[ITK-users] 3D registration problem

[Iyas Hamdan]

Hello,
and thanks again for your reply Brad,

I haven't actually give it a look yet, but I think it won't help in my case
since I'm working with images from different modalities. I mean I know that
the joint histogram should be concentrated in the diagnoal but isn't that
the case only when we're working with images from the same modalities ?

or should it work as well in my case ?

regards,

Iyas



On Wed, Jul 16, 2014 at 4:03 PM, Bradley Lowekamp <blowekamp at mail.nih.gov>
wrote:

> Have you looked at the histograms of the two image with the parameters
> provided to the metric?
>
> Perhaps this example will be of use:
>
> http://www.itk.org/Doxygen/html/RegistrationITKv3_2ImageRegistrationHistogramPlotter_8cxx-example.html
>
> Brad
>
> On Jul 16, 2014, at 9:52 AM, Iyas Hamdan <iyas.hamdan at gmail.com> wrote:
>
> 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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