Effect of cardiac flow on gradient recalled echo images of the canine heart.

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.