Saturated Multi‐Delay Renal Arterial Spin Labeling Technique at 5 T MR: A Comparative Study With 3 T

Background The feasibility of renal multi‐delay arterial spin labeling (ASL) imaging at 5 T remains unclear. Purpose To evaluate the feasibility of the saturated multi‐delay renal ASL (SAMURAI) sequence at 5 T by comparing image quality and perfusion quantification with 3 T. Study Type Prospective, cross‐sectional. Population Twenty healthy volunteers (28.6 ± 7.8 years, 9 males) for primary comparison; 6 volunteers (24.2 ± 1.5 years, 5 males) for reproducibility study at 5 T. Field Strength/Sequence SAMURAI sequence at 3 T and 5 T. Assessment The SAMURAI sequence was optimized at 5 T with renal‐specific B1 shimming and an optimized saturation scheme by numerical simulation. Each participant underwent 3 T and 5 T scans in randomized order. Cortical T1 value, renal blood flow (RBF), arterial and tissue bolus arrival times were measured. The signal‐to‐noise ratio (SNR) and cortico‐medullary contrast‐to‐noise ratio (CNR) were calculated from perfusion‐weighted images. Short‐term repeatability ( n = 20) and reproducibility ( n = 6) tests of quantitative parameters were performed at 5 T. Statistical Tests Differences and agreement between 3 T and 5 T were analyzed using the Wilcoxon signed‐rank test, intraclass correlation coefficients (ICC) and linear correlation analysis ( R 2 ). The repeatability at 5 T was assessed by ICC. A p < 0.05 was considered statistically significant. Results Renal cortical T1 values were significantly higher at 5 T than 3 T (1417.9 ± 75.7 ms vs. 1184.2 ± 84.4 ms), with R 2 = 0.509. Cortical RBF showed an insignificant difference between 5 T and 3 T: 324.4 (interquartile range [IQR]: 310.1–366.4) vs. 329.7 (IQR: 309.5–368.1) [mL/100 g/min] ( p = 0.333), with R 2 = 0.914. 5 T showed significantly higher mean SNR (4.6 vs. 3.9) and CNR (3.2 vs. 2.0) than 3 T across all inversion times, with excellent repeatability and reproducibility of quantitative parameters (ICC = 0.855–0.973). Data Conclusions Renal quantitative imaging with SAMURAI sequence at 5 T is feasible and repeatable, with significantly higher SNR and CNR than 3 T and strong interfield agreement of cortical RBF measurements. Level of Evidence 2. Technical Efficacy Stage 1.