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12 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is distortion?
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The misrepresentation of the size and shape of an object recorded on an image
Can we eliminate distortion? |
No, every image has some distortion. every object has some magnification and some shape distortion
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What effects size distortion?
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1. SID
2. OID |
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What effects shape distortion?
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1. alignment
2. angulation |
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Why is going to a standard of 48" SID better?
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Less magnification as well as pt dose reduced by 12%
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What is the formula for calculating magnification?
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M = SID/SOD
what is SOD and how do you calculate it? |
Source to object distance. it is SID - OID
Example: object is 2" SID is 40" and OID is 4", what is the magnification factor. SOD = 40-4= 36 so M = 40/36, which is 1.11 |
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How do we figure image size once we have the magnification factor?
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using this formula O = I/M
the image size is object size times magnification factor. so in the example already given the image is going to be 11% larger |
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What is shape distortion?
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unequal magnification of the actual structure being examined
what are the 2 types? |
1. Elongation
2. Foreshortening |
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Elongation, what is it and what causes it?
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Object appears longer and happens when the tube or IR are not properly aligned
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Foreshortening, what is it and what causes it?
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Object appears shorter and happens ONLY when the body part is not parallel to IR
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Why is CR centering so important?
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Because of beam divergence anything off center will be distorted
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What is the reason we angle the tube?
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2 reasons:
1. to see a body part in a way you wouldn't see otherwise 2. to avoid superimposition |
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In general when you angle the tube how much do we compensate for with SID?
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decrease SID 1" for every 5 degrees of angle
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