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How many Dof has affine transformation

What is a versor and how is it used to describe a rigid transform?

What are the four types of transformations

Rigid à simple
Similarity
(poly-)affine,
Non-rigid à complex

Projective does not preserves parallelism, length, and angle

What is meant by Procrustes?

Image registration, what for?

How many DoF has anisotropic scaling?

3 DoF à Scaling in x, y, z

What are the issues of mutual information?

What means mono-modal?

When we have same image modalities of two images à CT – CT, MRI – MRI

What for different dimensionality we can have?

- 2D – 2D
3D – 3D
2D – 2D

An example of multimodality is..
CT/MR
Multiple CT images
MR/MR
CT/CT of two different patients

- CT/ MR

- Finding a transformation that optimize a similarity metric

How is a joint histogram calculated?

What is the main idea of Free-Form Deformation (FFD)?

What are the advantages and disadvantages of Thin-plate splines?

How many DoF has similarity?

How many DoF has rigid transformation?

6 DoF à 3 translation, 3 rotations
Preserves distances between points
Preserves angels

What is the basic method of iterative closest point algorithm (ICP)?

Surface-to-point-cloud rigid alignment

What is the aim of image registration evaluation?

- Assess accuracy of th alignment

What are the three main motivations for registration?

How we have a high entropy?

If we have a uniform distribution à max entropy

How is the transformation from the grid space to the “real space” known? (three points)

Image Origin
Image dimensions
Voxel spacing (or voxel size)

What is a modern approach for multi-modality registration?

- Apply sophisticated similarity measures

A similarity transformation has…
3 parameters
6 parameters
9 parameters
12 parameters

- 9 parameters

What is Normalized Cross Correlation?

What are the types of non-rigid transformation?

What does entropy?

- Describes the distribution overlap

What stands FFD for?

Free-Form Deformation

What is the basic idea of interpolating spinec?

What forces is elastic deformation governed by?

What is non-rigid image registration used for?

For what is affine registration appropriate?

Why is image registration needed?

What is the limitation of SSD?

How many DoF has translation transformation?

3 DoF à x, y, z

What is image registration? And how?

How can we express FFD based on B-splines?

FFDs based on B-splines can be expressed as a 3D tensor product of 1D B-splines:

Does this image show a low or high entropy?

- Low entropy à aligned

When we have a low entropy?

If we have a non-uniform distribution

Name some image registration evaluation metrics:

Which addition we have for the mutual information?

- Additionally, to the joint histogram, we have an histogram of the image X and the image Y

How does the landmark-based evaluation works and what are the contras of this evaluation metric?

Landmark-based typically uses RMSE (root-mean-square-error) metrics
Cons: Landmark annotation

On what depends the complexity of the image registration evaluation?

Complexity of the evaluation depends on the type of registration

What is the main idea in linear interpolation?

Image registration happens at the level of…
Voxel units
Real units (e.g., mm)
It doesn’t matter

- Real units (e.g., mm)

What is the main idea in bilinear interpolation?

What are splines in a mathematical meaning?

What are the different types of information?

Intensity-bases à pure intensity of pixels
Non-intensity-based

What is A and B describing?

- A: describe rotations, shear, scaling
B: describe translation

What is used to compute a translation which is intensity-based?

similarity constructed based on voxel intensity information

When we need non-rigid registration in neuroimaging?

What is the problem if we using entropy?

What does mutual information

- It not just considers the overlap area but also the content of the image

What is used to compute a translation which is feature-based?

What is the difference between a Eulerian frame and a Lagrangian frame?

How we can optimize image registration?

What are splines in the mathematic context?

What is the difference between SSD (Sum of Squared Differences) and SAD (Sum of Absolut Differences?

For what is a joint histogram used?

What are some parameters of image registration optimization?

For what is rigid registration appropriate?

Appropriate for:
Brain (constrained by skull)
Bone (neck, vertebrae)

Describe the function of the ICP algorithm

What are some basic similarity metrics?

How does the Hausdorff distance evaluation works and what are the contras of this evaluation metric?

- doesn’t describe the entire transform

What are good similarity metric features?

Extremum for correctly aligned images
Smooth, best convex
Fast computation
Differentiable

What is the main idea in nearest neighbor interpolation?

On what is Mutual Information (MI) based?

What are the steps of ICP?

What's the difference between projective and affine transformations?

What means multi-modal?

When we have different image modalities of two images à CT – MRI, CT – PET

How can thin plate splines defined?

Thin-plate splines can be defined as a linear combination of radial basis functions θ:

Does this image show a low or high entropy?

- High entropy à not aligned