title: Gradient shimming during magnetic resonance imaging of the liver: comparison of a standard protocol versus a novel reduced protocol.
abstract: OBJECTIVE
  The aim of this study was to examine the effect of minimizing prescan adjustments on table time and image quality in magnetic resonance imaging (MRI) of the liver.
  
  
  METHODS
  This prospective Health Insurance Portability and Accountability Act-compliant study was approved by the institutional review board, and written informed consent was obtained. Ten volunteers were imaged twice using a noncontrast liver MRI protocol consisting of a total of 10 pulse sequences, once with a standard protocol and once with a fixed table position/minimized prescan adjustment protocol (in random order). Total examination time was evaluated according to a Lean Six Sigma framework. Quantitative sequences, including diffusion-weighted imaging with apparent diffusion coefficient, multi-echo Dixon fat percentage, and the transverse relaxation time, were evaluated and compared between the two protocols. Two experienced readers, blinded to the protocol used, compared image quality between the two protocols.
  
  
  RESULTS
  The average number of prescan adjustment steps per examination was reduced from 58.0 to 22.1 using the minimal shimming protocol compared with the normal shimming protocol (P < 0.001). Mean business value added time (scan preparatory time) was reduced by 58% (3 minutes 3 seconds vs 7 minutes 13 seconds), whereas mean total examination time was 20% lower (18 minutes 13 seconds vs 22 minutes 48 seconds, P < 0.001). Quantitative measures obtained using the two protocols were equivalent, and neither reader detected a significant difference in subjective image quality.
  
  
  CONCLUSIONS
  Fixing table position minimizes prescan adjustments and reduces total table time in liver MRI without adversely affecting image quality.
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, NC, USA. mustafa.bashir@duke.edu
authors.forename: Mustafa R
authors.initials: MR
authors.lastname: Bashir
authors.forename: Brian M
authors.initials: BM
authors.lastname: Dale
authors.forename: Rajan T
authors.initials: RT
authors.lastname: Gupta
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Horvath
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Boll
authors.forename: Elmar M
authors.initials: EM
authors.lastname: Merkle
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002985:Clinical Protocols; D005260:Female; D006801:Humans; D007089:Image Enhancement; D008099:Liver / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies