Assessment of myocardial inflammation post-infarct with PET/MRI: Getting into the nitty-gritty

Abstract

Integrated hybrid positron emission tomographymagnetic resonance imaging (PET/MRI) systems were first introduced a little over 10 years ago. Widespread adoption and utilization of PET/MRI has been hampered by several factors, including the substantial cost of the systems, challenges in obtaining accurate attenuation maps, and the overall effectiveness of PET-computed tomography (PET/CT) systems. To date, few PET/MRI applications stand out, most of which are driven by the overpowering superiority of MRI over CT in specific contexts. Neurology, neuro-oncology, prostate cancer, gynecologic malignancies, and pediatric imaging are good examples of areas where PET/MRI can shine. Cardiovascular imaging is another example where PET/ MRI systems could find valuable applications. After all, PET and MRI often play complementary roles in several cardiovascular pathologies, such as cardiac inflammation, vasculitis, cardiac tumors, and viability assessment. In addition, with PET/MRI systems, it is possible to apply corrections accounting for both breathing and cardiac motion, allowing for improved spatial resolution and quantification accuracy. One of the cardiovascular applications that has been evoked is imaging of post-ischemic inflammation in the heart. Acute myocardial infarction (MI) is associated with an inflammatory response, essential to clear dead cells and activate reparative pathways. However, excessive inflammatory response may be associated with suboptimal healing and undesirable left ventricular remodeling. Wollenweber et al have previously demonstrated the feasibility of imaging the inflammatory tissue response in acute MI in humans using multimodality imaging. In their study, 15 patients underwent both cardiac MRI and PET/CT imaging with fluorodeoxyglucose (FDG) within 7 days following MI and following a typical myocardial suppression protocol which included prolonged fasting ([12 hours) and intravenous heparin injection. On MRI, they observed edema extending beyond the area of late gadolinium enhancement (LGE). They also showed increased glucose metabolic rates in the infarcted segments (LGE) compared to normal segments and edema segments. Most of the published literature up to now has concentrated on the infarct and peri-infarct areas, yet it is known that an inflammatory response is also present in the remote myocardium. Despite the central role inflammation plays in post-MI healing, very few studies have investigated the role of PET/MRI in that setting. Thus, our understanding of this phenomenon and its potential application as a target for therapeutic intervention is currently limited. In this issue of the Journal, Smailovic et al and Wilk et al present companion articles which aim to improve our understanding of myocardial inflammation post infarction through the use of hybrid PET/MRI See related articles, https://doi.org/10.1 007/s12350-020-02486-6 and doi: http s://doi.org/10.1007/s12350-020-024875.