Purpose: To study inter- and intraobserver variability of volume measurements with a new, fast semi-automatic method and compare the results to a previously validated standard manual method for volume measurement.
Methods: Twenty abdominal computed tomographic angiography (CTA) datasets of patients with abdominal aortic aneurysms undergoing endovascular aneurysm repair (EVAR) were randomly selected from a clinical database (10 pre and 10 post EVAR). Aneurysm sac volume was measured by 2 independent observers using both the standard and semi-automatic methods. Intra- and interobserver variabilities and variability between the 2 methods were studied. Differences of each pair of measurements were plotted against their mean, and the repeatability coefficient (RC) was calculated according to Bland and Altman.
Results: For the standard method, the intraobserver mean difference was 0.9 mL (0.4% of the first measurement), with an RC of 8.4 mL (4.2%); the interobserver mean difference was 0.0 mL (0.0%), with a RC of 11.8 mL (5.9%). For the semi-automatic method, the intraobserver mean difference was 1.4 mL (0.7%), with an RC of 7.8 mL (4.1%); the interobserver mean difference was -1.8 mL (-1.0%), with an RC of 10.8 mL (5.7%). The mean difference between the methods was 8.3 mL (4.2%), with an RC of 25.1 mL (12.6%) for observer 1, and a mean difference of 6.4 mL (3.2%) and an RC of 21.3 mL (10.7%) for observer 2.
Conclusion: The semi-automatic method showed good intra- and interobserver variability for volume measurements of aortic aneurysms before and after EVAR. Volume measurements with the semi-automatic method correspond to measurements with the standard method. Sophisticated and fast postprocessing software may facilitate acceptance and clinical application of volume measurements in daily practice. The cutoff of 5% for relevant volume changes during follow-up, as advised in the reporting standards for EVAR, is sustained.