explaining the different doppler ultrasound principles

1. DOPPLER US (1)
Dr. Kamal Sayed MSc US UAA
Ok /dop/ techn/effect shift/dop types & ABPI/color maps/
dop packets/

2. What is the principle of ultrasound?
An electric current passes through a cable to the transducer and is applied to the crystals,
causing them to deform and vibrate. This vibration produces the ultrasound beam. The
frequency of the ultrasound waves produced is predetermined by the crystals in the
transducer.
•
Introduction
•
Doppler ultrasound, a special ultrasound technique, measures
the direction and speed of blood cells as they move through
vessels.
•
The movement of blood cells causes a change in pitch of the
reflected sound waves (called the Doppler effect).
•
A computer collects and processes the sounds and creates
graphs or color pictures that represent the flow of blood
through the blood vessels

3. •
1. Doppler Us study is a technique using sound waves to produce pictures
of blood vessels and evaluates blood flow through a blood
vessel
2. Dopp US measures direction & speed of blood cells as they move
through vessels.
(Normal doppelr US generates pictures in one dimension)
3. DUPplex US is a type of dopp us which generates pictures in Two
dimensions
4. Doppler effect is the change in the pitch of reflected sound waves
caused by movement of blood cells through blood vessels.

4. •
The Doppler effect is a phenomenon observed whenever the source
of waves is moving with respect to an observer.
The Doppler effect can be described as the effect produced by a
moving source of waves in which there is an apparent upward shift
in frequency for the observer and the source are approaching
and an apparent downward shift in frequency when the observer
and the source is receding.
The Doppler effect can be observed to occur with all types of waves
- most notably water waves, sound waves, and light waves.
•

5. •
Doppler ultrasound is a special ultrasound technique,
which measures :
1. the direction and
2. speed of blood cells
as they move through vessels.
The movement of blood cells causes a change in pitch of
the reflected sound waves (called the Doppler effect).
A computer collects and processes the sounds and creates
graphs or color pictures that represent the flow of blood
through the blood vessels.

6. •
# We are most familiar with the Doppler effect because of our
experiences with sound waves. Perhaps you recall an instance
in which a police car or emergency vehicle was traveling
towards you on the highway :
As the car approached with its siren blasting, the pitch of the
siren sound (a measure of the siren's frequency) was high;
and then suddenly after the car passed by, the pitch of the
siren sound was low. (((That was the Doppler effect - a shift in
the apparent frequency for a sound wave produced by a
moving source))).

7. •
Another common experience is the shift in apparent frequency of the
sound of a train horn :
As the train approaches, the sound of its horn is heard at a high pitch and
as the train moved away, the sound of its horn is heard at a low pitch.
(((This is the Doppler effect))
•
Explaining the Doppler Effect
## The Doppler effect is observed because the distance between the
source of sound and the observer is changing ##.
1. If the source and the observer are approaching, then the distance is
decreasing)
•
.

8. 2. and if the source and the observer are receding, then the distance is
increasing.
3. The source of sound always emits the same frequency.
4. Therefore, for the same period of time, the same number of waves
must fit between the source and the observer.
5. if the distance is large, then the
waves can be
spread apart;
6. but if the distance
is small, the waves must be compressed into the smaller distance.

9. # For these reasons,#
7. if the source is moving towards the observer, the observer
perceives sound waves reaching him or her at a more frequent rate
(high pitch).
8. And if the source is moving away from the observer, the observer
perceives sound waves reaching him or her at a less frequent rate
(low pitch).
9. It is important to note that the effect does not result because of
an actual change in the frequency of the source.
10. The source puts out the same frequency;

10. •
How is the procedure performed?
For most ultrasound exams, you will lie face-up on an exam
table that can be tilted or moved.
•
Patients may be turned to either side to improve the quality
of the images.
A clear water-based gel is applied to the area of the body
being studied.
•
This helps the transducer make secure contact with the body
and eliminate air pockets between the transducer and the
skin that can block the sound waves from passing into your
body.

11. •
The technologist or radiologist places the transducer on the
skin in various locations, sweeping over the area of interest.
•
The sound beam may also be angled from a different location
to better see an area of concern.
Doppler sonography is performed using the same transducer.
When the exam is complete, you may be asked to dress and
wait while the ultrasound images are reviewed.
This ultrasound examination is usually completed within 30 to
45 minutes.

12. The Doppler sound wave traveling at an angle through the flowing blood in
the blood vessel; the Doppler angle.
•
The Doppler shift and Doppler angle
•
are then calculated, allowing determination of blood
circulation patterns.
•
Note: the specific Doppler calculation will not be
explained further in this course.
•
image slide (13/14)
•

13. The Doppler sound wave traveling at an angle through the flowing blood in
the blood vessel; the Doppler angle.

14. Doppler shift; difference between emitted and received
frequencies.

15. •
As explained above, moving objects undergo a change in
frequency.
•
In color Doppler, frequency changes are converted into color
on screen.
•
Blue means the blood is moving away from the TXR ; red
means the blood is moving towards the TXR
•
image slide (17)

16. •
(note: blue and red does not necessarily mean low-oxygen
and high-oxygen blood respectively).
•
Explanation : when blood moves towards the transducer, the
wave length of the sound wave shortens, the sound frequency
increases (positive Doppler shift).
•
The opposite happens in blood moving away from the
transducer (= negative Doppler shift).
•
Image slide (17).

18. •
Carotid Doppler US is used
to screen pts for blockage or narrowing of carotid arteries (carotid
stenosis) which increases stroke risk.
when probe mechanically press skin through gel , the piezoelectric
crystals transform electrical energy into mechanical energy with high
frequency sound waves I.e (electrical energy transformed into sound
energy)
High frequency sound waves travel from probe through gel into the body .
The probe then collects the sound waves that are Reflectd
back (bounced back from the body organs & body)
•
these reflected back sound waves are analysed by the machine computer
to creat an US image of that organ

19. •
Because images are captured in REAL TIME they can
show the structure & movement of the body's
internal organs.
they can also show blood flowing through blood
vessels.
•
Major goals that indicate perform CAROTID
DOPPLER US
1. screen pts for carotid stenosis
2. HBP

20. 3. carotid Bruit ( brU-E)
in preparation for Coronary artery bypass surgery
4. DM
5. high cholesterol
6. family history of heart disease or stroke
•
7. to locate hematoma (a collection of clotted blood that may
•
slow & eventually stop blood flow)

21. 8. check the state of coronary artery after surgery to restore
blood flow
9. to verify position of a metal stent placed to maintain
carotid blood flow
10. clots or tumors
11. congenital vascular malformations
12. Reduced blood flow to organs such as testes and ovaries
13. Increased blood flow
14. detect abnoalities in lymph nodes & vessels

22. •
A Doppler ultrasound is a noninvasive test that can be used to
estimate the blood flow through your blood vessels by
bouncing high-frequency US waves off circulating
red blood cells. A regular US uses sound waves to produce
.images, but can't show blood flow
•
Doppler ultrasonography is medical ultrasonography that
employs the Doppler effect to generate imaging of the
movement of tissues and body fluids, and their relative
velocity to the probe.
•

23. •
Doppler Ultrasound types
•
1- COLOR Doppler imaging (CDI) OR COLOR FLOW DOPPLER
(CFD): This type of uses a computer to change sound waves into
different colors. ...
•
2- POWER Doppler (PD), a newer type of color Doppler. It can
provide more detail of blood flow than standard color Doppler
•
3- SPECTRAL Doppler
•
4- DUPLEX Doppler.
•
5- CONTINUOUS WAVE Doppler
(CWD)

24. •
CFD simultaneously interrogates multiple sample volumes
(with each pixel representing a sample volume) along an array
of scan lines
•
Information regarding the flow velocity and direction is
arbitrarily colour-coded and rendered onto a grey-scale (or M-
mode) image.
•
Flow that travels away from the TXR (negative Doppler shift) is
depicted in blue, and flow that is travelling toward the TXR
(positive Doppler shift) is depicted in red, with lighter shades
of each colour denoting higher velocities.
•
.

25. •
Colour flow Doppler (CFD) is used frequently in US to
semiquantitate overall blood flow to a region of interest.
•
Depiction of the general velocity and direction of blood flow
within the heart and blood vessels is of primary importance
in echocardiography and vascular ultrasound respectively.
•
It also allows the generation of unique phenomena such as
the fluid colour sign or the twinkling artifact and allows the
targeting of spectral Doppler for a quantitative assessment of
blood flow
•
Image slide (26/28/29/30/31)

26. . Image with color Doppler flow of the aorta (sagittal direction).

27. •
Color Doppler {COLOR FLOW DOPPLER} (CFD)
•
Color Doppler characterizes the flow.
•
There is a moving target and a stationary TXR.
•
When the transducer is positioned on a blood vessel the red
cells are moving.
•
They cause a change in the returning echoes.
•
If the cells are moving towards the transducer it is perceived
as a higher frequency and is displayed in red
•
Image slide (28/29/30/31)
•

29. Long axis color flow Doppler

31. Ultrasonic colour Doppler imaging

32. . Image without color Doppler flow of the aorta (sagittal direction).

33. •
If it is moving away form the transducer it is a lower
frequency and is displayed as blue.
•
So depending how the TXR is angled on the blood
vessel the color could be blue or red.
•
This color Doppler detection is worst when the
transducer is placed 90 degrees to the blood vessel.
•

34. •
Color Flow Doppler (CFD)
•
Instead of just looking at velocities at a single location (with
•
pulsed Doppler) or along a single cursor line (with CW
•
Doppler.) Color Doppler is ‘2-D doppler’ where velocities
•
are coded into colors and superimposed on a 2-D image.
•
@ black-and-white identifies anatomic structures
•
@ color identifies blood flow velocities and function
•
Image slide (35)

36. •
Color Doppler is pulsed US technique & is subject to:
•
1- range resolution 2- and aliasing
•
Color Doppler provides information regarding direction of
•
flow. It is semi-quantitative, so knowledge of angle is not
•
especially important.
•
The range spatial resolution(RSR) is an important factor
determining the image quality in US imaging. The RSR in US
imaging depends on the ultrasonic pulse length, which is
determined by the mechanical response of the PZT element in
an ultrasonic probe

37. •
Color Doppler
•
Blood stream patterns may be evaluated using echo
•
Doppler.
•
One of the applications of echo Doppler is color Doppler. This
technique can be used to evaluate the presence of flow and
flow direction in a blood vessel.
Sound reflections of a moving object undergo frequency
changes.
•
During the examination ,the difference between the emitted
and received frequencies is measured (the frequency
shift/Doppler shift)

38. •
POWER DOPPLER=COLOR POWER DOPPLER (CPD)=ENERGY
DOPPLER=AMPLITUDE DOPPLER=DOPPLER
ANGIOGRAPHY
•
Is an US technique that is used to obtain images that are
•
@ difficult or impossible to obtain using standard color Doppler @
and to provide greater detail of blood flow, especially in vessels that
are located inside organs.
•
SO DOPPLER PACKETS are used : see slides (40/41/42/43) :
•
Color Doppler where the amplitude is measured rather than
•
direction and velocity. Also energy mode, color angio.
•
Color flow measures mean velocity.
•

39. Color doppler (LEFT image)/ power doppler (RIGHT image)

40. Color doppler for comparison with power doppler next slide

41. Hepatic veins power doppler

42. Color doppler VS power doppler

43. •
Advantages of using doppler packets in CPD :
•
1. Increased sensitivity to low flows, e.g.: ASD flow
•
2. Not affected by Doppler angles, unless the angle = 90°
•
3. No aliasing (remember, we ignore velocity information!)
•
Limitations :
•
1. No measurement of velocity or direction
•
2. Lower frame rates (FR), reduced temporal resolution (TR)
•
3. Susceptible to motion & flash artifact.

44. •
An echo returning after striking mass of moving blood cells is
•
a complex signal with many Doppler shifted frequencies.
•
Spectral analysis is performed to extract the individual
•
component frequencies of the complex signal.
•
Current methods :
•
For CFD - autocorrelation or correlation function
•
Autocorrelation is used with CD because of the
•
enormous amount of Doppler information that requires
•
processing. Autocorrelation is slightly less accurate, but
•
substantiallyfaster,thanFFT(FastFourierTransform)
.

45. •
Imaging vs Doppler : image slide (87)
•
Imaging : 1- normal incidence (90°). 2- higher frequencies
•
3- pulsed wave only. 4- at least one crystal
•
Doppler:1-0°or180°incidence(oblique)2-lowerfrequencies
3- pulsed or continuous wave.
•
4- one (pulsed) or two (CW) crystals.
•
Aliasing is an issue with Doppler, not with imaging
•
ASD flow is best visualized with low PRF and high freqency
•
transducers. Low velocities require increased sensitivity.

47. •
Velocity mode
•
The colors present information on flow direction.
•
IF the color on our image appears on the top half of the color
•
map, blood is moving towards the TXR. The higher the position
•
on the color bar, the greater the velocity of the blood cells
•
towards the TXR. IF the color on our image appears on the lower
half of the map, blood is moving away fro the TXR
.
•
The lower the position on the color bar, the greater the blood’s
•
speed moving away from the TXR .

48. •
Variance Mode
•
Has a color map that also varies side-to-side.
•
The colors provide information on flow direction and
•
turbulence.
•
The System looks up the color based on the
•
direction of flow and then adds another color (often green
•
or yellow) to the picture if there is turbulence.

49. •
Left side —the flow laminar or parabolic, uniform and
•
smooth. Often normal flow.
•
Right side —the flow turbulent or disturbed, random and
•
chaotic. Often associated with pathology.

50. •
Doppler Packets
•
Multiple ultrasound pulses are needed to accurately
•
determine red blood cell velocities by Doppler.
•
This group is called a packet, or ensemble length.
•
More pulses in the packet has 2 advantages:
•
1. Greater accuracy of the velocity measurement
•
2. Sensitivity to low flows is also increased.

51. •
More pulses in the packet has this disadvantage:
•
1. Frame rate (FR) & temporal resolution (TR) is reduced.
•
The packet size must balance between accurate velocity
•
measurements and temporal resolution.
•
@ Spectral doppler (pulsed & CW) measures peak velocity.
•
@ Color flow (CFD)measures mean velocity.