[Insight-users] different spacing

[Luis Ibanez]

Hi Grace,


  *  Did your registration converged ?


  *  Could you please post the output of the Command/Observer
     class that you connected to the optimizer ?


  *  Why is that you end up with a vtkTransform
     if you are doing registration with ITK ?



Please let us know,


   Thanks


      Luis



-----------------
Grace Chen wrote:
> Hi Luis,
> 
> Thanx for the reply.  I know the registration should have been done in the
> physical space.  Even if the viewer I use is a naive viewer, after I apply
> the registration transform and then I scale the image, both images (now look
> approximiatly of the same size) should look aligned too, am I correct?  But
> that's not the case for me.
> 
> By looking at the result of the registration, I notice that the translation
> is ( 1.3884, -3.48145, 2.08022) which is not the movement I simulated i.e.
> through the call transform->Translate(5, -25, 0).<'transform' is a
> vtkTransform.>
> 
> Grace
> 
> ----- Original Message ----- 
> From: "Luis Ibanez" <luis.ibanez at kitware.com>
> To: "Grace Chen" <Grace.Chen at swri.ca>
> Cc: <insight-users at itk.org>
> Sent: Wednesday, December 28, 2005 1:32 PM
> Subject: Re: [Insight-users] different spacing
> 
> 
> 
>>Hi Grace,
>>
>>Please read with more attention the "Image Registration" Chapter
>>of the ITK Software Guide.
>>
>>
>>If the two images are taken from the same patient and the image
>>spacings are set correctly by the scanner, you *should not need*
>>to do *any scaling* when registering the images.
>>
>>
>>The fact that the images look of different sizes in your screen
>>just shows that you are using a poor image viewer.
>>
>>
>>You are probably comparing the images based on their number of
>>pixels instead of based on their physical extent in space.
>>
>>
>>
>>Please study Figure 8.7 in pdf-page 358.
>>
>>
>>The Transfrom that ITK compute is the one that maps the *physical*
>>space of one image into the *physical* space of the other image.
>>
>>
>>In that context, if the patient is the same, you shouldn't need
>>any scaling unless the head of the patient if physically shrinking
>>or expanding between the time of acquiring both scans. (hopefully
>>that doesn't happen in any hospital).
>>
>>
>>The transformations from the discrete image grid and the physical
>>space are done using the origin and spacing. (Transform T1 and T2
>>in Figure 8.7).
>>
>>
>>The transform that ITK computes for you is the "Space Transform".
>>
>>Please read Section 8.3, from the ITK Software Guide
>>
>>
>>and also read the Tutorial
>>
>>http://wiki.na-mic.org/Wiki/images/b/ba/Insight-Registration.ppt
>>
>>
>>
>>    Regards,
>>
>>
>>      Luis
>>
>>
>>
>>------------------
>>Grace Chen wrote:
>>
>>>Hi there,
>>>
>>>I am trying to perform multi-modality registration for two volumes.  The
>>>two image data have different physical attributes, etc.
>>>different origin, spacing and dimension (so, on the screen, one looks
>>>bigger than the other).  I simulated a movement (e.g. a translation (5,
>>>-25, 0) in the fixed image.  However, when the registration program
>>>returns, the final transform matrix is
>>>
>>>
>>> 0.999951     0.00912699   -0.00371374     1.3884
>>>
>>>-0.0091721   0.999882       -0.0123175       -3.48145
>>>
>>>0.00360089  0.0123509      0.999917         2.08022
>>>
>>>0                   0                     0                      1
>>>
>>>This result is wrong, isn't it?  Does the registration program scale the
>>>images before aligning them?  What's going on?
>>>
>>>Thanx!
>>>
>>>Grace
>>>
>>>
>>>
>>>
>>>------------------------------------------------------------------------
>>>
>>>_______________________________________________
>>>Insight-users mailing list
>>>Insight-users at itk.org
>>>http://www.itk.org/mailman/listinfo/insight-users
>>
> 
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