[Rtk-users] Online reconstruction

[Fredrik Hellman]

Thank you for your quick replies!

The rtkinlinefdk application is very interesting. I have read it and have
two observations:

1. The Parker short scan code is currently disabled in that application. I
guess the reason is that it cannot compute the overscan angle without the
full geometry, and that it has to be provided in some other way than
through the geometry object.

2. The reconstruction processing starts when there are at least 3
projections available (line 281), and it then starts with the second
projection. The reason for this (I suppose) is that the angular gaps are
computed based on adjacent projection angles, so projection angles 0 and 2
needs to be available to properly weight projection 1. Finally (line 343),
the first (0) and last (N) projection are backprojected, which I suppose is
because the angular gap between projection N and 0 should be available to
the angular gap weighting of projections 0 and N. Typically the RTK Parker
weighting puts 0 weight for first and last projection so that the very
large angular gap weighting (e.g. for half scans) for first and last
projection has no effect. (Line numbers relates to commit 4198eb3 of
https://github.com/SimonRit/RTK)

Are there any current plans or ideas on how to add support for inline
Parker weighting (and allow e.g. half scans)? If not, what is the procedure
for contributing to the RTK project with such a Parker weighting
implementation?

Best regards,
Fredrik


343
2018-02-22 15:36 GMT+01:00 Simon Rit <simon.rit at creatis.insa-lyon.fr>:

> Hi,
> Yes, you can even if you don't know the geometry in advance. The
> application rtkinlinefdk and its code rtkinlinefdk.cxx illustrates this.
> Best regards,
> Simon
>
> On Thu, Feb 22, 2018 at 2:05 PM, Chao Wu <wuchao04 at gmail.com> wrote:
>
>> Hi Fredrik, If the geometry and projection angles are known in advance, I
>> think it is possible to perform FDK online.
>> Regards, Chao
>>
>> 2018-02-22 11:11 GMT+01:00 Fredrik Hellman <fredrik.hellman at gmail.com>:
>>
>>> Hi,
>>>
>>> I am wondering if it is possible to do "online" reconstruction with RTK
>>> using FDK backprojection, i.e. that you populate the geometry object angle
>>> by angle and backproject only one or a few projections at a time with the
>>> geometry object not fully populated initially.
>>>
>>> I have seen that the backprojection can be done projection by
>>> projection, but it seems that the geometry object must be populated with
>>> all angles before starting. For example in the code for parker weighting,
>>> it seems that the overscan angle is estimated based on the actual angles in
>>> the geometry object. Also, computing the angular gap weighting done in the
>>> 2D weighting depends on adjacent angles.
>>>
>>> Best regards,
>>> Fredrik Hellman
>>>
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>>
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