5.4.3 ULTRASOUND

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Describe the properties of ultrasound
very high frequency/ longitudinal waves/ speed depends on substance through which it travels/ reflected at boundaries
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What is the frequency of medical ultrasound?
2-10MHz/ v small wavelength so smaller details detected
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Describe the piezoelectric effect
alternating p.d. applied to crystal (PZT/quartz) causes it to vibrate/ p.d. is resonant f so resonance occurs and maximises amplitude of waves/ crystal is damped to stop vibrations when no p.d.
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Why is the piezoelectric crystal backed in an epoxy resin?
backing material to damp and absorb backwards travelling sound waves
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How do ultrasound transducers emit and receive high-frequency sound?
traducer contains crystal/ emission - connected to alt. p.d. causes it to resonate and vibrate to produce ultrasound waves/ detection - ultrasound waves hit the crystal causing it to vibrate which produces an alternating p.d. which can be interpreted
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Describe the principles of ultrasound scanning
must be pulsed to enable use of echoes (pause in transmission while reflected echoes received)/ some waves reflected at tissue boundary used to identify/ time of delay determines thickness/
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Describe the difference between A-Scans and B-Scans
A-Scan in one direction/ find distances// B-scan uses number of sensors to build up 3D image - move around
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Describe acoustic impedance, what is its unit?
property of a material that determines reflected ultrasound intensity/ important in ultrasound as want to maximise amount of waves into the body/ kgm-2s-1
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Explain why a gel is required for effective ultrasound imaging
coupling medium ensures as much ultrasound is transmitted into body without being reflected/ difference in Z between air and skin is big so all would be reflected/ gel and skin is similar
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explain what the doppler effect means
change in frequency and wavelength of a wave/ caused by change in distance between origin of wave and detector of wave
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How can the doppler effect be used to determine the speed of the blood?
ultrasound waves/ reflected by moving blood cells/ change in freq or wavelength enables speed of blood flow to be found/ frequency is prop to speed of blood
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Other cards in this set

Card 2

Front

What is the frequency of medical ultrasound?

Back

2-10MHz/ v small wavelength so smaller details detected

Card 3

Front

Describe the piezoelectric effect

Back

Preview of the front of card 3

Card 4

Front

Why is the piezoelectric crystal backed in an epoxy resin?

Back

Preview of the front of card 4

Card 5

Front

How do ultrasound transducers emit and receive high-frequency sound?

Back

Preview of the front of card 5
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