Abstract Background Most abdominal aortic aneurysms (AAA) present intraluminal thrombous (ILT), but its effect on aneurysms progression remains unclear. ILT structure precludes flow shear stress on the aortic wall, possibly protecting aneurysms from wall weakening. However, mature thrombus and its cellular interaction causes hypoxia and cellular inflammation, which may degrade the aortic wall. 18F-Fluorodesoxiglucose (18F-FDG) Positron Emission Tomography (PET) uptake, an analogue of glucose, has been associated with inflammatory activity. Using PET/Magnetic Resonance (MR), the effect of thrombus on 18F-FDG uptake can be analysed. Purpose To analyse the association between thrombus characteristics and 18F-FDG uptake on the aortic wall of AAA. Methods Patients with infrarenal AAA underwent a 18F-FDG PET/MR protocol. Using a reproducible and validated technique, 3D maps of 18F-FDG uptake in the aortic wall were computed (Fig. 1A). The target-to-background ratio (TBR) was quantified as blood-pool normalization of the standard uptake value. The 3D maps of the aorta were discretized into 80 standardized patches, for colocalized analysis. For each of the patches placed in the AAA, the median TBR and the amount of thrombus (area and volume covered by thrombus) were obtained. For each aortic wall and thrombus point, the thickness to the blood-pool was computed (Fig 2A). Using the 5% TBR of a non-aneurysmal region, AAA areas with extremely low uptake (coldspots) were computed. Correlations between aortic wall and thrombus TBR and thrombus parameters were performed using Spearman (ρ). Results 36 patients (age 73 ± 7 years, 24 (85.7%) man) with infrarenal AAA (diameters 51 45, 57 mm) completed the protocol, of whom 28 (77.8%) presented ILT (volumes of 71 48, 114 mm3). The median TBR on AAA patches showed significant inverse correlation (p 0.001) with the surface (ρ = -0.41) and the volume (ρ = -0.48) of the patch covered by thrombus (Fig. 1B). The coldspot area showed significant positive correlation (p 0.001) with the AAA area covered by thrombus (ρ = 0.87) and the thrombus volume relative to the AAA volume (ρ = 0.85) (Fig. 1C). TBR both in the aortic wall and the thrombus volume (Fig. 2B), showed an inverse association with local ILT thickness (Fig. 2C and D, respectively). Conclusions The presence of thrombus is locally associated with reduced glucose absorption on the aortic wall, suggesting a possible hypoxic effect on the aortic wall. Further evaluation of longitudinal data is warranted to assess the prognosis and risks associated with low glucose consumption on AAA progression.FIG 1.Methodology (A) and comparison of FIG 2.Visualization of thrombus colored
Bragulat-Arévalo et al. (Thu,) studied this question.