Endogenous susceptibility contrast in myocardium during apnea measured using gradient recalled echo planar imaging.

Gradient recalled echo planar imaging was used to monitor changes in myocardial and left ventricular chamber blood intensity during apnea in rats. Significant signal loss in both blood (to 62 +/- 5% and 51 +/- 6% of baseline) and myocardium (to 79 +/- 2% and 76 +/- 3% of baseline) was observed at 45 and 90 s apnea while O2 saturation decreased from 98 +/- 1% to 62 +/- 7% and 36 +/- 9%, respectively. These results show that myocardial intensity is modulated by alterations in blood oxygenation.