Blood-pool MRI assessment of myocardial microvascular reactivity

Area of Science:

• Cardiovascular Imaging
• Physiology
• Biomedical Engineering

Background:

• Assessing myocardial microvascular function is crucial for understanding heart health and disease.
• Conventional methods using blood oxygenation lack specificity for blood volume changes.
• A novel blood-pool Magnetic Resonance Imaging (MRI) approach offers potential for precise vasomodulation assessment.

Purpose of the Study:

• To adapt and apply a blood-pool MRI technique for imaging cardiac vasomodulation in rats.
• To investigate the specificity of this MRI method in detecting microvascular responses.
• To explore potential sex-related differences in myocardial vasomodulation.

Main Methods:

• Healthy male and female Sprague Dawley rats underwent MRI scans under normoxia and hypercapnia.
• A blood-pool contrast agent (Ablavar) was administered intravenously.
• Pre-contrast T1 maps and 3D CINE sequences were acquired, alongside invasive laser Doppler flowmetry for validation.

Main Results:

• T1 maps visualized myocardial microvascular dilation during hypercapnia and constriction during normoxia.
• Female rats exhibited a significant 20% reduction in myocardial T1 during hypercapnia (vasodilation).
• Males showed no significant T1 change during hypercapnia, but both sexes demonstrated vasoconstriction upon return to normoxia.

Conclusions:

• Blood-pool MRI is a sensitive and specific tool for assessing myocardial microcirculation vasomodulation.
• Significant sex-related differences exist in the healthy myocardium's response to hypercapnic stimuli.