Chapter 7: Doppler
233
7
Fig. 9
Rouleau resulting in spontaneous contrast (visualization
of blood) in the common femoral vein
VIEW ONLINE ANIMATION AND IMAGE LIBRARY
KEY CONCEPT
8. Identifying the Doppler Angle (Insonification
or Insonation Angle)
8.1 Standardized Angle Determination
The Doppler angle is defined as the angle that is formed between
the observer’s line of sight and the direction of the target object. In
terms of ultrasound, this angle is often referred to as the insonifica-
tion angle or the angle of insonation, measured between the beam
steering direction and the direction of the flow. The ability to cor-
rectly identify the insonification angle is critical for many reasons
including:
1. The ability to determine flow direction.
2. The ability to assess Doppler measurement accuracy.
3. The ability to minimize Doppler error sources.
4. The ability to assess likelihood of artifact related issues
such as spectral broadening.
8.2 Examples of Insonification Angles
The following series of diagrams indicate how the Doppler angle
is determined.
Fig. 10
Doppler insonification angle = 0
0
Figure 10
illustrates measuring the angle between the beam direc-
tion and the flow direction. Since there is no angular displacement
between the two directions, the angle is specified as 0°, or directly
towards the transducer.
Fig. 11
Doppler insonification angle = 180
0
Figure 11
represents the exact opposite of
Figure 10
,since the blood
flow is directly away from the transducer beam, or 180°.
Fig. 12
Doppler insonification angle = 30
0
In
Figure 12
the angle is measured between the flow direction
(where the flow is going to - indicated by the arrowhead) and the
beamdirection. Since the angle is less than 90 degrees,and since the
cosine of an angle less than 90 degrees is positive, this represents a
positive frequency shift. However, you will note that the flow is not
directly toward the transducer, hence, the shift detected will be less
than 100%. Recalling that the cosine of 30° is 0.86, we know that
only 86% of the true shift is detected.
Fig. 13
Doppler insonification angle = 150
0
SAMPLE PAGE
