Synopsis

Keywords: Liver, Diffusion/other diffusion imaging techniques

Recently, diffusion-weighted (DW) imaging–based elastography was proposed for noninvasive liver staging by converting a shifted apparent diffusion coefficient (sADC) to tissue elasticity on the basis of two b values (200 and 1500sec/mm²). We retrospectively calculated sADC from DW MRI and converted it to DW MRI–based virtual shear modulus (µ_Diff) for evaluating liver fibrosis in 90 patients. Our results showed the µ_Diff was significantly correlated with liver fibrosis stage, and the areas under the curves were 0.864 and 0.821 for significant and advanced fibrosis, respectively, indicating DW imaging–based elastography is a promising method for predicting liver fibrosis.

Introduction

Recently, diffusion-weighted (DW) imaging–based elastography was proposed for noninvasive liver staging by converting a shifted apparent diffusion coefficient (sADC) to tissue elasticity on the basis of two b values (200 and 1500sec/mm²)¹. The purpose of this study was to evaluate the liver fibrosis by using diffusion-weighted (DW) MRI–based elastography, with histopathological findings as the reference standard.

Methods

This retrospective study included 90 patients (66 men and 24 women; mean age, 56.6±9.7 years; age range, 27–75 years) who underwent multiple b-values DW MRI with a 1.5T MR scanner (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany). Shifted apparent diffusion coefficient was calculated from DW MRI (b=200 and 1500 sec/mm²) and converted to DW MRI–based virtual shear modulus (µ_Diff) by using an in-house developed program based on MATLAB (Mathworks, Natick, Mass) according to the method proposed in the previous studies^1-2. Liver fibrosis stage was histologically determined according to Scheuer scoring system: S0 (n=16), S1 (n=11), S2 (n=11), S3 (n=16) and S4 (n=36). The correlation between µ_Diff with fibrosis stage was assessed by Spearman's rank correlation coefficient. Receiver operating characteristic (ROC) curves for µ_Diff were built to assess its diagnostic value in identifying different stages of liver fibrosis.

Results

The representative sADC map and DW MRI–based elastography were shown in Fig.1. The median values of µ_Diff for significant fibrosis (S≥2) were 5.305kp, and for advanced fibrosis (S≥3) were 5.380kp, respectively. The µ_Diff showed a significant correlation with liver fibrosis stage (rho=0.55, P<0.001). The ROC curves of µ_Diff for the diagnosis of significant fibrosis and advanced fibrosis are shown in the Fig. 2, and the areas under the curves were 0.864 and 0.821, with cutoff of >4.515kp and >4.945kp, respectively.

Discussion

Diffusion-weighted (DW) imaging can explore the increased hindrance of diffusion in water protons with the increased connective tissue in fibrotic liver parenchyma^1. DW imaging–based elastography staging liver fibrosis by converting a sADC to tissue elasticity with two b values (200 and 1500 sec/mm²), chosen theoretically and experimentally to provide an optimized sensitivity to both Gaussian and non-Gaussian diffusion^1,2. Previous studies have demonstrated highly significant correlation between sADC and MR elastography^1,2.

Conclusion

DW MRI–based elastography is a promising method for predicting liver fibrosis.

Acknowledgements

No.