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Imaging > Lecture 4 > Flashcards

Lecture 4 Flashcards

1
Q

what does the filter do for an Xray

A

it takes out the lower range of the images

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2
Q

how do you calculate the magnification of an image

A

M=image/object= a+b/b M>1

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3
Q

what is a

A

source to object

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4
Q

what is b

A

object to image

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5
Q

how do you calculate the object size from the image

A

object=image/magnification

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6
Q

how do we accomplish magnification in real life

A

do a size marker at the level of the object so then calibrate based off known object

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7
Q

film screen system what does it do and what are the light and dark areas

A

it sees optical light and optical density so darkness is high absorption, so bone?

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8
Q

what is the cassette

A

it is the light tight structure that supports the screen and film

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9
Q

what does the screen do

A

it gives off optical lights so when the X-ray hits it, it turns light and translates to the film

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10
Q

what does an intensifying screen do

A

screen converts X-ray to visible light and increases efficiency so increase intensifying. Close contact with fillm, cassette with compressible foam.

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11
Q

what is used to help improve light production

A

gadolinium oxysulfide, LaOBr, YTaO4 which are rare earth metasl

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12
Q

as the screen increases in thickness, what happens

A

increasing blur

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13
Q

what is radiographic film made of

A

plastic base coated with light sensitive emulsion consisting of silver halide help in water soluble gelatin.

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14
Q

what reaction does silver halide go through on the film

A

siler halide is exposed to light and a small number of silver ions reduced (gain an electron) and become metallic silver, and a latent image is formed and stored.

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15
Q

how do we process the film (basic

A

developer and fixer

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16
Q

what is the developer

A

when film contacts developing chemicals, it contains a reducing agent and the Ag in the latent image acts as a catalyst and causes the remaining silver ions in that grain to be reduced. A grain of Ag developed is a dark speck.

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17
Q

what is the fixer

A

it is the aqueous oxidizing solution that dissolves the remaining silver halide that not exposed to light and is then rinsed with water

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18
Q

with greater exposure what happens to the film-like lung

A

darker

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19
Q

with less exposure what happens to the film like heart

A

it is lighter

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20
Q

what is the characteristic curve called and look like

A

H&D curve. xaxis is exposure and yaxis is optical density

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21
Q

what is the toe of the characteristic curve

A

it is the area lowest on the curve where the low dose and some optical density

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22
Q

what is the shoulder of the characteristic curve

A

it is the highest dose, so it can represent saturation

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23
Q

what is the best dose range for the characteristic curve

A

it is the linear region

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24
Q

what is the base+fog

A

it is the base of the vurve

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25
Q

how do you calculate Optical density

A

OD=-log10(T) where T is the transmittance through the film,

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26
Q

what is T in formula

A

it is the I/I0

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27
Q

draw how the H&D curve changes as film speed increases and decreases

A

if the speed increases the dose decreases for the same OD. If the speed decreases, the dose increases for the same OD.

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28
Q

what is the latitude of the curve and what changes it

A

latitude is how wide the linear area is. if it is thinner than it is higher contrast so better for detail. If the lower contrast, wider range of doses so better if hard to tell what is happening

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29
Q

draw where the highest level of image contrast is on each of the images you drew

A

top of the linear portion

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30
Q

computed radiography- how does it work

A

photostimulatable phosphors (BaFBr) barium fluorohalide a fraxtion of the absorbed X-ray energy trapped in the PSP screen and amount of energy stored in phosphor is proportional to the entrance X-ray exposure. Stores a latent image and visible light is emitted upon stimulation with ease beam for readout

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31
Q

how is the computed radiography read

A

a laser stimulates the BaFBR and it creases an electronic signal and it creates and electrical signal. and trapped electrons are proportional

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32
Q

what does the curve look like for computed radiography

A

it is a line instead so it is linear and density/dose is limited because of the linearity

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33
Q

what is a flat panel thin film transister array detector

A

it is a pixelated flat panel and each pixel is light sensitive which generates a signal

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34
Q

what are the different digital radiography

A

direct and indirect

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35
Q

indirect digital radiography means what

A

X-rays reate visible light then electron charge and voltage signal and digital signal. The X-ray creates light through hitting a scintillator.

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36
Q

what is a scintillator usually made of

A

cesium iodide which is CsI

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37
Q

what are the common uses of indirect digital radiography

A

it is used for bones, lung, mammography, it is more expenstive, but it couples detection and readout, better read out. It is much quicker so can so fluoro. it is less versatile than CR

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38
Q

what is pixel fill factor

A

active area is limited by electrical gate lines and other electrical components. Fill factor is the percent of the defined pixel area that actively detects signal. Fill factor decreases as pixel size decreases

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39
Q

what happens to fill factor with smaller pixels

A

less usable area

40
Q

what happens to efficiency as fill factor decreases

A

it decreases

41
Q

what is direct digital radiography

A

xrays- electron charge- voltage signal- digital signal

42
Q

what chemical does direct DR use

A

selenium with no scintillator needed

43
Q

what is the fill factor of direct DR use

A

100% or close to it

44
Q

what factors affect spatial resolution

A

focal spot size, detector size, magnification

45
Q

geometric blurring

A

since the focal spot is not truly a point source, the edges of the image will have some blur called a penumbra. Draw it.

46
Q

as focal spot size increases what happens

A

increased penumbra

47
Q

as focal spot size decreases, what happens

A

decreased penumbra

48
Q

what happens as magnification increases

A

the penumbra increases with increased magnification,because it gets more spread out

49
Q

geometric magnification how do you minimize it

A

you place the image target closer to the image detector and use long source to image distance. long source to image is a large numerator. also the object and detector need to be close

50
Q

how to calculate the focal spot size

A

Fd= Fs (b/a)=Fsx (m-1)

51
Q

what is the optimum magnification for spatial resolution

A

the effect of source and detector size on spatial resolution is influenced by magnification. the source prefers lower magnification and the detector prefers higher magnification

52
Q

what is the dominant source of noise

A

xray quantum noise

53
Q

when is quantum X-ray noise most evident

A

under exposure results in images with increased appearance of quantum noise and mottle

54
Q

what is SNR approximated to

A

square root of barN

55
Q

in screen film, what does the brightness depend on

A

depends on exposure. over exposed is dark and underexposed is lighter. Brightness is dependent on exposure

56
Q

increased radiation does what to SNR

A

increased radiation leads to increased photons, increased SD, and increased signal so increased SNR

57
Q

in digital image receptors what is the brightness dependent on

A

controlled by image processing. The exposure matters, but the histogram adjusts it.

58
Q

when the noise highest for digital image rectpros

A

it is underexposures

59
Q

what generates scatter in the image sustem

A

it is from the human generating photons

60
Q

what does scatter do to image quality

A

reduction in image contrast

61
Q

what is the scatter to primary ratio

A

SPR=S/P

62
Q

what are ways to reduce scatter

A

grids, air gap, collimator

63
Q

what do grids do

A

place in front of the detector Anti-scatter because the have parallel things. It reduces aberrant signal while letting primary go through.

64
Q

what are the septa of grids made from

A

lead

65
Q

how do you calculate the grid ratio

A

H/W height of material/ grid opening width

66
Q

what does a high ratio grid do

A

it removes more scatter photons, because very marry margin, but need better alignment of patient

67
Q

what grid is used with fixed radiographic table

A

high ratio grid because decreased patient factors so need 10:1 or 16:1 grid

68
Q

what grid is used for portable Xray

A

it is a grid of 6:1 or 8:1 because the are manually position so need lower grid ration

69
Q

what happens if the grids are not foccused

A

it comes out bad

70
Q

what does off center grid look like

A

gradient

71
Q

in a lung what would off center look like

A

it could lead to a lung being brighter than the other

72
Q

what happens to a grid if the focal distance is off

A

it is a blurry less clear imagee

73
Q

what can happen with stationary grids in an image

A

can see the grid

74
Q

what is the bucky grid

A

the grid is movable so it has motion and it blurs the grid lines

75
Q

what is the bucky factor

A

the amount of primary photons removed from by a grid so need increased dose and have same exposure

76
Q

what is the primary transmission factor

A

T- and ideal is 1 and it is dependent on KV

77
Q

what is scatter transmission facotr

A

ideal is 0

78
Q

what is CDF

A

reduction of contrast due to scatter

79
Q

what is selectivity and what do you want it to be

A

want it towards infintity

80
Q

what is the airgap and how does it affect scatter

A

scatter increases with decreased aigret. increased aigret better imaged because scatter misses the plate. This means the gap of air between patient and detector

81
Q

what is collimation

A

reduces exposed volume of tissue and less scatter so better image contrast. Collimation means a smaller field is exposed so there is less scatter and reduces the exposed tissue to just whatever you want

82
Q

what are the technique factors that can be optimized for imaging

A

KvP, MA, exposure time, focal spot size, SID, and grid use

83
Q

what are the best parameters for heart radiography

A

long source to image disaffect to reduce geometric magnification of the heart, and high MA for short exposure time and large focal size for high MA. Geometric unsharpness is minimal due to long SID. High KV reduces visbility of bone and overall contrast

84
Q

what is best for pediatric radiography

A

small focal spot for best spatial resolution, and high MA for shorter exposure time because motion. low MAs for reduced patient dose, so do not use grid because want to eliminate higher doses

85
Q

what is automatic exposure control

A

photo timer used to regulate exposure level to the radiographic image receptor. Automatically shuts off X-ray when predetermined exposure level is reached. KVP, MA, and focal spot size are manually selected.

86
Q

in AEC what is used to regulate exposure level

A

photo time used to regulate exposure level to the radiographic image receptor and it shuts off X-ray when a certain level is reached

87
Q

what is controlled manually in AEC

A

kvp, coal spot, MA

88
Q

is there just one photo timer or multiple

A

multiple want AEC over what you want optimized tissue wise

89
Q

if the image is super bright when underexposed what system are they using

A

film screen

90
Q

what is best Ma for an image

A

want the lowest it can be with best image quality. Too much leads to excess exopsure and clipping. Under exposed need to retake from noise

91
Q

what is the exposure index

A

measure of detector response to incident radiation in a relevant image region. EI=K/100 K=radiation to the detector for a standard beam. Directly proportional to exposure of detector

92
Q

what happens to the MAS if the EI is doubled

A

it doubles

93
Q

what is the deviation index

A

it compares EI to a target EI so if you are shown a EI then you don’t need to factor in the target. SI is defined as body regions comapred.

94
Q

what is EI most dependent on

A

positioning of the patient. Relative region so anatomy is included and dark is exclused. Collimation is very important then

95
Q

what is dual energy radiography

A

it is z and rho so it gets rid of overlying so it can separate the things. it is dependent on the relationships

Imaging (19 decks)

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