Diffusion MRI - ISMRM's MR Pulse Blog

In biological tissue, for a very short time scale (a few ms), the diffusion of the water molecules can be described as:

Isotropic and Gaussian

Anisotropic and Gaussian

Isotropic and non-Gaussian

Anisotropic and non-Gaussian

Correct! Wrong!

Which of the following statements is true about the diffusion of water molecules in the brain, over a timescale of roughly 50 ms?

Please select 2 correct answers

The diffusion is anisotropic, i.e., relatively fast parallel compared to perpendicular to the fibers, in the white matter

The diffusion is relatively isotropic in the gray matter compared to the white matter

The diffusion is isotropic in both gray and white matter

All of the above

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Which parameter should be changed to increase the diffusion length/displacement?

Echo Time

Diffusion time (Delta)

Gradient strength (G)

None of the above

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How will the log of the diffusion weighted signal change if the diffusion sensitizing gradient strength is doubled?

It will increase twice

It will increase 4 times

It will decrease twice

It will decrease 4 times

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What is the relationship between the b-value and the resolution in q-space?

They are not related

They are equal

They are proportional

Correct! Wrong!

How is the signal intensity drift in dMRI data corrected?

By low-degree polynomial fitting of the b0 images

By low-degree polynomial fitting of the b0 and the diffusion weighted images

By high-degree polynomial fitting of the b0 images

Correct! Wrong!

When correcting for subject motion in diffusion MRI data, which processing step should be included to prevent a bias?

Rotation of the b-matrix.

Recalibration of the b-values.

Normalization of the diffusion gradient orientations.

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How does the size of a tract passing close by the grey matter or the ventricles determine the extent of the confound caused by partial voluming, for statistics computed for the entire tract volume?

Bigger ( in diameter) tracts are more affected

Bigger ( in diameter) tracts are less affected

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For which of the following studies is TBSS likely to be unreliable?

Evaluation of the FA in aging

Statistical comparison of different white matter regions in healthy athletes

Comparison of the FA variance in the corpus callosum of MS patients

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How often does more than one fiber orientation occupy a voxel in a diffusion MRI acquisition with 2 mm isotropic voxel size?

<10%

10% - 50%

50% - 90%

>90%

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What is the recommended step size and the order of interpolation for tractography?

1/10 of the voxel grid and low order interpolation

1/2 of the voxel grid and low order interpolation

1/10 of the voxel grid and higher order interpolation

1/2 of the voxel grid and higher order interpolation

Correct! Wrong!

What is the main drawback of probabilistic tracking?

It produces more invalid connections in comparison to deterministic approaches

It cannot track highly curved structures

It is not reproducible

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Which structures will be over-represented if the tractography is seeded from every voxel in the brain white matter?

Large and long bundles

Thin and long bundles

Large and short bundles

Thin and short bundles

Correct! Wrong!

The seeding bias can be overcomed by:

Including anatomical priors

Seeding from the grey-white matter interface

Particle filtering tractography

All of the above

Correct! Wrong!