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Visualization of myocardial infarction and subsequent coronary reperfusion with MRI using a dog model
A M Aisen1, A J Buda, R J Zotz
1Department of Radiology, University of Michigan Hospitals, Ann Arbor 48109.
Abstract:
Twelve anesthetized mongrel dogs underwent left thoracotomy with placement of a removable ligature around the left circumflex coronary artery. Following a 3 to 6 hour delay, ECG-gated spin-echo MRI was performed. The ligature was then removed reperfusing the heart, and after a 10-15 min period, MRI repeated. Finally, post-sacrifice images were obtained, and the hearts chemically stained for infarct evaluation. The MR images were subjectively and quantitatively evaluated for visibility of the endocardial border and of the injured myocardium, and for changes after reperfusion. The injured tissue was variably visible in vivo, the major limitation a result of motion blurring and artifact. The abnormal tissue was easily visible on MRI in 11 animals, and not clearly visible in one. The endocardial border was easily seen in 10 animals. The variation of calculated relaxation times was high for both normal and ischemic/infarcted myocardium in the beating hearts (normal: T1 = 566 +/- 288, T2 = 38 +/- 6; injured myocardium: T1 = 637 +/- 250, T2 = 41 +/- 12) in contrast, relatively stationary skeletal muscle measured in the same images had narrower ranges (T1 = 532 +/- 199, T2 = 28 +/- 2). Changes with reperfusion were seen, but not reliably. The infarcted or ischemic zones were easily visible on post-sacrifice images in all animals imaged. Post-sacrifice relaxation times were T1 = 564 +/- 69 msec, T2 = 39 +/- 3 msec for normal heart muscle, and 725 +/- 114, T2 = 47 +/- 5 for ischemic/infarcted tissue.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Magnetic Resonance Imaging (MRI) can visualize myocardial infarction in dogs, though in vivo imaging is limited by motion artifacts. Post-sacrifice MRI clearly identifies injured heart tissue, offering a reliable method for infarct evaluation.
Area of Science:
- Cardiovascular Imaging
- Medical Physics
- Veterinary Cardiology
Background:
- Assessing myocardial infarction (MI) is crucial for cardiac patient management.
- Magnetic Resonance Imaging (MRI) shows promise for non-invasively evaluating heart tissue damage.
- In vivo imaging of the beating heart presents challenges due to motion artifacts.
Purpose of the Study:
- To evaluate the efficacy of ECG-gated spin-echo MRI for detecting myocardial infarction in a canine model.
- To compare in vivo and post-sacrifice MRI findings with chemical staining for infarct confirmation.
- To assess the impact of reperfusion on MRI characteristics of injured myocardium.
Main Methods:
- Created a canine model of myocardial infarction using a removable ligature around the left circumflex coronary artery.
- Acquired ECG-gated spin-echo MRI scans before and after reperfusion, and post-sacrifice.
- Quantitatively and subjectively analyzed MRI for visibility of injured myocardium and endocardial border, and measured relaxation times (T1, T2).
Main Results:
- In vivo MRI visualized abnormal myocardial tissue in 11 of 12 dogs, with limitations from motion blurring and artifacts.
- The endocardial border was clearly visualized in 10 of 12 dogs.
- Post-sacrifice MRI clearly identified infarcted/ischemic zones in all animals, with distinct relaxation times compared to normal tissue.
Conclusions:
- ECG-gated spin-echo MRI can detect myocardial infarction in vivo, but motion artifacts reduce image quality.
- Post-sacrifice MRI provides clear visualization of infarct zones, serving as a reliable method for infarct evaluation.
- Further optimization of in vivo MRI techniques is needed to overcome motion-related limitations in cardiac imaging.