[Rtk-users] About Kaiser-Bessel Filter

[Simon Rit]

Hi,
About your other question, there is no plan to add Kaiser-Bessel basis
functions that I'm aware of. But I would strongly encourage you to give it
a try!
Good luck with your project,
Simon

On Tue, Nov 18, 2014 at 5:09 PM, Chao Wu <wuchao04 at gmail.com> wrote:

> Hi Guangming,
>
> To reconstruct a volume from a series of tiff files you have to let the
> algorithm know the geometrical relationship among the source, the volume
> and the projections stored in the tiffs. The idea is the same: RTK uses
> projection matrices and image coordinates to understand the positioning of
> those projections. The projection matrices are based on a lot of
> geometrical parameters like gantry angle, source position, detector
> position, in-plane and out-of-plane rotation angles of the detector etc. I
> won't go though all since most of them have no differences if you use tiff
> files or whatever format as input. I focus on some tiff tips.
>
> In the simplest situation, the tiff files contain correct resolution (DPI)
> information, then you need to do nothing on these files. You have to
> specify the correct detector offset though, since in the tiff image
> coordinates the origin is the first pixel (corner pixel) which is
> apparently not the intersection of the central ray and the detector. The
> detector offsets in x and y actually mean the position of the image origin
> (the first pixel) in the coordinate system centred at the intersection.
> Since the direction cosines is an identity matrix and pixel sizes are
> positive, the detector offsets in x and y will be negative.
>
> If the resolution information of the tiff files is not correct, you have
> to rewrite this information. You can of course perform a pre-processing to
> change the DPI of all tiff files with a third-party software, or you can
> alter the RTK code to allow such changes after reading the images, by using
> a itk::ChangeInformationImageFilter filter.
>
> Another non-geometrical issue with tiff files is that when their integer
> pixel values are converted into attenuation, the maximum possible integer
> is used as the reference value. This may not be correct in practice, e.g.
> in your 16-bit tiffs you use 62000 to represent air (no attenuation)
> leaving the integer range from 62001 to 65535 for statistical fluctuation.
> If for instance you only use the lower 14 bits for your data then this
> problem is more severe. For sure you can correct this by changing the code
> and specify the correct reference value.
>
> Hope these can help.
>
> Regards,
> Chao
>
> 2014-11-18 15:09 GMT+01:00 Guangming Zang <guangming.zang at kaust.edu.sa>:
>
>> Thanks
>>
>> *Guangming Zang (Alex)*
>> *King Abdullah University of Science and Technology(KAUST)*
>> *University of Chinese Academy of Sciences(UCAS)*
>>
>>
>> 2014-11-18 16:46 GMT+03:00 Guangming Zang <guangming.zang at kaust.edu.sa>:
>>
>>> Hi,
>>> I am using the sart reconstruction in RTK, it works well.Thanks for your
>>> great work.
>>> and i was wondering do you have any plan to add other filters except
>>> Joseph, such as Kaiser-Bessel???  ( described here
>>> http://wscg.zcu.cz/wscg2003/papers_2003/herman.pdf)
>>> BTW, i have read the messages sent by other users(
>>> http://public.kitware.com/pipermail/rtk-users/2014-October/000573.html)
>>> but i still can not make it. can u help me and explain again about using
>>> a series of .tiff images ans sart algorithms to get the volume.
>>> Thanks in advance
>>> Best
>>> *King Abdullah University of Science and Technology(KAUST)*
>>> *University of Chinese Academy of Sciences(UCAS)*
>>>
>>>
>>
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