Non-contrast-enhanced magnetic resonance imaging can be used to assess renal cortical and medullary volumes—A validation study

BACKGROUND: Magnetic resonance imaging (MRI) biomarkers can diagnose and prognosticate kidney disease. Renal volume validation studies are however scarce, and measurements are limited by use of contrast agent or advanced post-processing. PURPOSE: To validate a widely available non-contrast-enhanced MRI method for quantification of renal cortical and medullary volumes in pigs; investigate observer variability of cortical and medullary volumes in humans; and present reference values for renal cortical and medullary volumes in adolescents. MATERIALS AND METHODS: Cortical and medullary volumes were quantified from transaxial in-vivo water-excited MR images in six pigs and 15 healthy adolescents (13–16years). Pig kidneys were excised, and renal cortex and medulla were separately quantified by the water displacement method. Both limits of agreement by the Bland-Altman method and reference ranges are presented as 2.5–97.5 percentiles. RESULTS: Agreement between MRI and ex-vivo quantification were -7 mL (-10–0 mL) for total parenchyma, -4 mL (-9–3 mL) for cortex, and -2 mL (-7–2 mL) for medulla. Intraobserver variability for pig and human kidneys were <5% for total parenchyma, cortex, and medulla. Interobserver variability for both pig and human kidneys were ≤4% for total parenchyma and cortex, and 6% and 12% for medulla. Reference ranges indexed for body surface area and sex were 54–103 mL/m(2) (boys) and 56–103 mL/m(2) (girls) for total parenchyma, 39–62 mL/m(2) and 36–68 mL/m(2) for cortex, and 16–45 mL/m(2) and 17–42 mL/m(2) for medulla. CONCLUSION: The proposed widely available non-contrast-enhanced MRI method can quantify cortical and medullary renal volumes and can be directly implemented clinically.