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9 Cards in this Set
- Front
- Back
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What is cavitation? |
Ultrasound produces oscillating pressure wave which propagates through tissue.
This can cause micro bubbles to form, grow and oscillate in size within the tissue.
At high intensities and pressure bubbles can collapse. |
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What can cavitation do when it is above diagnostic output levels ? |
Lithotripsy - destroy kidney stones |
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What are the two forms of cavitation? |
Stable
Unstable |
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What is stable cavitation? |
Small micro bubbles are forced to oscillate in the presence of ultrasound.
Bubbles go through phrases of contraction and expansion.
Regarded as safe.
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What is unstable cavitation? |
The bubbles collapse due to intensity of the ultrasound.
This causes high pressures and temperatures localised to that area.
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Which ultrasound examination is at increased risk of cavitation? |
Early pregnancy as the tissues are more susceptible to damage
Using contrast agents increases cavitation |
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What is the mechanical index equation? |
MI= peak neg pressure (pr) ------------------------------- Square root of frequency |
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Discuss mechanical index relationships with frequency and pressure. |
Pressure is doubled the mi doubles.
Frequency increases mi deceases. |
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What do mi and ti give a value of? |
Risk- they are not absolute values but represent risk. |
