Biomedical Engineering Reference
In-Depth Information
in the an
gu
lar position
θ
a
≤
≤
θ
b
for a radial position
R
i
. We consider two
forms of
:
with no uniform distributed scatterers:
=
(
θ
a
+
θ
b
)
/
2
with uniform distributed scatterers:
j
=
1
j
N
R
1
N
R
=
1.5.4 Final Image Processing
The actual image obtained with only the original beams is very poor; we must
explore several smoothing procedures to improve the image appearance. The
procedures to obtain the final simulated image are as follows:
1. The echoes are obtained by the pivoting transducer (Fig. 1.23(a)).
2. Each
echo
profile
is
ordered
according
to
the
angular
position
(Fig. 1.23(b)).
3. The original image is transformed to a polar form (Fig. 1.23(c)).
4. Secondary beams are computed between two original neighboring beams
(Fig. 1.23(c)).
5. The image is smoothed by a 2
×
2 median filter.
6. The image is again transformed to Cartesian form. As a result of this trans-
formation, a significant number of pixels will be empty (Fig. 1.23(d)).
7. The empty pixels are filled in a recursive way form, using an average of
the eight nearest neighbors (Fig. 1.23(d)).
8. An image reference reticle is added and a Gaussian filter is applied.
Figure 1.24 shows the scatterers distribution for a concentric arterial structure
and an axial ultrasound beam position (a), and its corresponding echo profiles
(b). Each axial echo is positioned by an angular position (c). In this way, the 2D
echogram is constructed (d). The procedure of image smoothing is described in
Section 1.5.4.
