Quantifying microcalcification activity in the thoracic aorta

Standard methods for quantifying positron emission tomography (PET) uptake in the aorta are time consuming and may not reflect overall vessel activity. We describe aortic microcalcification activity (AMA), a novel method for quantifying ¹⁸F-sodium fluoride (18F-NaF) uptake in the thoracic aorta.

Twenty patients underwent two hybrid ¹⁸F-NaF PET and computed tomography (CT) scans of the thoracic aorta less than three weeks apart. AMA, as well as maximum (TBRmax) and mean (TBRmean) tissue to background ratios, were calculated by two trained operators. Intra-observer repeatability, inter-observer repeatability and scan-rescan reproducibility were assessed. Each ¹⁸F-NaF quantification method was compared to validated cardiovascular risk scores.

Aortic microcalcification activity demonstrated excellent intra-observer (intraclass correlation coefficient 0.98) and inter-observer (intraclass correlation coefficient 0.97) repeatability with very good scan-rescan reproducibility (intraclass correlation coefficient 0.86) which were similar to previously described TBRmean and TBRmax methods. AMA analysis was much quicker to perform than standard TBR assessment (3.4min versus 15.1min, P<0.0001). AMA was correlated with Framingham stroke risk scores and Framingham risk score for hard cononary heart disease.

AMA is a simple, rapid and reproducible method of quantifying global ¹⁸F-NaF uptake across the ascending aorta and aortic arch that correlates with cardiovascular risk scores.