DR projection technology

Question 1

where is the tube in fixed radiography system

Answer 1

generally ceiling mounted on rails

Question 2

fixed radiography system components (5)

Answer 2

ceiling mounted tube

generator cabinet

operators console

often two buckies

screen behind where exposures carried out

Question 3

what is in the bucky

Answer 3

grid

mechanism to ensure grid moves

AEC sensors

casette or DR detector

Question 4

purpose of AEC

Answer 4

correct amount of radiation to image receptor

taking out guesswork

Question 5

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

Answer 5

varying body thickness and tube voltage

Question 6

where is the AEC located

Answer 6

behind grid

in front of image receptor

excl. mammo

top to bottom:
xrays
patient
grid
AEC detector
image receptor

Question 7

what does the AEC consist of

Answer 7

ionisation monitor chambers

3-5 sensors

Question 8

how does AEC work

Answer 8

monitors air kerma

terminates exposure when predetermined limit reached

Question 9

requirement for AEC

Answer 9

transparancy to x rays

Question 10

major components of mobile radiography system

Answer 10

arm for positioning of tube

high voltage generator and batteries integrated

xray tube assembly

collimator assembly

Question 11

mobile radiography system components

Answer 11

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

Question 12

where are mobile systems used

Answer 12

in wards

Question 13

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

Answer 13

digital detector
tube and detector
gantry rotates
advanced imaging techniques

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

e.g. of fluoro imaging

Answer 17

barium swallow

Question 18

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

Answer 18

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

Question 19

what does c arm allow

Answer 19

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

Question 20

4 types of image receptors

Answer 20

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

Question 21

advantages of analogue imaging (3)

Answer 21

1. proven technology
2. high res
3. affordable

Question 22

e.g. of analogue radiography

Answer 22

screen film

Question 23

cons of analogue radiography (4)

Answer 23

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

Question 24

pros of digital imaging (5)

Answer 24

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

Question 25

cons of digital imaging (2)

Answer 25

1. lower res 2. start up costs

Question 26

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

Answer 26

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

Question 27

order of screen film components

Answer 27

x rays screen film screen latent image in film visible light produced in screen

Question 28

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

Answer 28

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

Question 29

3 main types of digital radiographic receptors

Answer 29

1. indirect 2. direct 3. CR

Question 30

indirect digital receptor order of mechanisms material

Answer 30

xrays light charge signal amorphous silicon flat panel

Question 31

direct digital receptor order of mechanisms material

Answer 31

xrays curent signal amorphous selenium flat panel

Question 32

CR digital receptor order of mechanisms

Answer 32

xrays delayed light signal

Question 33

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

Answer 33

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

Question 34

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

Answer 34

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

Question 35

4 steps of CR image acquisition and readout

Answer 35

1. erase 2. expose 3. readout out 4. display

Question 36

how to erase CR imaging plate

Answer 36

shine with intense white light

Question 37

two types of receptors for fluoro

Answer 37

image intensifier flat panel detector

Question 38

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

Answer 38

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

Question 39

what is flat panel detector similar to

Answer 39

radiographic detector

Question 40

components of flat panel detector (3)

Answer 40

Csl phosphor TFT photodiode array

Question 41

fps of readout in flat panel detector

Answer 41

up to 30

Question 42

order of events in flat panel detector

Answer 42

x rays into light into charge read out creates digital image

Question 43

two main types of radiographic image receptors

Answer 43

digital and computed radiography

Question 44

two main types of fluoro image receptors

Answer 44

image intensifer and flat panel

Question 45

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

Answer 45

contrast (from bg) noise in image object size

Question 46

what does PE effect provide and how

Answer 46

contrast by removing photons from beam

Question 47

PE effect: why is there bone-soft tissue contrast

Answer 47

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

Question 48

what is k-edge used for

Answer 48

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

Question 49

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

Answer 49

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

Question 50

formula for image contrast

Answer 50

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

Question 51

what does 'subject' or radiation contrast depend on

Answer 51

thickness of object difference in mu between object and background

Question 52

how to attenuation coefficients vary with energy

Answer 52

fall

Question 53

how does the difference in attentuation coeff change at higher energy

Answer 53

becomes smaller

Question 54

which energy (low or high) maximises contrast and why

Answer 54

low - greater diff between mu

Question 55

how does compton scatter affect contrast

Answer 55

reduces if deflected photons are captured by detector

Question 56

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

Answer 56

flat

Question 57

how does compton scatter vary with Z

Answer 57

independent

Question 58

when is compton scatter the dominant interaction

Answer 58

at higher energies and in thicker sections

Question 59

where is the anti scatter grid

Answer 59

between patient and receptor

Question 60

what does anti scatter grid improve in image

Answer 60

contrast

Question 61

what is noise

Answer 61

any extraneous info that obscures the desired signal

Question 62

3 types of noise in DR

Answer 62

quantum electronic fixed pattern

Question 63

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

Answer 63

1. random processes 2. fluctuations in the no. of x ray photons in an area 3. Poisson stats 4. st dev

Question 64

noise: 1. what is it proportional to 2. what is signal proportional to 3. what SNR is proportional to

Answer 64

1. the square of the no. detected photons 2. no. photons 3. sqrt (N)

Question 65

what noise dominates over clinical range

Answer 65

quantum

Question 66

when can electronic noise be significant

Answer 66

at low doses

Question 67

what is fixed pattern noise

Answer 67

pixel to pixel variation

Question 68

why would fixed pattern noise be low for digital radiography

Answer 68

because of flat fielding

Question 69

what detector characteristics affect spatial res

Answer 69

pixel size spread of signal electron focusing in image intensifier

Question 70

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

Answer 70

focal spot size magnification

Question 71

what is spatial res often quantified in

Answer 71

lp/mm