Inter-reader agreement of ¹⁸F-FDG PET/CT for the quantification of carotid artery plaque inflammation

A significant proportion of ischemic strokes are caused by emboli from unstable atherosclerotic carotid artery plaques. Inflammation is a key feature of plaque instability. Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-(¹⁸F)-fluoro-D-glucose (¹⁸F-FDG) is a promising technique to quantify plaque inflammation, but a consensus on the methodology has not been established. High inter-reader agreement is essential if ¹⁸F-FDG PET/CT is to be used as a clinical tool for the assessment of unstable plaques and stroke risk.

We assessed the inter-reader variability of different methods for quantification of ¹⁸F-FDG uptake in 43 patients with carotid artery stenosis ≥70%. Two independent readers delineated the plaque and collected maximum standardized uptake value (SUV_max) from all axial PET slices containing the atherosclerotic plaque.

Uptake values with and without background correction were calculated and intraclass correlation coefficients were highest for uncorrected uptake values (0.97-0.98) followed by those background corrected by subtraction (0.89-0.94) and lowest for those background corrected by division (0.74-0.79).

Quantification methods without background correction have the highest inter-reader agreement for ¹⁸F-FDG PET of carotid artery plaque inflammation. The use of the single highest uptake value (max SUV_max) from the plaque will facilitate the method's clinical utility in stroke prevention.