title: Field strength and diffusion encoding technique affect the apparent diffusion coefficient measurements in diffusion-weighted imaging of the abdomen.
abstract: OBJECTIVE
  The purpose of this study is to determine what effects a variety of diffusion encoding techniques at 1.5 T and 3 T have on measured abdominal apparent diffusion coefficient (ADC) values obtained in a healthy population.
  
  
  METHODS
  Sixteen healthy male volunteers were enrolled in this prospective Institutional Review Board-approved study following written informed consent. Imaging was performed on a 1.5 T and a 3 T magnetic resonance system (Siemens, Erlangen) with several abdominal axial diffusion weighted imaging (DWI) acquisitions: an orthogonal diffusion encoding with b-values of 0/400 seconds/mm, and a series of four 3-scan trace weighted acquisitions with b-values of 0/50, 0/400, 0/800, 0/50/400/800 seconds/mm, respectively. The mean ADC values were calculated for 3 regions of interest (ROI) in 5 locations (right hepatic lobe, spleen, pancreatic head, body, and tail). The ADC data were analyzed using a repeated-measures analysis of variance.
  
  
  RESULTS
  There was a significant difference between measured ADC values at 1.5 T and 3 T for liver (P < 0.001), but not for pancreas (P = 0.427) or spleen (P = 0.167). There was no significant difference (P > 0.999) in the measured ADC values between the orthogonal encodings and the 3-scan trace weighted encoding with the same b-value. There were significant differences (P < 0.001) between all 4 weighting schemes for the 3-scan trace with the measured ADC decreasing with increasing b-value.
  
  
  CONCLUSIONS
  Measured abdominal ADC values depend on the exact selection of b-value used for encoding for liver, pancreas, and spleen. In addition, the measured ADC values depend on the field strength of the scanner for liver.
authors.affiliation: Siemens Healthcare, Cary, NC; and daggerDepartment of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Dale
authors.forename: Adam C
authors.initials: AC
authors.lastname: Braithwaite
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Boll
authors.forename: Elmar M
authors.initials: EM
authors.lastname: Merkle
mesh_terms: D000005:Abdomen / Q000033:anatomy & histology*; D000328:Adult; D016477:Artifacts; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D016247:Information Storage and Retrieval / Q000379:methods; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014781:Viscera / Q000033:anatomy & histology*