# Innovative Tool for Automatic Detection of Arterial Stenosis on Cone Beam Computed Tomography
## 3 Results  
This study provides a tool to facilitate surgeons in detecting arterial stenosis. Critical vessels are identified on the corresponding 3D skeleton of the analyzed CBCT volume, as shown in Figure 5a, where the thickness of each branch is specified. When a branch is selected by the user, the colored skeleton turns gray, while the chosen segment turns red and its consecutive branches turn green, as shown in Figure 5b. Extraction of further vessels follows the same steps as described above. All vessels that have been selected at least once remain red, allowing the user to follow the flow of the vessel under study. This representation is schematized in Figure 5c. Once the skeleton is selected, the two-dimensional plot corresponding to that tract of the segment is also realized, as seen in Figure 5d. The phase of segmentation was previously validated in the paper of [PERSON] et al., from which we resumed the process to perform our segmentation [18]. They compared the results with the reference images obtained performing a manual segmentation. This analysis showed a sensitivity of 0.748 and a specificity of 0.999. Our system was able to identify the presence of stenosis in the upper mediastinum at the level of the epionic vessels. The value of the stenosis shown in the linear graph is 0.84 mm. This corresponds to a little more than a 50% stenosis of the left subclavian artery. This value was calculated from the y-coordinate measurement of 0.419 mm. Once the user selects the tract of interest, the corresponding linear representation appears. On the plot shown in Figure 6 is reported the two-dimensional representation of the segment and the values of the coordinates \(x\) and \(y\). This graph shows contemporaneously the length of the tract along the \(x\)-axis and the value of the diameter along the \(y\)-axis. The values on the y-axis are plotted with respect to each point of the skeleton of that branch starting from the values obtained with the distance transform. Specifically, the value of the diameter on the graph is obtained by taking these values and reversing them symmetrically with respect to the x-axis. Thus, given that the coordinate \(y\) on the graph of Figure 6 has value \(y=0.419\) mm, on the y-axis, the diameter is equal to double that value, that is 0.84 mm. This value was compared with the measurement performed by the radiologists, who identified, on the coronal plane, a diameter of about 1.06 mm, as shown in Figure 7. The relative error between the two estimates corresponds to approximately 20%. These measurements were performed manually using a digital ruler, and thus, as with any other  
Figure 4: Flow chart of the proposed vessel analysis tool. type of manual measurement, they are subject to human mistakes and inter-individual variability. However, the fact that the values measured both manually and by our tool are approximately similar suggests, first of all, that the system has detected correctly the narrowing point of interest and, secondly, that our tool can improve the accuracy of the human measurements by reducing human subjectivity. The system is able to detect even minimal narrowing, which might not be visible simply by just the CBCT volume, as shown in the example reported in Figure 8.  
The tool has the same ability for both wide and narrow vessels segments, as the detection of structural variations is based on short vessels tracts by comparing the variation of the diameter between the current point and the mean diameter of the analyzed tract. Figure 5: Overview of the vessel analysis tool functioning in response to the selection of two branches on the skeleton. (**a**) Skeleton of the vascular tree. (**b**) After selecting the first branch, the skeleton is shown in gray-scale skeleton, the selected branch is red, and its adjacent segments are green. (**c**) Once the second branch is selected, the GUI shows all selected branches in red and adjacent tracts of the last selected segment in green. (**d**) Linear representation of the vessels.