Microstructural Infarct Border Zone Remodeling in the Post-infarct Swine Heart Measured by Diffusion Tensor MRI

Area of Science:

• Cardiovascular Imaging
• Biomedical Engineering
• Cardiac Electrophysiology

Background:

• Computational cardiac models require detailed microstructural information to accurately represent electromechanics, especially in conditions like myocardial infarction.
• The infarct border zone (BZ) is a critical region of electromechanical transition, but its microstructural remodeling is poorly characterized by MRI.
• Late gadolinium-enhanced (LGE) MRI identifies infarcts and BZ, while diffusion tensor MRI (DT-MRI) quantifies microstructural properties like cellularity, fibrosis, and fiber organization.

Purpose of the Study:

• To segment remote, BZ, and infarcted myocardium using LGE MRI in post-infarct porcine hearts.
• To quantify microstructural remodeling in the BZ and infarcted regions using co-registered DT-MRI.
• To characterize the distinct microstructural changes within the BZ compared to remote and infarcted myocardium.

Main Methods:

• Chronic porcine infarcts were created and hearts were imaged 6-8 weeks post-infarction using LGE MRI and co-registered DT-MRI.
• Myocardium was segmented into remote, BZ, and infarct categories based on LGE signal intensity thresholds.
• Diffusion tensor (DT) invariants, including apparent diffusion coefficient (ADC), fractional anisotropy (FA), and tissue mode, were calculated to assess microstructural remodeling.

Main Results:

• The BZ showed significant microstructural remodeling compared to both remote and infarcted myocardium.
• BZ exhibited decreased cellularity (increased ADC), reduced tissue organization (decreased FA), and increased fiber disarray (decreased tissue mode) relative to remote myocardium (p < 0.05).
• Microstructural changes in the infarct were similar in nature but significantly greater in magnitude than in the BZ (p < 0.05).

Conclusions:

• DT-MRI can effectively identify and quantify significant microstructural remodeling within the infarct border zone.
• The microstructural characteristics of the BZ are distinct from both remote and infarcted myocardial regions.
• These findings provide crucial microstructural data for enhancing computational cardiac models of post-infarct hearts.