Magnetic susceptibility and R2*of myocardial reperfusion injury at 3T and 7T

Purpose Magnetic susceptibility (Delta chi) alterations have shown association with myocardial infarction (MI) iron deposition, yet there remains limited understanding of the relationship between relaxation rates and susceptibility or the effect of magnetic field strength. Hence, Delta chi and R2* in MI were compared at 3T and 7T. Methods Subacute MI was induced by coronary artery ligation in male Yorkshire swine. 3D multiecho gradient echo imaging was performed at 1-week postinfarction at 3T and 7T. Quantitative susceptibility mapping images were reconstructed using a morphology-enabled dipole inversion. R2* maps and quantitative susceptibility mapping were generated to assess the relationship between R2*, Delta chi, and field strength. Infarct histopathology was investigated. Results Magnetic susceptibility was not significantly different across field strengths (7T: 126.8 +/- 41.7 ppb; 3T: 110.2 +/- 21.0 ppb, P = NS), unlike R2* (7T: 247.0 +/- 14.8 Hz; 3T: 106.1 +/- 6.5 Hz, P < .001). Additionally, infarct Delta chi and R2* were significantly higher than remote myocardium. Magnetic susceptibility at 7T versus 3T had a significant association (beta = 1.02, R-2 = 0.82, P < .001), as did R2* (beta = 2.35, R-2 = 0.98, P < .001). Infarct pathophysiology and iron deposition were detected through histology and compared with imaging findings. Conclusion R2* showed dependence and Delta chi showed independence of field strength. Histology validated the presence of iron and supported imaging findings.

Automated summary

The study compared Delta chi and R2* in subacute myocardial infarction at 3T and 7T, finding that magnetic susceptibility did not significantly differ across field strengths, while R2* showed a significant difference. The study concluded that R2* was dependent on field strength, while Delta chi showed independence, with histology validating the presence of iron and supporting imaging findings.