Molecular imaging of coronary plaque vulnerability using 18F- fluorocholine PET-MRI in patients with coronary artery disease: validation with optical coherence tomography

Purpose ¹⁸ F-fluorocholine is a positron emission tomography (PET) tracer earlier found to be a marker of macrophage content in carotid plaques. We aimed to assess the feasibility of ¹⁸ F-choline PET-MRI to non-invasively localize vulnerable coronary plaques, using optical coherence tomography (OCT) as reference standard. Methods Patients with recent myocardial infarction who were scheduled for a secondary angiography of a non-culprit vessel, underwent ¹⁸ F-fluorocholine coronary PET-MRI. Subsequently, OCT was performed during the secondary angiography. Maximum target-to-background (TBRmax) values of ¹⁸ F-fluorocholine uptake were determined in two vessel sections that contained either vulnerable or stable plaques as defined by OCT. The OCT-based definition of a vulnerable plaque was a fibrous cap thickness <70µm. To enhance the detectability of coronary plaques using PET, three different motion-correction strategies were used: multigate respiratory gating motion correction (MRG-MOCO), extended MR-based motion correction (eMR-MOCO), and extended MR-based motion correction with ECG gating (eMR-MOCO-ECG). Results Fifteen patients were included in this study, of which eleven entered final analyses. Data of the other four subjects could only be partially analysed. TBRmax values were as follows for three different reconstructions in vulnerable versus stable plaques: MRG-MOCO: mean TBRmax 1.45 vs 1.35, p=0.52; eMR-MOCO mean TBRmax 1.47 vs 1.27, p= 0.26, eMR-MOCO-ECG: mean TBRmax 1.49 vs 1.26, p= 0.21. Conclusion ¹⁸ F-fluorocholine uptake in vulnerable atherosclerotic plaques in coronary arteries was not significantly different from uptake in stable plaques even though advanced motion-correction methods were applied. That may be caused by multiple factors, such as small coronary plaque size and remaining cardiac motion.