Should vascular wall 18F-FDG uptake be adjusted for the extent of atherosclerotic burden?

Vascular wall 18 F-FDG uptake is often used as a surrogate marker of atherosclerotic plaque inflammation. A potential caveat is that vascular wall 18 F-FDG uptake is higher simply because more atherosclerosis is present. To determine if the degree of inflammation is high or low relative to the extent of atherosclerosis, vascular wall 18 F-FDG uptake may require statistical adjustment for a non-inflammatory marker reflecting the extent of atherosclerosis, e.g. calcification. Adjustments is probably needed if (1) vascular wall 18 F-FDG uptake correlates sufficiently strongly with arterial calcification and (2) adjustment for extent of calcification affects determinants of vascular 18 F-FDG uptake. This study addresses these questions. 18 F-FDG PET/low-dose-CT scans of 99 patients were used. Cardiovascular risk factors were assessed and PET/CT scans were analysed for standardized 18 F-FDG uptake values and calcification. ANOVA was used to establish the association between vascular 18 F-FDG uptake and calcification. Multiple linear regression (with and without calcification as independent variable) was used to show whether determinants of vascular 18 F-FDG uptake were affected by the degree of calcification. 18 F-FDG uptake was related to increased calcification in the aortic arch, descending and abdominal aorta. However, 18 F-FDG uptake showed considerable overlap between categories of calcification. Age and body mass index were main determinants of vascular 18 F-FDG uptake. In multiple regression analyses, most standardized beta coefficients of these determinants were not affected by adjustment for the degree of calcification. Although vascular 18 F-FDG uptake is related to total atherosclerotic burden, as reflected by vascular calcification, the association is weak and unlikely to affect the identification of determinants of atherosclerotic inflammation implicating no need for adjustment in future studies.