Rotating Frame Spin‐Lock Cardiac MRI Method at 9.4 T Can Characterize Diffuse Fibrosis in Progressing Hypertensive Heart Disease in Mice

Purpose This study aimed to investigate the applicability of rotating frame spin‐lock continuous wave (CW) T 1ρ and relaxation along a fictitious field with Rank 2 (RAFF2) methods complementary to native T 1 and late gadolinium enhancement (LGE) for cardiac magnetic resonance imaging (CMRI) of diffuse fibrosis in mice with advancing hypertensive heart disease (HHD) and diastolic dysfunction. Methods HHD was induced in mice with angiotensin II infusion for 28 days; sham operated were used as controls. Phenotype progression was assessed with echocardiography. Characterization of diffuse fibrosis was performed with CMRI. CW‐T 1ρ and RAFF2 were compared with native T 1 and LGE acquired on Days 14 and 28 of the experiment. Regions of interest in CMRI relaxation time maps and Picrosirius red‐stained histological cardiac sections were compared. Results Diffuse fibrosis in the left ventricle was visible on Day 14 with T RAFF2 relaxation time maps in the HHD group with early diastolic impairment, and CW‐T 1ρ showed a slight increase. Both CW‐T 1ρ and T RAFF2 showed elevated values on Day 28 in HHD mice, whereas native T 1 showed an increase only on Day 28. LGE showed no accumulation. The presence of diffuse fibrosis was verified with cardiac histology. Conclusions Rotating frame spin‐lock CW‐T 1ρ and RAFF2 are more sensitive to native T 1 and LGE in the characterization of diffuse fibrosis in advancing HHD in mice, being an alternative for the imaging of fibrotic remodeling also in other cardiac pathologies.