Objective: The aim of this study was to apply multifrequency magnetic resonance elastography (MMRE) for assessment of kidney function based on renal stiffness of allografts in transplant recipients and native kidneys in controls.
Methods: In this prospective study, MMRE was used to measure stiffness in transplant kidneys in 22 recipients (age range, 23-73 years; 7 females) and in native kidneys in 11 controls (age range, 26-55 years; 4 females) after internal review board approval. The MMRE was performed on a 1.5 T magnetic resonance imaging scanner using 4 vibration frequencies from 40 to 70 Hz. Stiffness maps were computed by multifrequency reconstruction of the magnitude shear modulus (|G*|). Clinical markers such as glomerular filtration rate (GFR) and resistive index (RI) were acquired. Differences in renal stiffness among groups were compared by Mann-Whitney U test. Correlations were tested using Pearson correlation.
Results: Functioning transplants had higher stiffness (|G*| = 9.00 ± 1.71 kPa) than nonfunctioning transplants (|G*| = 5.88 ± 1.71 kPa, P < 0.001) and native kidneys (|G*| = 6.63 ± 1.63 kPa, P < 0.01). A cutoff value of 7.04 kPa provided sensitivity (83.33%) and specificity (86.67%) for detecting renal allograft dysfunction with an area under the receiver operating characteristic curve value of 0.9278 (95% confidence interval, 0.83-1.00). |G*| correlated positively with GFR (r = 0.52, P = 0.015) and negatively with RI (r = -0.52, P = 0.016).
Conclusions: Multifrequency magnetic resonance elastography has good diagnostic accuracy in detecting renal allograft dysfunction. Renal stiffness is significantly lower in recipients with nonfunctioning transplant kidneys and correlates with clinical markers such as GFR and RI.