Association of In Vivo Kidney Stiffness Measured by Multifrequency MR Elastography and Long-Term Renal Function in Transplant Recipients and Living Donors.

Background: Kidney transplant (KTx) function assessment is important in treatment planning, while conventional MRI markers lack sensitivity for KTx function. Mechanical kidney properties may serve as MRI markers for renal allograft function.

Hypothesis: To determine if multifrequency MR elastography (MRE) is associated with KTx function.

Study type: Prospective, longitudinal.

Subjects: Twelve kidney donors (51 ± 9 years, 8 females) and 12 allograft recipients (48 ± 17 years, 2 females).

Fieldstrength/sequence: 1.5 T, MRE, and diffusion-weighted MRI based on spin-echo echo-planar imaging and T2-weighted MRI volumetry.

Assessment: Kidney donors were imaged pre- and post-KTx, while allograft recipients were imaged post-KTx. Renal function was assessed using creatinine levels (at 1 week, 1 month, and 3 years post-KTx in recipients) and glomerular filtration rate (GFR; donors pre-KTx) based on Tc-99m-MAG3 scintigraphy. Kidney volumes were measured by MRI segmentations, and ADC, shear-wave speed (SWS), and loss-angle maps were reconstructed. The correlations between MR parameters, GFR, and creatinine level (minimum value over study period) were investigated.

Statistical tests: Wilcoxon tests and Pearson correlation coefficients (R). A p < 0.05 was considered statistically significant.

Results: No significant lateral differences in renal volume (153 ± 34 cm³, p = 0.34) or SWS (2.5 ± 0.4 m/s, p = 0.20) were found pre-KTx. Volume and SWS increased significantly post-KTx in reference kidneys (volume: +13%, SWS: +11%) and in transplants in recipients (volume: +20%, SWS: +32%). SWS, but not volume (p = 0.75), correlated positively with GFR in donors pre-KTx (R = 0.67) while both SWS (R = ‑0.62) and volume (R = -0.77) negatively correlated with creatinine levels post-KTx. ADC was sensitive to KTx-associated changes in renal function in donors (3% ± 5%) but not recipients (p = 0.88).

Data conclusion: MRE provides valuable information on renal function and could serve as a baseline for longitudinal monitoring of kidney transplants. Parenchymal stiffening post-KTx had significantly larger effect sizes in denervated allografts than in reference donor kidneys with intact autoregulation of renal blood flow.

Evidence level: 2.

Technical efficacy: Stage 2.