Enhanced T1 sensitivity and reduced artifacts in ferumoxytol-enhanced CMRI at 0.55 T compared to 3 T: a preclinical in vivo study

Background: Ferumoxytol-enhanced (FE) magnetic resonance imaging (MRI) has gained increasing interest due to its versatility across applications such as MR angiography, 4D flow imaging, tumor characterization, and myocardial assessment 1-6 .Despite its diagnostic potential, clinical adoption remains limited by factors including high cost and the risk of hypersensitivity reactions, leading to strategies that reduce contrast dose without compromising image quality 7,8 .Prior in vitro studies suggest that iron oxide nanoparticles like ferumoxytol may exhibit enhanced relaxivity at lower magnetic field strengths, potentially improving efficacy at reduced doses 9-11 .However, direct in vivo comparisons of ferumoxytol performance across different field strengths are lacking.In this study, we compare the T1 sensitivity to ferumoxytol and artifact severity at 3 T vs 0.55 T using large animal models and commercially available MRI platforms. Methods:We conducted a preclinical study using domestic swine scanned at 3 T (n=18) and 0.55 T (n=23) on commercial MRI systems under a protocol approved by local IACUC.Standard MOLLI T1 maps were acquired before and after slow infusion of ferumoxytol at doses up to 4 mg/kg.We defined T1 sensitivity as "the percent change in T1 after ferumoxytol infusion" (for blood and myocardium, separately).For each dose, myocardial and blood regions of interest (ROIs) were analyzed for T1 sensitivity.The susceptibility/ banding artifact severity on the T1 maps was independently scored by two expert readers blinded to the field strengths using a 0-3 scale (0=no artifacts, 3=severe artifacts).The T1 sensitivity and artifact severity at two field strengths were statistically compared using student's t-test.Results: As shown with the representative cases in Figure 1, T1 maps showed progressive T1 shortening with increasing ferumoxytol dose at both field strengths, as expected.However, 0.55 T demonstrated significantly higher T1 sensitivity (ΔT1) in both myocardium and blood for the same ferumoxytol dose.As shown in Figure 2a, myocardial T1 sensitivity to ferumoxytol was linear and nearly 2.5fold greater at 0.55 T compared to 3 T (p < 0.01).Blood T1 sensitivity showed a nonlinear trend at both field strengths but was also significantly higher at 0.55 T than 3 T (p < 0.01) as demonstrated in Figure 2-b.Artifact severity scores were significantly lower at 0.55 T (0.10 ± 0.35 vs. 1.64 ± 1.11 at 3 T, p < 0.01), with reduced susceptibility/banding artifacts evident in raw T1-weighted images and the T1 maps (Figure 3).Conclusion: FE CMR at 0.55 T offers superior T1 sensitivity and reduced susceptibility artifacts compared to 3 T.These findings suggest that low-field MRI can enable lower contrast doses while maintaining diagnostic performance, potentially reducing cost and improving safety.This work supports broader adoption of low-field CMRI for ferumoxytol-based cardiovascular imaging.