Biomedical Engineering Reference
In-Depth Information
If
z >
1250
15
5
11
4
8
3
s
s
s
Pz
(
)
3.3
10
z
2.6
10
z
8.5
10
z
s s
(6.6)
The system was tested to simulate human blood pressure at 1
Hz, and then used to circulate low while measuring stress on the
multilayered vasculature wall.
42
2
1.3
10
z
4
10
z
87.5
Controller
Piston Pump
Accumulator
Hz
f(z)
p
1
(z)
Hz
F( z)
C
1
P
1
A
mmHg
-
Hz
Controller
Lobe Pump
p
2
(z)
+
mmHg
Hz
+
P( z)
C
2
P
2
p
out
(z)
-
mmHg
Figure 6.6
Control diagram of the hybrid pump.
6.3
Image Processing Software for Stress
Measurement
The system shown in Fig. 6.7 was constructed for stress
measurements. Analyzed and result images are 640
×
480 pixels,
with
x
and
y
used to deine pixel locations in rows and columns.
N
0
is the image of the model when illed with and surrounded by
water and placed between the light source and camera.
D
(
x, y
)
is an
optical path length pixel belonging to
N
1
and is obtained by applying
Eq. 6.7 to the blue intensity of pixel
I
B(
x, y
)
of
N
0
in a similar way as
shown in Chapter 4. To eliminate the noise of
N
1
produced by the
background, all pixels with optical path length equal to 0.2 mm or
less were set to zero (black). Using the polariscope detailed in [6-7],
we captured images in which the photoelastic effect is visible.
N
2
and
N
3
are images of the vasculature model inside the polariscope,
N
2
when there is no low circulation inside the model and
N
3
when the
pressure inside the model is 182 mmHg. Based on previous results
[6, 8], we modeled the relation between retardation
Re
(
x, y)
and green
light intensity
I
G
(
x, y
)
in urethane elastomer model image as follows:
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