# Computing head model (MRI volume) Regular grid (grid resolution)

Forward model (meg, default anatomy)
I expected to have just one contour in the 2d map when we have 1 dipole radially oriented
but we still see 2 spot in 2d map:

may be if I make Computing head model (MRI volume) Regular grid (with grid resolution of few millimeters) then I will get ideal radial dipole?

In the brainstorm, does the orientation of the dipole is depending on the cortex mesh?
it means if we put a specific orientation does it will search for a near faces in the cortex mesh or not?

The amplitude of the simulated MEG values is probably quite low.
If you are using the "overlapping spheres" or "OpenMEEG BEM" head models, you will never get a "pure radial" dipole which leads to strictly no surface signal.

The new Simulations tutorial may help you a bit with this question:
https://neuroimage.usc.edu/brainstorm/Tutorials/Simulations

In the brainstorm, does the orientation of the dipole is depending on the cortex mesh?

Thank you,
then as I expected that the orientation of dipoles it depends on the mesh,
I changed the grid resolution (in forward model) from 5mm to 3 mm and I still not have pure radial, and as you said neither with openmeeg nor with overlapping we will have it, does it means with FEM may be we have it?

what do you mean by this? (no surface signal)

does it means with FEM may be we have it?

No, the more realistic the worse.
If you want to create a simulation with radial dipoles that are absolutely invisible for MEG sensors, you need to use a spherical model, and you need to compute the orientation of your dipole precisely. Maybe you should recode everything in your own scripts instead of trying to use Brainstorm for this...

what do you mean by this? (no surface signal)

The dipole not visible in the MEG.

I think you mean with single sphere,
because you mentioned above that with even overlapping spheres no pure radial will produced,

Indeed.

Just committed a new process "Simulate recordings from dipoles":
https://neuroimage.usc.edu/brainstorm/Tutorials/Simulations#Single_dipoles