Nature of
sound
General Definition
“Sound is a disturbance of mechanical energy that propagates through
matter as a pressure wave ”
Frequency
the measurement of the number of times that a repeated event occurs
per unit of time. It is also defined as the rate of change of phase of a
sinusoidal waveform.
Period
An interval of time that an event, chain of events, instance or happening,
takes place within. It is measured between a start point and an end point
and generally repeats, or progresses, in a cycle with the end point of one
period being the start point of the next.
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What is ultrasound

Speed of Sound
Speed of Sound in body  1500m/s ~
1600m/s
Average Speed of Sound in soft tissue
1540m/s

Sonar in the Sea

THERAPEUTIC
ULTRASOUND
(1920-1940)
• Researchers began to determine the conditions
under which ultrasound was safe.
• Applied ultrasound to therapy, surgery, and
cancer treatment
• Ultrasound was used to treat members of
European soccer teams as a form of physical
therapy, to appease arthritic pain and eczema
and to sterilize vaccines

The generation of images by ultrasound is
based on the pulse-echo principle. It is
initiated by an electric pulse that leads to
the deformation of a piezoelectric crystal
housed in a transducer. This deformation
results in a high-frequency (>1,000,000
Hz) sound wave (ultrasound), which can
propagate through a tissue when the
transducer is applied, resulting in
an acoustic compression wave that will
propagate away from the crystal through
the soft tissue at a speed of approximately
1530 m/s.. In diagnostic ultrasound
imaging, the applied frequency is generally
between 2.5 and 17 MHz, which is far
beyond the level audible by humans, and
is thus termed ultrasound .
HOW THE IMAGE IS FORMED IN
ULTRASOUND MACHINE

HOW THE IMAGE IS
FORMED IN
ULTRASOUND MACHINE
Electric field applied to piezoelectric crystals located on transducer
surface
Mechanical vibration of crystals creates sound waves
Each crystal produces an US wave
Summation of all waves forms the US beam
Wave reflects as echo that vibrates transducer
Vibrations produce electrical pulses
Scanner processes and transforms to image

 The principal determinants of the ultrasound wave are: (1) wavelength (λ),
which represents the spatial distance between two compressions
 frequency (f), which is inversely related to wavelength
 velocity of sound (c), which is a constant for any given medium
 These three wave characteristics have a set relationship as c = λf. An
increase in the frequency (i.e., shortening of the wavelength) implies less
deep penetration due to greater viscous effects leading to more attenuation

Lower frequencies = less resolution but deeper penetration
Higher frequencies = smaller wavelength
capable of reflecting from smaller structures
The shorter the wavelength, the better the resolution,
giving aclearer image
Readily absorbed by tissue = less penetration
Higher frequency = higher resolution
Muscles, tendons 7-18 mHz

AMPLIFICATION
 The echoes that return from
deeperstructures are not as
strong as thosethat come
from tissues nearer the
surface
 Amplification done by the
time-gain-compensation
(TGC) amplifier

TGC ( TIME GAIN
COMPENSATION
 Attenuation correction
settings.
 Optimal settings of time-gain
compensation (TGC) can
provide a uniform display of
signal intensity for echoes
from similarly reflecting
structures, across various
depths of the scan sector.

Transmitter(TX)
Beamformer
Beam steering
Receiver
Processor
Transducer Moniter
Memory
Scan
Converter
Hard copy
Digital Storage
Front End Back End
Transmitter(TX)
Beamformer
Beam steering
Receiver
Processor
Memory
Scan
Converter
1.Generate Ultrasound
2. Receive Echo signal
1.Change RF data to Image data
2.Process Image data can be
available to display on Monitor
BLOCK DIAGRAM OF ULTRASOUND
SYSTEM

BLOCK DIAGRAM OF ULTRASOUND SYSTEM
Front End

 a. TX Data / Pulser : produce high voltage to vibrate piezoelectric
transducer
 b. Limiter : eliminate high voltage
 c. Pre-amp : amplify Echo signal
 d. TGC : readjustment gain from attenuation by depth
 e. ADC : convert Analog signal to Digital signal
 f. BF : RX focusing to reduce the time delay
RX

Ultrasound
system modes

B-Mode (Brightness Mode)
in ultrasound is a setting that creates a two-dimensional (2D)
greyscale image on your ultrasound screen and is the most used
mode. It is also commonly called 2D mode.

M-Mode (Motion Mode)
 Ultrasound M-mode is defined as a motion versus time display of the B-
mode ultrasound image along a chosen line. The motion is represented by
the Y-axis and time is represented by the X-axis.

M-mode imaging step by step
• M-mode Step 1: Acquire 2D image and Center Structure of Image
• M-mode Step 2: Push the M-mode button to make the M-mode cursor line appear
• M-mode Step 3: Place the M-mode cursor line along the structure of interest
• M-mode Step 4: Push the M-mode button again to activate M-mode
• M-mode Step 5: Push the Freeze Button
• M-mode Step 6: Scroll to the desired image
• M-mode Step 7: Push the Measure Button
• M-mode Step 8: Measure Area of Interest

Second Harmonic
Imaging
 Current ultrasound systems are
based on fundamental and
harmonic imaging. In fundamental
imaging the transducer listens for
the ultrasound of equal frequency to
the emitted wave. However, at
higher amplitudes of the transmitted
wave, wave distortion may occur
during propagation, causing
harmonic frequencies (multiples of
the transmitted frequency), which
can be received by the transducer
when properly implemented, Such
second harmonic images have
significantly improved signal-to-
noise ratio and improved
endocardial border definition .

Doppler Imaging
 The Doppler effect states that the frequencies of
transmitted and received waves differ when the
acoustic source moves towards or away from the
observer (due to wave compression or expansion,
depending on the direction of motion)
 The Doppler effect can be applied to measuring blood
(and tissue) velocities, by measuring the difference
between the frequency of emitted and received
ultrasound, which will be reflected off moving red blood
cells
 This difference between the emitted and received
frequency is termed the Doppler shift or Doppler
frequency , which is directly proportional to the
velocity of the reflecting structures (red blood cells, i.e.,
blood flow)

Continuous Wave
Doppler
 The Doppler modalities used
in echocardiography are
pulsed wave (PW) and
continuous wave (CW)
Doppler, as well as color flow
mapping (color flow Doppler).
In CW, separate piezoelectric
crystals continuously emit and
receive ultrasound waves, and
the difference between the
frequencies of these waves
(the Doppler shift) is
calculated continuously

Pulsed Wave Doppler
 As opposed to CW, in PW
Doppler ultrasound is
emitted and received in a
similar manner to 2D
imaging: individual pulses
are emitted as brief. After
emitting such a pulse, the
transducer “listens” to
returning signals only
during a short, defined time
interval following pulse
emission.

Color Doppler Step
by step
• Color Doppler Step 1: Activate Color
Doppler
• Color Doppler Step 2: Adjust Color
Doppler Area
• Color Doppler Step 3: Adjust Color
Doppler Scale
• Color Doppler Step 4:Adjust Color
Doppler Gain

Power Doppler Mode
 There is a mode like color Doppler that
you may encounter called Power
Doppler. This mode does not show up
as red or blue on the screen but only
uses a single yellow color signifying
the amplitude of flow. So, you can’t tell
if the flow is going towards or away
from the probe given that it has only
one color. It is more sensitive than
color Doppler and is used to detect low
flow states such as venous flow in the
thyroid

PROBES

3D probe
types

Phased Array (Sector)
Ultrasound Probe
 The phased array (or sector array)
transducer is commonly branded as
the “cardiac probe” and has a
frequency range from 2-6MHz. It has
a similar frequency range as the
convex probe but has a smaller and
flat footprint.
 The advantage of this probe is
that piezoelectric crystals are layered
and packed in the center of the probe
making it easier to get in-between
small spaces such as the ribs

Linear Ultrasound Probe
 The linear ultrasound probe is a high-
frequency transducer (5-15 MHz) that will
give you the best resolution out of all the
probes but is only able to see superficial
structures. A general rule of thumb is that
if you are going to ultrasound
anything less than about 8cm, then use
the linear probe. Anything above 8cm you
won’t be able to see much.
 The linear probe will give you a
rectangular field of view that corresponds
with its linear footprint

CONVEX Ultrasound Probe
 The convex ultrasound probe has a frequency range
of 2-5MHz. It is considered a low-frequency probe
and has a large/wide footprint. The convex
ultrasound probe is often used for abdominal and
pelvic ultrasound exams. However, it can also be
used for cardiac and thoracic ultrasound exams but
is limited by the large footprint and difficulty with
scanning between rib spaces

Endocavitary Ultrasound Probe
 The Endo cavitary probe has a convex footprint with a wide
view but has a much higher frequency (8-13 MHz) than a
convex ultrasound probe. The image resolution of the endo
cavitary probe is exceptional, but like the linear probe, it must
be adjacent to the structure of interest since it has such a high
frequency/resolution, but poor penetration.

3D , 4D convex probe
 3D imaging allows fetal structures and internal
anatomy to be visualized as static 3D images. However,
4D ultrasound allows us to add live streaming video
of the images, showing the motion of the fetal heart
wall or valves, orblood flow in various vessels. It is thus
3D ultrasound in live motion

Indicator (Orientation
Marker) Position
 The “probe indicator” on the
ultrasound probe can be identified as
an orientation marker on one side of
the probe. This corresponds to the
indicator or orientation marker on the
ultrasound image.

Ultrasound IMAGE Indicator
(Orientation Marker) Position
 In general, for almost all standard applications and
procedures the indicator orientation marker
position will be on the LEFT side of the screen. In
cardiac mode, the indicator orientation marker will
be on the RIGHT side of the screen.

How to do ultrasound
examination step-by-
step
 Step 1: Power Button
 the most important button of all is the
power button! Simple enough!

 Step 2: Switch to the Correct
Ultrasound Probe/Transducer
 we should already know what
ultrasound probe we need to use
based on the application we are
performing. So after turning on the
ultrasound machine, the next most
important step is to switch to the
correct ultrasound transducer

 Step 3: Application Preset
 after switching to the correct
ultrasound probe, the next step is to
select the correct application preset
for that transducer.
 Each transducer will have a different
list of application presets based on its
frequency and footprint.

 Step 4: Depth
 there are some ultrasound settings
that may need to be adjusted to
optimize your ultrasound settings
further.
 The first of these ultrasound settings
you should adjust is the depth. The
ultrasound depth setting is simply
how deep you want the ultrasound
machine to be able to scan.

 Step 5: Gain (Overall)
 After optimizing your depth, the next
ultrasound setting you should adjust
is your gain.
 Ultrasound gain simply means how
bright or dark you want your image to
appear. It increases or decreases the
strength of the returning ultrasound
signals that you visualize on the
screen.

 All ultrasound machines will have an “Overall”
Gain setting that, when increased or decreased,
will make the entire ultrasound image brighter or
darker. This is good to use when your entire
imaged is too dark (under-gained) or too bright
(over-gained)

Step 6: Near/Far Field Gain and Time
Gain Compensation (TGC)
 Adjusting the Time Gain Compensation (TGC) allows
you to adjust the gain at almost any depth of your
ultrasound image, not just the near and far-fields. The
top rows of the Time Gain Compensation control the
nearfield gain and the bottom rows control the far-field
gain

Step 7: Freeze, Measure (Caliper), Image/Video Capture
 Freeze
 Just like the world implies, the “freeze” button freezes a frame for you, so you have time to view it in more
detail. The ultrasound machine will usually store a 10-30 seconds of data and you can scroll back to see
previous frames as well.
 Calipers (measure)
 Calipers are an important feature of ultrasound machines that allows you to measure the distance of specific
structures of interest.
 Image/Video Capture
 All ultrasound machines will allow you to save an image and/or video clip of your ultrasound scan. This is
important if you are trying to archive, bill, or use any ultrasound images/videos as teaching files.

Advantages of Ultrasound
 It’s a noninvasive process
 It’s a painless treatment
 This is the only way to tell the difference between a cyst and a solid mass by special
mode called elastography
 Patient is never exposed to radiation during an ultrasound
 Ultrasounds do not cause any health problems
 We can use ultrasound to detect blood flow through vessels
 Widely available
 Ultrasound devices are more accurate which can place objects within 5 mm of
distance
 It provides clear image of soft tissues which do not show up in X-Ray images

Disadvantages of Ultrasound
 Many cancers cannot be detected via an ultrasound
 ultrasound requires a highly experienced and skilled operator, as well as good
equipment
 It has poor penetration through bone or air
 The quality of results and use of equipment's depend on skills of operator
 Image resolution is less comparing to CT and MRI scan
 Air or bowel gas prevents visualization of structures
 Hard tissue cannot be imaged
 Deep structures cannot be visualized

Conclusion
 Ultrasound is a wide sector. It has so many advantages. As a technical engineer we
can be change maker by using ultrasound. So, considering all the positive sides
we can say we can make hope to people and provide them a healthy life by
bringing newer advances in ultrasound