INTRODUCTION Aortic aneurysms are prevalent diseases of the aorta, with limited knowledge about their aetiology, progression, and risk, and no effective pharmacological treatment. 18F-fluorodesoxyglucose Positron Emission Tomography (18F-FDG PET) provides molecular level information of glucose activity, serving as potential analogue of vascular inflammation, which may be relevant to improve knowledge and clinical management of aortic aneurysms. Nonetheless, current clinical assessment of 18F-FDG uptake presents several limitations. PURPOSE The aim of this study was to develop, test and validate an innovative aortic wall uptake mapping. METHODS PET/magnetic resonance (MR) data from 72 patients were acquired. The aortic lumen was segmented, and 9 anatomical landmarks were identified to create a standardised aortic lumen discretization including up to 80 patches. Black-blood MR images were used to guide thrombus segmentation if present, which was merged with lumen segmentation to generate a thoraco-abdominal aortic wall mask. This mask was then expanded by 1 to 5 mm in the inward and outward directions, resulting in an aortic wall volume of interest. Median and percentile 95th standard uptake value (SUV) was calculated on each aortic patch. A second observer performed the same analysis on 23 randomly selected patients for inter-observer reproducibility assessment. Validation was performed by comparisons with regional SUV measured by a nuclear medicine expert. RESULTS The technique was highly feasible, permitting the analysis of all 72 patients and in the 99.6% of aortic wall patches. The image analysis workflow was highly reproducible, resulting in Dice scores of 0.90 [0.57, 0.91] and 0.85 [0.78, 0.88] for aortic and thrombus segmentations, respectively, and in excellent co-localization for anatomical references (5.74 [3.62, 8.73] mm). The inter-observer reproducibility of aortic wall SUV mapping was excellent (ICC between 0.924 and 0.945), with limited differences with respect to aortic wall thickness and similar performances for SUV quantification in the thrombus. The validation of regional SUV values showed good agreement, with limited impact of aortic wall thickness values. A balance between reproducibility and accuracy was obtained with a volume of interest of 6 mm thickness. CONCLUSIONS An image analysis implementation based on multi-modality PET/MR data provides reproducible and accurate quantitative aortic wall 18F-FDG uptake maps. This approach may enable exploring local factors related to an inflammatory vascular state, with possible repercussions in clinical practice.

As abdominal aortic aneurysms (AAA) rupture results in a high mortality rate, early detection and risk stratification are critical for timely elective intervention. Although the maximum diameter is the sole imaging metric used to assess risk, other factors may provide complementary information. This study investigated the role of inflammation and hemodynamics in AAA progression. Methods: Patients with AAA underwent hybrid 18F-fluorodeoxyglucose ([18F]FDG) PET/CMR imaging, including a four-dimensional flow sequence and contrast-enhanced magnetic resonance angiography, and were followed to assess AAA diameter growth rate. Abdominal aorta hemodynamics and [18F]FDG PET target-to-background (TBR) were quantified at 28 standardized regions. Correlations between AAA diameter, hemodynamics, PET and growth rate were assessed. Results: Thirty-two AAA patients (84.4% men) with a median age of 73 and an interquartile range of [68; 77] years were prospectively recruited. The AAA maximum diameter was 48.1 [44.8; 55.0] mm, and the growth rate was 2.7 [1.3; 4.0] mm/year during a follow-up of 2 [1.1; 3.5] years. The AAA maximum diameter (R = 0.443, p = 0.011) and flow vorticity (R = 0.453, p = 0.009) showed significant bivariate correlation with the growth rate. When correcting for the aneurysm diameter, the helicity density was significantly correlated with the growth rate (p = 0.045), while the AAA thrombus volume was inversely associated with it (p = 0.042). Aneurysms with negative helicity density (counterclockwise rotation) grew significantly faster (p = 0.042) than those with positive helicity. In multivariable analysis, beyond the AAA diameter, the thrombus volume, helicity density and TBR were inversely related to the growth rate. Conclusions: Integrating flow, inflammatory and thrombus information may improve AAA growth rate prediction beyond the maximum aneurysm diameter.