When a sound source and the reflector are moving toward each other, the sound waves are spaced closer together and reach the receiver at a higher frequency than they were originally emitted “
5. PRINCIPLE OF DOPPLER
ULTRASOUND
“When a sound source and the
reflector are moving toward each
other, the sound waves are spaced
closer together and reach the
receiver at a higher frequency than
they were originally emitted “
22. DOPPLER EFFECT
● Change in the perceived frequency of sound
emitted by a moving source
● The basis of doppler ultrasonography is the
fact that reflected / scattered ultrasonic
waves from a moving interface will undergo a
frequency shift
23. ● In diagnostic ultrasound , the doppler effect is
used to measure blood flow velocity
● When the emitted ultrasound beam strikes
moving blood cells , the latter reflect the
pulse with a specific doppler shift frequency
that depends on the velocity and direction of
blood flow
25. ● IF RECEIVED FREQUENCY = TRANSMITTED
FREQUENCY, NO DOPPLER SHIFT
◻ Positive shift
⮚ Received freq >
transmitted freq
⮚ Flow towards the
transducer
◻ Negative shift
⮚ Transmitted freq
> received freq
⮚ Flow away from
the transducer
37. ● Angle
● Cos (a)
Doppler shift depends
on the cosine of the
angle between the
sound beam and the
direction of the
motion
V = Fd × C
2 fₒ × cos ᶱ
Optimal angle :
30°-60°
Angle Cos theta
0 1
45 0.7
60 0.5
90 0
38.
39. Goals of doppler
● Detection of flow
● Detection of direction of flow
● Detection of type of flow :
✔ Arterial or venous
✔ Normal or abnormal
● Measurement of velocity of flow
51. COLOUR DOPPLER
Colour (flow) Scanning involves displaying Colour Doppler
data on real time (B-mode) Grayscale images.
● The superimposition is such that tissue volumes
Containing
● no detectable flow are displayed in greyscale
● while those in motion are in colour ( usually red or blue)
52.
53.
54. Velocity Color Bar : controls the range
of frequencies displayed
Increasing flow
velocity away
from the
transducer
Zero
flow
Increasing
flow velocity
toward the
transducer
60. Physics of Spectral Flow
Vascular Flow
• Blood flow is normally laminar with
velocity decreasing from the center
outward to the vessel walls
61.
62.
63.
64.
65. Low Resistance Flow
• In these arteries, a moderate
systolic rise is followed by a
steady flow that persists
throughout diastole.
• This flow profile is typical of
the renal, hepatic, splenic,
internal carotid, and vertebral
arteries
66. High Resistance Flow
• High-resistance flow is typical
of the arteries supplying
Muscles and the skin
Triphasic flow
• Steep systole
• Refulx in early diastole
• Slow flow mid diastole
• Zero flow end diastole
67. Flow can either be:
•Mono-phasic
•Bi-phasic
•Tri-phasic
•Bidirectional
