CEUS and SMI Doppler ultrasound imaging for endovascular aneurysm repair

Patients who undergo endovascular aneurysm repair (EVAR) require regular imaging follow-up to detect potential endoleaks. Contrast-enhanced ultrasound (CEUS) is increasingly being used to detect and characterize endoleaks in lieu of computed tomography angiography (CTA).

Researchers in Poland conducted a study comparing the performance of CTA, color Doppler ultrasound (CDUS), CEUS, and superb microvascular imaging (SMI), published online June 9th in Abdominal Radiology. They determined that CEUS and SMI performed identically and were only slightly less accurate than CTA. Using these ultrasound technologies instead of CTA would eliminate steadily increasing radiation dose exposure to EVAR patients.

CEUS imaging using sulfur hexafluoride microbubbles as a contrast agent improves the resolution and sensitivity of microvessel visualization, but concerns exist about contrast agent use, according to the multi-institutional research team from Poznan. SMI does not require contrast agents and offers low-velocity flow visualization, high-resolution imaging, minimal motion artifacts, and high frame rates. The authors write that clutter artifacts are removed, and that lower-velocity blood flows can be visualized without motion artifacts arising from nearby structures. SMI can also rapidly confirm blood flow or detect absence of flow in cases of torsion and ischemia. Because SMI offers these capabilities and does not use contrast, the authors wanted to determine if it produced superior results to the other imaging methods.

The study’s patient cohort included 30 patients between ages 60 and 70 who underwent post-EVAR CTA, CDUS, CEUS, and SMI examinations at the Poznan University of Medical Sciences. A radiologist and a vascular surgeon independently assessed the videos and the images, recording the presence and types of endoleaks, the types of endoleak inflow vessels, and the patency of the stent-graft segments.

Led by Marcin Gabriel, MD, of the Department of Vascular and Endovascular Surgery, Angiology and Phlebology, the researchers found that CEUS and SMI both identified 15 endoleaks correctly and delivered one false-positive, compared to 15 endoleaks identified by CTA with no false-positives, the gold standard. CEUS and SMI had the same sensitivity (100%), specificity (93%), and accuracy (97%) in endoleak detection. This was comparable to CTA. The authors wrote that because SMI does not use contrast agents, it may be used repeatedly even in patients with renal insufficiency, it may eventually become preferable to CEUS. However, they noted that use of SMI is presently characterized by operator dependency, difficulty in interpreting results, and lack of defined protocol.

REFERENCE

1. Gabriel M, Tomczak J, Snoch-Ziólkiewicz M, et al. Superb Micro-vascular Imaging (SMI): a Doppler ultrasound technique with potential to identify, classify, and follow up endoleaks in patients after Endovascular Aneurysm Repair (EVAR). Abdom Radiol. Published online June 6, 2018. doi.org/10-1007/s00261-018-1633-x.