Magnetic resonance imaging demonstration of pharmacologic-induced myocardial vasodilatation using a macromolecular gadolinium contrast agent.

ABSTRACT

RATIONALE AND OBJECTIVES: Adenosine is a potent vasodilator used clinically in nuclear scintigraphy to assess coronary artery reserves. The potential to identify this vasodilating effect of adenosine using magnetic resonance imaging (MRI), which is superior in spatial resolution to nuclear scintigraphy, combined with a blood-pool MRI contrast agent, was investigated in normal rats. METHODS: Groups of Sprague-Dawley rats received successive infusions of either adenosine (3 mg/kg/minute; n = 7) or dipyridamole (negative control; up to 1.0 mg/kg/minute; n = 9), both before and after contrast enhancement, with a macromolecular blood-pool MRI contrast agent, albumin-gadolinium-DTPA35 (Gd-DTPA35) (4.0 mumol Gd per kilogram). Electrocardiographically (ECG) gated MRIs (2.0 Tesla), acquired serially before and after contrast enhancement, and with and without either adenosine or dipyridamole infusions, to monitor potential pharmacologic responses. RESULTS: During repeated infusions of adenosine, the postcontrast myocardial enhancement, reflecting blood volume, increased significantly (P < .05), up to 150%, compared with pre-adenosine enhancement. Infusions of dipyridamole, pharmacologically inactive in rats, produced no change in myocardial enhancement. CONCLUSIONS: The increased myocardial signal intensity observed during adenosine infusions after enhancement of the blood pool can be attributed to increased blood volume accompanying coronary vasodilatation. The method, which does not require a continuous infusion of contrast agent, has potential for the clinical evaluations of coronary artery reserves.