Vascular Imaging with ¹⁸F-FDG PET/CT: Optimal ¹⁸F-FDG Circulation Time?

TO THE EDITOR: We read with interest the paper by Menezes et al. (1) concerning the optimal circulation time for ¹⁸F-FDG in relation to atherosclerosis imaging. We think the paper considerably advances the knowledge base within this emerging field. We would like to raise a few points in relation to the work.

First, the reason for choosing to image patients with abdominal aortic aneurysm (AAA) is not clear. In order for one to draw conclusions about the optimum time to start PET/CT acquisition in atherosclerosis, surely the study of atherosclerosis patients would have been a better choice? Although the processes underlying both diseases are similar, inflammation may not be the dominant pathology at all stages of AAA (2). Given the decision to study patients with AAA, without intravenous contrast, it is hard to be sure that regions of interest were indeed placed on the wall of the aorta rather than on areas of thrombus.

Second, it is not clear whether the outcome variable used was a single hottest standardized uptake value within the aneurysm or whether a complete slice-by-slice analysis of the aorta was performed. Along the same line, was the ¹⁸F-FDG uptake in other regions of the aorta or in the carotid arteries measured? Those results, if available, would add considerable weight to the conclusions drawn because they would reflect atherosclerotic plaque inflammation rather than presumed atherosclerosis within AAA.

Finally, why did the authors choose the lumen of the aorta from which to derive background blood signal, rather than an adjacent vein such as the inferior vena cava or jugular as previously described (3,4)? The aortic lumen regions of interest may have been subject to partial-volume errors of activity spilling into the field. This possibility could explain some of the variability experienced in the later target-to-background measurements.

We congratulate the authors on their important study. We agree that standardization of imaging protocols (dose, acquisition mode, and imaging time points) across different vendors is crucial to the appropriate use of this technology for efficacy tests of novel antiatherosclerosis drugs and for possible prediction of future events.