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Investigation of T2-weighted and delayed enhancement magnetic resonance imaging in reperfused acute myocardial infarction in a porcine model
Journal of Cardiovascular Magnetic Resonancevolume 11, Article number: P215 (2009)
It is well konwn that high signal intensity of infarcted myocardium on T2-weighted image is related to increased hydrogen density and increased T2 relaxation time. However, in recent studies, it has been reported that affected myocardium in acute or subacute myocardial infarction could be present with low signal intensity on T2-weighted image, and it is related to microvascular obstruction (MO). Intramyocardial hemorrhage can result from MO and may be related with the extent of MO.
To assess the pattern of signal intensity on T2-weighted image (T2WI) and their relation to persistent microvascular obstruction (PMO) on DE-MRI and intramyocardial hemorrhage on gross specimen in a porcine model with reperfused acute myocardial infarction.
Of the 15 pigs studied, nine underwent a 90-minute occlusion of left anterior descending artery followed by a 90-minute reperfusion and six underwent a 180-minute occlusion followed by a 90-minute reperfusion. ECG-triggered, breath-hold, turbo spin-echo T2WI was obtained along the short axis of the heart before contrast administration. Fifteen minutes after contrast administration, DE-MRI was acquired. The pattern of the signal intensity on T2WI was evaluated. The contrast ratio of the signal intensities between the infarcted and normal areas was calculated on T2WI. Visual assessment of the extent of hemorrhage on the gross specimen was performed after sacrificing the animals. Each myocardial specimen was then stained with 2,3,5-triphenyltetrazolium chloride (TTC).
On T2WI, the infarcted area was shown as homogeneous high signal in eight (group A) and as low or iso-signal intensity in seven pigs (group B). In group B, T2WI of the infarcted area was observed as central low signal with peripheral high signal in five pigs and as diffuse low or iso-signal intensity in the entire infarted myocardium in two pigs. The T2 contrast ratio of the infarcted area in group B was significantly lower than that in group A (1.27 ± 0.24 vs. 1.73 ± 0.27, p < 0.05). Myocardial infarction was seen in all fifteen pigs on DE-MRI, and PMO was observed in 11 out of the 15 pigs. The T2 contrast ratio of the infarcted area in pigs with PMO was significantly lower than that in pigs without PMO (1.38 ± 0.25 vs. 1.89 ± 0.31, p < 0.05). A strong inverse correlation was found between the extent of PMO and the T2 contrast ratio (r = -0.8, p < 0.05). The T2 contrast ratio of infarcted area in the pigs who underwent the 180-minute occlusion was significantly lower than that in those underwent who the 90-minute occlusion (1.26 ± 0.27 vs. 1.68 ± 0.28, p < 0.05). The extent of PMO in the pigs who underwent the 180-minute occlusion was significantly larger than that in pigs who underwent the 90-minute occlusion (58.6% vs. 32.1%, p < 0.05). The myocardial infarcts on TTC staining were evident in all 15 pigs. On gross specimen, hemorrhage in the infarcted area was apparently visible in the pigs with PMO. A strong inverse correlation was found between the extent of hemorrhage in the infarcted area and the T2 contrast ratio (r = -0.78, p < 0.05). The extent of hemorrhage in the infarct area correlated well with the extent of PMO (r = 0.97, p < 0.05).
From this study, we conclude that the patterns of signal intensity in infarcted myocardium on T2WI were variable in a porcine model with reperfused acute myocardial infarction. The lower contrast ratio of infarcted area on T2WI significantly correlates with the extent of PMO on DE-MRI and intramyocardial hemorrhage on gross specimen.