Multiparametric MRI in a Prospective Cohort of Living Kidney Donors, Recipients, and Healthy Controls: Correlations With Markers of Renal Function, Fibrosis and Ageing

Development of renal fibrosis is a characteristic end point of various renal diseases and independently predicts adverse renal outcomes. The most common cause of kidney allograft failure after 1 year is chronic allograft nephropathy which is characterized by interstitial fibrosis and tubular atrophy. At present the only method for quantifying renal fibrosis is a renal biopsy. Although the risk of complications is relatively low, the procedure is invasive, limiting its use for repeated assessments in a clinical setting. Furthermore, as only the renal cortex is usually sampled and because of the miniscule amount of tissue obtained there are issues of sampling bias and information on total renal fibrosis is limited. Estimated glomerular filtration rate (eGFR) is widely used for monitoring renal function but is insensitive for detecting allograft fibrosis.

Epidemiological data suggests that living kidney donors (LKD) are at increased risk of end stage renal disease compared to matched non-donors. Lower predonation renal function and higher age accentuate the risk. In a recent prospective study, renal cortex volume predicted renal outcome after 1 year in LKD.

In recent years there has been a rapid development in renal magnetic resonance imaging (MRI) techniques, allowing assessment of total renal morphology, microstructure, hemodynamics, oxygenation, and diffusion of water. Multiparametric MRI (mpMRI) refers to the combination of several MRI-based measures sensitive to different biophysical tissue properties in a single scan session. The information obtained could possibly provide a means of characterizing several aspects of renal function and morphology.

The MRI based measures that show the greatest promise for clinical application are longitudinal relaxation time (T1), diffusion weighted imaging (DWI), blood oxygen-level dependent imaging (BOLD) and arterial spin labelling (ASL). In a cross-sectional study, patients with chronic kidney disease (n=22) and healthy volunteers (n=22) were assessed with MRI-based measures and renal biopsy. MRI based measures were reproducible and correlated with currently used methods for measuring renal function. Significant differences were found in T1-mapping, apparent diffusion coefficient (ADC) and ASL in persons with low and high degrees of renal fibrosis. In another cross-sectional study (n = 164) the corticomedullary ADC difference was highly correlated to and independently associated with renal fibrosis in both native kidneys and allografts. In a more recent prospective study, the corticomedullary ADC difference was predictive of kidney function decline and dialysis initiation in transplant recipients and patients with CKD. Reduced oxygenation determined by low BOLD has been linked to the progression rate of chronic kidney disease. Interestingly, a study found that diffusion-based MRI measures detected an increase in allograft fibrosis before apparent changes in the estimated glomerular filtration rate.

Before mpMRI of the kidneys can be utilized in the clinical setting there is a need for development of a larger evidence base. To date clinical studies employing MRI-based measures have been mostly cross-sectional. So far, only few studies have been performed in living kidney donors (LKD) and renal transplant recipients. To the best of our knowledge, no studies have been performed with long term follow-up including repeated mpMRI, renal biopsies and accurate measurement of glomerular filtration rate with DTPA clearance. Repeated imaging is necessary to establish how MRI-based measures change over time in association with currently used reference methods for quantifying renal function and fibrosis.