Magnetic induction

Discussions
1

How to find magnetic induction, having the values of 2 gradiometers and 1 magnetometer? How does MEG do this? Please tell me the math on fingers or where to watch it

2

There is no derivation of the full magnetic induction needed to use MEG. Source estimation of sensor signals is based on the modeling of the magneto and gradiometers, including their location and coil geometry. The Biot and Savart equation is then solved accordingly, w/o resorting to an estimate of the induction per se (BTW which cannot be derived in full based on the sensor with limited coil orientation etc.).

3

Thanks! Do I understand correctly that the SSS method is used to obtain induction? And if it’s not difficult, please recommend good literature on this issue

4

No, SSS is a spatial filter, denoising technique. (SSS= source space separation)

5

"I would like to understand how Brainsorm constructs magnetic induction, if it is impossible to obtain it entirely based on a sensor with a limited orientation of the coil? How "Magnetic interpolation" works?

6

Hi @Konstantin1

I recommend to you refer to the literature on the field; you can, for example, start from these two refs:

1- Electromagnetic brain mapping, S. Baillet et al

2- Magnetoencephalography -theory , instrumentation, and applications to noninvasive studies of the working human brain. Matti Hämäläinen et al

7

Hi @tmedani

Thank you! I read it, but still didn’t understand how to get induction using 2 gradiometer values and 1 magnetometer value. How to do this mathematically?

8

Hi @Konstantin1

Here is another reference that explains step by-step all the computation processes
https://www.bem.fi/book/index.htm

You can check directly the EEG and MEG sections.

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