Internal tissue references for 18Fluorodeoxyglucose vascular inflammation imaging: Implications for cardiovascular risk stratification and clinical trials

Abstract

Introduction18Fluorodeoxyglucose (FDG) positron emission tomography (PET) uptake in the artery wall correlates with active inflammation. However, in part due to the low spatial resolution of PET, variation in the apparent arterial wall signal may be influenced by variation in blood FDG activity that cannot be fully corrected for using typical normalization strategies. The purpose of this study was to evaluate the ability of the current common methods to normalize for blood activity and to investigate alternative methods for more accurate quantification of vascular inflammation.Materials and methodsThe relationship between maximum FDG aorta wall activity and mean blood activity was evaluated in 37 prospectively enrolled subjects aged 55 years or more, treated for hyperlipidemia. Target maximum aorta standardized uptake value (SUV) and mean background reference tissue activity (blood, spleen, liver) were recorded. Target-to-background ratios (TBR) and arterial maximum activity minus blood activity were calculated. Multivariable regression was conducted, predicting uptake values based on variation in background reference and target tissue FDG uptake; adjusting for gender, age, lean body mass (LBM), blood glucose, blood pool activity, and glomerular filtration rate (GFR), where appropriate.ResultsBlood pool activity was positively associated with maximum artery wall SUV (β = 5.61, P<0.0001) as well as mean liver (β = 6.23, P<0.0001) and spleen SUV (β = 5.20, P<0.0001). Artery wall activity divided by blood activity (TBRBlood) or subtraction of blood activity did not remove the statistically significant relationship to blood activity. Blood pool activity was not related to TBRliver and TBRspleen (β = −0.36, P = NS and β = −0.58, P = NS, respectively)ConclusionsIn otherwise healthy individuals treated for hyperlipidemia, blood FDG activity is associated with artery wall activity. However, variation in blood activity may mask artery wall signal reflective of inflammation, which requires normalization. Blood-based TBR and subtraction do not sufficiently adjust for blood activity. Warranting further investigation, background reference tissues with cellular uptake such as the liver and spleen may better adjust for variation in blood activity to improve assessment of vascular activity.

Clinical Factors Associated with Time-Specific Distribution of 18F-Fluorodeoxyglucose in Large-Vessel Vasculitis

“…Understanding the time-dependent factors associated with FDG distribution in arteries and background tissues may enable investigators to account for potential confounding variables when developing outcome measures for arterial FDG uptake. Age, in particular, was strongly associated with vascular FDG uptake, consistent with prior studies 19 . Potential differences in age and BMI could bias studies that compare arterial SUVs if these factors are imbalanced between study groups.…”

“…Quantification of FDG uptake in the arterial wall can be affected by many factors. Previous studies in atherosclerosis have examined how multiple clinical factors influence FDG distribution in the arterial wall and other tissues 19,20 . This study is unique in that factors associated with FDG distribution were studied in a time-dependent and tissue-specific manner in a cohort of patients with LVV.…”

“…Previous studies have shown that various factors can influence the distribution of FDG into specific tissues, including the arterial wall and tissues used for normalization of arterial FDG uptake 8,19 . The clinical factors associated with FDG distribution into the arterial wall and background tissues have not been comprehensively assessed in LVV.…”

Low-count whole-body PET with deep learning in a multicenter and externally validated study

“…All VOIs were subsequently copied from the standard scans to the low-count-enhanced scans. The SUV mean of the VOIs was evaluated for the aortic blood pool, liver, and the right gluteus muscle as internal organ reference regions 37 – 39 , while the SUV max was evaluated for the hypermetabolic lesions on the standard and low-count-enhanced scans.…”

Diagnosing giant cell arteritis: a comprehensive practical guide for the practicing rheumatologist

“…However, this challenge can be overcome by new PET scanning systems (dynamic PET) in which non-metabolised tracer is not visualised (129). The interrater-reliability appears to be very high (109).…”