Coronary high-signal-intensity plaques on T1-weighted magnetic resonance imaging reflect intraplaque hemorrhage

Abstract Coronary high-signal-intensity plaques (HIPs) detected by T 1 -weighted magnetic resonance imaging are associated with future cardiovascular events. This study aimed to identify pathological findings reflecting HIPs in coronary arteries obtained from autopsy cases. Formalin-fixed hearts were imaged with noncontrast T 1 -weighted imaging with a 1.5-T magnetic resonance system. We defined HIPs or non-HIPs as a coronary plaque to myocardial signal intensity ratio (PMR) of ≥1.4 or n =11) or non-HIPs ( n =25) were histologically and immunohistochemically analyzed. We calculated the T 1 relaxation time of human venous blood in vitro . Plaque and necrotic core areas, and the frequency of intraplaque hemorrhage in HIPs were significantly larger/higher than those in non-HIPs. HIPs were immunopositive for CD68 (11/11), glycophorin A (10/11), and fibrin (11/11). Glycophorin-A-, matrix metalloprotease 9 (MMP9)-, and tissue factor-immunopositive areas were larger in HIPs than in non-HIPs. The PMR was positively correlated with glycophorin-A-, fibrin-, MMP9-, and tissue factor-immunopositive areas. Blood coagulation shortened the T 1 relaxation time of the blood and plasma, and the T 1 relaxation times in coagulated whole blood and erythrocyte-rich blood were significantly shorter than those in plasma. Coronary HIPs may reflect intraplaque hemorrhage and may be a novel marker for plaque instability and thrombogenic potential.