Incidental extracardiac 82-rubidium uptake in myocardial perfusion PET-CT in a veteran population

Introduction: American and European societies recommend reporting incidental findings detected during myocardial perfusion imaging (MPI) studies. PET MPI studies provide CT that allows examination of the chest and upper abdomen in addition to the heart and coronary vessels. Previous studies demonstrated that malignancies and infections increased blood flow to the affected region. In addition, 82-rubidium uptake correlates with coronary blood flow and is the most widely used PET MPI radiopharmaceutical. The objective of this study was to determine the prevalence of incidental extracardiac 82-rubidium uptake in the chest and upper abdomen during PET-CT MPI. We hypothesized that the veteran population may have incidental extracardiac 82-rubidium uptake and that this incidental finding may correlate with underlying malignancy or infection detected by CT.

Methods: This IRB-approved single-center retrospective study included 935 patients, who underwent 82-rubidium-chloride PET-CT MPI between December 2016 and December 2018. Each patient received a low dose CT of the chest and upper abdomen for attenuation correction and anatomic localization. At our institution, the CT reports are an integral part of the final reporting system for each patient generated by board certified nuclear medicine physicians or cardiologists with special competency in CT interpretation. Data collected by reviewing the MPI reports resided in the PACS system. Incidental PET-CT findings with extracardiac 82-rubidium uptake were identified using the Syngovia (Siemens) PET-CT program. The SUV max values were determined for CT correlation of regions with extracardiac 82-rubidium uptake. The percentages of patients with extracardiac 82-rubidium uptake were calculated and electronic health records were reviewed for the patients.

Results: In addition to PET MPI findings, the thoracic CT led to incidental findings in the heart, aorta, pulmonary artery, coronary arteries, lung, lymph nodes, breast, and bone. The upper abdominal CT incidental findings involved the liver, gallbladder, spleen, pancreas, adrenal glands, kidneys, stomach, and colon. Extracardiac 82-rubidium uptake in the thorax or abdomen was identified in 2% of patients with 80% of these had a correlated finding on CT. Review of the electronic health records revealed that there was a 33% prevalence of underlying malignancy and 20% of infection/inflammation with significant extracardiac 82-rubidium uptake on PET-CT. The malignancies or metastatic disease with 82-rubidium uptake involved the lung, thyroid, or prostate metastasis but most commonly involved the lung and prostate. The most common infection/inflammation involved the lung which demonstrated the extracardiac 82-rubidium uptake.

Conclusions: There is a significant correlation between 82-rubidium uptake in the thorax and upper abdomen with underlying malignancy or infection/inflammation. Beyond assessment of the coronary vasculature by myocardial perfusion imaging, 82-rubidium uptake can also detect suspected malignancy and infection/inflammation. This observation needs to verified prospectively. Furthermore, adequate training and experience or a multispecialty approach may be necessary to identify such findings and provide accurate differential diagnosis and recommendation to maximize the clinical benefits and minimize the healthcare burden and anxiety for patients.