[Rtk-users] RTK calculating attenuation from Varian projection

[Simon Rit]

Hi Andy,
Yes you're right, I have actually noticed recently that but I have not
worked a lot on Varian images because we don't have a Varian CBCT in
Lyon. I only had a sub-sampled acquisition from Greg of a Catphan that
I used to roughly check the geometry. As far as I can remember, when I
wrote this piece of code, I tried to use the same code as Plastimatch
but I could well have done it wrongly. I'm actually waiting for a new
complete Catphan acquisition from Greg to correct for this but if you
already have a patch to suggest or a set of images to send, feel free
to do it.
Thanks,
Simon

On Tue, Oct 23, 2012 at 2:48 PM, Andy Shieh <hsieandy at gmail.com> wrote:
> Hi Simon,
>
> I was looking at "rtkVarianObiRawImageFilter.h", and realized that the
> attenuation is calculated from the projection image simply via a negative
> transformation (1-Intensity/HND_MaxIntensity).
> Is it usually the way this is done, and is there any reason for doing this?
> I would have thought attenuation should be calculated from intensity via
> logarithm (since I=I_0 exp(-mu x)).
> Thanks!!
>
> Cheers,
> Andy
>
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