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Medical uses of
ultrasound
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WHAT IS ULTRASOUND?
• Ultrasound or ultrasonography is a medicalimaging technique that uses high frequency
sound waves and their echoes.
• Known as a ‘pulse echo technique’
• The technique is similar to the echolocation
used by bats, whales and dolphins, as well asSONA used by submarines etc.
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Bats!
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Bats navigate using ultrasound
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Bats: Navigating with ultrasound
• !ats ma"e high#pitched chirps which are too high for
humans to hear. This is called ultrasound
• $i"e normal sound, ultrasound echoes off ob%ects
• The bat hears the echoes and wor"s out what caused
them
• &e can also use ultrasound to loo" inside the body'
• (olphins also navigate with ultrasound
• Submarines use a similar method called sonar
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Bats: Navigating with ultrasound
• )f a bat hears an echo *.*+ second after it ma"es a chirp,how far away is the ob%ect
• -lue + the speed of sound in air is //* ms#+
• -lue 0 The speed of sound equals the distance travelled
divided by the time ta"en
• Answer distance 1 speed 2 time
• 3ut the numbers indistance 1 //* 2 *.*+ 1 /./ m
• !ut this is the distance from the bat to the ob%ect andbac" again, so the distance to the ob%ect is +.45 m.
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Ultrasound imaging
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Ultrasound imaging : What does it look like?
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CATEGORIES OF
SOUND
•)nfrasound 6subsonic7 below 0*89
• Audible sound 0*#0*,***89•:ltrasound above 0*,***89
•Nondiagnostic medical applications
;+
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Ultrasound imaging : How does it work?
• An ultrasound element acts li"e a bat.
• >mit ultrasound 6+ to +0 megahert97 and detect echoes
•
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Ultrasound imaging : How does it work?
• Now put many elements together to ma"e a probe andcreate an image
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THE TRANSDUCER (Probe)
? PIE!E"E#$%I# E&&E#$ is a property of some
crystalline materials, li"e quart9 of 3@T 6lead 9irconate
titanate7 that allows them to convert electrical signals to
mechanical and vice versa. &hen compressed or
e2panded these materials show a voltage between thecompressed or e2panded surfaces 6due to the
molecular alignment in the crystal lattice7. -hanging
polarity is a means of electromechanical conversion.
Transmits pulses of sound into tissue and listens forechos
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Transducer Poweron
Power of Transducerreceiving
echoes
10-6sec
10-3sec
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Pie'oelectric crystal
• >mit sound after electric
charge applied• Sound reflected from
patient
• eturning echo is
converted to electricsignal grayscaleimage on monitor
• >cho may be reflected,
transmitted or refracted• Transmit + and receive
BB of the time
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Ultrasound imaging : develop(ent o) a pregnancy
C wee"s gestation 6out of a D* wee" pregnancy7
+C wee"s
0D wee"s
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Ultrasound imaging : )oetus )eet
This is a 0( ultrasound scan
through the foot of a foetus. Eou can
see some of the bones of the foot.
&e can process the image in a
computer to find the outline of the foot.
This is called surface rendering . 8ere,
the foot has been surface rendered
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Ultrasound imaging : (ore sur)ace rendering
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Ultrasound imaging : i(aging the heart
heart valves
atrium
ventricle
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Doppler ultrasound
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Doppler effect : change in wavelength with speed
• :ltrasound, li"e normal sound, is a wave.
• )f a source of sound moves towards the listener, the
waves begin to catch up with each other. The wavelength
gets shorter and so the frequency gets higher F the sound
has a higher pitch.
• &e use this principle to wor" out how fast blood cells
move. :ltrasound reflects off the blood cells and causes a
(oppler shift
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• The ultrasound probe
emits an ultrasound wave
• A stationary blood cellreflects the incoming wave
with the same wavelength
there is no (oppler shift
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• The ultrasound probe
emits an ultrasound wave
• A blood cell moving awayfrom the probe reflects the
incoming wave with a
longer wavelength
• )n reality, there is actually
two (oppler shifts. Thefirst one occurs between
the probe and the moving
blood cell 6not shown
here7 and the second one
occurs as the red blood
cell reflects the
ultrasound.
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• Now, the blood cell moves
towards the probe. )t
reflects the incoming wavewith a shorter wavelength
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Doppler effect : *lood )low in artery
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Doppler imaging : co(*ine i(aging and +oppler
• :se !OT8 normal ultrasound imaging and (oppler
imaging
• :sed to image blood flow
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Ultrasound imaging : carotid artery
• (oppler imaging
loo"s at artery
• Get image and trace
of blood flow
• This is a healthy
artery. The flow is
smooth and all in the
same direction, li"e
water in a large,
slow river
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Ultrasound imaging : carotid artery
• This is also a carotid
artery.
• The flow is not all in
the same direction.
)t is turbulent, li"e
rapids in a river.
• This is usually due
to a build#up of fatty
deposits in the
artery
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Ultrasound imaging : ,+ +oppler ultrasound
Hentricles
Atria
This is a complicated image
of the heart of a foetus. )t
shows the blood movingbetween the ventricles and
the arteries.
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INSTRUMENTATION ANDCONSIDERATIONS
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Attenuation
• -*sorption 1 energy is captured by thetissue then converted to heat
• %e)lection 1 occurs at interfaces between
tissues of different acoustic properties
• .cattering 1 beam hits irregular interface F
beam gets scattered
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Acoustic ImpedanceI The product of the tissueJs density and the sound
velocity within the tissueI Amplitude of returning echo is proportional to the
difference in acoustic impedance between the twotissues
I Helocities
F Soft tissues 1 +D**#+4**msec
F !one 1 D*C*
F Air 1 //*
I Thus, when an ultrasound beam encounters two
regions of very different acoustic impedances, thebeam is reflected or absorbed
F -annot penetrate
F >2ample soft tissue F bone interface
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re!uenc" and Reso#ution
I As frequency increases,
resolution improves
I As frequency increases,
depth of penetrationdecreases
F :se higher frequency
transducers to image
more superficialstructures
I >2 >quine Tendons
Penetration
re!uenc"
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Instrumentation $ U#trasound
ProbesA % C A
% C
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Transducers&Probes
I .ector scanner F Lan#shaped beam
F Small surface required for contact
F -ardiac imaging
I "inear scanner
F ectanglular beam
F $arge contact area required
I #urvilinear scanner
F Smaller scan head
F &ider field of view
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Monitor and Computer•
-onverts signal to an image archive• Tools for image manipulation – /ain F amplification of returning echoes
• Overall brightness – $i(e gain co(pensation 0curve1
• Ad%ust brightness at different depths – &ree'e – +epth
• @oom in for superficial view• @oom out for wide view• (epth limited by frequency
– &ocal 'one• Optimal resolution wherever focal 9one is
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Ima'e contro#s
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Modes o Disp#a"
I - (ode F Spi"es F where precise length and depth
measurements are needed F ophtho
I 2 (ode 0*rightness1 F used most often
F 0 ( reconstruction of the image slice
I 3 (ode 4 (otion (ode
F
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Artiacts
• Artifacts lead to the improper display of thestructures to be imaged
– Affect the quality of images
• )mproper machine settings F gain
– )mage too bright or too dar"
– -an disguise underlying pathology
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Artiacts
• %ever*eration – Time delays due to travel of echoes when there
are 0 or more reflectors in the sound path
–
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Mirror Ima'e Artiact
Dr. Matthews
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Dr. Matthews
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Comet Tai#s
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Re,erberation
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-.at Happened Here/
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Artiacts
I -coustic shadowing F :S beam does not pass through an ob%ect
because of reflection or absorption
F !lac" area beyond the surface of the
reflector F >2amples cystic calculi, bones
I -coustic enhance(ent
F 8yperintense 6bright7 regions below ob%ectsof low :S beam attenuation
F AKA Through transmission
F >2amples cyst or urinary bladder
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Acoustic S.adoin'
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Acoustic En.ancement
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Acoustic En.ancement
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Artiacts
• %e)raction5
– Occurs when the sound wave reaches two
tissues of differing acoustic impedances
– :S beam reaching the second tissue
changes direction
–
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-.at t"pe o artiact is t.is/
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U#trasound Termino#o'"
• Never use dense, opaque, lucent• Anechoic
– No returning echoes1 blac" 6acellular fluid7
• >chogenic – egarding fluid##some shade of grey dt returning
echoes
• elative terms – -omparison to normal echogenicity of the same
organ or other structure – 8ypoechoic, isoechoic, hyperechoic
• Spleen should be hyperechoic to liver • $iver is hyperechoic to "idneys
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Ultrasound safety
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Ultrasound : sa)ety
• Muestion 0( ultrasound has been usedto image the foetus for about 5* years. )tis thought to be completely safe and
does not cause significant heating
• D( ultrasound is new, requires more
energy and therefore generates more
heating. &e thin" it is safe.
•:ltrasound is energy and is absorbed bytissue, causing heating
• Should we use it to diagnose foetalillness
• Should we use it to ma"e videos of
healthy babies for parents
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Summary:
• &e can get images of the body by recording
echoes of ultrasound
• :ltrasound is good at imaging soft tissues
• The (oppler effect can be used to detect blood
flow
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Acknowledgements:
• Than"s to G> 8ealthcare, 3rof em 8ebden and 3rof Alf
$inney for providing images.
• This lesson was developed by Adam Gibson, eff ones,
(avid Sang, Angela Newing, Nicola 8annam and >mily
-oo"
• &e have attempted to obtain permission and ac"nowledge
the contributor of every image. )f we have inadvertently used
images in error, please contact us.