Abdominal Aortic Aneurysm Volume Measurement with Three-Dimensional Ultrasound—A Feasibility Study

Abstract

Introduction Endoluminal stent grafts are replacing conventional abdominal aortic aneurysm (AAA) surgery in an increasing number of patients in an attempt to minimize morbidity and mortality. Long-term follow-up of endograft-treated AAA demands image-based surveillance to detect endoleak, graft migration, and morphology change in the excluded AAA. AAA diameter is a traditional but simplistic measurement that has inherent flaws and has been shown to be insensitive to changes in AAA sac morphology. Volume measurement, performed by CT data acquisition and computerized postprocessing, has been proposed as the most sensitive index of successful AAA stent graft exclusion. We evaluated two ultrasound (US) volume measuring techniques for AAA volume determination: Virtual Organ Computer-aided AnaLysis (VOCAL) and Multi-Plane Area Summation (MPAS). Methods US images of an endograft-treated AAA were obtained with a commercially available three-dimensional (3-D) scanner. A fast rotating motor inside the probe allowed registration of multiple two-dimensional (2-D) images in real time. Data from these images were assembled in a 3-D dataset. With VOCAL, the 3-D AAA boundaries were identified, and volume was calculated. The operator traced AAA boundaries in six virtual planes selected by the software. With MPAS, aneurysm boundaries were traced in 2-D virtual images perpendicular to the longitudinal axis of the aneurysm obtained every 1 mm. AAA area was calculated and multiplied by this 1-mm step to obtain incremental volumes that were summed to obtain the AAA volume. VOCAL and MPAS volumes were calculated 10 times each for one AAA scan. Results Average AAA volumes were 86.7 ± 3.7 cm3 with VOCAL and 87.6 ± 3.1 cm3 with MPAS. These averages were not statistically significantly different by t test ( p = 0.54). Standard deviation (SD) to average ratio was 4.3% for VOCAL and 3.5% for MPAS. Conclusion Volume of an endograft-treated AAA was successfully measured multiple times with two 3-D US techniques. Volumes obtained were comparable, demonstrating feasible reproducibility.