Basics of Echocardiography

1. BACK TO BASICS
Phase
Frequency
Amplitude
Wavelength

2. Sound
▪ Mechanical vibration transmitted through an elastic medium
▪ Pressure waves when propagate through air at appropriate frequency
produce sensation of hearing
Vibration Propagation

3. As sound propagates through a medium
the particles of the medium vibrate
Air at equilibrium, in the
absence of a sound wave
Compressions and rarefactions
that constitute a sound wave

4. ULTRASOUND
▪ Ultrasound is sound with a frequency over 20,000 Hz, which is the
upper limit of human hearing.
▪ The basic principles and properties are same as that of audible sound
▪ Frequencies used for diagnostic ultrasound are between 2 to 20 MHz

5. COMPONENTS OF AWAVE
Phase
Frequency
Amplitude
Wavelength

6. Sine wave:
▪ Amplitude - maximal
compression of particles
above the baseline
▪ Wavelength - distance
between the two nearest
points of equal pressure
and density
One Compression and rarefaction constitute one sound wave . It can be
represented as “Sine wave”.
wavelength = speed/frequency

7. Amplitude
• Defines the Brightness of the image
Irrespective of the Freq the Amp remains
constant
The Higher the Amp the brighter the image
and the lower the more darker the images
Returning Waves

8. FREQUENCY:
▪ Number of cycles per second
▪ Units are Hertz
▪ Ultrasound imaging frequency range 2-20Mhz

9. Wave Length and Frequency:

10. Velocity = Distance/Time
( 100 meters in 9.81 sec)

11. Velocity:
▪ Speed at which a sound wave travels through a medium(cm/sec)
▪ Average speed of ultrasound in body is 1540 m/sec
Phase
Frequency
Amplitude
Wavelength
velocity = frequency x wavelength
• Dependent on physical properties of the medium through which it travels
• Directly proportional to stiffness of the material
• Inversely proportional to density within a physiological limit

12. Rule Of Thumb:
▪ Stiffness and Speed ---- Same Direction
▪ Density and Speed ---- Opposite Direction
▪ Stiffness is related to change in shape – squishability
▪ Density is related to Weight

13. Sound velocity in different materials
Material Velocity ( m/s)
Air 330
Water 1497
Metal 3000 - 6000
Fat 1440
Blood 1570
Soft tissue 1540

14. Pulsed Ultrasound
▪ In diagnostic imaging short pulses of acoustic energy are used to
create anatomic images.
▪ Continuous wave sound can not create images. CW is used for
Doppler
▪ Two component of Pulsed Ultrasound:
– The cycles (Transmit time)
– Dead time (Receive time)

15. 5 Parameters Of Pulsed Sound
▪ Pulse Duration
▪ Spatial Pulse Length
▪ Pulse repetition Period
▪ PRF
▪ Duty Factor

16. Pulse Duration
▪ The time from the start of pulse to end of pulse
▪ Transmit time
▪ Can not be changed by sonographer
▪ In clinical imaging its 2-4 cycles

17. Spatial Pulse Length
▪ The distance from start to the end of one pulse.
▪ Can not be changed by sonographer
▪ Determines Axial Resolution
Spatial pulse length
Time
Distance

18. Pulse Repetition Period
▪ Time from the start of one pulse to the start of next pulse
▪ Includes one pulse and one Listening time
▪ Sonographer can change PRP (listening time only and not pulse duration of period)
Time
Distance Spatial pulse length

19. Pulse Repetition Period
• No change in pulse (only listening
time) while changing depth
PRP
PRP

20. Pulse Repetition Frequency (PRF)
▪ Number of Pulses created by system in one second.
▪ Not related to Frequency
▪ Determined by depth
– Shallow image -- High PRF
– Deep Image – Low PRF

21. PRP and PRF (Inverse Relation)
Depth
PRP
PRF
PRP
PRP
PRF
PRF

22. 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

23. Frequency, Penetration & Resolution
Higher the frequency Lower the penetration and Higher the
resolution
Low the frequency higher the penetration and lower the
resolution

24. The Trade Off
▪ The trade-off between tissue resolution and penetration
▪ 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

26. How Is Ultrasound Imaging Done?

27. Pierre Curie (1859-1906),
Nobel Prize in Physics, 1903
Jacques Curie (1856-1941)
PIEZOELECTRIC EFFECT

28. Piezoelectric Effect
Vibration

29. Piezoelectric effect results in Compression
& Rarefaction:

30. Damping Material is used to “ring down” the
Pulse Length & Bandwidth which results in
improved resolution

31. INTERACTIONS OF ULTRASOUND WITH TISSUE
▪ Reflection
▪ Transmission
▪ Attenuation
▪ Scattering

32. Reflection
– Occurs at a boundary between 2 adjacent tissues or media
– The amount of reflection depends on differences in
acoustic impedance (z) between media
– The ultrasound image is formed from reflected echoes
Transducer
Z = Density xVelocity

33. Angle of Incidence
Reflection from a tissue interface at
right angle. There is
stronger reflection resulting in brighter
echo.
Reflection at an angle equal to
the angle of incidence
producing less bright echo.

34. Reflected Echoes
▪ 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

35. ▪ Not all the sound wave is reflected, some continues
deeper into the body
▪ These waves will reflect from deeper tissue
structures
Transducer
Transmission

36. ▪ The deeper the wave travels in the body, the
weaker it becomes
▪ The amplitude of the wave decreases with
increasing depth
Attenuation
 Higher frequency ,
more attenuation
 Longer the distance
(Depth), more the
attenuation

37. Scattering
▪ Redirection of sound in several directions
▪ Caused by interaction with small reflector or rough surface
▪ Only portion of sound wave returns to transducer

38. ▪ The resistance that a material offers to the passage of sound wave
▪ Velocity of propagation “v” varies between different tissues
▪ Tissues also have differing densities “ρ”
▪ Acoustic impedance
“Z = ρv”
▪ Soft tissue / bone and soft tissue / air interfaces have large “Acoustic
Impedance mismatch”
▪ Difference between Air and Blood
Acoustic Impedance

39. How Does An Ultrasound Machine Make An Image ?
– Ultrasound transducer produces “pulses” of
ultrasound waves
– These waves travel within the body and interact
with various tissues
– The reflected waves return to the transducer and are
processed by the ultrasound machine
– An image which represents these reflections is
formed on the monitor
Pulse-Echo Method

40. Imaging By Ultrasound
▪ Ultrasound imaging is performed by emitting a pulse, which is partly
reflected from a boundary between two tissue structures, and partially
transmitted.
The amount of energy being reflected from each point is given
in the diagram as the Amplitude.

41. B- Brightness
mode shows
the energy as
the brightness
of the point
M- Motion mode the
reflector is moving so
if the depth is shown
in a time plot, the
motion will be seen
as a curve
A
B
C

42. 2-Dimensional Imaging
▪ Provides more structural and functional
information
▪ Rapid repetitive scanning along many different
radii with in an area in the shape of a fan
▪ 2-D image is built up by firing a beam , waiting
for the return echoes, maintaining the
information and then firing a new line from a
neighboring transducer along a neighboring line

44. A single ‘FRAME’ being formed
from one full sweep of beams
A ‘CINE LOOP’ from multiple FRAMES

45. Position of Reflected Echoes
▪ How does the system know the depth of the
reflection?
▪ TIMING
– The system calculates how long it takes for the echo to return
to the transducer
– The velocity in tissue is assumed constant at 1540m/sec
Velocity = Distance xTime
2

46. How Is An Image Formed On The Monitor?
▪ The amplitude of each reflected wave is represented by a
dot
▪ The position of the dot represents the depth from which
the echo is received
▪ The brightness of the dot represents the strength of the
returning echo
▪ These dots are combined to form a complete image

47. End Of Part 1

48. Part II

49. Goal of an Ultrasound System
▪ The ultimate goal of any ultrasound system is to make
like tissues look alike and unlike tissues look different.

50. ▪ Axial Resolution
▪ Lateral Resolution
▪ Temporal Resolution
▪ Contrast resolution
Types Of Resolution

51. ▪ Spatial Resolution
– also called Detail Resolution
– the combination ofAXIAL and LATERAL resolution
– some customers may use this term
Types of Resolution

52. Axial Resolution
– specifies how close together two objects can be
along the axis of the beam, yet still be
detected as two separate objects
– frequency (wavelength) affects axial resolution
▫ Determinants:
▫ Wavelength – smaller the
better
▫ Pulse length – shorter the
train of cycles greater the
resolution

53. Lateral Resolution
– the ability to resolve two adjacent objects that are
perpendicular to the beam axis as separate objects
– Beamwidth affects lateral resolution
▫ Determinants:
▫ Beam width – smaller
the better
▫ Depth
▫ Gain

54. Lateral Resolution
•
• •
•
Only one here
2 structures seen here

55. Lateral Resolution

56. ▪ The lateral resolution is approximately equals
the beam diameter.
▪ Since the beam diameter varies with depth,
the lateral resolution also varies with depth.
▪ It is best at near zone ( focal ) length.

57. ▪ The ability to accurately locate the position of moving
structures at particular instants in time
▪ The temporal resolution is limited by the sweep speed of
the beam.
▪ And the sweep speed is limited by the speed of sound, as
the echo from the deepest part of the image has to return
before the next pulse is sent out ad a different angle in the
neighboring beam
Temporal resolution:

58. As the depth of the sector determines
the time before next pulse can be sent
out, higher depth results in longer time
for building each line, and thus longer
time for building the sector from a
given number of lines, i.e. lower frame
rate.
Thus reducing the desired depth of the
sector results in shorter time between
pulses, and thus shorter time for
building each line, shorter time for
building the same number of lines, i.e.
higher frame rate.

59. • Use Depth and NOT Zoom
• Adjust sector size
• Adjust gain
• Decreasing the line density
Improving Temporal Resolution (Frame Rate)

60. • Use Depth and NOT Zoom
In the image to the left, the depth has been halved, reducing the time for
building each line to half, thus also halving the time for building the full
sector, doubling the frame rate
(Temporal Resolution)

61. Reducing the line density instead and maintaining sector
width, results in lower number of lines, i.e. lateral resolution,
and gives the same increase in frame rate.
Reducing sector width, but maintaining the line density, gives
unchanged lateral resolution but higher frame rate, at the cost
of field of view.
• Line density & Sector width
(Temporal Resolution)

62. ▪ Contrast Resolution
– the ability to resolve two adjacent objects of similar
intensity/reflective properties as separate objects
Types of Resolution

63. The Classic Trade off ..

64. How To Make Better Images

65. DEPTH:
The deeper the field of the image, the slower the frame rate
The smallest depth that permits display of the region of interest should be employed

66. Gain This function adjusts the displayed amplitude of all received signals

67. Signal-To-Noise Ratio
▪ Returning ultrasound waves are referred to as signal,
while background artifact is referred to as noise.
▪ Increasing the gain increases the signal-to-noise ratio.

68. Time Gain Compensation
• TGC will change the gain factor so that equally reflective
structures will be displayed with the same brightness
regardless of their depth.
• TGC allows amplification of ultrasound beams from deeper
depths because different amplitudes of ultrasound signals
are produced when received from different depths.
• MoreTGC is required for higher frequency transducers,
which create more attenuation.

69. Time Gain Compensation

70. Focusing The Beam
• Near Field
• Far Field
• Imaging quality is best within the near field.
• The length of the near field is greater at higher transducer frequencies
and wider transducer diameters.

71. FOCUS:
Indicates the region of the image in which the ultrasound beam is narrowest
Resolution is greatest in this region

72. Focusing The Beam
▪ Focusing the ultrasound beam does not affect the length of the
near field
▪ It produces a narrower beam (and higher resolution) within the
near field
▪ But makes the beam wider in the far field
▪ A phased-array transducer also offers electronic focusing, which
allows the sonographer to control the depth at which the
ultrasound beam is most tightly focused.

73. Harmonic Imaging
• When an ultrasound wave passes through the body, the
tissue generates "harmonic ultrasound waves" because
the tissue resonates.
• The resonance frequency is typically a multiple of the
original frequency (transmitted frequency)
• Fundamental components are filtered out.
• Images produced with harmonic imaging have a higher
resolution and are associated with fewer artifacts than
conventional (fundamental) imaging

74. Harmonic Imaging

75. Thanks for your patience

76. ▪ Thus frame rate is a compromise
between sector size (width and depth),
resolution (line density).

77. ▪ High frequency transducers produce pulses with
shorter wave length and higher longitudinal resolution.

78. Lateral resolution.
▪ The minimum distance that 2 side by side structures can be
separated and still produce 2 distinct echoes.
•• •
•
Only one here
2 structures seen here

80. More foci per image.
▪ More sound pulses per line.
▪ Superb lateral resolution at all depths.
▪ More time per image scan line.
▪ More time to create a frame.
Lower frame rate.

81. Multiple focal zones.
▪ An ultrasound pulse has only a single focal zone.
▪ By using multiple sound beams with different focal
depth to create a single image line the lateral
resolution is optimal at all depths

82. Tissue Harmonics

83. Tissue Signature

84. Tissue Harmonic Imaging

85. Ultrasound Interactions with Tissue Interfaces
Arrow representVectors whose length equal the strength & direction
of the reflected signal
A and B represent specular (mirror like) reflectors,
the B return signal does not return to the transducer
C and D have a rough surface that is typical of human tissue
E are objects smaller than a wavelength & therefore scatter the
energy

86. Interactions of Ultrasound Waves with
Tissue
The interactions will determine the types of images &
artifacts that are generated

87. Reflection, Attenuation & Time Gain
Conpensation Settings

88. Transducer Frequency & Wavelength
affect Resolution & Penetration

91. Understanding
Ultrasound physics.

92. Reflection:
▪ Occurs when some of the propagating acoustic energy
is redirected and returns toward the transducer.
▪ Reflection off of a very smooth reflector such as a
mirror are called specular
Reflection and incidence.

93. ▪ if the boundary between 2 media has
irregularities, then the wave is distributed in a
number of different directions.
▪ It occurs when a sound wave strikes material
whose size is approximately equal to or smaller
than the wavelength of the cycles in the pulse.
Scattering:

95. Incidence:

98. Reflection with normal incidence.

99.  In clinical ultrasound imaging 99% or more of
the incident energy is transmitted forward at a
boundary between soft tissues.

100. Reflection with oblique incidence.
▪ With oblique incidence, we cannot predict whether
transmission and/ or reflection will occur.

101. Refraction.
▪ Is a change in direction, or a bending away from a straight
line path, of a wave traveling from one medium to another.
▪ Refraction occurs only when there are:
1. Different Propagation Speed.
2. Oblique Incidence between the sound wave and the
boundary.

102. Snell’s Law.

103. Range equation.
How does an imaging system
determine the depth of a reflecting
surface?
Time-Of-Flight.

104. ▪ Time-Of-Flight: the go-return time
Is the elapsed time between pulse production and echo
reception by the transducer.
▪ Estimating distance from the go-return time is called
echo ranging.

109. Machines
There are 5 basic components of an ultrasound scanner that are required for
generation, display and storage of an ultrasound image.
1. Pulse generator - applies high amplitude voltage to energize the crystals
2. Transducer - converts electrical energy to mechanical (ultrasound) energy
and vice versa
3. Receiver - detects and amplifies weak signals
4. Display - displays ultrasound signals in a variety of modes
5. Memory - stores video display

110. ▪ Depicted as sine wave-peaks and troughs
▪ One cylce=one compression + one rarefaction
▪ Distance between 2 similar points represent
wavelength
▪ 0.15 to 1.5 mm in soft tissue
▪ Frequency- number of wavelengths per unit time
▪ V=f X λ(v=velocity,f =frequency, λ is wavelength)

111. ▪ Velocity of sound=1540 m/sec in soft tissue
▪ Wavelength=1.54/f
▪ Amplitude
Measure of strength of the sound wave
Indicated by height of sine wave above and below baseline

114. ▪ Higher the frequency greater the resolution
▪ Higher frequency,lesser the penetration
▪ Loss of ultrasound as it propogates through a medium is
called attenuation

115. PRICIPLES OF PEIZO ELECTRIC CRYSTALS
The charges in a piezoelectric crystal are exactly
balanced, even if they're not symmetrically
arranged.
The effects of the charges exactly cancel out, leaving
no net charge on the crystal faces
the electric dipole moments—vector lines
separating opposite charges—exactly cancel one
another out.
If you squeeze the crystal , you force the charges out
of balance.

116. ▪ Now the effects of the charges (their dipole moments) no
longer cancel one another out and net positive and
negative charges appear on opposite crystal faces.
▪ By squeezing the crystal, voltage is produced across its
opposite faces- piezoelectricity
▪ The piezoelectric effect was discovered in 1880 by two French physicists, brothers Pierre and
Paul-Jacques Curie, in crystals of quartz, tourmaline, and Rochelle salt (potassium sodium
tartrate).They took the name from the Greek work piezein, which means "to press."

117. ▪ The phenomenon of generation of a voltage under mechanical stress
is referred to as the direct piezoelectric effect
▪ mechanical strain produced in the crystal under electric stress is
called the converse piezoelectric effect.

118. ▪ Ferro electrics,barium tianate,lead zirconate titanate are used
as peizo electric crystals.
▪ Dampening material-shortens the ringing response
Also absorbs backward and laterally transmitted acoustic
energy
▪ Frequency emitted by transducer is directly proportional to
propagation speed within crystal and inversely related to
thickness

119. ▪ Important feature of ultrasound is ability to direct or focus
the beam as it leaves the transducer
▪ Proximal cylindrical and distally divergent
▪ Proximal zone –Fresnel zone
▪ Divergent field is called Fraunhofer zone
▪ Imaging is optimal in near field
▪ Decreasing wavelength or increasing transducer size
increase near field

121. Haemo”dynamics”
▪ Blood flow is a complex phenomenon
▪ Not a uniform liquid
▪ Flow pulsatile
▪ Vessel walls are elastic

122. Properties of Blood
▪ Density-mass of blood per unit volume
▪ Measure of resistance to accelaration
▪ Greater the density,greater the resistance to flow
▪ Viscosity:resistance to flow offered by fluid in motion
▪ 0.035 poise at 37 degree.

124. Factors determining flow
▪ Flow rate is determined by
– Pressure gradient
– Resistance
▪ Viscosity of blood
▪ Radius of lumen
▪ Length of vessel

125. Types of flow
Laminar flow
Shape of parabola
Concentric layers,each parallel to vessel wall
Velocity of each layer differs
Maximal velocity is at centre of vessel
Decreasing profile towards peripheries

129. Turbulent flow
▪ Obstruction produce increased velocities, flow vortices
▪ Whirlpools shed off in different directions producing variable
velocities- chaos
▪ Predicted by Reynolds number
▪ Reynolds number depends on
Re=( ρ x c x D)/v
ρ-Density of blood
D-Vessel diameter
c-Velocity of flow
V-viscosity

130. The Reynolds number is dimensionless
If Re is less than 1200 the flow will be -laminar
1200-2000 flow is described as -transitional
Greater than 2000 -turbulent