MYOCARDIAL SIGNAL RESPONSE TO DIPYRIDAMOLE AND DOBUTAMINE - DEMONSTRATION OF THE BOLD EFFECT USING A DOUBLE-ECHO GRADIENT-ECHO SEQUENCE

The purpose of this study was to examine the differential myocardial s ignal responses due to the blood oxygen level dependent (BOLD) effect in magnetic resonance imaging (MRI) under differing conditions of myoc ardial oxygen supply and demand. The signal response was measured when myocardial blood flow was increased in excess of oxygen demand or whe n flow was increased in response to increased myocardial oxygen demand . Normal volunteers were studied using a segmented, interleaved, doubl e-echo, gradient-echo sequence at baseline conditions and during pharm acological stress with either dipyridamole (n = 5) or dobutamine (n = 6). Changes in T-2() in the myocardium during stress were calculated. Peak coronary Row velocity was measured at rest and during stress usi ng a breath-hold phase contrast technique. Administration of dipyridam ole induced a 124 +/- 27% increase in coronary blood flow which result ed in a 46 +/- 22% increase in T-2(), consistent with a decrease in m yocardial venous deoxyhemoglobin concentration as myocardial oxygen su pply exceeds demand. In contrast, the administration of dobutamine res ulted in a 41 +/- 25% increase in coronary blood flow but no significa nt change in T-2() (-5 +/- 19%), consistent with a lack of change in myocardial venous deoxyhemoglobin concentration and balanced oxygen su pply and demand. Thus, alterations in the relationship between myocard ial oxygen supply and demand appear to be detectable using BOLD MRI.