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P3 Physical > Fusion, Co-Registration, Technical Issues & Limitations > Flashcards

Fusion, Co-Registration, Technical Issues & Limitations Flashcards

1
Q

What is the need and rationale for fusion, co-registration and technical issues?

A

Research:

- understanding functional pathways in a subjects population

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2
Q

What are the clinical applications for the need and rationale?

A
  1. EEG: location of focus epilepticus
  2. fMRI: vicinity of eloquent areas to lesions
  3. DTI: vicinity of tracts to lesion
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3
Q

What are the problem for the need and rationale?

A

Poor anatomical definition in DTI and functional imaging (fMRI, EEG, PET)

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4
Q

What is the solution to the problem for the need and rationale?

A

Co-registration to images with high anatomical definition and high resolution

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5
Q

What is 3D Rigid-body transformations?

A

3 translations: in X, Y & Z directions

3 rotations: about X, Y & Z

The order of the operations matters

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6
Q

What is affine transformation?

A

3 translations: in X, Y & Z directions

3 rotations: about X, Y & Z axes

Zoom

Shear

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7
Q

What are the different methods for the fusion methods?

A
  1. Manual
  2. Interactive
  3. Semi-automatic
  4. Automatic
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8
Q

Manual method

A

Provide tools to align the images manually

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9
Q

Interactive method

A

Perform certain key operations automatically: user guides the registeration

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10
Q

Semi-automatic method

A

Perform more of the registration steps automatically; user verifies correctness of refisteration

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11
Q

Automatic method

A

Do not allow any user interaction; perform all registeration steps automatically

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12
Q

What is semi-automatic methods?

A
  1. Coarse image registeration done manually
  2. More precise image registeration done automatically
  3. User verified registeration and is able to finely modify it if necessary
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13
Q

What is automatic methods?

A

Image registration is done by optimisation

Optimisation involves finding some best parameters according to an “objective function” which is either minimised or maximised

The “objective function” is often related to a probability based on some model

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14
Q

What are the 2 different types of objective functions?

A
  1. Intra-model

2. Inter-model

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15
Q

What are examples of intra-model?

A
  1. Mean squared difference (minimise)
  2. Normalised cross correlation (maximise)
  3. Entropy of difference (minimise)
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16
Q

What are examples of inter-modal?

A
  1. Mutual information (maximise)
  2. Normalised mutual information (maximise)
  3. Entropy correlation coefficient (maximise)
  4. AIR cost function (minimise)
17
Q

What is intra-modal?

A

Within subject; within modality

18
Q

What is mean-squared difference (minimise)?

A

Simple relationship between intensities in one image, versus those in the other
- assumes normally distributed differences

19
Q

What can re-sampling introduce?

A

Interpolation errors

20
Q

What can cause aliasing artefacts?

A

Gaps between slides

21
Q

What is not accounted for by rigid body model?

A

Rapid movements

22
Q

Why may image artefacts not move according to a rigid body model?

A
  1. Image distortion (possible correction; unwrap, field maps)
  2. Image dropout
  3. Nyquist ghost
23
Q

What is co-registeration?

A

Match images from same subject but different modalities

24
Q

What does spatial normalisation minimise?

A

Mean squared difference from template image(s)

25
Q

What is the consequence of no regularisation?

A

The non-linear spatial normalisation can introduce unneccessary warps

26
Q

What is DARTEL?

A

Non-linear and regularised registration method

More accurate than normalised

Used for VBM

27
Q

What are the limitations or re-aligning images?

A

Possible residual errors (interpolation, aliasing artefacts, distortion, dropouts)

28
Q

What are the limitations for co-register?

A

Possible residual errors, especially if signal drop-out or distortions present

29
Q

What are the limitations for normalisation?

A
  1. Introduction of unnecessary warps

2. Presence of lesions

30
Q

What doesn’t the activation maps have?

A

Anatomical information
Not possible to check alignment
Person performing the analysis need to make appropriate checks

31
Q

What is visualisation?

A

Check co-registeration of functional, structural MR and DTI

32
Q

What are the basic concepts behind image co-registeration?

A
  1. Objective function created using data from two images

2. Optimisation (minimisation or maximisation) of the objective function

P3 Physical (21 decks)

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