BOLD MRI for myocardial ischemia evaluation

BOLD MRI for myocardial ischemia evaluation

BOLD MRI for myocardial ischemia evaluation: Blood-oxygen-level dependent MRI (BOLD MRI) is technique useful in detecting myocardial ischemia. Oxyhaemoglobin and deoxyhaemoglobin differ in their magnetic properties – the former is mildly diamagnetic while the latter is paramagnetic [1]. This difference in magnetic properties can be used as an endogenous contrast to visualize tissue oxygenation. This technique has been termed BOLD MRI. Deoxygenation of hemoglobin causes inhomogeneity in the local magnetic field and hence a change in T2 weighted MRI images.

BOLD MRI can detect changes in deoxyhemoglobin levels as a result of changes in blood flow and oxygen consumption. So BOLD MRI can assess both the supply side and demand side of myocardial ischemia like positron emission tomography (PET) without the radiation risk of the latter [1].

When coronary vasodilation is induced by giving dipyridamole, the levels of deoxyhemoglobin in the coronary venous blood falls as the blood flow increase is disproportionate to the oxygen demand. Occlusion of a coronary artery on the other hand increases the myocardial venous blood deoxyhemoglobin concentration due to myocardial ischemia. In areas supplied by a stenotic coronary artery, there will be no vasodilatory reserve as the capillaries are already maximally dilated. Hence dipyridamole can be used to identify ischemic myocardium by BOLD MRI as these regions will show decreased signal on MRI suggesting hypoperfusion.

Reference

1. Jonathan W Weinsaft, Pascal Spincemaille. BOLD new directions in myocardial ischemia imaging-myocardial oxygenation assessment by cardiac magnetic resonance. J Am Coll Cardiol. 2012 May 29;59(22):1965-7.