Why PI added in Cos[# Pi]& in an InverseRadon option in documentation

In V8 of Mathematica, the documenation for the InverseRadon transform (added in V开发者_高级运维8), and for the filter option, it says the following

# Cos[# Pi]&    ramp filter multiplied by cosine function

And I am not sure why they added 'Pi' in the above. I thought someone here might have a guess of an idea. Documentation is very sparse for this function.

I've seen this sometimes done in the definition of sinc(z), since some define sinc(z) as sin(Pi z)/(Pi z) and some define it as sinc(z) = sin(z)/z.

It is because (from the documentation):

InverseRadon takes a option that specifies a frequency filter to be applied before computing the back projection. The domain of the filter is scaled to be 0 to 1.