2. ULTRASONOGRAPHY
• Application of medical with ultrasound-based
imaging diagnostic technique used to
visualize internal organs, their size, structure
and their pathological lesions.
3. ULTRASOUND PHYSICS
• INTRODUCTION
• Sound waves are mechanical pressure waves
which propagate through a medium with the
acoustic energy causing the particles of the
medium to oscillate backward and forward as
alternating bands of compression and
expansion (rarefaction) of the material.
4. Introduction
It results in cyclic change in the resting pressure
of the medium.
The cyclic variations of the pressure can be
plotted graphically as a sine wave.
Produced when a vibrator, such as a piezoelectric
crystal in an ultrasound transducer, transmits its
back and forth oscillation into a medium.
5. Cont……
• It is not capable of transmitting its energy
through a vacuum thus it requires a medium
through which it propagates.
• It is a longitudinal wave in which the particles
of the medium are made to oscillate in a
direction parallel to the direction that the
wave moves.
• It travels in a straight line
7. SOUND FREQUENCY SPECTRUM
• Infrasound- below 20Hz (cant be head by
humans)
• Audible sound (20Hz-20KHz)- range detectable
by the human ear.
• Ultrasound > 20KHz
• Medical Ultrasound (2- 20MHz)
• Note: Medical imaging – 3-10MHz
8. PROPERTIES OF SOUND WAVES
• INCLUDE
Amplitude
Wavelength (λ)
Frequency (f)
Velocity (C)
10. Amplitude
• Is the peak pressure of the wave.
• When applied to ordinary sound, this term
correlates with the loudness of the sound wave.
• When applied to ultrasound images, it correlates
with the intensity of the returning echo.
• The amplitude of the pulse as it leaves the
transducer is generally determined by how hard
the crystal is "struck" by the electrical pulse.
11. Cont…
• Relative amplitude- measure of how much
the amplitude ( A) of a pulse decreases as it
passes through a given thickness of tissue.
• Relative amplitude (dB) = 20 log A2/A1
12. Velocity
• The speed of the wave. Cal as (V= f λ )
• It is constant in a given medium and is
calculated to be 1,540m/s in soft tissue
• Using this principle, an ultrasound machine
can calculate the distance /depth of a
structure by measuring the time it takes for an
emitted ultrasound beam to be reflected back
to the source.
13. Wavelength
• Is the distance the wave travels in a single
cycle.
• It is inversely related to frequency.
• Therefore, high frequency decrease
wavelength (and thus penetration), and lower
frequency increases wavelength (and thus
penetration)
λ = c / f
14. Frequency
• Is the number of times per second the wave is
repeated.
• One Hertz is equal to one wave cycle per
second
• Frequency and period are inversely related
thus f = 1/ T
f = c / λ
15. ULTRASOUND PULSE
• A typical ultrasound pulse consists of several
wavelengths or vibration cycles.
• The number of cycles within a pulse is
determined by the damping characteristics of
the transducer.
• Damping is what keeps the transducer
element from continuing to vibrate and
produce a long pulse.
16. Cont….
• Pulse length = wavelength X number of cycles
within the pulse
pulse length = λ f
f is the number of cycles within the pulse
17. SPEED OF SOUND
• Speed of sound is determined by Stiffness and density
of matter.
• Speed of sound is significantly higher in very stiff
materials like bone, gallstones.
• Stiffness- the speed of sound is directly proportional to
the stiffness or resistance to compression
• Density- speed is inversely proportional to the density
of the material.
• Thus the stiffer the medium the higher the propagating
speed while the dense the medium the slower the
speed.
18. SOUND VELOCITIES
• Material Meters/sec
• Vacuum 0
• Air 330
• Pure water 1430
• Fat 1450
• Soft Tissue 1540
• Muscle 1585
• Bone 4080
22. Cont…
• The time (t) is the time between transmission
of the pulse and reception of the echoes
known as the (pulse-echo time, time of flight,
go-return time)
• Deep structures have long go return times
• Superficial structures have short go-return
times
• Pulse –echo time is usually 13µs per cm
27. Reflection
• A reflection occurs at the boundary between two materials
provided that a certain property of the materials known as
the acoustic impedance (Z) is different.
• A reflection of the beam is called an echo and the
production and detection of echoes forms the basis of
ultrasound.
• Occurs at the interface, or boundary, between two
dissimilar materials the different physical characteristic is
known as acoustic impedance Z
• Classified into two
• Specular
• Scatter
28. cont
• Specular Reflection:
• These originates from relatively large , strongly reflective,
regularly shaped objects with smooth surfaces.
• Echoes are reflected as a mirror reflects light. Since
ultrasound scanners only detect reflections that return to
the transducer, the display of specular interfaces depends
heavily on the angle of intonation.
• Specular reflectors (e.g. the diaphragm, urine filled
bladder) only return echoes to the transducer if the sound
beam is perpendicular to the interface. If not, the sound
beam will be transmitted away from the transducer, and
the echo will not be detected.
29. Formula (reflection)
• R = Ir/Ii = (Z2 – Z1/Z1 + Z2) squared
• And
• T = It/Ii = 4Z1 – Z2/ (Z1 + Z2) Squared
• Where
R = reflection intensity coefficient
T = transmission intensity coefficient
Ir = reflected U/S intensity
It = Transmitted U/S intensity
Z1 = Acoustic impedance of first medium
Z2 = Acoustic impedance of second medium
30. Cont…
• . Diffuse reflection (Scattering)-
• These echoes comes from smaller interfaces
within solid organs with structures much
smaller than the wavelength of the incident
sound.
• Echoes are scattered in all directions. The
direction does not follow the laws of reflection
rather depends on relative size of scattering
objects and U/S beam diameter
31. Acoustic Impedance
• The product of medium density and
ultrasound velocity in the medium
• It is the measure of the resistance of the
particles of the medium to mechanical
vibrations.
• This resistance increases in proportion to the
density of the medium, and the velocity of
ultrasound in the medium.
33. Acoustic boundaries
• Acoustic Boundaries
• Positions within tissue where the values of
acoustic impedance change are very
important in U/S interactions.
• Positions = acoustic boundaries or tissue
interfaces
• EX-urine (bladder) has Z value different from
bladder wall- common interface constitutes an
acoustic boundary
34. Refraction
• The bending or change in direction of the
sound wave when it passes from adjacent
tissues having different acoustic propagation
velocities and is governed by Snell’s Law.
35. Absorption
• A process by which ultrasound energy is
converted to heat in the medium. It is
responsible for tissue heating.
• Attenuation and absorption is often expressed
in terms of decibels.
36. Attenuation
• As the U/S wave propagates through a
medium, the intensity reduces with distance
travelled.
37. ULTRASOUND FIELD
• Divided into two regions- near and far fields
• Close to the transmitter the radiation field is very
complex, changing relatively rapidly both in
amplitude and phase position.
• Close to the transmitter, these phase differences
are relatively large, since the differences in path
length are comparable to the shortest path
between transmitter surface and field point.
Small changes in the position of the field point
can make large differences to the overall sum
38. Cont…
• In the far field, differences between path
lengths are small in comparison with the
shortest distance from transmitter to field
point thus all contributions arrive with nearly
the same phase.
• Small changes make little difference to the
overall sum
• Amplitude stays relatively constant with
position along or across the sound beam
39. Piezoelectric Effect
• Ultrasound waves are generated by
piezoelectric crystals (Quartz crystals)
• When an electric current is applied to a quartz
crystal, its shape changes with polarity.
• This causes expansion and contraction that in
turn leads to the production of compression
and rarefaction of sound waves
40. Cont…
• The reverse is also true and an electrical
current is generated on exposure to returning
echoes that are processed to generate display
• Hence the crystals are both transmitters and
receiver.
43. Types of transducers
1. Mechanical swept Probe: seldom used now
2. Electronically steered Probe:
i. Linear array transducers
ii. Phased /sector array transducers
iii. Convex /curved
iv. Annular array
44. Types of transducers cont…
• The choice is a compromise between Spatial
resolution and Imaging depth (Tissue
penetration)
• Rule of thumb is use the highest freq that will
penetrate to the depth of interest.
45. TRANSDUCERS
• Linear
Gives rectangular image
Generally has higher frequency
Good for looking at a smaller area and for
gauging depth
Gives more of a one dimensional view
Sometimes referred to as the vascular probe
46. Cont….
• Curvilinear
Uses same linear orientation but arranged on
a curved surface
Generally lower frequency
Gives a wider angle of view
48. Transducers
• The higher the frequency, the better the
resolution
• The better the resolution, the better you can
distinguish objects from each other
49. Knobology
• Power
Controls the strength or intensity of the sound
wave
Use ALARA principle
As low as reasonably achievable
50. Cont….
• Gain
Degree of amplification of the returning sound
Increasing the gain, increases the strength of
the returning echoes and results in a lighter
image
Decreasing the gain, does the opposite
51. Cont…
• Time gain compensation
Used to equalize the stronger echoes in the near
field with the weaker echoes in the far field
Should be a gentle curve
Zoom
Can place zoom box on a portion of a frozen
image to enlarge that portion of the image
May lose some resolution because pixels are
enlarged
52. Cont…
• Focal Zone
Where the narrowest portion of the beam is
Gives the optimal resolution
Depth
Each frequency has a range of depth of
penetration
Decrease the depth to visualize superficial
structures
May need to increase the depth of penetration to
visualize larger organs
53. Medical challenges it addresses
• Capitalized on the deficiencies of conventional
radiography in imaging anatomical structures
of body organs except lungs and bones.
• Supersedes the invasive conventional
procedures to that of non-invasive
• Offers a cheaper route to quick diagnosis
compared to CT and MRI
• Assures safety - obstetric imaging
54. Strength of ultrasound imaging
Images muscle and soft tissue very well and is
particularly useful for delineating the
interfaces between solid and fluid-filled
spaces.
Renders “live” images, where the operator can
dynamically select the most useful section for
diagnosing and documenting changes, often
enabling rapid diagnoses.
55. Cont…
Demonstrates structures as well as some
aspects of the function of organs.
No undesirable side effects
Equipment is widely available and
comparatively flexible; exam can be
performed at the bedside
56. Weaknesses of ultrasound imaging
• Ultrasound can not penetrate bone and
performs poorly when there is air between
the scanner and the organ of interest.
• Even in the absence of bone and air, the depth
penetration of ultrasound is limited, making it
difficult to image structures that are far
removed from the body surface.
• Operator- dependant
57. U/S Image: Generation & Display
• An U/S transducer, T, sends a beam of U/S into
the subject over a selected area of interest
• At an acoustic boundary such as B within the
tissue, some of the U/S energy is reflected,
either specularly or by scattering.
• Under favourable conditions, some of the
reflected U/S will go back towards T.
58. Cont….
• At the transducer, the returning echo will
interact with the piezoelectric crystal and
generate an electric signal.
• This signal will be electronically processed and
measured. The location of its origin at B will
be determined.
60. Cont….
• Transducer- The transducer is the component
of the ultrasound system that is placed in
direct contact with the patient's body.
• Pulse Generator- The pulse generator
produces the electrical pulses that are applied
to the transducer. For conventional ultrasound
imaging the pulses are produced at a rate of
approximately 1,000 pulses per second.
61. Cont…
• Amplification- increase the size of the electrical
pulses coming from the transducer after an echo
is received.. The amount of amplification is
determined by the gain setting.
• Scan Generator- controls the scanning of the
ultrasound beam over the body section being
imaged. This is usually done by controlling the
sequence in which the electrical pulses are
applied to the piezoelectric elements within the
transducer.
62. Cont..
• Scan Converter- converts from the format of the
scanning ultrasound beam into a digital image
matrix format for processing and display.
• Image Processor- The digital image is processed
to produce the desired characteristics for display.
This includes giving it specific contrast
characteristics and reformatting the image if
necessary
• Display –monitor
63. IMAGE Formation
• By measuring the time between when the sound
was sent and received, the amplitude of the
sound and the pitch of the sound, a computer can
produce images, calculate depths and calculate
speeds.
• The strength or amplitude (brightness) of each
reflected wave is represented by a dot.
• The position of the dot represents the depth from
which the returning echo was received.
• These dots are combined to form an image.
64. Cont..
• Modern transducers use multiple small
elements to generate the ultrasound wave.
• If multiple small elements fire simultaneously
however the individual curved wave fronts
combine to form a linear wave front moving
perpendicularly away from the transducer
face.
• This system, that is multiple small elements
fired individually, is termed phased array
66. Image Display
• Once the diagnostic information has been
acquired and electronically processed, it has
to be displayed for viewing and recording.
• Different methods are used to display the
information acquired in modes (A-mode, B-
mode, M-mode, Real-Time mode and
Doppler mode).
67. Defining modes
• A-mode- the original display mode of U/S
measurements, in which the amplitude of the
returned echoes along a single line is displayed
on an oscilloscope.
• B-mode (2D)- the current display mode of choice.
This is produced by sweeping the transducer from
side to side and displaying the strength of the
returned echoes as bright sports in their
geometrically correct direction and distance
68.
69. Cont…
• M-mode- followed A mode by recording the
strength of the echoes as dark spots on
moving light sensitive paper. Object that
move, such as the heart cause standard
patters of motion to be displayed.
• And a lot of diagnostic information such as
valve closures rates, whether valves opened
and closed completely and wall thickness
could be obtained from this mode.
70. 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 are
presented (on a time line)
71. Cont…
• 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.)
72. Artefacts
• Artifacts are errors in images.
• They are normally caused by physical
processes that affect the ultrasound beam and
that in some way alter the basic assumptions
the operator makes about the beam
73. Cont…..
• Reverberation artefact
This occurs when ultrasound is repeatedly
reflected between two highly reflective surfaces.
• Ring Down
Ring-down artifacts are produced when small
crystals such as cholesterol or air bubbles resonate
at the ultrasound frequency and emit sound.
Because the sound is emitted after the transducer
receives the initial reflection, the system thinks the
emitted sound is coming from structures deeper in
the body
74. Cont….
• Mirror Images
Sound can bounce off a strong, smooth
reflector such as the diaphragm.
The surface acts as mirror and reflects the
pulse to another tissue interface.
The ultrasound system believes the second
interface is beyond the first surface, and this is
where it appears on the scan.
75. Reflection artefact
• similar to the mirror image but has a very
different appearance and is caused by
multiple reflections.
• Sound can bounce off a strong, smooth
reflector, such as the posterior bladder wall,
and be reflected back to the transducer, giving
the appearance of the structure deep to the
bladder wall as would be seen with fluid
collection.
76. Enhancement artefact
• Enhancement is seen as an abnormally high
brightness.
• This occurs when sound travels through a
medium with an attenuation rate lower than
surrounding tissue.
• Reflectors at depths greater than the weak
attenuation are abnormally bright in
comparison with neighboring tissues
77. Attenuation artefact
• Tissues deeper than strongly attenuating
objects, such as calcification, appear darker
because the intensity of the transmitted beam
is lower
78. Clinical Application
• Ultrasonography is widely utilized in medicine,
primarily in gastroenterology, cardiology,
gynecology and obstetrics, urology and
endocrinology.
• It is possible to perform diagnosis or
therapeutic procedures with the guidance of
ultrasonography (for instance biopsies or
drainage of fluid collections).
79. Other applications
• Description Anaesthesiology- used by
anaesthesiologists to guide injecting needles
when placing local anaesthetics solutions near
nerves
• Neonatology
80. Image Quality
• Resolution
The ability to distinguish echoes in terms of
space, time or strength and good resolution is
thus critical to the production of high quality
images.
• Spatial resolution
The ability of the ultrasound system to detect
and display structures that are close together.
81. Cont…
• Axial resolution- ability to display small targets
along the path of the beam as separate entities.
• Contrast resolution- ability of an ultrasound
system to demonstrate differentiation between
tissues having different characteristics e.g.
liver/spleen.
• Temporal resolution- ability of an ultrasound
system to accurately show changes in the
underlying anatomy over time, this is particularly
important in echocardiography.
82. 1. Axial Resolution
• Factors affecting axial resolution include
Spatial Pulse Length (SPL) and frequency.
• It is improved by higher frequency (shorter
wavelength) transducers but at the expense of
penetration.
• Higher frequencies therefore are used to
image structures close to the transducer.
83. 2. Lateral Resolution
• Factors affecting lateral resolution are width
of the beam, distance from the transducer,
frequency, side and grating lobe levels.
• To optimize lateral resolution therefore:
Use the highest frequency transducer
(reduced penetration)
Optimize the focal zone
Use the minimum necessary gain
84. 3. Temporal Resolution
• The number of frames generated per second
(frame rate) determines temporal resolution.
85. Recent Advances
• Superb Micro-Vascular Imaging Technology
expands the range of visible blood flow and
provides visualization of low velocity
microvascular flow never before seen with
ultrasound.
SMI's level of vascular visualization, combined
with high frame rates, advances diagnostic
confidence when evaluating lesions, cysts and
tumors, improving patient outcomes and
experience.
86. Fly Thru Imaging
• a 3D volume rendering technique that allows you
to soar through cavities, ducts and vessels from
the inside and in 3D.
• Similar to virtual endoscopy, Fly Thru is a
revolutionary tool for exploring lesions and
masses and planning interventional procedures.
This technology function is available both during
or post exam.
• Fly Thru displays structures similar to the way
they would appear using a virtual endoscope.
87. Smart Fusion
• offers the best of both worlds by synchronizing
ultrasound with CT or MR images for locating
hard-to-find lesions and improving confidence
during ultrasound-guided biopsies.
• Smart Fusion reads 3D DICOM data sets from CT
or MR systems then, using position sensors
located on the ultrasound transducer, displays
the corresponding images, side-by-side with the
live ultrasound image.
88. Wireless Transducers
• In 2012, Siemens Healthcare introduced the
world’s first ultrasound system with wireless
transducers, the Acuson Freestyle.
• Completely untethered from the console, the
Acuson’s wireless transducer can be used to
image from up to 10 feet away
89. 3-D Ultrasound
• uses a dataset that contains a large number of
B-mode 2D planes.
• Once the volume data is obtained it is possible
to optimize the ultrasound image of the area
of interest by
rotating, reconstructing and rendering,
allowing viewing in different planes and angles
without further exposure of the patient to
ultrasound
90. Contrast agents
• Reflection of sound depends on the acoustic
impedance which are defined by its density
and the velocity of sound in the medium.
• Acoustic impedances differences are very
small between soft tissues.
• Echopharmaceuticals have been proposed to
increase acoustic impedance differences at
tissue interfaces & increase echo intensities
91. Cont….
• The most effective principle by far that has
emerged is the diffraction of ultrasonic
• waves on gas bubbles (microbubble containing
solutions ) and colloidal, sometimes
• temperature dependent diphasic systems.
92. 4 Dimensional
• also known as ‘real-time 3D ultrasound’.
• the ultrasound equipment can acquire and
display the 3D datasets with their multiplanar
reformations and renderings in real time.
• 3D or 4D can only build on the 2D B-mode
images, therefore the limitations and artefacts
that affect B-mode imaging, such as presence
of gas and overlying structures, will also affect
the quality of the 3D and 4D imaging
93. SAFETY
• Ultrasound is energy and is absorbed by
tissue, causing heating
• 2D ultrasound has been used to image the
foetus for about 50 years. It is thought to be
completely safe and does not cause significant
heating
• 4D ultrasound is new, requires more energy
and therefore generates more heating. We
think it is safe.
