[Insight-users] different spacing

[Luis Ibanez]

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
> 
>  
> 
> 
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