QUANTIFICATION OF THE EXTENT OF AREA AT RISK WITH FAST CONTRAST-ENHANCED MAGNETIC-RESONANCE-IMAGING IN EXPERIMENTAL CORONARY-ARTERY STENOSIS

Fast magnetic resonance (MR) imaging techniques have the capability of demonstrating regions of ischemia caused by stenosis. The size of the potentially ischemic area determines the importance of the stenosis. The purpose of this study was to determine the relative values of rela xivity-enhancing and magnetic-susceptibility MR contrast media in dete cting and sizing the area at risk in dogs. Eight dogs were subjected t o critical left circumflex coronary artery (LCX) stenosis. Sixty seque ntial inversion-recovery- and driven-equilibrium-prepared fast gradien t recalled echo images were acquired during bolus administration of 0. 03 mmol/kg gadodiamide or 0.4 mmol/kg sprodiamide in basal and vasodil ated (dipyridamole-stress) states. The size of the area at risk was me asured and compared with that measured post mortem. In the basal state , gadodiamide and sprodiamide equivalently altered the signal intensit ies of nonischemic myocardium and the territory of stenosed coronary a rtery. Dipyridamole produced a significant increase in left anterior d escending coronary artery flow with a decrease in LCX flow. The hypope rfused region was observed as a low- and high-signal intensity region after administration of gadodiamide and sprodiamide, respectively. The size of the hypoperfused region was slightly smaller with gadodiamide (37.4% +/- 2.8%) and sprodiamide (34.0% +/- 2.2%) than the true area at risk measured post mortem (41.8% +/- 2.2%; p < 0.05). Dipyridamole perfusion MR imaging with relaxivity or susceptibility contrast media is a noninvasive method to identify and quantify the area at risk in t he territory of a stenotic coronary artery. Changes in myocardial sign al intensity on fast gradient recalled echo images reflect the augment ation of flow and volume induced with dipyridamole and are consistent with the ''steal phenomenon.''