Biomedical Engineering Reference
In-Depth Information
Figure 16.
Drawings depict (a) the contour of a tumor, and (b) the convex hull of a tumor.
The outer polygon (arrow) is the convex hull of the tumor, while the convex hull is the
smallest convex set containing the tumor.
5.4. Experimental Protocol and Results for 2D Strain Data
In the experiments we used 100 pathology-proven cases, including 60 benign
breast tumors and 40 malignant ones, to evaluate the classification accuracy of
the proposed method. The segmentation results in different compressed images
using the level set framework are shown in Figures 17 through 20. The mean
values of three strain features—
C
d
,
M
d
,
A
d
—and one shape feature (
S
o
) in cases
of malignant tumors were 3
.
52
±
2
.
12, 2
.
62
±
1
.
31, 1
.
08
±
0
.
85, and 1
.
70
±
1
.
85,
whereas those in the cases of benign tumors were 9
.
72
±
4
.
54, 5
.
04
±
2
.
79,
3
.
17
±
2
.
86, and 0
.
53
±
0
.
63, respectively. These values are significantly different,
as shown in Table 1 (with
p
values all smaller than 0.001). The noncontinuous stain
values are also given in Table 1. In the noncontinuous strain imagingmethod, strain
values are computed by the first (
I
1
) and final (
I
57
) frames. All the noncontinuous
stain values are also statistically significant. Moreover, the strain values with the
noncontinuous method are larger due to the fact that these values are computed
from the first and last frames.
In the scatter graph in Figure 21, the three values of the strain features for
malignant tumors concentrated around the origin and were smaller than those for
the strain features for benign tumors. The receiver operating characteristic (ROC)
curves of the four feature values with the support vector machine (SVM) classifier
(see Vapnik [45], Pontil et al. [46], and Chapelle et al. [47]) are shown in Figure 22.
The
A
z
values of three strain features were significantly higher than that of the
single shape feature (
p<
0
.
01). The SVM using all four feature values produced
the best performance, with an
A
z
value of 0.91.
