[Insight-users] Anisotropic image

[Luis Ibanez]

Hi Camilo,

The resampling process will necessarily change the image size.

Please note that "image size" is an ambiguous term here.

You seem to be concerned by the "image size" as measured in
pixels.

There is also an "image size" measured in millimeters, which
in medical image is the size that really matters, simply because
tumors, lungs, hearts and people come in millimeters and not in
pixels  :-)


The size that this example is preserving is the "physical" size
of the image. Therefore, if the original image was of size (in pixels)

                  512 x 512 x 20  pixels

and let's say spacing:  0.5 x 0.5 x 2 mm

the physical extent of the image was:

                  256mm x 256mm x 40mm

If you resample it to an isotropic spacing of 1.5mm, the physical
extent should be preserved. Otherwise you will be missing
anatomical pieces from the image, (something that doctors and
patients tend not to like...)

Your output image should then still be of physical extent:

                 256mm x 256mm x 40mm


and therefore the number of pixels must be


             170 pixelx 170 pixels x 27 pixels


In medical imaging, iIt is very helpful to measure everything
in physical units (millimeters, centimeters, microns...) and
to keep in mind that the image is simply a digital sampling
of a physical reality.



     Regards,


        Luis



-----------------
Camilo Diaz wrote:
> 
> Hello Luis:
> 
> Well, actually, it happened that the output is an image with diferent 
> size of the original one.
> the original is 512x512x20  and after the isotropic process 112x 
> .....x112 ( well, i dont really remember the size , but it was a lot 
> diferent). Besides that, the voxel size became 2.05x2.05x2.05  that is 
> not bad, but i was expecting a 1mm size.
>  
> I hope you can help me with that.
> 
> Camilo
> 
> 
> On Wed, Feb 4, 2009 at 9:27 AM, Luis Ibanez <luis.ibanez at kitware.com 
> <mailto:luis.ibanez at kitware.com>> wrote:
> 
> 
>     Hi Camilo,
> 
>      What's wrong the with output of
>      the ResampleToVolumenIsotropic.cxx example ?
> 
> 
>      Please let us know,
> 
> 
>          Thanks
> 
> 
>             Luis
> 
> 
>     -----------------
>     Camilo Diaz wrote:
> 
>         Hello List:
> 
>         I was wondering if anyone has a way to transform an anisotropic
>         image to isotropic besides the itk example on
>         ResampleToVolumenIsotropic.cxx ??
> 
>         Camilo
> 
>         -- 
>         Kmilo
> 
> 
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> 
> 
> 
> -- 
> Kmilo