Brief report
Automated Quantification of Aortoaortic and Aortoiliac Angulation for Computed Tomographic Angiography of Abdominal Aortic Aneurysms before Endovascular Repair: Preliminary Study

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The degree of angulation of abdominal aortic aneurysms (AAAs) has emerged as an important factor in assessing eligibility for endovascular aneurysm repair (EVAR). The authors developed an automatic algorithm that reduces variability of measurement of aortoiliac angulation. For highly structured manual methods, intraobserver variability was 8.2 degrees ± 5.0 (31% ± 20) and interobserver variability was 5.6 degrees ± 2.5 (20% ± 9.1) compared with 0.6 degrees ± 0.8 (2.2% ± 3.6) (intraobserver) and 0.4 degrees ± 0.4 (1.4% ± 1.9) (interobserver) for the automatic algorithm (P < .01). In phantoms, the automatically measured angles were equivalent to reference values (P < .05). This algorithm was also faster than manual methods and has the potential to enhance the clinical utility and reliability of computed tomographic angiography for preoperative assessment for EVAR.

Section snippets

Algorithm

At our institution, the angulation of the aorta and iliac arteries at four anatomic locations are measured manually by technologists for every patient with an infrarenal aortic aneurysm. Measurements of angulation are provided at (1) the level of the superior boundary of the aneurysm sac (termed the ”proximal neck angle”), (2) the middle of the aneurysm sac (termed the ”aneurysm angle”), and (3) each common iliac artery origin (termed the ”common iliac artery angle”) for a total of four angles.

Results

Figure 5 shows the correlations between automatically measured and known angles in the ”virtual phantoms,” with R2 values of 0.99 in all cases and slopes very close to 1. Over all phantoms and angles, the mean error between the actual and measured angles was 0.7 degrees ± 0.5 (standard deviation). The P value for Schuirmann's two one-sided equivalence test was less than .05, allowing us to reject the null hypothesis and conclude that there was no statistically significant difference between

Discussion

Manual measurement of aortoiliac angulation may be excessively variable (6, 7, 10). Clinically significant variability has also been reported in manual measurements of angulation using CT in other structures, such as in extremities (8, 14) and pulmonary veins (9). The interobserver variability of manual measurements in this article is slightly less than that reported by Diehm et al (approximately 6 degrees vs approximately 13 degrees, 20% vs 32%) (10). This reduction in variability could be due

Acknowledgment

The authors are grateful to Carl R. Crawford, PhD, for providing the core of the CT scanner simulation software used for validating this algorithm.

References (15)

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This research was supported by National Institutes of Health grants 5RO1HLO58915 and 1RO1HL67194. None of the authors have identified a conflict of interest.

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