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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
higher kVp produces
shorter wavelengths with a greater ability to penegrate the body tissue
26
contrast
difference in density between 2 structures | contrast makes detail visible
27
what controls contrast?
kVp, they are inversely related
28
low kvp looks like..
high contrast, short scale
29
low kVp produces less
scatter, however, the amount of radiation absorbed by the patient is increased
30
to lower your contrast you/longer scale of contrast you..
have more shades of grey | you must increase kVp by 15% and decrease mA by 50%
31
to raise your contrast/shorter scale of contrast you...
more black and white | decrease kVp and increase mAs by 100%
32
an increase in ___ by 15% will____the density of the film
kVp | double
33
a decrease in ___by 15% will____the density of the film
kVp double
34
describe what the different physiologic parts of the body will show up on film
gas-black fat- black muscle, water, soft tissue- grey bone, metal- white
35
anode heel effect
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
give an example of the anode heel effect
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
anode side
less xray smaller effective focal spot more detail use thinner body part
38
cathode side
more xray larger effective focal spot less detail use on thicker body part
39
FFD/SID
focal film distance source image distance represents the length of space from the focal spot to the recording medium
40
as you increase FFD..
the image gets smaller and clearer | decreases magnification distortion
41
inverse square law
2/1 inversed= (1/2)^2 AKA 1/4
42
example of inverse square law for xray
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
intensifying screens
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
large crystals in an intensifying screen..
work quickly less detail faster screens=higher contrast= short scale (less pt exposure)
45
small crystals in an intensifying screen..
work slowly, but offer more detail | slow screens=lower contrast= longer scale (more patient exposure)
46
definition
describes the clarity and sharpness of an image
47
umbra
picture made by useful beam
48
penumbra
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
OFD
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
screen film contact and definition
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
scatter radiation
when xrays strike an object one of 3 things can occur: scatter, absorb, or penetrated
52
scatter can be reduced by?
grids air gap technique collimators filters
53
grid
device of alternating strips of lead and spacer material | placed between patient and film
54
sole purpose of grid
improve quality of radiograph by abdorbing scatter radiation
55
what will be required if you use a grid?
increase in exposure factors to maintain density (increases patient dose of radiation)
56
grid ratio
height of the lead strips to the distance between the strips | 12:1 ratio in chiro office
57
air-gap technique
6-10" between patient and film | lat. cervical, flexion, extension
58
distance between body part and film causes?
scatter radiation to diverge away from the film | reduces patient dose, can distort/magnify image
59
collimation
limits the size of the beam to the size of the body part you need to capture on film
60
collimation is the best way to?
reduce scatter radiation to patient and film
61
filtration
preferential removal of low energy photons | usually made of aluminum
62
what does the filter do?
stops the weak photons from entering the aptient's body thus protecting them from scatter radiation
63
radiation absorbed dose (RAD)
used to identify irradiation in patients measures the radiation energy absorbed 1 RAD= 1 REM
64
radiation equivalent man (REM)
typically applied to occupationally exposed persons identifies the biological effectiveness of the radiation abdorbed 5 REMS is the safe limit per year
65
maximum permissible dose (MPD)
rumber of REMS a person can get in a lifetime without getting radiation poisoning MPD= 5(age-18)
66
bremsstrahlung radiation
AKA braking radiation majority of useful beam interacts with target nucleusq
67
characteristic radiation
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
types of scatter radiation
compton scatter classical scatter photoelectric effect quantum mottle
69
compton scatter
primary form of scatter | moderate energy xray knocks out an outer shell electron, which causes a loss of energy
70
classical scatter
AKA thompson scatter AKA coherent scatter low energy xray that schanges direction with no energy loss contributes to film god
71
photoelectric effect
low energy photon is absorbed by the subject creating a latent image on the film
72
quantum mottle
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
what decreases quantum mottle?
high mAs | low kVp

Part 2 boards (19 decks)

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