This document discusses Doppler ultrasound principles and techniques. It covers topics like Doppler signal processing including transmitters, amplifiers, mixers and filters. It describes how Doppler is used to measure blood flow velocity and direction. It also discusses optimization of Doppler settings like range gate size, gain, filter and steering angle to improve flow detection and spectral waveform analysis. Color Doppler imaging principles are also covered like mapping Doppler shifts to a color map and factors affecting color box placement and pulse repetition frequency.

6. 262 Hz
311 Hz 220Hz

8. PitcherCatcher

11. fr >>>> fs

32. Transmitter
Amplifier
Mixer / Demodulator
Wall filter
fT
fT
fR
fR
fR
fT + fT
fT - fT
fT - fT

40. Transmitter
Amplifier
Mixer / Demodulator
Wall filter
fT
fT - fT
fR

42. Transmitter
Amplifier
Mixer / Demodulator
Wall filter
fT
fT - fT
fR

44. Transmitter
Amplifier
Mixer / Demodulator
Wall filter
fT
fT - fT
fR

47.  Separate crystal for
transmitting & receiving
Range ambiguity
Can measure high velocities
 Single crystal transmits & receives
 Range resolution
 Can’t measure very high velocities

52. This is the
DOPPLER
signal

53. RANGE
GATE
1-D SECTION
SPECTRAL
WINDOW

61. AXIAL
RESOLUTION
RANGE GATE
CONTROL
DOPLER
GAIN
DUPLEX
CONTROL
DOPPLER
ANGLE
CONTROL

66. AXIAL
RESOLUTION
RANGE GATE
CONTROL
DOPLER
GAIN
DUPLEX
CONTROL
DOPPLER
ANGLE
CONTROL

68. Sample
volume

71. Gate size
Decrease gate size decrease spectral broadening

72. AXIAL
RESOLUTION
RANGE GATE
CONTROL
DOPLER
GAIN
DUPLEX
CONTROL
DOPPLER
ANGLE
CONTROL

75. Optimise gain control

76. AXIAL
RESOLUTION
RANGE GATE
CONTROL
DOPLER
GAIN
DUPLEX
CONTROL
DOPPLER
ANGLE
CONTROL

79. AXIAL
RESOLUTION
RANGE GATE
CONTROL
DOPLER
GAIN
DUPLEX
CONTROL
DOPPLER
ANGLE
CONTROL

81. SPECTRA
FILL IN

86. Steering
angle

90.  To produce the color flow image, the mean
Doppler shift is encoded according to a preset
color map.
 This color information is superimposed on the
gray scale anatomic scan in real time.

94. Increasing flow velocity
away from the transducer
Zero flow
Increasing flow velocity
toward the transducer

95. Near occlusion Total occlusion

97. Color box is an operator-adjustable area
within US image in which all color Doppler
information is displayed.
Box should be as small & superficial as
possible while still providing necessary
information.
A deep color box will result in a slower PRF,
which may produce aliasing of depicted color
flow.

100. PRF = NFPRF = 2NF

104. B-mode imaging + Doppler

106. Assess the following:
1. Presence of flow
2. Direction of flow
3. Amplitude
4. Window
5. Pulsatility

107. Check for Flow
Flow
Detected
No Flow
Detected
Check
GATE Placement
Sensitive
Decreased
Sensitivity
Improve
Sensitivity
Check
Sensitivity
Check Beam-
flow angle

108. Sensitivity can be improved by:
• Increasing power or gain.
• Decreasing the velocity scale.
• Decreasing the reject or filter.
• Slowly increasing the GATE size.

109. Direction of Flow
Pulsed Doppler use quadrature phase detection to provide bidirectional Doppler
information.

110. Flow can either be:
• Mono-phasic
• Bi-phasic
• Tri-phasic
• Bidirectional

111. Frequency
Time
Mono-phasic Flow
Flow on just on side
of the Baseline.

112. Frequency
Time
Bi-phasic Flow
Flow start on one
side of the Baseline
and then crosses to
the other.

113. Frequency
Time
Tri-phasic Flow
Flow start on one side
of the baseline side,
then crosses to the
other, then returns to
the original side.

114. Time
Frequency
Bidirectional Flow
Flow which occurs
simultaneously on
both sides of the
baseline.

115. Amplitude
The spectrum displays echo amplitude by varying the
brightness of the display.
The amplitude of the echoes are determined by:
• Echo intensity
• Power
• Gain
• Dynamic range

116. Window
• Received Doppler shift consist of a range of
frequencies.
• Narrow range of frequencies will result in a
narrow display line.
• The clear area underneath the spectrum is
called the window.

117. Sonic Window
Velocity
Time
A narrow range of frequencies
results in large clear window.

118. Sonic Window
Velocity
Time
A broad range of frequencies
results in diminished window.

119. Loss of the Spectral window is called
Spectral Broadening.

125.  Power / intensity of
Doppler signal is measured
rather than Doppler shift.
Limitations :
 No direction / velocity
information
 Slow frame rate

126. Advantages :
 Increased sensitivity of flow
detection
 Less angle dependence
 No aliasing
 Noise – a homogenous
background

128. Depiction of Doppler shift
information in waveform
Utilize the Doppler shift
information to show blood flow in
color

129.  Filters eliminate
typically low-
frequency high-
intensity noise that
may arise from
vessel wall motion

132. loss of the low-velocity-flow
component of the spectral waveform
immediately above the baseline.
Higher-velocity flow is
well depicted, and accurate flow
quantification can still occur.
High filter
spectral waveform
progressively fills in toward the
baseline.
Optimal filter 50-100 Hz

133. Colour gain

134. Spectral gain

136. 45°
’
>90°

137.  Ability to manually
invert the spectral
wave or color
settings.