This tutorial shows how to clean MEG data with Maxwell filtering.
Maxwell filtering in MNE can be used to suppress sources of external intereference and compensate for subject head movements.
See Maxwell filtering for more details.
import mne
from mne.preprocessing import maxwell_filter
data_path = mne.datasets.sample.data_path()
Set parameters
raw_fname = data_path + '/MEG/sample/sample_audvis_raw.fif'
ctc_fname = data_path + '/SSS/ct_sparse_mgh.fif'
fine_cal_fname = data_path + '/SSS/sss_cal_mgh.dat'
Preprocess with Maxwell filtering
raw = mne.io.read_raw_fif(raw_fname)
raw.info['bads'] = ['MEG 2443', 'EEG 053', 'MEG 1032', 'MEG 2313'] # set bads
# Here we don't use tSSS (set st_duration) because MGH data is very clean
raw_sss = maxwell_filter(raw, cross_talk=ctc_fname, calibration=fine_cal_fname)
Out:
Opening raw data file /home/ubuntu/mne_data/MNE-sample-data/MEG/sample/sample_audvis_raw.fif...
Read a total of 3 projection items:
PCA-v1 (1 x 102) idle
PCA-v2 (1 x 102) idle
PCA-v3 (1 x 102) idle
Range : 25800 ... 192599 = 42.956 ... 320.670 secs
Ready.
Current compensation grade : 0
Maxwell filtering raw data
Loading raw data from disk
Bad MEG channels being reconstructed: ['MEG 2443', 'MEG 1032', 'MEG 2313']
Processing 204 gradiometers and 102 magnetometers
Using fine calibration sss_cal_mgh.dat
Adjusting non-orthogonal EX and EY
Adjusted coil positions by (μ ± σ): 0.5° ± 0.4° (max: 2.1°)
Automatic origin fit: head of radius 91.0 mm
Using origin -4.1, 16.0, 51.7 mm in the head frame
Computing regularization
Using 87/95 harmonic components for 0.000 (72/80 in, 15/15 out)
Processing 27 data chunks of (at least) 10.0 sec
[done]
Select events to extract epochs from, pick M/EEG channels, and plot evoked
tmin, tmax = -0.2, 0.5
event_id = {'Auditory/Left': 1}
events = mne.find_events(raw, 'STI 014')
picks = mne.pick_types(raw.info, meg=True, eeg=False, stim=False, eog=True,
include=[], exclude='bads')
for r, kind in zip((raw, raw_sss), ('Raw data', 'Maxwell filtered data')):
epochs = mne.Epochs(r, events, event_id, tmin, tmax, picks=picks,
baseline=(None, 0), reject=dict(eog=150e-6))
evoked = epochs.average()
evoked.plot(window_title=kind, ylim=dict(grad=(-200, 250),
mag=(-600, 700)))
Out:
320 events found
Events id: [ 1 2 3 4 5 32]
72 matching events found
Created an SSP operator (subspace dimension = 3)
3 projection items activated
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
72 matching events found
0 projection items activated
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Total running time of the script: ( 0 minutes 7.443 seconds)