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37 Cards in this Set
- Front
- Back
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What is מעבר? מנת |
Primary radiation + scatter radiation |
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Why is scatter radiation bad? |
Hurts contrast, can hurt staff |
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How does scatter radiation hurt contrast? |
Adds חשחרה darkness |
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What is scatter radiation? |
Compton effect--photon hits an electron in the outer ring and loses only some of its energy then continues on a different path. |
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KV + Scatter ? Contrast ? |
KV + Scatter +Contrast - |
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Thickness of organ + Scatter ?Contrast ? |
Thickness of organ + Scatter +Contrast - |
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Size of field - Scatter ?Contrast ? |
Size of field - Scatter -Contrast + |
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OFD +Scatter ?Contrast ? |
OFD +Scatter -Contrast + |
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What are the three methods for reducing scatter? |
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What does the culimeter do? |
Changes the size and shape of the field with lead plates, reduces scatter |
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How does the culimeter reduce scatter? |
Reduces the field so reduces the number of photons getting to the body, reducing scatter and improving contrast |
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How can we see the צמצום? |
Dark room, light and mirror shine field on pt |
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How does a grid help with scatter? |
Absorbs secondary radiation from getting to cassette, improving contrast, but does not actually reduce scatter |
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Where is the grid located? |
Between the pt and the film |
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What is the grid made of? |
Lamelot (thin plates of lead) |
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What measures the effectiveness of the grid? |
יחס סורג grid ratio |
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What is meant to pass between the lamelot? |
Primary radiation (to get to the film) passes through permeable material |
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How does the grid work? |
Primary radiation passes through, scatter radiation is absorbed |
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True or false. Since the grid absorbs some of the primary radiation, we must increase the MAS. |
True |
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What is the grid ratio? |
R = h/d (height of the lamelot ÷ distance between lamelot) |
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What is important about the thickness of the lamelot? |
Too thick, we see them. But not a factor in grid ratio. |
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How can we raise the grid ratio? |
Increase the height or decrease the distance |
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Higher grid ratio means ___ scatter is absorbed. |
More |
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What are the 3 types of grids? |
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Why are parallel grids not suited for large area x-rays? |
Fanlike beams will be blocked so edges will appear white. תת השחרה |
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What are the advantages and disadvantages of the unfocused (parallel) grid? |
+ absorbs scatter - doesn't calculate geometry of beams, cuts off edges |
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What are the advantages and disadvantages of the focused grid? |
+ absorbs scatter (also on edge) - needs to be perfectly lined up - tube has to be at set distance of 1 - 1.20 |
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Higher grid ratio means we should ___ the FFD. |
decrease |
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What are the advantages and disadvantages of the crossed grid? |
+ absorbs most scatter - can't use with angles other than 90° |
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What is the job of the booky? |
To absorb scatter radiation! Moves to blur the lines of the lamelot. |
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Higher grid ratio increases the chance of ____. |
grid cutoff |
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Disadvantage of using a grid: |
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Using a grid requires ___ times the amount of radiation. |
6 |
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What is the booky factor? |
MAS with grid/MAS without grid |
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How does an air gap work? |
Body part is 15-25 cm from film, meaning that less scatter radiation will get to film (+ OFD). Contrast is better but חדות is worse--we compensate by moving tube away (+ FFD). |
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KV + 》 contrast ? Thickness of part + 》 contrast ? Size of field - 》 contrast ? Grid 》 contrast ? Air pocket 》 contrast ? Scatter radiation 》 contrast ? |
KV + 》 contrast -Thickness of part + 》 contrast -Size of field - 》 contrast +Grid 》 contrast +Air pocket 》 contrast +Scatter radiation 》 contrast - |
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What is scatter radiation and why is it important to contrast? What leads to scatter radiation? What can we do to reduce scatter radiation? |
Secondary radiation occurs with radiation getting to film, comes from pt not tube. Compton effect, prevents a true recording of body's natural density. Causes reduction in contrast and fog. Caused by high kv, large fields, large people, small OFD Avoid by grid, air gaps, צימצום, reasonable kv grid, air gaps, צימצום, reasonable kv |
