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

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4.4. Experiments 73<br />

(a) Orig<strong>in</strong>al dataset. (b) Shape prior. (c) Graph cut segmentation.<br />

(d) GVF-based segmentation.<br />

Figure 4.4: <strong>Segmentation</strong> <strong>of</strong> a diseased abdom<strong>in</strong>al aorta.<br />

Bottom row: slice based visualization.<br />

Tow row: <strong>3D</strong> visualization.<br />

show a qualitative difference – the graph cut segmentation <strong>in</strong>cludes calcifications while<br />

the GVF-based method does not – the segmentation results were also compared to reference<br />

segmentations <strong>in</strong>clud<strong>in</strong>g/exclud<strong>in</strong>g calcifications. As segmentation performance<br />

measures, the segmentation overlap, the unsigned volume error, and the unsigned surface<br />

distance are used. Given the segmentation result S and the reference segmentation R, the<br />

segmentation overlap Φ is def<strong>in</strong>ed as Φ = 2V (S ∈ R)/(V (S)+V (R)) where V corresponds<br />

to the volume, the unsigned volume error Υ is Υ = |V (S) − V (R)|/V (R), and the mean<br />

unsigned surface distance error µ d is the average distance <strong>of</strong> all surface po<strong>in</strong>ts <strong>of</strong> S to<br />

the closest po<strong>in</strong>t on the surface R. The results on the four datasets are summarized <strong>in</strong>

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