Variability and Uncertainty of ¹⁸F-FDG PET Imaging Protocols for Assessing Inflammation in Atherosclerosis: Suggestions for Improvement

Abstract

PET with 18 F-FDG shows promise for the evaluation of metabolic activities in atherosclerotic plaques. Although recommendations regarding the acquisition and measurement protocols to be used for 18 F-FDG PET imaging of atherosclerosis inflammation have been published, there is no consensus regarding the most appropriate protocols, and the image reconstruction approach has been especially overlooked. Given the small size of the targeted lesions, the reconstruction and measurement methods might strongly affect the results. We determined the differences in results due to the protocol variability and identified means of increasing the measurement reliability. Methods: An extensive literature search was performed to characterize the variability in atherosclerosis imaging and quantification protocols. Highly realistic simulations of atherosclerotic carotid lesions based on real patient data were designed to determine how the acquisition and processing protocol parameters affected the measured values. Results: In 49 articles, we identified 53 different acquisition protocols, 51 reconstruction protocols, and 46 quantification methods to characterize atherosclerotic lesions from 18 F-FDG PET images. The most important parameters affecting the measurement accuracy were the number of iterations used for reconstruction and the postfiltering applied to the reconstructed images, which could together make the measured standardized uptake values (SUVs) vary by a factor greater than 3. Image sampling, acquisition duration, and metrics used for the measurements also affected the results to a lesser extent (SUV varying by a factor of 1.3 at most). For an acceptable SUV variability, the lowest bias in SUV was observed using an 8-min acquisition per bed position; ordered-subset expectation maximization reconstruction with at least 120 maximum likelihood expectation maximization equivalent iterations, including a point spread function model using a 1 mm 3 voxel size; and no postfiltering. Because of the partial-volume effect, measurement bias remained greater than 60%. The use and limitations of the target-to-blood activity ratio metrics are also presented and discussed. Conclusion: 18 F-FDG PET protocol harmonization is needed in atherosclerosis imaging. Optimized protocols can significantly reduce the measurement errors in wall activity estimates, but PET systems with higher spatial resolution and advanced partial-volume corrections will be required to accurately assess plaque inflammation from 18 F-FDG PET.

18F-FDG PET/CT for the quantification of inflammation in large carotid artery plaques

“…13,21,22 The rationale for background correction has been strongly criticized. 9,23 The aim of this study was to explore different methods for the quantification of 18 F-FDG uptake in large carotid artery plaques, and to correlate the uptake values to the amount of inflammation on histology.…”

“…Two parallel phenomena are known to influence measured activity in a lesion: 8 signal from the lesion lost to the surroundings (spill-out), and signal added to the lesion from the vessel lumen and adjacent anatomic structures (spill-in). 8,9 Different acquisition protocols and quantification methods have been suggested. [10][11][12][13][14][15][16][17] They all address the same concerns but have diverging solutions.…”

“…A literature search identified 53 different acquisition protocols, 51 different reconstruction protocols, and 46 different quantification methods used in 49 studies. 9 The most common measure is the mean of all the maximum standardized uptake values (SUVs) (mean SUV max ) of the regions of interest (ROIs). The ROIs include the whole plaque (in localized stenosis), or one or more vessel segments (in subclinical/generalized disease).…”

Can FDG-PET imaging play a role in guiding indications to endovascular treatments in patients presenting acute aortic syndromes?

“…Measurements performed in the vascular wall are very sensitive to parameters selected for image acquisition and reconstruction as well as to partial-volume effects, in particular in relation to the residual blood signal. 17 In this study, the mean SUV of blood was 2.5. This high residual signal of blood might have impacted the max.…”

Nuclear imaging for patients with a suspicion of infective endocarditis: Be part of the team!

“…Even in the presence of FDG accumulation in vegetations, motion and partial volume effects will significantly impact and decrease the intensity of the signal detected with PET. 12 Furthermore, vegetations develop more frequently on native valve than on prosthetic ones, whereas suppurative collections are most often found in PVE than in IE of native valves. Taken together, this study confirms that patients with prosthetic material are the best candidates for FDG-PET imaging for the detection of IE.…”