Take a look at the graph below, it shows the Kv
sensitivity of different screen emulsions, the absorption at low
energies i.e. those energies possessed by scattered radiation
generally below 55-60Kv. the green line shows typical sensitivity of
Lanex screens which primarily absorbs radiation above around 50 Kv
the K edge absorption of Gadolinium. However the phosphor used in CR
image plates is based on are europium-doped barium fluorohalide
crystals have a K edge at 37 Kv making the receptors more sensitive
to scattered radiation Kv values
With FS radiography we know that the image density and contrast
is controlled by the Kv and mAS respectively
The range of subject densities affect the contrast of the organs
on the image
 The
Exposure values set control where the subject density levels appear
on the range of densities on the film and how squashed up or
extended along the range of densities available on the film
Other factors effecting Contrast in FS radiography
 The effect of
scatter on an image 
The graph below shows where the scattered energies appear on the
graph of screen absorption - note the more scatter radiation
energies falling below the K edge of the phosphor decreases the
amount of image produced by the scatter
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