Information Technology Reference
In-Depth Information
Fig. 3 Flowchart of the algorithm for segmenting vertebral bodies
1
g
ðÞ¼
~
x
1
ð
2
Þ
I
n
g
1
þ
exp
~
where I is the gradient magnitude of the grey level image at voxel
x. The two
parameters
n
and
g
are typically computed using the equations [
46
]:
K
1
K
2
K
1
þ
K
2
g ¼
n ¼
ð
3
Þ
6
2
where K
1
is the minimum gradient magnitude value along the object
s boundary
and K
2
the average gradient magnitude inside the object where the level set is
initialized. Those de
'
nitions ensure that the level set advances over internal gra-
dients but stops at the minimum gradient along the boundary, as Eq. (
2
) maps
gradients values up to K
2
to approximately 1 and gradient values equal or larger
