title: Diffusion-weighted imaging of the liver: comparison of navigator triggered and breathhold acquisitions.
abstract: OBJECTIVE
  To compare a free breathing navigator triggered single shot echoplanar imaging (SS EPI) diffusion-weighted imaging (DWI) sequence with prospective acquisition correction (PACE) with a breathhold (BH) DWI sequence for liver imaging.
  
  
  METHODS
  Thirty-four patients were evaluated with PACE-DWI and BH DWI of the liver using b-values of 0, 50, and 500 s/mm(2). There were 29 focal liver lesions in 18 patients. Qualitative evaluation was performed on a 3-point scale (1-3) by two independent observers (maximum score 9). Quantitative evaluation included estimated SNR (signal to noise ratio), lesion-to-liver contrast ratio, liver and lesion apparent diffusion coefficients (ADCs), and coefficient of variation (CV) of ADC in liver parenchyma and focal liver lesions (estimate of noise contamination in ADC).
  
  
  RESULTS
  PACE-DWI showed significantly better image quality, higher SNR and lesion-to-liver contrast ratio when compared with BH DWI. ADCs of liver and focal lesions with both sequences were significantly correlated (r = 0.838 for liver parenchyma, and 0.904 for lesions, P < 0.0001), but lower with the BH sequence (P < 0.02). There was higher noise contamination in ADC measurement obtained with BH DWI (with a significantly higher SD and CV of ADC).
  
  
  CONCLUSIONS
  The use of a navigator echo to trigger SS EPI DWI improves image quality and liver to lesion contrast, and enables a more precise ADC quantification compared with BH DWI acquisition.
authors.affiliation: NYU Medical Center, Department of Radiology, New York, NY, USA. btaouli@yahoo.com
authors.forename: Bachir
authors.initials: B
authors.lastname: Taouli
authors.forename: Alison
authors.initials: A
authors.lastname: Sandberg
authors.forename: Alto
authors.initials: A
authors.lastname: Stemmer
authors.forename: Tejas
authors.initials: T
authors.lastname: Parikh
authors.forename: Samson
authors.initials: S
authors.lastname: Wong
authors.forename: Jian
authors.initials: J
authors.lastname: Xu
authors.forename: Vivian S
authors.initials: VS
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002908:Chronic Disease; D003287:Contrast Media; D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008099:Liver / Q000473:pathology*; D008107:Liver Diseases / Q000473:pathology*; D008113:Liver Neoplasms / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012119:Respiration
chemical_list: D003287:Contrast Media