Myocarditis or inflammatory cardiomyopathy refers to inflammation of the heart muscle (the myocardium). Sarcoidosis is a multisystem granulomatous disorder that may involve the heart, causing inflammation, and potentially resulting in complications including arrhythmia and sudden death. The objective of this study is to evaluate the diagnostic and prognostic significance of simultaneous combined 18F-FDG PET and cardiac MRI imaging in the evaluation of inflammatory cardiomyopathies including cardiac sarcoidosis. Combined PET/MRI imaging may allow for detection and quantification of active myocardial inflammation as well as chronic fibrosis and scarring. Results of this study may allow for earlier detection of cardiac inflammation when compared with methods in current clinical use, and may lead to better understanding of the disease processes contributing to adverse outcomes. Elucidation of imaging findings associated with future adverse event risk may impact patient management such as providing an indication for pacemaker or defibrillator implantation, or escalation of medical therapy.

Myocarditis or inflammatory cardiomyopathy refers to inflammation of the myocardium. Sarcoidosis is a multisystem granulomatous disorder of unknown etiology, which can result in myocardial inflammation. Approximately 5% of patients with sarcoidosis have clinically apparent cardiac involvement, yet autopsy series indicate that cardiac involvement is present in up to 25% of cases. This discrepancy suggests that cardiac sarcoidosis may be under-diagnosed in clinical practice. Recent studies have demonstrated high diagnostic accuracy of both cardiac MRI and 18F-labelled fluoro-2-deoxyglucose (FDG) PET for detection of cardiac involvement. However, cardiac MRI may fail to identify areas of active inflammation even with fluid sensitive T2-weighted sequences.

Fasting 18F-FDG positron emission tomography (PET) has been shown to identify early cardiac sarcoidosis with relatively high sensitivity. To date, simultaneous PET/MRI evaluation of cardiac inflammation and sarcoidosis has only been described in limited case reports. The objective of the proposed research is to evaluate the utility of simultaneous PET/MRI imaging in patients with cardiac sarcoidosis and other inflammatory cardiomyopathies.

Inclusion Criteria:

• The primary criterion for enrolment will be patients ≥18 years of age with known or suspected sarcoidosis or other inflammatory cardiomyopathy who are referred for clinically indicated 18F-FDG PET/CT imaging

Exclusion Criteria:

• Standard cardiac MRI contraindications include arrhythmia, claustrophobia, history of allergic reaction or other contraindication to gadolinium-based contrast agent, impaired renal function with eGFR < 60 ml/min/1.73m2, pregnancy, breast-feeding, or any other general contraindication to MRI (pacemaker, cerebral aneurysm clips, shrapnel, etc).

Patients 18 years or older with known or suspected cardiac sarcoidosis or other inflammatory cardiomyopathy who are referred for clinically indicated 18F-FDG PET/CT imaging at University Health Network.