The radiotracer 18F-sodium fluoride (18F-NaF) serves as a biomarker of calcification activity in patients with aortic stenosis and may predict disease progression, according to a study published in the March issue of Circulation: Cardiovascular Imaging.

Marc R. Dweck, MD, PhD, of the Centre for Cardiovascular Science and the Clinical Research Imaging Centre at the University of Edinburgh in the UK, and colleagues wanted to evaluate uptake of two PET radiotracers, 18F-NaF and 18F-fluorodeoxyglucose (18F-FDG), as markers for calcification activity and inflammation in patients with aortic stenosis. They also wanted to assess if the radiotracers were good predictors of disease progression.

To do that, Dweck et al designed a study that compared uptake of the radiotracers to histological assessments. They recruited two groups of patients with aortic stenosis, all of whom underwent combined CT and PET scans using 18F-NaF and 18F-FDG. In the first group, 12 patients underwent valve replacement surgery. In the second group, 18 asymptomatic patients had repeat scans after one year.

The excised valves in the surgery group were tested using tissue nonspecific alkaline phosphatase (TNAP), immunohistochemical staining for osteocalcin and CD68, with results compared with radiotracer uptake. The researchers found good correlation between in vivo 18F-NaF uptake and TNAP and osteocalcin staining but not between 18F-FDG and CD68 staining.

In the second group, they found good correlation between 18F-NaF activity and calcium scores on CT. They noted that 18F-NaF uptake is greater at sites of powdery microcalcification and that the radiotracer binds more readily in regions of developing calcification activity.

“18F-NaF uptake in the absence of underlying calcium occupied a median of 8.3 percent of the total valve area, emphasizing that 18F-NaF provides distinct and complementary information to CT calcium scoring,” they wrote.

Aortic calcium scores increased from 314 at baseline to 365 at one year. “Not only did uptake values demonstrate a correlation with histological markers of active calcification (TNAP and osteocalcin), but they were also a good predictor of the subsequent progression in aortic valve CT calcium scores at 1 year.”

The study was small and the findings are preliminary. They recommended larger studies with longer follow-up to confirm their findings.