A novel magnetic resonance imaging technique to assess tissue viability following acute myocardial infarction, simultaneous T1 and T2* signal intensity monitoring following bolus injected contrast agent
Mark, John K.
This study was designed to determine whether injured myocardium can be identified by simultaneously monitoring contrast-induced T1 and T2* signal intensity changes with an interleaved T1-T2* imaging sequence and to compare these results to techniques that calculate relaxation rate following contrast agent injection. Eight pigs were subjected to 'in situ' coronary artery occlusion for 2 hours, followed by 1-hour of reperfusion. The hearts were then excised and imaged 'ex vivo'. Gadolinium-diethylene triamine pentaacetic acid (0.05 mmol/kg) was injected as a bolus and T1 and T2* signal intensities were monitored using alternating T1 and T2*-weighted imaging to obtain simultaneous T1 and T2* timecourses during the first pass. The T2* signal at maximum T1 signal intensity displayed a percentage recovery that was significantly different (p < 0.05) between normal (30.5 +- 2.4% of baseline value), reperfused-infarcted (63 +- 7.2%), and low-reflow infarcted myocardium (90 +- 2.8%) respectively. This may reflect differences in membrane integrity between regions. On the other hand, R1 and R2* relaxation rates did not show any significant difference (p > 0.05) in the low-reflow infarcted myocardium relative to normal tissue. These results suggest that observing contrast-enhanced R1 and R2* rates early after contrast injection cannot fully differentiate viable from non-viable myocardium, but simultaneously monitoring both T1 and T2* signal intensity may help in the assessment of myocardial injury.