Multimodality imaging assessment of the deleterious role of the intraluminal thrombus on the growth of abdominal aortic aneurysm in a rat model

Objectives: To evaluate imaging changes occurring in a rat model of elastase-induced abdominal aortic aneurysm (AAA), with emphasis on the intraluminal thrombus (ILT) occurrence. Methods: The post-induction growth of the AAA diameter was characterized using ultrasound in 22 rats. ILT was reported on 13 rats that underwent 14 magnetic resonance imaging (MRI) 2-18 days post-surgery, and on 10 rats that underwent 18 fluoro-deoxyglucose (FDG) positron emission tomography (PET)/microcomputed tomography examinations 2-27 days post-surgery. Logistic regressions were used to establish the evolution with time of AAA length, diameter, ILT thickness, volume, stratification, MRI and FDG PET signalling properties, and histological assessment of inflammatory infiltrates. Results: All of the following significantly increased with time post-induction (p <0.001): AAA length, AAA diameter, ILT maximal thickness, ILT volume, ILT iron content and related MRI signalling changes, quantitative uptake on FDG PET, and the magnitude of inflammatory infiltrates on histology. However, the aneurysm growth peak followed occurrence of ILT approximately 6 days after elastase infusion. Conclusion: Our model emphasizes that occurrence of ILT precedes AAA peak growth. Aneurysm growth is associated with increasing levels of iron, signalling properties changes in both MRI and FDG PET, relating to its biological activities. Key Points: • ILT occurrence in AAA is associated with increasing FDG uptake and growth. • MRI signalling changes in ILT reflect activities such as haemorrhage and RBC trapping. • Monitoring ILT activities using MRI may require no exogenous contrast agent.