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DR Flashcards

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1
Q

What is the pixel size?

A

Pixel size is FOV/ matrix size

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2
Q

What is a byte?

A

a byte can carry up to 8 bits, ie a number up to a value of 2 (8)-1=255

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3
Q

T/F?

matrix size greater than 512x512 would significantly improve SR.

A

FALSE

matrix size greater than 512x512 would NOT significantly improve SR.

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4
Q

T/F?

Rx has an intrinsic SR that is high.

A

TRUE

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5
Q

What is the SR of film-screen radiography?

A

10 lp/mm

* DR needs large matrix size.*

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6
Q

What does influence the bit depth for image storage?

A

It is influenced by the noise and dynamic range of imaging device.

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7
Q

What is the bit depth in radionuclide imaging and why?

A

With an image asso with high level of noise such as radionuclide imaging , bit depth may need to be no greater than 8.

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8
Q

What bit depth is used in DR?

A

In DR detectors have a wide dynamic range so for data acquisition bit depth of 16 may beused.

The full range of data may not be needed in final image and 12 or 14 bit depth may be sufficient for data storage.

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9
Q

What are the different types of compression in DR?

A

a. lossless or reversible- image can be restored into identical version of the original. Reduces the file size by factor of 2 or 3.

b. lossy or irreversible- results in a displayed image that does not perfectly reproduce the original. compression of data by much greater factors up to about 40.
Image quality may not be acceptable for primary diagnosis.

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10
Q

How could you reduce noise in fluoroscopy?

A

By adding the signal from successive frames to give a timed average image.–> Frame averaging. Useful when there is no movement bwn frames, otherwise= blurring.

This is equivalent to increasing exposure time in radiography.

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11
Q

How could you reduce noise in fluoroscopy?

A

Frame averaging

Low pass spatial filtering

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12
Q

what is low pass spatial filtering?

A

this is a technique in which the greyscale value stored in each pixel has added into it a proportion of the value of neighbouring pixel and the resultant value averaged.
The effect is to smooth the final image but it will blur small details or edges.

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13
Q

what is edge enhancement or high pass filtering?

A

this is opposite to low pass filetring.
Rather than display a weighted average value of neighbouring pixels, a high pass filter adds in a proportion of the difference bwn the greyscale value of the pixel and of its neighbours.
the effect is to exaggerate the contrast at the boundary bwn structures thus making the structures more visible.
Process also serves to increase noise. It may generate false structures in the image.

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14
Q

what is the disadvantage of edge enhancement ?

A

it increases noise. It may generate false structures in the image when a high level of filtering is applied.

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15
Q

What are the two types of image display?

A

a. cathode ray tube

b. flat panel monitoring

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16
Q

how does the cathode ray tube function?

A

uses a scanning electron beam whose intensity is modulated in accordance with the stored pixel value.

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17
Q

How many scan lines in cathode ray tube?

A

1250 scan lines, limiting the resolution in perpendicular directions

with the resolution parallel to the scan lines being limited by frequency of modulating signal.

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18
Q

What is the most common used flat panel monitor?

A

liquid crystal display

screen is made up of individual pixels with matrix sizes up to 2000 by 2500 in rectangular arrays.

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19
Q

What is the pixel value related to?

A

It is related to the intensity of signal in the corresponding part of image.

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20
Q

What is a fourier analysis?

A

The imaging signal is broken down into a series of sine waves that vary in terms of spatial frequency and amplitude.

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21
Q

How do we assess the fourier analysis?

A

By Modulation transfer function-MTF

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22
Q

What is the Nyquist criterion?

A

It states that the high signal must be sampled at least twice in every cycle or period ,

ie the sampling freq must be at least twice the highest frequency present in the signal.

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23
Q

What is the Nyquist frequency?

A

The maximum signal frequency that can be accurately sampled is called the Nyquist freq.
This is equal to half of the sampling frequency.

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24
Q

What is aliasing?

A

This is when the high signal is recorded as low.

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25
Q

what type of artefact would you get in CT with aliasing?

A

streak artefact

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26
Q

What artefact would you get in MRI with aliasing?

A

Wrap around - translocation of anatomy from one side of the image to the other.

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27
Q

What happens in pulsed doppler imaging with aliasing?

A

The fast flow in one direction will be interpreted as a slower flow in the opposite direction.

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28
Q

What is MTF?

A

This is the output : input modulation

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29
Q

What is the effect of spatial frequency on MTF?

A

MTF varies with spatial freq.

Generally reducing progressively from 100% at low spatial frequency towards 0 at higher frequency.

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30
Q

Define modulation:

A

Modulation is the difference between the max and min amplitude as a proportion of the averaged signal.

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31
Q

It is a common way to compare two systems by quoting a single figure such as the spatial frequency at which the MTF is …..

A

10%

32
Q

what is a photostimulable phosphor?

A

CR uses a storage phosphor that requires light that is proportional to the x ray intensity.
This is referred as photostimulable phosphor

33
Q

What is photostimulable phosphor is made of?

A

barium fluoro halide doped with europium- BaFX:Eu

in which the halide -X- is a combination of bromide and iodide. (85% and 15%)

34
Q

what happens to Ph in powdered form?

A

The Ph in powdered form is mixed with a binder or adhesive material and laid down on a base with a thickness of about 0.3mm

35
Q

what is the function of the surface coat?

A

it protects the Ph from physical damage.

36
Q

T/F?

The imaging plate formed in CR is similar to Int screen in conventional radiography.

A

true

37
Q

What happens to the imaging plate?

A

The imaging plate is then inserted into a light tight cassette similar to conventional Rx.
The signal from plate is read in a CR reader.

38
Q

What happens in a CR reader?

A

The plate is removed from the cassette and scanned by a laser beam.

39
Q

Hows scanning achieved?

A

Scanning is achieved using a rotating mirror.

40
Q

What is placed above the imaging plate?

A

Above the plate there is an array of optical fibres to direct the emitted light to one or more photomultiplier tubes to measure its intensity.

41
Q

What end of the spectrum is Ph used for CR?

What laser colour is used for stimulation?

A

Most ph used for CR emit light at the blue end of the spectrum and need a scanning laser emitting red light for stimulation.

42
Q

how would you erase the plate after reading?

A

By exposing it to a bright light source

43
Q

T/F?

Photostimulable phosphors have a very wide DR.

A

True

44
Q

What is a latitude? Compare latitude of CR with conventional:

A

This is the range of doses that can be imaged . In CR it is much greater than conventional radiography.

45
Q

The raw CR image would be equivalent to a film screen image with a film latitude of about……… compared with 2 to 3.

A

0.4

46
Q

What are the 3 steps if processing data from the reader:

A
  1. detect the collimated edges of the x-ray beam.
  2. histogram analysis
  3. Map the intensity values.
47
Q

What could be done post processing: (2)

A

Edge enhancement and noise reduction

48
Q

T/F?

Spatial resolution with CR is more than conventional film screen radiography.

A

False

Spatial resolution with CR is LESS than conventional film screen radiography.

49
Q

T/F?

a. SR is affected by pixel size.
b. Pixel size varies with plate size

A

a. True

b. True

50
Q

compare small and large plates in terms of pixel size and limiting resolution.

A

smaller plates (18 x 24cm), pixel size 90microm, matrix size 2000 x 2670 pixels- 5.3 Mpixels, limiting reolution of 5.5 lp /mm

Larger plates (35 x43cm), 140 microm, matrix size 2500 x 3070- 7.7 Mpixels, limiting resolution of 3.5 lp/mm

51
Q

T/F?

The increased size for the larger plate is a physical limitation.

A

False

The increased size for the larger plate is NOT a physical limitation.

52
Q

what is the effect of larger pixel size on scanning time and file size

A

Larger pixel size helps to reduce scanning time and image file size

53
Q

What factors affect the limiting SR? (4)

A
  1. pixel/ matrix size
  2. scattering of laser light in the ph layer. this effect increases with the thickness of the ph.
  3. size of ph grains
  4. diameter of the scanning laser beam.

CR ph are being developed that have a crystalline structures that act as a light guide as its used in image int screen

54
Q

T/F?

mammography screens have a thicker phosphor layer and permits a reduced pixel size of 50 microm.

A

False

mammography screens have a THINNER phosphor layer and permits a reduced pixel size of 50 microm.

55
Q

How could you enhance the ability to detect finer details in the CR image.

A

Partial volume effect and by use of edge enhancement algorithm.

56
Q

T/F?

CR image should display more contrast that can be seen in film screen radiography.

A

True

57
Q

T/F?

There is no obvious indication as to whether the imaging plate has received the correct dose

A

True

58
Q

T/F?

The detector has narrow lattitude

A

False

The detector has a very wide lattitude.

59
Q

what is a detector dose indicators?

A

these are analogous to optical density of film.
It is determined by the signal from the plate averaged over a broad region of the plate but restricted to signal values that lie within the region of histogram used for mapping the signal to the gradation curve.

60
Q

T/F?

Definition of DDI are manufacture dependent.

A

True

61
Q

T/F?

CR systems use photostimulable phosphors.

A

True

62
Q

Classify DR:

A

Direct

Indirect

63
Q

What is a transistor?

A

This is a devise that amplifies an electrical signal and in the TFT array the amplified signal is stored as an electrical charge.

The e charge can be released by applying a high potential.

64
Q

The most common DR detectors are based on what?

A

The most common DR detectors are based on amorphous silicon thin film transistor- TFT.

The dimensions of the array being the size of the area to be imaged.
Each row is connected to activating potential and each column to a charge measuring device.

65
Q

T/F?

In TFT array there are more transistors as there are pixels.

A

False

In TFT array there are as many transistors as there are pixels.
The size of each transistors/ pixel is in the range of 100-200microm
The electronic and detectors are deposited in several layers on a glass substrate.

66
Q

What is the most common class of flat plate detector?

A

Indirect conversion of x ray pattern into an electronic signal.

67
Q

what converts x ray photons to light?

A

phosphor- a common phosphor is caesium iodide laid down as a crystalline structure above the photodiode array.

68
Q

T/F?

The elongated crystal with diameter smaller than the pixel are grown so that they are perpendicular to the surface of detectors.

A

True

69
Q

Name the two different types of ph that could be used: compare the two

A

CsI- thicker layer is used due to the layout.
Gadolinium oxysulphide - this is most commonly used for film screen radiography. Greater light spread so that a thinner layer is used thus 1. reducing detection effeciency.
2. cheaper to peroduce
3. more robust

70
Q

What sort of ph is used for ward radiography- portable?

A

Gadolinium oxysulphide

71
Q

what detector is used in direct conversion?

A

amorphous selenium. this is a photoconductor, it will pass electrical charge on irridation.

72
Q

How would you measure the efficiency of an x ray detector system?

A

DQE- detector quantum efficiency

73
Q

What is teh DQE for DR and CR system?

A

DR- 65%
CR-30%

Therefore DR systems can be used at lower doses without any increase in quantum noise.

74
Q

What are the disadv of Dr as opposed to CR

A

Cost and versatility

75
Q

What are CCDs detectors used in?

light sensitive detectors.

A

mammography for stereotactic films used for biopsy localisation

They cannot be manufactured in a size that is greater than 5cm2

76
Q

What does a PACS broker do?

A

they provide an interface between systems and the work flow manager.
They also ensure effective communication between systems.

FRCR Physics (9 decks)

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