[Rtk-users] Realistic Image Quality?

[Chao Wu]

Hi Solomon,

The magnification is about 1.8. Given that the voxel spacing of your volume
is 0.4688x0.4688x0.6, the corresponding projection spacing is roughly
0.84x1.08. Therefore 0.3 or 0.75 pixel spacing of your detector would not
give much difference. There were just interpolation instead of real
additional information that were introduced by 0.3 spacing.
If you do have small structures in your object and you use a much finer
grid for your volume in the simulation, I would expect to see more
difference then.

Regards,
Chao

2016-06-29 0:09 GMT+02:00 Solomon Tang <solomoncztang at gmail.com>:

> Thanks for the feedback Chao and Simon,
>
> My geometry was using default RTK sdd/sid settings. I have now changed it
> to match the DICOM header from the original images (1085.6 SDD, 595 SID),
> but not much has qualitatively changed.
>
> How do you suggest adding photon noise? I have discovered an
> itkShotNoiseImageFilter but I'm not sure what is an acceptable scaling
> level. I'm assuming the reconstructed image should be passed through the
> filter, and not the projection.
>
>
>
> On Tue, Jun 28, 2016 at 1:34 AM, Simon Rit <simon.rit at creatis.insa-lyon.fr
> > wrote:
>
>> Hi,
>> I don't expect a drastic change, only a slight loss of spatial resolution
>> if the ray distance at the isocenter (I agree with Chao that it plays an
>> important role) is larger than the original voxel size. Maybe it's there
>> but you would need to zoom more to see it.
>> You would see a more realistic difference if you were adding photon noise
>> to your data.
>> Simon
>>
>> On Tue, Jun 28, 2016 at 9:14 AM, Chao Wu <wuchao04 at gmail.com> wrote:
>>
>>> What is the magnification factor of your geometry?
>>>
>>> 2016-06-27 23:56 GMT+02:00 Solomon Tang <solomoncztang at gmail.com>:
>>>
>>>> Hi Simon,
>>>>
>>>> I am using RTK to simulate CT acquisitions using different detector
>>>> sizes to see how this impact on image quality might change some of our
>>>> in-house metrics.
>>>>
>>>> The images I have linked to below have been created using
>>>> rtkforwardprojections with different projection spacings (0.3 isometric and
>>>> 0.75 isometric) reconstructed with rtkfdk with the same pixel spacing and
>>>> image dimensions (0.4688x0.4688x0.6 | 512x512x225). The CUDA projection
>>>> stepsize is equal to the projection spacing. The window levels between
>>>> images of their respective rows are the same.
>>>>
>>>> I am simply wondering if the differences between these images are
>>>> realistic. I would expect the image with a detector size than is more than
>>>> twice as large as the original would be drastically different when in fact
>>>> they turn out to be incredibly similar. Are the assumptions made about
>>>> projection spacing == cuda stepsize == simulated hardware detector size
>>>> incorrect?
>>>>
>>>> <http://goog_1486088111>
>>>> https://gyazo.com/e86436826f687a2db4b234699d050450
>>>>
>>>> https://gyazo.com/ca9612218f082e78ba3082950a27fa4c
>>>>
>>>> Solomon
>>>>
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>>>>
>>>>
>>>
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>>
>
>
>
>
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