Segmentation of 3D Tubular Tree Structures in Medical Images ...

106 Chapter 6. Coronary Artery Tree Extraction
significantly better, but it utilizes information about the exact endpoint of the reference
centerline.
Accuracy:
Regarding centerline accuracy, our method is about average compared to the
other methods. Many of the other automated methods show a higher centerline accuracy.
6.4 Discussion
In the previous section, we presented results achieved with our method on a publicly
available database and presented a comparison to other approaches.
Contrary to other methods, our presented approach performed a bottom-up extraction
of tubular structures with a consecutive grouping/linkage of these structures to become
more robust against local disturbances. As the results show, this allows achieving
a high overlap with the provided references, comparable to that achieved with interactive
methods. Only methods utilizing information about the exact endpoint of the reference
centerlines showed a higher overlap. However, in practice these exact endpoints of the
vessels are not known and their position may vary depending on the observer when selected
by a human user. This point was also shown by Schaap et al. [124] who compared
the performance of different observers. Compared to the performance of different human
observers, our method even performed slightly better regarding the achieved overlap with
the reference centerlines.
Another issue with required reference points is, that obtaining such a set of reference
points for each vessel in case the complete coronary artery trees are of relevance may be
a laborious task and the result may also vary between observers. Our presented method
on the other hand obtains the complete coronary artery trees without the need to specify
such reference points (e.g. Fig. 6.3(a)). However, an evaluation about the completeness/correctness
of the complete coronary artery tree structures has not been performed
because of limitations of the database.
Compared to most other automated methods, our method shows a slightly larger
average centerline distance. There are two possible reasons for this. First, the ridge
traversal used for the centerline extraction as described in Section 2.4 is at most voxelaccurate.
Second, the linkage strategy that is applied in regions where our TDF does
not respond (e.g. at junctions) does not guarantee centered paths. However, in case a
higher accuracy is required, a further refinement of the centerline point positions as a
post-processing step can be applied.