Quantitative ischemia detection during cardiac MR stress testing

Because ECG alterations due to ischemia cannot be reliably detected in the high-field MRI environment, detection of wall motion abnormalities are often the only method to ensure patient safety. In this study, we investigate the use of real-time Harmonic Phase (HARP) MRI for the quantitative, operator-independent detection of the onset of ischemia during acute coronary occlusion. Six mongrel dogs underwent acute coronary artery ischemia of 2 minutes´ duration while continuous HARP MR images were acquired followed by 5 minutes of reperfusion. During a second ischemic episode, conventional cine wall motion images were acquired. The time from occlusion to the detection of ischemia by each MR technique, as well as ECG ischemic alterations, was determined. In 5 of 6 animals, the onset of ischemia was detected significantly earlier by HARP than by cine MRI (11 ± 5 s HARP vs. 34 ± 14.8 s cine, P<0.03). HARP ischemia detection preceded ECG changes, on average, by 66 seconds. Cine MRI did not detect ischemia significantly earlier than when ECG changes were apparent (P=0.11). The rapid acquisition and detection of ischemia using HARP MRI shows promise as a nonsubjective method to diagnose significant coronary lesions in patients while ensuring patient safety during stress testing.