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diagnostic radiology (ionising) > DR projection technology > Flashcards

DR projection technology Flashcards

1
Q

where is the tube in fixed radiography system

A

generally ceiling mounted on rails

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2
Q

fixed radiography system components (5)

A

ceiling mounted tube

generator cabinet

operators console

often two buckies

screen behind where exposures carried out

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3
Q

what is in the bucky

A

grid

mechanism to ensure grid moves

AEC sensors

casette or DR detector

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4
Q

purpose of AEC

A

correct amount of radiation to image receptor

taking out guesswork

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5
Q

what two things does the AEC need to be able to cope with

A

varying body thickness and tube voltage

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6
Q

where is the AEC located

A

behind grid

in front of image receptor

excl. mammo

top to bottom:
xrays
patient
grid
AEC detector
image receptor

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7
Q

what does the AEC consist of

A

ionisation monitor chambers

3-5 sensors

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8
Q

how does AEC work

A

monitors air kerma

terminates exposure when predetermined limit reached

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9
Q

requirement for AEC

A

transparancy to x rays

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10
Q

major components of mobile radiography system

A

arm for positioning of tube

high voltage generator and batteries integrated

xray tube assembly

collimator assembly

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11
Q

mobile radiography system components

A

integrated generator
tube on adjustable arm
integrated console
generally no grid or AEC
no screen

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12
Q

where are mobile systems used

A

in wards

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13
Q

mammo system: what kind of detector
where is mounted on arm
what does the gantry do
what is possible

A

digital detector
tube and detector
gantry rotates
advanced imaging techniques

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14
Q

intra-oral dental:
size of mA
what kind of anode
what receptors are used
where is exposure switch

A

low mA
stationary anode (small tube)
film and digital
on a long cable for rad protection

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15
Q

panoramic dental unit:
1. what is it for
2. anode type
3. what do the tube and detector do
4. what about the receptor

A
  1. looking at dentition and the jaw
  2. stationary
  3. rotate about patient
  4. translates
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16
Q

fixed fluoro:
1. what is mounted
2. what are they mounted on
3. how is it operated
4. where are exposures carried out
5. where are the screens

A
  1. x ray tube and image receptor
  2. c arm sometimes ceiling
  3. console and sometimes pedestal with controls
  4. in the room
  5. ceiling mounted
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17
Q

e.g. of fluoro imaging

A

barium swallow

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18
Q

mobile fluoro:
1. where is generator
2. where is image display
3. where are x ray tube and receptor mounted
4. what doesnt it have

A
  1. integrated
  2. on seperate cart
  3. often on c arm
  4. screen
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19
Q

what does c arm allow

A

large degree of movement (of x ray tube and image receptor)

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20
Q

4 types of image receptors

A

glass plates
film
screen film systems
digital radiography detectors
and computed radiography

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21
Q

advantages of analogue imaging (3)

A
  1. proven technology
  2. high res
  3. affordable
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22
Q

e.g. of analogue radiography

A

screen film

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23
Q

cons of analogue radiography (4)

A
  1. contrast-latitude compromise
  2. limited dyn range
  3. no post processing
  4. film processing stability
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24
Q

pros of digital imaging (5)

A
  1. contrast performance
  2. larger dyn range
  3. dose efficency
  4. image processing
  5. integration with pacs
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25
Q

cons of digital imaging (2)

A
  1. lower res
  2. start up costs
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26
Q

how does screen film radiography work

what happens when photons reach screen
what is light recorded on
how to get image

what is a challenge

A
  1. photons captured by fluorescent screens and give off light
  2. light recorded on double emulsion film
  3. chemically process the film

very non-linear response so needs precise exposure

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27
Q

order of screen film components

A

x rays
screen
film
screen

latent image in film
visible light produced in screen

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28
Q

how does digital radiography work
1. how are photons captured (2)
2. what happens to the signal
3. what happens to image

advantage

A
  1. by fluorescent screens or digitally
  2. digitals and assigned to pixel
  3. processed and displayed on variable image display

linear response over wide dyn range

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29
Q

3 main types of digital radiographic receptors

A
  1. indirect
  2. direct
  3. CR
30
Q

indirect digital receptor
order of mechanisms
material

A

xrays
light
charge
signal

amorphous silicon flat panel

31
Q

direct digital receptor
order of mechanisms
material

A

xrays
curent
signal

amorphous selenium flat panel

32
Q

CR digital receptor
order of mechanisms

A

xrays
delayed light
signal

33
Q

direct and indirect digital detectors electronics array
1. consists of
2. what do they do
3. where is the array normally deposited
4. how is image created

A
  1. thin film transistors
  2. each transistor forms a pixel
  3. on a glass base
  4. signal from pixels transferred to computer
34
Q

CR
1. where is the imaging plate housed
2. what is a laser used for
3. what is emitted and from what
4. what happens to the light
5. last step to produce image

A
  1. in a cassette
  2. read out of the imaging plate
  3. blue light from imaging plate
  4. collected by light gate and amplified by PMT
  5. digitise the signal
35
Q

4 steps of CR image acquisition and readout

A
  1. erase
  2. expose
  3. readout out
  4. display
36
Q

how to erase CR imaging plate

A

shine with intense white light

37
Q

two types of receptors for fluoro

A

image intensifier
flat panel detector

38
Q

x ray image intensifier (used in fluoro)
1. what is x ray incident on
2. what is produced
3. what is the light incident on and what is then produced
4. how is flux gained
5. how is minification gained
5. what is light detected by and what for

A
  1. input phosphor
  2. light produced
  3. photocathode - electrons
  4. electrons accelerated across vacuum , gain energy and incident on output phosphor
  5. input phosphor area large and mapped to small area of output
  6. camera to display image
39
Q

what is flat panel detector similar to

A

radiographic detector

40
Q

components of flat panel detector (3)

A

Csl phosphor
TFT
photodiode array

41
Q

fps of readout in flat panel detector

A

up to 30

42
Q

order of events in flat panel detector

A

x rays
into light
into charge
read out
creates digital image

43
Q

two main types of radiographic image receptors

A

digital and computed radiography

44
Q

two main types of fluoro image receptors

A

image intensifer and flat panel

45
Q

3 main things which determine whether you can see an object in an image

A

contrast (from bg)
noise in image
object size

46
Q

what does PE effect provide and how

A

contrast by removing photons from beam

47
Q

PE effect: why is there bone-soft tissue contrast

A

rapid increase of probability of photons removed with beam with Z (proportional to Z^3)

48
Q

what is k-edge used for

A

to optimise x ray capture in image receptor
and as contrast agents

49
Q

contrast
if I1=intensity through whole patient
I2=intensity through object
what is contrast defined as

A

decrease in intensity of imaging the patient with and without the object
i.e. I2-I1 / I1

50
Q

formula for image contrast

A

I2-I1 / I1 = 1 - exp(x(mu1-mu2))

51
Q

what does ‘subject’ or radiation contrast depend on

A

thickness of object
difference in mu between object and background

52
Q

how to attenuation coefficients vary with energy

A

fall

53
Q

how does the difference in attentuation coeff change at higher energy

A

becomes smaller

54
Q

which energy (low or high) maximises contrast and why

A

low - greater diff between mu

55
Q

how does compton scatter affect contrast

A

reduces if deflected photons are captured by detector

56
Q

how does prob. of compton scatter vary over diagnostic energy range

A

flat

57
Q

how does compton scatter vary with Z

A

independent

58
Q

when is compton scatter the dominant interaction

A

at higher energies and in thicker sections

59
Q

where is the anti scatter grid

A

between patient and receptor

60
Q

what does anti scatter grid improve in image

A

contrast

61
Q

what is noise

A

any extraneous info that obscures the desired signal

62
Q

3 types of noise in DR

A

quantum
electronic
fixed pattern

63
Q

noise:

  1. what is the no. of x ray photons in a small area governed by
  2. how does quantum noise arise
  3. what describes quantum noise
  4. e.g. of a measure of noise
A
  1. random processes
  2. fluctuations in the no. of x ray photons in an area
  3. Poisson stats
  4. st dev
64
Q

noise:

  1. what is it proportional to
  2. what is signal proportional to
  3. what SNR is proportional to
A
  1. the square of the no. detected photons
  2. no. photons
  3. sqrt (N)
65
Q

what noise dominates over clinical range

A

quantum

66
Q

when can electronic noise be significant

A

at low doses

67
Q

what is fixed pattern noise

A

pixel to pixel variation

68
Q

why would fixed pattern noise be low for digital radiography

A

because of flat fielding

69
Q

what detector characteristics affect spatial res

A

pixel size
spread of signal
electron focusing in image intensifier

70
Q

what two other factors (not detector characteristics) affect spatial res

A

focal spot size
magnification

71
Q

what is spatial res often quantified in

A

lp/mm

diagnostic radiology (ionising) (7 decks)

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