Add one or several exercises to the CSD lesson

[jhlegarreta]

Add one or several exercises to the CSD lesson, including their solutions.

[jhlegarreta]

An interesting exercise could be to:

• Provide synthetic peaks at different crossing angles (e.g. 90°, 60°, 45°, 30°, 20°) and tell learners to deconvolve them with an FRF to see the problems CSD faces. This could also be done for the DTI lesson, which would then allow people to compare both methods.

More theoretic and somewhat harder exercises (also because they require developing additional methods/tools) could be to:

• Tell learners to represent a given (diffusion-like spherical) signal using the SH expansion of different orders/degrees. We would need to come up with a good signal to do this.
• Tell learners to deconvolve a diffusion signal with increasing levels of noise to see how the CSD result degrades.
• Tell learners to visualize the spherical harmonics using different orders and degrees (might be hard, requires the episode to better introduce the SH representation (cross referencing Improve CSD lesson theory #28), and may not be that informative).

Might be interesting to add them in the (very) long run either as exercises or contents for extras.

[jhlegarreta]

A note on the first proposed exercise: it implies using synthetic data (a voxel) (or voxels from the data containing crossings at different angles might do the job) to simulate a signal containing crossings at different angles