Although 23Na MRI has been shown to delineate acute myocardial infarction (MI), the time course of in vivo 23Na MRI during infarct healing remains unknown. In this study 23Na MRI was combined with contrast-enhanced (CE) 1H MRI to noninvasively characterize infarct healing in vivo. Serial in vivo 3D 23Na MRI and 1H MRI were performed for up to 9 weeks postinfarction in 10 dogs. Radioactive microspheres were used to measure myocardial perfusion, and Hematoxylin-Eosin (H&E) and Masson's trichrome (MT) staining were used to assess interstitial cell infiltrate and collagen content. In vivo 23Na MRI accurately delineated infarct size up to day 5 postinfarction in comparison with 1H MRI (8.9% ± 8.1% vs. 8.6% ± 7.9% on day 1 postinfarction, P = NS; and 6.3% ± 6.2% vs. 6.2% ± 6.2% on days 4/5 postinfarction, P = NS). The in vivo 23Na MRI signal intensity, expressed as the signal intensity ratio of infarcted tissue vs. noninfarcted tissue (MI/R) peaked on day 1 of infarction (2.04 ± 0.23) but decreased significantly to 1.27 at 9 weeks postinfarction (P < 0.05) due to granulation tissue infiltrate and collagen deposition. To confirm the MI/R decrease during scarformation ex vivo, we performed 23Na MRI in 12 rats on day 3 post-MI (N = 5) and after 6 weeks (N = 7). H&E and Picrosirius Red staining confirmed granulation tissue infiltrate on day 3 and scar formation after 6 weeks. MI/R decreased significantly from 1.91 ± 0.45 on day 3 post-MI to 1.3 ± 0.09 after 6 weeks. Thus, in vivo 23Na MRI accurately delineates infarct size up to day 5 postinfarction. In vivo 23Na MRI signal intensity decreases during infarct healing as a result of the underlying infarct healing process.
- Magnetic resonance imaging
- Myocardial infarction
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging