Standardization of Semiautomatic Tortuosity Measurements in the Carotid Artery

Introduction - Increased arterial tortuosity has been suggested as a predisposing factor for carotid artery dissection, which is an important etiological risk factor for development of extracranial carotid artery aneurysms (ECAA). Conversely, little is known about tortuosity of the carotid artery in patients with ECAA. Prior to comparison with non-ECAA controls, the optimal measurement technique should be defined. This study aimed to determine the difference between software packages in terms of reproducibility and absolute outcome of arterial tortuosity measurements in patients with ECAA. Methods - Four commercial software packages were compared: 3mensio Vascular (Pie Medical Imaging BV, Maastricht, NL), TeraRecon (Aquarius, Foster City, CA, USA), Vital Images (Toshiba Medical, Minnetonka, MN, USA), and Aycan OsiriX PRO (Aycan Medical Systems, Rochester, NY, USA). Patients with ECAA were selected from our ECAA registry. Two observers independently scored two rounds of 12 thin slice computed tomography angiography (CTA) scans using the software packages. The tortuosity index (TI) was calculated from skull base until 1) carotid bifurcation and 2) aortic arch, and was defined as the true length of the centerline divided by the straight distance. Intraclass correlation coefficients (ICC) with 95% confidence intervals were calculated to quantify inter- and intraobserver variability within one software package, and differences in measured TI between the software packages. Results - The interobserver agreement was close to perfect for 3mensio, excellent for Vital Images and OsiriX, and substantial for TeraRecon, with ICC 0.99 (0.96-1.0), 0.90 (0.69-0.97), 0.84 (0.53-0.95), and 0.72 (0.28-0.91), respectively. The intraobserver agreement ranged from ICC 1.0 for 3mensio to ICC 0.91 for TeraRecon. Agreements between software packages on measured TI ranged from ICC 0.99 (0.98-1.0) for 3mensio vs. OsiriX, to ICC 0.95 (0.82-0.98) for 3mensio vs. TeraRecon. Median time needed to complete one round of measurements was highest for OsiriX (p=0.013). Conclusion - Carotid artery tortuosity measurements are reproducible and comparable between current commercially available software packages, with high intraobserver agreement. Although the reproducibility differed per software packages, all packages scored an acceptable interobserver agreement.