1. Medical uses of Ultrasound
Further information:
Stephen Hughes (2001) Medical ultrasound imaging Phys. Educ. 36 (November 2001)
P N T Wells (1999) Ultrasonic imaging of the human body Rep. Prog. Phys. 62 (May 1999)
A Fenster, D B Downey and H N Cardinal (2001) Three-dimensional ultrasound imaging Phys. Med. Biol. 46 (May 2001) R67-R99
P N T Wells (1994) Ultrasonic colour flow imaging Phys. Med. Biol. 39 (December 1994)
Richard Fox (1996) Probing the body with Doppler ultrasound Phys. Educ. 31 (March 1996) 85-90
History:

2. Bats!

3. Bats navigate using ultrasound

4. Bats: Navigating with ultrasound
Bats make high-pitched chirps which are too high for humans to hear. This is called ultrasound
Like normal sound, ultrasound echoes off objects
The bat hears the echoes and works out what caused them
Dolphins also navigate with ultrasound
Submarines use a similar method called sonar
We can also use ultrasound to look inside the body…

5. Bats: Navigating with ultrasound
If a bat hears an echo 0.01 second after it makes a chirp, how far away is the object?
Clue 1: the speed of sound in air is 330 ms-1
Clue 2: The speed of sound equals the distance travelled divided by the time taken
Answer: distance = speed x time
Put the numbers in:
distance = 330 x 0.01 = 3.3 m
But this is the distance from the bat to the object and back again, so the distance to the object is 1.65 m.

6. Ultrasound imaging

7. Ultrasound imaging: What does it look like?
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8. Ultrasound imaging: How does it work?
Need to clarify difference between probe and element
Mention coupling gel
An ultrasound element acts like a bat.
Emit ultrasound and detect echoes
Map out boundary of object

9. Ultrasound imaging: How does it work?
Now put many elements together to make a probe and create an image

10. Ultrasound imaging: development of a pregnancy
24 weeks
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8 weeks gestation (out of a 40 week pregnancy)
18 weeks

11. Ultrasound imaging: foetus feet
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This is a 2D ultrasound scan
through the foot of a foetus. You can see some of the bones of the foot.
We can process the image in a computer to find the outline of the foot. This is called surface rendering. Here, the foot has been surface rendered

12. Ultrasound imaging: more surface rendering
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13. Ultrasound imaging: imaging the heart
heart valves
atrium
ventricle
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14. Ultrasound imaging: kissing!
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15. Ultrasound imaging: kissing – an inside view!
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16. Doppler ultrasound

17. Doppler effect: change in wavelength with speed
Ultrasound, like normal sound, is a wave.
If 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 – the sound has a higher pitch.
We use this principle to work out how fast blood cells move. Ultrasound reflects off the blood cells and causes a Doppler shift
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18. The ultrasound probe emits an ultrasound wave
A stationary blood cell reflects the incoming wave with the same wavelength: there is no Doppler shift

19. The ultrasound probe emits an ultrasound wave
A blood cell moving away from the probe reflects the incoming wave with a longer wavelength
In reality, there is actually two Doppler shifts. The first one occurs between the probe and the moving blood cell (not shown here) and the second one occurs as the red blood cell reflects the ultrasound.

20. Now, the blood cell moves towards the probe
Now, the blood cell moves towards the probe. It reflects the incoming wave with a shorter wavelength

21. Doppler effect: blood flow in artery
Picture and sound from Adam
Radial artery – same one as you measure your pulse from

22. Doppler imaging: combine imaging and Doppler
Use BOTH normal ultrasound imaging and Doppler imaging
Used to image blood flow
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23. Ultrasound imaging: carotid artery
Doppler imaging looks at artery
Get image and trace of blood flow
This is a healthy artery. The flow is smooth and all in the same direction, like water in a large, slow river
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24. Ultrasound imaging: carotid artery
This is also a carotid artery.
The flow is not all in the same direction. It is turbulent, like rapids in a river.
This is usually due to a build-up of fatty deposits in the artery
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25. Ultrasound imaging: 4D Doppler ultrasound
Ventricles
Atria
This is a complicated image of the heart of a foetus. It shows the blood moving between the ventricles and the arteries.
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26. Ultrasound safety

27. Ultrasound: safety
Ultrasound is energy and is absorbed by tissue, causing heating
Question: 2D ultrasound has been used to image the foetus for about 50 years. It is thought to be completely safe and does not cause significant heating
4D ultrasound is new, requires more energy and therefore generates more heating. We think it is safe.
Should we use it to diagnose foetal illness?
Should we use it to make videos of healthy babies for parents?

28. Summary:
We can get images of the body by recording echoes of ultrasound
Ultrasound is good at imaging soft tissues
The Doppler effect can be used to detect blood flow
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29. Bye!
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31. Acknowledgements:
Thanks to GE Healthcare, Prof Jem Hebden and Prof Alf Linney for providing images.
This lesson was developed by Adam Gibson, Jeff Jones, David Sang, Angela Newing, Nicola Hannam and Emily Cook
We have attempted to obtain permission and acknowledge the contributor of every image. If we have inadvertently used images in error, please contact us.
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