The joints with synovitis had notably greater F-18 sodium fluoride (NaF) uptake as compared to those with no synovitis in rheumatoid arthritis (RA) patients. Therefore, the use of F-18 NaF positron emission tomography/computed tomography (PET/CT) as an imaging tool to analyze the disease activity might be useful in RA patients. 

A prospective diagnostic study was carried out to study the clinical efficacy of F-18 NaF PET/CT for the evaluation of disease activity in RA patients.

The study incorporated 17 people with RA. These patients went through F-18 NaF PET/CT apart from the physical checkup, blood test, and ultrasonography. The joint SUV and joint-to-bone uptake ratio were calculated for each of the 28 tender joints included in estimating the DAS28-ESR i.e. the disease activity score via erythrocyte sedimentation rate. 

Association between PET/CT and clinical factors and the prognostic values of PET/CT factors for high disease activity and joints with synovitis were assessed.

Tender joints and both tender plus swollen joints had a considerably greater ratio of joint SUV and joint-to-bone uptake as compared to the joints with no synovitis, as shown in the following table:

The total joint and summed joint-to-bone uptake ratio of 28 joints revealed a strong positive association with DAS28-ESR. The summed joint SUV displayed significant positive correlations with ultrasonography outcomes.

For joint SUV, the sensitivity for predicting synovitis was 83.2% and specificity was 92.7% while for joint-to-bone uptake ratio, sensitivity and specificity were 81.5% and 90.7% respectively. The aggregate of both PET/CT constraints of 28 joints revealed 100% diagnostic accuracy for the likelihood of high disease activity in RA.

The total joint uptake portrayed a strong positive relationship with DAS28-ESR and precisely projected the high disease activity.