Myocardial Scar Delineation Using Diffusion Tensor Magnetic Resonance Tractography.

Area of Science:

• Cardiovascular Imaging
• Biomedical Engineering
• Medical Physics

Background:

• Late gadolinium enhancement (LGE) is the current standard for myocardial scar delineation.
• Diffusion tensor imaging (DTI) offers a non-invasive method to assess tissue microstructure.
• Myofiber curvature is a potential indicator of myocardial scar and arrhythmogenic substrate.

Purpose of the Study:

• Introduce tractographic propagation angle (PA), a DTI-derived metric of myofiber curvature, as an alternative to LGE for myocardial scar assessment.
• Compare the accuracy of PA with LGE and invasive endocardial voltage mapping in delineating myocardial scar.
• Evaluate the correlation between PA, infarct size, and arrhythmogenic substrate characteristics.

Main Methods:

• Performed DTI on healthy and infarcted human volunteers and mice.
• Utilized LGE with a 2D inversion recovery gradient-echo sequence for scar delineation.
• Conducted ex vivo DTI on normal and infarcted human and sheep hearts, alongside endocardial electroanatomic mapping.

Main Results:

• PA in normal human hearts was <4 degrees/unit distance, significantly lower than in infarct zones (10.34±1.02 degrees/unit distance).
• A PA threshold >4 demonstrated the highest accuracy for infarct size estimation and strong correlation with LGE (r=0.95).
• PA values showed an inverse relationship with endocardial voltage, indicating scar characterization.

Conclusions:

• PA derived from DTI strongly correlates with LGE for infarct size assessment in both animal models and humans.
• PA effectively characterizes arrhythmogenic substrate by showing an inverse relationship with endocardial voltage.
• PA offers a potential contrast-agent-free method for myocardial scar delineation and substrate characterization.