Biomedical Engineering Reference
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Figure 10.22: Heart MRI image. Top row: initial snake, and standard geometric
snake. Bottom row: GGVF snake and final RAGS snake showing better conver-
gence and no leakage (original image courtesy of GE Medical Systems).
snake is shown along with the RAGS results on both oversegmentation and
undersegmentation regions.
In Fig. 10.25, a full application of RAGS is presented where the result-
ing regions from the RAGS snake are quantitatively evaluated against those
hand-labeled by an expert ophthalmologist. The first column represents these
groundtruth boundaries. The second column shows the position of the starting
RAGS snakes. The boundary of the optic disk is quite fuzzy and well blended with
the background. The region force helps the proposed snake stop at weak edges
while the standard geometric snake leaks through (as shown in Fig. 10.24) and
the accuracy of the GGVF snake is highly dependent on where the initial snake
is placed (hence GGVF snake results are not provided). The last two columns
illustrate the RAGS results using oversegmented and undersegmented regions
of the mean shift algorithm respectively.
A simple measure of overlap is used to evaluate the performance of the RAGS
snake against its corresponding groundtruth:
n ( A B )
n ( A B )
M =
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