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radiology exam 1 > attenuation > Flashcards

attenuation Flashcards

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1
Q

primary components of x ray machine

A
  • tube and power supply in tube head; head supported by arm

- control panel to adjust duration, energy, and exposure rate

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2
Q

kvp controls

A

how strong beam is

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3
Q

mA controls

A

filament heating

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4
Q

when do you change kvp and ma

A

for larger or pedo patients

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5
Q

high mA and kV means

A

high density

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6
Q

mA is

A

quantity of x ray

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7
Q

kV is

A

quality of x ray

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8
Q

alternating current

A

when flow of electrons move in one direction and then reverse in opposite direction

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9
Q

frequency

A

of alternating current cycles/second = 60 Hz

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10
Q

voltage

A

electrical pressure pushing electrons thru a wire

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11
Q

current (ampere)

A

number of electrons flowing in a wire/second

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12
Q

x ray generator

A

supplies electric power to tube

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13
Q

low voltage circuit

A
  • heats tungsten filament

- provides electrons by heating the filament to incandescence

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14
Q

high voltage circuit

A
  • create flow of electrons bw anode and cathode

- provides potential difference between anode and cathode

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15
Q

step up transformer

A

high voltage current (60-120)

creates potential difference between anode and cathode

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16
Q

step down trans

A

low voltage current

heats tungsten filament

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17
Q

primary functions of autotransformer

A
  • stabilize incoming electricity (voltage)

- adjusts the voltage flowing to the tube head

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18
Q

mA controls

A

temperature of filament and size of electron cloud

  • high–> more e- strike target making more xrays
  • low–> fewer e- strike target making fewer x rays
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19
Q

longer time–>

A

more x rays

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20
Q

shorter time–>

A

fewer x rays

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21
Q

double exposure time–>

A

2X more radiation

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22
Q

in old x rays, only —- were usable

A

60 of alterations

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23
Q

modern dental x rays

A

-replace 60 cycle with high f power supply resulting in constant potential bw cathode and anode

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24
Q

tube rating

A

-guide the longest exposure time for range of KV and mA without damage

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25
duty cycle
freq with which successive exposures can be made without overheating the anode
26
quantity
number of photons
27
quality
energy of photons
28
intensity
total energy (quality x quantity) contained in the beam per unit time per unit area
29
how manufacturer controls intensity
- target material | - filtration
30
how practitioner controls intensity
kVp mA time source-receptor distance
31
why use tungsten for target
- high atomic number - high melting temp - large # of electrons
32
filtration
reduces intensity of primary x ray beam by selectively absorbing out useless, low energy x rays
33
inherent filtration
- glass wall of tube, oil, aperture window | - not sufficient to meet NCRP standards
34
added filtration
thin sheet of aluminum
35
total filtration=
added + inherent
36
influence of filtration
- mean photon energy increases - total number of photons decrease - most photons removed are lower energy photons - helps reduce harmful effects of radiation
37
50-70 kVp -->
1.5 mm Al
38
above 70 kVp-->
2.5 mm Al
39
what happens if you double the mA
twice as many electrons will be released but mean energy doesn't change
40
the longer the exposure time, the ----
more x rays are produced
41
exposure time affects the ---, not the ---- of the beam
affects the quantity not the quality
42
increasing kVp-->
increases number of x rays produced (quantity) and also increases energy of beam (quality)
43
15 kVp increase
increases intensity by 2X
44
15 kVp decrease
decreases intensity by 1/2 or 50%
45
half value layer
- expresses quality of beam | - thickness of an absorbing material necessary to reduce the x ray intensity to 1/2 of its original intensity
46
what are allowed to exit the tube housing
only useful, primary beam xrays
47
the intensity ---- as distance from the focal spot ----
intensity decreases as distance from focal spot increases
48
inverse square law
intensity of radiation varies inversely as square of the source-film distance
49
change from 8 to 16 BID -- whats the intensity
(distance doubled) | 1/(2^2)=1/4 original intensity
50
three interactions bw patient and x ray
- photons scattered - photons absorbed - photons pass completely thru patient
51
coherent scattering
incoming photon interacts with atom and sets it in motion and then disappears - low energy photon - interacts with whole atom & incident photon ceases to exist - excited atom returns to stable state and generates another photon - secondary photon has same energy as incident photon - minimal contribution to film fog
52
compton scattering
- x ray interacts with outer shell e- in pt's tissue - electron ejected - scattered photons and e continue and interact - photons travel in all directions and cause image degradation/film fog
53
photoelectric absorption
- incident x ray has more energy than binding energy of k shell e- in tissue - incident x ray completely disappears - photoelectron is generated (ejected from atom)
54
no interaction =
black/radiolucent
55
scattering=
hazy (fog)
56
absorption=
radiopaque (white and gray)
57
factors influencing absorption
1. photon energy (kVp) 2. thickness of structure 3. density of structure 4. atomic number
58
higher kVp results in
shorter wavelengths - increased energy --> greater penetration of radiation - higher energy--> less absorption
59
the thicker the structre, the greater---
the amount of absorption
60
density of tissues
compactness of material - mass/volume - greater density--> greater absorption
61
atomic number's effect on absorption
more effect than density or thickness - increased probability of interactions - greater atomic number--> greater absorption
62
differential absorption
different tissues absorb x rays in varying degrees

radiology exam 1 (7 decks)

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