Factors in myocardial “Perfusion” imaging with ultrafast MRI and Gd‐DTPA administration

Abstract Ultrafast magnetic resonance imaging (MRI) and first pass observation of an interstitial contrast agent are currently being used to study myocardial perfusion. Image intensity, however, is a function of several Parameters, inculding the delivery of the contrast agent to the intersitium (coronary flow rate and diffusion into the intersitium) and the relaxation properties of the tissue (contrast agent concentration, proton exchange rates, and relative intra‐and extracellular volume fractions). In this study, image intensity during gadopen tetate dimeglumine (Gd‐DTPA) adminstration with T 1 weighted ultrafast MR imaging was assessed in an isolated heart preparation. With increasing Gd‐DTPA concentration the steady‐state myocardial image intensity increased but the time to reach steady state remained unchanged, resulting in an increased slope of image intensity change. A range of physiologic perfusion pressures (and resulting coronary flow rates) had insignificant effects on Gd‐DTPA in wash in or steady‐state image intensity, suggesting that diffusion of Gd‐DTPA into the interstitium is the rate limiting step in image intensity change with this preparation. Following global ischemia and reperfusion, transmural differences in the slope of image intensity change were apparent. However, the altered steady state image intensity (due to postichemic edema) makes interpretation of this finding difficult. The studies described here demonstrte that although Gd‐DTPA administration combined with ultrafast imaging may be a sensitive indicator of perfusion abnormalities factors other than perfusion will affect image intensity. Extensive studies will be required before image intensity with this protocol is fully understood. © 1991 Academic Press, Inc.