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56 Cards in this Set
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BOLD?

Bloodoxygenlevel dependent


What does fMRI measure?

Haemodynamic response (change in blood flow).


What is BOLD?

The MRI contrast of blood deoxyhaemoglobin.


Relationship between size of BOLD signal and strength of magnetic field.

BOLD signal increases as the square of the MF strength (Tesla).


How is BOLD acquired?

Using contrast weighted by T1 or T2.


How is BOLD computed?

Ratio of oxyhaemoglobin with deoxyhaemoglobin.


Effect size conversion in fMRI

Converted to percentage of signal change.


What is diffusion?

Movement of particles from high to low concentration areas.


How diffusion relates to entropy?

Diffusion increases the entropy of a system.


What causes Brownian motion?

Brownian motion is caused by collision.


What is (diffusion) anisotropy?

Probability of displacement in certain directions is higher than in others.


What is (diffusion) isotropy?

Probability of displacement is equal in all direction.


Diffusion in the absence of concentration gradient?

Selfdiffusion or tracer diffusion.


Example of isotropic tissue in brain.

CSF


Tensor of rank 2 in R^n.

Matrix of order n*n = n^2.


Tensor of rank 3 in R^n.

Array of order n*n*n = n^3.


Tensor of rank 0 in R^n.

Scalar.


Which diffusion gradient is most important?

Principal eigenvector of gradient tensor.


Interpretation of eigenvalues from diffusion tensor.

Amount of diffusion in the diffusion gradient given by corresponding eigenvector.


Interpretation of eigenvectors from diffusion tensor.

A diffusion gradient.


Mean diffusivity?

Trace of diffusion tensor.


Properties of quantities based on diffusion tensor?

Rotational invariant.


What is tractography?

Followup of local diffusion gradients.


What are tensors in comparison to matrices?

Generalization of vectors and matrices to any rank (i.e. more than 2).


Another name for a square wave?

A boxcar function.


What is the effective imaging resolution in fMRI.

About 3mm, as constrained by the size of capillaries.


One major limitation of DTI.

Fibres are not parallel (e.g. kissing fibres)


What causes an increase in BOLD signal?

Decrease of deoxyhemoglobin.


What an increase in BOLD signal mean?

Increase in oxygen consumption.


What does increase in oxygen consumption mean?

Increase in oxyhemoglobin and decrease in deoxyhemoglobin.


Why fMRI focuses on deoxyhemolgobin?

Causes greater dephasing than oxyhemoglobin.


What does HRF stand for?

Hemodynamic Response Function.


Where does diffusion occur?

Diffusion is mainly extracellular.


Prewhitening?

Removing unwanted autocorrelations from time series, prior to analysis.


Fractional Anisotropy.

Normalized standard deviation of eigenvalues (dimensionless quantity).


Mean Diffusivity.

Mean of Eigenvalues.
MD has a (diffusion) unit. 