In vivo detection of reperfused myocardium by nuclear magnetic resonance imaging.

To assess the potential of in vivo nuclear magnetic resonance imaging for the detection of reperfused myocardium, in vivo T2-weighted spin echo images were obtained of dogs at 0.15 tesla. Imaging was done during 3 hours of coronary occlusion (group I), and during 3 hours of coronary occlusion followed by 1 hour of reperfusion (group II). On sacrifice, the hearts were drained of blood and imaged in situ to determine the effect of in vivo imaging on myocardial signal intensity. The hearts were then excised and imaged at 1.4 tesla to compare the effect of high resolution imaging on image quality. Of the six hearts in group I and the eight hearts in group II with a myocardial infarction and suitable image quality, four of the former hearts and six of the latter demonstrated a small but visible increase in infarct signal intensity at 3 hours of occlusion on the time to echo [TE] = 60 ms, single echo images. The T2 (transverse) relaxation time of the infarct (measured in vitro by spectrometer) increased by 13% when compared with normal tissue. In contrast, the reperfused infarct was more easily visualized, with signal intensity increasing by 31 +/- 17% and infarct T2 increasing by 20%. Imaged at 1.4 tesla, the excised hearts showed the infarct to be subendocardial during occlusion and extending transmurally with reperfusion. It is concluded that, although visualized, the increase in infarct signal intensity at 3 hours of coronary occlusion is small and this is consistent with the small increase in infarct signal intensity and T2 relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)