Evaluation of phase-sensitive versus magnitude reconstructed inversion recovery imaging for the assessment of myocardial infarction in mice with a clinical magnetic resonance scanner.

PURPOSE: To evaluate phase-sensitive inversion-recovery (PSIR) imaging at 1.5 T in a mouse model of permanent coronary artery ligation as a potentially rapid and robust alternative for the accurate assessment of myocardial infarction (MI) by cardiac magnetic resonance imaging (MRI). MATERIALS AND METHODS: PSIR late gadolinium enhancement (LGE) imaging was compared to conventional 2D segmented inversion-recovery imaging for the assessment of murine MI. RESULTS: PSIR images provided comparable contrast and kinetics of intravenously injected gadopentetate dimeglumine (Gd-DTPA). At the mid-ventricular level there was good agreement between conventional IR and PSIR for infarct size assessment. After intravenous injection a limited time window of ∼6 minutes is available for delayed enhancement imaging in mice. Whole-heart infarct imaging with 1 mm thick slices was only possible in this restricted time frame when the PSIR method is applied, avoiding the need for repetitively adapting the correct inversion time. Infarct size determined by PSIR MRI demonstrated good agreement with postmortem histology. Infarct size determined by PSIR LGE MRI inversely correlates with left-ventricular function on day 7 after MI. CONCLUSION: The PSIR technique provides stable and consistent contrast between hyperenhanced and remote myocardium independent of the selected inversion time (TI) and proved to be a robust, fast, and accurate tool for the assessment of MI in mice

Assessment of myocardial infarction and post-infarction scar remodeling with an elastin-specific magnetic resonance agent.

BACKGROUND: -To prospectively evaluate an elastin-specific magnetic resonance contrast agent (ESMA) for in-vivo targeting of elastic fibers in myocardial infarction and post-infarction scar remodeling. METHODS AND RESULTS: -Myocardial infarction (MI) was induced in C57BL/6J mice (n=40) by permanent ligation of the left anterior descending coronary artery (LAD). Magnetic Resonance Imaging (MRI) was performed at 7 and 21 days post MI. The merits of gadolinium-based ESMA (Gd-ESMA) were compared to Gd-DTPA in terms of infarct-size determination, contrast-to-noise ratio (CNR) and enhancement kinetics. Specific binding in-vivo was evaluated by blocking the molecular target using non-paramagnetic Lanthanum-ESMA (La-ESMA). In-vivo imaging results were confirmed by post-mortem triphenyltetrazoliumcholride (TTC) staining, Elastica-Van-Gieson (EvG) staining and Western Blotting. Delayed enhancement MRI revealed prolonged enhancement of Gd-ESMA in the post-ischemic scar compared to Gd-DTPA. Infarct size measurements showed good agreement between Gd-ESMA and Gd-DTPA and were confirmed by ex-vivo TTC staining. Pre-injection of the blocking La-ESMA resulted in significantly lower CNR of Gd-ESMA at the infarct site (p=0.0019). While no significant differences in CNR were observed between delayed-enhancement imaging with Gd-DTPA between day 7 and 21 (1.8 ± vs 3.8, p=ns), Gd-ESMA showed markedly higher CNR on day 21 post MI (14.1 vs 4.9, p=0.0032), which correlated with increased synthesis of tropoelastin detected by Western Blot analysis and histology. Higher CNR values for Gd-ESMA further correlated with improved ejection fraction of the mice on day 21 after MI. CONCLUSIONS: -Gd-ESMA enables targeting of elastin within the infarct scar in a mouse model of myocardial infarction. The imaging properties of Gd-ESMA allow quantification of intra-scar elastin content in-vivo and thereby provides potential for non-invasive characterization of post-infarction scar remodeling. &nbsp