10. Exposure technique factors: Primary and Secondary technique factors Flashcards

(63 cards)

1
Q

what are 2 factors that contribute to compton scatter

how

A

kVp = affects beam penetrability

Volume of irradiated material = field size and patient thickness

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2
Q

increasing the kVp has what effect on transmission

A

increases transmission

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3
Q

increasing the kVp has what effect on photoelectric scatter

A

decreases photoelectric scatter

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4
Q

increasing the kVp has what effect on compton scatter

A

increases compton scatter

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5
Q

increasing the kVp has what effect on patient dose

how

A

decreases dose

increase penetrability of beam so less is attenuated in tissues

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6
Q

increasing the kVp has what effect on image quality

A

lower amounts of contrast

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7
Q

decreasing the kV means what needs to be done for the mAs

A

Decrease in kv is more absorbtion but need to increase mAs to compensate (15% rule to maintain image quality)

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8
Q

what does increasing mAs result in for the beam

A

increases number of photons in the beam

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9
Q

what are the 3 factors of the volume of irradiated material

A

field size

patient thickness

average tissues density

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10
Q

increasing the field size does what to the volume of tissue radiated

what effect does this have on the scatter

A

increases it

increases scatter

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11
Q

increasing FS has what effect on the beam quantity

what are the 3 factors causing this

A

increases it

increases scatter and amount of remnant radiation hitting the receptor

can increase image noise without mAs compensation

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12
Q

what is the field size

A

how big the image is

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13
Q

what is the tradeoff when you decrease the field size

what needs to be done to compensate for this trade off

A

fewer photons reach the IR so exposure decreased

increase in mAs must accompany significant reduction in the field size to maintain image exposure

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14
Q

what 2 factors of the nature of body parts produce more scatter

why

A

thicker and denser parts = more scatter

both increase number of interactions x-ray beams undergo as it passes through the body

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15
Q

why do denser body parts produce more scatter

A

higher e- density present in thicker/denser tissues

increased likelihood of interactions occurring especially photoelectric

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16
Q

compression devices are used to improve spatial resolution and contrast how

in terms of thickness and dose and OID

A

decrease patient thickness
makes thickness more uniform

lowers patient dose and brings tissue closer to receptor by decreasing the OID

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17
Q

what are the 3 primary exposure factors

A

mAs

kV

exposure time

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18
Q

what does increasing mAs do to the beam

A

more photons in beam

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19
Q

what does increasing the kVp do to the beam

A

increase quantity and quality

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20
Q

mAs increase has what effect on the quantity of radiation reaching the IR

what is the relationship

A

direct proportional

increases quantity

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21
Q

mA and exposure time have an ___ ___ relationship when maintaining the mAs

A

inverse proportional

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22
Q

how does kV affect the x-ray beam penetration and absorption in anatomic tissues

A

increase kV increases penetration and decreases absorption

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23
Q

how does kV affect the subject contrast

A

increasing kVp decreases subject contrast

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24
Q

what does lower kV do to the variation in the x-ray intensities exiting the patient

A

greater variation in the x-ray intensities exiting the patient

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25
what is the 15% rule in terms of the IR exposure what are the equations for increasing and decreasing the exposure and maintaining the exposure
to increase exposure to the IR multiply the kVp by 1.15 1.15 x (original kV + 15%) to decrease the exposure to the IR multiply by 0.85 0.85 x (original kV - 15%)
26
what is the 15% rule in terms of the IR exposure what are the equations for maintaining the exposure when kVp is increased or decreased
to maintain the exposure to IR, when increasing the kVp by 15% (kVp x 1.15), divide the original mAs by 2 when decreasing the kVp by 15% (kVp x 0.85), multiply the mAs by 2
27
is image brightness dependent on mAs and kVp
no
28
is image contrast dependent on kVp
no
29
what does it mean when people say that digital IRs have a wide dynamic range
can use a wide range of exposure factors and still get a good quality range
30
what happens to the exposure and image brightness/contrast if there is too much mAs and/or kV used
patient overexposed computer processing adjust image brightness and contrast
31
what happens to the quantum noise if there is too little mAs and/or kV used
it will be visible
32
the screen film comes in different speeds what does it mean when its faster/higher speed in terms of exposure factors
Faster/higher speed = more exposure characters, syst takes the few pixel it has and gives you the info you want Fast = lower exposure factors
33
what are 10 secondary factors
focal spot size SID OID central ray-anatomic part image receptor alignment Grids beam restriction generator output tube filtration compensating filters patient factors
34
what do secondary factors affect
don't affect production of beam directly affects the radiation but not directly during its production
35
how does the focal spot size affect unsharpness and spatial resolution
increasing focal spot size increases unsharpness and decreases spatial resolution
36
what is the penumbra
unsharpness/blurring at the edge of the beam
37
what is the size of a small focal spot
0.5-0.6mm
38
what is the size of a large focal spot
1.0-1.2mm
39
how does SID affect the radiation intensity
inverse square law increasing SID decreases the radiation intensity reaching the IR
40
how does SID affect the size distortion (magnification) and recorded detail/spatial resolution
increasing the SID will decrease magnification and increase resolution
41
what is the SID
distance between x-ray tube and IR
42
what is the SID and mAs equation
mAs1/mAs2 = (SID1)^2/(SID2)^2
43
what is the equation for the radiation intensity and distance
I2/I1 = (d1)^2/(d2)^2
44
what is the OID
distance between the anatomic part and the IR
45
which 4 things does the OID affect
radiation intensity reaching the IR amount of scatter radiation reaching the IR magnification spatial resolution
46
a smaller OID has what effect on magnification
less magnification
47
in terms of OID an air gap will have what effect on the radiation intensity reaching the IR and scatter
increase OID so decreases intensity and increases scatter
48
increasing the OID ahs what effect on the IR exposure, contrast and magnification and spatial resolution
decrease IR exposure increase contrast and magnification decrease spatial resolution
49
what is subject contrast
the anatomy and the contrast due to difference of structures eg. anatomy in chest has got many differences of structures (bone, ribs, lungs all diff thicknesses in chest)
50
what is the magnification factor what is the equation for the MF and SOD and object size
MF = SID/SOD
51
what is the equation for the SOD
SOD = SID - OID
52
what is the equation for the object size
object size = image size/MF
53
as OID increases the image size ___
decreases
54
what is the equation for MF, Lim and Lobj
MF = Lim/Lobj ``` Lim = width of image Lobj = width of object ```
55
what are the 3 factors of the CR misalignment
tube part image receptor
56
what is the purpose of the grid
limit the amount of scatter radiation that reaches the IR and improves the quality of the radiograph
57
what effect of less scatter or unwanted exposure on the image is to
increase the radiograph contrast
58
what does beam restriction do what is the tradeoff
increased collimation = smaller field size = reducees the amount of tissue irradiated and reduces both the scatter radiation produced and the amount of radiation reaching the IR higher contrast but needs increase in mAs
59
generators with more efficient output require what exposure techniques to produce an image comparable to those of a single phase unit
lower exposure techniques
60
how might tube filtration affect the quality of images how significantly
small variations wont have any effect on the quality
61
what are 3 patient factors
body habitus part thickness effects pathology
62
what 3 things does the part thickness affects
beam attenuation exposure reaching the IR scatter production and image contrast
63
what does pathology affect
increase or decrease kV (penetration)