The importance of spatial resolution in detecting chronic myocardial iron remnants following hemorrhagic myocardial infarction with T2* MRI.

Purpose. Intramyocardial hemorrhage following revascularized myocardial infarction is associated with increased mortality and morbidity. T2* cardiac MRI is the noninvasive imaging standard for visualizing the chronic iron deposits from hemorrhagic myocardial infarction (hMI). However, the impact of spatial resolution on detection performance of these iron deposits remains unclear.Methods. We investigated the influence of spatial resolution on the detection of iron deposits following hMI using (i) digital phantom simulations across voxel sizes (0.4-2.0 mm2in-plane; 2-8 mm slice thickness) at multiple Signal-to-noise ratio (SNR) levels, (ii)ex-vivoswine hearts (n= 10) with 8 week hMI.ex-vivoimaging studies employed multi-gradient-echo sequences with various in-plane and through-plane resolutions with minimal SNR constraints (Unconstrained Acquisitions) and within-vivotime constraints (Constrained Acquisitions), and (iii)in-vivoT2* imaging at standard spatial resolution (1.6 × 1.6 × 6 mm3). Detection performance was assessed using receiver operating characteristics analysis and its area-under-the-curve (AUC), along with SNR and contrast-to-noise-ratio. Histopathology and mass spectrometry validated iron distribution.Results. Simulations demonstrated that finer voxels minimized partial volume but reduced SNR, while coarser voxels increased SNR but masked focal lesions. Optimal performance (AUC = 0.80) was identified at 1.3-1.6 mm2pixel size with 2-4 mm slice thickness underConstrained Acquisitions. Detection accuracy declined sharply for iron depositions that were thin in the transmural direction (<1 mm) with limited pixel representation at clinical resolutions. Inductively coupled plasma mass spectrometry confirmed significantly elevated iron content in hMI regions vs remote myocardium (45.1 ± 9.3 vs 35.3 ± 4.7μg g-1,p= 0.012) and correlated with the transmural width of hMI remnants (R2= 0.83).Conclusion. Spatial resolution critically determines the detectability of chronic iron remnants on T2* maps. While current clinical protocols can identify larger deposits, small (<1 mm) yet proinflammatory lesions may be missed. These results highlight the need for technical improvements to enhance detection.