Contrast-free postoperative imaging of the pulmonary arteries: Intraindividual comparison of Relaxation-Enhanced Angiography without Contrast and Triggering (REACT) and time-resolved contrast-enhanced MRA

To compare a flow-independent, 3D isotropic non-contrast MRA (REACT), with time-resolved contrast-enhanced MRA (4D CE-MRA) for postoperative assessment of the pulmonary arteries in patients with congenital heart disease (CHD), with emphasis on different implant types. In this retrospective single-center study, 53 patients with CHD underwent clinically indicated cardiovascular magnetic resonance (CMR) including both 4D CE-MRA and REACT at 1.5 T. Three radiologists independently scored image quality (IQ) as well as motion and susceptibility artifacts on 5-point Likert scales and measured the diameters of the pulmonary arteries (PAs) [main (MPA), left (LPA) and right pulmonary artery (RPA)]. Subgroup analysis was performed for stents, conduit/patch/valve (CPV), and no implant. Pooled across readers and PA segments, REACT achieved higher overall IQ than 4D CE-MRA (median 3.67 [3.00–4.17] vs. 3.00 [2.33–3.33]; p < 0.001) and provided significantly better motion scores ( p < 0.001), whereas susceptibility scores were comparable between techniques. The proportion of fully diagnostic studies (3/3 segments) was similar (REACT 77.4%, 41/53; 4D CE-MRA 83.0%, 44/53; McNemar, p = 0.38). Diameter measurements showed excellent inter-reader agreement (ICC ≈ 0.89–0.95) and minimal bias between techniques; only the RPA yielded slightly smaller diameters in REACT (mean difference –0.85 ± 1.51 mm, p < 0.001). In subgrou p analysis, stented segments showed no IQ advantage of REACT ( p > 0.99) with IQ being limited due to susceptibility artifacts in both 4D CE-MRA and REACT. In the CPV and the no implant group, REACT yielded a one point higher median IQ score (both p = 0.002) and one point less impaired by motion artifacts (CPV: p < 0.001; no implant: p = 0.002), while both techniques provided very high shares of diagnostic image quality (defined as IQ ≥ 2; both > 90%; p > 0.99). REACT enables robust, contrast-free postoperative imaging of the pulmonary arteries in patients with CHD with superior IQ and reduced motion artifacts compared to 4D CE-MRA, while maintaining highly reproducible diameter measurements. Stented segments remain a shared limitation.