[Rtk-users] Preprocessing

[Simon Rit]

Hi,
For scatter and assuming you have the planning CT, you could consider
the solution
of Yang et al <http://www.openrtk.org/RTK/news/201507_press.php> (that he
implemented from Niu et al) that is much simpler than Monte Carlo. I know
two teams that have already implemented it using RTK and we will try to do
our own in the future.
For photon statistics, Cyril has recently been working on a weighted least
square solution, see, e.g., this commit
<https://github.com/SimonRit/RTK/commit/b133c0bb96bff6805dd28c7820a89310629ff031>.
But I don't think it's mature yet.
Note that we discussed pre-processing in July in Lyon, the minutes are here
<http://wiki.openrtk.org/index.php/RTK/Meetings/TrainingNov15#Pre-processing>
.
Good luck, it's not an easy task,
Simon

On Tue, Dec 1, 2015 at 9:50 AM, Jonathan Mason <s1015431 at staffmail.ed.ac.uk>
wrote:

> Thank you Simon and Chao,
>
> I apologise for the confusion—I can see that my message was not very
> clear. I am essentially trying to compensate for low photon flux and
> scatter, but am finding it difficult with pre corrected data. I will
> certainly take time to look through your suggested publications, so thanks
> for that.
>
> Without having access to low level physical data, I am considering
> simulating a scanner with MC, where I will have the ground truth for
> scatter field and photon statistics, and try to produce reconstructions on
> this.
>
> Many thanks,
>
> Jonathan
>
> On 1 Dec 2015, at 07:27, Simon Rit <simon.rit at creatis.insa-lyon.fr> wrote:
>
> 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.
>>>
>>> _______________________________________________
>>> Rtk-users mailing list
>>> Rtk-users at public.kitware.com
>>> http://public.kitware.com/mailman/listinfo/rtk-users
>>>
>>
>>
>> _______________________________________________
>> Rtk-users mailing list
>> Rtk-users at public.kitware.com
>> http://public.kitware.com/mailman/listinfo/rtk-users
>>
>>
>
>
> The University of Edinburgh is a charitable body, registered in
> Scotland, with registration number SC005336.
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/rtk-users/attachments/20151201/d328b3f3/attachment-0010.html>