Journal of Nuclear Cardiology | 2019
PET/MR imaging of inflammatory cardiomyopathy as a two for one deal: Great value or too good to be true?
Abstract
Sarcoidosis is a granulomatous condition of unknown etiology that can affect any organ system. The prevalence of cardiac sarcoidosis (CS), a major cause of morbidity and mortality, is not well known and is estimated around 25% based on autopsy studies and up to 55% based on advanced imaging in patients with biopsy known extra-cardiac sarcoidosis. Endomyocardial biopsy is insensitive, thus a true gold standard for diagnosis of cardiac CS does not exist. Advanced imaging with 18F-FDG cardiac PET and MRI (CMR) has become crucial in diagnosis, management, and longterm follow-up in patients with suspected and confirmed inflammatory cardiomyopathy, in particular CS. In CS, cardiac PET and MRI image complementary but distinct pathophysiologic processes. PET, a metabolism-based test, uses radiolabeled 18F-FDG to imageenhanced glucose metabolism in the areas where myocardial inflammation is present. CMR, on the other hand, traditionally uses pre and post-gadolinium-based contrast tissue characterization techniques to image areas of increased interstitial edema and fibrosis or scar. Gadolinium is an extracellular contrast agent, thus areas of increased gadolinium concentration in the myocardium suggest expansion of the myocardial extracellular volume (ECV) due to inflammation, infiltration, infarction, or fibrosis. CMR does provide diagnostic value regarding active edema/inflammation, but the diagnostic accuracy of CMR-based techniques for inflammation is inferior to PET and less useful clinically. Although both CMR and PET have diagnostic and prognostic implications individually, they have complimentary value in diagnostic accuracy and management of CS. Expert centers use either CMR or PET for initial diagnosis of inflammatory cardiac disease such as sarcoidosis, although CMR is favored due to having zero radiation and being highly sensitive. On the other hand, clinicians generally employ PET to clarify difficult diagnostic cases or for serial imaging and to evaluate response to therapy (Figure 1). This concept has sparked interest in hybrid imaging techniques using PET/MRI and development of integrated scanner platforms, which have been rapidly expanding in research and clinical arenas ever since their introduction in 2010. The question has remained if the hybrid PET/MRI platform is able to provide the convenience of a single scan without sacrificing the quality of the individual components. In this issue of the Journal, Wisenberg et al. prospectively evaluated the imaging characteristics and diagnostic information obtained in a cohort of ten patients with suspected CS who underwent same-day PET/CT and PET/MRI. They demonstrate similar presence/absence and distribution of 18F-FDG uptake in all subjects, with improved contrast between areas of enhanced myocardial uptake compared to background in patients who underwent PET/MRI. This observation is attributed to greater clearance of tracer from the blood pool and longer scan acquisition times which were used Reprint requests: Edward A. Hulten, MD, MPH, FACC, FASNC, Cardiology Service, Department of Medicine, Fort Belvoir Community Hospital, DeWitt Loop 9300, Fort Belvoir, VA 22060; [email protected] J Nucl Cardiol 2020;27:2130–4. 1071-3581/$34.00 Copyright 2019 American Society of Nuclear Cardiology.