Hybrid Magnetic Resonance Imaging and Positron Emission Tomography With Fluorodeoxyglucose to Diagnose Active Cardiac Sarcoidosis

Objectives: The purpose of this study was to explore the diagnostic usefulness of hybrid cardiac magnetic resonance (CMR) and positron emission tomography (PET) using ¹⁸F-fluorodeoxyglucose (FDG) for active cardiac sarcoidosis.

Background: Active cardiac sarcoidosis (aCS) is underdiagnosed and has a high mortality.

Methods: Patients with clinical suspicion of aCS underwent hybrid CMR/PET with late gadolinium enhancement (LGE) and FDG to assess the pattern of injury and disease activity, respectively. Patients were categorized visually as magnetic resonance (MR)+PET+ (characteristic LGE aligning exactly with increased FDG uptake), MR+PET- (characteristic LGE but no increased FDG), MR-PET- (neither characteristic LGE nor increased FDG), and MR-PET+ (increased FDG uptake in absence of characteristic LGE) and further characterized as aCS+ (MR+PET+) or aCS- (MR+PET-, MR-PET-, MR-PET+). FDG uptake was quantified using maximum target-to-normal-myocardium ratio and the net uptake rate (K_i) from dynamic Patlak analysis. Receiver-operating characteristic methods were used to identify imaging biomarkers for aCS. FDG PET was assessed using computed tomography/PET in 19 control subjects with healthy myocardium.

Results: A total of 25 patients (12 males; 54.9 ± 9.8 years of age) were recruited prospectively; 8 were MR+PET+, suggestive of aCS; 1 was MR+PET-, consistent with inactive cardiac sarcoidosis; and 8 were MR-PET-, with no imaging evidence of cardiac sarcoidosis. Eight patients were MR-PET+ (6 with global myocardial FDG uptake, 2 with focal-on-diffuse uptake); they demonstrated distinct K_i values and hyperintense maximum standardized uptake value compared with MR+PET+ patients. Similar hyperintense patterns of global (n = 9) and focal-on-diffuse (n = 2) FDG uptake were also observed in control patients, suggesting physiological myocardial uptake. Maximum target-to-normal-myocardium ratio values were higher in the aCS+ group (p < 0.001), demonstrating an area under the curve of 0.98 on receiver-operating characteristic analysis for the detection of aCS, with an optimal maximum target-to-normal myocardium ratio threshold of 1.2 (Youden index: 0.94).

Conclusions: CMR/PET imaging holds major promise for the diagnosis of aCS, providing incremental information about both the pattern of injury and disease activity in a single scan. (In Vivo Molecular Imaging [MRI] of Atherothrombotic Lesions; NCT01418313).