Color Doppler Ultrasound - Basic physics - Easy to Learn

1. Color Doppler Ultrasound
(Basic/Physics)
by Syed Yousaf Farooq

2. PRINCIPLE OF DOPPLER ULTRASOUND
• BASIS – ‘ DOPPLER EFFECT’
• DISCOVERY – Physicist Christian
Johann Doppler in 1842.
• ‘When a sound source and the reflector
are moving toward each other, the sound
waves are spaced closer together and reach
the reciever at a higher frequency than
they were originally emitted.

3. DOPPLER SHIFT
• Doppler shift is the
difference between the
transmitted and received
frequencies.
• Transmitted and received
Frequencies are in the MHz
range.
• Doppler shift frequencies
often in audible range.

4. DOPPLER EQUATION
• Relationship between Doppler shift frequency
(FD) and reflector velocity (v).
• f o is the ultrasound frequency, or the transmitted beam
frequency.
• v is the reflector velocity (m/s; cm/s).
• q is the Doppler angle .
• c is the speed of sound.

5. DOPPLER ULTRASOUND
MODES/INSTRUMENTATIONS
• Continuous wave Doppler.
• Pulsed wave Doppler.
Spectral doppler.
Colour doppler.
Power doppler.

6. CONTINUOUS WAVE DOPPLER

7. PULSED-WAVE (PW) DOPPLER
• Uses brief pulses of ultrasound energy using
only one crystal.

8. DUPLEX ULTRASOUND SCANNING
• Duplex ultrasound instruments are real-time
B-mode scanners with built-in Doppler
capabilities.
• ● B-mode Imager ( Outline anatomic
structures ).
• ● Pulsed-Doppler ( Flow and movement
patterns ).

9. PULSE REPETITION FREQUENCY ( PRF )
• No. of pulses transmitted per second.
• With increasing scanning depth PRF decreases as more
time is needed for the echoes to return.
• At a minimum, the PRF must be at least twice the
frequency of the Doppler signal to construct the signal
successfully.
• This sets upper limit to the flow velocities to be
accurately recorded
• Use higher PRF setting for high flow velocities, low PRF
for slow venous flow.

10. A (PRF = 700 Hz) B (PRF = 4500 Hz)

11. Continuous wave (CW) Doppler Pulsed wave (PW) Doppler

12. COLOURDOPPLER
•
• Based on pulsed doppler technique .
•
• Doppler shifts - converted to colour and the
moving blood is displayed in colors that
correspond to its velocity and direction.
• Positive Doppler shifts are encoded as red and negative
shifts are encoded as blue.
• Velocity of the flow is represented in shades of color -
faster - brighter

13. COLORDOPPLER
B
A

14. •
•
•
•
COLOR BOX
Operator adjustable area within the
US image.
Affects Image resolution & quality
( change in box size )- Frame rate
decreases with increasing box
size.
As small & superficial as possible
Deep color box – slower PRF
results aliasing.
COLORDOPPLER.

15. COLOR BOX

16. COLORDOPPLER.

17. COLOUR DOPPLER
Advantages
 It provides an overall view of flow in organ or structure.
 Provides directional information about flow,
 Provides velocity information about flow and shows
turbulent type flow.
Limitations
•
•
•
•
•
SEMI QUANTITATIVE
Angle dependence
Aliasing
Artifacts caused by the noise
Poor temporal resolution

18. Doppler frequency spectrumdisplay
B
A, Color Doppler maging
B, Doppler frequency spectrum waveform
A

19. SPECTRAL DOPPLER
• DEPICTION OF DOPPLER
SHIFT INFORMATION IN
WAVEFORM
COLOUR DOPPLER
• UTILIZE DOPPLER SHIFT
INFORMATION TO SHOW
BLOOD FLOW IN COLOR

20. SPECTRALDOPPLER
ADVANTAGES
• depicts quantitaive flow at
one site
• allows calculations
of velocity and
indices
• good temporal resolution
COLORDOPPLER
ADVANTAGES
• Overall view of flow
• Directional information
about flow
• Averaged velocity
information about flow

21. OPTIMISATION OFCOLORFLOW
DOPPLEREXAMINATION
1. TransducerFrequency.


For superficial structures 7-10MHZ is used. For deep
abdominal structures – 3MHZ – 5MHZ is optimal.
Choice of transducer frequency is paramount because the
intensity of the scattered sound varies in proportion to the 4th
power of the Doppler frequency.

22. OPTIMISATION OFCOLORFLOW
DOPPLEREXAMINATION
2.DopplerAngle.
• Strongest signals of Doppler results when
the motion is parallel to beam.
• A Doppler angle of 900 does not display
flow because no doppler shift detected.

23. OPTIMISATION OFCOLORFLOW
DOPPLEREXAMINATION
3. Sample Volume.
•
•
• Ideal sample volume – 2/3rd of the vessel
width positioned in the center of the vessel.
If sample volume is more: - Spectral
broadening
If sample volume is less: Measured velocity is
too low.

24. OPTIMISATION OFCOLORFLOW
DOPPLEREXAMINATION
6. Velocity scale.
•
•
•
n
Controls the range of frequencies displayed
Too high scale- dynamic range is too large and low
velocity signals are missed simulating an area of
thrombosis
If scale is too low the dynamic range is too small to
display the high velocity signals accurately resulting i
aliasing.

25. REFERENCES
1. Diagnostic Ultrasound, Carol M Rumack and others, 4th ed.
2. Grainger & Allison’ s Diagnostic Radiology- A Textbook of Medical
Imaging, 6th ed.
3. Teaching Manual of Color Duplex Sonography,2nd ed.
4. Frederick W. Kremkau, Diagnostic Ultrasound - Principles and
Instruments, 7th Edition, St. Louis,-Missouri, Saunders Elsevier, 2006
5. Rubin JM ,Bude RO CarsonPL et al ;Power Doppler US; A
potentiallyuseful alternative to to mean frequency based color Doppler
US.

26. THANK
YOU….