presentation for ultrasound machine

1. Lecture One:
Ultrasound Machine

2. History
Uses of ultrasonic energy in the 1940s. Left, in gastric ulcers. Right, in arthritis
Ultrasonic
therapy
generator, the
"Medi-Sonar" in
the 1950s.
A British
ultrasonic
apparatus for the
treatment of
Meniere's disease
in the late 1950s

3. History
Denier's Ultrasonoscopic apparatus
with ultrasound generator, emitter
transducer and oscilloscope. This
can be adapted for both therapeutic
and diagnostic purposes
The first hand-held imaging instrument
was developed by John Wild and John
Reid in the early 1950's

4. Physics of Ultrasound
Sound
• Mechanical &
Longitudinal wave
• Travels in a straight Line
• Human ear range is 20Hz
- 20kHz
• Cannot travel through
Vacuum
Ultrasound
• Mechanical & Longitudinal
wave
• Exceeding the upper limit
of human hearing
• > 20,000H or 20kHz.
4

5. Characteristics of Ultrasounds
• Velocity
• Frequency
• Wavelength
• Amplitude
• The Relationship b/w v, f and λ
is:
v = f λ
• Average speed of ultrasound in
body is 1540m/sec
• Imaging range is 2 to 20MHz
5

6. Power and Intensity
• A sound wave transports Energy through a medium from a source. Energy is
measured in joules (J)
• The Power, P,produce by a source of sound is the rate at which it produces energy.
Power is measured in watts (W) where 1 W = 1 J/s
• The Intensity, I, associated with a sound wave is the power per unit area. Intensity is
measured in W/m2
• The power and intensity associated with a wave increase with the pressure amplitude,
p
Intensity, I  p2
Power, P  p

7. Wavelength, Frequency and Speed
• Waves are characterised by their
wavelength, frequency and speed
• The Wavelength,  , is the distance
between consecutive peaks or other
similar points on the wave.
• The Frequency, f, is the number of
oscillations per second
• Frequency is measured in Hertz (Hz)
where 1 Hz is one oscillation per second.

8. Characteristics of Ultrasounds
Velocity
8

9. Advanatges
• Real-time
• Portable
• No ionizing radiation
• Inexpensive?
• Side-side comparison
• Patients love it!
• Guide procedures

10. Disadvanatges
• Operator dependent
• Expensive?
• Limited penetration through bone and air
• Imaging deep structures

11. Ultrasound machine

12. Basic Ultrasound Physics
Amplitude
oscillations/sec = frequency - expressed in Hertz (Hz)

13. Bats: Navigating with ultrasound
• Bats make high-pitched chirps which are too high for
humans to hear. This is called ultrasound
• Like normal sound, ultrasound echoes off objects
• The bat hears the echoes and works out what caused
them
• Dolphins also navigate with ultrasound
• Submarines use a similar method called sonar
• We can also use ultrasound to look inside the body…

14. • An ultrasound element acts like a bat.
• Emit ultrasound and detect echoes
• Map out boundary of object
• Medical Ultrasound 2MHz to 16MHz

15. • Electric field applied to
piezoelectric crystals located
on transducer surface
• Mechanical vibration of
crystals creates sound waves
Each crystal produces an US
wave
• Summation of all waves
forms the US beam
• Wave reflects as echo that
vibrates transducer
• Vibrations produce electrical
pulses
• Scanner processes and
transforms to image

16. Ultrasound Production
• Transducer produces ultrasound pulses
• These elements convert electrical energy into a
mechanical ultrasound wave
• Reflected echoes return to the scan head which
converts the ultrasound wave into an electrical signal

17. Frequency vs. Resolution
• The frequency also affects the QUALITY of the ultrasound image
– The HIGHER the frequency, the BETTER the resolution
• The LOWER the frequency, the LESS the resolution
• A 12 MHz transducer has very good resolution, but cannot
penetrate very deep into the body
• A 3 MHz transducer can penetrate deep into the body, but the
resolution is not as good as the 12 MHz

18. Image Formation
Electrical signal produces ‘dots’ on the screen
• Brightness of the dots is proportional to the
strength of the returning echoes
• Location of the dots is determined by travel
time. The velocity in tissue is assumed constant
at 1540m/sec
Distance = Velocity
Time

19. 16

20. 17

21. 18

22. Activity 1
• If an echo is detected from a reflector in human soft tissuein 0.065 ms
. How far is the reflector from the transducer.

23. • Acoustic impedance (AI) is dependent on the density of
the material in which sound is propagated
- the greater the impedance the denser the material.
• Reflections comes from the interface of different AI’s
• greater  of the AI = more signal reflected
• works both ways (send and receive directions)
Medium 1 Medium 2 Medium 3
Transducer
Interactions of Ultrasound with
Tissue

24. Interactions of Ultrasound with
Tissue
• Reflection
• Refraction
• Transmission
• Attenuation

25. Interactions of Ultrasound with Tissue
• Reflection
– The ultrasound reflects off tissue and returns to
the transducer, the amount of reflection depends on
differences in acoustic impedance
– The ultrasound image is formed from reflected echoes
transducer

26. Reflection
• Reflection (specular reflection) occurs at
tissue boundaries where there is a difference
in the acoustic impedance, Z, of the two
tissues
• When the incident ultrasound wave is
perpendicular to the boundary, a fraction of
it’s energy is reflected (an echo) directly
back towards the source
• The remaining energy is transmitted into the
second tissue and continues in the initial
direction
Z1
Z2
Incident
Reflectio
n (echo)
Transmission

27. 31

28. Reflection
• The fraction of ultrasound intensity reflected
at an interface is given by the intensity
reflection coefficient, R
• The fraction of ultrasound energy reflected
depends on the difference between the Z
values of the two materials
• R increases rapidly as the difference in Z
increases
Z1
Z2
Ii
Ir
It
R =
Z2 –Z1
Z1 +Z2
i
Ir
I
= ( )
2

29. Reflection
• The fraction of ultrasound intensity
transmitted at an interface is given by the
intensity transmission coefficient, T
• Ultrasound imaging is only possible when
the wave propagates through materials with
similar acoustic impedances – only a small
fraction of energy is reflected and the rest is
transmitted
Z1
Z2
Ii
Ir
It
T =
It
Ii
= 1 - R

30. Reflection
TissueInterface R T
Liver – Fat 0.01 0.99
Fat– Muscle 0.02 0.98
Muscle - Bone 0.41 0.59
Muscle -Air 0.99 0.01
At soft tissue – soft tissue
interfaces 1-2% of the
ultrasound intensity is
reflected
At soft tissue – air
interfaces 99% of the
incident intensity is
reflected
• At soft tissue – air or soft tissue – bone interfaces, a large proportion of the
incident intensity is reflected, making anatomy beyond such interfaces
unobservable
• Acoustic coupling gel is used between the face of the ultrasound transducer
and skin to eliminate air pockets

31. Reflection
• When the wave is not incident perpendicular
to the interface, non-normal incidence, the
reflected angle is equal to the incident angle
(i.e. θr = θi)
• Echoes are directed away from the source of
ultrasound and may be undetected
• The transmitted wave does not continue in the
incident direction (i.e. θt ≠ θi)
• The change in direction is described by
Refraction
Z1
Z2
Incident Reflection
(echo)
Transmission
(refraction)
θi θr
θt

32. Activity
2
Approximately what fraction of an ultrasound beam is transmitted from an
interface between two media with Z values of 1.65 and 1.55?
41

33. ACTIVITY 3
Calculate the remaining intensity of a 100 W/m^2 ultrasound pulse that
loses 30 dB while traveling through tissue?
56

34. 57

35. Activity 4
•

36. 59

38. Transmission
– Some of the ultrasound waves continue deeper into
the body
– These waves will reflect from deeper tissue
structures
transducer
Interactions of Ultrasound with Tissue

39. Attenuation
– Defined - the deeper the wave travels in the
body, the weaker it becomes -3 processes:
reflection, absorption, refraction
– Air (lung)> bone > muscle > soft tissue >blood >
water
Interactions of Ultrasound with Tissue

40. Reflected Echo’s
• Strong Reflections = White dots
Diaphragm, tendons, bone
‘Hyperechoic’

41. Weaker Reflections =
Grey dots
– Most solid organs,
– thick fluid – ‘isoechoic’
Reflected Echo’s

42. Reflected Echo’s
• No Reflections = Black dots
– Fluid within a cyst, urine, blood
‘Hypoechoic’ or echofree

43. What determines how far ultrasound waves can
travel?
• The FREQUENCY of the transducer
– The HIGHER the frequency, the LESS it can
penetrate
– The LOWER the frequency, the DEEPER it can
penetrate
– Attenuation is directly related to frequency

44. 7.5 MHz
3.5 MHz
Thinner crystal produces
smaller sound waves.
The Transducer
Thicker crystal
produces bigger sound
waves.

45. The Transducer
The LOWER the
frequency the better
the penetration
Bigger, Stronger
The HIGHER frequency
the less the penetration
Smaller, weaker
3.5 MHz 7.5 MHz

46. The Transducer
Short pulses of sound are sent (transmits) into the body
and then the transducer listens for the returning signals
(receives).
The ultrasound system processes the returning signals
into images that are displayed on the ultrasound monitor
Transmits
Waits
Receives

47. The strength of the returning echoes also
depends on the differences in the acoustic
impedance between various structures.
Acoustic impedance relates to tissue density.
The greater the difference in density between
two structures, the stronger the returning echo
Examples:
different: aorta and liver
same: kidney and liver
Grayscale Imaging

48. • Attenuation:
A decrease in the strength of the sound wave as it
passes through tissue and further into the body.
• Acoustic Impedance:
The resistance of the sound wave traveling through
tissue .Each tissue has its own acoustic impedance
due to the density of the tissue.
• Through Transmission:
There is no attenuation of the sound wave traveling
through the tissue.
Grayscale Imaging

49. WHITE DOTS = STRONG = e.g., bone
BLACK DOTS = NO reflections = e.g., fluid
GRAY (different shades) = WEAKER
reflections
Grayscale Imaging

50. The strength of the returning echo is
directly related to the angle at which the
ultrasound beam strikes an interface.
Grayscale Imaging
The more perpendicular the
ultrasound beam, the stronger the
returning echo.

51. Resolution
• Clarity of picture
• The ability to identify structures very close
together./
• Ability of equipment to detect
2 separate reflectors in tissue and to display
them as 2 separate reflectors on the monitor
without merging them.

52. Image Resolution
Types of Resolution
Axial Ability to identify structures that are one in
front of the other
Lateral Ability to identify structures that are side by
side
Temporal Ability to accurately locate a moving structure
Spatial Ability to display very small structures in their
correct anatomic location.

53. Next class
• Principles of A-Mode, B-Mode, M-Mode
• Application area of ultrasound
• parts of ultrasound machineineParts of
Ultrasound Machine

54. Summary of previous class
• SOUND to IMAGE
• producing a sound wave,
• receiving echoes, and
• interpreting those echoes

55. A-mode
• A-mode (amplitude mode) is the simplest type
of ultrasound.
• A single transducer scans a line through the
body with the echoes plotted on screen as a
function of depth.
• One use of the A scan is to measure length. For
an example, ophthalmologists can use it to
measure the diameter of the eye ball.

56. B-mode or 2D mode
• B-mode (brightness mode) ultrasound: a linear
array of transducers simultaneously scans a
plane through the body that can be viewed as a
two-dimensional image on screen.
• B-flow is a mode that digitally highlights moving
reflectors (mainly red blood cells) while
suppressing the signals from the surrounding
stationary tissue.
• It can visualize flowing blood and surrounding
stationary tissues simultaneously

57. M-mode
• In M-mode (motion mode) ultrasound, pulses are
emitted in quick succession – each time, either an A-
mode or B-mode image is taken. Over time, this is
analogous to recording a video in ultrasound. As the
organ boundaries that produce reflections move
relative to the probe, this can be used to determine
the velocity of specific organ structures.
• Used to study rhythmically moving structures

58. Application
• In the field of obstetrics and gynecology, where
ionizing radiation is to be avoided whenever possible.
• To evaluate fetal size and maturity and fetal
and placental position.
• It is a fast, relatively safe, and reliable techni
que for diagnosing multiple pregnancies. Uteri
ne tumors and other pelvic
masses, including abscesses, can be identified
by ultrasonography.

59. 3.5MHz
7.5 MHz
Axial Resolution
The shorter the pulse,
the better the axial
resolution
Increasing the
frequency increases
axial resolution

60. Characteristics of Sound
Frequency
Sound
Frequency
Sound
Penetration
Axial
Resolution
High
Low

61. A transducer
with a large
surface area
will resolve
better in the
lateral
dimension
• Very important for ultrasound guidance with
needles/probes
Lateral Resolution

62. Parts of Ultrasound Machine
Transducer
Probe
Pulse
control
CPU
(Central
Processing
Unit)
Key Board Display
Storage
device
Printer
62

63. Parts of Ultrasound Machine
63

64. Components/ parts of Ultrasound machine

65. • Transducer probe - probe that sends and receives the sound waves
• Central processing unit (CPU) - computer that does all of the
calculations and contains the electrical power supplies for itself and
the transducer probe
• Transducer pulse controls - changes the amplitude, frequency and
duration of the pulses emitted from the transducer probe
• Display - displays the image from the ultrasound data processed by
the CPU
• Keyboard/cursor - inputs data and takes measurements from the
display
• Disk storage device (hard, floppy, CD) - stores the acquired images
• Printer - prints the image from the displayed data

66. Transducer
Transducer Probe
• Mouth and ears of the machine.
• It makes the sound waves and receives the echoes
• Piezoelectric crystals
• Electric current is applied and change shape rapidly
• When sound waves hit the crystals, they emit electrical
currents
66

67. Transducer
Transducer (pulse controls)
• The operator, called the ultra sonographer, changes the
amplitude, frequency and duration of the pulses
emitted from the transducer probe
67

68. Types of Ultrasound Transducer
68

69. Central Processing Unit (CPU)
• Brain of an ultrasound machine
• Contains the microprocessor, memory and amplifiers
• The transducer receives electrical currents from the CPU
and sends electrical pulses that are created by returning
echoes
69

70. Keyboard/Cursor
It allows the operator to add notes and to take measurements
of the image
70

71. Display
• Displays the image from the ultrasound data processed by
the CPU
• This image can be either in black-and-white or color,
depending upon the model of the ultrasound machine
71

72. How is an image formed on the monitor?
• Strong Reflections = White dots
Pericardium, calcified structures, diaphragm
• Weaker Reflections = Grey dots
Myocardium, valve tissue, vessel walls, liver
• No Reflections = Black dots
Intra-cardiac cavities, gall bladder
72

73. Disk Storage & Printers
The processed data and images can be stored on disks
• Hard disks, floppy disks, compact disks (CDs), or digital
video disks (DVDs)
• Most of the time, ultrasound scans are filled on floppy disks
and stored with the patient's medical records
• Most ultrasound machines have printers which are thermal
73

74. Block Diagram
74

75. Main Parts of Block Diagram
• User interface
• Controller
• Front End
•Scanner(beamforming and signal processing)
•Back End
75

76. User interface
• Desired mode of operation
• Information in and out of the system through connectors to the system
• VCRs & memory storage devices such as read/write CD-ROMs and DAT
drives
76

77. Controller
• System have one or more microprocessors
• Senses the settings of the controls and input devices
• Control the hardware to function in the desired mode.
• Estimate the level of acoustic output in real time
77

78. Front End
• This grouping within the scanner is the gateway of signals
going in and out of the selected transducer
• Pulses are sent to the transducer from the transmitter
circuitry
• Pulse-echo signals from the body are received by array
elements These signals then pass on to the receive beam
former.
78

79. Front End
• Organizing the many signals of the elements
• The transmit beamformer sends pulses to the elements
• Analog to Digital Converter
• Filters
79

80. Scanner(beamforming and signal processing)
• This grouping of functions is associated with image
formation, display and image metrics
• Image formation is achieved by organizing the lines and
putting them through a digital scan converter that
transforms them into a scan format for display on a video or
PC monitor.
• Image overlays containing alpha-numeric characters and
other information are added in image planes
80

81. 30-Nov-18 Medical imaging modalities 60

83. Ultrasoun
d
Transducer

84. Ultrasound Transducer
Major components of transducers include:
the piezoelectric material
matching layer
backing block
acoustic absorber
insulating cover
Sensor electrodes and
transducer housing

86. piezoelectric
material
• A piezoelectric material (often a crystal or ceramic) is the
functional component of the transducer.
• It converts electrical energy into mechanical (sound) energy
by
• physical deformation of the crystal structure.
• Conversely, mechanical pressure applied to its surface creates
electrical energy.
• Piezoelectric materials are characterized by: a well-defined
molecular arrangement of electrical dipoles

87. Cont’d…
• An electrical dipole is a molecular entity containing
• positive and negative electric charges that has no net charge.
• When mechanically compressed by an externally applied
pressure,
• the alignment of the dipoles is disturbed from the equilibrium position to
cause an imbalance of the charge distribution.
• A potential difference (voltage) is created across the element
• with one surface maintaining a net positive charge and one surface a net
negative charge.
• Surface electrodes measure the voltage,
• which is proportional to the incident mechanical pressure amplitude.
• Conversely, application of an external voltage through
conductors attached to the surface electrodes induces
• the mechanical expansion and contraction of the transducer element

88. Piezo-electric
materials

96. Cont’d
…
• There are natural and synthetic piezoelectric materials.
• An example of a natural piezoelectric material is quartz crystal
• Ultrasound transducers for medical imaging applications employ:
• a synthetic piezoelectric ceramic, most often lead-zirconate-titanate (PZT).

97. 30-Nov-18 Medical imaging modalities 78

98. Cont’d ….
• The thickness of layer is equal to one-fourth the wavelength of center
operating frequency
• determined from the center operating frequency of the transducer and speed of
sound in the matching layer.
• In addition to the matching layers, acoustic coupling gel (with acoustic
impedance similar to soft tissue)
• is used between the transducer and the skin of the patient
• to eliminate air pockets that could attenuate and reflect the ultrasoundbeam.

99. Activity 5
What is the optimal thickness of the matching layer used for PZT
transducer of 1 milli- meter thickness (assume the speed of sound in PZT
is 4000 m/s)?

100. Image Data
Acquisition
• Images are created using a pulse echo method of ultrasound production
and detection.
• Each pulse transmits directionally into the patient, and then experiences
partial reflections from tissue interfaces
• that create echoes, which return to the transducer.

101. Cont’d ….
Image formation using the pulse echo approach requires a number of
hardware components:
the beam former,
pulser,
receiver,
amplifier,
scan converter/image memory, and
display system

105. The transmit/receive
switch
The transmit/receive switch, synchronized with the pulser,
isolates the high voltage used for pulsing (~150 V) from the
sensitive amplification stages during receive mode with
induced voltages ranging from ~1 V to ~2 ~V from the
returning echoes.
After the ring-down time, when vibration of the piezoelectric
material has stopped, the transducer electronics are switched to
sensing small voltages caused by the returning echoes, over a
period up to about 1000 micro sec (1milli sec).

106. 91

107. 92

108. 93

109. 94

110. 95

111. 96

112. Basic Principals of Image Formation

113. Pulse Echo Principal
• A short ultrasound pulse is delivered to the tissues, and where there are changes in the
acoustic properties of the tissue, a fraction of the pulse is reflected (an echo) and
returns to the source (pulse-echo principal)
• Collection of the echoes and analysis of their amplitudes provides information about
the tissues along the path of travel
Tissue 1 Tissue 2 Tissue 3
Transducer
US Pulse
Reflected Echoes

114. Pulse Echo Principal
Tissue 1 Tissue 2 Tissue 3
Transducer
US Pulse
Reflected Echoes
The ultrasound pulse will travel at the speed of sound and the time between the pulse
emission and echo return will be known.
Therefore, the depth, d, at which the echo was generated can be determined and
spatially encoded in the depth direction.
Distance (D) = speed (c) x time (t)  2d = c t

115. Tomographic Imaging
Repeating this process many times with incremental changes in pulse direction allow
a volume to be sampled and a tomographic image to be formed.
i.e. A tomographic image is formed from a large number of image lines, where each
line in the image is produced by a pulse echo sequence
Transducer

116. 101
Modes of
ultrasound

117. 102

118. B-Mode Image
 A B-mode image is a cross-sectional image representing tissues and organ
boundaries within the body
 Constructed from echoes which are generated by reflection of US waves at tissue
boundaries, and scattering from small irregularities within tissues
 Each echo is displayed at a point in the image which corresponds to the relative
position of its origin within the body
 The brightness of the image at each point is related to the strength (amplitude) of
the echo
 B-mode = Brightness mode

119. B-Mode Image – How Long Does it Take?
1. Minimum time for one line = (2 x depth) / speed of sound = 2D / c seconds
2. Each frame of image contains N lines
3. Time for one frame = 2ND / c seconds
E.g. D = 12 cm, c = 1540 m/s, Frame rate = 20 frames per second
Frame rate = c / 2ND
N = c / (2D x Frame rate) = 320 lines (poor - approx half of standard TV)
Additional interpolated lines are inserted between image lines to boost image quality to
the human eye
4. Time is very important!!!

120. Time Gain Compensation (TGC)
• The deeper the source of echo Smaller signal intensity
• Due signal attenuation in tissue and reduction of the initial US beam intensity by
reflections
• Operator can TGC use to artificially ‘boost’ the signals from deeper tissues to
compensate for this (like a graphic equaliser)

121. M-Mode Image
• Can be used to observe the motion of tissues (e.g.Echocardiography)
• Image the same position (one image line) repeatly.
• One direction of display is used to represent time rather thanspace
Transducer at fixed point Time
Depth

122. More on ultrasound
Mod
es
• A-mode: A-mode (amplitude mode) is the simplest type of
ultrasound. A single transducer scans a line through the body with
the echoes plotted on screen as a function of depth. Therapeutic
ultrasound aimed at a specific tumor or calculus is also A-mode,
to allow for pinpoint accurate focus of the destructive wave
energy.
• B-mode or 2D mode: In B-mode (brightness mode) ultrasound, a
linear array of transducers simultaneously scans a plane through
the body that can be viewed as a two-dimensional image on screen.
More commonly known as 2D mode now.
• M-mode: In M-mode (motion mode) ultrasound, pulses are
emitted in quick succession – each time, either an A-mode or B-
mode image is taken. Over time, this is analogous to recording a
video in ultrasound. As the organ boundaries that produce
reflections move relative to the probe, this can be used to
determine the velocity of specific organ structures.

123. More on Imaging
Modes
• Doppler mode: This mode makes use of the Doppler effect in
measuring and visualizing blood flow
• Color Doppler: Velocity information is presented as a color coded overlay on
top of a B-mode image
• Continuous Doppler: Doppler information is sampled along a line through
the body, and all velocities detected at each time point is presented (on a time
line)
• Pulsed wave (PW) Doppler: Doppler information is sampled from only a
small sample volume (defined in 2D image), and presented on a timeline
• Duplex: a common name for the simultaneous presentation of 2D and
(usually) PW Doppler information. (Using modern ultrasound machines
color Doppler is almost always also used, hence the alternative name
Triplex.)
• Harmonic mode: In this mode a deep penetrating fundamental frequency is
emitted into the body and a harmonic overtone is detected. In this way depth
penetration can be gained with improved lateral resolution.

124. Ultrasound maintenance
Lab activity???
109

125. The end …..
Any ?