Global quantification of coronary artery calcification in rheumatoid arthritis

Objectives: ¹⁸F-sodium fluoride (NaF) is a PET tracer than can identify site of active calcification in atherosclerotic plaques. However, limited PET spatial resolution and physiologic motion decrease the accuracy of attempts to quantify calcification of the coronary arteries by measuring vessels discretely. The aim of this study was to quantify global NaF uptake in the coronary arteries in patients with rheumatoid arthritis (RA), who are at higher risk of atherosclerosis, compared to matched control subjects.

Methods: NaF-PET/CT images of 15 patients with RA and 15 healthy control subjects who were matched by sex and age (±4 years) were analyzed retrospectively. Coronary uptake was measured by manually defining a region of interest (ROI) around the cardiac silhouette on each axial PET/CT slice. The ROI did not include any parts of the skeleton, cardiac valves, or aortic wall. Global SUVmean was defined as the averaged SUVmean of all the ROIs. Blood pool was measured by placing a ROI in the lumen of the superior vena cava. Target-to-background ratio (TBR) was calculated by dividing the global coronary SUVmean by the measured blood pool SUVmean. The global coronary SUVmean and TBR of RA patients and controls were compared using the Mann-Whitney U test, with a 2-tailed p<0.05 being considered statistically significant.

Results: The average global coronary SUVmean in RA subjects was 1.05 (range: 0.51-1.71) compared to 0.64 (range: 0.41-0.90) in controls (p<0.001). The average TBR in RA subjects was 1.03 (range: 0.81-1.44) compared to 0.83 (range: 0.54-1.10) in controls (p<0.001). Coronary NaF uptake was observed to be higher in RA patients compared to control subjects by both global SUVmean and TBR.

Conclusions: Global quantification of coronary calcification with NaF-PET/CT is a feasible method of assessing atherosclerotic disease activity in high-risk patients such as those with RA. Both parameters assessed, global SUVmean and TBR, indicated more active coronary calcification in RA patients compared to matched control subjects.