Ultrasound

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T1, T3, T4, T6
April 27, 2013
Review of how sound propagates
 Longitudinal wave (consisting of compression and
rarefaction areas)
 Speed of sound is dependent on the properties of
the media it is traveling through
 Frequency=rate of oscillations, so a frequency of
50Hz= 50 compressions a second.
Ultrasound
o Utilizes sound waves of
very high frequency way
above the human
hearing range
o (2MHz- 17MHz).
o Human hearing
range:
o Noninvasive, safe, painless,
Approximately 20
and dye free procedure.
kHz
o The higher the frequency, the
o Similar to sonar or
less depth penetration but
echolocation in bats
the resolution is improved.
o It is propagated from
o Imaging technique used
waves of compression
primarily in medical
and rarefaction, and
practices.
requires a tissue to
travel.
How Ultrasounds Work
• A transducer creates sound waves and
receives echoes using the piezoelectric effect
• Piezoelectric crystals within the probe
change shape when an electric current is
applied
– This causes vibrations and the production
of sound waves
– Needs a gel couplant to travel into tissues
since the high-frequency sound cannot
travel through air.
• Some sound reflects off of internal structures
while some sound refracts further into the
tissue
– A reflection occurs at the boundary
between two materials provided that a
certain property of the materials is different
• Sound waves are transformed into electric
signals then turned into an image stating
where reflection occurred in the body
 A probe that sends and receives
the sound waves, the inside of
the probe is cluster of quartz
crystals.
 Quartz crystals have a physical characteristics that if an
electric current is applied, will change shape and
vibrate to create sound wave, also in reverse if sound
vibrate of off it will convert that sound waves into
electric current.
Physics Behind Ultrasound
• The machine uses echolocation
to perceive the image in the
computer
• The machine sends out millions
of pulses per second and
calculates how long it takes for
the echoes to return back
• Waves reflect off of internal
surfaces
• Computer receives echoes and
uses time it takes to echo as well
as speed of sound to create
image/depth.
Applications of Physics
 Attenuation – A decrease of the amplitude
and frequency of a wave as it travels through
a medium, in this case the medium is
human tissue. Occurs with:
 Conversion of mechanical energy of waves to
thermal energy.
 Reverberation off of dense tissues
 Dispersion when reverberating.
Applications of Physics
 Enhancement – Sound does not attenuate as it flows
through fluid-filled mediums (blood, for example).
 Velocity – Speed of sound depends on its medium, so
the speed at which the waves return determines the
density and type of tissue.
 For example, sound travels at 1540 m/s in soft tissue
at 37°C.
 Doppler shift – Change in frequency of waves can be
used to determine velocity of blood flow.
 Equation: v = Δf*C/2f*cos(ϑ)
 Where v = velocity of blood, Df = returning
frequency by Doppler shift, c = speed of sound, and
q = angle of sound beam and direction of blood cell
travel.
Doppler Ultrasound
 Ultrasound can be used to examine
blood flow in vessels
 The sound waves striking the moving
blood will cause a frequency shift in
the echo and the computer can detect
this and create an image from it.
 High Doppler frequencies = Low
blood flow
 Low Doppler frequencies = High
blood flow
 Equation: v = Δf*C/2f*cos(ϑ)
 Where v = velocity of blood, Df =
returning frequency by Doppler
shift, c = speed of sound, and q =
angle of sound beam and direction
of blood cell travel.
Bats using echolocation
Bats transmit Ultrasound
frequencies. They produce very
short wavelength and high
frequency pitches between 14,000
Hz and 100,000 Hz (Most are well
above 20,000 Hz)
1) - Ultrasound waves are
generated either by the larynx or
nasal cavity
2) – Waves are sent out at regular
intervals until the bat detects a
moving object
3) – Ultrasound waves bounce off
an object and the emitted pulse
returns to the bat’s ears.
Bats using echolocation
4) – The ears of the bat
determine the location of the echo
based on the subtle difference in
time it takes for the sound to
reach 1 ear and then the other
5) – The bat determines if the
object is getting closer or farther
away by the speed at which the
echo returns
6) – Once a moving object is detected, the bat increases the
number of waves so that it can track it’s prey faster
7) – The bat moves to intercept and adjusts it’s trajectory in the
direction where the echoes are returning fastest
Uses of Ultrasound
 Human medical purposes:
 Obsterics/gynecology
 Cardiology
 Urology
 Look for abnormal lumps in the breasts ,
ovaries, or prostate in early stages of cancer
 Killing bacteria
 As an antibiotic
 In sewers
 Welding
 Cleaning jewelry and surgical instruments
 Used by many animals, including bats and
dolphins.
Ultrasound in Pregnancy
The machine measures the intensity of the waves by the
number of echoes that are received in an area.
Random waves that are reflected back by various tissues
and fluid are less intense so they do not compare to the
intensity of the waves that display the fetus
The machine calculates the
distance from the probe to the
tissue or organ using the speed of
sound in tissue (1,540 m/s)
The machine displays the
distances and intensities of the
echoes on the screen and forms a
two dimensional image
Ultrasound in Pregnancy
Probe transmit ultrasound
waves at frequencies of 1 – 5
MHz
Waves travel into the body until
they hit a boundary between
tissue and are reflected back
Multiple waves are sent out
every second
The reflected waves that
bounce back are received by the
probe and transmitted to the
machine
Babies!
 Being able to see if the
baby is male or female
 Abnormalities with the
heart
 Umbilical cord in the
correct place
 Size and growing cart
3D ultrasound
• Transducer is run along the body
surface at various angles rather than
just directly sending the sound waves
straight in
• Allows multiple angles and depth
levels of the echoes to be created
• Advanced computers are able to
detect the multiple reflected sound
waves
• Provides greater depth of image so
doctors can more accurately detect
normal development
Why do physicians prefer Ultrasound over any other
medical treatment?
 Physicians prefer to use
Ultrasound because it is consider
as a safe test over x-rays, MRI’s,
or CT’s.
 It is much cheaper, and does not expose
the patient to any form of radiation.
 Ultrasound can cause a minor
physical pain due to cavitation,
which is when gases contained in
the tissue cell nuclei are heated.
This cause a burning feeling.
 Only real drawback
Differences in High and Low Frequencies
 Physicians decide whether to
use high or low frequencies
based on what they are using
the Ultrasound for.
 When they are looking more
at the surface of the body it is
preferred to use high
frequencies
 Produce better images
 Low frequencies are used
when they are trying to look
deeper into the body.
Ultrasonic Images
• Used in modern medicine to create images
•
•
•
•
of inside the human body
Transmits ultrasonic wave into the body
Interprets the intensity of the echoes to
create image
Black images: ultrasonic waves were able to
diffuse through tissue
– Muscle tissue and fluid
White images: ultrasonic waves were NOT
able to diffuse through tissue
– Skin and bone
Ultrasonic Delivery of Medication
• Intravenous injections of microbubbles are
administered into the patient
• Certain properties of the microbubble allow it
to attach drugs and peptides with high affinity
• The microbubbles bind to specific receptors on
tissue at a target site and begin to accumulate
• (Research has shown that these microbubbles
enhance the permeability of cellular
membranes)
Ultrasonic Delivery of Medication
 High intensity ultrasound pulses are created by a
probe
 The pulse targets the accumulated microbubbles
and causes them to lyse
 The bound drug or peptide is released into the
vasculature at the target site
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