title: An in vivo comparison of the DREAM sequence with current RF shim technology.
abstract: OBJECTIVE
  In the present study the performance of the dual refocusing echo acquisition mode (DREAM) B1 (+) mapping sequence is evaluated for RF shimming in the abdomen at 3 T and validated against existing RF shim technology.
  
  
  METHODS
  In vivo experiments were performed on 19 normal volunteers using a clinical 3 T dual channel MRI system. For each volunteer three different B1 (+) mapping techniques [DREAM, actual flip angle imaging (AFI) and saturated double angle method (SDAM)] were employed for RF shimming of the liver and to subsequently assess the quality of the obtained RF shim settings in terms of the achieved B1 (+) homogeneity and accuracy of the mean B1 (+).
  
  
  RESULTS
  DREAM-based B1 (+) calibration led to an average homogeneity improvement of 39.1 % (AFI = 38.7 %, SDAM = 38.1 %) and a mean B1 (+) of 90.9 % of the prescribed B1 (+) (AFI = 88.9 %, SDAM = 92.0 %). The duration of the B1 (+) calibration scan was reduced from 30 s (AFI) and 15 s (SDAM) to 2.5 s (DREAM).
  
  
  CONCLUSIONS
  DREAM accelerates RF shimming of the liver by an order of magnitude without compromising RF shimming performance.
authors.affiliation: Philips Research Laboratories, Röntgenstraße 24-26, 22335, Hamburg, Germany, kay.nehrke@philips.com.
authors.forename: Kay
authors.initials: K
authors.lastname: Nehrke
authors.forename: Alois M
authors.initials: AM
authors.lastname: Sprinkart
authors.forename: Peter
authors.initials: P
authors.lastname: Börnert
mesh_terms: D000005:Abdomen / Q000033:anatomy & histology*; D000328:Adult; D000465:Algorithms; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011846:Radio Waves; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
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