St George's Vascular Institute Protocol: An Accurate and Reproducible Methodology to Enable Comprehensive Characterization of Infrarenal Abdominal Aortic Aneurysm Morphology in Clinical and Research Applications

Abstract

To define the reproducibility of a protocol for the analysis of infrarenal abdominal aortic aneurysm (AAA) morphology for clinical and research purposes. A protocol for the comprehensive assessment of preoperative AAA morphology based on formal systematic review and expert opinion featured 114 morphological parameters (maximum and minimum diameters, cross-sectional areas, vessel lengths, volumes, angulation, and calcification and tortuosity indices) in each of 3 regions: the neck, sac, and access vessels. To validate the protocol, 4 observers measured these variables on the preoperative computed tomographic angiograms from 50 patients (45 men; mean age 75 years, range 52-89) scheduled for endovascular aneurysm repair using software for 3-dimensional image reconstruction. One observer performed repeated measurements. The intra- and interobserver variabilities were calculated for all parameters; measurement time for all 114 features was recorded. Aortoiliac diameter, length, volume, area, and tortuosity index measurements showed good inter/intraobserver agreement. Aortic neck and aortoiliac angle measurements displayed high intra/interobserver repeatability coefficients (28%-43% and 29%-61%, respectively). Calcification measurements had the highest variability within and between observers: 39%-65% and 44%-96%, respectively. The measurement protocol was completed in a mean 105 minutes (range 55-420). Accurate 3-dimensional analysis of AAA morphology can be performed reliably within a reasonable time. Measurements that relied on consistent anatomical landmarks were most reproducible. Assessment of angulation and calcification required a number of subjective judgments, increasing the potential for variation. Automated methods are likely to be more suitable for certain measurements.