monitors Flashcards
what are the original radiology display monitors called
originally cathode ray tube (CRT)
what are the radiology display monitors we use now called
liquid crystal display monitors (LCD)
how many liquid crystal pixels/cells sandwhiched between 2 pieces of polarized glass
1000s
what is the backlight source of LCDs
light emitting diodes LEDs
traits of LCDs
- thin and light
- draw much less power than CRTs
what are single LC pixel - parallel polarisers
- orderly arranged crystals
- placed between two plates of polarized glass
- coated with transparent electrodes
how does light pass in an LC
light passes through from left
- interlayer film polarises light
why is there varying voltage in an LC
- alter amount of light allowed through to give a certain grey level for that cell/pixel
LCD
liquid crystal display
how are LCDs arranged
arranged in a matrix on a glass substrate
what does each LC represent
one pixel
how many levels of brightness per pixel
256
how long is the capacitor in the LCD able to hold the charge for
until next refresh cycle
pixel colour filters
- red
- green
- blue
how many colours can be made up
16.8 million
what lights up LCD
LEDs
luminous efficacy for LEDS
HIGH
lifetime of LED
50,000+
what is resolution
number of pixels demonstrated
what is a dot pitch/ pixel pitch
distance between centres of two same colour phosphor dots (0.2 to 0.4 mm)
when would you use a larger monitor
for higher resolution
what is luminance
brightness of screen or photon energy that reaches the eye
what rate does luminance describe
the rate at which light is emitted from surface
what is luminance given in
candelas per square metre
what does luminance ratio equal to
the maximum luminance to minimum luminance
(Lmax/Lmin)
grey scale range consumer displays
256 (8 bit)
grey scale range medical displays
4096 (12-bit)
what has a poor greyscale response
colour displays
SMPTE
society of motion picture and television engineers
what is the SMPTE test pattern used for
a test pattern that we use in imaging to evaluate our quality of our monitors
- required to check SMPTE pattern on a CT on monthly basis
SMPTE pattern checks
- the 5% patch within the 0% patch is visible
- the 95% patch within the 100% patch is visible
why is it important to ensure the patches are visible in SMPTE
you can distinguish between very small changes in grey levels
what is luminance uniformity
brightness being completely uniform in all forms of display
- ensure no dark spots/ ineligibility of information on screen
display screen equipment (DSE) user regulations
- regular breaks
- essential use only
- specific requirement
- no more than 2 hours at a time
DSE equipment
- safe, efficient, comfortable
- minimal heat + noise
- minimal glare
- promote good posture
- large display
DSE workstation
- adjustable screen
- keyboard at normal height
- keyboard independent of screen
- allow comfortable head position
- adjustable chair
- assess environment if changed
- not in contact with uncovered window
what considerations do you need to take
- image quality - resolution, luminance and LR, bit depth
- physical size/ orientation
- viewing distance should be 60cm
- hi resolution = larger sizes
- aspect ratio
- portrait vs landscape
- room to work?
- how many monitors
- cost?
- standardise monitors in dept (dont have too many different types)
- use
- can performance be affected by environment and room lighting?
- protective cover or not
- QA
what does pixel size depend on
primary application
primary class
diagnostic (reporting)
secondary class
review (workstation)
