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Effect of cardiac flow on gradient recalled echo images of the canine heart
R S Balaban1, J F Taylor, R Turner
1Laboratory of Cardiac Energetics, National Heart Lung and Blood Institute, Bethesda, MD 29817.
Insights
Gradient recalled echo (GRE) MRI signal intensity in canine hearts increases with coronary blood flow and oxygenation. Changes in GRE signal intensity reflect alterations in tissue blood volume and deoxyhemoglobin concentration during altered flow states.
Area of Science:
- Cardiovascular imaging
- Magnetic resonance imaging
- Physiology
Background:
- Gradient recalled echo (GRE) magnetic resonance imaging (MRI) is sensitive to blood flow.
- Understanding the relationship between coronary blood flow and GRE signal intensity is crucial for cardiac MRI applications.
Purpose of the Study:
- To evaluate the effect of coronary blood flow on GRE MR signal intensity in the canine heart at 4 Tesla.
- To investigate the underlying physiological mechanisms influencing GRE signal changes during altered coronary perfusion.
Main Methods:
- Utilized a fully instrumented canine model with a 4 Tesla MRI scanner.
- Induced controlled hyperfusion (adenosine infusion) and ischemia (local occlusion) while monitoring coronary blood flow and venous oxygen tension.
- Acquired GRE MR images with varying echo times (TE) and repetition times (TR).
Main Results:
- GRE signal intensity increased proportionally with enhanced coronary blood flow and venous oxygenation.
- Local coronary occlusion led to a minor decrease in signal intensity in the affected cardiac region.
- Signal intensity changes were dependent on TE and TR, suggesting alterations in apparent T1 and T2 relaxation times.
- Apparent T2 changes correlated with deoxyhemoglobin concentration, while apparent T1 changes suggested inflow effects.
Conclusions:
- Coronary blood flow and oxygenation significantly modulate GRE MR signal intensity in the heart.
- GRE signal changes are linked to variations in tissue blood volume, deoxyhemoglobin concentration, and inflow effects.
- These findings enhance the understanding of GRE imaging in assessing myocardial perfusion and oxygenation.
Abstract:
The effect of coronary flow on the signal intensity of gradient recalled echo (GRE) MR images of the canine heart was evaluated at 4 T. Using a fully instrumented canine model, hyperfusion (local adenosine infusion) and ischemia (local occlusion) were evaluated while coronary blood flow and venous oxygen tension were monitored. These studies demonstrated an increase in GRE signal intensity with increases in coronary blood flow and venous oxygenation. A local occlusion resulted in a small decrease in signal intensity in the affected area of the heart. The dependence of the signal changes on TE and TR indicated that the effects of high flow were associated with changes in the apparent T2 and T1. Both relaxation effects could reflect changes in tissue blood volume associated with the conditions studied. In addition, the apparent T2 changes were consistent with alterations in total tissue deoxyhemoglobin concentration and the changes in apparent T1 were consistent with inflow effects.