Biomedical Engineering Reference
In-Depth Information
tries to force the curve to stop at the edge, but the convergence quality still
highly depends on this stopping term. If g ( · ) is not small enough along edges,
there will be an underlying constant force caused by c .
The geodesic or geometric active contour can be numerically implemented
using level sets. This is demonstrated later in Section 10.4.4 when we deal with
the extended formulation of the standard geometric snake into RAGS.
10.2.1 Examples of the Standard Geometric Snake
The standard geometric snake has been applied successfully in many applica-
tion areas, not least in the medical imaging arena. Figure 10.5(left) shows an
example of a geometric snake initialized in the stomach region of an abdomi-
nal section in a CT image. The final snake is shown in Fig. 10.5(right). In the
next example an extension of the geometric snake for color images is shown
in Fig. 10.6, a thigh slice from the Visible Human project. The figure on the left
shows the initial snake as before and the final converged snakes are shown
on the right, demonstrating the topological adaptation of the snake's level set
implementation. Note that the top snake has failed to fully converge. Hence,
while adequate for many situations, geometric snakes can suffer from certain
shortcomings and the next section briefly deals with the nature of some such
failings.
Figure 10.5: Example of geometric snake segmenting an inner boundary: re-
covery of the stomach region of an abdominal CT section—from [5],
c
2003
IEEE.
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