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ICMS > Diagnostic Imaging - Interaction of Ionizing Radiation w/ Tissue (Image Production Processing) > Flashcards

Diagnostic Imaging - Interaction of Ionizing Radiation w/ Tissue (Image Production Processing) Flashcards

1
Q

What are the different digital processing systems for images?

A

CR - computed radiography processing
DR - digital radiography processing

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2
Q

Compare CR and DR.

A

CR: cheaper, more time consuming, need to remove/replace IR, less efficient QDE, more artifacts, less portable, cassettes easier to replace, prone to dust, damage of CR reader/PSP

DR: more expensive, faster, no need for repositioning, better QDE, less artifacts, very portable, IR sensitive to cold/damage, better qlty image

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3
Q

Describe the process of CR.

A

Primary excitation: xray passes through upper layer to phosphor, reacts w/ electrons w/i phosphor, exciting them to higher energy levels, majority of electrons drop back to initial state, remaining get trapped, stores image w/i plate.

Secondary excitation: plate removed from cassette & scanned by laser beam, beam stimulates trapped electrons, causes light photons to be emitted. Light produced channeled to photomultiplier using optics

Photomultiplication
Digitisation
Plate erasure

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4
Q

The number of light photons produced by secondary excitation is directly proportional to

A

the number of electrons that were trapped in the storage phosphor (in CR)

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5
Q

How should an imaging plate be maintained?

A
  • store away from radiation
  • store cassettes in an upright position
  • check imaging plates for damage
  • dust-free environment
  • erase imaging plates before use
  • screen cleaning
  • dirt on intensifying screens or PSP plates can appear as artefacts & mimic pathology
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6
Q

What are practical disadvantages of CR?

A

slower than DR
not as portable, less useful for off-site imaging
CR reader artefacts
PSP need to be replaced/maintained
need to erase cassettes prior to using
need to keep PSP clean & dust free
need to be processed relatively quickly
prone to scatter radiation

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7
Q

IDR stands for…

A

indirect digital radiography

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8
Q

IDR transforms x-ray energy to

A

light, then transforms light into an electric impulse

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9
Q

What are the two types of IDR?

A

Charge-coupled device
Flat panel detector

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10
Q

What two chemical compounds are used in a scintillator?

A

Gadolinium oxysulfide (Gadox)
Cesium iodid (CsI)

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11
Q

Flat Panel Detector uses

A

photodiode and TFT

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12
Q

photodiode converts light into

A

an electrical signal

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13
Q

TFT converts electrical charge into

A

an image displayed on monitors

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14
Q

How should flat panel detectors be maintained?

A
  • wireless system batteries/ tablets must be charged
  • may need to warm up detector to required temp
  • careful handling systems/ electric board
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15
Q

What is DDR?

A

Direct digital radiography

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16
Q

What takes place in DDR?

A

Photodiode converts x-ray energy to electrical signal which is then converted to TFT to produce digital image. Then sent to PACS

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17
Q

What are characteristics of the optimal image?

A
  • demographic info
  • correct markers
  • good positioning and centering
  • geometric integrity/sharpness
  • radiation safety/protection
  • optimal exposure, brightness, contrast & grey scale, with minimal noise
  • no preventable artefacts
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18
Q

How is the spatial resolution in CR?

A

Size of pixels detected by field of view

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19
Q

how is the spatial resolution in DR?

A

array of detectors linked together to form matrix, in which individual detector elements form the pixels of the matrix

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20
Q

Contrast is affected by

A
  • exposure factors - kVp/mAs
  • subject region of interest
  • dynamic range of imaging system
  • artefacts
  • quantum mottle/noise
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21
Q

In digital systems, contrast is a result of…

A

selecting appropriate look-up table setting, providing an appropriate scale of displayed contrast for exam selected

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22
Q

Image contrast is affected by…

A

subject contrast

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23
Q

Contrast digital processing means

A

the dynamic range is wider, copes better w/ wider range of exposure

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24
Q

Underexposure means the image has a…

A

grainy appearance/quantum mottle

25
Q

Overexposure is often tolerated because

A

software brings image to required greyscale value

26
Q

What does it mean to window the image?

A

matching the dynamic range to maximise the contrast

27
Q

Window level is the

A

midpoint of the greyscale values

28
Q

Window level controls

A

image brightness

29
Q

Window width is the number of

A

shades of grey

30
Q

Window width controls

A

image contrast

31
Q

Exposure indicators/index (EI) is the measure of

A

the amount of exposure received by the image receptor

32
Q

EI is dependent on

A

mAs
total detector area irradiated
beam attenuation

33
Q

EI is an indicator of

A

image quality

34
Q

What is wide exposure latitude?

A

Range of exposures used to obtain very wide diagnostic images

35
Q

What is the benefit of wide exposure latitude?

A

fewer repeat films due to incorrect exposure settings

36
Q

What is the risk of wide exposure latitude?

A

overexposure of image

37
Q

What does increased dynamic range do?

A

Allows assessment of soft tissues and bone in the same exposure by altering the image in the monitor

38
Q

What is post-processing of images?

A

the ability to manipulate the image to change the contrast, brightness, edge enhancement, etc.

39
Q

What are some common problems with technique?

A

CR reader artifacts
algorithm used
positioning and centering
exposure

40
Q

What makes a noisy image?

A

pixelated, mottled

41
Q

Quantum noise often causes…

A

underexposure, so the image appears pixelated

42
Q

How can you fix quantum noise?

A

increase exposure to improve image qlty

43
Q

Electronic noise is caused by…

A

photon noise

44
Q

Saturation due to electronic noise can lead to overexposure which means…

A

too many photons reach the receptor

45
Q

Chessboard patterns can be caused by…

A

overexposure

46
Q

Radiographs should not be repeated in digital radiography due to…

A

mild to moderate overexposure
brightness
contrast

47
Q

Radiographs may need to be repeated for…

A

gross overexposure
underexposure

48
Q

Scatter radiation decreases

A

tissue contrast

49
Q

What are ways of reducing scatter?

A
  • collimate the primary beam
  • Choose best exposure factors
  • use a grid
50
Q

What are the best exposure factors in DR?

A

Lower KV means more photoelectric effect, greater contrast, less Compton interactions = less scatter

51
Q

When should you use a grid in DR?

A

if tissue depth is >10cm or >15 cm in the thorax

52
Q

What is a grid?

A

a number of parallel strips of lead held apart & parallel to each other by x-ray-transparent interspace material

53
Q

What is the function of a grid?

A

to reduce scatter affecting IR/radiographs

54
Q

Where do you place a grid?

A

above IR, under the patient

55
Q

What is a linear grid?

A
  • lead strips are parallel
  • decrease in number of photons at the periphery because more are absorbed
56
Q

What is a focused grid?

A

lead strips are angled progressively from the center

57
Q

What is an advantage of a grid?

A

increases contrast by reducing scatter reaching IR

58
Q

What is a disadvantage of a grid?

A

increases exposure factors
must be properly aligned
+/- grid lines

59
Q

when buying a DR system, what are some things to consider?

A

Cost
reputation of supplier/panel manufacturer
Where to have it serviced
warranty on detector/tablet
storage of images
can you trial the system?

ICMS (22 decks)

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