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Part 2 boards > Xray Physics > Flashcards

Xray Physics Flashcards

1
Q

cathode consists of?

A

large filament
small filament
focusing cup

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2
Q

filament serves as?

A

the source of electrons in the production of xrays and are made of tungsten

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3
Q

when does thermonic emission occur?

A

when a current is applied to a filament

coil of the wire becomes very hot, boiling off electrons

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4
Q

the temp of the filament controls?

A

quantity of electrons (mA) emitted from it

the number of electrons determines the number of xrays created

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5
Q

the temp of the filament controls?

A

quantity of electrons (mA) emitted from it

the number of electrons determines the number of xrays created

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6
Q

focusing cup/filament cup

A

part of the cathode
encases the two filaments
this is where thermionic emmision occurs
each filament sits in its own cup, the cup consolidates the electron cloud

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7
Q

anode

A

positive electrode in the xray tube
most xray tubes consist of a rotating anode
rotating target receives electrons as they move from cathode to anode

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8
Q

rotating anode target

A

dissipates the heat generated

creates the focal spot

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9
Q

focal spot

A

an area of tungsten target of the anode

will be determined by the size of the filament that is chosen

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10
Q

why is a smaller filament better?

A

better detail, less penumbra (unclear borders)

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11
Q

line focus/beam hardening principle

A

has the effect of making the actual focal spot size appear smaller when viewed from the position of the film
the smaller the target angle, the smaller the effective spot
stream of electrons narrows down to an effective beam

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12
Q

mA

A

milliamperage

heats the filament causing a boiling off of electrons

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13
Q

mAs

A

more current=more electrons produced= greater radiograph density (darker)

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14
Q

density

A

overall blackening of the film

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15
Q

radiolucent

A

structures that produce more blackening on the film

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16
Q

radiopaque

A

structures that produce more whitening on the film

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17
Q

the relationship between mAs and density

A

directly proportional

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18
Q

what does changing mAs do to the film?

A

controls the blackening of the film

more mAs= more film exposure

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19
Q

how much change in mAs does it change to perceive a change in the film?

A

30%

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20
Q

if mAs is doubled..

A

density is doubled

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21
Q

kVp

A

force applied to accelerate the electrons from the cathode to the anode at the time of exposure
greater force= greater number of high energy photons will be produced

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22
Q

wavelength and frequency are..

A

inversely related

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23
Q

low kVp=

A

low energy= weak penetration

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24
Q

high kVp=

A

high energy= greater penetration

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25
Q

higher kVp produces

A

shorter wavelengths with a greater ability to penegrate the body tissue

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26
Q

contrast

A

difference in density between 2 structures

contrast makes detail visible

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27
Q

what controls contrast?

A

kVp, they are inversely related

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28
Q

low kvp looks like..

A

high contrast, short scale

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29
Q

low kVp produces less

A

scatter, however, the amount of radiation absorbed by the patient is increased

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30
Q

to lower your contrast you/longer scale of contrast you..

A

have more shades of grey

you must increase kVp by 15% and decrease mA by 50%

31
Q

to raise your contrast/shorter scale of contrast you…

A

more black and white

decrease kVp and increase mAs by 100%

32
Q

an increase in ___ by 15% will____the density of the film

A

kVp

double

33
Q

a decrease in ___by 15% will____the density of the film

A

kVp double

34
Q

describe what the different physiologic parts of the body will show up on film

A

gas-black
fat- black
muscle, water, soft tissue- grey
bone, metal- white

35
Q

anode heel effect

A

when theintensity and desnity decrease on the anode side of the film, place the thinner portion of what is being xrayed toward this end

36
Q

give an example of the anode heel effect

A

the toes are thinner than the ankle

if you ray the foot, you aim the tube so the anode is toward the toes and the cathode is at the ankle

37
Q

anode side

A

less xray
smaller effective focal spot
more detail
use thinner body part

38
Q

cathode side

A

more xray
larger effective focal spot
less detail
use on thicker body part

39
Q

FFD/SID

A

focal film distance
source image distance
represents the length of space from the focal spot to the recording medium

40
Q

as you increase FFD..

A

the image gets smaller and clearer

decreases magnification distortion

41
Q

inverse square law

A

2/1 inversed= (1/2)^2 AKA 1/4

42
Q

example of inverse square law for xray

A

if a 40 ubcg FFD is doubled to an 80 inch FFD, the intensity of the radiation at 80 inches is 1/4 the intensity at 40 inches if no factors are changed

43
Q

intensifying screens

A

consists of fluorescent crystals
when hit by the xray, fluorescent salt changes xray photons into visible light photons
can expose the film and decrease patient exposure

44
Q

large crystals in an intensifying screen..

A

work quickly
less detail
faster screens=higher contrast= short scale (less pt exposure)

45
Q

small crystals in an intensifying screen..

A

work slowly, but offer more detail

slow screens=lower contrast= longer scale (more patient exposure)

46
Q

definition

A

describes the clarity and sharpness of an image

47
Q

umbra

A

picture made by useful beam

48
Q

penumbra

A

blurry halo parts of the image (unsharpness)
caused by having tube too close to the film (short FFD), having patient too far from the film (long OFD), having too fib filament on cathode, making focal spot too big

49
Q

OFD

A

distance between patient and film
as you increase OFD, image becomes bigger and blurrier
as you decrease OFD, image becomes smaller and more clear

50
Q

screen film contact and definition

A

screen film contact is the pressure eerted by the film holder as it encloses the xray film
pressure should be evenly distributed across the surface of film
wire mesh test is best for screen film contact
poor screen film contact reduces the image sharpness of the image

51
Q

scatter radiation

A

when xrays strike an object one of 3 things can occur: scatter, absorb, or penetrated

52
Q

scatter can be reduced by?

A

grids
air gap technique
collimators
filters

53
Q

grid

A

device of alternating strips of lead and spacer material

placed between patient and film

54
Q

sole purpose of grid

A

improve quality of radiograph by abdorbing scatter radiation

55
Q

what will be required if you use a grid?

A

increase in exposure factors to maintain density (increases patient dose of radiation)

56
Q

grid ratio

A

height of the lead strips to the distance between the strips

12:1 ratio in chiro office

57
Q

air-gap technique

A

6-10” between patient and film

lat. cervical, flexion, extension

58
Q

distance between body part and film causes?

A

scatter radiation to diverge away from the film

reduces patient dose, can distort/magnify image

59
Q

collimation

A

limits the size of the beam to the size of the body part you need to capture on film

60
Q

collimation is the best way to?

A

reduce scatter radiation to patient and film

61
Q

filtration

A

preferential removal of low energy photons

usually made of aluminum

62
Q

what does the filter do?

A

stops the weak photons from entering the aptient’s body thus protecting them from scatter radiation

63
Q

radiation absorbed dose (RAD)

A

used to identify irradiation in patients
measures the radiation energy absorbed
1 RAD= 1 REM

64
Q

radiation equivalent man (REM)

A

typically applied to occupationally exposed persons
identifies the biological effectiveness of the radiation abdorbed
5 REMS is the safe limit per year

65
Q

maximum permissible dose (MPD)

A

rumber of REMS a person can get in a lifetime without getting radiation poisoning
MPD= 5(age-18)

66
Q

bremsstrahlung radiation

A

AKA braking radiation
majority of useful beam
interacts with target nucleusq

67
Q

characteristic radiation

A

high intensity electron hits an inner shell electron, which is knocked out of its position in orbit
outer shell electron then fills its spot

68
Q

types of scatter radiation

A

compton scatter
classical scatter
photoelectric effect
quantum mottle

69
Q

compton scatter

A

primary form of scatter

moderate energy xray knocks out an outer shell electron, which causes a loss of energy

70
Q

classical scatter

A

AKA thompson scatter
AKA coherent scatter
low energy xray that schanges direction with no energy loss
contributes to film god

71
Q

photoelectric effect

A

low energy photon is absorbed by the subject creating a latent image on the film

72
Q

quantum mottle

A

AKA radiographic noise
fluctuation of the number of photons absorbed by the intensifying screens to form the image on the film
faster screens porduce more quantum mottle

73
Q

what decreases quantum mottle?

A

high mAs

low kVp

Part 2 boards (19 decks)

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