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24 Cards in this Set
- Front
- Back
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What happens when fast moving electrons strike target atoms? |
Collisions slow the electrons and they give up their energy. If stopped - give up all energy - high energy exrays |
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What does the x-ray head contain? |
Cathode- negatively charged, releases electrons Anode - positively charged, slows the electrons allowing generation of x-rays Vacuum - allows passage of electron beam |
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What is mAs? |
Intensity Greater number of electrons striking the target, great number of X-rays produced Measured in mA milliamperes |
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What is kV? |
penetration Greater speed of electrons when they hit the target - more energy to lose and greater energy of X-ray. Kilovolts |
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What is inside the cathode? |
Coiled tungsten wire - heats up - releases electrons |
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What does the focussing cup to? |
At negative potential - repels electrons so form a narrow beam |
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What happens at the anode? |
Electrons strike anode target 99% energy lost as heat, 1% xray |
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What does the light beam diaphragm? |
Prevents low-energy xrays leaving tubing head Also helps reduce scatter |
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What are the different types of x-ray machine? |
Stationary anode Anode is small rectangular block of tungsten embedded in copper stem Copper conducts heat to colling fins in oil bath Rotating anode Target is tungsten rim of a metal disc Disc rotates so target area constantly changing Used for more powerful machines |
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What should a control panel display? |
kV, mAs and alteration options |
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What are the 2 stages of button pressing? |
Depress half way - heats up cathode filament - rotates anode Depress to all the way -application of potential difference between cathode and anode = exposure |
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What are the types of xray machine? |
Portable Mobile Fixed |
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Which substance is used in an xray anode? |
Tungsten |
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What is the journey of the x-ray? |
Poor, weak x-rays get caught by aluminium filter Most x-rays join primary beam. Leave diaphragm, travel in a straight line down Patient - absorbed (bone/metal), pass through - gas Some bounce off surfaces they hit as scatter |
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What do kV and mAs influence? |
kV - speed of electrons, power of the x-ray, how likely to be absorbed/pass through tissues mAs - influences the number of x-rays so determines detail of image |
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How do kV and mAs interlink? |
both high = over expose If you increase one, decrease other |
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When do you need to increase and decrease kV? |
the power determines how easily the x-rays penetrate All white image - need to increase power All black images- need to decrease power |
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When do you need to increase or decrease mAs? |
the density and partially influences contrast Flat white image with poor detail - increase density Very dark image with no shades of grey - decrease density |
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What is the penumbra effect? |
Xrays come from 2 different points and cause the image to be produced slightly differently from both xrays This causes blurring/shadowing of the edges |
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What is FFD? |
Focal-film distance Distance between focal spot and X-ray film Intensity of beam reduces as X-rays spread out from focal spot |
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What is inverse square law? |
intensity of radiation at a particular point is inversely proportional to the square of the distance between source and that point |
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What happens if FFD is increased? |
the intensity which reaches the film is reduced - need to compensate by increase mAs |
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What happens if FFD is reduced? |
X-rays are move divergent so penumbra effect is increased |
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If the object film distance is large, what does this mean? |
The primary beam continues to diverge after passing through the object. This causes -magnification -distortion -greater penumbra effect |
