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Diagnostic Imaging 1 > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

CR

A

photostimulable storage phosphor (PSP)
- inside a CR cassette
- portable (bucky/tabletop)
- can adapt to existing radiography equipment
- PSP is exposed - taken to a reader and processed
considered indirect digital
- the detector is moved between image acquisition (stage 1) and display (stage 2)

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2
Q

DDR

A

direct digital radiography
- detector and reader are a part of the wall, table unit or mobile you are using
- detector - permanent/tethered/wireless - all have the ability to be tethered but they are typically wireless because there is no stop between A and B

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3
Q

Indirect Acquisition

A

two-part process
scintillator
- converts x-ray photons to light - CsI
photodetector
- converts light into an electronic signal - Amorphous Silicon
X-ray photons hit scintillator = light and then goes to photodetector

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4
Q

Direct Acquisition

A

Directly convert x-ray photons to an electronic signal
- Amorphous Selenium - stops the light phase, wavelength directly into binary code
Flat panel detectors
- term used to describe both indirect nd direct acquisition plates

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5
Q

How is the DI formed?

A

digital image
- matrix of pixels

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6
Q

What is a pixel?

A

represented by a numerical value
value is related to brightness
contains series of bits
limiting factor of SR = pixel acquisition

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7
Q

What is a matrix?

A

a digital radiographic image is formed as an electronic image that is displayed on a grid called a matrix. The image is laid out in rows and columns called an image matrix.

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8
Q

Binary number system

A

2 digits (0 or 1)
computer performs all operations by converting alphabetic characters, decimal values etc to binary values

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9
Q

Pixel bit depth

A

of bits available to represent each pixel brightness
4 bits - 16 values per pixel
8 bits - pixel can have 256 different values

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10
Q

Dynamic range (grey scale)

A

the range of values over which a system can respond
number of brightness values (grey shades) that can be represented
Human eye 32 shades (white to black)
DR can capture many more

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11
Q

Contrast resolution

A

increase dynamic range (increase bit depth)
- better contrast resolution
- the ability to distinguish many shades of gray from black to white
- more ‘gradual’ the changes in the range will be within the grey scale representing the range from min to max x-ray intensity

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12
Q

computed radiography

A

excite electrons to a higher energy level
produces latent image
trapped temporarily when jump to higher energy more photons are excited
release of the energy = light = binary numbers, brightness value
when you expose the plate e- jumps up to a higher level

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13
Q

PSP

A

captures the latent image
composed of extremely small particles (pixels) which store and release energy
Barium fluorohalide bromides and iodides with europium activators
- act as electron traps or F-centers
- trap and store the electrons
# excited electrons trapped is proportional to the # x-ray photons
- latent image is stored until processing

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14
Q

PSL

A

Photostimulable luminence
emits light when exposed to a different light source
- high intense infra-red
electrons return to ground state

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15
Q

The read process

A

PMT - converts light to electrical signal
Electrical signal is amplified - sent to A/D converter
A/D converter produces binary number - depends on bit depth

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16
Q

Direct aquisition

A

x-rays interact with the photoconductor - creates an electronic signal
storage capacitors in the DEL’s collect the charge
After exposure the charge is released to the ADC
ADC converts the charge to a digital signal which is used to produce the digital image
better spacial resolution than indirect
more expensive to purchase and repair
commonly used in mammography

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17
Q

Indirect Acquisition - charged coupled devices

A

Scintillation layer is coupled to each CCD chip (pixel) by lenses or fiber optics
Scintillation layer - cesium iodide - converts x-rays to light, light spreads which causes blur, reduces spatial resolution
cesium iodide can be formed into small needles like columns
helps to focus the light - improves spatial resolution
CCD chips convert the light photons to an electrical signal
ADC converts the charge to a digital signal which is used to produce the digital image during processing

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18
Q

Indirect acquisition - thin film transistor

A

scintillation layer - cesium oxide - converts x-rays to light
photodiode layer converts the light into an electronic signal - transferred to the TFT array
TFT sends the signal to the ADC
ADC converts the charge to a digital signal which is used to produce the digital image during processing

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19
Q

Indirect acquisition

A

CCD and TFT used in general radioagraphy
TFT used in angiography and fluoroscopy
cheaper than direct acquisition detectors
easier to repair and replace parts
better contrast resolution compared to direct acquisition
less spatial resolution compared to direct acquisition

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20
Q

Fuji (CR)

A

S number
s (200-400)
inversely proportional to exposure

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21
Q

Carestream (CR, DDR)

A

by kodak
exposure index (1800-2200)
directly proportional to exposure

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22
Q

Agfa (CR, DDR)

A

log median value (1.95-2.6)
directly proportional to exposure

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23
Q

GE (DDR)

A

Detector Exposure Indicator
DI - Deviation index
Directly proportional to exposure
-3.0 to 2.0 optimal (green)
-5.0 to -3.0, 2.0 to 4.0 acceptable (yellow)
< - 5.0 and >4.0 out of desired range (orange)

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24
Q

S number repeatability

A

> 1000 severly undexposed (repeat)
< 50 severly overexposed (may be a repeat)

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25
Q

How do you calculate EI values in Carestream/Kodak?

A

EI = Log (exposure in mR) x 1000 + 2000

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26
Q

How does doubling or halving the exposure in Carestream/Kodak affect the EI?

A

changes it by 300

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27
Q

Carestream/Kodak repeatability?

A

<1250 Severly underexposed (repeat)
>2750 overexposed (may need to repeat)

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28
Q

What factors affect the S#?

A

Technique selection, collimation, IP size, Part, Beam, Receptor alignment, scatter and image algorithm

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29
Q

What is the controlling factor for spatial resolution?

A

acquisition pixel size - in the IR
each pixel is only 1 colour

30
Q

What is geometrical sharpness (spatial resolution)?

A

attributed to the geometrical aspects of the X-ray tube and positioning

31
Q

What is spatial resolution?

A

the abruptness of where one step ends and the next starts
Crisp edges
the structural sharpness of the image

32
Q

what is spatial resolution limited by?

A

acquisition pixel size

33
Q

What is spacial resolution affected by?

A

focal spot size, movement, OID and SID

34
Q

How does focal spot size affect geometrical sharpness?

A

decrease fss - increase sharpness (better spatial resolution)
increase fss - reduce sharpness

35
Q

How does SID affect geometrical sharpness?

A

Increase SID - increase sharpness
Decrease SID - decrease sharpness
don’t always use long SID as harder on the tube

36
Q

How does OID affect geometrical sharpness?

A

decrease OID - increase in sharpness
increase OID - decrease in sharpness

37
Q

What is the difference between acquisition pixel size and display pixel size?

A

acquisition pixel size is determined by the IR, display pixel size is determined by the monitor

38
Q

You expose a PA knee on a fuji CR plate using 75 kVp, 20mAs, and get an S# of 50. Does this image need to be repeated? If so, what new mAs would you use?

A

The image would be very overexposed, likely need to repeat. I would use a new mAs of 5 because for S# to be 4x higher S# needs to be 4x lower.

39
Q

System DQE at 70 kVp, 1- 55%, 2- 79%, 3- 48%. If patient dose was a concern, which system should you select and why?

A

system 2, higher the % the more effective it is and you can use a lower technique

40
Q

How could you accurately assess and compare spatial frequency between 2 systems?

A

the more lp/mm the greater the spatial resolution, would need to view both on same monitor so not affected by display pixel size

41
Q

What is the difference between matrix and FOV?

A

the field of view is the image, the matrix is the rows and columns of pixels in the image

42
Q

a 1024 x 1024 matrix will contain how many pixels?

A

1024x1024 = 1,048,576

43
Q

What is the difference between WW and WL?

A

WW is window width - controls image contrast, if you increase WW you decrease image contrast, if you decrease WW you increase image contrast
WL is window level and it controls the image brightness, the higher the WL the brighter the image

44
Q

You image a 21-step wedge. In order to represent each step with the image, what is the minimum # of bits your system must have?

A

5 bits - 32 steps - 2^5
4 bits only gives 16 steps

45
Q

For the same FOV what is the difference between a 512x512 matrix and a 1024x1024 matrix in terms of visual affect?

A

1024x1024 will have more pixels and be able to represent more detail
more spatial resolution due to smaller pixel pitch

46
Q

Describe quantum mottle?

A

unequal distribution of photons
makes the image grainy
see graininess in soft tissue before bone

47
Q

How do you adjust exposure factors to follow ALARA?

A

higher kVp with lower mAs, provided image quality isn’t going to suffer

48
Q

What is windowing?

A

changing the value of pixels
as we adjust the windowing, the system reassigns pixels different values that correspond to different brightness’s

49
Q

what bit depth do digital images have?

A

16, there are over 65,000 levels of grey that can be recorded, however we can only see 30-32 at a time with the human eye

50
Q

what are the advantages to digital radiography?

A

lower patient dose
fewer repeats
higher contrast resolution
no darkroom or film costs

51
Q

What is DQE?

A

detective quantum efficiency
the ideal detector would have a DQE of 100% or 1
- that would mean all incident radiation to the detector is absorbed by the detector and converted into the image signal or image information
when comparing two systems, a higher DQE value would mean that less radiation is required to achieve identical image quality

52
Q

What are the advantages of DR?

A

post-processing, image storage and transferability

53
Q

what are the disadvantages of DR?

A

capital costs
lower spatial resolution compared to film radiography
collimation and centering
dose creep

54
Q

What is subject contrast determined and affected by?

A

determined by differential absorption - atomic number, physical/mass density, thickness differences and kVP
affected by scatter

55
Q

What needs to occur for there to be image contrast?

A

subject contrast needs to occur or we will not have any image contrast

56
Q

How much subject contrast do you need in film radiography?

A

need a subject contrast difference of 10% between structures for us to be able to identify one structure from the next

57
Q

How much subject contrast do you need in digital radiography?

A

there only needs to be 1% difference in the subject contrast between structures for the system to be able to identify one structure from the next

58
Q

DDR flat panel detector types of acquisition?

A

indirect acquisition - offers a higher DQE
direct acquisition - better spatial resolution - smaller pixels

59
Q

Signal to noise ratio?

A

amount of information getting to the IR
the higher the signal, the less noise
as SNR increases - noise decreases

60
Q

What factors contribute to the overall quality of the image?

A

brightness
spatial resolution
contrast resolution
distortion
noise (QM or excessive scatter)

61
Q

What is the exposure indicator?

A

EI values help determine whether the detector received the appropriate amount of radiation to produce the required detail within the image. They are also a predictor of whether you have a good SNR or not

62
Q

what is spatial resolution?

A

ability to image small objects
limited by pixel size (acquisition pixels)

63
Q

How is spatial resolution described?

A

spatial frequency
more lp/mm

64
Q

what is pixel pitch?

A

the distance from the centre of one pixel to the centre of the pixel next to it
the smaller the pixel pitch the better the spatial resolution

65
Q

what is pitch density?

A

for the same FOV, the greater the number of pixels the greater the pixel density
greater pixel density, smaller pixels, better spatial resolution

66
Q

Spatial resolution limited and affected by?

A

limited by acquisition pixel size
affected by: focal spot size, geometric factors, and motion

67
Q

What is dynamic range?

A

identified by bit depth - # of brightness values each pixel can represent - increase bit depth - increase # of values
post processing allows visualization of all shades

68
Q

What is the exposure index?

A

exposure at the IR

69
Q

What is the target index?

A

pre-programmed into the system, however, should be changed to match the exposure/procedure created based on the techniques that are used in your department

70
Q

What is the Deviation index?

A

compares EI with TI
DI = log(EI/TI) x 10

Diagnostic Imaging 1 (4 decks)

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