Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

202 MEDIMAGE > 7. Digital Imaging: Image Receptors > Flashcards

7. Digital Imaging: Image Receptors Flashcards

1
Q

what are the 2 types of digital IRs

what are their differences and similarities

A

computed and direct

different construction techniques and acquire latent images differently however how this digitized and processed is the same regardless of technique

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the latent image

A

image on an exposed film or print that has nor yet been made visible by developing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

for CR what is done to the exposed image plate and processed

A

placed/sent to a reader and converted from analog plate to digital data for processing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

for CR the reader units have drive mechanisms what does these do

A

move the plates through the scanner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

for CR the reader units have an optical system
what components does it consist of
what do these do

A

laser, laser scanner and erasure unit

laser scans the exposed image plate to release the stored energy via visible light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

for CR the reader units have photomultiplier tube what does these do

A

collect, amplifies and converts the light to a electrical signal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

for CR reader units the readers have analog to digital converter what does these do

what 2 characteristic of the ADC?

A

convert analog to digital data

sampling frequency and pitch

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

in a CR reader units what are the 4 main components

A

drive mechanisms
optical system
photomultiplier tube
analog to digital converter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

in CR the cassette holds what

A

the image plate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

the image plate of CR what interactions occur at the Image plate

A

exiting radiation interacts with the IP

photon intensities are absorbed by the phosphor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is luminesence and what does it create

A

emission of light when stimulated by radiation

creates latent image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what 3 components make up the image plate in CR

what are the 2 types of phosphor

A

phospor, protective layers and support

photostimulatble phosphor
photostimulatable luminescence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what do the image plates do in terms of the radiation and photon absorption

A

stores images from exit radiation via photon intensities absorbed by the phosphor layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how are images erased off the CR image plate

A

expose to bright white light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is the photostimulatable phosphor made of

what is its important feature

A

It is composed of barium flourohalide crystals doped with europium

it’s luminescent so when stimulated by a high-intensity laser beam it emits a visible light. (absorbed energy released as light)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

in CR imaging what are the 2 steps to creating the image

A

1/ Image capture

2/ image readout

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

in CR what happens in the 1st step of creating an image when the image is captured

what happens in terms of exit x-rays and atom excitation

A

latent image is formed in the photostimulable phosphor when the exit x-ray is obsorbed.

exit x-ray is energy which excites the atoms in the phosphor layer

When an atom is excited it gets a higher energy level and that allows it to move. Spme atoms retun to normal state but some atoms get trapped in their new place until released by the processing laser and this is what gives us the tissue differential from the x-ray absorption.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

the image plates in the CR imaging should be processed quickly why

A

(within an hour) as latent images dissipate over time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is exit radiation

A

photons that made it through tissue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what are the 3 stages when digitizing the CR latent image

A

scanning
sampling
quantization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the purpose of the scanning stage when digitizing the CR latent image

A

convert latent image into an electrical signal - voltage - that can be digitized and displayed as an image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

once in the reader unit what has happened to the IP

A

IP removed from cassette and scanned with a He neon laser beam to release the stored energy as visible light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what does absorption of the laser beam for a CR digitization of image do to the e- in the IP

A

releases trapped e- and they return to a lower energy state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

the scanning of the IP in CR digitization of the image results in what happening to the light intensities and where is it sent to

A

continuous pattern of light intensities being sent to the PMT which is then directed to the ADC for sampling and quantization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what does the PMT do in terms of CR digitization of an image

A

collects, amplifies and converts the visible light to an electrical signal proportional to the energies stored in the IP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

why is sampling needed in the digitization of the image in CR

A

to digitize the analog signal from the PMT

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what is the sampling frequency and related to in the process of image digitization in CR

A

ADC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what is the sampling frequency and what does it determine

A

determines how often the analog signal is reproduced in its discrete digitized form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

increasing the sampling frequency of an analog signal has what effect on the pixel density and spatial resolution

A

increases pixel density and improves the spatial resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what is the sampling pitch

A

the distance between 2 sampling points

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

increasing the sampling frequency will have what effect on the sampling pitch

what relationship do they have with eachother

A

increase sf = decrease sp and results in smaller sized pixels

inverse relationship

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

the larger the sampling pitch the ___ the pixel size

A

larger

33
Q

what is the pixel pitch

A

the distance between the midpoint of one pixel to the midpoint of an adjacent pixel

34
Q

in terms of the size of pixels and the number of pixels what improves the spatial resolution

A

increasing number and smaller sized pixels

35
Q

increasing the sampling frequency results in what effect on the sampling pitch and pixel pitch and spatial resolution

A

the smaller the gap between pixels so smaller for both pitches

improves spatial resolution

36
Q

why would fixed matrix size system improve the spatial resolution

A

to maintain the same matrix size and number of pixel the pixels must be smaller in size

37
Q

what does it mean when the spatial resolution for an IP is fixed in terms of matrix and IP size

what is fixed

A

matrix size is proportional to the IP size (larger IP size means it will have a larger matrix to maintain the same pixel size)

sampling frequency is fixed

Fixed sampling keep pixels the same size

38
Q

what does it mean when the matrix size for an IP is fixed

A

change the sampling frequency to maintain the matrix size

changing the size of the IP would affect the spatial resolution of the digital image as the pixels in a smaller image plate will be diff size/smaller than those in a large one.

a larger IP size will result in a larger pixel size and decreased spatial resolution

39
Q

what is a matrix

A

Number of pixels = matrix

40
Q

for a fixed matrix size CR system using a smaller IP (decreasing the IP) for a given field of view has what effect on the spatial resolution

A

improves the spatial resolution of the digital image

41
Q

what does it mean when the degree of CR quantization is mentioned

A

the pixel bit depth

42
Q

what does CR quantization control

A

number of grey shades/contrast of the image

the bigger the pixel bit depth = more values of grey

43
Q

what does CR quantization reflect

A

precision at which each sampled point is recorded

44
Q

before CR plates are reused/returned to service what must be done and why

A

exposed to intense white light to release residual energy that could affect future exposures

45
Q

what is the DR’s scanning system like

A

self-scanning

46
Q

DR systems convert x-ray intensities into proportional ______

A

electronic signals for digitization

47
Q

what does DR allow in terms of image acquisition and readout

A

reduces the delay between the 2 processes

48
Q

what is the difference between DR and CR in terms of the image acquisition process

A

CR requires 2 step process and results in a delay between image acquisition and readout

DR combines the 2 processes so images are available directly after exposure

49
Q

what are flat panel detectors and which type of radiography are they used in

A

DR

solid state IRs using a large area active matrix array of electronic components

50
Q

what are the 3 processes integrated into the flat panel detector

A

signal storage, readout and digitizing

51
Q

in a DR flat panel detector do the first, second and third layers composed of

A

1st layer = x-ray converter

2nd layer = thin film transistor array

3rd layer = glass substrate

52
Q

what is the thin film transistor in the flat panel detector divided into

what do these divisions do

A

square detector elements (DEL)

they store electrical charges and a switching transistor for readout

53
Q

what does the electronic signal get sent to after being processed by the flat panel detector in DR

A

ADC for digitization

54
Q

what is the limitation of the DEL in the flat panel detector in DR

in terms of the pixel size

A

the DEL has a x-ray sensitive area representing each pixel in the image matrix

the pixel is therefore smaller than the DEL and can only capture a % of the x-rays reaching the detector

55
Q

what is the fill factors for DELs of DR

what is its value normally

A

the percentage of x-ray capture by the DEL

normally around 80%

56
Q

flat panel detectors with smaller DELs have what pro and con

A 
pro = smaller pixel size so improved spatial resolution
con = fill factor decreased

Efforts to further decrease the DEL for improved spatial resolution would require more radiation exposure to reach the IR to create the digital image as smaller pixel size means more radiation is needed as there is more sampling

57
Q

what are 3 advantages of using flat panel detectors DR in terms of dose, spatial resolution and pixel size/pitch

A

highly dose efficient

better spatial resolution than CR

fixed pixel size and pitch so limits spatial resolution to square detector elements

58
Q

what are the 2 ways that flat panel detectors create electrical charges proportional to the x-ray exposure

A

indirect and direct

59
Q

indirect conversion detectors use a ___ to convert ___ radiation into ___ ___

A

scintillator

exit radiation into visible light

60
Q

in indirect conversion detectors the visible light is converted into electrical charges by ____ and the electrical charge is stored by __ in the __ ___ before being digitized and processed in the computer

A

converted to electrical charges by photodetectors

stored in the capacitor in the TFT array

61
Q

what are the 3 steps in indirect conversion detectors

A

scintillators detectors converts exit radiation into visible light

photodetector converts visible light to proportional electrical charges

electrical signals sent to the ADC for digitization

62
Q

what are the 2 stage processes in indirect conversion detectors

A

convert x-ray intensities first to visible light

and then to electrical charges during image acquisition

63
Q

are the 2 steps in the direct conversion detectors

A

amorphous selenium coated detector converts exit radiation directly into electrical charges

electrical signals are sent to the ADC for digitization

64
Q

why is an electrical field applied across the selenium later of a direct conversion detector

A

limit the lateral diffusion of e- as they migrate towards the thin film transistor array

65
Q

what are the similarities between the indirect and direct conversion detectors in the process of charge storage

A

electrical charge is stored in a TFT array before its amplified, digitized and processed in the computer

66
Q

what stage does the direct conversion detector skip when compared to the indirect

A

skips the stage of needing to create physical light

67
Q

what is the dynamic range

A

ability of a detector to accurately capture the range of photon intensities that exit the patient

68
Q

what does a wider dynamic range mean for the contrast and exposure

A

more contrast and risk over exposure

69
Q

what is the detective quantum efficiency

A

measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiograph image

70
Q

what does 100% detective quantum efficiency mean

A

no info is lost

71
Q

the higher the detective quantum efficiency what happens to the radiation exposure to produce a quality image and patient exposure

A

lowers the radiation exposure required to produce a quality image

decreases the patient exposure

72
Q

which 2 factors is the detective quantum efficiency affected by

A

the type of material used in the IR to capture the exit radiation

the energy of the x-ray

73
Q

what is the signal to noise ratio

A

describes the strength of the radiation exposure compared with the amount of noise apparent in a digital image

74
Q

what is the signal in the signal to noise ratio

A

the signal is the strength of the radiation exposure

75
Q

what is the noise in a digital image from

A

sources include e- that capture, process and display the image

76
Q

what is quantum noise

A

too few x-ray photons captured by the image receptor to create a latent image

77
Q

what does increasing the signal to noise ratio do for the quality of the digital image

A

improve the quality by improving the visibility to anatomical details

78
Q

what is the contrast to noise ratio

A

describes the contrast resolution compared to the amount of noise apparent in a digital image

79
Q

increasing the contrast to noise ratio does what to the visibility of anatomic details

A

increases visibility

202 MEDIMAGE (18 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions