Rubidium uptake in chest tumors on positron emission tomography/computed tomography

Abstract

Chest tumors are often found incidentally on cardiac scans; we aimed to describe the findings of rubidium in incidentally discovered extracardiac tumors. We reviewed a database of cardiac rubidium scans performed over a period of 11 years and identified those with a previously unsuspected malignancy seen on the plane of section. We then measured maximum standardized uptake value for each of the tumors, as well as background lung, liver, mediastinum, and body wall. In cases where fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) was available, we compared rubidium results to FDG-PET/CT. We identified 63 patients meeting criteria including full visualization of a tumor of at least 1.0 cm with no prior treatment. Of these patients, 17 had breast, 36 had lung, and 10 had miscellaneous other tumors. We selected patients with either breast or lung tumors for further analysis. Overall uptake was relatively stable between rest and stress but lower than FDG-PET/CT; it was generally low and similar to blood pool. There was a small but statistically significant correlation between estrogen receptor positivity and rubidium uptake in breast tumors. There was a stable pattern of uptake in background tissues, with liver being greater than mediastinal blood pool, which in turn was more avid than lung, which was more avid than subcutaneous body wall tissues. The lung showed a noticeable tendency toward increased uptake in dependent regions, likely reflecting low-level atelectasis. Uptake was stable between rest and stress but low relative to FDG-PET/CT; some correlations with receptors suggest it may be useful in molecular imaging.