attenuation Flashcards

(62 cards)

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

kvp controls

A

how strong beam is

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

mA controls

A

filament heating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

when do you change kvp and ma

A

for larger or pedo patients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

high mA and kV means

A

high density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

mA is

A

quantity of x ray

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

kV is

A

quality of x ray

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

alternating current

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

frequency

A

of alternating current cycles/second = 60 Hz

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

voltage

A

electrical pressure pushing electrons thru a wire

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

current (ampere)

A

number of electrons flowing in a wire/second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

x ray generator

A

supplies electric power to tube

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

low voltage circuit

A
  • heats tungsten filament

- provides electrons by heating the filament to incandescence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

high voltage circuit

A
  • create flow of electrons bw anode and cathode

- provides potential difference between anode and cathode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

step up transformer

A

high voltage current (60-120)

creates potential difference between anode and cathode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

step down trans

A

low voltage current

heats tungsten filament

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

primary functions of autotransformer

A
  • stabilize incoming electricity (voltage)

- adjusts the voltage flowing to the tube head

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

longer time–>

A

more x rays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

shorter time–>

A

fewer x rays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

double exposure time–>

A

2X more radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

in old x rays, only —- were usable

A

60 of alterations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

modern dental x rays

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

tube rating

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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