Imaging of Abdominal Aortic Aneurysm: the present and the future

Abstract

Abdominal Aortic Aneurysm (AAA) is a common, progressive, and potentially lethal vascular disease. A major obstacle in AAA research, as well as patient care, is the lack of technology that enables non-invasive acquisition of molecular/cellular information in the developing AAA. In this review we will briefly summarize the current techniques (e.g. ultrasound, computed tomography, and magnetic resonance imaging) for anatomical imaging of AAA. We also discuss the various functional imaging techniques that have been explored for AAA imaging. In many cases, these anatomical and functional imaging techniques are not sufficient for providing surgeons/clinicians enough information about each individual AAA (e.g. rupture risk) to optimize patient management. Recently, molecular imaging techniques (e.g. optical and radionuclide-based) have been employed to visualize the molecular alterations associated with AAA, which are discussed in this review. Lastly, we try to provide a glance into the future and point out the challenges for AAA imaging. We believe that the future of AAA imaging lies in the combination of anatomical and molecular imaging techniques, which are largely complementary rather than competitive. Ultimately, with the right molecular imaging probe, clinicians will be able to monitor AAA growth and evaluate the risk of rupture accurately, so that the life-saving surgery can be provided to the right patients at the right time. Equally important, the right imaging probe will also allow scientists/clinicians to acquire critical data during AAA development and to more accurately evaluate the efficacy of potential treatments.

Fig. 1

Representative anatomical images of AAA in patients and preclinical models, acquired with various imaging techniques. Top left: Contrast-enhanced ultrasound obtained 30 seconds after injection shows contrast extravasation (arrow) in ruptured AAA. Top right: Ultrasound images showing the aneurysm (A) and lumen (L) in a mouse. Scale bar: 0.5 mm. Center: Volume-rendered images of a patient from non-enhanced CT studies at stent placement and 1 year follow-up. Bottom: magnetic resonance angiogram (maximum-intensity projection) before (left) and after (right) endograft delivery in a swine model. Adapted from [47,55,64,75].

Fig. 2

Functional imaging of AAA. The cells can be labeled first and then intravenously injected or the tracer itself can be intravenously injected. A representative image after injection of radiolabeled red blood cells which delineates endoleak is shown. Adapted from [88].

Fig. 3

Optical imaging of VEGFR expression in AAA with scVEGF/Cy. Both in situ images after abdominal evisceration and bilateral nephrectomies and ex vivo images of the aorta are shown. Adapted from [105].

Fig. 4

Frontal views of infrarenal aortic aneurysm in a rat as visualized by SPECT/CT imaging after injection of ^99mTc-annexin V. Arrow indicates the upper part of the aneurysm. Adapted from [109].

Fig. 5

¹⁸F-FDG PET/CT of an AAA vessel wall (arrows) in a patient. Adapted from [127].

Fig. 6

A brief summary of various imaging techniques for AAA diagnosis and management.