In vivo nuclear magnetic resonance imaging of myocardial perfusion using the paramagnetic contrast agent manganese gluconate
Previous nuclear magnetic resonance (NMR) imaging studies have indicated that coronary occlusion does not produce sufficient changes in standard tissue relaxation times to allow the detection of acute ischemia. To identify acute myocardial perfusion abnormalities, the use of the paramagnetic agent manganese gluconate combined with calcium gluconate (MnGlu/CaGlu) was investigated in canine models of acute coronary artery occlusion.
In vitro studies showed that MnGlu/CaGlu was a more efficient relaxing agent than gadolinium-DTPA (relaxivity of 7.8 versus 5.1 s−1 mM−1) and demonstrated affinity for normal myocardium. The distribution of MnGlu/CaGlu as measured by manganese-54 tracer studies was proportional to myocardial blood flow in both normal and ischemic tissue. Hearts excised from dogs after coronary artery occlusion and administration of 0.035 mM/kg MnGlu/CaGlu were imaged ex vivo using a relatively spin-lattice relaxation time (TI)-weighted gradient reversal technique (repetition time [TR] 50 ms and echo time [TE] 9 ms). These images showed increased signal intensity in the normally perfused myocardium with a mean signal intensity ratio of hypoperfused to normal myocardium of 0.55 ± 0.12 (mean ± SD).
In vivo images obtained in nine dogs after coronary artery occlusion and administration of the same dose of MnGlu/CaGlu demonstrated the region of hypoperfused myocardium in six dogs with a signal intensity ratio of hypoperfused to normal myocardium of 0.64 ± 0.23 (p < 0.05 versus control). When a higher dose of 0.1 mM/kg MnGlu/CaGlu was utilized and in vivo imaging was performed using a relatively spin-spin relaxation time (T2)-weighted (TR gated, TE 60 ms) spin-echo sequence in six dogs, the signal intensity of normal myocardium was decreased. The hypoperfused region was seen as a region of relatively higher signal in all dogs with a signal intensity ratio of hypoperfused to normal myocardium of 2.07 ± 0.55 (p < 0.01 versus control).
Therefore, it is concluded that NMR imaging with a manganese-containing paramagnetic contrast agent can be used to detect acute regional myocardial perfusion abnormalities.