[Insight-users] Inconsistent registration result.

Seth Gilchrist seth at mech.ubc.ca
Mon Mar 11 13:52:46 EDT 2013 

Hi Lien,
Could you use create a sub class of the MattesMetric and define a new
function GetFixedImageIndexes() to give you the indexes? You could then use
SetFixedImageIndexes( <your index list> ) and that would
prevent re-sampling. Maybe put in a request to have GetFixedImgeIndexes()
added at some point.

Seth


On Mon, Mar 11, 2013 at 10:29 AM, lien lee <lienlee at gmail.com> wrote:

>  Hi Bradley,
>
>  Sorry for the late response.
>
>  Just now, I tried what you have suggested, and I do see consistent
> results among different runs on the two computers I have. So, the problem
> should be that it is not thread safe when applying the two masks. I am
> wondering what I should do next, since the single-threaded program runs
> slowly. Is there any solution that I can use faster multi-threading
> technique and still keep the results consistent? Does ITK v4 do a better
> job in this regards?
>
>  BTW, another trial was done before I set ITK_GLOBAL_DEFAULT_NUMBER_OF_THREADS
> to 1.
> I called vMetric->SetNumberOfThreads(1), and I noticed that most of the
> time only one thread was working through starring at the CPU usage in
> Windows Task Manager.  But still, the results were inconsistent in
> different runs. I could not explain this. I mention it just because it
> might mean something to itk-developers.
>
> Thanks!
>
>
> 2013/3/1 Bradley Lowekamp <blowekamp at mail.nih.gov>
>
>> Hello,
>>
>>  How many threads are you running? Have you tried setting the
>> environment variable ITK_GLOBAL_DEFAULT_NUMBER_OF_THREADS to 1, to see of
>> the results then become consistent?
>>
>>  Brad
>>
>>   On Feb 28, 2013, at 5:52 PM, lien lee <lienlee at gmail.com> wrote:
>>
>>   Hi itk-users,
>>
>>  I took a further step today.  I derived a class
>> from MattesMutualInformationImageToImageMetric, and made it being the
>> metric, so that, I could sneak into itk and visit the protected
>> member ImageToImageMetric< TFixedImage, TMovingImage
>> >::m_FixedImageSamples. I printed out a couple of sample points (their
>> coordinates and image values), and I also printed out the seed value of the
>> random number generator, which I set as ReinitializeSeed(76926294).  I get
>> the seed value by
>> calling Statistics::MersenneTwisterRandomVariateGenerator::GetInstance()->GetSeed();
>> In different runs, I do see same seed were used, but I also do see
>> different sample points.  I tried this on two different computers, at both
>> of which I saw the inconsistent results. Seems to be the random number
>> generator is non-deterministic even with same seed.  However, the weird
>> thing is if I do not use the image mask, it would be consistent.
>>
>>  Any thoughts?
>>
>>
>> 2013/2/26 lien lee <lienlee at gmail.com>
>>
>>> Hi Seth,
>>>
>>>  By clicking the link you provided, the code I saw there is as partly
>>> attached, which is different from what I have with ITK 4.2 on my computer.
>>>
>>>  I do not have experience with this code, and I am not exactly sure how
>>> it works.  But, looks to me, optimizer would call the function during each
>>> iteration, and the function would rebuild all the sample points again and
>>> again for all the iterations.  If my understanding were correct, this would
>>> be quite different from what I have with ITK 4.2 on my computer, where all
>>> the samples were created
>>> in MattesMutualInformationImageToImageMetric::Initialize() as *a one
>>> time thing*, and the counted points would be determined for each
>>> iteration using the current transform by checking whether the mapped points
>>> were inside the moving image mask. Therefore, for the code I am working on,
>>> to my understanding, if I called ReinitializeSeed(76926294) before
>>> generating all the sample points
>>> in MattesMutualInformationImageToImageMetric::Initialize(), the results
>>> should be deterministic, no matter whether I applied the image masks or
>>> not. But, the testing results with image mask applied does NOT support my
>>> understanding.
>>>
>>>  BTW, to your question, my moving image mask may not be "restrictive"
>>> because it occupied pretty much about 80% of the whole moving image.
>>>
>>>  Thanks again for your inputs.
>>>
>>>
>>>    106<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l106>template <class TFixedImage,
>>> class TMovingImage>
>>> 107<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l107>void
>>> 108<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l108>MutualInformationImageToImageMetric<TFixedImage, TMovingImage>
>>> 109<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l109>::SampleFixedImageDomain(
>>> 110<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l110>  SpatialSampleContainer & samples) const
>>> 111<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l111>{
>>> 112<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l112>  typedef ImageRandomConstIteratorWithIndex<FixedImageType> RandomIterator;
>>> 113<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l113>  RandomIterator randIter( this->m_FixedImage, this->GetFixedImageRegion() );
>>> 114<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l114>
>>> 115<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l115>  randIter.SetNumberOfSamples(m_NumberOfSpatialSamples);
>>> 116<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l116>  randIter.GoToBegin();
>>> 117<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l117>
>>> 118<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l118>  typename SpatialSampleContainer::iterator iter;
>>> 119<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l119>  typename SpatialSampleContainer::const_iterator end = samples.end();
>>> 120<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l120>
>>> 121<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l121>  bool allOutside = true;
>>> 122<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l122>
>>> 123<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l123>  this->m_NumberOfPixelsCounted = 0;    // Number of pixels that map into the
>>> 124<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l124>                                        // fixed and moving image mask, if
>>> 125<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l125>                                        // specified
>>> 126<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l126>                                        // and the resampled fixed grid after
>>> 127<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l127>                                        // transformation.
>>> 128<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l128>
>>> 129<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l129>  // Number of random picks made from the portion of fixed image within the
>>> 130<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l130>  // fixed mask
>>> 131<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l131>  SizeValueType numberOfFixedImagePixelsVisited = 0;
>>> 132<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l132>  SizeValueType dryRunTolerance = this->GetFixedImageRegion().GetNumberOfPixels();
>>> 133<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l133>  for( iter = samples.begin(); iter != end; ++iter )
>>> 134<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l134>    {
>>> 135<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l135>    // Get sampled index
>>> 136<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l136>    FixedImageIndexType index = randIter.GetIndex();
>>> 137<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l137>    // Get sampled fixed image value
>>> 138<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l138>    ( *iter ).FixedImageValue = randIter.Get();
>>> 139<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l139>    // Translate index to point
>>> 140<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l140>    this->m_FixedImage->TransformIndexToPhysicalPoint(index,
>>> 141<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l141>                                                      ( *iter ).FixedImagePointValue);
>>> 142<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l142>
>>> 143<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l143>    // If not inside the fixed mask, ignore the point
>>> 144<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l144>    if( this->m_FixedImageMask
>>> 145<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l145>        && !this->m_FixedImageMask->IsInside( ( *iter ).FixedImagePointValue ) )
>>> 146<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l146>      {
>>> 147<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l147>      ++randIter; // jump to another random position
>>> 148<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l148>      continue;
>>> 149<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l149>      }
>>> 150<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l150>
>>> 151<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l151>    if( allOutside )
>>> 152<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l152>      {
>>> 153<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l153>      ++numberOfFixedImagePixelsVisited;
>>> 154<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l154>      if( numberOfFixedImagePixelsVisited > dryRunTolerance )
>>> 155<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l155>        {
>>> 156<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l156>        // We randomly visited as many points as is the size of the fixed image
>>> 157<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l157>        // region.. Too may samples mapped ouside.. go change your transform
>>> 158<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l158>        itkExceptionMacro(<< "Too many samples mapped outside the moving buffer");
>>> 159<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l159>        }
>>> 160<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l160>      }
>>> 161<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l161>
>>> 162<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l162>    MovingImagePointType mappedPoint =
>>> 163<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l163>      this->m_Transform->TransformPoint( ( *iter ).FixedImagePointValue );
>>> 164<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l164>
>>> 165<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l165>    // If the transformed point after transformation does not lie within the
>>> 166<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l166>    // MovingImageMask, skip it.
>>> 167<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l167>    if( this->m_MovingImageMask
>>> 168<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l168>        && !this->m_MovingImageMask->IsInside(mappedPoint) )
>>> 169<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l169>      {
>>> 170<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l170>      ++randIter;
>>> 171<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l171>      continue;
>>> 172<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l172>      }
>>> 173<http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l173>
>>> <http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD#l174>
>>>
>>>  2013/2/26 Seth Gilchrist <seth at mech.ubc.ca>
>>>
>>>> Hi Lien,
>>>> Unfortunately I have not used masks when performing registrations, so
>>>> can't help you with this specific problem.
>>>>
>>>>  I took a look at the git blob for the MattesMutual...Metric and was
>>>> examining how the decision to keep or reject a give point is handled. If
>>>> you are setting a mask on both the fixed and moving images, this will
>>>> change what points are used because a check is done to see if a point is in
>>>> the fixed mask and if it is in the moving mask after applying the current
>>>> transform. Could your moving image mask be too restrictive for the early
>>>> stages of the registration?
>>>>
>>>>  You can read the code at:
>>>>
>>>> http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Registration/Common/include/itkMutualInformationImageToImageMetric.hxx;h=1244e5c0be768696cf042f6f39739f4b2bdcbba6;hb=HEAD
>>>>
>>>>  Starting on line 108, specifically on line 162.
>>>>
>>>>  Cheers,
>>>> Seth
>>>>
>>>> *Seth Gilchrist, MASc, PhD Candidate
>>>> +---------------------------------------+
>>>> Orthopaedic and Injury Biomechanics Group
>>>> UBC Department of Mechanical Engineering
>>>> 6th Floor-2635 Laurel Street
>>>> Vancouver, BC V5Z-1M9
>>>> +---------------------------------------+
>>>> seth at mech.ubc.ca
>>>> Fax 604-675-2576*
>>>>
>>>>
>>>
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