title: Phase Error Correction in Time-Averaged 3D Phase Contrast Magnetic Resonance Imaging of the Cerebral Vasculature.
abstract: OBJECTIVE
  Volume flow rate (VFR) measurements based on phase contrast (PC)-magnetic resonance (MR) imaging datasets have spatially varying bias due to eddy current induced phase errors. The purpose of this study was to assess the impact of phase errors in time averaged PC-MR imaging of the cerebral vasculature and explore the effects of three common correction schemes (local bias correction (LBC), local polynomial correction (LPC), and whole brain polynomial correction (WBPC)).
  
  
  METHODS
  Measurements of the eddy current induced phase error from a static phantom were first obtained. In thirty healthy human subjects, the methods were then assessed in background tissue to determine if local phase offsets could be removed. Finally, the techniques were used to correct VFR measurements in cerebral vessels and compared statistically.
  
  
  RESULTS
  In the phantom, phase error was measured to be <2.1 ml/s per pixel and the bias was reduced with the correction schemes. In background tissue, the bias was significantly reduced, by 65.6% (LBC), 58.4% (LPC) and 47.7% (WBPC) (p < 0.001 across all schemes). Correction did not lead to significantly different VFR measurements in the vessels (p = 0.997). In the vessel measurements, the three correction schemes led to flow measurement differences of -0.04 ± 0.05 ml/s, 0.09 ± 0.16 ml/s, and -0.02 ± 0.06 ml/s. Although there was an improvement in background measurements with correction, there was no statistical difference between the three correction schemes (p = 0.242 in background and p = 0.738 in vessels).
  
  
  CONCLUSIONS
  While eddy current induced phase errors can vary between hardware and sequence configurations, our results showed that the impact is small in a typical brain PC-MR protocol and does not have a significant effect on VFR measurements in cerebral vessels.
authors.affiliation: Departments of Radiology, University of Calgary, Calgary, AB, Canada.|Department of Clinical Neuroscience, University of Calgary, Calgary, AB, Canada.|Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada.|Seaman Family MR Research Centre, Foothills Medical Centre, Alberta Health Services, Calgary, AB, Canada.
authors.forename: M Ethan
authors.initials: ME
authors.lastname: MacDonald
authors.affiliation: Departments of Radiology, University of Calgary, Calgary, AB, Canada.|Department of Clinical Neuroscience, University of Calgary, Calgary, AB, Canada.|Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada.
authors.forename: Nils D
authors.initials: ND
authors.lastname: Forkert
authors.affiliation: Departments of Radiology, University of Calgary, Calgary, AB, Canada.|Department of Clinical Neuroscience, University of Calgary, Calgary, AB, Canada.|Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada.|Seaman Family MR Research Centre, Foothills Medical Centre, Alberta Health Services, Calgary, AB, Canada.
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Pike
authors.affiliation: Departments of Radiology, University of Calgary, Calgary, AB, Canada.|Department of Clinical Neuroscience, University of Calgary, Calgary, AB, Canada.|Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada.|Seaman Family MR Research Centre, Foothills Medical Centre, Alberta Health Services, Calgary, AB, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Frayne
mesh_terms: D001783:Blood Flow Velocity; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000295:instrumentation / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging