Bias and Precision in Magnetic Resonance Imaging‐Based Estimates of Renal Blood Flow: Assessment by Triangulation

Abstract

Background Renal blood flow (RBF) can be measured with dynamic contrast enhanced‐MRI (DCE‐MRI) and arterial spin labeling (ASL). Unfortunately, individual estimates from both methods vary and reference‐standard methods are not available. A potential solution is to include a third, arbitrating MRI method in the comparison. Purpose To compare RBF estimates between ASL, DCE, and phase contrast (PC)‐MRI. Study Type Prospective. Population Twenty‐five patients with type‐2 diabetes (36% female) and five healthy volunteers (HV, 80% female). Field Strength/Sequences A 3 T; gradient‐echo 2D‐DCE, pseudo‐continuous ASL (pCASL) and cine 2D‐PC. Assessment ASL, DCE, and PC were acquired once in all patients. ASL and PC were acquired four times in each HV. RBF was estimated and split‐RBF was derived as (right kidney RBF)/total RBF. Repeatability error (RE) was calculated for each HV, RE = 1.96 × SD, where SD is the standard deviation of repeat scans. Statistical Tests Paired t‐tests and one‐way analysis of variance (ANOVA) were used for statistical analysis. The 95% confidence interval (CI) for difference between ASL/PC and DCE/PC was assessed using two‐sample F‐test for variances. Statistical significance level was P < 0.05. Influential outliers were assessed with Cook's distance (Di > 1) and results with outliers removed were presented. Results In patients, the mean RBF (mL/min/1.73m2) was 618 ± 62 (PC), 526 ± 91 (ASL), and 569 ± 110 (DCE). Differences between measurements were not significant (P = 0.28). Intrasubject agreement was poor for RBF with limits‐of‐agreement (mL/min/1.73m2) [−687, 772] DCE‐ASL, [−482, 580] PC‐DCE, and [−277, 460] PC‐ASL. The difference PC‐ASL was significantly smaller than PC‐DCE, but this was driven by a single‐DCE outlier (P = 0.31, after removing outlier). The difference in split‐RBF was comparatively small. In HVs, mean RE (±95% CI; mL/min/1.73 m2) was significantly smaller for PC (79 ± 41) than for ASL (241 ± 85). Conclusions ASL, DCE, and PC RBF show poor agreement in individual subjects but agree well on average. Triangulation with PC suggests that the accuracy of ASL and DCE is comparable. Evidence Level 2 Technical Efficacy Stage 2

Noninvasive Assessment of Diabetic Kidney Disease With MRI: Hype or Hope?

“…ASL shows an accuracy for the assessment of renal perfusion, which is competitive with contrast-based dynamic contrast enhancement based perfusion techniques. 102 Consistent results were obtained in recent clinical studies, which reported a reduction in renal cortical perfusion in early DKD patients including T1DM and T2DM compared to healthy volunteers. 77,103,104 Ritt et al reported a moderate correlation between ASL and the noninvasive "gold standard" measurement of RBF, the clearance of para-amino-hippuric acid (PAH) (r = 0.575, P < 0.001) in subjects with metabolic syndrome.…”

Renal MRI: From Nephron to NMR Signal

“…Alhummiany et al found no differences between PC-MRI, DCE, and ASL in a cohort of type-2 diabetes patients. 104 Bland-Altman and correlations between each of the measures showed PC-MRI and ASL to have the best agreement. The repeatability error is lower for PC-MRI than for ASL in healthy volunteers (79 AE 41 vs. 241 AE 85 mL/ min/1.73 m 2 ).…”

Magnetic Resonance Imaging to Diagnose and Predict the Outcome of Diabetic Kidney Disease—Where Do We Stand?

“…Only limited studies using renal PC-MRI in diabetic patients are available. In a renal blood flow validation study in 25 patients with type 2 diabetes (36% female), a good agreement between ASL, delayed contrast enhancement (DCE), and PC RBF was observed on average, but not in individual patients [32]. Of interest, PC-MRI showed a significantly smaller reproducibility error than ASL [32].…”

“…In a renal blood flow validation study in 25 patients with type 2 diabetes (36% female), a good agreement between ASL, delayed contrast enhancement (DCE), and PC RBF was observed on average, but not in individual patients [32]. Of interest, PC-MRI showed a significantly smaller reproducibility error than ASL [32]. PC-MRI has mainly been used in patients with suspected or confirmed renal artery stenosis, and fewer studies have focused on CKD or DKD.…”

“…Indeed, the filtration fraction of CKD patients was lower, and the R2* values did not differ between the CKD patients and the controls. In a randomised, double-blind, placebo-controlled, crossover trial in adults with type 1 diabetes and albuminuria, a single 50 mg dose of the SGLT2 inhibitor dapagliflozin and placebo in random order, separated by a two-week washout period, did not change renal perfusion or blood flow, but improved renal oxygenation [32,34].…”