Early diagnosis of acute experimental autoimmune myocarditis in mice with preserved left ventricular ejection fraction: a feasibility study based on 9.4 T magnetic resonance

Background: The application of ultrahigh-field cardiac magnetic resonance imaging (MRI), such as 9.4 T imaging, in mouse models remains challenging, especially under rapid heart rates (500–600 beats per minute), and its feasibility and reproducibility have yet to be thoroughly studied. Therefore, this study aimed to evaluate the feasibility and reproducibility of combining cardiac magnetic resonance feature tracking (CMR-FT)-derived strain parameters and conventional cardiac MRI parameters to image an acute experimental autoimmune myocarditis (EAM) mouse model under a 9.4 T ultrahigh field system and to assess its potential for the early diagnosis of acute EAM. Methods: This retrospective study (conducted from December 2023 to December 2024) included 45 male BALB/c mice (30 EAM mice and 15 controls). EAM mice were injected with Complete Freund’s Adjuvant (CFA; Sigma-Aldrich) to induce myocarditis. The control mice were treated with equal amounts of normal saline at the same time and position as those in experimental mice. CMR was performed with a 9.4 T scanner (Biospec 94/30; Bruker BioSpin) at 7 days, which included precontrast T1, postcontrast T1 and T2, and extracellular volume fraction (ECV) mapping. Left ventricular (LV) strain was evaluated via feature tracking. The diagnostic performance of CMR was evaluated through receiver operating characteristic (ROC) analysis. Results: A total of 45 mice (30 EAM mice and 15 controls) were included. All parameters were feasible in the mice that underwent CMR, and there was excellent reliability, as indicated by intraclass correlation coefficients greater than 0.9 for both intra- and interobserver agreement across all parameters. Intra- and interobserver agreement was analyzed by intraclass correlation coefficients (ICC). EAM mice demonstrated significantly impaired strain parameters compared to healthy controls [global radial strain (GRS): 34.07%±2.49% vs. 38.20%±2.76%, P