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1015 Medical Radiation Sciences > attenuation processes > Flashcards

attenuation processes Flashcards

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USMLE® Step 1 flashcards
1
Q

what matter do low/med/high E radiation interact with?

A

low - atoms/molecules
med - electrons
high - nuclei

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2
Q

what is attenuation

A

anything that reduces the x-ray beam intensity

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3
Q

what is the photoelectric effect

A

a photon ionizes an atom, ejecting the k-shell electron
ALL ENERGY gets absorbed
outer shell drops down, creating SECONDARY ch rad

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4
Q

what is the formula for the energy of a photoelectron

A

KE = hf - BE

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5
Q

when is the photoelectric effect the most probable

A

when the photon energy is just above the BE

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6
Q

how does the photoelectric effect affect the image

A

no scatter
magnifies subject contrast

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7
Q

how does the photoelectric effect affect the pt

A

very high dose -all energy absorbed
photoelectron can cause new ionizations
secondary characteristic radiation

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8
Q

what is coherent scatter

A

when a photon strikes an atom, and the excitation causes energy (IDENTICAL) to be released

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9
Q

which are ionizing interactions?
photoelectric effect
coherent scatter
Compton scatter

A

photoelectric effect
Compton scatter

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10
Q

when is coherent scatter the most probable

A

with high Z, low energy

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11
Q

how common is coherent scatter in diagnostic radiagraphy

A

<5% of scatter

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12
Q

what is Compton scatter

A

photon ionizes an atom, releasing a Compton electron and changing direction

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13
Q

how much of the original photon energy does a scatter Compton x-ray retain

A

at least 2/3

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14
Q

what are the end products of Compton scatter

A

ion pair (pos atom, Compton electron)
scattered photon

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15
Q

when is Compton scatter most likely

A

when photon E is much higher than the BE

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16
Q

how does Compton scatter affect the image

A

degrades image quality:
reduces contrast
creates noise

17
Q

what are the dose effects of Compton scatter

A

minimal photon energy loss, but compton electron, bad for pt
high E scatter to staff

18
Q

what is pair production

A

HIGH E - >1.02 MeV
a photon interacts with the nuclear field, creating an electron and a positron

19
Q

what is photodisintegration

A

VERY HIGH E - >10MeV
photon interacts with nucleus, ejecting a nucleon or nuclear fragment

1015 Medical Radiation Sciences (13 decks)

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