[Insight-users] Re: DRR generation problem

[Luis Ibanez]

Hi Jian,


Thanks for reporting the difficulties you are facing with the
example

        Insight/Examples/Filtering/
            DigitallyReconstructedRadiograph1.cxx


It seems that the source of the confusion is that the program is
using the default coordinate system. That is, the focal point is
by default, aligned with the origin.


When you don't provide an input image to this example, it creates
a default synthetic image that contains the brigth edges of a cube.


See lines:   316-402.


This default image has the following characteristics:


      Size in pixels =    61,  61,  61

      Pixel size     =   3.0, 3.0, 3.0

      Origin         =   0.0, 0.0, 0.0


So, by default, the projection will of course be off centered
because the line of sight of the projection is aligned with
on of the edges of the image, not crossing through its center.


If you want the projection to be centered with respect to the
image, then you should simply use the option "-t", with a
translation that is equal to half the physical extent of the
image (and negative).


In this case, the extent is

          (3*61, 3*61, 3*61) = ( 181, 181, 181 ) mm


Therefore,

         if you put translations of   "-t -90,-90,-90"

      then you will get a centered projection of the cube.


More specifically,


            Please use the following command line:


   DigitallyReconstructedRadiograph1 -t -90 -90 -90 -o CubeDRR.img



This will give you a centered projection.


for an example using a real image, you could also try:



   DigitallyReconstructedRadiograph1 -t -90 -109 -90
                         -o brain.img  brainweb165a10f17.mhd



(in a single line)

The brainweb image can be downloaded from the Data page of www.itk.org:

             http://www.itk.org/HTML/Data.htm
             ftp://public.kitware.com/pub/itk/Data/BrainWeb





   Please let us know if you have further questions,


      Thanks


         Luis



-------------
Jian Wu wrote:
> Hi Luis,
> I'm wondering if you have paid attention to the email I sent to you on 
> Dec 29, 2005. I'm sending you the mail again and hope you could help. 
> Thanks!
> Jian Wu
> 
> Hi Luis,
> 
> Thanks for your work. But the problem is still there. Please try to use the
> following parameters for the test.
> 
> DigitallyReconstructedRadiograph1 -res 2 2 -o CubeDRR.img
> 
> The output image was not centered. Moreover, it appears the ray that passes
> through the origin of the 3D image is not normal to the 2D image plane.
> Please check it out.
> 
> By the way, I have a suggestion. In medical application, the projection
> geometry is usually specified by a source-to-image distance (sid) and a
> source-to-object ditance (sod), i.e., the distance from the source to the
> origin of the 3D volume. It would be more practical if those two parameters
> were used in the code instead of using a focal length and positioning 
> the 3D
> volume half way between the source and the screen.
> 
> Jian Wu
> 
>> From: Luis Ibanez <luis.ibanez at kitware.com>
>> To: Jian Wu <eewujian at hotmail.com>
>> CC: insight-users at itk.org, samant at ufl.edu, mmhuang at 
>> ufl.edu,        xiajunyi at hotmail.com, john.hipwell at kcl.ac.uk, 
>> thomas at hartkens.de
>> Subject: Re: [Insight-users] Problem with DRR generation
>> Date: Thu, 29 Dec 2005 08:27:41 -0500
>>
>>
>> Hi Jian,
>>
>> Looking at the Code of the DigitallyReconstructedRadiograph1.cxx
>> it seems that it is missing to take the image origin into account.
>>
>>
>> If your image has an origin different than zero, the computation
>> of the image center will be incorrect.
>>
>>
>> We just committed a fix for this issue to the CVS repository.
>> You may want to update your CVS checkout (if you have one)
>> or you can apply the same corrections to your local code.
>>
>>
>> The modifications can be found at:
>> http://www.itk.org/cgi-bin/viewcvs.cgi/Examples/Filtering/DigitallyReconstructedRadiograph1.cxx?root=Insight&sortby=date&r2=1.15&r1=1.14 
>>
>>
>>
>>
>>   Please let us know if you find any problems,
>>
>>
>>
>>      Thanks
>>
>>
>>         Luis
>>
>>
>>
>> ---------------
>> Jian Wu wrote:
>>
>>> Dear ITK users:
>>>
>>> I'm wondering if anyone have generated correction DRRs using the 
>>> example programs GenerateProjection.cxx or 
>>> DigitallyReconstructedRadiograph1.cxx.
>>>
>>> I ran both codes using the parameters and the image given in the 
>>> README.txt file. But the generated DRRs appear to have a different 
>>> projection and image center than I expected.
>>> I also tried to simply the test data in 
>>> DigitallyReconstructedRadiograph1.cxx. Instead of using the orignal 
>>> cubic structure, I constructed a 61x61x61 3D image with a single 
>>> point at the center of the image. The resulting DRR has a point 
>>> centered at pixel index (81, 81). The DRR has the size of 501x501, 
>>> and the point is supposed to be at the center of the image. I can't 
>>> figure out how the projection works. I really wish the projection 
>>> geometry were better documented.
>>>
>>> When real CT data sets were used, the objects in the output DRRs 
>>> appear to have been shifted toward the left-bottom corner of the 
>>> images. I searched the emails that have been posted before. It 
>>> appears someone has pointed out the problem before. However, I did 
>>> not find any answers to the question. By the way, the 
>>> IntensityBased2D3DRegistration.cxx example code does not work. I have 
>>> posted the problem a couple of days ago.
>>>
>>> Someone help me out please!
>>>
>>> Jian Wu
>>>
>>>
>>> _______________________________________________
>>> Insight-users mailing list
>>> Insight-users at itk.org
>>> http://www.itk.org/mailman/listinfo/insight-users
>>>
>>>
> 
> 
> 
>