Real-time source localization 2

💬 Support & Discussions
1

Dear MNE users, I would like to do real-time source localization from real-time EEG signals.

I think there is real-time MNE package.
Real-time M/EEG Acquisition — MNE-Realtime 0.1.dev0 documentation

But, I did not discover real-time source localization example. If you know it, let’s share the useful information.

Best,
Kyu

2

There isn’t an existing example. It ought to be possible in principle, however: if you can determine in advance your forward model and noise covariance, then you ought to be able to use mne.minimum_norm.apply_inverse to each Realtime epoch as it comes in.

3

Dan, I see. Great information for me! Kyu

4

This might help: https://gist.github.com/jasmainak/61497ceec1fb0532a21b

The code is a bit old but can perhaps be adapted for your usecase.

Mainak

5

Hi Mainak, Thank you so much! Your code is so helpful for me!

Kyu

6

Hi Mainak, thanks for your helpful comments. When I looked at your code, you used ‘compute_source_psd_epochs’. Is there any time delay related to this function?

Using your code, we can implement real-time source localization. One thing that I am worried is time-delay. Didn’t you feel any delay in your realtime system?

7

Hi Kyu,

Apologies for the delayed response. You might want to look at my Masters thesis here:

https://aaltodoc.aalto.fi/bitstream/handle/123456789/15550/master_Jas_Mainak_2015.pdf

Specifically, take a look at this figure:

image.png
image.png722×403 24.4 KB

If I remember correctly, the total time delay depends on: 1) the buffer length in FieldTrip buffer, 2) the buffer size of the data requested by the FieldTrip buffer client in MNE-Python, and 3) the processing speed. If you precompute the forward, 3) may not be a bottleneck. I would recommend measuring the time with time.time or some such tool. 1) usually depends on the vendor. For Elekta systems on which I tested, I think 28 samples is the minimum buffer length. Now, depending on the timing of the start of the buffer and query from MNE-Python, the actual delay may have a distribution as shown in the figure above. Note that get_data_as_epoch requests only the last n_samples, so you do get pseudo-realtime at the expense of missing some samples. If on the other hand, you’d like to get all the samples corresponding to a trigger, you should use iter_evoked.

Hope that helps!
Mainak

8

Hi Mainak, thanks for you helpful information. Your information is so important for me. I think for your master study you worked very hard and did a lot!

Kyu