The utility of magnetic resonance imaging for noninvasive evaluation of diabetic nephropathy

Abstract

Background: Noninvasive quantitative measurement of fibrosis in chronic kidney disease (CKD) would be desirable diagnostically and therapeutically but standard radiologic imaging is too variable for clinical usage. By applying a vibratory force, tissue shear wave stiffness can be measured by magnetic resonance elastography (MRE) that may correlate with progression of kidney fibrosis. Since decreased kidney perfusion decreases tissue turgor and stiffness, we combined newly available three-dimensional MRE shear stiffness measurements with MR arterial spin labeling (ASL) kidney blood flow rates to evaluate fibrosis in diabetic nephropathy.

Methods: Thirty individuals with diabetes and Stage 0-5 CKD and 13 control individuals without CKD underwent noncontrast MRE with concurrent ASL blood flow measurements.

Results: MRE cortical shear stiffness at 90 Hz was decreased significantly below controls in all CKD stages of diabetic nephropathy. Likewise, ASL blood flow decreased progressively from 480 ± 136 mL/min/100 g of cortical tissue in controls to 302 ± 95, 229 ± 7 and 152 ± 32 mL/min/100 g in Stages 3, 4 and 5 CKD, respectively. A magnetic resonance imaging (MRI) surrogate for the measured glomerular filtration fraction [surrogate filtration fraction = estimated glomerular filtration rate (eGFR)/ASL] decreased progressively from 0.21 ± 0.07 in controls to 0.16 ± 0.04 in Stage 3 and 0.10 ± 0.02 in Stage 4-5 CKD.

Conclusions: In this pilot study, MRI with ASL blood flow rates can noninvasively measure decreasing kidney cortical tissue perfusion and, with eGFR, a decreasing surrogate filtration fraction in worsening diabetic nephropathy that appears to correlate with increasing fibrosis. Differing from the liver, MRE shear stiffness surprisingly decreases with worsening CKD, likely related to decreased tissue turgor from lower blood flow rates.

Keywords: chronic kidney disease; diabetic nephropathy; kidney fibrosis; kidney perfusion; magnetic resonance elastography.

FIGURE 1

3D MRE cortical shear stiffness plotted by eGFR levels: (A) in 11 normal controls and 29 diabetic patients (80 total kidneys) at 60 Hz and (B) in 12 normal controls and 30 diabetic patients (84 total kidneys) at 90 Hz.

FIGURE 2

MR ASL renal blood flow (A) compared with eGFR levels in 12 normal controls and 28 diabetic patients (79 total kidneys) and (B) compared with 3D MRE cortical shear stiffness at 90 Hz in 11 normal controls and 28 diabetic patients (77 total kidneys). The solid line depicts the linear regression with an x-axis intercept of 3861 Pa, which may represent the residual shear stiffness of the average kidney at zero ASL blood flow rate.

FIGURE 3

3D MRE cortical shear stiffness at 90 Hz compared with ASL cortical blood flow in kidneys of normal controls and patients with diabetes grouped by CKD stage. Both MRE shear stiffness and ASL blood flow decrease significantly with worsening diabetic nephropathy, but separation of CKD stages is more clearly shown by ASL blood flow.

FIGURE 4

sFF = eGFR/ASL renal blood flow plotted against eGFR in 12 normal controls and 28 diabetic patients. The sFF decreases with decreasing GFR in the normal controls and diabetic patients.