00 1 Basics and Color Doppler For students.pdf

An ultrasound is a non-invasive imaging technique that uses high-frequency sound waves to create real-time pictures of organs, tissues, and other structures inside the body. A transducer, or probe, is placed on the skin with a gel, and it emits sound waves that bounce back as echoes. A computer converts these echoes into images called sonograms to help doctors diagnose conditions, monitor fetal development during pregnancy, and guide medical procedures.
How it works
Sound waves: A transducer sends high-frequency sound waves into the body. These waves are higher than the range of human hearing, hence the name "ultrasound".
Echoes: As the sound waves travel through the body, they bounce off different tissues and organs, creating echoes.
Image creation: The transducer collects these echoes, and a computer uses the speed and time of the echoes' return to calculate the distance from the transducer to the tissue boundary. This data is used to generate a two-dimensional image of the internal structures on a screen.
No radiation: Unlike X-rays, ultrasound does not use ionizing radiation, making it a safe imaging method.
Common uses
Pregnancy: To monitor a baby's growth and development, check for birth defects, and assess the placenta.
Soft tissues: To examine soft tissues, organs, and blood vessels, making it ideal for diagnosing problems with the abdomen, heart, and other organs.
Medical guidance: To guide medical procedures, such as biopsies, to ensure accuracy.
Vascular health: A special type called Doppler ultrasound can be used to evaluate blood flow through arteries and veins, helping to identify issues like blood clots or narrowed arteries. Common uses
Pregnancy: To monitor a baby's growth and development, check for birth defects, and assess the placenta.
Soft tissues: To examine soft tissues, organs, and blood vessels, making it ideal for diagnosing problems with the abdomen, heart, and other organs.
Medical guidance: To guide medical procedures, such as biopsies, to ensure accuracy.
Vascular health: A special type called Doppler ultrasound can be used to evaluate blood flow through arteries and veins, helping to identify issues like blood clots or narrowed arteries.
Types of ultrasound images
B-mode (Brightness mode): Creates a standard black-and-white image based on the strength of the returning echoes.
Doppler modes: Can show the movement of blood or tissues. Color Doppler shows the direction and speed of blood flow with color overlays, while spectral Doppler displays it on a graph.
M-mode (Motion mode): Displays a single line of echoes over time, allowing the visualization of movement, such as the motion of the heart.
3D and 4D ultrasound: Creates three-dimensional images, with 4D showing them in motion.

1. My Lord! Open my heart, and make my task easy for me, loosen the
knot in my tongue, so that they may understand my speech.” (20:25-29)

2. Dr. Raham Bacha
Ph.D. Diagnostic Ultrasound
Associate Professor
The University of Lahore
Doppler Ultrasound

3. DOPPLER PRINCIPLES AND
INSTRUMENTATION .
➢Echo is interrogated for change in frequency in the Doppler
ultrasound.
➢In grayscale sonography there were only two types of information in
the echo the go-return time and amplitude.
➢But now there is a third information the Doppler shift. The change in
receiving and transmitted frequency is known as Doppler shift.

4. The Doppler Effect in Ultrasound
➢The phenomenon of change in frequency and wavelength
due to moving source, receiver or both of them. Whenever
the source is moving towards the receiver the resultant
frequency increases and the wavelength decreases. In contrast
when the source is mobbing away from the receiver the
resultant wave will have low frequency and high wavelength.

5. A.Receiving frequency is increased than the transmitted frequency.
B.Receiving frequency is decreased than the transmitted frequency.
C.Transmitted frequency is increased than the receiving frequency.
D.Receiving and transmitted frequencies remain the same
The phenomenon of change in frequency and wavelength due to moving source,
receiver, or both of them. What will happen with the frequency if the reflector is
moving towards the transducer?

6. The Doppler Effect in Ultrasound
Grouping of
elements for
vibration
Grouping of
elements for
vibration
Grouping of
elements for
vibration
Stationary Reflector
Reflector moving
toward the transducer
Reflector moving
Away the transducer

7. The Doppler Shift
•The difference between received frequency and
transmit frequency is called Doppler shift.
F
d= F
r - F
t

9. ➢PositiveDopplershift:If the received frequency is
greater than transmitted frequency then then the
Doppler shift is positive and it is towards the
transducer.
➢NegativeDopplershift:If the received frequency is
lesser than the transmitted frequency then the Doppler
shift is negative and it is away from the transducer.

10. •Doppler shift is the difference between receiving and transmitted
frequency therefore it should be represented in the unit of Kilo-
Hertz rather than in Mega-Hertz.
•Doppler therefore falls in audible range and can be heard through
Ultrasound machine.
For example:
•Transmitted frequency is 4 MHz and receiving frequency is 4.005
MHz so the Doppler shift is 5 KHz and it falls in audible range.

11. •Positive and negative sign doesn't effect the magnitude of the
shift but it only shows the direction of the moving reflector.
For example:
•Transmitted frequency is 4 MHz and receiving frequency is
3.005 MHz
Then the Doppler shift frequency will be
3.005-4.0= -0.005MHz is equal to -5KHz.

12. The Doppler Equation
•??????
??????=2???????????? ??????
?????????????????? θ
??????

•??????
??????

stands for Doppler shift.
•??????
??????

Stands for Transmitted frequency, If we increase transmitted frequency
Doppler shaft will increase and vice versa.
•V is the velocity of moving reflector, Velocity of the moving reflector is directly
proportional to Doppler shift.

13. •C is the speed of sound which is inversely proportional to
Doppler shift.
•Cos θ is the cosine value of the angle between flow and
incident beam. If we increase the angle it means we r going to
decrease Cos θ because Cos 0 is equal to “1” and Cos 90 is
equal to “0”.
??????
??????=2???????????? ??????
?????????????????? θ
??????

14. Effect of angle on the Doppler shift
Transducer
Transducer

15. Incident sound waves and direction of flow

16. CW and PW in Mitral valve assessment

17. •If we keep the angle at 0 and the calibrations speed of
ultrasound machine is kept constant which is 1.540mm/sec.
then the Doppler shift is directly proportional to transmitted
frequency, which is also determined by the machine. So the
Doppler shift is directly proportional to the velocity of the
moving reflector. Greater the velocity greater will be the
shift and thinner will be the sound.

18. Doppler Instrumentation

19. Overview -Color Doppler is one of the most commonly
used Doppler modalities. Color Doppler’s primary use
is to evaluate a relatively large area for the presence
and direction of blood flow.
Color Doppler

20. •The detected Doppler shifts are assigned colors
presented within a “color box” superimposed over the
grayscale image. The Doppler shifts are displayed in
color based on colors assigned to “color map”.

21. Cardinal features of Color Doppler.
•Color Bar
•Color box

22. •The most common map assigns colors that are shades
of red and blue. Positive shifts are assigned one color;
negative shifts are assigned the other. Higher
magnitude Doppler shifts are displayed in lighter
shades of the assigned color.

23. Color Box
•The color box is the region on the display within which
the Color Doppler information is displayed.
•The color box is superimposed over a region of the
grayscale image.
•The shape of the color box depends upon the type of
transducer being used.
•Rectangular: linear array transducers produce a
rectangular
Color Box of
Linear
transducer
Color box
of
convex transducer

24. Sector-type or trapezoid color box is used
in the case of Convex arrays and phased
arrays transducer.
convex transducer
Phased Array

26. Steering of Color box
•The color box of linear
transducer is steered to
right and left with the
help of a steering nob.
Left sided
steered
Color Box
of Linear
transducer
Un-steered
Right sided
steered
Color Box
of Linear
transducer

27. •For all transducers, the position and size of the color box can
be changed by the sonographer. Increasing the size of the
color box will enlarge the region that is being assessed for
Doppler shifts. However, this will have a Rectangular Color
Box with Three Directional Options detrimental effect on
frame rate (lower temporal resolution). Clinically, it is best to
use a color box that provides the best balance between color
area and frame rate. If the frame rate is too low, reducing the
width of the color box should improve the frame rate and
improve temporal resolution.

28. Color Map
•The color map is usually located at the side of
the screen. The two most common
configurations for the color map are the color
bar and the color wheel. Of these two styles,
the color bar is far more common.
•

30. •The color map determines which colors are assigned to the
detected Doppler shifts. You cannot make sense of a Color
Doppler image without referring to the color map.
• The color map has two channels: a positive channel and a
negative channel. The two channels are separated by a black bar
known as the baseline.

31. The channel above the baseline, on a the color bar is
ALWAYS the positive channel, and the channel below the
baseline is ALWAYS the negative channel.
Baseline
The black bar separates
positive and negative channels
It corresponds to no Doppler
shift
It can be adjusted to increase
or decrease one channel at the
expense of the other.

32. •The colors in the positive channel are used to map
positive Doppler shifts, and the colors in the negative
channel are used to map negative Doppler shifts. On
the color wheel map, the positive channel is usually
indicated with an “up arrow”, and the negative channel
with a “down arrow”.

33. •This is called a red/blue map. It is important to note
that in a red/blue map the positive channel can be
either red or blue to suit the sonographer’s preference.
A simple ‘INVERT’ button will switch the positive
channel from red to blue and vice versa.
•Color mapping is a post processing feature, so the
color map can be changed on the frozen image.

34. In a typical map, the shades of color
closer to the baseline are dark, and
become lighter (or change to a lighter
color) farther away from the baseline.
The end of each channel farthest
from the baseline is called the
Nyquist limit.
It is uppermost or
lowermost point on
the scale
Aliasing occurs when
the Doppler shift
exceeds the Doppler
shift

35. Color Assignment
•Positive Doppler shifts are mapped in colors from the
positive channel. Negative Doppler shifts are mapped in
colors from the negative channel. Lower magnitude shifts
are assigned shades close to the baseline, while higher
magnitude Doppler shifts are assigned shades farther from
the baseline.

36. •If a shift exceeds the
Nyquist limit, it is
mapped with a lighter
shade from the
opposite channel.
+
-
Fast flow toward the
transducer
Fast flow away the
transducer
Slow flow toward the
transducer
Slow flow away the
transducer
No flow

38. Variance Maps
•A variance map is a specialized form of color map that can
display one additional piece of information. In addition to the
two main colors used for the positive and negative channels,
the variance map displays a third color to indicate locations in
the color box from which a wide range of Doppler shifts are
being detected.

39. •The third color commonly used to display this variance is
green. You can usually recognize a variance map because it
has a green stripe down the side of both channels.
•Using a variance map, if the system detects a wide range of
Doppler shifts from a particular location it will map the
region with green rather than with red or blue.

41. •Turbulent blood flow is the most common cause for a wide
degree of variance in the detected Doppler shifts. Variance
maps are used primarily in pediatric echocardiography when
searching for the turbulent flow that can occur with small
ventricular septal defects (VSDs) or atrial septal defects
(ASDs).

42. Color Aliasing
•Aliasing is a Doppler artifact that can occur with
both Color and Pulsed Doppler displays. Aliasing
occurs when the detected Doppler shift exceeds
the upper limit that the system can accurately
detect.

43. •This upper limit is called the Nyquist limit. When a
detected Doppler shift exceeds the Nyquist it is
erroneously wrapped around and displayed in the
upper end of the opposite channel.

44. •With Color Doppler this means that the aliased
signals are mapped in the light shades of the
color from the opposite channel. For example,
increasingly high Doppler shifts in a red channel
will be displayed in lighter shades of red as the
shifts increase.

45. •If the Doppler shifts exceed the Nyquist
limit, the display will alias and the shifts that
exceed the Nyquist limit will be displayed in
light blue.

47. •It is important to distinguish color aliasing from color
flow reversal. Flow reversal is NOT an artifact. It is a
change in color from one channel to another due to the
blood flow changing direction relative to the
transducer.

48. •An example might be blood flow in a tortuous vessel that was
moving away from the transducer curving back and now
flowing towards the transducer. In this scenario, the color box
would display the dark colors from the negative channel, then
black from the baseline, then dark colors from the positive
channel. This is quite a different appearance than color
aliasing.

51. Color aliasing versus flow reversal
•Color aliasing: light shades from one channel
adjacent to light shades from the opposite channel
•Flow reversal: dark shades from one channel
adjacent to black and dark shades from the opposite
channel

55. The Most frequently used knobs of Color
Doppler are:
•Selection of transducer
•Selection of appropriate preset
•Adjustment of Output power
•Adjustment of image depth (+/- zoom)
•Adjustment of Color box angle
•Adjustment of Color box width
•Adjustment of Color gain
•Adjustment of Scale
•Knob for the inversion Scale

56. Color Doppler knobs which are not
frequently used:
•Adjustment of Wall filter
•Adjustment of Doppler frequency
•Packet size
•Echo-write priority
•Adjustment Baseline

57. Example 5:Assessing Flow Direction:
Try one more convex array. The color map tells us
that red is mapping positive shifts and blue is
mapping negative shifts. Blood must be flowing
towards the transducer at A (positive shifts) and away
from the transducer at B (negative shifts).

58. •Thus the overall direction of flow is
from A to B. Again, note the lack of
Doppler shifts in the center of the box
due to the poor Doppler angles, and the
increasing shifts towards the edges of
the box due to the improving Doppler
angles.

59. Use of Color Doppler
•Color Doppler is usually the first Doppler
modality that is applied when a
sonographer is doing a Doppler study.
When set up correctly, its primary use is to
quickly evaluate a region of interest for
evidence of blood flow.

60. •In most clinical situations, with the use of Color
Doppler the sonographer should be able to determine
the presence or absence of flow as well as the
direction of flow relative to the transducer.