Histological Validation of Cardiovascular Magnetic Resonance T1 Mapping for Assessing the Evolution of Myocardial Injury in Myocardial Infarction: An Experimental Study

Fig. 1. The following chart shows the different steps from coronary artery occlusion to histological staining. *Two of the 22 pigs were euthanasia for other purposes. CMR = cardiovascular magnetic resonance, MI = myocardial infarction

Fig. 2. LGE images (left), native T1 maps (middle), ECV maps (right). The infarcted myocardium was defined using the threshold of 5 standard deviations above the remote myocardial signal intensity. Microvascular obstruction was defined as a hypointense area within the hyperintensity on LGE and included in the measurement of infarct size. The optimal contrast among infarcted, peri-infarcted, and remote myocardium was observed in native T1 and ECV maps in acute and subacute MI but was not significant in the chronic stage. ECV = extracellular volume, LGE = late gadolinium enhancement

Fig. 3. Native T1, CMR-derived ECV, and pathological findings varied with time in different severity of myocardium injury. A. The histological ECV showed a trend in infarcted and peri-infarcted myocardium, similar to the results of CMR-based ECV. B. Infarcted native T1 reached a peak value at the subacute phase. C. Infarcted ECV progressively increased with time.

Fig. 4. Representative sections from three areas of the myocardium: remote myocardium, peri-infarcted myocardium, and infarcted myocardium (magnification, × 200). H&E staining showed myocytolysis, inflammatory cell recruitment, and intracellular and extracellular edema in acutely infarcted myocardium. The inflammation and edema of the infarcted myocardium gradually released over time. On the other hand, Masson staining (red = myocardial cells) demonstrated the progressive deposition of collagen and increased ECV in infarcted myocardium with a longer duration of ischemia. H&E = hematoxylin and eosin

Fig. 5. Correlation between T1 mapping (native T1 and ECV) and histological ECV at three time-points. Both native T1 and ECV correlated well with histological ECV at each imaging time point.