[Rtk-users] Angular gaps

[Andy Shieh]

1. OK thank you! That makes sense.

2. Yes that did help a lot! Thank you!

Andy


2013/5/15 Simon Rit <simon.rit at creatis.insa-lyon.fr>

> Hi Andy,
> Unfortunately I'm not going to the AAPM so we'll have to continue
> communicating by email. Let us know if there are developments that would be
> of interest for RTK.
> Regarding your questions:
> 1. you can not have both a short scan and a displaced detector, otherwise
> you have missing data. The consequence of missing data is probably what you
> observe here. We could add a check to inform the user but there is
> essentially not enough information to reconstruct this.
> 2. We do weight the projections by uneven angles in the FDK algorithms.
> This is done during the 2D weighting. Follow the variable
> m_AngularWeightsAndRampFactor in rtkFDKWeightProjectionFilter.txx:
>
> https://github.com/SimonRit/RTK/blob/master/code/rtkFDKWeightProjectionFilter.txx
> I hope this helps. Cheers,
> Simon
>
>
> On Wed, May 15, 2013 at 8:15 AM, Andy Shieh <hsieandy at gmail.com> wrote:
>
>> Hi Simon,
>>
>> First of all, I regret not being able to going to ICCR, otherwise I could
>> really thank you for your work in RTK. It has really helped me a lot in my
>> research! Fortunately a few of my colleagues got a chance to talk to you
>> (Ricky and John, if you remember). Hopefully I'll see you this year in
>> AAPM!!
>>
>> So today I want to ask you about two things.
>>
>> 1. Failed reconstruction (due to maximum angular gap too big?)
>> I noticed that occasionally RTK gives reconstruction that looks like this.
>> [image: 內置圖片 1]
>> In case the picture is not sent through, the image has a big angular
>> region where the intensity is essentially zero when viewed axially. This
>> happens when I use displacement binning, and using half-fan data.
>> I summarized all my reconstructions and realize this only happens when
>> the "maximum angular gap" of the projections in that bin is greater than 20
>> degrees. Therefore I assume it's because the half-fan projection on one
>> side not being able to find its corresponding projection image on the other
>> side. I just want to check with you if that's what's happening here.
>>
>> 2. There is a paper on direct weighting of uneven angular spaced
>> projections.
>> http://link.springer.com/chapter/10.1007%2F978-3-642-33415-3_23
>> I think the idea is basically lower the weight of closely spaced
>> projections.
>> Is this already implemented in RTK?
>>
>> Thanks Simon !! :)
>>
>> Cheers,
>> Andy
>>
>> _______________________________________________
>> Rtk-users mailing list
>> Rtk-users at openrtk.org
>> http://public.kitware.com/cgi-bin/mailman/listinfo/rtk-users
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/rtk-users/attachments/20130517/408685c7/attachment-0009.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 53548 bytes
Desc: not available
URL: <http://public.kitware.com/pipermail/rtk-users/attachments/20130517/408685c7/attachment-0009.png>