BACKGROUND: Most abdominal aortic aneurysms (AAA) present intraluminal thrombus (ILT). Whether its role is detrimental or protective for AAA evolution and patients outcomes is debated. ¹⁸ F-fluorodeoxyglucose positron emission tomography analysis in patients with AAA has shown contradictory results and has not widely explored ILT. The aim of this cross-sectional study was to investigate the colocalized association between ¹⁸ F-fluorodeoxyglucose and ILT presence and characteristics in AAA. METHODS: Consecutive patients with infrarenal AAA were prospectively enrolled and underwent positron emission tomography/magnetic resonance imaging. From the abdominal aorta segmentation, an aortic wall volume was defined and discretized into 28 standardized aortic patches, permitting colocalized interpatient and intrapatient analyses. The target-to-background ratio (TBR) was extracted in each patch, and extremely low (coldspots) and high (hotspots) absorption areas were computed. Local AAA diameters and ILT characteristics were computed in each patch. Linear mixed-effect models were used to test the association between AAA and ILT characteristics and ¹⁸ F-fluorodeoxyglucose uptake. RESULTS: Thirty-six patients (median age, 73 [interquartile range, 68–77] years, 31 [86.1%] men) completed the protocol. The AAA maximum diameter was 49.6 (45.0–56.2) mm, and most patients (28 [77.8%]) presented ILT. Patients with thrombus presented higher coldspot area and lower hotspot area ( P <0.001). Patches in nondilated regions presented higher TBR compared with AAA patches ( P <0.001), which showed a negative association of TBR with local diameter ( β =−0.006) and thrombus presence ( β =−0.003). TBR decreased with increased ILT coverage ( β =−0.002), while coldspot area increased ( β =0.046). In both the ILT and thrombus-covered wall, TBR decreased with increasing ILT thickness. CONCLUSIONS: Decreased metabolic activity as per 18-fluorodeoxyglucose positron emission tomography is observed in the AAA wall compared with the nondilated abdominal region. This effect is exacerbated by local thrombus presence and thickness, suggesting that ILT contributes to the further degradation of the aortic wall in the diseased region.

18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) could be useful to assess inflammation of the aortic wall, a potential early indicator of aneurysm formation. Nonetheless, its current clinical assessment presents several limitations. The study aimed to develop and validate an innovative technique to obtain thoraco-abdominal aortic wall PET uptake maps. PET/magnetic resonance (MR) was acquired in 82 patients with aortic aneurysms. The thoraco-abdominal aorta was segmented and expanded inward and outward (by 1 to 5 mm) and discretized into 80 standardized wall patches. Standard uptake values (SUV) were calculated for each patch and the thrombus. For inter-observer reproducibility, a second blinded observer analyzed 26 random patients. Validation against manual expert measurements was performed. The feasibility of the patch-wise PET analysis was 98.4%. Inter-observer Dice scores were 0.89 for lumen and 0.82 for thrombus segmentations. SUV mapping presented excellent reproducibility, modestly improving with wall thickness (ICC 0.950 to 0.966), while its agreement with expert measurements improved with thinner walls (ICC 0.848 to 0.755). An optimal balance between reproducibility and accuracy was obtained at 6 mm wall thickness. Reproducible and accurate thoraco-abdominal aortic wall 18F-FDG uptake maps can be obtained from PET/MR, potentially facilitating the exploration of local factors associated with vascular inflammation.