Magnetic Resonance Elastography of kidneys: SE-EPI MRE reproducibility and its comparison to GRE MRE.

The purpose of this study is 1) to demonstrate reproducibility of spin echo-echo planar imaging (SE-EPI) magnetic resonance elastography (MRE) to estimate kidney stiffness; and 2) to compare SE-EPI MRE and gradient recalled echo (GRE) MRE-derived stiffness estimations in various anatomical regions of the kidney. Kidney MRE was performed on 33 healthy subjects (8 for SE-EPI MRE reproducibility and 25 for comparison with GRE MRE; age range: 22-66 years) in a 3 T MRI scanner. To demonstrate SE-EPI MRE reproducibility, subjects were scanned for the first scan and then asked to leave the scan room and repositioned again for the second (repeat) scan. Similar set-up was used for GRE MRE as well. The displacement data was then processed to obtain overall stiffness estimates of the kidney. Concordance correlation analyses were performed to determine SE-EPI MRE reproducibility and agreement between GRE MRE and SE-EPI MRE derived stiffness. A high concordance correlation (ρc  = 0.95; p-value<0.0001) was obtained for SE-EPI MRE reproducibility. Good concordance correlation was observed (ρc  = 0.84; p < 0.0001 for both kidneys, ρc  = 0.91; p < 0.0001 for right kidney and ρc  = 0.78; p < 0.0001 for left kidney) between GRE MRE and SE-EPI MRE derived stiffness measurements. Paired t-test results showed that stiffness value of medulla was significantly (p < 0.0001) greater than cortex using SE-EPI MRE as well as GRE MRE. SE-EPI MRE was reproducible and good agreement was observed in MRE-derived stiffness measurements obtained using SE-EPI and GRE sequences. Therefore, SE-EPI can be used for kidney MRE applications.