PET Imaging in Cardiac Sarcoidosis: A Narrative Review with Focus on Novel PET Tracers

Sarcoidosis is a multi-system inflammatory disease characterized by the development of inflammation and noncaseating granulomas that can involve nearly every organ system, with a predilection for the pulmonary system. Cardiac involvement of sarcoidosis (CS) occurs in up to 70% of cases, and accounts for a significant share of sarcoid-related mortality. The clinical presentation of CS can range from absence of symptoms to conduction abnormalities, heart failure, arrhythmias, valvular disease, and sudden cardiac death. Given the significant morbidity and mortality associated with CS, timely diagnosis is important. Traditional imaging modalities and histologic evaluation by endomyocardial biopsy often provide a low diagnostic yield. Cardiac positron emission tomography (PET) has emerged as a leading advanced imaging modality for the diagnosis and management of CS. This review article will summarize several aspects of the current use of PET in CS, including indications for use, patient preparation, image acquisition and interpretation, diagnostic and prognostic performance, and evaluation of treatment response. Additionally, this review will discuss novel PET radiotracers currently under study or of potential interest in CS.

Stable Extent of Recurrently Active Cardiac and Cutaneous Sarcoidosis

Background: Recurrent or persistently active sarcoidosis is a risk factor for permanent organ damage. Whether this damage is due to accumulated focal injuries or progressive disease extent is not known, as the natural history of chronic inflammation in sarcoidosis is poorly characterized. The objective of this study is to determine the pattern of disease in recurrently active sarcoidosis.Methods: We identified patients with recurrent cardiac sarcoidosis (N = 21) retrospectively from an imaging database, and with recurrent cutaneous sarcoidosis (N = 17) from a prospective registry. The longitudinal patterns of cardiac sarcoidosis were established by findings on cardiac positron emission tomography scans, and of cutaneous sarcoidosis by the validated Cutaneous Sarcoidosis Activity and Morphology Instrument clinical scoring system. Patterns of recurrent disease were compared to baseline findings.Results: Recurrent sarcoidosis occurred in a nearly identical pattern and distribution as baseline disease, and spread of disease was rarely observed for both cardiac and cutaneous sarcoidosis: 97% of heart segments positive on recurrence scans were positive on baseline scans, and only one new region of facial disease was observed. In some cases, recurrence followed years of apparent remission.Discussion: Across phenotypes, and across a long period of follow-up, the extent of sarcoidosis was stable in spite of fluctuations in disease activity. For patients with a demonstrated history of recurrent disease affecting critical organs, our findings support the need for long-term follow-up.

Intravenous insulin administration preparation for myocardial 18F-fluorodeoxyglucose viability imaging has the potential to reduce radiation exposure dose

Purpose This study aimed to identify and validate the optimal 18F-FDG activity and acquisition time for cardiac viability imaging with intravenous insulin administration based on a fixed 18F-FDG activity. Methods Cardiac positron emission tomography (PET) images from 30 patients with coronary artery disease (CAD) were retrospectively reconstructed into 900, 360, 180, 90, and 45 s durations. An optimal product of the maximum standardized uptake value (SUV) of the myocardium and segmental uptake (SU) and acquisition time (MSAT) was determined through a receiver operating characteristic curve. The optimal acquisition time (OAT) was equal to MSAT divided by mean SUV of the myocardium (MyoSUV) and validated in another 26 patients with CAD. Results The MyoSUV, mean SUV of the blood, SU, and their biases on reconstructed image durations of 90, 180, and 360 s were equivalent to those on an image duration of 900 s. The optimal MSAT was 848.2. In the validation group, the OAT was 129 ± 76 s (95% confidence interval, 99–160), approximately one-third of the usual acquisition time. The MyoSUV and SU were equivalent for the difference (0.15 ± 0.21, P < 0.001; −0.01 ± 0.03, P < 0.001) between PET image duration of OAT and 600 s (7.71 ± 3.01 vs. 7.56 ± 2.94, 67.1 ± 15.4% vs. 67.7 ± 15.6%). Conclusion Intravenous insulin administration preparation has the potential to reduce radiation exposure and acquisition time of cardiac 18F-FDG viability imaging without losing the accurate measurement of MyoSUV and SU when reaching an OAT.

Intravenous insulin administration preparation for myocardial 18F-fluorodeoxyglucose viability imaging has the potential to reduce radiation exposure dose

Purpose This study aimed to identify and validate the optimal 18F-FDG activity and acquisition time for cardiac viability imaging with intravenous insulin administration based on a fixed 18F-FDG activity. Methods Cardiac positron emission tomography (PET) images from 30 patients with coronary artery disease (CAD) were retrospectively reconstructed into 900, 360, 180, 90, and 45 s durations. An optimal product of the maximum standardized uptake value (SUV) of the myocardium and segmental uptake (SU) and acquisition time (MSAT) was determined through a receiver operating characteristic curve. The optimal acquisition time (OAT) was equal to MSAT divided by mean SUV of the myocardium (MyoSUV) and validated in another 26 patients with CAD. Results The MyoSUV, mean SUV of the blood, SU, and their biases on reconstructed image durations of 90, 180, and 360 s were equivalent to those on an image duration of 900 s. The optimal MSAT was 848.2. In the validation group, the OAT was 129 ± 76 s (95% confidence interval, 99–160), approximately one-third of the usual acquisition time. The MyoSUV and SU were equivalent for the difference (0.15 ± 0.21, P < 0.001; −0.01 ± 0.03, P < 0.001) between PET image duration of OAT and 600 s (7.71 ± 3.01 vs. 7.56 ± 2.94, 67.1 ± 15.4% vs. 67.7 ± 15.6%). Conclusion Intravenous insulin administration preparation has the potential to reduce radiation exposure and acquisition time of cardiac 18F-FDG viability imaging without losing the accurate measurement of MyoSUV and SU when reaching an OAT.

Cardiac sarcoidosis masquerading as arrhythmogenic right ventricular cardiomyopathy: a case report

Background Cardiac sarcoidosis (CS) and arrhythmogenic right ventricular cardiomyopathy (ARVC) are rare causes of ventricular arrhythmias and are associated with sudden cardiac death. Differentiation between both is important for proper management. Case summary We present a 56-year-old man with sudden cardiac arrest and was diagnosed to have ARVC based on cardiac magnetic resonance imaging (MRI). He developed gradually worsening shortness of breath over the next 1 year. CS was unmasked after a cardiac positron emission tomography (PET). Patient was treated with methotrexate. A repeat cardiac PET scan showed improvement. Discussion The distinction between ARVC and CS is challenging. Both these entities have a patchy involvement and can have similar presentations. ARVC has a predominant right heart involvement. It is diagnosed with the help of an MRI, which shows regional right ventricular wall motion abnormality. These findings can have an overlap with CS. It is important to note that, even though sarcoidosis is a pathologic diagnosis, cardiac biopsy is rarely done owing to its patchy involvement. Cardiac PET scan has a high sensitivity and specificity to diagnose this entity. Once diagnosis is made, patients should be treated with immunosuppressants and should be closely followed. Repeat imaging should be considered at intervals to monitor disease progression. This case highlights the importance of multimodality imaging and tissue diagnosis to unmask the diagnosis of CS, a treatable infiltrative disorder which shares features with a potentially untreatable ARVC.