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APPH 226 > Digital Imaging > Flashcards

Digital Imaging Flashcards

1
Q

Digital imaging

A

Defined as

  • any imaging acquisition process that produces an electronic image that can be VIEWED and MANIPULATED on a computer
  • these digital images can be sent through a computer network to various locations as needed
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2
Q

Computer

A

Used throughout the department for a number of purposes: front desk, tech work area, radiologists reading room
-computer set up chosen to fulfill purpose
-basically consists of:
🔹input devices
🔹output devices
🔹processing devices

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3
Q

Input and output devices

A

Input devices: keyboards, mice, microphones, barcode readers, touch screens, image scanners
Output devices: monitors, printers (paper and laser film), speakers

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4
Q

Monitors

A 
Two main types
-CRT (cathode ray tube)
-LCD (liquid crystal display)
Third type in development
-OLED (organic light: emitting diode)
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5
Q

Pixels

A

-individual controllable set of dot triads
-dot triad (grouping of dots)
-basic picture element on display
-resolution: # of pixels on a display
🔹higher resolution = higher # of pixels
-arranged in a matrix that represents the pixel intensity to be displayed
-dot pitch: how close the dots are in the pixel
🔹the smaller the dot pitch, the higher the resolution

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6
Q

Monitors

A

CRT
-refresh rate
-how fast the monitor rewrites the screen or the number of times the image is redrawn on the display/second, controls the ‘flicker’ seen by user, higher refresh rate = less flicker
LCD
-response rate
-the amount of time for crystal to go from off state to on and vice versa, slower response time will cause blurring during viewing of dynamic images

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7
Q

Aspect ratio

A

Ratio of the width of the monitor to the height of the monitor

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8
Q

CRT

A
  • consists of a cathode and anode in a vacuum tube
  • works like an x-ray tube (electrons sent to the monitors anode which is a sheet of glass coated with phosphors)
  • electrons strike phosphors causing glass to emit a colour determined by the intensity of the interaction and area with which electrons interacted
  • electron beam starts in the upper left corner and scans across the glass from side to side, top to bottom
  • after reaching the bottom, it starts again at the top left
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9
Q

LCD

A

-images are produced by shining or reflecting light through a layer of liquid crystal and a series of colour filters
-made of two pieces of polarized glass with a liquid crystal layer in between the two
-light passes through the first layer, and when a current is applied to the crystal layer, it aligns and allows light varying intensities through to the next layer
🔹colour filters in that layer of glass form the colours and images seen on the display

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10
Q

Digital imaging

A
  • a digital image is one that has been converted into numerical values for transmission or processing
  • requires a means to acquire the image formation (DR,CR)
  • information gathered by scanning an area using array detection
  • array processing is when information is received from an entire area at once
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11
Q

Array processors

A

-special computer that functions as a peripheral device
-uses its own memory to perform simultaneous mathematical operations at extremely high speeds
🔹compiles all the image information
-allows us to see the image instantaneously

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12
Q

Factors that remain unchanged in digital imaging

A
  • collimation
  • patient positioning
  • projections
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13
Q

Digital is better because

A
  • wider range of exposure
  • linear response
  • greater range of densities
  • easily manipulated with computer
  • post processing
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14
Q

Characteristics of a digital image

A

-digital image begins as an analog signal
-critical characteristics of a digital signal are:
🔹spatial resoluton
🔹contrast resolution
🔹noise
🔹dose efficiency (of the IR)

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15
Q

Pixel size

A
  • size of pixel is directly related to the amount of spatial resolution or detail in the image
  • the smaller the pixel, the greater the detail
  • can be affected by matrix size
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16
Q

Pixel bit depth

A

-each pixel contains bits of information
-is the # of bits within a pixel
Ex: bit depth = 8 means 2^8 (meaning 256 shades of grey can be produced by that pixel
-higher the bit depth, the more grey levels can be displayed by the pixel
🔹more shades of grey gives more accurate representation of the image

17
Q

Bit systems

A

8 bit system is 2^8 (256 shades of grey)
10 bit system is 2^10 (1024 shades of grey)
12 bit system is 2^12 (4096 shades of grey)
14 bit system is 2^14 (16384 shades of grey)

18
Q

Matrix

A

-image is recorded as a matrix
-described in numerical values
-divided into many small cubes/boxes
🔹each square region is a pixel
🔹assigned one binary value that is equal to the radiation exposure received
🔹binary value = shade of grey

19
Q

Matrix

A
  • ⬆️ matrix size = ⬆️ resolution
  • larger the matrix = smaller the pixels (if the same size detector)
  • matrix size is not the same as screen size
  • pixel size controls resolution
20
Q

Dynamic range

A

-the ability to respond to varying levels of exposure
🔹dynamic range wider for digital vs film/screen
-the range of grey values that can be displayed
-human eye can differentiate about 30 shades
-dynamic range of digital imaging systems is identified by the bit capacity of each pixel
-although the response of digital system can produce a huge range of greys, limited by human visual system (can only see about 30 of them)
-through the use of window and level, any region/range of greys can be rendered into the 30 shades of grey that the human eye can see
-white is designated as 1

21
Q

Windowing

A
  • allows us to see only a portion of the entire dynamic range
  • raw data image will show the full dynamic range (appears very low contrast, as so many shades of grey are displayed)
22
Q

Window level

A
  • DENSITY (BRIGHTNESS) enhancement
  • controls image BRIGHTNESS
  • brightness is controlled by varying the numerical value of each pixel
  • direct relationship: ⬇️ window level = ⬆️ image brightness
23
Q

Altering image brightness

A
  • INCREASING the brightness of the image: all pixels are raised to a higher value by the same factor
  • DECREASING the brightness of the image: all pixels are decreased to a lower value by the same factor
24
Q

window width

A
  • CONTRAST ENHANCEMENT
  • controls image CONTRAST
  • sometimes called grey scale expansion or compression
  • inverse relationship: ⬇️ window width = ⬆️ image contrast
  • varies the dynamic range (grey scale) of the densities to adjust the contrast
  • NARROW WW: ⬇️ window width = ⬆️ in contrast
  • WIDE WW: ⬆️ window width = ⬇️ in contrast
  • controls the visibility of detail
  • any value outside of the chosen window width is lost from diagnosis
25
Q

Windowing

A

-using window and level, any region and range of available # of greys, can be rendered as 30 shades of grey

APPH 226 (23 decks)

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