Groupwise Registration in NAMICkit

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Group-wise Registration in NAMIC-kit

• Serdar K Balci (MIT)
• Lilla Zöllei (MGH)
• Kinh Tieu (BWH)
• Mert R Sabuncu (MIT)
• Polina Golland (MIT)

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Robust Group-wise Registration

• Entropy based group-wise registration
• ITK implementation
• Empirical Evaluation

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Background Groupwise Registration

• Images Transforms
• Transforms
• Affine
• Non-rigid using B-Splines

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Registering to the Mean of the Population
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Groupwise Registration Congealing
L . Zöllei, E. Learned-Miller, E. Grimson, W.M.
Wells III. "Efficient Population Registration of
3D Data."
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Congealing Intuition

• If Gaussian

• If also
• Registering to the mean with LS metric

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Implementation

• ITK classes
• Group-wise registration using congealing
• Variance
• Entropy

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Results
Before Affine BS 4 BS 8
BS 16
Entropy
Variance
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Overlap Measures
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Full Term Babies
Before Affine
BS 4
BS 8 BS 16
BS 32
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Pre Term Babies
Before Affine BS 4
BS 8 BS 16
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Summary

• Implemented group-wise registration in ITK
• Congealing Entropy based registration
• Affine and BSpline
• Multithreaded implementation
• Bspline optimization
• Initial Evaluation
• A population of 50 subjects
• Used segmentation labels to evaluate

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Ongoing Work

• Finding optimal parameters
• B-Spline mesh size,
• of hierarchical levels
• Subsampling
• Quantitative comparison to other methods
• Pair-wise registration to the mean using MI

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Congealing with Two Images

• Using Parzen windows

• As we only have two images

• Pairwise registration using LS metric

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Groupwise Reg. using Pairwise Reg.

• If we assume that images are independent given a
  subject, representative of the population

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Registering to the mean

• We assume independence over images

• and draw i.i.d. samples from each image

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Groupwise Registration using Joint Entropy

• Assume i.i.d over space, but dont make any
  assumptions about images

• Estimating entropy of an N-dimensional
  distribution is a challenging task

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Results Congealing with Entropy
Before After
(B-Splines 20mm)