Brainscape's Knowledge GenomeTM

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


See full index

Radiation Safety 2 (Year 3 Revision) > Image displays > Flashcards

Image displays Flashcards

1
Q

What are hard and soft copy display systems?

A
  • Hard: Film with image on.
  • Soft: Image on computer screen.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the main stages of the imaging chain?

A
  • Acquisition device.
  • Display processing software.
  • Display controller.
  • Softcopy/hardcopy display.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does the display processing software do?

A

Transforms ‘image values’ to digital driving levels.

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

What does the display controller do?

A

Converts the digital driving levels produced by the display processing software to signals appropriate for the display device. These typically conform to a specific standard.

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

What are the two categories of soft copy devices?

A
  • Secondary (e.g. review monitors).
  • Primary (e.g. diagnostic workstations).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What kinds of soft copy display are available? Which are most common?

A
  • Cathode ray tube (essentially obsolete).
  • Liquid crystal display (still common).
  • Emissive flat display e.g. active matrix organic light emitting displays (becoming more common).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does a cathode ray tube work?

A
  • Vacuum tube, phosphor and electron beam.
  • Electrons emitted by cathode.
  • Accelerated towards phosphor.
  • Deflection coils used to scan electron beam across phosphor.
  • Light produced in phosphor where beam strikes.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does a liquid crystal display work?

A
  • Polarised light from backlight enters liquid crystal cell.
  • Orthogonal grooves in the two alignment layers sandwiching the liquid crystal cell cause preferential alignment of liquid crystal cell molecules to the grooves they are in close proximity to. This creates a ‘twist’ in the molecular structure.
  • The degree of twist is altered across the liquid crystal cell by altering the electric field across the cell with the TFT.
  • The twist causes the plane of polarisation of the light entering the cell to be rotated.
  • The amount of light transmitted by the liquid crystal cell depends on how much the plane of polarisation is twisted with respect to the front polariser.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What affects the actual pixel size of of a liquid crystal display when compared to nominal?

A

Electronic elements (e.g. TFT switch) mean the actual pixel size is smaller than nominal.

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

What do the maximum and minimum luminance of a liquid crystal display depend on?

A
  • Minimum: How opaque the liquid crystal cell is in its full off state (i.e. how good is it from preventing light from backlight passing to front).
  • Maximum: Brightness of backlight, nature of polarisers (i.e. how much they transmit) and the transmission of the liquid crystal cell in its full on state).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What determines the uniformity of a liquid crystal display?

A
  • Uniformity of the backlight.
  • Uniformity of the liquid crystal elements.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are some disadvantages of liquid crystal displays?

A
  • Lower refresh rate than cathode ray tubes.
  • Emission of light can change depending on viewing angle which can result in contrast loss and greyscale inversion.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the main components of an active matrix organic light emitting display? What does each component do?

A
  • Backplate (substrate).
  • TFT array (control the current to each pixel).
  • Organic emissive layers (semiconductor material which produces light due to the recombination of electron-hole pairs).
  • Cathode.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is one of the main differences between liquid crystal displays and active matrix organic light emitting displays?

A

LCDs have a backlight whereas AMOLEDs are emissive devices which produce light themselves.

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

What are the advantages/disadvantages of active matrix organic light emitting displays?

A

Advantages:
- High resolution, brightness and contrast (blacker blacks than LCD).
- Wide viewing angle when compared to LCD.
- Lightweight, thin and low power.
Disadvantages:
- Limited lifespan of organic material (especially blue) which can cause a shift in colour balance.
- Susceptibility to water damage.

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

What are the typical properties of a common ‘consumer’ display?

A
  • Low-mid resolution (~ 2 million pixels).
  • Low maximum luminance (100-250 cd m^-2).
  • Low bit depth (2^8 = 256 grey levels).
  • No built in image greyscale standard display function (GSDF) calibration.
  • Not too stable over time.
  • Cheap and commonplace.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What options are available when displaying a large medical image on a small ‘consumer’ display?

A
  • Display the full image. However, this would result in pixel binning and loss of information.
  • Display the full resolution. However, this would mean only a certain portion of the image could be viewed at a time.
  • Use an ‘in between’ of the above two methods.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the typical properties of reporting workstations?

A
  • High resolution (3-5 million pixels and up to 10).
  • High maximum luminance (600 + cd m^-2).
  • Large bit depth (up to 16 000 grey levels).
  • Built in image greyscale standard display function (GSDF) calibration.
  • Stable luminance.
  • Very expensive.
19
Q

What is luminance?

A

Rate at which visible light is emitted from a surface in units of cd m^-2. It is independent of the distance from the source.

20
Q

What is illuminance?

A

Rate at which visible light falls upon a surface in units of lux. Used as a measure of ambient light.

21
Q

What is optical density?

A

Log of the ratio of the amount of light incident on a film to that transmitted.

22
Q

What is the luminance ratio? What is L_amb?

A
  • Luminance ratio = Max luminance/Min luminance.
  • L_amb: Luminance added to display by ambient light.
23
Q

What are some examples of hardcopy devices? When may these be used?

A
  • Dry laser printer (backup if PACS is down).
  • Thermal imager (on some ultrasound units).
  • Conventional x-ray film (essentially obsolete except for dental).
24
Q

What is the difference between a wet laser and a dry laser?

A

In both cases, a film is scanned to produce a latent image. For a wet laser, the film is then chemically processed to produce an image. For a dry laser, the film is heated to produce an image.

25
Q

What is DICOM?

A

Digital imaging and communication in medicine is a standard for transmitting, storing and viewing information in medical images. It enables integration of scanners, servers, workstations, printers etc. from multiple manufacturers into a picture archiving and communications system (PACS).

26
Q

What can a DICOM file store?

A
  • One slice per file.
  • Header with lots of information (e.g. information on patient, machine, image details, acquisition parameters, radiation dose information etc.).
27
Q

What does the display window/level correspond to?

A
  • Lookup table to adjust the relationship between p-values and DDL.
  • Controls the range of image pixel values displayed on the monitor. The size of the range is controlled by the window width and the centre of the range by the level.
28
Q

Apart from window/level, what are some other common workstation controls?

A
  • Callipers (distance/angle measurements).
  • Magnification.
  • Pan/zoom.
  • Image overlays (e.g. text annotation).
  • Lookup table change (e.g. from greyscale to colour).
  • Basic filtering (e.g. edge enhancement, noise filtering etc.).
  • 3D functionality.
29
Q

What is GSDF? What is it based on?

A
  • Greyscale standard display function.
  • This is a standardised response function to simplify the application of image transformations across the wide range of different devices. It allows applications to know beforehand how P-values are transformed to viewed luminance.
  • Also standardises image presentation on different devices if the luminance ratio and the GSDF are the same.
  • The GSDF curve is based on the Barton model of the human visual system which has a non-linear response.
30
Q

What does the Barten model curve show?

A

The minimum relative change in luminance (luminance contrast) required to be ‘just noticeable’ by the observer as a function of luminance. At higher luminance contrast, the luminance contrast required to be just noticeable is lower.

31
Q

How is a display calibrated?

A
  • Luminance vs DDL is measured and a lookup table that makes the luminance at each presentation value follow the GSDF curve between L_min and L_max.
  • p-values are then linearly proportional to jnd indices.
32
Q

What is an 8 bit - 8 bit lookup table? Why is this important?

A
  • First part is the input of the lookup table (e.g. 256 for 8 bit).
  • Second part is the output of the lookup table (i.e. the precision of luminance output).
  • This determines the number of ‘just noticeable differences’ per driving level and, therefore, can impact on information losses.
33
Q

What is used for quality assurance of image displays? What can they be used to check?

A

Downloadable test patterns (e.g. AAPM TG18) which can be viewed on the image display. They include various resolution and contrast features for qualitative and quantitative assessment. They can be used to check:
- Luminance and contrast response.
- Luminance uniformity.
- Resolution.
- Contrast transfer.
- Diffuse reflection.
- Bit depth.
- Noise
- Veiling glare.

34
Q

What initial checks are performed prior to image display quality assurance?

A
  • Ensure viewing conditions are appropriate.
  • Check room ambient light levels are within limits (less than 10 lux for reporting workstation).
  • Check general condition of monitors.
  • Clean following manufacturers instructions, if necessary.
35
Q

How does image display quality assurance proceed?

A
  • Test pattern displayed at full resolution (each pixel in image represented by 1 pixel in display).
  • Qualitative assessment of distortion, flickers, artefacts and reflections on images (check borders and other lines).
  • Proceed to check each aspect of test pattern in more detail.
36
Q

How is resolution checked during image display quality assurance?

A

Horizontal and vertical bar patterns: Check that all high contrast bars are distinguishable.

37
Q

What is the greyscale step wedge used for during image display quality assurance?

A

Qualitative check on the calibration of the monitor. Each step should be noticeably different in brightness from its neighbours.

38
Q

What measurement units are required for quantitative assessments of image display performance?

A
  • Instruments to measure luminance and illuminance.
39
Q

How are luminance and contrast response checked quantitatively?

A
  • Photometer used to measure luminance of each square L_1 - L_18 under ideal conditions. L_amb also measured from a blank display.
  • A spreadsheet can then be used to check performance and compliance with DICOM greyscale standard display function (GSDF). GSDF is calculated and compared to standard.
  • L_max and L_min compared to remedial levels.
  • Luminance ratio compared to remedial level and baseline.
40
Q

How is uniformity checked quantitatively?

A
  • Uniformity test pattern displayed.
  • Luminance measured at each corner and at the centre.
  • Percentage difference between centre and each corner calculated.
41
Q

What do we have remedial levels for with regards to image display quality assurance? How may these vary?

A
  • L_max, L_min, Luminance ratio, uniformity and luminance difference between paired monitors.
  • Different depending on whether the display is a reporting or review monitor. Monitors used for mammography also have tighter tolerances than that for general radiography.
42
Q

How is image display ambient light measured? Why is this important to measure?

A
  • Measured with normal viewing conditions and display off. The amount of illumination at the monitor is measured in lux with an illuminance sensor.
  • Ambient light can affect performance (e.g. monitor may meet the greyscale standard display function (GSDF) in one location but not another). It reduces the number of ‘just noticeable differences’ available. It reduces contrast via diffuse reflection. It increased specular reflections.
43
Q

How are automated image display QC checks undertaken?

A

Clip on detectors or internal sensors.

Radiation Safety 2 (Year 3 Revision) (30 decks)

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