Biomedical Engineering Reference
In-Depth Information
90
80
c = 2000 m/s
c = 1500 m/s
70
60
50
40
30
20
1000
1200
1400
1600
1800
2000
2200
Transducer angular speed ( ) [rpm]
Figure 1.17: Functional dependence between parameter
β
and transducer an-
gular speed
ω
.
between two angular consecutive positions. Note that:
d
t
=
2
R
d
θ
=
ω
d
t
,
=
Rd
θ
(1.9)
c
,
Taking into account these definitions,
β
can be rewritten as:
r
R
2
c
β
=
ω
where
r
is the transducer radius,
R
is the maximum penetration depth,
c
is
the ultrasound speed, and
ω
is the transducer angular speed. The parameter
β
implies that the transducer area is
β
times the sweeping area for the rotatory
beam and the maximal depth penetration. This assures that a high percentage
of echoes is received by the transducer before it changes to the following an-
gular position. We can determine the parameter
β
by calculating the frequency
at which the ultrasound pulse should be emitted. Figure 1.17 shows the func-
tional dependence between parameter
β
and the transducer angular velocity for
several typical velocities in biological tissues. We emphasize the typical IVUS
transducer angular velocity. Figure 1.18 gives the relation between the sample
frequency (
f
m
=
1
/
d
t
) and the typical IVUS transducer angular velocity
ω
.
1.4.4 Determining the Scatterer Number of
Arterial Structures
1) The
red blood cells
(RBCs)
number
swept by the ultrasound beam (Fig. 1.19)
can be estimated by taking into account the plastic sheathing dimensions of
