[ITK-users] 3D registration problem

[Iyas Hamdan]

Hello,

Thanks for your reply!

It's true I haven't shared alot of information about the methode I'm using
sorry about that.

My code is based on the example "ImageRegistration20.cxx" with some
modifications;

So I'm basically using a 3D Affine registration with Mattes mutual
information being the metric and the regular step gradient descent as the
optimizer and finally a linear interpolator.

For the initialization, its good and there's no problem here.

But for the result, concerning the registered volume, the scale is good as
well but the problem is that the its not aligned with the fixed volume.

And for the parameters, I have only a few ones for the metric ( number of
histogram bins and spatial samples ) and I dont think they would have that
much of effect on the output, but I tried to change them and I ended up
always with almost the same result.
And for the optimizer, same as before I tried so many values for the
relaxation factor and the max/min step lengths as well.

So the problem is not the scale nor the parameters but the registration
itself; since it can't find, for each slice of the fixed volume, the slice
in the moving volume that corresponds the maximum. So on the output I have
a volume that has the same scale as the fixed one but they are not aligned
and have no mutual information between them I would say. Even though I
tried to change the initialization to prevent the local minimas and I'm
starting now with a good initialization but still the same result.


And what I found wierd is that when I deleted few slices from the end of
the moving volume, the registration worked perfectly and I had good results!



Hope this was clear and these information was enough, and please let me
know if you have any other suggestions or advices.

Thanks in advance,

Iyas


On Wed, Jul 16, 2014 at 3:17 PM, Bradley Lowekamp <blowekamp at mail.nih.gov>
wrote:

> Hello,
>
> This not the expected behavior for a good registration program.
>
> Is your initialization good?
>
> You haven't shared anything about the registration components you are
> using. Perhaps you scales are way off? How does the convergence look when
> monitoring the output?
>
> Perhaps you have too many free parameters? Maybe you are trying to
> optimize an transform with too many parameters when you are not close.
> Perhaps you need to do a Translation + Rotation transform such as Euler or
> Versor first?
>
> Hope that helps,
> Brad
>
> On Jul 15, 2014, at 5:26 AM, Iyas Hamdan <iyas.hamdan at gmail.com> wrote:
>
> > Hello itk users,
> >
> > I'm working on 3D image registration, currently I'm trying to register a
> CT volume to an MRI volume ( the two volumes have different sizes
> concerning the number of slices used to construct the 3D volume).
> >
> > I'm doing an affine registration using the mutual information as a
> metric, and I'm having problems registering those two volumes.
> >
> > What I thiink the problem is, I have a different field of view between
> both volumes, so when I try to register the whole CT volume to the MRI one
>  the registration falis. However, when I deleted a dozen of slices from the
> CT volume ( so that I had the same field of view in both volumes) it works
> just fine and I was able to register the volumes.
> >
> >
> > And by "the registration failed" I meant it worked with no errors but
> the result was really bad! and that the registered volume was nothing like
> the fixed one, so if I try to find the difference between each two
> corresponding slices for example , they were not aligned at all!
> >
> > Is that normal that the registration doesnt work when I have a different
> field of view in each volume ? or should it deform one volume so that it
> corresponds to the other one even if they had two different fields of view ?
> >
> > Any help would be really appreciated,
> >
> > Thanks in advance,
> >
> > Iyas
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