Ultrasonography uses ultrasonic waves to form images of internal body structures. It works by transmitting high frequency sound pulses into the body using a transducer. Echoes are reflected back and detected by the transducer. The echoes are processed by the ultrasound machine to form real-time images showing internal organs and tissue movement. Key components include the transducer probe which uses the piezoelectric effect to transmit and receive ultrasound waves, and the processing unit which calculates echo times and forms the images. Ultrasound provides a non-invasive way to visualize internal body structures.

1. USG
Ultrasonography
-- Muskan Mehta --
RDG-1804
MAMC,Agroha

2. Ultrasono Graphy
Uses
ultrasonic
waves
Forms
images

3. SOUND
 MECHANICAL ENERGY – because it can
not travel through vaccum and requires
a medium to travel.
 LONGITUDINAL WAVE – motion of
medium particles is parallel to the
direction of energy transport.
 Vibrating source produces sound.
 Unit – hertz [Hz]
 One hertz is equal to one vibration per
second.
 Travels with a velocity of 330m/s at
normal temp.

4. Types of waves:
(i) Transverse waves
(ii) Longitudinal waves

5. OTransverse waves : The particles vibrate
perpendicular to the direction of
propagation of the wave.
Characteristics : (i) crest
(ii) trough
OCrest : Maximum displacement of the
particles in the upward direction.
OTrough : Maximum displacement of the
particles in the downward direction.

6. O Longitudinal waves : The particles vibrate along
the direction of propagation of wave.
O Characteristics : (i) compression
(ii) rarefaction
O 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.
O Rarefaction : The fall in pressure causes the
molecules in these region to move apart, with the
result a region of rarefaction is formed.

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

10. Parts of sound
spectrum
1. Audible sound
2. Infrasound
3. Ultrasound

11. AUDIBLE SOUND-
 Perceived by human ear
 Frequency – approx. 20Hz – 20,000 Hz[20KHz]
INFRASOUND
 Not perceived by human ear
 Frequency - <20Hz
ULTRASOUND
 Sound of frequency higher than that of human
perception
 Frequency - >20,000 Hz [ 20KHz]

13. ULTRASOUND
PROPERTIES
PROPAGATION
PRESSURE VARIATION
VELOCITY

14. PROPERTIES OF ULTRASOUND
O Non ionizing longitudinal waves.
O Need medium for propagation.
O Transmitted by mechanical vibrations using
compression and rarefactions.
O Ultrasound in bones propagated as transverse
waves.
O Frequency of ultrasound remains constant
during propagation.

15. Propagation of ultrasound
Source of ultrasound vibrates
Mechanical disturbance transferred in the medium
contact with it
Medium particle oscillates about their mean
position i.e. to and fro
Neighbouring particles affected
Direct transfer of energy takes place from one
particle to another

16. Ultrasound propagated in 2 phases
1. COMPRESSION PHASE
 Also called condensation phase
 Forward particles to source are compressed
 Compression increase their concentration per
unit volume and creates increased pressure
 Also called high pressure phase
2. RAREFACTION PHASE
 Reverse particles are decompressed giving rise
to this phase
 Also called low pressure phase
PRESSURE VARIATION

18. Velocity of ultrasound
-Velocity of ultrasound varies
from medium to medium
- Velocity depends upon:-
1. DENSITY
2. COMPRESSIBILITY

19. DENSITY:-
Massive particle
Greater force required for
vibration or to overcome inertia
Velocity of ultrasound is lower in
dense medium

20. COMPRESSIBILITY
Referred to the ease with
which a medium can
mechanically deformed and
reformed
FOR Eg:-
continued…..

21. GAS
Particles farther apart
Easy to compress [high compressibility]
Large movement of particle requires for
transfer of energy
Transfer of energy is slow
Low velocity of ultrasound in material of
high compressibility

22. Role of density appears to contradict the
role of compressibility-
- One factor play more predominant role.
- Effect of 2 factor may moderate each
other.
Eg:-
-Bone has more density – reduces velocity
-Bone has low compressibility – increases
velocity.
COMPRESSIBILITY IS MORE PREDOMINANT HERE

23. 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

25. ULTRASONOGRAPHY:-
 It is detection and display of high frequency sound
reflected from interfaces within the body
Real time images
Shows structure and movement
of body internal organs
Non invasive medical test

26. History of ultrasonography
1912
• Unsuccessful research by sir sunken titanic in north atlantic
1918
• SONAR [ sound navigation and ranging] by sir reginald fessenden
• Finding objects under water by using sound waves[ submarine]
1937
• Use of sound waves in anatomical imaging by australian brothers dussik
• Scanned human head immersed in water using a transmitter reciever pair.
1942
• Result of first attempt published by steven garber
1945
• Piezoelectric effect become a reality and modern investigative ultrasound
with digital processing came
1950
• First systematic review on safety of ultrasound given by sir anil CR

27. Principle of
ultrasonography
Ultrasonography is based on ‘pulse echo
principle’.
REASON:-
Probe generated pulse and echos return
from various tissue boundaries are
detected by the probe.
Info from the probe is processed by the
computer and visualized as an image

28. Reflected waves are detected by the probe and relayed to the
machine
Some waves reflect back to probe and some travel on further and
reach another boundary and reflect back to probe
Sound wave travel into body and hit a boundary between the
tissues e.g. [between fluid and soft tissue , soft tissue and bone]
Ultrasound machine transmits high frequency sound pulse into
the body using the probe

29. A 2D or 3D image is formed on the screen
Distance and intensities of the echos are displayed on the screen
Machine amplifies the signal
Machine then converts the signal into electrical signal
Machine calculates the distance from the probe to the tissue using
speed of sound in tissue and time of echo return

30. ULTRASOUND MACHINE

31. USG
machine

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

33. SERIES OF STEPS
DURING PROCEDURE
•Ultrasound production
•Tissue interaction
•Echo reception
•Image formation

34. PRODUCTION OF
ULTRASOUND
Produced by TRANSDUCER
Transducer converts one form of energy
into another
Transducer works on PIEZOELECTRIC
EFFECT and contains piezoelectric
crystals
Transducer length is generally 5 to 15cm

35. ULTRASONIC TRANSDUCER
- Most important and expensive part of
ultrasound unit
Electric signal Ultrasonic energy
Ultrasonic energy Electric signal

36. COMPONENTS OF TRANSDUCER
1.The piezoelectric
crystal
2. Positive and ground
electrodes
3. Damping [backing ]
block
4. Matching layer
5. Housing

37. 1. THE PIEZOELECTRIC CRYSTAL
O Most important component.
O Thin disc of piezoelectric material.
O Near the front surface of transducer.
O Usually LEAD ZIRCONATE TITANATE [PZT].
O About 0.5mm thick.
O Thicker crystal produces lower frequency oscillation
and vice versa.
O Most crystal used in medical ultrasound are man
made and are called ferroelectrics.
O Barium titanate was the first ferroelectrics to be
discovered and then replaced by PZT.
O 128-512 elements are present in a transducer and
each is individually insulated.

38. THE PIEZOELECTRIC
PHENOMENON
 Certain material are such that the application of an
electric field causes a change in their physical
dimension and vice versa.
This is called PIEZOELECTRIC EFFECT.
 Described by Sir pierre and jacques curie in 1880.
 Piezoelectric elements are made up of
innumerable dipoles in a geometric pattern
 Electric dipole is a distorted molecule that appears
to have a positive charge on one end a negative on
another

39. ELECTRIC DIPOLES IN
PIEZOELECTRIC
CRYSTAL

40. HOW PIEZOELECTRIC CRYTAL OBTAINED?
To possess piezoelectric effect diploes must be arranged in
specific geometric pattern.
HOW TO PRODUCE POLARIZATION?
Ceramic is heated to a high temp. in strong electric field
At high temperature, dipoles are free to move.
Electric field brings them to a desired alignment.
Crystal is gradually cooled while subjected to a constant high voltage
As room temp reached diploes become fixed
Piezoelectric crystal obtained

41. HOW PIEZOELECTRICITY IS LOST?
OPIEZOELECTRIC CRYSTALS are damaged by
the heat.
OAbove a critical temperature , called CURIE
TEMPERATURE , crystal loses its polarization
and loses its piezoelectric properties and
become a worthless piece of ceramic.
OSo obviously, transducers should never be
heated.

42. Material
Barium titanate
quartz
PZT 4
PZT 5A
Curie temperatures
100 C
573 C
328 C
365 C

43. 2. POSITIVE AND GROUND
ELECTRODES
O Present on the face of the
piezoelectric element.
O This allows for electric
connection
O Positive electrode is in the
back of the element
O Ground electrode is in the
front of the element.

44. 3. Backing block
O Adhered to the back of the
crystal
[behind the positive
electrode].
O Absorbs ultrasound energy
that is directed backwards.
O Dampens the resonant
vibrations of the crystals for
better resolution .
O Generally made of
combination of tungsten and
rubber powder in an epoxy
resin.

45. 4. Matching layer
O Interface element between transducer element and
the tissue
O Allows 100% transmission of the ultrasound from
element to the tissue by minimizing reflection due to
propagation of ultrasound through different
interfaces.
O May consists of one or multiple layers
O The acoustic impedence of the matching layer is
between the acoustic impedence of the soft tissue
and the transducer material.

46. ACOUSTIC IMPEDENCE
O It is the product of density and velocity of sound in that
material.
O Acoustic impedance = density × velocity
O Both density and velocity are independent of frequency.
O It depends only on tissues mechanical properties
O Unit of acoustic impedance is Rayl which is 1 × 10-5
g/cm2sec
O The amount of reflection is determined by the difference
in the acoustic impedance of two tissues.
O The greater the difference, the greater the percentage
reflected.

47. 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

48. 5. HOUSING
OElectrical insulation and protection
of the element
OIncludes a plastic case , metal
shields and a acoustic insulator.
OAcoustic insulator protects the
patient from shock

49. HOW A TRANSDUCER WORKS?
Voltage is applied in sudden burst
Crystal vibrates like a cymbal that has struck a sharp blow
Positive and negative end of crystal realign and dimension of crystal
changes , reverse piezoelectric effect takes plce
Ultrasound wave generated
Backing block quickly dampens the vibrations so that the transducer
detect the returning echoes

50. Ultrasound passes through the body
Energy carrying Echoes reflect back towards the
transducer from each tissue interface
Physical compression of crystal element takes place
Tiny dipoles changes their orientation, piezoelectric
effect takes place
Voltage between electrodes induced
Voltage amplified
Ultrasonic signal obtained

52. SOME OTHER TERMS TO
KNOW…!
1. Resonant frequency of crystal
2. Transducer Q factor

53. 1. RESONANT FREQUENCY OF
CRYSTAL
OUltrasound transducer is designed to be
maximally sensitive to a certain natural
frequency
OThis natural frequency is called
RESONANT FREQUENCY.
OIt depends on the thickness of the
crystal element.

54. Surface of piezoelectric crystal behaves like two electric cymbals
There is a open space between the 2 surfaces
cymbal of Crystal struck with a sharp voltage spike
One surface vibrates
Vibrations generates sound waves that causes other surface to vibrate
Vibration in the second surface is maximum when ‘THE SPACE BETWEEN
THE SURFACES IS EQUAL TO ONE HALF OF THE WAVELENGTH OF THE
SOUND WAVES GENERATED’
At this distance or space , the sound waves are from and the vibration of
the two cymbals are equally synchronized
Now the crystal is vibrates with its natural frequency and the ultrasound
produced has the frequency called ‘FUNDAMENTAL RESONANT
FRREQUENCY’.

56. MATHEMATICAL EXPRESSION FOR THE
THICKNESS OF THE CRYSTAL
As we know ,
frequency = velocity of ultrasound in crystal
element/wavelength
Also ,
Wavelength = 2x thickness = 2t
Therefore , frequency = velocity/2t
Hence, t = v/2f

57. For e.g.
If we want a vibration frequency of 5MHz then, what should be the
thickness of the element if the velocity of ultrasound in the crystal
element is 4000m/s ?
As we seen before,
t= v/2f
t= 4000m/s
2x5x106/s
t = 4x10-4m
t = 0.4mm
Crystal thickness for diagnostic ultrasound
For high frequency – 0.1 mm
For low frequency – 1.0 mm
THINNER THE CRYSTAL, HIGHER THE FREQUENCY AND VICE
VERSA

58. 2. 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 factor transducer produces a nearly pure
sound made up of narrow range of frequency and vice
versa.
 The high Q crystal when struck by a short voltage pulse
produces a long time vibration and produce a long
continuous sound.
 The time the crystal take to stop vibrating is called RING
– DOWN TIME.
 Backing block helps the crystal to stop vibrating.

59. TRANSDUCER WITH….
1.Broad frequency range and short ring
down time > ORGAN IMAGING
2. Narrow range of frequency and long
ring down time > DOPPLER USG

60. TYPES OF TRANSDUCERS
TRANSDUCER
MECHANICAL
ROTATING
WHEEL
OSCILLATING
ENCLOSED
CRYSTAL
UNENCLOSED
CRYSTAL
ELECTRONIC
LINEAR
ARRAY
PHASED
ARRAY
CONVEX
TRANSDUCER

61. 1. MECHANICAL TRANSDUCER
OSingle element transducer.
OUltrasound is achieved by the physical
movement of some parts of the transducer
usually the crystal element.
OThere is a sector angle of image which is
between 45 to 90 degrees
ODecreasing the sector angle increases the
resolution of the image
OFrame rate is equal to no of swings per
sec.

62. a. Oscillating transducer –
unenclosed crystal
O Sector angle is 15 to 60 degrees i.e. the
crystal is oscillated at an angle of 15 to 60
degrees and the frame rate is 15 to 30
seconds

64. b. Oscillating transducer –
enclosed crystal
OTransducer is enclosed in oil or water filled
container.
OIt is driven by a motor of electromagnet
Otype of image produced depends on the
distance between the transducer and the
front surface of the casing
OIf distance is short – sector image produced
OIf distance is more – trapezoid image is
formed

66. c. Rotating wheel transducer
O3 – 4 transducers are mounted 90
to 120 degrees apart on a wheel
OThis wheel is rotated at a constant
speed in one direction.
ODepending on the design, sector or
trapezoid image is produced

68. 2. ELECTRONIC ARRAY
TRANSDUCERS
OConsists of a array of small
rectangular transducers
arranged adjacent to one
another
OThey are not movable
OThese are activated
electronically.

69. a. Linear array transducers
O Crystals elements are arranged in a row.
O Generate rectangular field of view
O 64-200 transducers
O 4-10cm long array
O Frequency of ultrasound is 2-3 MHz
O Transducer elements are pulsed in group of 4 to
produced a focused image
O Useful in obstetric scans , breast and thyroid scans.
O Crystal activated either sequentially or segmentally

71. b. Phased or steered array
transducers
O Same geometric configuration as linear array
O Procedure of activating the crystal element is different.
O Neither sequential nor segmental pulsing is employed
O Crystal element is pulsed almost instantaneously as one
group
O Contains 32 elements
O Operates at frequency of 2-3MHz
O Scan obtained are fan shaped or sector shaped
O Used in upper abdomen scan, gynecological and
cardiologic exams.

73. c. Convex transducers
OThe scans produced from convex
transducers are midway between those
from linear and sector scanners
OConvex transducer of 3.5MHz is ideal for
general purpose USG examinations
OCan not be used for echocardiography

76. Some other transducers

77. TRANSDUCER SELECTION
O The highest ultrasound frequency permitting penetration
to the depth of interest should be selected.
High Frequency Transducer
O Good resolution
O Poor penetration
Low Frequency Transducer
O Poor resolution
O Good penetration
O 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
O 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.

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

80. REFLECTION
O 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.

81. Refraction
OThe bending of waves as they pass
from one medium to another.
OWhen sound passes from one medium
to another, its frequency remains
constant but its wavelength changes to
accommodate a new velocity.

82. Absorption
O 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.
O Three factors determine the amount of
absorption:
1. The frequency of sound
2. The viscosity of conducting material
3. Relaxation time

84. ECHO RECEPTION
OThe same transducer acts as the receiver
OWhen returning echoes strike the
transducer face, minute voltages are
produced across the piezoelectric
elements
OThe receiver detects and amplifies these
weak signals

85. Image Formation
OElectric signals produce dots on the
screen
OBrightness of dots is proportional to the
strength of the returning echoes
OLocation of dots is determined by the
travel time

86. ULTRASONIC DISPLAY
A MODE
O Echoes are displayed as spikes projecting from a
baseline.
O The base line identifies the central axis of the
beam
O Spike height is proportional to echo intensity,
with strong echoes producing large spikes.
O Used in opthalmology, echoencephalography,
echo cardiology.

88. TM Mode
O The spikes are represented as dots displayed
along a vertical base line
O Location of dots is an indicator of depth
O Brightness of dots is proportional to the
strength of returning echoes
O Horizontal base line is an indicator of time
O Used in cardiac examinations

90. B Mode
OIt produces a picture of a slice of a tissue.
OEchoes are displayed as dots
OThe transducer is moved so that the sound
beam transverse a plane of the body
OB mode is the basis for all static and real
time ultrasound

91. B MODE
O Static
O Transducer moved manually over an area to produce
image
O Scan of each area produces a line
O All lines are added to form an image
O Real time
O Real time is the dynamic presentation of multiple image
frames per second over selected areas of body.
O Crystals within the transducer sweep the beam over an
area automatically
O The lines produced are added together to form the image
O Updating of image is rapid and continous

93. USG MACHINE CONTROLS
O Power
Modifies the voltage applied and
intensity of sound and returning
echoes can be increased
O Gain
amplification of returning echoes
O Reject
elimination of weaker signals
O Time Gain Compensation
Near echoes are minimally (if at all) amplified
Far echoes are greatly amplified

94. Thank you