[Insight-users] different spacing

[Grace Chen]

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
> >
> >
> >
> >
> > ------------------------------------------------------------------------
> >
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