Usefulness of diffusion derived vessel density computed from a simplified IVIM imaging protocol: an experimental study with rat biliary duct blockage induced liver fibrosis.
Résumé
Aim: Liver vessel density can be evaluated by DDVD (diffusion derived vessel density): DDVD(b0b1) = Sb0/ROIarea0-Sb1/ROIarea1, where Sb0 and Sb1 refer to the liver signal when b is 0 or 1 (s/mm 2); ROIarea0 and ROIarea1 refer to the region-of-interest on b= 0 or 1 images. Sb1 and ROIarea1 may be replaced by Sb25 and ROIarea25 or Sb50 and ROIarea50 (i.e., by images of b=25 or 50 s/mm 2). With rat biliary duct ligation (BDL) model, this study assessed the usefulness of liver DDVD computed from a simplified IVIM imaging protocol. Materials and Methods: Male Sprague-Dawley rats were used, and 1, 2, 3, 4 weeks post BDL had rat number of 5, 5, 5,3 respectively. Partial recanalization (n=12) was performed with rats had BDL for 7 days and MRI was done mean 14 days after recanalization. Liver diffusion MR images were acquired using with a 3.0T magnet with a b-value distribution of 0, 30, 50, 75, 100, 150, 300, 700, 1000 s/mm 2. DDVDmean (control rats n=6) was the mean of DDVD(b0b25) and DDVD(b0b50). IVIM fitting started from b = 0 with segmented fitting and a threshold b of 50 s/mm 2 (n=5 for control rats). Three 3-D space was constructed using PF, D slow , and D fast ; PF, D slow , and DDVD mean ; or PF, D fast , and DDVD mean. Results: BDL week 1, 2, 3, 4 rats and partial recanalization rats had mean liver fibrosis METAVIR score of 1.5, 2.4, 3.25, 3.7 and 2.42 respectively. The control rats and BDL rats (n=18) had a liver DDVD mean of 84.0±26.2 and 44.7±14.4 au/pixel (p<0.001). Each diffusion MRI parameter alone could not totally separate healthy livers and all fibrotic livers (n=30, BDL and BDL+ recanalization rats). All 3-D spaces totally separated healthy livers and all fibrotic livers. The mean relative distance between healthy liver cluster and fibrotic liver cluster was 0.331 for PF, D slow , and D fast ; Dfast, 0.381 for or PF, D fast , and DDVD mean ; and 0.384 for PF, D slow , and DDVD mean. Conclusion: A combination of PF, D slow , and D fast allows a total separation of all healthy livers and fibrotic livers, with the integration of DDVD improved the separation.
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