[Rtk-users] About Kaiser-Bessel Filter

[Chao Wu]

No, at the moment I mainly work on FDK.

Regards, Chao
Sent from Samsung Galaxy Note 3
2014年11月18日 5:43 PM于 "Guangming Zang" <guangming.zang at kaust.edu.sa>写道：

> Hi Chao,
> Thanks very much for your prompt and so kind reply.
> I will recheck the process of setting carefully with your suggestions and
>  a short report may be given later.
>  BTW, do you have any plan recently to add other interpolation filter(e.g.Kaiser-Bessel
> or Trilinear)??
> Thanks for your time.
> Regards
> Guangming
>
>
>
> 2014-11-18 19:09 GMT+03:00 Chao Wu <wuchao04 at gmail.com>:
>
>> 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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>>
>
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