three-dimensional time-of-flight MR angiography of the Circle of Willis.
abstract: OBJECTIVE
  The purpose of this study was to investigate the efficacy of a retrospective adaptive motion correction technique known as autocorrection for reducing motion-induced artifacts in high-resolution three-dimensional time-of-flight MR angiography of the circle of Willis.
  
  
  METHODS
  Ten consecutive volunteers were imaged with an unenhanced gradient-recalled echo three-dimensional time-of-flight MR angiography sequence of the circle of Willis. Each volunteer was asked to rotate approximately 2 degrees after completion of one third and one half of the acquisition in the axial, sagittal, and oblique planes (45 degrees to the axial and sagittal planes). A single static data set was also acquired for each volunteer. Unprocessed and autocorrected maximum-intensity-projection images were reviewed as blinded image pairs by six radiologists and were compared on a five-point image quality scale.
  
  
  RESULTS
  Mean improvement in image quality after autocorrection was 1.4 (p < 0.0001), 1.1 (p < 0.0001), and 0.2 (p = 0.003) observer points (maximum value, 2.0), respectively, for examinations corrupted by motion in the axial, oblique, and sagittal planes. All three axes had statistically significant improvement in image quality compared with the uncorrected images. Changes in image quality after the application of the autocorrection algorithm to static angiogram data were not statistically significant (mean change in score = -0.13 points; p = 0.29).
  
  
  CONCLUSIONS
  Autocorrection can reduce artifacts in motion-corrupted MR angiography of the circle of Willis without distorting motion-free examinations.
authors.affiliation: MRI Research Laboratory, Department of Diagnostic Radiology, Mayo Clinic, 200 First St., S.W., Rochester, MN 55905, USA.
authors.forename: K P
authors.initials: KP
authors.lastname: McGee
authors.forename: J P
authors.initials: JP
authors.lastname: Felmlee
authors.forename: C R
authors.initials: CR
authors.lastname: Jack
authors.forename: A
authors.initials: A
authors.lastname: Manduca
authors.forename: S J
authors.initials: SJ
authors.lastname: Riederer
authors.forename: R L
authors.initials: RL
authors.lastname: Ehman
mesh_terms: D016477:Artifacts; D002941:Circle of Willis / Q000000981:diagnostic imaging*; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods*; D011859:Radiography