Longitudinal ¹⁸F-FDG PET imaging in a rat model of autoimmune myocarditis

Although mortality rate is very high, diagnosis of acute myocarditis remains challenging with conventional tests. We aimed to elucidate the potential role of longitudinal 2-Deoxy-2-¹⁸F-fluoro-D-glucose (¹⁸F-FDG) positron emission tomography (PET) inflammation monitoring in a rat model of experimental autoimmune myocarditis.

Autoimmune myocarditis was induced in Lewis rats by immunizing with porcine cardiac myosin emulsified in complete Freund’s adjuvant. Time course of disease was assessed by longitudinal ¹⁸F-FDG PET imaging. A correlative analysis between in- and ex vivo¹⁸F-FDG signalling and macrophage infiltration using CD68 staining was conducted. Finally, immunohistochemistry analysis of the cell-adhesion markers CD34 and CD44 was performed at different disease stages determined by longitudinal ¹⁸F-FDG PET imaging. After immunization, myocarditis rats revealed a temporal increase in ¹⁸F-FDG uptake (peaked at week 3), which was followed by a rapid decline thereafter. Localization of CD68 positive cells was well correlated with in vivo¹⁸F-FDG PET signalling (R² = 0.92) as well as with ex vivo¹⁸F-FDG autoradiography (R² = 0.9, P < 0.001, respectively). CD44 positivity was primarily observed at tissue samples obtained at acute phase (i.e. at peak ¹⁸F-FDG uptake), while CD34-positive staining areas were predominantly identified in samples harvested at both sub-acute and chronic phases (i.e. at ¹⁸F-FDG decrease).

¹⁸F-FDG PET imaging can provide non-invasive serial monitoring of cardiac inflammation in a rat model of acute myocarditis.