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Rapid Fire Abstracts

Rapid Fire 07- Metabolism, Spectroscopy, Molecular Imaging, and Hyperpolarized MRI & contrast agents

Validation and reproducibility of 18F-FDG PET uptake mapping in the aortic wall and thrombus (RF_FR_383)

Friday, January 31, 2025
2:10 PM – 2:20 PM East Coast USA Time
Location: Blue Room PreFunction
Background:

Positron Emission Tomography (PET) uptake allows for the assessment of molecular activity, with 18F-FDG uptake being analogue of glucose metabolism. Commonly, PET uptake is quantified by manually drawing regions of interest, but this method is subjective, poorly-reproducible and may miss relevant information. This study aimed to develop, test and validate an image analysis implementation to quantify 18F-FDG uptake maps in the aortic wall.

Methods: PET-MRI was acquired in 72 patients with either thoracic or abdominal aortic aneurysms. The lumen and thrombus were semi-automatically segmented in the MR angiography and merged. A superficial mesh was created and expanded by 3 mm inward and outward, representing the aortic wall space. PET uptake was interpolated over this volume with a uniform spatial resolution of 1 mm. By means of 9 reference points, the aortic wall was discretized into 52 (thoracic) or 80 (thoraco-abdominal) standardized regions (i.e. wall patches). For each aortic patch and for the whole thrombus volume, the median standard uptake value (SUV) was quantified. Maximum uptake in regions were compared with expert annotation for validation. The whole procedure was repeated by a second observer in 23 randomly-selected patients.

Results:

The technique was feasible in the 100% of patients and 99.6% of aortic wall patches. The image analysis workflow was very reproducible, resulting in Dice scores of 0.9 [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 of 0.93 [0.93, 0.94]) as it was for SUV quantification in the thrombus (Figure 1, Figure 2). The validation of regional SUV values showed excellent agreement (Figure 3).

Conclusion:

A reproducible and accurate image analysis method to map PET uptake along the aortic wall was developed, extending the possibilities to study the interaction between aortic wall molecular activity and local characteristics.