ULTRASOUND QUESTION AND ANSWER 3 MARKS
Name of the student
Total number of
assignmentquestions done
Iniya sanjana.A 5
Nandha kumar.A 8
Nithya.M 9
Mano.L 7
Melhin Hebi.J 8
Simon.I 6
Bharath.v 4

1.Brightness mode ( by Sanjana)
 Two dimensional 2D slice of anatomy of the patient is
imaged.B-Mode is a two-dimensional ultrasound
image display composed of bright dots representing
the ultrasound echoes.
 The brightness of the dot is proportional to echo
intensity.
 To create a 2D display, the transducer is moved back
and forth and echoes are collected as dots from the
patient.
 Thousands of such dots of varying brightness give the
grey scale image.
 The B- mode made the ultrasound as a diagnostic tool,
especially in abdominal diseases.
 It provides a picture of a slice of tissue.
 Since sweeping motion refers to sector it is known as
sector scanning.

2.Types of Doppler ultrasound: by Iniya Sanjana
Doppler ultrasound is useful to investigate variation
of blood flow in arteries and veins.
Types of Doppler ultrasound:
1, Continuous Doppler.
Continuous transmissionand reception of
ultrasound waves. This is accomplished by two dedicated
transducer elements: one that solely sends a signal and
another that only receives.

2 Pulsed Doppler.
Pulsed Doppler combines continuous wave Doppler and
pulse echo imaging. The former gives velocity and the
later gives depth information.

3 Duplex scanning
The term "duplex" refersto the fact that two modes
of ultrasound are used, Doppler and B-mode. Duplex
ultrasound involves using high frequency sound waves to
look at the speed of blood flow, and structure of the leg
veins.

4 Color Doppler
Color Doppler is a technique in which colors are
superimposed on an image of a blood vessel indicate the
speed and direction of blood flow in the vessel.

5. Power Doppler
Power Doppler sonography is a new technique that
displays the strength of the Doppler signal in color,
rather than the speed and direction information. It has
three times the sensitivity of conventional color Doppler,
for detection of flow and is particularly useful for small
vessels and those with low-velocity flow.

3.Fraunhofer zone or far field( by Sanjana)
• Fraunhofer zone or far field is one, in which the
beam diverges and obey sin ø=1.22 y/d where ø is the
beam divergence, d is transducer effective diameter.
• Less beam divergence occurs with high frequency
and with large diameter Crystals.
• The us intensity decreases with distance.
• The beam intensity falls off in both zones, due to
attenuation, and in the far zone because of beam
divergence.
• Normally Fresnel zone is used for imaging, because
the resolution is poor in Fraunhofer zone.

4.Clinical probes ( by Sanjana)
The transducers are also made to suit the
individual clinical applications. The clinical probes are as
follows:
• Endo vaginal – pelvic region
• Endorectal – prostate
• Transoesophageal – heart
• Intravascular – blood vessels.

1.Time Gain Compensation ( by Sanjana)
The time gain compensation, TGC, amplify the
signal proportional to the time delay between
transmissionand detection of US pulses. Generally, US
imaging is done with pulses of 1 ms duration. There is
enough time in between two pulses to receive echoes.
The tissues are larger in size compared to US wavelength
and also in different depths. Though, echoes give
information about the tissues, but are highly attenuated
and signal is weak. Hence scanner circuit amplify and
digitise the signal, and use Time gain Compensation
(TGC) to compensate attenuation.

6.ACOUSTIC IMPEDANCE (by Nandha kumar)
Acoustic impedance is a physical property of tissue.
It describes how much resistance an ultrasound beam
encounters as it passes through a tissue.
 Acoustic impedance depends on:
 The density of the tissue (d, in kg/m3)
 The speed of the sound wave (c, in m/s)
o They are related by:
 Z = d x c
 So, if the density of a tissue increases, impedance
increases.

7.DRAW A NEAT DIAGRAM OF ULTRASOUND
TRANSDUCER ( By Nandha kumar )

8.IMAGE FORMATION IN ULTRASOUND (by Nandha
kumar)
 Ultrasound machine, with patient adjacent to
sonographer, who is adjusting the machine in order
to optimize image quality.
 Within the piezoelectric crystals or ceramic of the
transducer, energy is converted from electrical to
mechanical energy.
 It uses a smallprobe called a transducer and gel
placed directly on the skin.
 High-frequency sound waves travel from the probe
through the gel into the body.
 The probe collects the returning reflected US waves
are the basis for image formation.
 A computer uses those sound waves to create an
image.

9.WRITE ANY THREE COMMON ULTRASOUND
ARTIFACT (By Nandha kumar)
BEAM WIDTH ARTEFACTS :
 Caused due to the widening of the main beam after the
focal spot
SIDE LOBE ARTEFACTS
 Side lobes are multiple beams of low-amplitude
ultrasound energy that project radially from the main
beam axis, mainly seen in linear array transducer.

COMET TAIL ARTEFACTS :
 Comet tail artefact is a form of reverberation.
 In this artefact, the two reflective interfaces
and thus
sequential echoes are closely spaced. On the
display, the
sequential echoes may be so close together
that individual signals are not perceivable.
• In addition the later echoes may have
decreased
amplitude secondary to attenuation; this
decreased
amplitude is displayed as decreased width.

10.WHAT IS ULTRASOUND? HOW IT IS PRODUCED
( By Nandhakumar )
 Ultrasound describes sound waves of frequency
exceeding the range of human hearing (> 20 kHz). In
medicine the ultrasound energy and the acoustic
properties of the body, produce image from stationary
and moving bodies.
 Diagnostic ultrasound uses 1-20 MHz frequency and
the velocity depends on the nature of medium through
which it travel and independent of frequency

 A transducer with piezoelectric crystals(quartz crystal )
is used to produce the ultrasound beam. This is a
material in which mechanical energy is converted into
electrical energy and vice versa. This means that
transmitting an electric voltage through the material
will cause it to vibrate, producing a sound wave.
Similarly, the returning echo sound wave vibrates the
crystals producing an electric voltage that can be
measured. In this way, the material acts as a receiver
and a transmitter.
Piezoelectricity is the electricity generated by piezo
element by effect called the piezoelectric effect. It is

the ability of certain materials to generate an AC
(alternating current) voltage when subjected to
mechanical stress or vibration, or to vibrate when
subjected to an AC voltage, or both.
Some examples of piezoelectric materials are PZT (also
known as lead zirconate titanate), barium titanate, and
lithium niobate. These man-madematerials have a
more pronounced effect (better material to use) than
quartz and other natural piezoelectric materials.
11.PHASED ARRAY TRANSDUCER (by Nandhakumar)
• The transducer is named after the piezoelectric
crystals arrangements which is called Phased array and
it is the most commonly used crystal Phased array
transducer has a small footprint and low frequency (its
central frequency is 2 Mhz – 7.5 Mhz)
• The beam point is narrow but it expands depending
on the applied frequency. Furthermore, the beam
shape is almost triangular and the near- field
resolution is poor
Use this transducer for various application such as
• Cardiac examinations

• Abdominal examinations
• Brain examinations
12. Reverberationartifact in ultrasonography
(by Nandha kumar)
Reverberation artifact is a common ultrasound artifact
and occurs when a sound pulse reverberates back and
forth between two strong parallel reflectors.
With the exception of comet-tail artifact, a subtype of
reverberation, reverberation artefact has little diagnostic
use.
The artifact can be improved by changing the angle of
insonation. If the angle is changed, the pulse is reflected

off at an angle and either a) does not encounter the
second parallel strong reflector, or b) is reflected away
from the transducer.
13.Role of ultrasound in obstetrics ( by Nandhakumar)
• Ultrasound as a diagnostic tool. A screening test is
one that is used to assess the risk of a particular outcome
• Ultrasound can also be used to screen an obstetric
population to diagnose a fetal problem.
• The widest use of ultrasound in obstetrics is in the
diagnosis of fetal malformation.
• The clinical applications and uses of ultrasound
include confirmation of pregnancy, localisation of
placenta and monitoring of foetal wellbeing.

14.Propagationof ultrasound waves in tissue
( by nithya)
 Ultrasound is produced by piezoelectric effect and it
travels in straight line. It travels in a medium in the
form of wave with compression and rarefaction.
 It has wavelength, frequency, velocity and amplitude.
 Wavelength is the distance between consecutive
crests, frequency is the number of cycles per second
and it is equal to 1/f.
 Diagnostic ultrasound uses 1-20 MHz frequency and
the velocity depends on the characteristics of the
medium and independent of frequency.
 It is inversely proportional to compressibility
 Sound waves travel faster in solids and slower in gases.
 The intensity of ultrasound is a measure of beam and is
proportional to the square of amplitude.

15.Pulse echo frequency (by nithya)
 Ultrasound transducer produces pulses of ultrasound
waves.
 The number echo pulses received per second is known
as pulse echo frequency.
 These waves travel within the body and interact with
tissues by transducer.
 The reflected wave return to the transducer and
processed by the ultrasound machine.
 An image which represents these reflections is formed
on the monitor
 Pulsing is determined by the transducer or probe
crystal and echoes are interpreted and processed by
ultrasound machine

16.Ultrasound transducer frequency (by nithya)
 Ultrasound frequencies in diagnostic radiology range
from 2 MHz to approximately 15 MHz.
 higher frequencies of ultrasound have shorter
wavelengths and are absorbed/attenuated more
easily. Therefore, higher frequencies are not as
penetrating.
 Higher frequencies are used for the superficial body
structures and lower frequencies are used for those
that are deeper.
 2.5 MHz: deep abdomen, obstetric and gynecological
imaging
 3.5 MHz: general abdomen, obstetric and
gynecological imaging
 5.0 MHz: vascular, breast, pelvic imaging
 7.5 MHz: breast, thyroid
 10.0 MHz: breast, thyroid, superficial veins, superficial
masses, musculoskeletal imaging.

 15.0 MHz: superficial structures, musculoskeletal
imaging

17.Patient positioning in ultrasound (by nithya)
 Keeping the body part to be scanned directly in front
of the sonographer.
 We Instruct patients to orient themselves to assist
the sonographer in using neutral postures while
performing scans. For instance, while performing
scans on the side of a patient, have them roll onto
their side.
 We Instruct patients to move as close to the
sonographer as possible during scans.
 Patient needs to Keeping the torso straight. Do not
bend And Keeping the elbow bent at about 90 to 110
degrees and close to the body. Do not reach out and
away from the body.

18.Frequency and resolution( by nithya)
Frequency- number of complete cycles per unit of
time
 Units are hertz
 Ultrasound imaging frequency range is 2 -20 Mhz
Resolution is the ability to identify two objects
 Wavelength (frequency) dependent
 it includes spatial and temporal resolution
 Lower the frequency higher the penetration and
lower the resolution
 Higher the frequency lower the penetration and
higher the resolution
19. Any one ultrasound artifact (by nithya)
1. Refractionartifact
When us waves enter into one medium from
another different medium, travelling direction is
changing and this is known as refraction.
• Refraction is the change of direction of the
transmitted pulse. Refracted beam causes
misregistration of echo, resulting in misplaced
anatomy e.g. eyes and fatty tissues.

• Misplacement depends on the position of the
transducer and angle of incidence with tissue
boundaries.
• It appears as misregistration, defocusing, and
ghost images.
• Misregistration cause improper placement, and
distortion of size or shape.
• Defocusing is due to loss of beam coherence,
and cause shadowing at the edge of large curved
structures
• Ghost images are due to altered sound beam
path

20. basic principle of doppler imaging (by nithya)
• In ultrasound, the Doppler effect is used to
measure blood flow velocity
• Ultrasound reflected from red blood cells will
change in frequency according to the blood flow
velocity and direction of flow.
• When direction of blood flow is towards the
transducer, the echoes from blood reflected back to
the transducer will have a higher frequency that the
one emitted from the transducer.
• When the direction is away from the transducer,
the echoes will have a lower frequency than those
emitted.
• The difference in frequency between
transmitted and received echoes is called doppler
frequency shift, and this shift in frequency is
proportional to the blood flow velocity.

21. Recent advanced in ultrasonography ( by nithya)
• Wireless transducer- Is used to image from up
to 10 feet away. And it can also be used to aid in
vascular access procedures.
• Shear wave elastography – SWE can record
elasticity more accurately than conventional
elastography and produce more objective, real time
colour coded map to show tissue stiffness.
• Tissue harmonic imaging – is a grayscale
ultrasound mode based on the phenomenon of non
linear distortion of acoustic signal. It improved axial
resolution, better lateral resolution, less side lobes
artifact, and better imaging option for obese patient.
By using focused ultra sound waves we can treat
fibroids in uterus.

22. Spatial and temporal resolution(by nithya )
Resolution- Resolution is defined as the
ability to distinguish echoes in term of space, time or
strength.
Temporal resolution- is the ability of an ultrasound
system to accurately show changes in the underlying
anatomy over time, this is particularly important in
echocardiography
Spatial resolution – is the ability of ultrasound to
detect and display structures that are close together.
There are two types of spatial resolution
Axial& lateral
Axial resolution - the ability to displays small targets
along the path of the beam as separate entities.
Lateral resolution – the ability to distinguish
between two separate targets perpendicular to the

beam path, its depend upon the width of ultrasound
transducer
23. WHAT ARE THE COMPONENTS OF ULTRASOUND
MACHINE (BY MANO)
Transducer probe :
Probe is transmitter and receiver the sound wave.
Central processing unit (CPU):
Computer that does all of the calculation and
contains the electrical power supplies for itself and
the transducer probe.
Display:
Displays the images from the Ultrasound data
processing by the CPU.

Keyboard:
Input data and takes measurements from the
display.
Disk storage device:
Store the acquired image.
Printer:
Prints the image from the displayed data.
24. What are the advantages and disadvantages of
Ultrasound examinations. (by mano)
ADVANTAGE
 Non invasive
 Non ionizing radiation is used
 Simple
 Real time imaging
 Portable machine
 Can repeat and easy to store
DISADVANTAGES:
 Operator and equipment dependant
 Hard tissue cannot be imaged
 Deep structures cannot be visualized

25. Write about the sector transducer. ( by mano)
Sector transducers produce a fan-like image that is
narrow as it leaves the transducer and increases
with depth. It is ideal for imaging through small
“windows” such as the cranial window in the temple,
or between the ribs. They are commonly used for
transcranial and cardiac imaging. These transducers
provide good depth penetration, but have very poor
near field resolution
This transducer is named after the piezoelectric
crystal arrangement which is called phased-array
and it is the most commonly used crystal.
Phased Array transducer has a small footprint
and low frequency (its central frequency is 2Mhz –
7.5Mhz).
The beam point is narrow but it expands
depending on the applied frequency.

Furthermore, the beam shape is almost
triangular (see picture below) and the near-field
resolution is poor.
Cardiac examinations
Abdominal examinations
Brain examinations
26. Write about the uses of transducer jelly.(by mano)
Ultrasound gel is a conductive medium that creates a
bond between the skin and the ultrasound transducer.
The ultrasound sound waves have a hard time
traveling through air, so the gel prevents any extra air
space between the probe and your skin in order to create
a clear image of the anatomy. Ultrasound requires an
aqueous interface between the transducer and the skin

or else all you see is black. Ultrasound gel is a clear goo,
looks like hair gel or aloe vera, and is made by several
companies out of various combinations of propylene
glycol, glycerine, perfume, dyes, phenoxyethanol or
carbapol R 940 polymer along with lots of water.
Ultrasound Gel – Alternatives are
KY Jelly. One of the most common ultrasound gel
alternatives, KY Jelly is a water-based and water-soluble
product that is used as a personal lubricant. ...
Bio Oil. ...
Moisturizers & Creams. ...
Hand Sanitizer. ...
Skin Gel or Aloe Ver

27. Write about the piezoelectricmaterial.(by mano)
Piezoelectric materials are materials that have the
ability to generate internal electrical charge from
applied mechanical stress.
Several naturally occurring substances in nature
demonstrate the piezoelectric effect. These include:
Bone
Crystals (quartz )
Certain ceramics
DNA
Enamel
Silk
Dentin, and many more.
Materials that exhibit the piezoelectric effect
also demonstrate the inverse piezoelectric effect
(also called the reverse or converse piezoelectric
effect).
The inverse piezoelectric effect is the internal
generation of mechanical strain in response to an
applied electrical field

28. DEPTH RESOLUTION IN ULTRASONOGRAPHY.
( BY MANO)
Deep resolution.
The ability of an ultrasound system to distinguish
between two points at a particular depth in tissue,
that is to say, axial resolution and lateral resolution,
is determined predominantly by the transducer.
The lower frequency, at 2-6 MHz allows for deep
penetration.
The curved linear array transducer with frequency
2-6 MHz offers high resolution imaging for deep
abdominal scanning. The curved linear array of the

transducer allows for a wider field view, and
conformity to the abdominal area, making scanning
patient and doctor friendly.

29. FOCUSED TRANSDUCER . (by mano)

Beam focusing refers to creating a narrow point in the
cross-section of the ultrasound beam called the focal
point. It is at the focal point where the lateral resolution
of the beam is the greatest also. Before the focal point is
the near field or Fresnel zone, where beams converge.
Distal to this focal point is the far field or Fraunhofer
zone where beams diverge.
30. Write about beam width artifact. (J. Melhin)
 Caused due to the widening of the main
beam after the focal spot.
 The ultrasound image localization software
assumes an imaging plane as indicated by
the dotted lines. Echoes generated by the
object located in the peripheral field ( gray
circle) are displayed as overlapping the
object of interest (white square).

31.DOPPLER EFFECT (J. Melhin)
The Doppler effect (or Doppler shift) is the
change in frequency of a wave in relation to an observer
who is moving relative to the wave source.
In medical ultrasound the Doppler effect is
used to measure the velocity of blood in blood vessels,
especially arteries to determine if a stenosis is present.
The Doppler equation is modified when used for medical
ultrasound to take into account the pulse–echo cycle , as
each part produces a Doppler shift .

32.Reflectionof ultrasound with matter. ( J. Melhin)
Reflection is divided into specular and non–
specular reflection. A specular reflection is one in
ultrasound strike a large smooth boundary , where
structure size >structure size > lambda. This is major
contributor of ultrasound imaging .
Non specular reflection is one in which the
ultrasound strikes a irregular boundary, where the
irregular boundary /structure size is < lambda. When
sound wave travels from a medium of low Z to medium
of high Z , reflection occurs and it obeys Snell ‘s law¦
n1 and n2 are velocity of ultrasound in the medium.

33. Relationship between resonance frequency and
crystal thickness. (J. Melhin)
The frequency is inversely proportional to crystal
thickness.
 Changing the thickness of the crystal changes the
frequency but not the ultrasound amplitude
 ( determined by applied voltage waveform) or
speed ( determined by piezoelectric crystal).
 High frequency transducers are thin and low
frequency transducers are thicker.
To change the frequency one has to change the
transducer.

34.Write about resonance and non resonance
transducer. (J. Melhin)
Resonant transducer:
 Resonant type transducers follow relation
=2T,where T is the thickness of the crystal.
 It is used in pulse echo ultrasound imaging.
 High frequency transduce requires thinner
crystals and low frequency requires thicker
crystals.
Non resonant transducer:
 Non resonant transducers are made by
machining a piezoelectric material.
 The matching layer thickness is less.
 It will produce multiple frequency.

35.Write about reverberationartifact.( J. Melhin)
 Appearance :
Multiple equidistantly spaced linear reflections,
ladder.
 Physics:
Parallel highly reflective surfaces, the echoes
generated from a primary US beam may be repeatedly
reflected back and forth before returning to the
transducer for detection.
 Prevention:
# decrease TGC near in the near gain.

# change beam angle /alternative window.
36. Role of frequency in imaging. (J. Melhin)
Ultrasound waves have frequencies that exceed the
upper limit for audible human hearing ,i.e ., greater than
20 kHz. Medical ultrasound devices use sound waves in
the range of 1–20 MHz. Proper selection of transducer
frequency is an important concept for providing optimal
image resolution in diagnostic and procedural
ultrasound.

 High frequency ultrasound waves (short
wavelength) generate images of high axial
resolution.
 Low frequency waves (long wavelength)
generate images of lower resolution.
High frequency =high spatial resolution but limited depth
of penetration.
Low frequency =greater depth of penetration but lower
spatial resolution.
37. TISSUE HARMONIC IMAGING in ultrasound. ( J.
Melhin)
Tissue harmonic imaging (THI) is a new gray –scale
sonographic technique that improves image clarity.
Harmonics form within the insonated tissue as a
consequence of nonlinear sound propagation. Imaging
with endogenously formed harmonics means that the
distorting layer of the body wall is traversed only once by
the harmonic beam during echo reception.

Both image contrast and lateral resolution
are improved in harmonic mode compared with
conventional (fundamental mode) sonography.
38. Doppler ultrasound ( by simon)
The Doppler effects refers to change in frequency
that results from a moving sample or ultrasound source.
Movement of object in the US beam changes the
frequency of the reflected echo, and the change in
frequency is called Doppler Shift(fd).

Doppler shift is the difference between incident
frequency and reflected frequency.
Fd = 2fi( v/c) cos ∅
V is the velocity of moving blood
C is the speed of sound
Fi is the incident sound frequency
∅ is the angle between the US beam and the moving
object.
Doppler ultrasound is useful to investigate variation
of blood flow in arteries and veins.
Doppler system employ high Q transducer with
low frequencies.
39. Phased Array Transducer (by simon)
The phased array sweeps across the patient anatomy
and gives sector fields.
• Smaller number of elements with small foot print is
used.
• Each element has separate transmit and receive
circuits.

• It has application in echocardiography, abdomen,
rectum, vagina and oesophagus
• If all the elements are energized simultaneously,
they act as a single transducer.
• If energized separately, the pulses reinforce only in
one direction called steering.
.

40. Piezoelectriceffect(by simon)
 In Greek pieze it means squeeze or press
 The principle of converting energy by applying
pressure to a crystal.
 When an electric voltage is applied to a transducer
crystal, the crystal gets excited and is deformed.
 Electric energy is converted into ultrasound energy
through the transducer. Based on the pulse-echo
principle , transducers converts:
-Electricity into sound = Pulse
-Sound into electricity = Echo.

42.Focused Transducer: by simon
Single elementTransducer are Focused by using
- A curved piezoelectric element or
- A curved acoustic lens
To reduce the beam profile.
It would then seem logical to use low
frequency transducers and to increase the size of the
transducer to keep the beam coherent for sufficient
depth to increase the point of interest.
Focused Transducer reduces beam
width which improves lateral resolution.
They also concentrate beam intensity
thereby increasing penetration and echo intensity thus
improving image quality.
A focused transducer produces a
narrow beam at the focal zone and therefore has an
better lateral resolution than an unfocused transducer
of the samesize.

43. Spatial resolution( by simon)
More lines per frame, therefore decrease
spatial resolution and great detail ability to image fine
detail and distinguish two closely spaced structures.
Overall detail of image.
Line density determines spatial resolution.
Low line density: lines placed far apart meaning less
lines per frame , therefore increase spatial resolution
and poor details.
Spatial resolution is also called as detailed resolution.
44. A MODE IN ULTRA SOUND ( by Bharath)
*A-mode is the simplest type of ultrasound. A single
transducer scans a line through the body with the echoes
plotted on screen as a function of depth.
* Therapeutic ultrasound aimed at a specific tumour or
calculus is also A-mode, to allow for pinpoint accurate
focus of the destructive wave energy
APPLICATIONOF A-MODE:
* A mode is used in Ophthalmology,
echoencephalography, and echocardiography.

* used as an adjunct to B mode display when accurate
depth measurements are required

45. LINEAR TRANSDUCER (by bharath)
* Linear transducers produce a rectangular field of view
with uniform beam density throughout. They are useful
for imaging shallow structures and smallparts.
A linear probe uses high frequency ultrasound to create
high resolution images of structures near the body
surface. This makes the probe ideal for vascular imaging
and certain procedures such as central line placement.
Linear probe frequency range 5 To 12 MHZ.
It is used for imaging superficial structures, such as
Thyroid, skin lesions and blood vessels.

46.REFLECTION OF ULTRASOUND WITH MATTER
( by bharath)
* the change in acoustic impedance between tissue at an
interface can affect the ultrasound wave is reflected.
* This could be the surface transitioning from fat to
muscle tissue or it could be the surface of a cyst or mass
within a soft tissue.
* The angle of the reflected beam is equal to the angle of
the incident beam assuming the surface is smooth.
* In a perfect 90degree angle, the beams will reflect back
directly towards the transducer. The following formula
looks at an incident beam with an angle of 90 degrees,
directly perpendicular to the interface.
* The percentage of the ultrasound wave reflected can
be described by the intensity reflection coefficient (IR) .
Sound wave interacting perpendicular to a smooth tissue
boundary.
* The wave is perfectly reflection where Z is the density
of the tissue. ultrasound wave is reflected or transmitted
through the interface is a function of how resistant these
tissues are to allowing ultrasound pass through.

47.REFRACTION OF ULTRASOUND WITH MATTER
(by Bharath)
* Refraction occurs when the ultrasound signal is
deflected from a straight path and the angle of deflection
is away from the transducer.
* Ultrasound waves are only refracted at a different
medium interface of different acoustic impedance.
* Refraction allows enhanced image quality by using
acoustic lenses. Refraction can result in ultrasound
double-image artifacts.
* If the angle of incidence is less than 3 degree, than then
very little refraction is seen.
* It passes deeper into the body where it give rise to
artifacts.

Tissue harmonic imaging (by nithya)
Is a grayscale ultrasound mode that provides images of
higher quality than conventional sonography
It is based on the phenomenon of nonlinear distortion of
acoustic signal as it travels through the body
Imaging begins with insonation of tissue with ultrasound
waves of a specific transmitted frequency
Harmonics are multiples of the fundamental beam
Harmonics are produced by tissue vibration and are
usually integral multiples of the transmitted frequency
As ultrasound wave travels through more tissue, more
harmonic are generated.
The production of harmonics is proportional to the
square of the fundamental intensity
Harmonic are generated predominantly by the main
transmit beam.
Only the lowest frequency harmonic is used to form
images.
The processed image is formed with use of the harmonic
frequency bandwidth in the received signal after the
transmitted frequency spectrum is filtered out.

Advantages of THI
 Improved axial resolution- due to shorter
wavelength
 Better lateral resolution- due to improved focusing
with higher frequency
 Less artifact than with conventional ultrasound
 Less side lobes artifacts
 Better imaging option for obese patients.

Resonant transducer and non resonant transducer
 They are manufactured to operate in a resonance
mode whereby a voltage commonly 150 v of very
short duration is applied causing the piezoelectric
material to initially contract and subsequently
vibrate at a natural resonance frequency
Operating frequency is determined from
 The speed of sound and the thickness of the
piezoelectric material
 It is used in pulse echo ultrasound imaging.
 Higher frequencies are achieved with thinner
elements, and lower frequencies with thicker
elements.
Non resonant transducer
 Non- resonant transducer are made by machining a
piezoelectric material and dully filled with epoxy
resin
 The acoustic properties are closer to that of tissue,
the matching layer thickness is less which ensures
increased transmissionefficiency.

 It will produce multiple frequency and the
bandwidth is about 80% of the center frequency.
 The bandwidth response permits the reception of
echoes within a wide range of frequencies.

48. Transducer selection
Transducer selection is ultimately determined by two
factors; frequency and “footprint”. Selection is often
determined by the depth of the structures to be imaged.
Compare the two images of the same neck below. The
image on the left was generated with a high frequency
(9MHz) linear array transducer, while the image on the
right was taken with a low frequency (4MHz) curved
array transducer. Note how the high frequency image
differentiates the homogeneous tissue of the thyroid
from the heterogeneous tissue of the fascia and muscle,
whereas in the low frequency image it is much more
difficult to separate them. With the exception of the
sciatic nerve at the sub-gluteal level (which is an
advanced block), almostall nerves and major blood
vessels can be located at less than 4cm of depth, making
the high frequency transducer the preferred probe for
performing regional and vascular access.