Diffusion–based virtual mr elastography of the liver: Can it be extended beyond liver fibrosis?

Abstract

Background: Strong correlation has been reported between tissue water diffusivity and tissue elasticity in the liver. The purpose of this study is to explore the capability of diffusion–based virtual MR elastography (VMRE) in the characterization of liver tumors by extending beyond liver fibrosis assessments. Methods: Fifty‐four patients (56 liver tumors: hepatocellular carcinoma (HCC), 31; metastases, 25) who underwent MRE, diffusion‐weighted imaging (DWI) (b: 0, 800 s/mm2), and VMRE (b: 200, 1500 s/mm2) were enrolled. The MRE shear modulus (μMRE), apparent diffusion coefficient (ADC), and shifted ADC (sADC) were obtained. Virtual stiffness (μdiff) was estimated from the relationship between μMRE and sADC. A linear discriminant analysis combining VMRE and MRE to classify HCC and metastases was performed in a training cohort (thirty‐two patients) to estimate a classifier (C), and evaluate its accuracy in a testing cohort (twenty‐two patients). Pearson’s correlations between μMRE, sADC, and ADC were evaluated. In addition to the discriminant analysis, a receiver operating characteristic (ROC) curve was used to assess the discrimination capability between HCC and metastases. Results: The correlations between μMRE and sADC were significant for liver, HCC, and metastases (r = 0.91, 0.68, 0.71; all p < 0.05). Those between μMRE and ADC were weaker and significant only for metastases (r = 0.17, 0.20, 0.55). μdiff values were not significantly different between HCC and metastases (p = 0.56). Areas under the curves (AUC) to differentiate HCC from metastases were as follows: VMRE, 0.46; MRE alone, 0.89; MRE + VMRE, 0.96. The classifier C also provided better performance than MRE alone, in terms of sensitivity (100 vs 93.5%, respectively) and specificity (92 vs 76%, respectively, p = 0.046). Conclusion: The correlation between sADC and μMRE was strong both in the liver and in tumors. However, VMRE alone could not classify HCC and metastases. The combination of MRE and VMRE, however, allowed discriminant performance between HCC and metastases.