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22 Cards in this Set
- Front
- Back
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What does PACS stand for?
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Picture archive and communications System
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What does DICOM stand for?
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Digital Imaging and Communications in Medicine
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What is the QC workstation
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Extension of the PACS system that allows the technologist to see how the images should appear to the radiologist
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What are the DICOM Grayscal Presentation State (GSPS) and Grayscale Standard Display Function (GSDF)?
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Two standards that provide consistent presentation of images across different displays from the modality to the reading room.
greyscale values are tagged to luminance values to maximize resolution on a compliant display. |
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How much backlight brightness is lost by the time the image is displayed.
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95%
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How is the backlight modulated to produce different gray values and color
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The backlight is first polarized then "twisted" by the liquid crystal array. The light is then passed through a second polarizer which filters the light.
The liquid crystal will twist the light to allow for either a red/blue or green light to pass. |
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What kind of artifacts occur from displaying an image on a monitor that has a larger matrix than the image and is not an integer multiple
what if there are fewer pixels? |
L: Interpolation artifacts: Aliasing, blur or edge halo (Cambridge)
S: You will have to zoom in see all of the image information |
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What determines the brightness of a screen?
What determines the black-level |
The brightness of the backlight and how much light passes through the LCD panel
The darkness depends on how much light is blocked |
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Difference between stabilized and non-stabilized displays?
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stabilized displays will maintain steady luminance values during lifetime. Non-stabilized displays will decay almost linearly with time
displays are stabilized by auto adjusting the voltage to the backlight to keep it steady |
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What is spatial and temporal noise?
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spatial noise is due to variations in the pixels
temporal noise is due to variations in the backlight |
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What is contrast ratio
what is the realized contrast ratio? |
ratio of maximum White to black
affects contrast resolution realized ratio includes ambient light reflecting off the display |
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Describe off axis viewing angle
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contrast fall of to 1/10th that of normal on-axis viewing
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Contrast resolution of a display can be altered by performing what?
What does it mean for a display to be perceptually linear? |
grayscale calibration
A HU of 8 will appear 2x as bright as a HU of 4 |
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How does the DICOM GSDF (gray scale display function) work?
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standardizes grayscale presentation between displays of different manufacturers (contrast ratios) by correcting the brightness levels to the contrast sensitivity of the human visual system.
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Primary vs secondary displays have different performance requirements
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primary displays for radiologists
secondary displays for anyone else |
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Display quality control frequency is dependent on what?
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the stability of the display. Medical grade displays will require fewer QC checks than consumer grade displays
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Desirable features:
Luminance stabilization Luminance uniformity correciton Remote management Remote calibration Power management End user validation Ambient light sensing |
Luminance stabilization: minimizes luminance variations and frequency of QC
Uniformity correction: pixel by pixel correction Remote management: gives local monitor status Remote calibration: Power managment: displays can last 3x as long if shut off at night |
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Ambient light should be kept
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20-40 lux, no overhead lighting, incandescent rather than fluorescent
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Ideal viewing is (Orthaganal, off axis)
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orthoganol
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Optimal temperature and humidity control
minimize noise good chairs |
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What is asthenia
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reduced ability to focus especially at close distances after a long day of reading
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what is the 20-20-20 rule
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Every 20 minutes, look 20 ft away for 20 seconds
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