Angiographic data of 17 consecutive patients, whom undergoing aneurysm treatment with Tubridge FD between May 2018 and September 2018 in our center, were retrospectively collected. The retrospective study was approved by institutional review board of our hospital, and the informed consents were waived.
Baseline characteristics included patient gender and age, as well as aneurysm location and maximum diameter. We recorded the additional use of embolic material such as coils and whether a single Tubridge or multi-Tubridge construct was used.
Perioperative complications and outcome
Perioperative complications, such as Tubridge deployment failure, occlusion of covered branches, and occurrence of hemorrhage or ischemic stroke, were recorded. Radiologic outcome, including the presence of residual aneurysm perfusion, was recorded for all patients with 6 months imaging follow-up.
Stent length measurement
Three important variables were documented: 1) nominal length of the Tubridge, which was stipulated by the manufacturer; 2) simulated length, which was calculated by the software; and 3) measured length which was measured by a neurointerventionist after deployment. The length of the implanted Tubridge inside the artery was measured from 2D angiographic sequences after operation. The 3D model obtained from the 3DRA images performed before operation was used to generate a centerline. The 3D model was manually registered to the same point of view as the 2D image were acquired. The contrast phase obtained from 2D sequence was used to determine the anatomical location and orientation for a precise alignment between 3D model and 2D image sequence. Finally, the distal and proximal markers of the device were identified on the 2D image and projected on the centerline. The length of the Tubridge FD was calculated as the distance between the distal end and proximal end along the centerline. Biplane acquisitions were available in all cases to choose more clear visibility.
Simulation of FD length
Tubridge FD length was simulated using the braided device foreshortening (BDF) algorithm. A 3D model of the vessel is used to extract the centerline and characterize the local vessel morphology. The computational models used to simulate each device are based on numbers of wires of the stent and the length at two different diameters, which was available from device manufacturer specifications. The obtained model was used to parameterize the simulation following the procedure described by Fernandez.
Local morphological descriptors were used to assess length change at each region of the vessel. The distal end position of the simulated FD was matched to the position observed on the 2D angiographic sequences and the proximal one was obtained by running the BDF algorithm. The final length of the FD (simulated length) is the distance between the distal end and the proximal end of the simulated FD along the centerline.
Error assessment between measurements
The simulation was assessed using an error measure. The error between both the measured length and the simulated length was compared to the nominal length stated by the manufacturer using the following criteria:
MSE [mm2] (L, N) = mean ((L - N)²) The mean squared error (MSE) that accounts for the squared differences between nominal length and approximated stent length.
MAE [mm] (L, N) = mean |L - N| The mean absolute error (MAE) that quantifies the absolute differences between nominal length and approximated stent length.
ME [mm] (L, N) = mean (L - N) The mean error (ME) represents the mean difference between nominal length and approximated stent lengths.
In the above, L is either the measured (M) length or the simulated (S) length, and N is the nominal length stated by the manufacturer.
Differences in baseline characteristics were evaluated with a Student t test, Fisher exact test, and Wilcoxon signed rank test, as applicable. The Statistical Package for the Social Sciences (SPSS, Chicago, USA) was used for statistical analysis, and a p-value < 0.05 was considered statistically significant. Bland-Altman plot was used to evaluate the consistency of simulated or nominal and measured lengths.