Assessment of Myocardial Microstructural Dynamics by In Vivo Diffusion Tensor Cardiac Magnetic Resonance

Area of Science:

• Cardiovascular Imaging
• Cardiac MRI
• Biomedical Engineering

Background:

• Cardiomyocytes form microstructures called sheetlets, which change orientation during left ventricular thickening.
• Dilated cardiomyopathy (DCM) involves abnormal heart muscle with poorly understood sheetlet function.
• Diffusion tensor cardiac magnetic resonance (DT-CMR) offers a potential noninvasive method to study cardiac microstructure dynamics in vivo.

Purpose of the Study:

• Validate in vivo DT-CMR measures of cardiac microstructure against histological data.
• Characterize microstructural dynamics during left ventricular wall thickening.
• Apply DT-CMR to study hypertrophic cardiomyopathy (HCM) and DCM patients.

Main Methods:

• Acquired in vivo DT-CMR throughout the cardiac cycle in healthy swine.
• Validated DT-CMR measures against in situ and ex vivo DT-CMR and histology.
• Performed in vivo DT-CMR in human subjects: 19 controls, 19 DCM patients, and 13 HCM patients.

Main Results:

• In swine, sheetlet reorientation (E2A) correlated strongly with wall thickening (r²=0.75-0.89) and aligned with histology.
• Healthy humans showed significant E2A increase from diastole (18°) to systole (65°).
• HCM patients exhibited reduced E2A mobility (23°) and altered diastolic conformation; DCM patients showed reduced systolic E2A (40°) and impaired mobility (20°).

Conclusions:

• In vivo DT-CMR can characterize myocardial microstructure dynamics.
• DCM shows abnormal sheetlet function with altered systolic conformation and reduced mobility.
• HCM demonstrates reduced mobility with altered diastolic conformation, offering new insights into contractile dysfunction.