Monocyte imaging after myocardial infarction with ¹⁹F MRI at 3 T: a pilot study in explanted porcine hearts

Inflammation is a hallmark of cardiac healing after myocardial infarction and it determines subsequent cardiovascular morbidity and mortality. The aim of the present study was to explore whether inflammation imaging with two perfluorocarbon (PFC) nanoemulsions and fluorine magnetic resonance imaging (¹⁹F MRI) is feasible at 3.0 T with sufficient signal-to-noise ratio (SNR) using explanted hearts, an ¹⁹F surface coil and dedicated MR sequences.

Acute myocardial infarction (AMI) was induced by balloon angioplasty (50 min) of the distal left anterior descending artery in 12 pigs. One day thereafter, PFCs were injected intravenously to label circulating monocytes. Either emulsified perfluoro-15-crown-5 ether or already clinically applied perfluorooctyl bromide (PFOB) was applied. Four days after AMI and immediately after gadolinium administration, hearts were explanted and imaged with a 3.0 T Achieva MRI scanner. ¹⁹F MRI could be acquired with an SNR of >15 using an in-plane resolution of 2 × 2 mm² within <20 min for both agents. Combined late gadolinium enhancement (LGE) and ¹⁹F MRI revealed that ¹⁹F signal was inhomogenously distributed across LGE myocardium reflecting patchy macrophage infiltration as confirmed by histology. In whole hearts, we found an apico-basal ¹⁹F gradient within LGE-positive myocardium. The ¹⁹F-positive volume was always smaller than LGE volume. Ex vivo experiments on isolated monocytes revealed that pig and human cells phagocytize PFCs even more avidly than mouse monocytes.

This pilot study demonstrates that ¹⁹F MRI at 3.0 T with clinically applicable PFOB is feasible, thus highlighting the potential of ¹⁹F MRI to monitor the inflammatory response after AMI.