title: Intrasession and Intersession Repeatability of Diffusion Tensor Imaging in Healthy Human Liver.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effect of signal to noise ratio (SNR) and number of gradient directions (NGD) on intra- and intersession repeatability of liver diffusion tensor imaging (DTI) metrics.
  
  
  METHODS
  At each of 3 liver DTI scan sessions, liver diffusion was assessed in 5 healthy volunteers using a 6-direction DTI scan performed 9 separate times (ie, number of signal averages [NSA]). In addition, 4 combinations of NSA and NGD were acquired (NSA/NGD = 1/30, 3/10, 3/12, and 5/6) to determine the combined effect to DTI metrics, which was based on intersubject variability and intrasession (Vintra) and intersession (Vinter) repeatability.
  
  
  RESULTS
  Intersubject variability was less than 20%, whereas Vintra and Vinter repeatability were less than 5% and less than 10%, respectfully. Vinter was not affected by the NGD used. Decreases in Vinter(FA), Vinter(λ1), Vinter(RD), and Vinter(MD) were observed with increasing NSA, and hence SNR.
  
  
  CONCLUSIONS
  Increased SNR may improve intrasession and intersession repeatability of liver DTI metrics. Scan repeatability was not influenced by NGD.
authors.affiliation: From the *Department of Medical Physics and Applied Radiation Science, McMaster University, Hamilton, Ontario; †Imaging Research Center, St. Joseph's Healthcare, Hamilton Ontario, Canada; ‡Medical Physics and Research Department, §Comprehansive Oncology Center, and ∥Intervention and Radiology Department, Hong Kong Sanatorium & Hospital, Hong Kong Special Administrative Region (SAR), China; ¶School of Biomedical Engineering, and #Department of Electrical and Computer Engineering, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Oi Lei
authors.initials: OL
authors.lastname: Wong
authors.forename: Thomas Wai Tong
authors.initials: TWT
authors.lastname: Leung
authors.forename: Gladys Goh
authors.initials: GG
authors.lastname: Lo
authors.forename: Jing
authors.initials: J
authors.lastname: Yuan
authors.forename: Wing Wa
authors.initials: WW
authors.lastname: Li
authors.forename: Michael D
authors.initials: MD
authors.lastname: Noseworthy
mesh_terms: D000328:Adult; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000033:anatomy & histology*; D008297:Male; D015588:Observer Variation; D012016:Reference Values; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio