When to image carotid plaque inflammation with FDG PET/CT

Objective Quantification of 18-fluorodeoxyglucose (FDG) uptake in inflamed high-risk carotid atherosclerotic plaques is challenged by the spatial resolution of positron emission tomography (PET) and luminal blood activity. Late acquisition protocols have been used to overcome these challenges to enhance the contrast between the plaque and blood-pool FDG activity. However, for prospective studies the late acquisition is inconvenient for the patient and staff, and most retrospective studies of plaque uptake use data from early acquisition protocols. The objective was to evaluate changes in the quantification methods of FDG uptake in carotid artery plaques between early and late PET scans. Methods FDG uptake 1 and 3 h after tracer injection was compared in 19 carotid artery plaques. The average plaque maximum standardized uptake value (SUV(max)) and a target to background ratio (TBR), using venous blood-pool activity as background, were evaluated at the two time points. These methods have been shown earlier to quantitate the degree of inflammation in late hour scans. Results A good individual plaque FDG uptake consistency was found between the two time points for SUV(max), r(2) = 0.86. In contrast, the ratio method did not conserve the results between the two time points: TBR r(2) = 0.34. For both methods, absolute values changed over time. TBR values generally increased as blood pool activity decreased, whereas the individual plaque SUV(max) values showed both increases and decreases over time. Conclusion Identification of carotid plaque inflammation with PET can be performed 1 h after FDG injection using SUV(max) for plaque FDG uptake quantification. Nucl Med Commun 31:773-779 (C) 2010 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.