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Dental Radiology > X-Ray Interactions with Matter > Flashcards

X-Ray Interactions with Matter Flashcards

1
Q

what are the 3 ways that photons interact with matter

A

transmission, absorption, scatter

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2
Q

what is transmission

A

photon passes directly through tissue unchanged

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3
Q

what is absorption

A

energy fully deposited into tissue and photon ceases to exist

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4
Q

what is scatter and absorption

A

photon deflected by tissue
partial deposition of energy into tissue
photon continues in new direction

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5
Q

what is attenuation

A

reduction in intensity of x-ray beam (can include absorption and scatter)

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6
Q

what is x-ray beam intensity

A

quantity of photon energy passing through a cross-sectional area of the beam per unit time

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7
Q

what is intensity proportional to

A

energy and number of photons

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8
Q

what does minimal attenuation give

A

black image

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9
Q

what does partial attenuation give

A

grey image

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10
Q

what does complete attenuation give

A

white image

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11
Q

what are predictions of x-ray photon interactions based on

A

physical properties of matter being exposed

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12
Q

what are the 2 specific attenuation interactions

A

photoelectric effect and compton effect

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13
Q

what is the photoelectric effect

A

photon in x-ray beam interacts with inner shell electron in subject, resulting in absorption of the photon and creation of photoelectron

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14
Q

when does the photoelectric effect take place

A

when energy of incoming photon is equal to or greater than the binding energy of inner shell electron

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15
Q

when does the photoelectric effect predominate

A

with lower energy photons

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16
Q

what can a photoelectron do to tissues

A

ionise and damage adjacent tissues

17
Q

why does photoelectric effect lead to lighter areas on radiographs

A

it prevents x-ray photons reaching the receptor

18
Q

what is the photoelectric effect proportional to

A

atomic number cubed

19
Q

what is the compton effect

A

photon in x-ray beam interacts with outer shell electron in subject, resulting in partial absorption and scattering of the photon and creation of a recoil electron

20
Q

when does the compton effect occur

A

when energy of incoming photon is much greater than binding energy of electron

21
Q

when does the compton effect predominate

A

with higher energy photons and outer shell electrons

22
Q

what can a recoil electron do to tissues

A

ionise and damage adjacent tissues

23
Q

what is scatter influenced by

A

energy of incoming photon

24
Q

where are higher energy photons scattered

A

more forward - forward scatter

25
Q

where are lower energy photons scattered

A

more backward - back scatter

26
Q

what is the majority of the scatter from an x-ray beam

A

forward scatter

27
Q

what is the reason for the controlled area to surround the patient

A

scatter

28
Q

what is the probability of the compton effect occurring

A

proportonal to the density of material

29
Q

what does collimation do

A

decrease surface area irradiated
decrease volume of irradiated tissues
decrease number of scattered photons produced in tissue
decrease scattered photons interaction with receptor
decrease loss of contrast on radiographic image

30
Q

what is the photoelectric effect on radiation dose

A

increase patient dose but is necessary for image formation

31
Q

what is the compton effect on radiation dose

A

increased patient dose but scattered photons do not contribute usefully to image

32
Q

what is the effect of lowering kV on x-ray unit

A

increased contrast between tissues with different atomic numbers but increased patient dose

33
Q

what is the effect of raising kV on x-ray unit

A

decreased dose absorbed by patient but decreased contrast between tissues with different atomic numbers

34
Q

what is the UK guidance for range of kV in intraoral units

A

between 60-70kV

Dental Radiology (16 decks)

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