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

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3.5. Dicussion and Conclusion 63<br />

3.5 Dicussion and Conclusion<br />

In this chapter, we were concerned with the group<strong>in</strong>g and l<strong>in</strong>kage <strong>of</strong> tubular structures <strong>in</strong>to<br />

complete tree structures. Therefor, two methods have been presented: (a) a structurebased<br />

approach has been presented (Section 3.2) that is capable <strong>of</strong> group<strong>in</strong>g/separat<strong>in</strong>g<br />

tubular structures <strong>in</strong> case <strong>of</strong> multiple <strong>in</strong>terwoven tree structures <strong>in</strong>to valid tree structures<br />

and (b) an image based methods has been presented (Section 3.3) for extraction <strong>of</strong> centered<br />

l<strong>in</strong>kage paths. In Section 3.4 we studied these two methods <strong>in</strong> several examples show<strong>in</strong>g<br />

some <strong>of</strong> their properties.<br />

As shown by these examples, the GVF-based approach for identification <strong>of</strong> tubular objects<br />

and for extraction <strong>of</strong> l<strong>in</strong>kage paths between these tubular objects allows us to extract<br />

high quality curve skeletons directly from gray value images. This approach comb<strong>in</strong>es the<br />

advantages <strong>of</strong> a bottom-up tube detection filter with the GVF’s ability for extraction <strong>of</strong><br />

medial curves, also <strong>in</strong> cases where the tube detection is perturbed due to larger deviations<br />

from the typical tube shape such as furcations, stenosis, or aneurysms. The presented<br />

image based l<strong>in</strong>kage approach allows for extraction <strong>of</strong> medial curves also <strong>in</strong> these areas.<br />

We showed that the accuracy <strong>of</strong> the result<strong>in</strong>g centerl<strong>in</strong>es is comparable to that achieved<br />

with state <strong>of</strong> the art skeletonization approaches that are all based on the same known segmentations.<br />

Thus, the result<strong>in</strong>g CSs are directly applicable for tasks requir<strong>in</strong>g high quality<br />

skeletons and this supersedes the need to deal with segmentations and skeletonizations <strong>in</strong><br />

these applications.<br />

However, as shown <strong>in</strong> the experiments, pure image based methods are not capable <strong>of</strong><br />

handl<strong>in</strong>g disturbances such as overlapp<strong>in</strong>g tubular tree structures or cases where parts<br />

<strong>of</strong> the tubular tree structure are not identifiable <strong>in</strong> the image doma<strong>in</strong> (e.g. the tumor<br />

<strong>in</strong> case <strong>of</strong> the airway tree; see Fig. 3.4). In such a case, only some k<strong>in</strong>d <strong>of</strong> centerl<strong>in</strong>e<br />

<strong>in</strong>terpolation can be utilized as done with our structure based approach. As we showed <strong>in</strong><br />

the experiments, the presented structure based approach allows a separation <strong>of</strong> <strong>in</strong>terwoven<br />

overlapp<strong>in</strong>g tubular tree structures and handl<strong>in</strong>g <strong>of</strong> various k<strong>in</strong>ds <strong>of</strong> disturbances, but it<br />

cannot guarantee a centered path <strong>in</strong> these disturbed regions.<br />

Also a comb<strong>in</strong>ation <strong>of</strong> the two approaches could be applied, us<strong>in</strong>g the image based<br />

l<strong>in</strong>kage path extraction <strong>in</strong> cases <strong>of</strong> deviations from a tubular shape and a l<strong>in</strong>ear centerl<strong>in</strong>e<br />

<strong>in</strong>terpolation <strong>in</strong> case <strong>of</strong> imag<strong>in</strong>g artifacts or partly overlapp<strong>in</strong>g tubular tree structures.<br />

Therefor the validity <strong>of</strong> the centerl<strong>in</strong>e paths extracted with the image based method should<br />

be verified based on structural properties and additional l<strong>in</strong>ear centerl<strong>in</strong>e paths added <strong>in</strong><br />

case the structure based method requires a l<strong>in</strong>k between two tubular structures. This

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