title: Diffusion-weighted magnetic resonance imaging of the liver using tracking only navigator echo: feasibility study.
abstract: OBJECTIVE
  To introduce and assess the TRacking Only Navigator echo (TRON) technique for diffusion-weighted magnetic resonance imaging (DWI) of the liver.
  
  
  METHODS
  A total of 10 volunteers underwent TRON, respiratory triggered (RT), and free breathing (FB) DWI of the liver. Scan times of TRON and RT DWI were measured, and image sharpness in TRON, RT, and FB DWI was assessed and compared using nonparametric tests. Furthermore, 14 patients with liver metastasis who had undergone TRON and RT DWI of the liver were retrospectively assessed. Relative contrast ratios (RCRs) and apparent diffusion coefficients (ADCs) of the largest hepatic metastasis in TRON and RT DWI were measured. RCRs were compared using a parametric test and agreement in ADCs was assessed using the Bland-Altman method.
  
  
  RESULTS
  In the volunteers, mean scan times of TRON and RT relative to FB DWI were 110% to 112% and 261% to 290%, respectively. On axial images, there were no significant differences in images sharpness among TRON, RT, and FB DWI, but on coronal images image sharpness in TRON was nearly always significantly better (P < 0.05) than in RT and FB DWI. In the patients, mean RCRs between TRON and RT DWI were not significantly different (P = 0.9091). Mean difference in ADC +/- limits of agreement (in 10 mm/s) between TRON and RT DWI was -0.16 +/- 0.79.
  
  
  CONCLUSIONS
  TRON offers sharp diffusion-weighted images of the liver using an efficient scan time, making it an excellent alternative to RT and FB DWI. The moderate to poor agreement in ADCs of liver metastases between TRON and RT DWI requires further investigation.
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands. tarorin@gmail.com
authors.forename: Taro
authors.initials: T
authors.lastname: Takahara
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Kwee
authors.forename: Maarten S
authors.initials: MS
authors.lastname: Van Leeuwen
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Ogino
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Horie
authors.forename: Marc
authors.initials: M
authors.lastname: Van Cauteren
authors.forename: Gwenael
authors.initials: G
authors.lastname: Herigault
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Imai
authors.forename: W P Th M
authors.initials: WP
authors.lastname: Mali
authors.forename: Peter R
authors.initials: PR
authors.lastname: Luijten
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000473:pathology*; D008113:Liver Neoplasms / Q000175:diagnosis* / Q000556:secondary*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D012680:Sensitivity and Specificity