[Rtk-users] Preprocessing

[Simon Rit]

Hi Jonathan,
I'm not sure I fully get it either. What I can say is that I was a postdoc
at the NKI until the end of 2009 where I was working on the Elekta
reconstruction software. The way rtk::ProjectionsReader
<http://www.openrtk.org/Doxygen/classrtk_1_1ProjectionsReader.html> works
for Elekta projections is close to what they were doing at the time, i.e.,
Boellaard scatter correction, cropping and simple log to go to a line
integral. I know they have been improving it since (with lag and scatter
corrections) but I'm not sure what's commercialized what's not. In any
case, they publish / present what they do (see publications of M. van Herk,
J-J. Sonke and L. Ploeger).
I'm not expert of Varian data but for sure, when you get pre-corrected
projections, it's hard to know what part you're correcting (uncorrected
problems or miscorrections). Instead of reverse engineering, which can be
tough because Varian does a lot of stuff on the raw data I believe (look at
the publications of J. Star-Lack), I would start from the raw data if you
can access them.
Good luck,
Simon

On Mon, Nov 30, 2015 at 7:50 PM, Chao Wu <wuchao04 at gmail.com> wrote:

> Hi Jonathan,
>
> I do not quite understand your problem.
> I think most information can be retrieved by the relationship between flux
> (I) and attenuation (u):
> I = I0 * exp (- integral(u * dL) )
> Of course there are other effects like beam hardening and scattering
> involved but this model is the basic.
>
> Regards,
> Chao
>
> 2015-11-30 17:29 GMT+01:00 Jonathan Mason <j.mason at ed.ac.uk>:
>
>> Good afternoon RTK users,
>>
>> I have access to "raw data" from a Varian OBI scanner, and have
>> experimented with RTK for performing its reconstruction. However, it is
>> not really "raw" in the sense that the coefficients are proportional to
>> the photon flux recorded at a given sensor, but is instead proportional
>> to the Hounsfield attenuation along that path. With this data, it means
>> that one can reconstruct using FDK and other iterative techniques, which
>> assume a linear model, but the connection to the underlying physics is
>> abstract.
>>
>> The problem I then have when trying to develop reconstruction
>> techniques, is that I do not know whether I am really correcting for
>> physical distortions or just correcting for Varian's preprocessing,
>> which has been finely tuned for its own FDK method.
>>
>> My question is whether anybody has dug into the steps that manufacturers
>> such as Varian or Elekta perform to arrive at these projection images?
>> And if they think that if reverse engineered, could provide a richer set
>> of information to facilitate advanced strategies.
>>
>> Best wishes,
>>
>> Jonathan Mason
>>
>> --
>> The University of Edinburgh is a charitable body, registered in
>> Scotland, with registration number SC005336.
>>
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>
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