Convert data from A.m to Volts

Discussions
1

Hi,

The data we get from the solving of the inverse problem are in A.m, is there a way to deduce data in Volts ?

Thanks

2

These are current strength values (current density actually). To convert in Volts, you need to compute the voltage produced by these currents on “virtual” electrodes through an intracranial EEG forward model for instance. This is possible in BST: you may refer to the Feb 2015 update section in http://neuroimage.usc.edu/brainstorm/News

3

Pizzaiolo,

See also EEG units for discussion on units in EEG. The forward model in EEG converts the nA-m units of source intensity into volts at the EEG sensors.

  • John
4

Hi,

Thanks a lot for these answers. Actually, my initial data are MEG data, I applied an inverse problem on these data, so I got 15002 dipoles on the cortex in A.m, then I installed OpenMEEG BEM as you advised me. I hoped I would be have been able to compute intracranial eeg data in Volts (idealy to get these 15002 sources on the cortex but in Volts, not in A.m). Yet, I dind’t manage to do it, and I didn’t find any complete tutorial for this. Could you explain me how to do so ?

Thanks

5

Sorry I forgot to precise, I compute the head model with openMEEG BEM, but what I got is a head model with this description :

|
|- MEGMethod: ‘openmeeg’
|- EEGMethod: ‘’
|- ECOGMethod: ‘’
|- SEEGMethod: ‘’
|- Gain: [185x45006 double]
|- Comment: ‘OpenMEEG BEM’
|- HeadModelType: ‘surface’
|- GridLoc: [15002x3 double]
|- GridOrient: [15002x3 double]
|- GridAtlas: []
|- GridOptions: []
|- SurfaceFile: ‘@default_subject/tess_cortex_pial_low.mat’
|- Param: []
|- History: {‘09-May-2017 00:47:33’, ‘compute’, ‘Compute head model: OpenMEEG BEM | Scalp 1.0000 1082V | Skull 0.0125 642V | Brain 1.0000 642V’}

So nothing for SEEG

6

From the MEG sources, you can model the corresponding EEG data on intracranial electrodes using BST’s simulation tool via the head model you will have computed with OpenMEEG on these very intracranial electrodes.

7

Hello,

Thanks for your answers. Actually, the problem with this method is that since we consider the potential at the same points where we have the dipoles, and since a dipole creates an infinite potential at the point where it is located, we get a gain matrix with infinite values and brainstorm stops its execution. Maybe there is an other way with brainstorm ?