Capturing Acute and Subchronic Myocardial Infarct by MRI Rotating Frame Relaxation Times in Mice In and Ex Vivo.

Area of Science:

• Cardiovascular Imaging
• Magnetic Resonance Imaging (MRI)
• Biophysics

Background:

• Cardiovascular diseases are a leading global cause of death, with myocardial infarction being a critical concern.
• Conventional MRI for acute myocardial infarction uses T2 mapping, while chronic infarction relies on contrast agents.
• Rotating frame relaxation times (T1ρ and T2ρ) offer robust measurements sensitive to molecular motion, potentially characterizing both acute and chronic infarctions.

Purpose of the Study:

• To evaluate rotating frame relaxation time mappings for imaging acute and subchronic myocardial infarcts in vivo and ex vivo.
• To assess the potential of these methods as noninvasive diagnostic markers without contrast agents.

Main Methods:

• Applied adiabatic T1ρ, adiabatic T2ρ (with HS1 and HS4 pulses), continuous wave T1ρ, and conventional T2 mapping in vivo and ex vivo mouse models.
• Imaged mice 2 hours and 7 days after inducing myocardial infarction.
• Verified infarcts using histology (dystrophin and H&E staining) post-MRI.

Main Results:

• Rotating frame relaxation time mapping clearly distinguished infarcted from normal myocardium at 2 hours post-infarction.
• Adiabatic T2ρ with HS4 pulse showed significant differences between infarcted and control hearts in vivo.
• Adiabatic T1ρ (HS1, HS4) and continuous wave T1ρ demonstrated significant differences at both time points, in vivo and ex vivo.

Conclusions:

• Rotating frame relaxation time mappings show potential as noninvasive MR diagnostic markers for acute and subchronic myocardial infarcts.
• These contrast-agent-free MRI techniques can differentiate myocardial tissue states effectively.