title: Improved correction for gradient nonlinearity effects in diffusion-weighted imaging.
abstract: OBJECTIVE
  To provide an improved correction for gradient nonlinearity (GN) effects in diffusion-weighted imaging (DWI). These effects produce spatially varying apparent diffusion coefficient (ADC), a result that will be significant in large field-of-view imaging, and may be confounded by distortion and concomitant fields related to the DWI acquisition.
  
  
  METHODS
  The effect of more accurate gradient field maps on GN correction (GNC) of ADC was evaluated. A simulation compared GN effects in commonly imaged anatomy. A temperature-controlled phantom was imaged at positions 0 cm and 11 cm from isocenter and in two whole-body MRI systems at 1.5T with different patient bore diameters (55 cm and 60 cm). Varying correction methods were applied to determine the errors from spatial variance and interscanner reproducibility.
  
  
  RESULTS
  As compared to conventional fifth-order spherical harmonics, a seventh-order GNC improved ADC accuracy by 1%. The combination of GNC with a dual-spin-echo pulse sequence and a retrospective concomitant field correction reduced ADC error due to spatial variance from 9.5% to 1.8% (55 cm bore) and from 4.2% to 1.8% (60 cm bore). The error in ADC attributed to interscanner reproducibility was reduced from 5.8% to 0.15% (at isocenter) and from 10% to 0.63% (11 cm from isocenter).
  
  
  CONCLUSIONS
  GNC in DWI improved spatial accuracy and interscanner reproducibility of ADC.
authors.affiliation: GE Global Research, Niskayuna, New York 12309, USA. ek.tan@ge.com
authors.forename: Ek T
authors.initials: ET
authors.lastname: Tan
authors.forename: Luca
authors.initials: L
authors.lastname: Marinelli
authors.forename: Zachary W
authors.initials: ZW
authors.lastname: Slavens
authors.forename: Kevin F
authors.initials: KF
authors.lastname: King
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hardy
mesh_terms: D000465:Algorithms; D016477:Artifacts; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D017711:Nonlinear Dynamics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D051598:Whole Body Imaging / Q000379:methods*