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56 Cards in this Set
- Front
- Back
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BOLD?
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Blood-oxygen-level dependent
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What does fMRI measure?
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Haemodynamic response (change in blood flow).
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What is BOLD?
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The MRI contrast of blood deoxyhaemoglobin.
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Relationship between size of BOLD signal and strength of magnetic field.
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BOLD signal increases as the square of the MF strength (Tesla).
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How is BOLD acquired?
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Using contrast weighted by T1 or T2.
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How is BOLD computed?
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Ratio of oxyhaemoglobin with deoxyhaemoglobin.
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Effect size conversion in fMRI
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Converted to percentage of signal change.
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What is diffusion?
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Movement of particles from high to low concentration areas.
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How diffusion relates to entropy?
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Diffusion increases the entropy of a system.
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What causes Brownian motion?
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Brownian motion is caused by collision.
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What is (diffusion) anisotropy?
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Probability of displacement in certain directions is higher than in others.
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What is (diffusion) isotropy?
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Probability of displacement is equal in all direction.
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Diffusion in the absence of concentration gradient?
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Self-diffusion or tracer diffusion.
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Example of isotropic tissue in brain.
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CSF
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Tensor of rank 2 in R^n.
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Matrix of order n*n = n^2.
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Tensor of rank 3 in R^n.
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Array of order n*n*n = n^3.
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Tensor of rank 0 in R^n.
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Scalar.
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Which diffusion gradient is most important?
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Principal eigenvector of gradient tensor.
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Interpretation of eigenvalues from diffusion tensor.
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Amount of diffusion in the diffusion gradient given by corresponding eigenvector.
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Interpretation of eigenvectors from diffusion tensor.
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A diffusion gradient.
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Mean diffusivity?
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Trace of diffusion tensor.
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Properties of quantities based on diffusion tensor?
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Rotational invariant.
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What is tractography?
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Follow-up of local diffusion gradients.
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What are tensors in comparison to matrices?
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Generalization of vectors and matrices to any rank (i.e. more than 2).
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Another name for a square wave?
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A boxcar function.
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What is the effective imaging resolution in fMRI.
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About 3mm, as constrained by the size of capillaries.
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One major limitation of DTI.
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Fibres are not parallel (e.g. kissing fibres)
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What causes an increase in BOLD signal?
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Decrease of deoxyhemoglobin.
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What an increase in BOLD signal mean?
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Increase in oxygen consumption.
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What does increase in oxygen consumption mean?
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Increase in oxyhemoglobin and decrease in deoxyhemoglobin.
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Why fMRI focuses on deoxyhemolgobin?
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Causes greater dephasing than oxyhemoglobin.
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What does HRF stand for?
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Hemodynamic Response Function.
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Where does diffusion occur?
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Diffusion is mainly extracellular.
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Prewhitening?
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Removing unwanted autocorrelations from time series, prior to analysis.
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Fractional Anisotropy.
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Normalized standard deviation of eigenvalues (dimensionless quantity).
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Mean Diffusivity.
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Mean of Eigenvalues.
MD has a (diffusion) unit. |