Assessment of myocardial ischemia with proton magnetic resonance: effects of a three hour coronary occlusion with and without reperfusion.

Abstract

Proton (hydrogen-1) magnetic resonance imaging techniques have potential for the detection and characterization of changes associated with myocardial ischemia. Since image contrast is dependent on TI and T2 relaxation times, we examined these parameters in a canine preparation of occlusion of the left anterior descending coronary artery. Of 16 dogs studied, seven underwent 3 hr of coronary artery occlusion and nine underwent 3 hr of occlusion followed by 1 hr of reperfusion. After the dogs were killed, the hearts of four from each group were imaged in a small bore, 1.4 tesla magnet. From all hearts myocardial segments were obtained from the normal zone and the central ischemic zone (CZ). These segments were divided into epicardial and endocardial sections and studied in a spectrometer (20 MHz). After 3 hr of occlusion, CZ endocardial Ti and T2 increased significantly (p < .01 and p < .05, respectively). Changes in CZ epicardial relaxation times were not as marked. Although Tl and T2 tended to be higher in the reperfused group compared with the nonreperfused group, the differences did not reach statistical significance. In keeping with the spectrometric findings, Ti-dependent inversion recovery images and T2-dependent spin-echo images of the excised hearts demonstrated excellent contrast between normal and ischemic myocardium. Modest correlations were noted for both groups between blood flows during occlusion measured by the microsphere technique and TI and T2 relaxation times. In summary, relaxation times Tl and T2 increase regionally after 3 hr of coronary artery occlusion and tend to be accentuated by reperfusion. These changes are associated with high-resolution magnetic resonance image contrast, suggesting that such imaging may be useful for the characterization of early myocardial ischemia.Circulation 71, No. 3, 595-601, 1985. MAGNETIC resonance imaging provides a potentially useful method for noninvasive detection and characterization of early myocardial ischemia. Since signal intensity is dependent in part on T1 and T2 relaxation times,' delineation of these parameters after an ischemic insult is of importance in predicting image con-

Delayed Enhancement and T2-Weighted Cardiovascular Magnetic Resonance Imaging Differentiate Acute From Chronic Myocardial Infarction

“…Our results of transmural T2 signal abnormality in reperfused infarcts agree with those of Nilsson et al 24 but disagree with those of Johnston et al, 25 who found no significant change in epicardial T2 relaxation times after 3 hours of coronary occlusion with or without reperfusion. In a later report, however, Johnston and colleagues studied patients with acute reperfused MI and found that a high T2 signal was consistently transmural.…”

Serial changes in nuclear magnetic resonance relaxation times after myocardial infarction in the rabbit: Relationship to water content, severity of ischemia, and histopathology over a six‐month period

“…In the study by Pflugfelder et al (2) infarct signal intensity was shown to increase from 5 f 24% (mean f standard deviation) before coronary occlusion to 116 & 100% after 3 to 4 h of occlusion. Such a large change in signal intensity would imply a much greater increase in T2 relaxation than was observed in our studies (3). Unfortunately, the study by Pflugfelder et al did not confirm their findings by measuring in vitro relaxation times in a spectrometer.…”

“…Although an increase in infarct signal intensity (compared to normal myocardium) could be readily appreciated in the excised heart imaged under optimal conditions, these changes were slight and difficult to appreciate in the beating heart. The increases in T, and T2 relaxation times as measured by spectrometer were small in both instances, with TI increasing by 10% and T2 increasing by 1 1% in one study (3). In the study by Pflugfelder et al (2) infarct signal intensity was shown to increase from 5 f 24% (mean f standard deviation) before coronary occlusion to 116 & 100% after 3 to 4 h of occlusion.…”

Imaging of ischemic heart disease

“…Depending upon the duration of ischemia [150,152] edema in the infarcted myocardium prolongs the T1-and T2-relaxation time [151,153]. Differences in T1-relaxation may not be clinically useful for infarct detection unless paramagnetic contrast agents are administered (see below).…”