Improving the Accuracy and Repeatability of Renal Stiffness Measurement With Magnetic Resonance Elastography: Influence of Vibration Frequency, Acquisition Orientation, and Postprocessing-A Phantom and Volunteer Study.

MR elastography (MRE) is validated for liver fibrosis but remains highly challenging for renal imaging. Our aim was to optimize a prototype MRE sequence developed by Philips Healthcare for accurate and repeatable stiffness measurement using standardized phantoms and pipeline and to translate it to in vivo kidney imaging. Hence, in this prospective single-center study, 21 silicone-based phantoms with known stiffness ranging between 2 and 57.7 kPa were imaged at 1.5-Tesla using a 2D-gradient echo MRE acquisition. Mechanical vibrations were generated through a pneumatic driver with an actuator fixed on a dedicated 3D-printed phantom container. Four frequencies (60, 80, 100, and 120 Hz), three orientations (axial, sagittal, and coronal), and three MRE postprocessing algorithms were investigated (local frequency estimation [LFE], multifrequency dual elasto-visco inversion [MDEV], and wavenumber-based MDEV [kMDEV]). Acquisitions were repeated twice and coregistered. The best combinations of frequency, orientation, and postprocessing in terms of repeatability (measured with intraclass correlation coefficient [ICC]) and accuracy (measured with using root mean square error [RMSE]) were translated on five healthy volunteer's kidneys. The lowest/best RMSE was obtained with sagittal orientation, 120 Hz and LFE (RMSE = 8.9). The highest ICC was obtained with axial orientation, 120 Hz and LFE (ICC = 0.864, p < 0.0001). On phantoms with stiffness < 25 kPa, the best performing combination was sagittal orientation, 60 Hz and LFE (RMSE = 4.2). Multiple-way analysis of variance showed a strong influence of frequency (F = 47.8, p < 0.0001) and postprocessing (F = 49.5, p < 0.0001), but not orientation (p = 0.4771). Best image quality in volunteers was obtained with coronal orientation and mechanical vibrations of 60 Hz with anterior-posterior direction and LFE. In conclusion, our study showed that vibration frequency of 120 Hz provided the highest MRE accuracy across all phantoms (2-57.7 kPa), while 60 Hz was more suitable for stiffness values < 25 kPa and in vivo. Postprocessing significantly influenced stiffness values, with LFE offering superior accuracy and repeatability, whereas the orientation had minimal effect.