[Rtk-users] trouble projecting phantom

[Simon Rit]

Hi,
I have pushed a fix so it should work now, but be aware that putting your
source in the volume has no sense with FDK because the weighted
backprojection in the algorithm consists in dividing by the distance to the
source. So it implies a division by 0.
Simon

On Fri, Mar 1, 2013 at 8:52 AM, Simon Rit <simon.rit at creatis.insa-lyon.fr>wrote:

> The size of your image is determined by origin, number of pixels
> (dimension in command line tools or size in itk) and spacing. From this
> information, you can check if the source to isocenter (point 0,0,0)
> distance puts the source in or out of the volume.
> I will try to correct this bug asap possible,
> Simon
>
>
> On Wed, Feb 27, 2013 at 6:45 AM, M Miller <croow at yahoo.com> wrote:
>
>> Scaling the phantom worked perfectly.
>> You mentioned that a reconstruction will need to specify the source
>> outside of the volume. How can I specify that? What parameters would you
>> pass to rtkfdk.exe to reconstruct the phantom?
>>
>> Thanks
>> Micah
>>
>> --- On *Tue, 2/26/13, Simon Rit <simon.rit at creatis.insa-lyon.fr>* wrote:
>>
>>
>> From: Simon Rit <simon.rit at creatis.insa-lyon.fr>
>> Subject: Re: [Rtk-users] trouble projecting phantom
>> To: "M Miller" <croow at yahoo.com>
>> Cc: rtk-users at openrtk.org
>> Date: Tuesday, February 26, 2013, 12:36 AM
>>
>>
>> Hi Micah,
>> I have given it a try and I think I obtain the expected result if you use
>> the SheppLogan file that we provide here
>> http://midas3.kitware.com/midas/download?items=27326
>> However, the result might surprise you because your source is in the
>> phantom (sid=65.93 vs largest ellipsoid which is A=88.32 B=115.2 C=117.76).
>> You can scale the shepp logan phantom using the following command
>> rtkprojectshepploganphantom -g geo.xml -o proj.mha --spacing 1
>> --dimension 1024 --phantomscale 10
>> You will then obtain more meaningful results, i.e., the full phantom will
>> be in the beam.
>> Note by the way that if you use rtkfdk afterwards, you will have to be
>> careful to have the source outside the volume as well. I have recently
>> noticed that there was a bug when the source was in the volume, I will fix
>> it as soon as possible.
>> Simon
>>
>> On Tue, Feb 26, 2013 at 2:23 AM, M Miller <croow at yahoo.com<http://us.mc1638.mail.yahoo.com/mc/compose?to=croow@yahoo.com>
>> > wrote:
>>
>>   I've been unable to project a phantom, or anything else, at high
>> magnification. Here's the steps I've think should work, but don't.
>>
>> "rtksimulatedgeometry.exe --output=geo.xml --nproj=1600 --arc=360
>> --sdd=870.86 --sid=65.93"
>>
>> These are the values from my actual CT system. Next I try using
>> rtkprojectgeometricphantom to create some projections.
>>
>> "rtkprojectgeometricphantom -g geo.xml -o projs\projections1024.mha
>> --spacing 1 --dimension 1024 --phantomfile
>> SheppLogan.txt"
>>
>> Inspecting the output projections shows they're mostly unrecognizable.
>> Repeating these steps with a higher SID does produce the expected phantom
>> projections. I've had no luck using real data, so I thought I'd try a
>> simple phantom, but it's turned out to be not so simple.
>>
>> Is RTK limited somehow with respect to magnification, or are my
>> expectations unrealsitic? Am I missing a command-line switch?
>>
>> Thanks
>> Micah
>>
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>>
>>
>>
>
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