Lesson 10 - Ultrasound

8/18/2019 Lesson 10 - Ultrasound

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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.

Lesson 10 - Ultrasound

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