Segmentation of Pulmonary Vascular Trees from Thoracic 3D CT Images

Figure 4

An illustration of the tracking process from a thin segment. The seed point is shown by a gray sphere. At the seed point, the tracking front can take both 𝐞₃ or −𝐞₃ as the initial direction. Either way, tracking will be terminated after 𝜆₃ changes its sign twice and becomes a positive value. The sign of 𝜆₃ becomes negative before the front reaches a junction center. To ensure that the branch is reconnected by tracking, the process needs to wait until the sign changes twice—which indicates that the front truly passed through the junction area. Then the intensity value at the termination points is examined and either trajectory whose intensity value at the termination point is less than the other will be discarded. The other will be used for boundary recovery with the radius estimation.