Assessment of Kidney Stiffness in a Swine Model of Renal Arterial Stenosis with 7-D MR Elastography

Introduction: MR Elastography (MRE) is an MRI-based technique for quantitatively assessing the mechanical properties of soft tissues by visualizing propagating shear waves in tissues (1). Ideally, the MRE acquisition would involve obtaining displacement data for 3 dimensions in space, 3 cyclic displacement directions (x, y, and z) at each point in space, and at multiple time points in the wave cycle. The acquisition time required for such a 7-dimensional imaging task in vivo can be lengthy. When simple wave propagation patterns can be generated in large organs like the liver, it may suffice to acquire only 2-D wave field data (2). However, when smaller and more complex structures are evaluated, it is in general necessary to acquire 7-D MRE data, due to the complexity of wave propagation. The goal of this study was to develop a practical 7-D EPI-based renal MRE protocol and to test the following hypotheses: 1) 7-D MRE provides renal parenchymal stiffness measurements that have similar mean values but a smaller standard deviation than 2-D measurements for the same kidney in a porcine model of acute renal arterial stenosis (RAS); 2) 7-D MRE is sufficiently sensitive to detect expected reactive stiffness changes in the contralateral kidney in an experimental animal model of renal artery stenosis.