Abstract
Background18F-FDG-PET(/CT) is increasingly used in studies aiming at quantifying atherosclerotic plaque inflammation. Considerable methodological variability exists. The effect of data acquisition and image analysis parameters on quantitative uptake measures, such as standardized uptake value (SUV) and target-to-background ratio (TBR) has not been investigated extensively.ObjectiveThe goal of this study was to explore the effect of several data acquisition and image analysis parameters on quantification of vascular wall 18F-FDG uptake measures, in order to increase awareness of potential variability.MethodsThree whole-body emission scans and a low-dose CT scan were acquired 38, 60 and 90 minutes after injection of 18F-FDG in six rheumatoid arthritis patients with high cardiovascular risk profiles.Data acquisition (1 and 2) and image analysis (3, 4 and 5) parameters comprised:1. 18F-FDG uptake time, 2. SUV normalisation, 3. drawing regions/volumes of interest (ROI’s/VOI’s) according to: a. hot-spot (HS), b. whole-segment (WS) and c. most-diseased segment (MDS), 4. Background activity, 5. Image matrix/voxel size.Intraclass correlation coefficients (ICC’s) and Bland Altman plots were used to assess agreement between these techniques and between observers. A linear mixed model was used to determine the association between uptake time and continuous outcome variables.Results1. Significantly higher TBRmax values were found at 90 minutes (1,57 95%CI 1,35–1,80) compared to 38 minutes (1,30 95%CI 1,21–1,39) (P = 0,024) 2. Normalising SUV for BW, LBM and BSA significantly influences average SUVmax (2,25 (±0,60) vs 1,67 (±0,37) vs 0,058 (±0,013)). 3. Intraclass correlation coefficients were high in all vascular segments when SUVmax HS was compared to SUVmax WS. SUVmax HS was consistently higher than SUVmax MDS in all vascular segments. 4. Blood pool activity significantly decreases in all (venous and arterial) segments over time, but does not differ between segments. 5. Image matrix/voxel size does not influence SUVmax.ConclusionQuantitative measures of vascular wall 18F-FDG uptake are affected mainly by changes in data acquisition parameters. Standardization of methodology needs to be considered when studying atherosclerosis and/or vasculitis.
Highlights
18F-Fluorodeoxyglucose positron emission tomography (18F-FDG PET) is a nuclear imaging modality that is increasingly used for assessment of vascular inflammation in patients with atherosclerosis.[1,2] Its clinical relevance is related to the role of inflammation in atherosclerotic plaque development and instability.[3]Quantitative characteristics of 18F-FDG PET are increasingly recognized as providing a more accurate and less observer-dependent measure of inflammatory atherosclerosis than qualitative assessment of PET images.[4]
Intraclass correlation coefficients were high in all vascular segments when SUVmax HS was compared to SUVmax WS
SUVmax HS was consistently higher than SUVmax most-diseased segment (MDS) in all vascular segments
Summary
Quantitative characteristics of 18F-FDG PET are increasingly recognized as providing a more accurate and less observer-dependent measure of inflammatory atherosclerosis than qualitative assessment of PET images.[4] Maximum Standardized Uptake Value (SUVmax) is regularly used for quantification in PET-atherosclerosis studies.[5] SUV is the decay-corrected tissue concentration of intravenously injected 18F-FDG normalised for either body weight, lean body mass or body surface area.[6] In addition to SUV, the target-to-background ratio (TBR), which is the ratio of vascular wall and blood pool SUV, is frequently used.[5] Both SUV and TBR correlate with histologically determined macrophage content in atherosclerotic lesions.[7]. The effect of data acquisition and image analysis parameters on quantitative uptake measures, such as standardized uptake value (SUV) and target-to-background ratio (TBR) has not been investigated extensively.
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