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10 Cards in this Set
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- Back
- 3rd side (hint)
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What is the inverse square law?
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If distance doubles the intensity of radiation decreases four fold and inversely if distance is cut in half, intensity increases fourfold.
what effects its validity? |
scatter radiation, has to be a point source |
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What is the inverse square law equation?
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I 1 / I 2 = d 2 squared/d 1 squared
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A gamma source produces a reading of 150 mRem/hr at 3m. At what distance will the meter read 500 mRem/hr?
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1.64m
A syringe containing 5 mCi of Tc99m reads 25mR/hr at 1 meter. What is the dose rate at the surface of the syringe, assuming the syringe is 2cm? |
250,000 mR/hr |
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What is the allowable dose to the public?
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2 mR/week or 100 mR/yr or no single dose of 2 mR/hr
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What are the 2 areas NM depts are divided into?
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Restricted and Non-restricted
give some examples |
Restricted: hot lab, radioactive storage areas Non-restricted: waiting or scanning area, office, etc |
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What are the 6 factors to consider for shielding radioactive material?
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1. occupancy factor
2. distance from the source 3. how long is the source present 4. area restricted or non-restricted 5. type radiation sourced emits 6. existing shielding |
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How is an image created with a CT scanner?
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the average linear attenuation coefficient change in intensity between tube and detector
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What is the average linear attenuation coefficient for water, air and bone?
and how is the CT# arrived at? |
water=0; air=-1000; bone=1000
CT# is calculated by µtissue - µwater/ µwater x 1000 |
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What are the advantages of PET/CT fusion imaging?
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small time between PET and CT, body does not change
anatomy is better visualized with CT rather than PET alone greatly improves ability to locate lesions and other patholgy |
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Why is PET/CT not perfect?
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CT is much faster than PET so motion artifacts can occur, especially with lungs
difference in matrix sizes |
