title: Effect of diffusion time on liver DWI: an experimental study of normal and fibrotic livers.
abstract: OBJECTIVE
  To investigate whether diffusion time (Δ) affects the diffusion measurements in liver and their sensitivity in detecting fibrosis.
  
  
  METHODS
  Liver fibrosis was induced in Sprague-Dawley rats (n = 12) by carbon tetrachloride (CCl(4)) injections. Diffusion-weighted MRI was performed longitudinally during 8-week CCl(4) administration at 7 Tesla (T) using single-shot stimulated-echo EPI with five b-values (0 to 1000 s/mm(2)) and three Δs. Apparent diffusion coefficient (ADC) and true diffusion coefficient (D(true)) were calculated by using all five b-values and large b-values, respectively.
  
  
  RESULTS
  ADC and D(true) decreased with Δ for both normal and fibrotic liver at each time point. ADC and D(true) also generally decreased with the time after CCl(4) insult. The reductions in D(true) between 2-week and 4-week CCl(4) insult were larger than the ADC reductions at all Δs. At each time point, D(true) measured with long Δ (200 ms) detected the largest changes among the 3 Δs examined. Histology revealed gradual collagen deposition and presence of intracellular fat vacuoles after CCl(4) insult.
  
  
  CONCLUSIONS
  Our results demonstrated the Δ dependent diffusion measurements, indicating restricted diffusion in both normal and fibrotic liver. D(true) measured with long Δ acted as a more sensitive index of the pathological alterations in liver microstructure during fibrogenesis.
authors.affiliation: Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong SAR, China; Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
authors.forename: Iris Y
authors.initials: IY
authors.lastname: Zhou
authors.forename: Darwin S
authors.initials: DS
authors.lastname: Gao
authors.forename: April M
authors.initials: AM
authors.lastname: Chow
authors.forename: Shujuan
authors.initials: S
authors.lastname: Fan
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Cheung
authors.forename: Changchun
authors.initials: C
authors.lastname: Ling
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Liu
authors.forename: Peng
authors.initials: P
authors.lastname: Cao
authors.forename: Hua
authors.initials: H
authors.lastname: Guo
authors.forename: Kwan
authors.initials: K
authors.lastname: Man
authors.forename: Ed X
authors.initials: EX
authors.lastname: Wu
mesh_terms: D000818:Animals; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004195:Disease Models, Animal; D017352:Echo-Planar Imaging; D008103:Liver Cirrhosis / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity; D013997:Time Factors
keywords: b-value; diffusion time; liver fibrosis; rat; restricted diffusion