Physics

1. ULTRASOUND PHYSICS
PRESENTER Dr.Dinesh

2. Ultrasound
• Ultrasound is a mechanical, longitudinal wave with a
frequency exceeding the upper limit of human hearing,
which is 20,000 Hz or 20 kHz,
• Typically at 2 —20 Mhz.

3. Basic Ultrasound Physics

4. Velocity of sound
• Speed at which a sound wave travels through a medium(cm/!
• Independent of frequency and depends primarily on the
physical makeup of material through which sound is being
transmitted
• Determined by
1. Compressibility 2. Density
• Velocity -Slowest in air/gas
- Fastest in solids
• Average speed of ultrasound in body is 1540m/sec

5. Frequency
• Number of cycles per second
• Units are Hertz
• Ultrasound imaging frequency range 2-20Mhz
• In ultrasonic frequency range, the velocity of sound is
constant in any particular medium, when frequency is
increased the wavelength must decrease.

6. Higher the frequency lower the penetration and higher the resolution
Lower the frequency higher the penetration and lower the resolution

7. Wavelength
• Distance over which one cycle occurs

8. Velocity(v),Frequency(f) and wavelength(λ)
Given a constant velocity, as frequency increases wavelength decreases.
V=fλ

9. Intensity OR Loudness
• Determined by the length of oscillation of the particle: conducting the wave
• Greater the amplitude of oscillation, the more intense the sound
• Ultrasonic intensities are expressed in watts per squ® centimeter

10. Relative Sound Intensity
• Sound intensity is measured in decibels
• - comparison of relative power of two sound beams
expressed log-arithmically using the base 10
• The number of decibels is obtained by multiplying the
number of decibels by 10
:

11. Transducer
• It is a device that converts energy from one form to another
• ULTRASOUNDTRANSDUCER converts electric energy into
sound energy and sound energy back into electric energy.

12. Ultrasound Transducer
Acts as both speaker & microphone
Emits very short sound pulse
Listens a very long time for returning echoes
Can only do one at a time

13. Pulse-Echo Method
• 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

14. TRANSDUCER DESIGN
1.Matching layer
2.Piezoelectric crystal
3.Backing block
4. Acoustic absorber
5. Metal shield
6. Signal cable

15. Transducer schematic diagram

16. 1. MATCHING LAYER
• It minimizes the acoustic impedence differences between
transducer and the patient.
• Its impedence is intermediate to that of the soft tissue and the
transducer.
• Its thickness is equal to one-forth of the wavelength, which is
known as quarter wave matching
• Matching layer is made of perspex or plexiglass loaded with
aluminium powder,

17. 2. PIEZOELECTRIC CRYSTALS
• Some naturally piezoelectrc occurring materials
include Berlinite(structurally identical to
quartz),cane sugar,quartz,Rochelle
salt,topaz,tourmaline,and dry bone
•An example of man-made piezoelectric materials
include barium titanate and lead zirconate
titanate (PZT)
•They can be designed to vibrate in either the
thickness or radial mode.

18. Piezoelectric Principle :
• Voltage generated when certain materials are
deformed by pressure
• Reverse also true!
— Some materials change dimensions
when voltage applied
■ dimensional change causes pressure
change
— when voltage polarity reversed, so
is dimensional change

21. Crystal layer :
• Molecules of piezoelectric crystal are polarized, one end is
positive and other negative.
• When high frequency current is applied, it alternatively thickens
and thins in its short axis, and generates ultrasound waves as a
beam in air infront and back of the crystal face.

22. 3. DAMPING BLOCK
• Located on the backside of the crystal made up of tungsten
particles suspended in epoxy resin
It absorbs backward IJS pulse and attenuates stray US signals.
Transducer and damping block are separated from the casing by an
insulator(rubber cork).

24. Function of damping block:
In B- Mode operation,
• It must stop the vibration within a microsecond so that the
transducer becomes ready to immediately receive the reflected
echoes from the body

25. RESONANT FREQUENCY
• A crystal exhibits its greatest response at the resonance frequency .
• The resonance frequency is determined by the thickness Of the
crystal and propagation velocity in its material
• Most efficient operation is achieved for a crystal with a thickness
equal to half the wavelength of the desired ultrasound
• In most of the pulsed mode of operating ultrasound the output sound
has frequency both above and below the resonance frequency.
• The range of frequencies are called bandwidth. Generally shorter
the pulse length of the transducer more is the bandwidth.
• Broad bandwidth helps to reduce speckle by frequency compounding

27. TRANSDUCER Q FACTOR
• Refers to two characteristics of piezoelectric crystals:
-purity Of sound
-length oftime that the sound persists
• High Q transducer:- Nearly pure sound made up of narrow range of
frequencies.
• LOW Q transducer:- Whole spectrum Of sound covering a much wider
range Of frequencies
• Ring down-time —Interval between initiation of the wave and
complete cessation of vibrations.

29. Where Q=Qfactor ,
fo= resonance frequency
f2 = frequency above resonance at which intensity reduced by half
f1= frequency below resonance at which intensity reduced by half
• Narrow range of sound frequencies and long ring down-time :
Useful for Doppler ultrasound transducer
• Broad range of sound frequencies and short ring down-time Useful for
organ imaging because it can furnish short ultrasound pulses and will
respond to a broad range of returning frequencies.

30. Spatial Pulse Length
• Distance in space traveled by ultrasound during one pulse
SPL=Cycles per pulse X Wavelength
• Depends on source & medium
• as wavelength increases, spatial pulse length increases

32. Wavelength= Speed/Frequency
• as # cycles per pulse increases, spatial pulse
length increases
• as frequency increases, wavelength decreases &
spatial pulse length decreases
- speed stays constant
■ Spatial pulse length determines axial resolution

33. CHARACTERISTICS OF AN ULTRASONIC BEAM
■ The ultrasound pulses produced by the transducer
results in a series of wave fronts that form a three
dimensional beam of ultrasound.
■ the features of beam are influenced by constructive
and destructive interferences of the pressure waves.

34. ULTRASOUND BEAMS
. Ultrasound from a point source creates spherical wave fronts. Ultrasound
from a two-dimensional extended source creates planar wave fronts,
. These sources can be considered to be a collection of point sources, each
radiating spherical wave fronts (termed wavelets) into the medium.
. In regions where compression zones for one wavelet intersect those of
another. a condition Of constructive interference is established & the
wavelets reinforce each other, Reverse that is cancellation occurs in
destructive interference

35. Interference of the waves

36. • In this figure, the reinforcement and cancellation of individual
wavelets are most noticeable in the region near the source of
ultrasound.
• They are progressively less dramatic With increasing distance
from the ultrasound source .
• The near field where pressure
amplitude change is maximum that
zone is called "Fresnel zone"
• Beyond the Fresnel zone. some Of
the energy escapes along the
periphery of the beam to produce a
gradual divergence of the
ultrasound beam_— called
Fraunhofer ( or far) zone

39. Ultrasound beam characters:
An unfocused ultrasound beam leaving a flat crystal has 2 parts:
1. Initial cylindrical segment(nearfield or frensnal zone)
2. Diverging conical portion ( far field or fraunhoferzone)

40. Where, x`= length of Frensel zone (cm)
r = radius of the transducerccm)
A =wavelength(cm)
• Zone longest with largest transducer and high frequency sound
• Zone shortest with small transducer and low frequency sound

41. The length of near field and divergence of the far field depend upon:
A. FREQUENCY: higher the frequency longer the near fields and less divergent the
far field Depth resolution increases with higher frequencies Major drawback-
Tissue absorption increases with increasing frequency
B. CRYSTAL DIAMETER: increasing diameter increases the near field
length but worsens the lateral and depth resolution.

42. FOCUSED TRANSDUCER
1)A focused ultrasound transducer produces a beam that is narrower at some distance
from the transducer face than its dimension at the face of the transducer.
2)In the region where the beam narrows (termed the focal zone Of the transducer), the
ultrasound intensity may be heightened by 100 times or more compared with the
intensity outside of the focal zone
3)Because Of this increased intensity, a much larger signal will be induced in a
transducer from a reflector positioned in the focal zone.
4)The distance between the location for maximum echo in the focal zone and the
element responsible for focusing the ultrasound beam is termed the focal length of the
transducer.
5)An ultrasound beam also may be focused with mirrors and refracting lenses or
phasing the linear array electronically

43. Focused Transducers

44. Ultrasound tissue interaction
1. Reflection
2. Refraction
3. Absorption
4. Attenuation
5. Scattering

45. 1.REFLECTION
• A reflection of a beam is called ECHO.
• The production and detection of echoes forms the basis of
ultrasound.
• Reflection occurs at the interface between two materials.
• - It depends on the
1. tissue’s- "ACOUSTIC IMPEDENCE”
2. beam’s angle of incidence
• If two materials have same impedence , no echo produced.

46. Acoustic Impedance
Acoustic Impedance = Density X Prop.Speed
(rayls) (kg/m3) (m/sec)
• increases with higher
_ Density
— Stiffness
— propagation speed
■ independent of frequency

47. Acoustic Impedance of SoftTissue:
Density:
- 1000 kg/m3
Propagation speed:
— 1540 m/sec
Acoustic Impedance = Density X Prop. Speed (Ray’s) (kg/m3) (m/sec)
1000 kg/m3 X 1540 m/sec = 1540,000 rayls

48. • Differences in acoustic impedance determine fraction of intensity
echoed at an interface
If the difference in acoustic impedence is:
• Small —weak echo is produced and most of the sound waves will
continue in second medium
• Large- strong echo is produced
• Very large- all sound waves will be totally reflected back, Example:
tissue-air interface of beam is reflected back,

49. Reflected wave

50. Angle of incidence
The amount Of reflection is determined by the angle Of incidence between
the sound beam and reflecting surface
• The higher the angle of incidence(i.e.r the closer it is to a right angle)rthe
less the amount of reflected sound
Where, R = percentage of beam reflected
Z1=acoustic impedence of medium 1
Z2=acoustic impedence of medium 2

51. • Lung-chest wall interface : 99-9%
• Kidney-fat intelface :0.64%
• Skull-brain interface : 44%
Where, R = percentage of beam transmitted
Z1=acoustic impedence of medium 1
Z2=acoustic impedence of medium 2
The sum of reflected and transmitted portions of sound beam must
be 100%

52. • Specular Reflections, which occur at large change in impedance
producing a large reflection, and also reducing the continuing wave
amplitude.
• Medium Reflections, which occur with dense tissues such as muscle.
• Diffuse Reflections, which occur with soft tissues such as liver.

53. Specular reflectors :
• Diaphragm
• Wall of urine filled urinary bladder -
Endometrial stripe

54. Different types of reflections

55. 2. REFRACT1ON
Angle of incidence = angle of reflection

56. REFRACTION
When a propagating ultrasound wave encounters a Specular
interface at an oblique angle. it is Refracted in the same way
that light is refracted through a lens.
The portion of the wave that is not reflected continues into the
second medium, with a change in direction.
It is dependent on the velocities of the two medium. If the
velocities are equal, There would be no refraction occurred and
the beam goes straight into the second medium.
For the velocities Of the different tissues in the human body
are quite close, refraction's can be ignored

57. ■ The angle of refraction is governed by Snell’s law, which is
Where Θ1= incidence angle
Θ2=transmitted angle
V1=velocity of sound for incidence medium
V1=velocity of sound for transmitting medium
Refraction can cause artifacts, which cause spatial distortion(real structures are
imaged in wrong location)

58. 3. ABSORPTlON
Cause
a. Removal of energy from the ultrasound beam and
b. Eventual dissipation of this energy primarily as heat.
• . Ultrasound is propagated by displacement Of molecules 0t a medium
into regions of compression and rarefaction
• - Therefore, the energy of the ultrasound beam is gradually reduced as it
passes through the medium,

59. . Three factors determine the amount of absorption:
1) the frequency of the sound
2) the viscosity of conducting medium
3) the "relaxation time" of the medium
Liquids — Low viscosity — Little absorption
Soft tissues — High viscosity — Medium absorption
Bones — Very high viscosity — High absorption
Relaxation time is the time that it takes for a molecule to return to its original
position after it has been displaced –

60. • The relaxation time is a constant for any particular material
• A molecule with a longer relaxation time may not be able to return
completely before a second wave arrives
• Compression wave is moving in one direction and molecule in opposite
direction and hence more energy required to reverse the direction of
molecule and converted to heat.
• In soft tissues there is linear relationship between absorption of
ultrasound and frequency
• The proper frequency is a compromise between the best resolution
(higher frequency) and the ability to propagate the energy into the
tissues(lower frequency)

61. QUARTER WAVE MATCHING
• Method of improving energy transfer is that of mechanical impedance
matching
• A layer of material of suitable thickness and characteristic impedance is
placed on the front surface of the transducer, the energy is transmitted
into the patient more efficiently
• The thickness of matching layer must be equal to one fourth the
wavelength of sound in the matching layer
Zmatching layer =Ztransducer X Zsoft tissue
• Use of quarter-wave matching will also improve the transmission of
ultrasound pulses returning from tissues back into the transducer

62. 4.ATTENUATlON
• Loss of intensity of sound during propagation.
• Due to mainly reflection. refraction and absorption Attenuation Of
ultrasoune wave occurs when it is propagating tnrougn the medium. •
• Loss of propagating energy will be in the torm of heat absorbed by
the tissue, approximately 1 dB/cm/MHz, or caused by wavefront
dispersion or wave scattering

63. 5.SCATTERING
• Not all echoes are reflected back to probe.
• Some of them are scattered in all directions in a non
uniform manner,
• More so with very small objects or rough surfaces.
• Part of scattering goes back to transducer and
generate images is called BACKSCATTER

64. • Backscatter
Backscatter or Rayleigh scattering occurs with
structures smaller than the transmitted
wavelength. Reflected energy is very low,
but contributes to the texture Of the image.

65. IMAGE
DISPLAY

66. A-MODE (Amplitude mode)
A-mode is the simplest form of ultrasound imaging, producing a simple representation of the depth
of tissue interfaces along a single line.
In the A-mode presentation Of ultrasound images, echoes returning from the body are
displayed as signals .

67. A-mode reveals the location of echo-producing structures only in the direction
of the ultrasound beam.

68. -
• No memory is built into the display mechanism,so it discards previous
pulses as it receives new ones.
• A permanent record is made by photographing the electronic display
Applications of A-MODE:
• Opthalmology-distance measurements
• Echoencephalography
• Echocardiography
• Detecting a cyst in breast
• Studying midline displacement in brain

70. • Contact scaning — transducer is placed on patients skin with mineral oil on
skin acting to exclude air and to ensure good acoustic coupling between
transducer and skin, •
• If the angle between the perpendicular from the tranducer surface surface
and the interface to be imaged is greater than 50 the amount of reflected
ultrasound returning to the transducer will be too little to produce an
image.
• Compound scanning motion is required to present the surface of the
transducer to the wide variety of interface angles require lung
imaging

71. •B Mode
•The ultrasound beam is scanned sequentially across a two-dimensional section,
either:
•Linearly to produce a rectangular image
•Rotationally to produce a sector image
•Only boundaries approximately perpendicular to the scan lines will be imaged.
•The returning echo pulses are displayed as bright pixels on the screen.
• The image is built up as a series of vertical lines on the screen, corresponding
to each ultrasound beam in the sequence, and displayed on the monitor screen
in a matrix of pixels corresponding to the matrix of voxels in the scanned
anatomy

72. •The lateral (horizontal) pixel position is determined by
the position of the beam relative to the patient surface,
or the angle of the beam.
•The axial (vertical) pixel position is determined by the
depth calculated from the round-trip time.
•The brightness of the pixel is determined by the
strength of the received signal.
•As the signal strength depends on the strength of
reflection from the corresponding interface, this
enables tissue differentiation based on the pixel
brightness.
• A real-time image is displayed on the monitor screen
in a matrix of pixels, corresponding to the matrix of
voxels in the body

73. REAL-TIME IMAGING
In most B-mode scanners, these two-dimensional images
are produced continuously in a rapid succession of frames
so that moving structures can effectively be viewed in real-
time.
Various aspects of the real-time image can be influenced
directly or indirectly by the user either by choice of
transducer, or of scanner settings.

74. Scan line density:
The image is divided into several vertical lines with a width defined by
the distance between each beam.
The greater the number of lines per unit distance, or line density, the
better the lateral resolution.
Pulse repetition frequency (PRF):
The rate at which pulses are transmitted along one line, measured in Hz
(pulses per second):

75. Frame rate:
To produce a two-dimensional frame, all lines in the frame must be produced
sequentially, before starting again to produce the next frame.
The frame rate is the number of frames produced each second (Hz).
To successfully image moving structures, a sufficiently high frame rate is
required.
If the frame rate is too low, this can result in image ‘lag’ and blurring,
particularly as the probe is moved across the patient.
It is therefore not possible to achieve a high frame rate, high line density, and
image at a large depth, and these aspects must be balanced.
Combining the above: depth of view *number of scan lines * frame rate =
constant

77. •M-mode
• is used to examine the position of moving structures over time.
•The B-mode image is frozen and used to direct a single beam (as in A-
mode) along a line of interest, intersecting the moving surfaces as close
to right angles as possible.
•This line of echoes is displayed vertically on the screen.
•Each new line is displayed alongside the last one to show how the
position changes with time horizontally across the screen.
•The high temporal resolution of this technique allows quantitative
analysis of fast-moving structures such as heart valves and the heart wall,
which is hard to achieve with B-mode.

79. • Controls
They are designed to regulate the intensity of echos from various depths :
1.Time gain compensation
2.Delay
3.1ntensity
4.Coarse gain
5 . Reject
6. Near gain
7. Far gain
8. Enhancement

80. 1 .TIME GAIN COMPENSATION
• TGC amplifies the signal proportional to the time delay between
transmission and detection of US pulses.
• It amplifies and brings the signal in the range of 40-50 dB.
• This process compensates for tissue attenuation and makes all
equally reflective boundaries equal in amplitude irrespective of
depth.

81. 2. DELAY CONTROL : Regulates depth at which the TGC begins to augment
weaker signals
3. INTENSITY CONTROL Determines the potential difference across the
transducer. Increasing intensity produces more energetic ultrasonic beams and
thus stronger echoes at all level.
4. COARSE GAIN : Regulates the height of echoes from all depths
5. REJECT : It discriminate echoes below a minimum amplitude. Cleans up the
image by removing small useless signals.
6 NEAR GAIN CONTROL : Used primarily to diminish and not to enhance
near echoes.
8. FAR GAIN CONTROL : Used to enhance all distant echoes
9. ENHANCEMENT CONTROL : Augment a localised portion of TGC curve.lt
gates a specific depth and enhances echoes within the gate to any desired
level

82. .
Time gain compensation
On the right the gain has been corrected and the returning echoes are of
equal strength throughout.
On the left the far gain is too low and no echoes have returned from
the deeper tissues

83. Ultrasound Beam Profile
• Beam comes out as a slice
• Beam Profile
Approx. 1 mm thick
Depth displayed - controlled
• Image produced is "2D"
tomographic slice
Assumes no thickness
• You control the aim

84. Accomplishing this goal depends
upon...
■ Resolving capability of the system
-axial/ lateral resolution
-spatial resolution
-contrast resolution
-temporal resolution
■ Processing Power
— ability to capture, preserve and display the information

85. •Axial (or depth) resolution
•is the ability to separate two interfaces along the same scan line.
•If the interfaces are too close together, the echo pulses will overlap and be
recorded as a single interface.
•Axial resolution is about half the pulse length, so shorter pulses produce
better axial resolution.
•This can be achieved by:
•Greater damping (i.e., a low Q) achieved through use of a backing layer.
Increased frequency: keeping the number of cycles in a pulse constant, a
shorter wavelength will result in a shorter pulse

87. •Lateral resolution
• is the ability to separate two structures side-by-side
at the same depth.
•This depends on the beam width being narrower than
the gap
•The lateral resolution is measured perpendicular to
the direction of the ultrasound beam and depends on
the beam width which, in turn, depends on the
diameter of the PZT crystals and the focusing.
•To differentiate between two objects, you need at
least three beams to interact, one on each object and
then one in the space between the two objects.
•Lateral resolution is always worse than axial
resolution and it corresponds to ~1/3 of the

88. Slice resolution
is the ability to image a structure in a narrow plane, without
contribution from structures in adjacent planes.
This requires a narrow beam in the slice, or elevation, plane.
Poor slice resolution leads to partial voluming, which blurs
the edges of structures such as vessels and reduces visibility
of small lesions.
This is improved with physical focussing, or the additional
electronic focussing made possible in 1.5D/3D transducers.

89. •Temporal Resolution
• This is the ability of the system to display events occurring
at different times as separate images.
•It is measured in frames per second.
•It is reduced by:
1. Greater number of focal zones.
2. Having doppler on.
3. Deeper object (echo takes longer to reach object and
return) .
4. Large sector width (more space to scan)

90. Contrast Resolution
_ the ability to resolve two adjacent objects Of similor
intensity/reflective properties as separate objects dependant
on the dynamic range

91. Receiver
Another function of the receiver is compression of the wide range of amplitudes
returning to the transducer into a range that can be displayed to the user. The
range is called dynamic range of the transducer: Compression and remapping of
the data is required to adapt the dynamic range of backscattered signal intensity
to the dynamic range of display

92. Receiver dynamic range

93. ARRAYS
(TRANSDUCER
TYPES)

94. Linear Array
• The linear array scanners produce sound waves parallel to each other
and produces a rectangular image.
• The width of the image and number of scan lines are the same tissue
levels.
• This has the advantage Of good near field resolution.
• Often used with high frequencies i,E, 7mhz,
• There disadvantage is artifacts when applied to a curved part
of the body creating air gaps between Skin and transducer.

95. Sector/Phased array
Produces a fan like image that is narrow near the transducer and
increase in width with deeper penetration.
It is useful when scanning between the
ribs as it fits in the intercostals space.
The disadvantage is poor near field
resolution

96. Curved Array
• Often with frequencies of 2 - 5 MHz (to allow for a range of patients from
obese to slender).
• It is a compromise of the Linear and Sector scanners, The density of the
scan lines decreases with increasing distance from the transducer.
• Can be difficult to use in curved regions of the body eg- the spleen behind
the left costal margin.
• For abdominal ultrasound curved type scanners are used as the best
compromise of two other standard type probes the linear and the sector
scanner.

97. Annular Array
A series of concentric elements nested within one another in a circular piece
of piezoelectric crystal to produce an annular array.
Use of multiple concentric elements enables precise focussing-

98. Linear & Phased array
Linear array-individual elements or groups are fired in sequence
resulting parallel US beams
Phasic array: produce a sector field of view by firing multiple
transducer elements in precise sequence to generate interterence of
acoustic wave fronts

100. Transducer selection
In choosing a transducer frequency for a particular investigation, it is
necessary to compromise between the conflicting requirements of
penetration depth (which decreases) and image resolution (which
improves) as frequency is increased.
Typical figures are:
•1-8 MHz for general purpose abdominal and cardiac scanning
including liver, uterus, and heart.
•5-18 MHz for thyroid, carotid, breast, testis, and other superficial
tissues, and for infants .
•10-15 MHz for the eye, which is small and acoustically transparent
Higher frequencies still may be used in imaging the skin, vessel walls,
or joints

101. COUPLING AGENTS
• Commonly known as "GEL"
• Fluid medium needed to provide a link between the transducer and the
• patient
• Composition:
Carbomer — 10,0 gm
Propylene glycol — 75.0gm(72.4mI)
Trolamine — 12.5gm(11 ,2rnl)
EDTA — 0.25gm
Distilled water — upto 500gm or 500ml

102. IMAGE ARTIFACTS

103. • Artifacts are the errors in images produced by physical
processes that affect ultrasound beam.
• They are potential pitfalls that might confuse the examiner.
• Some artifacts provide useful information for novel
interpretation.

104. Reverberation
Reverberation artifacts appear as multiple equally lines along a ray line. Reverberation is caused by th bouncing
back and forth between tissue boundarie then returning to the receiver.

105. Figure.Ring-down artifact, (a) Diagram shows the main ultrasound beam encountering a
ring of bubbles with fluid trapped centrally, (b) Vibrations from the pocket of fluid cause
a continuous source of sound energy that is transmitted back to the transducer for
detection, (c) The display shows a bright rellcctor with an echogenic line extending
posteriorly, (d) Left lateral decubitus US image of the gallbladder shows air and fluid in
the duodenum causing ring-down artifact (arrow)
Ring down artifacts

106. Mirror Image Artifact
• This is where a strong reflector at an anale to the probe causes structures
that lie in front and to the Side of it to appear as if they lie behind it, just
as something viewed through a mirror appears to lie behind it.e.g.
diaphragm

107. Comet tail artifacts
• This is the same process as reverberation. but occurs within a very small Structure, with
smooth highly reflective borders, e.g. metal fragment.
• Tiny bright reverberations are seen deep to the structure slowly diminishing is size as if
had a tail

108. Refraction Artifact
This can lead to subtle miss placement of
structures and some degradation Of
image quality when the angle of
incidence is particularly acute.
Rectus abdominis acting as refracting
lens

109. Range Artifact

110. Side Lobe Artifacts
The probe cannot produce a pulse that travels purely in one direction.
Pulses also travel off at specific angles,
Side lobes may interact With Strong reflectors that lie outside the scan plane.
These side lobes are relatively weak and so normally do little to degrade the image.
Can be reduced by repositioning of the transducer .or its focal zone or using a
different transducer.

111. Acoustic shadowing
Marked reduction in the intensity Of ultrasound deep to a strong reflector or
attenuator
( other cause of loss of image information are improper system gain and
TGC setting. poor scanning angles and poor resolution)

112.  ACOUSTIC SHADOWING
• Tissues deeper to strongly attenuating objects like
calcification, appear darker because the intensity of
transmitted beam is lower.
Example:
Strong after shadowing due to gall stones.
Rib shadow
.

113. Acoustic enhancement
Due to high penetration of sound through a structure and then being reflected
from the tissue behind it

114. ENHANCEMENT
• Seen as abnormally high brightness.
• Occurs when sound travels through a medium with attenuation rate
lower than surrounding tissue.
Example:
 Enhancement of tissues below cyst or ducts.
 Tissues deeper to gall and urinary bladder.

115. Ovarian cyst-- false mural nodule
Multipath artifact
Echoes reflected (e.g. from diaphragm and wall of ovarian cyst) may create
complex echo path that delay return Of the reflected signal thus Showing
false deeper/abnormal position of the tissues

116. Speckle Artifact
Usual grainy appearance of the USG image Due
to random interference of the scatterer .
Interference pattern. Here is Simulated two
wave sources or scatterers at the far field
(white points).
Irregular interference pattern.
This is generated by more Scatterers
somewhat randomly distributed. The
speckle pattern is thus random too.

117. THANK YOU