histogram types
aw air exposure between anatomical structure and the collimation borders eg extremities
no tail or high spiked area on the far right
all data is included for processing
if you tell computer to thin the PA
youre telling it how to process
windowing
vary the greys
1000s pixel value
need to apply grey levels to visualise
need to apply the grey levels so
optimise brightness and contrast and to visualise
contrast is
changed by the changing of pixel value
look up table
assign output value to every input value
you loose contrast if it isnt on look up table
window width
The range of grey scales displayed in an image
256 shades of grey
Window width relates to contrast in the image, narrower window width gives higher contrastcovers the pixel value to the tissues of intrest
below ww= black
above ww = white
window level
The centre of the window width
Higher window level - higher pixel values (less dense areas) have grey scales associated with them
Window level relates to the brightness of the image, higher window level gives brighter image
central pixel value of the numbers with ww
ww and wl can be set independetly
narrower window width..
the higher the contrast in the image
anything outside that sits outside window has 0 contrast
too low contrast
too wide
too high
too narrow
windowing controls
contrast and brightness but the histogram data must be good enough to do this
unsharpness
geometry
patient movement
brightness
windowing
contrast
L.U.T
quality of data
noise
underexposure
spacial resolution
detector, monitor
