4.Physics of Ultrasound.ppt

Physics of ULTRASOUND
Mr. Rohit Bansal
Assistant Professor
Department of Radio-Diagnosis
Maharaja Agrasen Medical College, Agroha

SOUND
• Sound is a mechanical energy which produces a
sensation of hearing,
• For hearing sound, following conditions must be
fulfilled.
• a vibrating body— capable of transferring its energy to
its surroundings.
• a material medium --- pick up the energy and propagate
it in the forward direction.
• a receiver– receive vibrations and then transmit to the
brain for final interpretation, such as human ear.

Types of sound
• Musical sounds : produced by regular and periodic
vibrations, pleasing to the ear. (e.g) piano or violin
music.
• Noise : produced by irregular and non-periodic
vibrations, unpleasant to the ear. (e.g) rattling of keys,
hammering of metal sheets.

Characteristic of wave motion
• Wave motion is a periodic disturbance which advances
forward with time. Such waves are called progressive
waves.
• Types (progressive) :
(i) Elastic waves
(ii) Electromagnetic waves
Types (elastic waves) :
(i) Transverse waves
(ii) Longitudinal waves

• Transverse waves : The particles vibrate perpendicular to
the direction of propagation of the wave.
Characteristics : (i) crest
(ii) trough
• Crest : Maximum displacement of the particles in the
upward direction.
• Trough : Maximum displacement of the particles in the
downward direction.

• Longitudinal waves : The particles vibrate along the
direction of propagation of wave.
• Characteristics : (i) compression
(ii) rarefaction
• Compression : The region in which energy is imparted to
the air molecules which, in turn, get compressed and thus
forming a region of high pressure and high density.
• Rarefaction : The fall in pressure causes the molecules in
these region to move apart, with the result a region of
rarefaction is formed.

Images of compression and
rarefaction

Terms of wave motion
• Amplitude : The maximum displacement of a vibrating
particle about its mean position.
• Frequency : The number of vibrations produced by a
vibrating particle in one second.
• Wave length : The linear distance between two
successive crests or troughs.
• Time period : The time taken for one complete vibration.

Relation
• Relation between wave
velocity, frequency and
wavelength is given by
c = f λ
• Relation between
frequency and time
period T = 1/f

• Sound are longitudinal waves consisting of compression
and rarefaction.
• Sound requires material medium for propagation.
• Sound wave travels with a velocity of 330m/s at normal
temperature.

Factors affecting the velocity of sound
• Temperature : With every 1K(or 1°C) rise in
temperature, the speed of sound increases by 0.6 m/s
and vice versa.
• Humidity : With the increase in humidity, the speed of
sound increases.
• Wind : Sound travels faster if the wind is blowing along
its direction of travel.

• State of matter :
Sound travels faster
in solids, slower in
liquids and slowest in
gases.
Material Velocity of
sound m/s
iron 5,000
bone 4,100
Soft tissue 1,540 (Av.)
water 1,480
fat 1,450
air 330

Factors not affecting the velocity of
sound in gases
Wavelength
Frequency
Amplitude
Pressure

Range of hearing
• The range of audible frequencies to which human ear
can respond is from 20Hz to 20,000Hz.
• Vibrations with frequencies beyond 20,000Hz are called
ultrasonic vibrations. e.g squeak of bat, dog whistle
• Vibrations with frequencies below 20Hz are called
infrasonic vibrations. e.g vibration of a pendulum.

History of Ultrasound
• Piezoelectricity discovered by the Curies in 1880 using
natural quartz.
• Diagnostic Medical applications in use since late1950’s.
• The technical term for ultrasound imaging is
sonography.
• Ultrasound technology was originally developed as
SONAR to track submarines during World War I in
1940’s.
• It was first used medically in 1950s and is considered
very safe.

Ultra Sound
• The sound of frequencies above 20,000 Hz is called
ultrasound, which can not be detected by the human air.
• The velocity of ultrasound depends on the nature of the
medium and is independent of frequency.
• Ultrasound travels faster in solids and slower in gases.
• The average velocity of ultrasound in soft tissue is 1540
m/s.

Properties of ultrasound
Audible sound does not have the following properties
• The energy carried by the ultrasound is very high.
• The ultrasound can travel along a well defined straight
path.
• It does not bend appreciably at the edges of an obstacle
i.e., they have high directivity.

Ultrasound similar to echolocation
• Ultrasound or ultrasonography is a medical imaging
technique that uses high frequency sound waves and
their echoes.
• The technique is similar to the echolocation used by bats,
whales and dolphins, as well as SONAR used by
submarines.

Bats
• Bats use ultrasounds to
move in the darkness.
• Bats use a variety of
ultrasonic ranging
(echolocation) techniques
to detect their prey.
• They can detect
frequencies from 10Hz to
100kHz

Cats
• Cats can hear sound at
higher frequencies than
humans can.
• They can detect
frequencies from 80Hz
to 60kHz

Dogs
• A dog whistle exploits
this by emitting a high
frequency sound to call
to a dog.
• Many dog whistles, such
as the silent whistle,
emit ultrasound at a
frequency in the range
18–22 kHz.
• They can detect
frequencies from 20Hz
to 50kHz

Dolphins and whales
• Some whales can hear
ultrasound and have their
own natural sonar
system.
• Some whales use the
ultrasound as a hunting
tool (for both detection of
prey and as an attack).
• Dolphins can detect
frequencies from 200 Hz
to 150 kHz

Grasshopper
• They can detect
frequencies from 90 Hz to
1.0 kHz

Fish
• Several types of fish can
detect ultrasound. Of the
order Clupeiformes,
members of the
subfamily Alosinae
(shad), have been shown
to be able to detect
sounds up to 180 kHz,
while the other
subfamilies (e.g. herrings)
can hear only up to
4 kHz.

Human
• Children can hear sounds
of some what higher
frequencies up to 30kHz.
• Old person can hear
sound up to frequencies
12 kHz.
• Hence the audible range
of frequency for an
average person is
considered to be from 20
Hz to 20 kHz.

Ultrasound Production
• Ultrasound waves are produced by a transducer, which works on
the piezoelectric effect.
• Piezoelectricity from the Greek word "piezo" means pressure
electricity.
• The main component of the transducer is the piezoelectric crystal
such as quartz and lead ziroconate titanate (PZT), PVDF
(Polyvinyldifluoride).
• When the crystal is subjected to a given pressure, it develops a
voltage across its opposite surface.
• If a voltage is applied across the crystal, a pressure wave
(ultrasound) is generated in the opposite surface.
• The crystal converts electrical energy into ultrasound and vice versa.

Transducer
• Transducer is a device that convert one form of energy
into another.
• Ultrasonic transducers are used to convert an electric
signal into ultrasonic energy that can be transmitted into
tissues, and to convert ultrasonic energy reflected back
from the tissues into an electrical signal.

• The source of high
frequency current is
conveyed by the
coaxial cable to a
transducer.
• The current is applied
to the crystal through
electrodes.
• The crystal vibrates
due to piezo electric
effect and produces
ultrasound.

• The most important component is a thin piezoelectric
crystal (0.5mm) located near the face of the transducer.
• The front and back faces of the crystal are coated with a
thin conducting film to ensure good conduct with the two
electrodes that will supply the electric field.
• The surfaces of the crystal are plated with gold or silver
electrodes .

• The outside electrode is grounded to protect the patient
from electrical shock, and its outside surface is coated with
a watertight electrical insulator.
• The (Inside electrode) thick backing block absorbs sound
waves transmitted back into the transducer.
• The housing is usually a strong plastic.
• An acoustic insulator of rubber or cork prevents the sound
from passing into the housing.

The Ultrasound Machine
• 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

Medical use of ultrasound
• Ultrasound is a procedure that uses high-
frequency sound waves to view internal
organs and produce images of the human
body.
• Noninvasive, which means it does not
penetrate the skin or body openings.
• Diagnostic, which means it is used to
determine what disease or condition is
present .
• The original ultrasound scanners produced
still images, but modern scanners produce
moving pictures, which are easier to
interpret.

Working
• The ultrasound machine transmits high-frequency (1 to
20 megahertz) sound pulses into your body using a
probe.
• The sound waves travel into your body and hit a
boundary between tissues (e.g. between fluid and soft
tissue, soft tissue and bone).
• Some of the sound waves get reflected back to the probe,
while some travel on further until they reach another
boundary and get reflected.

• The reflected waves are picked up by the probe and
relayed to the machine.
• The machine calculates the distance from the probe to the
tissue or organ (boundaries) using the speed of sound in
tissue (5,005 ft/s or1,540 m/s) and the time of the each
echo's return (usually on the order of millionths of a
second).
• The machine displays the distances and intensities of the
echoes on the screen, forming an image.
• In a typical ultrasound, millions of pulses and echoes are
sent and received each second. The probe can be moved
along the surface of the body and angled to obtain various
views

• Ultrasound image of a
growing fetus (approximately
12 weeks old) inside a
mother's uterus. This is a side
view of the baby, showing
(right to left) the head, neck,
torso and legs

Advantages
• Ultrasound is a painless procedure.
• Ultrasound is widely available, low cost and easy to use.
• Because it does not use radiation, the side effects of
radiation are not an issue.
• So, ultrasound is the preferred technique for monitoring
pregnant women and their unborn children.

• Ultrasound can display the movement and actual
function of the body's organs and blood vessels.
• There are no known harmful effects of standard
ultrasound imaging.
• The main limitation of ultrasound imaging is that it does
not reflect clearly from bone or air.
• Therefore, other imaging techniques are preferred for
areas such as the lungs and the bones.

• Ultrasound has been used in a variety of clinical
settings, including obstetrics and gynecology,
cardiology and cancer detection.
• The main advantage of ultrasound is that certain
structures can be observed without using radiation.
• Ultrasound can also be done much faster than X-rays
or other radiographic techniques.

Disadvantages of ultrasound compared
with other techniques
• 1. The major disadvantage is that the resolution of images is often
limited.
• This is being overcome as time passes, but there are still many
situations where X-rays produce a much higher resolution.
• 2. Ultrasound is reflected very strongly on passing from tissue to
gas, or vice versa.
• This means that ultrasound cannot be used for examinations of
areas of the body containing gas, such as the lung and the
digestive system.
• 3. Ultrasound also does not pass well through bone, so that the
method is of limited use in diagnosing fractures. It is possible to
obtain quite good ultrasound scans of the brain, but much greater
detail is obtained by an MRI scan.

Diagnostic Ultrasound X-rays
(radiology)
wave type longitudinal mechanical
waves
electromagnetic waves
transmission
requirements
elastic medium No medium
generation stressing the medium accelerating electric
charges
velocity
depends on the medium
through which it
propagates
It is relatively constant:
299,792.456.2 m/s
similar waves seismic, acoustic radio, light

Acoustic Impedance
• It is the product of density and velocity of sound in that
material.
• Acoustic impedance = density × velocity
• Both density and velocity are independent of frequency.
• It depends only on tissues mechanical properties
• Unit of acoustic impedance is Rayl which is 1 × 10-5
g/cm2sec.
44

• The amount of reflection is determined by the difference
in the acoustic impedance of two tissues.
• The greater the difference, the greater the percentage
reflected.
• Note that the difference between most body structures is
fairly small, the two exceptions being air and bone.
• A soft tissue-air interface reflects almost the entire beam,
and a soft tissue-bone interface reflects a major portion
of it. The sum of the reflected and transmitted portions is
100%. For example, if 90% of a beam is reflected, 10%
will be transmitted.
• At a tissue-air interface, more than 99.9% of the beam is
reflected, so none is available for further imaging.
45

• Transducers, therefore, must be directly coupled to the
patient's skin without an air gap.
• Coupling is accomplished by use of a slippery material
such as mineral oil for contact scanning or by a water
bath when the transducer cannot be placed directly on
the patient.
• The velocity of sound in tissue is fairly constant over a
wide range of frequencies, so a substance's acoustic
impedance is a constant.
• In the SI system we must express the velocity of sound
(v) in units of meters per second (m/s) and density (p) in
units of kilograms per cubic meter (kg/m3).

Acoustic Impedance
Tissue Velocity Acoustic
impedance
Bone 4080 7.8
Blood 1570 1.61
Fat 1450 1.38
Kidney 1560 1.62
Liver 1550 1.65
Soft Tissue 1540 1.63
Air 330 0.0004
47

Ultrasonography
• Sound production
• Tissue interaction
• Echo reception
• Image formation
48

Sound production
• Sound waves are produced by a device known as
transducer.
• A transducer is a device that can convert one form of
energy to other.
• Ultrasonic transducers convert an electric signal to
ultrasonic energy and convert reflected ultrasonic
energy into electric signal.
• The most important component of a transducer is a
piezoelectric crystal. (Piezoelectric effect first described
by Pierre and Jacques Curie in 1880).
49

• Piezoelectric crystal is a pure form of multiple diodes arranged
in a specific orientation.
• Natural Piezoelectric crystal is quartz.
• Man made piezoelectric crystal is Lead, Zirconate and Titanate
(PZT).
• Nowadays, all ultrasound transducers use PZT crystal.
• Great advantage of piezoelectric crystal is that they can be
formed into different shapes, depending on the application for
which they are intended.
• When current of a particular polarity is applied to the dipoles, it
changes its orientation and lie in a new orientation resulting in
the change in shape of the crystal.
• When polarity of current is reversed, dipoles change their
orientation again, causing the change in the shape of crystal
again.
• When the polarity of current is reversed rapidly, crystal change
its shape rapidly, producing the sound waves of high frequency.

Interaction between ultrasound
and matter
• Interaction between ultrasound and matter are similar
to those of light and include :-
1. Reflection
2. Refraction
3. Absorption
54

Reflection
• In x-ray imaging, the transmitted radiation blackens the
film and creates the actual image. Attenuated radiation
creates defects or holes in the transmitted beam,
contributing to image formation in a passive way. Scattered
radiation fogs the film and is detrimental to image quality.
• With ultrasound, however, the image is produced by the
reflected portion of the beam. Transmitted sound
contributes nothing to image formation, but transmission
must be strong enough to produce echoes at deeper levels.
• Reflection depends upon:
1. Tissue acoustic impedance : greater the difference in
impedance of two tissues greater is the reflection.
2. Beam’s angle of incidence: the higher the angle of
incidence, the less is the reflected sound.
55

Refraction
• The bending of waves as they pass from one medium to
another.
• When sound passes from one medium to another, its
frequency remains constant but its wavelength changes
to accommodate a new velocity.
• Refraction can cause artifacts. Refraction artifacts cause
spatial distortion (real structures are imaged in the
wrong location) and loss of resolution in the image.
56

Absorption
• It refers to the conversion of ultrasound energy to
thermal energy which is the result of functional forces
that oppose the motion of particle in the medium.
• Three factors determine the amount of absorption:
1. The frequency of sound
2. The viscosity of conducting material
3. Relaxation time
57

Curie Temperature
• The dipoles of the piezoelectric crystals are arranged in a
specific geometric configuration by heating the ceramic to a
high temperature in a strong electric field.
• The temperature at which the dipoles are free to move and the
electric field brings them to desired alignment.
• The crystal is then gradually cooled while subjected to a
constant high voltage. As room temperature is reached, the
dipoles become fixed, and the crystal then possesses
piezoelectric properties.
• The temperature at which this polarization is lost is called
curie temperature.
• Quartz 573 degree Celsius
• Barium Titanate 100 degree Celsius
• PZT-4 328 degree Celsius
• PZT-5A 365 degree Celsius 59

Ultrasonic Gel
• Ultrasound gel is a type of conductive medium that enables a tight
bond between the skin and the probes or transducer, letting the
waves transmit directly to the tissue.
• It is used to remove air gap between transducer and skin. The
presence of air reflets all the sound waves back to transducer.
• The purpose of the ultrasound gel is the sound emitted by the
transducer has to penetrate into the body, where echo's off to various
structure.
• The reflected sound waves then propagate out of the body where the
transducer receive them.
• Without the gel, sound wave have to pass through a layer of air on
the way in, and again on the way out.
• the gel conduct the sound waves/signals much better than air, so
transducing the sound waves through the gel into and out to the
body results in a much clear image, due to better transmission of
sound. 60

Ultrasonic Gel
• Properties of ideal ultasound gel:
1. Salt free.
2. Water soluble.
3. Non-greasy.
4. Non-Corrosive.
5. Non-Irritant.
6. Alcohol Free.
7. Proper Viscosity.
• Component of ultrasound gel:
1. Water
2. EDTA
3. Anti-Microbial Agents: Anti bacterial (Methyl chloride Isothiazolinone),
Anti Fungal (Imidazolinyl Urea).
4. Propylene Glycol
5. Sodium hydroxide (NaOH)
6. Blue Pantane 61

Resonant Frequency
• An ultrasound transducer is designed to be
maximally sensitive to a certain natural
frequency. The thickness of a piezoelectric
crystal determines its natural frequency, called
its "resonant frequency.“
• Crystal thickness is analogous to the length of a
pipe in a pipe organ. Just as a long pipe
produces a low-pitched audible sound, a thick
crystal produces a low-frequency ultrasound.
62

Transducer Q Factor
• It refers to two characteristics of piezoelectric crystal.
a) purity of sound
b) length of the time that sound persists
• A high-Q transducer produces a nearly pure sound made up
of a narrow range of frequencies, whereas a low-Q transducer
produces a whole spectrum of sound covering a much wider
range of frequencies.
• Almost all the internal sound waves of a high-Q transducer
are of the appropriate wavelength to reinforce vibrations
within the crystal.
• When an unsupported high-Q crystal (i.e., a crystal without a
backing block) is struck by a short voltage pulse, it vibrates
for a long time and produces a long continuous sound.) The
interval between initiation of the wave and complete
cessation of vibrations is called the "ring down-time." 63

Echo Reception
• The same transducer acts as the receiver.
• When returning echoes strike the transducer face,
minute voltages are produced across the piezoelectric
elements.
• The receiver detects and amplifies these weak signals.
• The time gap between transmission of sound and
reception of echo determines the depth of organ in the
image.
• The brighness of organ will be determined by the
strength of pulse.
64

Image Formation
• Electric signals produce dots on the screen
• Brightness of dots is proportional to the strength of the
returning echoes
• Location of dots is determined by the travel time
65

Resolution
• It is the ability of beam to separate two objects
• Depth Resolution : It is ability of beam to separate two
objects lying in tandem along the axis of the beam
• Two objects will be resolved if the spatial pulse length is
less than twice the separation.
67

Spatial Resolution
• Spatial resolution of any imaging system is defined as its
ability to distinguish two points as separate in space.
• Spatial resolution is measured in units of distance such
as mm. The higher the spatial resolution, the smaller the
distance which can be distinguished.
• Spatial resolution is commonly further sub-categorized
into axial resolution and lateral resolution.

Axial Resolution
• Axial resolution also known as longitudinal, depth or
linear resolution refers to the ability of an ultrasound
system to resolve objects in close proximity to each other
along the direction of beam.
• Axial resolution depends on the effective length of the
transmitted pulse.
• The minimum distance between two axial point targets
that can be resolved can be obtained as:
Xmin=VT/2
• Where V= Velocity of ultrasound propagation.
• T= Effective duration of the interrogating ultrasound
pulse along the time axis, thus, shorter pulses will lead
to better resolution.

Lateral Resolution
• Lateral resolution refers to the ability to resolve two
closely lying objects along the beam direction.
• Lateral resolution depends on the narrowness of the
beam in the lateral direction.
• Use the thinnest beam possible to get the best resolution.
• The beam lateral thickness is proportional to the wave
length of the ultrasound- the smaller the wavelength
(The higher the frequency) better resolution.
• Larger transducer also produce thinner beams.

Reverberation Echoes
• The returning echoes from the second surface reflect off
the back surface of first surface & initiate a third echo ,
the transducer interpret as an other object , the three
surfaces are displayed with third being a reverberation
image.
72

Focused Transducer
• They restrict the beam width and improve lateral
resolution. They are designed to focus the beam at a
specific depth or depth range.
• Sonic beams can be focused with either a curved
piezoelectric crystal or with an acoustic lens which is
made of polystyrene or epoxy resin.
73

Near Zone
• Fresnel zone or near field, is adjacent to the transducer
face, in which the beam is drawn as a parallel bundle for
a certain distance, beyond which it disperses.
• Length of near zone= r square/4L.
• r square= diameter of crystal/transducer.
• Higher frequency and larger diameter always provide
longer near field length.

Far Zone
• Also known as Fraunhofer zone.
• It is the area where ultrasound beam begins to diverge.
• Divergence starts after near zone, angle of divergence is
given by 1.22 L/d.
• Less beam divergence occurs with high frequency and
with large diameter.
• The US intensity decreases with distance.

Transducer selection
• Real time scanners can be classified according to how
they form the beam (focusing) and how the beam is
steered (scanned) to form the beam.
• Mechanical scanner:-
o They have a single element or group of elements.
o Transducer is mechanically moved to form the image
in real time.
o The images are in sector format encompassing an arc
between 45 degree to 90 degree.
o Decrease the sector angle increase the resolution of
image. 78

 Oscillating transducer
a) Unenclosed crystal
b) Enclosed crystal
1. Unenclosed Crystal: In this a single transducer crystal
is made to oscillate through an angle (15-60 degree) at a
frame rate of 15-30/ second, which depends on the rate
of oscillation.
2. Enclosed Crystal:
 In this the transducer is enclosed in oil or water filled
container and is driven by a motor of electromagnet.
 The type of image produced depends on the distance
between the transducer and the front surface of the
casing.
 If near, a sector image is produced, if distance is more,
a trapezoid image is produced.

 Rotating wheel transducer:-
 It employs 3 or 4 transducers that are mounted 120 or
90 degree apart on a wheel of diameter 2 and 5 cm.
 The wheel is rotated by an external motor.
 This design allows for rapid framing without flicker,
typically at a rate of 30 or more frames per second
 Depending on design it produces a sector or Trapezoid
shaped field of view.
81

Advantages of mechanically steered transducers
• Requires less sophisticated electronics
• Image artifacts due to side lobes and grating lobes are
less
Disadvantages
• The beam focus and beam pattern are fixed, to change
focus transducer has to be changed.
• Image framing rate depends upon how rapidly the
transducer is oscillated. The framing rate may become
quite low when larger field of view is chosen
83

Electronic array scanning
• Included in this category are:
1. Multi element linear sequenced array scanners
2. Linear phased array scanners
3. Phased array scanners
84

Multi element linear sequenced
array transducers
• Transducer array is composed of many (usually 128 or
256) small piezoelectric elements arranged in a row.
• They are pulsed so as to produce a wave front that
moves normally to the face of the transducer ,yielding a
rectangular field of view
85

Linear phased array transducers
• In these rectangular transducer element are arranged in
a line with their narrow dimension ion contact.
• There are 64-200 transducer forming an array 4-10 cm
along at a frequency of 2-10 MHz.
• The tranducer element are usually pulsed in group of 4
at slightly different times to achieve a focused image.
• The scan from a linear array transducer are rectangular
in format.
• linear array transducer are especially useful in obstetric
scan and in scanning of breast and thyroid.
• Referred to as electronic Sector scanners.
86

Phased array scanners
• These are used for real time scanning.
• By electronically controlled steering and focusing the
ultrasound beam is made to sweep back and fourth across
the patient.
• A typical transducer contains 32 elements and operates at
a frequency of 2-3 MHz.
• In this all the elements are pulsed to form each line of the
image as against linear array transducer in which only a
few elements (typically 4) from each line of the image.
• The scan obtained are fan shaped or sector shaped.
• This is of advantage when scanning is to be done through
very small acoustic window as in upper abdomen,
gynocological and cardiological examination.
88

Convex Transducer
• The scans produced from convex transducer are
midway between those from linear and sector
scanners.
• Convex transducers of 3.5 MHz and focus of 7-9
cm are best for general purpose ultrasound
examinations.
• In case of thin adults or children 5 Mhz transducer
with a focus of 5-7 cm is ideal. this cann’t be used
for electrocardiography.

On the basis of shape and use
• Sector Transducer
• Linear Transducer
• CurvilinearTransducer

Sector Transducer
• The crystal elements are arranged in a convex row.
• The image formed by this transducer is Trapezoid
in shape and it covers wide area.
• It has the lowest frequency 3-5 MHz and therefore
has highest penetration.
• The spatial resolution is poor in sector transducer.
• E.g. Used in Abdomen and Pelvis.

Linear Transducer
• This transducer has linear arrangement of PEC
elements.
• The resulatant image is rectangular in shape.
• It’s frequency is intermediate (7.5-10 MHz).
• It convert limited area and has intermediate
penetrating power.
• The spatial resolution is better than sector
transducer.
• It is used in Brain, Neck, Buccal mucosa, Orbits,
Superfical muscles and ligaments, Breast, Scrotum
Etc.

Curvilinear Transducer
• It has a highest frequency (10-15 MHz).
• It is thin and long in shape and has semicircular
arrangement of piezoelectric crystal element.
• It covers the widest area and has best spatial
resolution but least penetration.
• So, it can be used for only superficial organs, such as
internal organs, adjoining cavities.
• Used in transvaginal- To see cervix, uterus and
fallopian tubes.
• Used to see prostate gland.

Transducer selection
• The highest ultrasound frequency permitting
penetration to the depth of interest should be selected.
94

High Frequency Transducer
• Good resolution
• Poor penetration
Low Frequency Transducer
• Poor resolution
• Good penetration
96

• For superficial vessels and organs such as thyroid,
breast, or testicle lying within 1-3 cm of the surface,
imaging frequencies of 7 to 15 MHz are generally used
• For evaluation of deeper structures in the abdomen or
pelvis more than 12 or 15 cm , frequencies as low as 2.25
to 3.5 MHz may be required.
97

• 2.5 MHz- Deep Abdomen, Obstetric and Gynecological
imaging.
• 3.5 MHz- General Abdomen, Obstetric and
Gynecological imaging.
• 5.0 MHz- Vascular, Breast and Pelvic Imaging.
• 7.5 MHz- Breast and Thyroid.
• 10 MHz- Breast, Thyroid, Superficial veins, Superficial
masses, Musculoskeletal imaging.
• 15 MHz- Superficial structures, Musculoskeletal
imaging.

ULTRASONIC DISPLAY
A MODE
• The probe is held stationary, and pulses of nanosecond
duration is sent into the patient, and echo is generated.
• Echoes are displayed as spikes projecting from a baseline.
• The base line identifies the central axis of the beam
• Spike height is proportional to echo intensity, with
strong echoes producing large spikes.
• Used in ophthalmology-distance measurements,
echoencephalography, echocardiography, examinations
of the eye, detecting a cysts in the breast, studying
midline displacement in the brain, etc.
99

TM Mode
• The spikes are represented as dots displayed along a
vertical base line
• Location of dots is an indicator of depth
• Brightness of dots is proportional to the strength of
returning echoes
• Horizontal base line is an indicator of time
• It provides excellent temporal resolution of motion
patterns
• Its application includes evaluation of cardiac value
motion and other cardiac anatomy. Real-time 2D
echocardiography, Doppler and color flow imaging
101

B Mode
• It produces a picture of a slice of a tissue.
• Echoes are displayed as dots
• The transducer is moved so that the sound beam transverse a
plane of the body
• B mode is the basis for all static and real time ultrasound.
• Echoes are displayed as dots, and brightness is proportional to
echo intensity
• Thus, thousands of echo signal strengths of varying brightness
of points gives grey scale image.
• The image displays a section of an anatomy.
• The image depth depends on transducer frequency, focus, etc.
• The B-mode scanning is usually done with electronic scanning
either with linear array or phased array
103

B mode
• Static
– Transducer moved manually over an area to produce
image
– Scan of each area produces a line
– All lines are added to form an image.
104

B Mode
• Real time
– Real time is the dynamic presentation of multiple
image frames per second over selected areas of body.
– Crystals within the transducer sweep the beam over
an area automatically
– The lines produced are added together to form the
image
– Updating of image is rapid and continous
106

Biological Effects of USG
• Ultrasound is the safest of the main medical imaging
modalities.
• The biological effects of ultrasound refers to the adverse
effects of the imaging modalities has on human tissue.
• These are primarily two main mechanism:
1. Thermal Effects
2. Mechanical Effects.
• Despite this, ultrasound has a remarkable record for
patient safety with no significant adverse biological
effect recorded.

Thermal Effects
• Due to the law of conservation of energy, all of the
sound energy attenuated by tissue must be converted to
other forms of energy. The majority of this is turned into
heat.
• As such, it is possible for ultrasound to raise tissue
temperature to up to 15 degree C.
• For sensitive tissue (e.g. Fetal) this rise in temperature
may have significant effects, it present for an extended
period of time.
• The thermal index ‘T’ is the ratio of the power produced
by the transducer to the power required to raise a tissue
in the beam by 1 degree C.

Thermal Threshold Temperature
Physiological Level 37° C – Safe Region
Embryonic Level 39.5° - Risk Factor Obstruction Pediatrics
Adult Tissue 41° C – General Risks

Mechanical Effects
• The mechanical bio effects of ultrasound refers to damage
caused by the actual oscillation of the sound wave on tissue.
• The most common is referred to as cavitations and is caused
by the oscillation of small gas bubbles within the ultrasound
field.
• In certain circumstances, these bubbles may energies to
adjacent tissue. This can increase tissue temperature more
than 1000° C.
• In general biological risks depends on:
1. Physical characteristics of the sound wave (Mode, intensity
and Frequency).
2. Sensitivity of the tissue examined to ultrasound action (Size,
Structure and Attenuation)

Safety Aspects of USG
• Selects transducer of appropriate type and frequency.
• Adjust the output power at the lowest possible setting to
produce an image.
• Adjust the focus to the area of interest.
• The choice of B-mode, M-mode or Doppler greatly
affects the energy absorbed by the tissue.
• Set the Doppler output at the lowest level to produce a
clear signal.
• Care must be taken when doing Doppler in obstetrics
patients or Fetal Doppler, especially in 2nd and 3rd
trimester.

Ultrasound Machine Controls
• The number and intensity of echoes from any particular
area are extremely variable and setting the scanner to
demonstrate one area optimally frequently detracts from
image quality in other area. Multiple controls are built
into ultrasonic machines to regulate the intensity of
echoes from various depths
113

The various controls are
• Power
• Gain
• Reject
• Time Gain Compensation
114

POWER
• Modifies the voltage applied to pulse the crystal
• Increases the intensity of sound output
• Uniform increase in strength of returning echoes
• Excessively high settings will cause artifacts
• 40-80% is recommended
115

GAIN
• Amplification of returning echoes
• Uniform increase in strength of returning echoes
• Excessively high settings will cause artifacts
• 40-80% is recommended
116

REJECT
• Uniform elimination of weaker signals which do not
contribute to image formation
• Increasing reject will eliminate stronger and stronger
and stronger echoes
• Excessive reject will eliminate echoes which do
contribute to image formation
117

Time Gain Compensation
• Amplification of returning echoes
• Graded increase in strength of returning echoes
• The longer the echo return time the greater the
amplification
• Near echoes are minimally (if at all) amplified
• Far echoes are greatly amplified
118

TGC CONTROLS
• Near gain
• Slope delay
• Slope rate
• Far gain
120

ADVANCEMENTS IN ULTRASOUND
DOPPLER ULTRASOUND
•The Doppler effect is a change in the perceived
frequency of sound emitted by a moving source.
•It was first described by CHRISTIAN JOHNN
DOPPLER in 1843.
-Doppler techniques are used to study motion primarily
that of the circulatory system
•Doppler mode is an audio mode .
•Two transducers are used, one as a transmitter and
one as a receiver
123

• Ultrasound beam is reflected by clumps of moving RBCs
within the blood vessels
• The resulting change in the sound frequency is
measured to determine the direction and velocity of
blood flow.
• Doppler Shift : difference in sound frequency between
the ultrasound beam transmitted into tissue and echo
produced by reflection from the moving RBCs
124

Doppler ultrasound is a noninvasive test based upon the
Doppler effect.
The Doppler effect is used in ultrasound to examine the
movement of blood.
When the ultrasound is reflected from a moving surface of
blood cell, the frequency of the ultrasound is changed.
The change in frequency depends upon the velocity of
moving objects. If the object is moving towards the
transducer, it creates high frequency, and if the object is
moving away from the transducer, it creates a low
frequency.
The Doppler ultrasound measure the rate of blood flow by
calculating the frequency of reflected echo and image is
displayed on monitor.

• Doppler Angle : The doppler beam intercepts moving
blood within a vessel at an angle called doppler angle
• Doppler Equation : the amount of frequency shift is
proportional to the frequency of the moving RBCs .
127

• According to Doppler equation
• FD is the frequency shift .
• F0 is the transmitted frequency in MHz.
• C is the velocity of sound in the tissue.
• V is moving blood cell velocity.
• α(θ)-the angle between the sound beam and direction of
blood flow
 Doppler Shift= 2*velocity of blood*Transducer
frequency*Cos θPropagation velocity of sound.
128

Continuous wave Doppler
• Simple and least expensive device for measuring blood
velocity.
• 2 transducers are used one for transmitting U-S waves &
one for receiving it continuously, enabling the measurement
of high velocity blood flow.
• Sometimes, only one transducer is act as transmitter and
receiver.
• The recorded echoes are amplified and its frequency is
compared with incident frequency , to estimate the Doppler
shift.
• An audio amplifier converts the Doppler shift frequency to
an audible sound..
• No anatomical image formed.
• Ultrasound is always on. 129

Advantages Of Continuous Doppler
• Simple and inexpensive
• Good quality image, low noise.
• No aliasing.
• No practical limit of velocity to be measured
130

Disadvantage of CWD
• Lack of depth resolution.
• Sensitive to weak signals.
• Confined to examination of more superficial structures
131

• For superficial structures like carotid artery and limb
vessels.
• Useful for examination of arteries of eyes and breasts.
• To monitor foetal heart sound
132
Application of CWD

Pulsed Doppler
• It allows both velocity and depth information to be obtained (pulse-
echo).
• Single transducer is used.
• Doppler information is only provided for a selected area (electronic
gate) specified by a operator (Signal from particular depth can be
detected).
• After transmission, the transducer is turned on for a specific period
of time over the gate and receives signals that are originating from a
specific tissue depth and collect the signals and reject all other
signals.
• Short bursts of ultrasound waves are given for 0.5 to 1 micro sec. at
precise rate .
• The operator can vary the gate position, to select Doppler signals
from any depth, along the axis of transducer.
• Repetition frequency = 8-15 MHZ.
133

Advantages of PWD:
• Identification of source to signal possible.
• Blood flow information from ranges gate (Depth
information)
134
Disadvantages
Background noise.
Aliasing.

Application of Pulsed Wave Doppler
• Diastolic function.
• Right ventricular function.
• Renal artery.
• Abdominal aortic velocities.
• Carotid artery imaging.

Duplex Scanner
• It refers to the combination of 2D B-Mode imaging
(Visual guidance) and pulsed Doppler data acquisition.
• In this system, the real time image of the anatomy of
interest is taken first and the image is frozen in viewing
screen.
• Then, the Doppler mode is switched on, the operator
mark the position & location of the signal on the frozen
image.
• Thus, the system allows velocity and position
information and gives visual display of anatomy.
• Multiple gates can be operated with several parallel
channels, hence Doppler signal consists of spectrum of
frequencies (Doppler spectrum) within the sampling
gate for a given time.
• The video monitor display the spectrum below the B-
mode image, as a moving trace, which is known as
Doppler spectrum.
136

• ADVANTAGES:
1.Selection of site and sample volume for
Doppler.
2.No overlap of information from other
vessels/structures.
3.Beam vessel angle can be measured.
• DISADVANTAGES:
1.Blood vessel’s angle is restricted.

Doppler Color-flow Imaging
• Color flow imaging provides a 2D visual display of
moving blood in the vessels, which is superimposed
upon the conventional gray scale image.
• Blue and red color are assigned, depending on motion
towards or away from the transducer.
• BART= Blue away, Red towards
• Turbulent flow can be displayed as green or yellow.
• Color intensity varies with flow intensity.
• Spatial resolution of color image is much lower than that
of gray scale image.
• Mainly useful in imaging of valves & chambers of heart,
carotid, cardiac arteries or veins.
138

Advantages of Color Doppler
• Visual determination of flow direction.
• Improved definition of lumen.
• Small vessels on gray scale image can be seen.
• Improved definition of stenosis.
• Images of surrounding tissue is also obtained.
139

Limitations:
• Color out everything.
• High cost.
• Don’t give detailed study.
• Artifacts caused by noise.
• Limitation of slow blood flow.
140

Power Doppler
• Power Doppler is a signal processing method that relies
on the total strength of Doppler signal (amplitude) and
ignores directional information.
• It does not provide any information related to flow
direction and velocity.
• Power mode Doppler permits noise to be assigned to a
homogeneous background color that does not greatly
interfere with the image .
• It results in higher effective gain settings for flow
detection and increased sensitivity for flow detection
141

• ADVANTAGES:
1. No aliasing.
2. Angle independent.
3. Increased sensitivity to detect low velocity flow.
• DISADVANTAGES:
• Do not provide velocity of flow.
• Do not provide direction of flow.

Real time ultrasound
• Imaging system fast enough to allow movement to be
studied .
• Unlike B- mode 10 frames per second are obtained
• Thus structures are visible as they change position in
time to produce real time image
• It permits assessment of both anatomy and motion
• Types
1. Mechanical scanner.
2. Electronic scanner.
MAJOR APPLICATIONS IN CARDIAC IMAGING &
VESSEL PULSATIONS IN ABDOMINAL IMAGING
143

Role Of Ultrasound In
Interventional Procedures
• Main role of ultrasound is in FNAC i.e. Fine Needle
Aspiration Cytology.
• FNAC has got wide acceptance in clinical practice
because of:
• Simplicity.
• Safety.
• Accuracy.
144

• Modalities like CT and ultrasound help in accurate
placement of needle in deep seated cancer in
various interventional procedures like PTBD, PTC
etc
145

Advantages In Intraventional
Procedures
• Accurate.
• Expeditious.
• Needle visualization.
• Real time control.
• Portable.
• Inexpensive.
• Major disadvantage is inability to view structure
obscured by bone air & bowel gas.
146

Guidance System
• U.S. guided interventional procedures can be performed
by no. of methods:
 Free hand puncture allows direct visualization needle
but require special skills to assess relationship between
needle and image plane.
 INDIRECT GUIDANCE SYSTEM: In this U.S. probe is
only used to select the site of puncture.
 Needle guidance systems:
 Dedicated biopsy transducer.
 Attachable biopsy needle.
147

Advancements in Probes
• INTRACAVITORY SCANNER:
• Insertion in normal body cavities like esophagus ,
rectum , vagina etc…
• Advantages: avoidance of intervening tissue which
occur during normal transcutaneous approach.
148

Transrectal Scanning
• These probes have been developed to perform
ultrasound of prostate and rectum
• Probes should be at least of 7.5 MHz frequency.
• Initially linear array and rotating radial probe designs
were used
• Nowadays manufacturers have developed probes for
biplane transrectal prostate scanning with either single
probe or multiple probes on the same machine
149

• Some probes use a water path between the crystal and
rectal mucosa .This decreases near field artifact and can
be useful for examining the rectal wall itself or structures
close to the rectal wall.
150

Transvaginal Scanning
• Either mechanical or electronic focus sector probes are
used.
• Mechanical consists of one or more crystal operating in
oily medium.
• Less expensive and less resolution.
• Electronic transducer are more expensive and better
resolution.
• Frequency 5-7.5 MHz.
151

Endoluminal scanning
• For Investigation of vascular we use flexible low profile
1 - 1.3 cm catheter which is passed over arterial guide
wire and can be safely directed into distal artery.
• Normally 20 MHZ transducer is used because of close
opposition of catheter tip and transducer to vessel wall.
153

Intra cavitary scanning
• Small transducer are used.
• Because these have to be put in surgical field therefore
they should be sterilized either by rubber sheath and by
gas sterilization.
154

Broad Bandwidth Technology
• The range of frequencies produced by a transducer is
termed as its bandwidth.
• The shorter the pulse produced by the transducer the
greater the bandwidth.
• Ultrasound bandwidth refers to the range of frequencies
produced and detected by the ultrasound system
• Each tissue in the body has a characteristic response to
ultrasound of a given frequency and different tissues
respond differently to different frequencies.
155

• The range of frequencies arising from the tissues
exposed to ultrasound is referred to as the frequency
spectrum bandwidth of the tissue or tissue signature.
• Broad bandwidth technology provides a means to
capture the frequency spectrum of insonated tissues
preserving acoustic information and tissue signature
156

• Broad band width beam formers permit the reduction of
the speckle artifact by a process of frequency
compounding .
• It is possible because speckle pattern at different
frequencies are independent of one another and
combining data from multiple frequency bands results
in the reduction of speckle in the final image leading to
improved contrast resolution
157

Tissue Harmonic Imaging
• Tissue harmonic imaging is a new sonographic
technique which is based on the phenomenon of non
linear distortion of an acoustic signal as it travels
through the body.
• Imaging begins with insonation of tissue with
ultrasound waves of specific transmitted frequency.
• Harmonic waves are generated within the tissue and
build up with depth to a point of maximal intensity
before they decrease because of attenuation
158

• Conventional ultrasound waves are generated at the
surface of the transducer and progressively decrease as
they traverse the body
• Harmonic wave frequencies are higher integral
multiples of transmitted frequency
• Currently the second harmonic frequency is used for
tissue harmonic imaging in conventional us machines
159

Advantages of tissue harmonic imaging
• Improved axial resolution
• Better lateral resolution
• Reduced artifacts due to relatively small amplitude of harmonic
waves which reduces the detection of echoes from multiple
scattering events
• Side lobe artifacts are also less likely to occur
• THI has advantage in obese patients as harmonic waves are
produced beyond the body wall
• Improved signal to noise ratio
• Image noise is also reduced as harmonics from scattered low level
echoes are weaker
160

Contrast media in ultrasound
• Used to enhance the tissue and vessels, after
introduction intravenously or any other introducing
method.
• Ideal ultrasound contrast media should
 require little preparation
 be small enough to pass through pulmonary(7µm) ,
cardiac, and capillary systems.
 be stable enough to undergo the shear forces ,hydrostatic
pressure changes and diameter changes induced by the
acoustic pulse without breaking.
 useful half life should be sufficient to allow a complete
examination of a vessel or organ.
161

• Two basic types of UCA are
A) non encapsulated
B) Encapsulated micro-bubbles
Different types of contrast media used are
162
Microbubbles: [albunex] can pass through pulmonary
capillary circulation of the lungs.
Levovist: separate the gas-to-liquid interface and slows
their dissolution
Echovist: a galactose agent that produces visible
enhancement of renal parenchyma.
Colloidal solutions: effectively detectable in color
imaging

3 Dimensional Imaging
• Dedicated three dimensional scanners are now available
& used primarily for fetal & gynecologic imaging .
• It allows creation of 3D image from a single sweep of US
probe that provides 360 viewing of the area scanned this
eliminates problem of user dependent variation in
scanning which is a significant problem with
conventional 2D US techniques.
• Volume data can be viewed in multiple imaging plane .
• Accurate measurement of lesion volume may be
obtained & reviewed serially.
163

Advantages
• Short acquisition time
• Greater confidence in interpretation & ability to
manipulate the image in any plane
Limitations
• Requirements of highly trained personnel who are
skilled in obtained & manipulating the large data set
used in 3D reconstruction
• Artifacts may cause misdiagnosis
• Costly as centers using 3D US must invest in
computational infrastructure that can meet hardware,
software storage, transfer, Retrieval & support
requirements
164

Application of 3D USG
• Early detection of malignant and benign tumors.
• Visualization of fetus to assess its development specially
for observing at normal development of the face and
extremities.
• Visualizing blood flow in various organ of the fetus.

3 Dimensional USG.. Nipple areola
complex in profile
166
Duct ectasia with multiple simple cysts

4D UltraSound
• 4D US incorporates a temporal dimension to 3d US
• This approach is useful for performing volume
assessments as a function of time in dynamic systems
such as cardiac cycle
• 4D US has been applied for interventional procedures
such as solid organ biopsy
• 4D is a more intuitive modality for performing biopsy
because 2D images can be displayed for viewer while the
volumetric processing is being performed
• Additional presentation of 4D reconstruction is
continuous there by presenting delays experienced with
3d imaging
Limitations
• As of 3D ultra sound
167

Elastography
• Small amount of deformation (0.2 – 0.6 mm ) is applied to the tissues
. Pre and post deformation map of the anatomy are compared
• Displacement each small portion of tissue undergoes is calculated
• Strain images can be produced in real time with free hand
screening technique
• Can be integrated into clinical USG system with only software
changes
• Benign lesions appear of equal size in B mode and elasticity image
• Invasive ductal carcinoma appears almost twice larger
168

Elastography
169
X – BENIGN ; Y – malignant tissue

Other advances…
Compound imaging:
• Spatial compounding sums images from different scanning
angles
• Improves margin definition for cysts and other masses and
provides better visualization of micro calcifications
170
Multi Dimensional arrays:
• 1.5 dimensional arrays provide dynamic focusing in the
slice thickness plane.
• This feature dramatically improves lesion contrast close to
the transducer, where most breast imaging occurs.
• Can improve micro calcification detection.

Ultrasound Biomicroscopy
• With currently available transducers routine clinical
imaging of superficial structures at frequencies of up to
15 MHz is possible, with axial resolution in the range of
250 to 500 µm
• US Biomicroscopy using frequencies of 40 to 60 MHz
offers the possibility of imaging living tissues at
microscopic resolution, supplying information
previously available only from biopsies
• The availability of high frequency US Biomicroscopy
with real time imaging & doppler has important
implication for medical application in ophthalmology,
intravascular scanning & dermatology
171

Therapeutic UltraSound
• The future of US promises an increased role for US in
intervention & therapy
• Tissue ablation with high intensity focused US
• Image guided percutaneous excision
• And interaoperative guidance for surgical procedures
• Highly focused US beams are capable of delivering large
amount of thermal energy to small targets with in the body
with no damage to intervening structures producing highly
localized tissue destruction
• US energy is also a means for the activation or release of
therapeutic agents in target tissues taking advantage of
mechanical forces to release pharmaceuticals 172

Clinical Application of Ultra
Sound
1. Abdomen & Retroperitoneum
• Liver : The anatomy of the liver, portal circulation,
hepatic arteries & veins, pathology, tumor, cysts, fatty,
degeneration, cirrhosis, & ascites
• Gallbladder & Ducts : To demonstrate size, wall
thickness, & presence of sludge, gallstones, polyps, or
other masses
• Kidneys : Size, shape, cortical system, pyramid, calycle
system, echotexture pattern, tumour, cysts, stones,
presence of hydronephrosis, renal transplant study,
pyonephrosis
173

• Pancreas : Size shape, ducts, & normal pattern
calcification of pancreatic ducts
• Spleen : Size shape, pathology etc
• Retroperitoneal space : Presence of mass & mesentery
echo pattern
• Urinary bladder : Bladder abnormalities prostate, BEP (
Benign enlargement of prostate ) B.H.P benign
hypertrophic prostate ) Ca.urinary bladder
174

Obstetrics :
US is nonionic radiation which does not cause any
radiation hazard to the fetus as well as mother . Patient
examined with full bladder it provides an acoustic
window for view of uterus & pelvic organ, 3.5 MHZ
transducer is used
1. It confirms the pregnancy intra or extra uterine
2. Site of pregnancy i.e. Intra or extra uterine
3. Position of fetus, no. of fetus, & all fetal parameters can
be known
4. Amniotic fluid & placental localization
5. CMF – Congenital malformation like : Hydrocephaly,
Anencephaly, Meningeomyelocele, I.U.D.- Intra
uterine death
175

Gynecological:
Fluid filled bladder acts as a sonic window to
help elevate the uterus out of pelvic cavity &
push small bowel away from the field of view
The gynecological USG shows.
• Uterus & ovarian pathology
• Cervix
• Vagina
• Ovaries for any cyst or tumors
• Localization of IUCD 3-5 MHZ for pregnancies
176

Interventional procedures:
• FNAC done under us guidance helps in localization of a
mass, site of lesion, depth of tumor and direction and
angulation of needle placement etc.
• PTC, PTBD,PCN are done under US guidance as no ionizing
radiation are involved and most accurate
177

• Infant head
When internal fontanels are open to know the
abnormalities like hydrocephaly and ventricle diseases
• Superficial structures: like breast’ thyroid, scrotum etc.
a high resolution transducer is required so high
frequency transducers are used.
• US plays important role in Mass , solid, cystic,
malignant, benign tumors.
• Transvaginal : internal structures of ovaries and uterus
can be clearly seen . 5 MHz probes are used
178

• Transrectal : Rectal wall , seminal vesicle and prostate
studies are done very accurately.
• Intracavitary: endoscopy attached ultrasound
• Intra operative: for intraoperative ultrasound very
high frequency and high resolution transducers are
used up to 10 MHz
• Vascular studies: can be done by applying doppler
ultrasound.
179

Risks and benefits
1. No confirmed biological effects on patients or
instrument operator caused by exposure given has
been reported.
2. Although possibility exists that such biological effect
may be identified in future but current data states that
benefit to the patient will outweigh the risk if any that
may be present.
180

Artifacts in ultrasound image
Useless
– Technical errors
Useful
-Inherent properties of sound
-Interaction of sound with matter
181

Useless artifacts
• Patient preparation
• Inadequate coupling agent
• Machine related
Equipment selection
– Too high a frequency transducer for depth
– Sector versus linear transducer
– Near field artifact
182

Machine settings
-excessive gain or power
-inadequate time gain compensation
Scanning procedure
-off normal artifact
-echo displacement
183

Useful artifacts
• Reverberation
• Acoustic shadowing
• Refraction
• Mirror Image
• Side Lobe Artifact
184

Reverberation
• They arise when the ultrasound signal reflects
repeatedly between highly reflective interfaces
• They may give the false impression of solid structures in
areas where only fluid is present
• They are helpful as sometimes they allow the
identification of a specific type of reflector
• A soft tissue to gas interface is the common structure
causing this type of artifact
185

Shadowing
• It results when there is marked reduction in the intensity
of ultrasound deep to a strong reflector or attenuator.
• Highly attenuating objects such as bones or kidney
stones will manifest a low intensity streaking in the
image
187

Refraction
• It causes bending of the sound beam so that targets not
along the axis of the transducer are insonated
• The reflections are then detected and displayed in the
image
• This may cause structures to appear in the image that
actually lie outside the volume being examined
189

Multipath reflection and mirror
image artifact
• Mirror image appears deep to the actual image
• Reflection between a large curved interface and
structures
• Time of echo return is delayed
• Structures are placed deeper in image than their actual
location
191

Side Lobe Artifact
Side lobe artifacts occur where side lobes
reflect sound from a strong reflector that
is outside of the central beam, and where
the echoes are displayed as if they
originated from within the central beam.
Ultrasound transducer crystals expand and
contract to produce primary ultrasound
beams in the direction of expansion and
contraction.

Purpose, Indication and Procedure of
Ultrasound Imaging
Ultrasound imaging uses sound waves to produce pictures of
internal organs of the body. It is a noninvasive procedure and
does not use ionizing radiation for imaging. Ultrasound is
useful to diagnose the pathology of internal organs and also
evaluate the size of the fetus, the position of the fetus, and
the development of the fetus. It is used to extract sample
cells such as needle biopsies. It provides adequate
information to confirm a patient's diagnosis. Ultrasound is
used in the following indications:
•Detection of pregnancy.
•Identification of infection and inflammation in various
organs.
•Evaluation of testes, uterus, ovaries.

• Detection of joint inflammation (synovitis)
• Identification of vascular anomalies.
• Assessment of developing fetus.
• Detection of a breast lump.
•Determination of heart disease.
•Evaluation of blockages in vessels.
•Assessment of narrowing of vessels.
•Diagnose gallbladder and kidneys stones.
• Guide a needle for biopsy from an abnormal area or
tumors.
• Determination of structural or functional abnormalities of
various organs such as liver, gallbladder, spleen, pancreas,
kidneys, bladder, etc.

Patient Preparations in USG
• The patient's previous history and Pre-procedure investigations must be
reviewed by the radiologist.
• The radiologist will describe the whole procedure to the patient and
obtain consent from the patient for permission for the procedure.
• The patient is instructed to remove all metallic objects and metallic
jewelry from the body.
• The patient is asked to remove clothing and wear a hospital gown.
• For the Abdomen ultrasound, the patient is asked not to eat or drink for
up to six hours before the exam.
• For Pelvis and Bladder ultrasound, the patient is asked to drink up to five
to six glasses of water before the exam and instruct not to urinate until the
exam is completed.
•No special preparation is needed in color Doppler of Breast and for
Extremities ultrasound procedure.

• Ultrasounds provide real-time and adequate information on the internal
organs of the body.
•The ultrasound examination is usually performed by the radiologist.
•The patient is placed in a supine position on the USG table.
•The radiologist will apply a special lubricating jelly on the skin of the
area being examined.
•The gel prevents air pockets.
• During the examination, a transducer (probe) is placed directly on the
skin or inside a body cavity.
• The radiologist will rub the ultrasound transducer on the area being
examined.
•The transducer sends high-frequency sound waves.
•These high-frequency sound waves are transmitted from the
transducer through the gel into the body.
•The High-frequency sound waves hit an organ and then reflected back.

•These reflected sound echoes are
collected by the probe.
• The collected sound waves are sent to
the computer.
• During the procedure, the radiologist may
ask to change positions for better access.
• After completion of the procedure, the gel
will be cleaned off from the skin, and the
patient is allowed to leave the examination
room for his routine activities.

Benefits, Limitations, Risks and Uses
of Ultrasound
Benefits and Uses of Ultrasound
Ultrasound imaging uses sound waves to produce pictures of
internal organs of the body. It is a noninvasive procedure and
does not use ionizing radiation for imaging.
• Ultrasound is useful to diagnose the pathology of internal
organs.
• Ultrasound can evaluate the abnormalities of the heart,
blood vessels, Liver, Kidneys, Uterus, ovaries, and Bladder.
• Ultrasound is used to evaluate the size of the fetus, the
position of the fetus and the development of the fetus.
• Ultrasound is useful in detecting the position of the placenta
and diagnoses the ectopic pregnancy.

• Ultrasound is used to extract sample cells, such as needle biopsies.
• Ultrasound is used to determine the structural anatomy and functions of
the heart and also evaluates the blood flow through the heart.
Risks
• Diagnostic ultrasound is a safe procedure and has no known harmful
effects on humans, but it is proven by some studies that Ultrasound
waves produce biological effects on the body.
•In some cases, the sound waves slightly heat the tissues and also
produce small pockets of gas in body fluids or tissues.
Limitations of Ultrasound
•Ultrasound waves are interrupted by gas.
•Therefore it is not an excellent imaging technique for air-filled organs.

•The internal structure of bones is more difficult to image by ultrasound.
•It provides only superficially visualization of the outer surface of bony
structures
•Examination of fatty patients is more difficult because a large number of
sound waves is attenuated by the tissues.

4.Physics of Ultrasound.ppt

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4.Physics of Ultrasound.ppt