[Insight-users] Problem about LevelSetMotionRegistrationFunct ion

[Miller, James V (Research)]

Siwei,
 
The LevelSetMotionRegistrationFunction calculates the speed value as
 
  double speedValue = fixedValue - movingValue;

where
 
  fixedValue = (double) m_FixedImage->GetPixel( index );

and 
 
  movingValue = m_MovingImageInterpolator->Evaluate( mappedPoint );

where mappedPoint is calculated as
 
  for( j = 0; j < ImageDimension; j++ )
    {
    mappedPoint[j] = double( index[j] ) * m_FixedImageSpacing[j] + 
      m_FixedImageOrigin[j];
    mappedPoint[j] += it.GetCenterPixel()[j];
    }

 
In the above loop, index[] is the index of the pixel under consideration in
the fixed image.  By multiplying by the spacing and adding the origin, the
index[] is converted to a physical position in the fixed image.  By adding
it.GetCenterPixel(), we are adding the current displacement field value to
the position, i.e. (u,v). So we evaluate the moving image at a position that
takes into account the current displacement field.
 
So the speed value is calculated as I1(i,j) - I2(i-u, j-v)
 
Does this clarify the code?
 
Jim
 
 
 
 

-----Original Message-----
From: Siwei Yang [mailto:s.yang at dkfz-heidelberg.de]
Sent: Friday, November 19, 2004 10:48 AM
To: insight-users at itk.org
Subject: [Insight-users] Problem about LevelSetMotionRegistrationFunction


Hello all, 
I want to use the Levelsetmotionregistrationfilter, but in the ComputeUpdate
(LevelsetmotionregistrationFunction) I fand something doesn't seems to be
comprehensible.  According to equation 27 in the paper of (B.C. Vemuri, J.
Ye, Y. Chen, C.M. Leonard. "Image registration via level-set motion:
applications to atlas-based segmentation". Medical Image Analysis. Vol. 7.
pp. 1-20. 2003.), the speed term should be     I2(ij) -I1(i-u.., j-v..)
instead of  I2(ij)-I1(ij), which is in the implementation.    I' m not sure,
if what I say is correct . Perhaps some one can give me a good answer. 

Thanks 
best wishes 

Siwei Yang 

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