[Insight-users] Unit for displacement field

[pinpress]

Hi there,

The answer is actually pretty straightforward. However, I would strongly
suggest that you can do some experiment to find out yourself. For one, you
can create a fixed and a moving image with "known" displacements and run
your registration code, and then you can see which interpretation makes more
sense. Whether the displacement is in mm or voxels unit?

You mentioned that your voxel size is 0.01. That means the two
interpretations of displacement units could differ by 100 times, or 2-order
of magnitude. To me, this is already enough to "guess" which interpretation
is correct.

Sorry not to tell you the answer directly, but I hope the above analogies
would shed insight how to approach a problem like this in the future. In
fact, I myself have been using these type of "reverse engineering" rather
often to figure out things that may appear to be obvious. 

Good luck.


Li Yufei wrote:
> 
> Hi,
> 
> I have a displacement field generated from demons deformable registration.
> It is saved in mhd file format with element spacing [0.01 0.01 0.01]. Can
> anyone tell me the unit of the vectors in the field? is it in pixels or in
> millimeters? Thanks!
> 
> Regards
> 
> Yufei
> 
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