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Objective:
Accurate noninvasive diagnostic methods are of utmost importance in nonalcoholic fatty liver disease (NAFLD). Magnetic resonance elastography (MRE) can quantify tissue biomechanics noninvasively and represents a promising technique to assess hepatic fibrosis. Here, we present preliminary results of a prospective study designed to investigate the diagnostic performance of 2D/3D-MRE utilizing the gravitational transducer concept combined with a gradient echo (GRE) sequence, in comparison to the current product solution (2D-MRE Resoundant). Furthermore, we investigated the added value of 3D-MRE data when correlating imaging biomarkers with blood markers that reflect liver damage.

Materials and Methods:
Thirty-two participants with different stages of NAFLD were recruited. Patients were examined twice at 60 Hz mechanical vibration frequency (Aera, 1.5T, Siemens Healthineers, Germany): firstly, using the Resoundant MRE system (2D-MRE, SE-EPI sequence, 11 secs BH) and secondly, using the gravitational transducer approach (2D-MRE and 3D-MRE, GRE sequence, TE = 9.2 ms [in-phase] and fractional motion encoding at 30 mT/m, 14 secs BH). While 2D-MRE provides solely the magnitude of the complex shear modulus |G*|, 3D-MRE allows for the additional quantification of both real and imaginary parts of G*. Data extraction/analysis were performed twice by two experienced readers.

Results:
Elasticity values originating from 2D-MRE correlated very well between both methods (<em>r</em> = 0.83 [95% CI, 0.69 to 0.92], <em>p</em> < 0.001) with an excellent agreement in Bland-Altman plots. Interrater agreement was excellent (= 0.91). 3D-MRE (gravitational) correlated excellently with 2D-MRE (Resoundant) (<em>r</em> = 0.95 [95% CI, 0.90 to 0.98], <em>p</em> < 0.001). However, the Bland-Altman plot showed a clear bias with 2D-MRE overestimating stiffness values. We found 2D-MRE correlated to GOT in a binary fashion: for |G*| < 4kPa we found GOT< 30, while for |G*| > 4kPa we found GOT > 30. 3D-MRE on the contrary demonstrated correlations: for GOT < 30 wave attenuation show a clear trend wrt GOT (<em>r</em> = -0.27, <em>p</em> = 0.37), while for GOT > 30 viscosity correlated very well to GOT (<em>r</em> = 0.61, <em>p</em> = 0.047). Viscosity for GOT < 30 just clustered at low values, similarly to attenuation for GOT > 30. Interestingly, shear modulus or wave speed did not show any pertinent correlations.

Conclusion:
Gravitational MRE represents a novel and promising method for the noninvasive, accurate, and sensitive characterization of patients with NAFLD, and 3D-MRE carries the potential to provide imaging biomarkers that correlate to liver damage. Considering the disadvantages of liver biopsy for screening and monitoring of NAFLD, noninvasive methods that accurately assess liver damage represent very attractive alternatives.