The Use of SMI in Surveillance of Endovascular Aneurysm Repair

Endovascular aneurysm repair (EVAR) has rapidly become the treatment of choice in the repair of abdominal aortic aneurysms (AAA). Whilst EVAR using commercially available devices has been associated with a low rate of aneurysm-related death, late aneurysm rupture is a potential risk of all devices. Therefore, continued surveillance after EVAR to detect aneurysm growth due to endoleak, device migration, or structural failure is recommended [1]. There has been much discussion regarding the optimal imaging strategy for EVAR surveillance. Initial studies recommended computed tomography arteriography (CTA) at one, six, and 12 months after initial repair and yearly thereafter [2]. However, the frequent use of CTA has raised concerns about the cumulative effects of radiation from repeat exposure and the lifetime risk of cancer, in addition to the added cost of these studies. This led some to question whether colour duplex ultrasound (CDUS) could replace CTA. Although ultrasound avoids radiation exposure and the nephrotoxicity of iodinated contrast agents, concerns were raised regarding the sensitivity of ultrasound in identifying endoleaks [3, 4]. However, more recent studies have suggested that the lower sensitivity of CDUS is offset by a high degree of correlation between CDUS and CTA in the detection of clinically significant endoleaks [5]. If neither an endoleak nor residual aneurysm sac enlargement is documented on the first annual CTA, most centres will use a combination of CTA, CDUS, and plain abdominal radiography at six-month or yearly intervals to follow up the EVAR [6]. Thus, the Society for Vascular Surgery recommends annual surveillance with either CTA or CDUS if the original post-operative CT scan does not demonstrate any of the above concerns [7]. Nevertheless, convention has dictated that if an endoleak is detected, particularly a type II endoleak, it should be followed up by CTA due to the reduced sensitivity of CDUS. Consequently, many centres have reported the use of contrastenhanced ultrasonography (CEUS) as an alternative to CTA due to the improved spatial resolution of CEUS over conventional CDUS. The accuracy of CEUS in detecting endoleaks has been shown to be markedly better than CDUS and similar to CTA and MRA [8]. However, CEUS has limitations and the potential for adverse effects and contraindications. It also takes ultrasound from the realms of a nonor minimally invasive procedure to a more invasive, costly and time-consuming investigation. Recently, Toshiba Medical Corporation has developed a novel microvascular flow imaging technique called SMI (Superb Microvascular Imaging) which has been implemented on its new Prof. Neil Pugh Consultant Clinical Scientist Cardiff and Vale University Health Board, United Kingdom The Use of SMI in Surveillance of Endovascular Aneurysm Repair