The pericardium is a thin, double-layered sac around the heart that helps reduce friction as the heart moves. When this sac gets inflamed, it is called pericarditis, which can cause serious health problems and even be life-threatening. Pericarditis often comes back after the first episode. About 10-30% of people will have it again, and half of those will have it multiple times. Although there are treatments available, they are costly and not often used because we can't predict who best to use them on. Finding a way to predict which patients would benefit from these treatments could help reduce the burden on patients and the healthcare system.

This study will use a test called an 18F-FDG PET/CT with CTA Scan (18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) with computer tomography angiography (CTA)) to measure inflammation in the pericardium.

The purpose of the study is to create easy-to-use tools for doctors to identify people at high risk of pericarditis coming back, so they can get advanced treatment early. This study will help fill knowledge gaps about key predictors like clinical signs, blood tests, and imaging results.

This is a single-center, prospective cohort study designed to compare imaging biomarkers identified by CMR and FDG PET between patients who experience recurrent pericarditis and those who do not. In this prospective study, 44 patients will be recruited from the Ottawa Pericardial Clinic, all with a history of recurrent pericarditis. These patients will be followed prospectively for a period of one year.

It is hypothesized that patients who develop further episodes of recurrent pericarditis will exhibit significantly elevated markers of pericardial inflammation on both FDG PET/CT imaging as well as CMR imaging.

Inclusion Criteria:

1. History of recurrent pericarditis* (i.e. presentation of at lease 2nd episode of acute pericarditis).

2. Age >/= 18 years

3. Given informed consent

   • standard definitions will be used to define an episode of pericarditis. Pericarditis will be diagnosed by using available published criteria, which includes typical pericardial chest pain, pericardial friction rubs, widespread ST segment elevation or PR-segment depression that was not previously reported and new or worsening pericardial effusion on echocardiography. A clinical diagnosis of acute pericarditis will be made when at least 3 of these criteria are present.

Exclusion Criteria:

1. severe valve disease requiring intervention
2. claustrophobia that precludes FDG/PET or CMR imaging
3. pregnancy (all women of child bearing potential will have a negative BHCG test)
4. breastfeeding
5. glomerular filtration rate (GFR) <50 m/min/1.72m2