[FieldTrip] Seizure localization problems

[Azeez Adebimpe]

Hi Mathias,
I will suggest you try other method like eLORETA or MNE  first and compare
the result.

Best,

AZ

On Thu, Jun 23, 2016 at 9:34 AM, Dr.-Ing. Matthias Dümpelmann <
matthias.duempelmann at uniklinik-freiburg.de> wrote:

> Dear colleagues,
>
> we are trying to evaluate systematically the localization  of rhythmic
> activity at the onset of epileptic seizures in patients, who are
> subsequently evaluated with intracranial recordings.
>
> We are trying to use DICS but quite often receive results, which are
> obviously wrong. In the attached screenshots you can see the peace of EEG,
> which is evaluated and the localization result with a maximum in the
> cerebellum.
>
> This a typical localization for the cases with obvious miss localizations.
> A further seizure with a similar EEG pattern was localized in the right
> temporal lobe, which matches the EEG pattern and also the intracranial
> findings.
>
> Head model is generated with ASA, also the electrodes file is in the ASA
> format. The geometrical match of source points, head model and electrodes
> is checked using ft_plot_.... methods.
>
> Here is the code sniplet relevant for the localization algorithm:
>
> % Analysis frequency
> SourceFrequency = 4.0
>
> % read eeg, electrodes and volume conductor model
> %[dat] = ft_read_data(filename);
> hdr = ft_read_header(filename);
> elec =  ft_read_sens(elecfile,  'fileformat','asa_elc');
> headmodel = ft_read_vol(volumefilename,'fileformat','asa_vol');
> mri = ft_read_mri(mrifilename, 'fileformat','asa_mri');
>
> % eeg data preprocessing
> cfgeeg.dataset = filename;
> cfgeeg.continuous   = 'yes'
> cfg.covariance       = 'yes';
> cfg.covariancewindow = 'all';
> cfg.demean = 'yes'
>
> [data] = ft_preprocessing(cfgeeg);
>
> % Freqanalysis for beamformer
> cfg = [];
> cfg.channel      = {'*'};
> cfg.method       = 'mtmfft';
> cfg.foilim     = [1 100];
> cfg.tapsmofrq  = 4;
> cfg.taper    = 'hanning';
> cfg.output       = 'powandcsd';
>
>
> % for common filter over conditions
> powcsd_all      = ft_freqanalysis(cfg, data);
>
> % Create leadfield grid
> cfg                 = [];
> cfg.channel         = elec.label;
> cfg.elec            = elec;
> cfg.headmodel       = headmodel;
> cfg.dics.reducerank = 3; % default for MEG is 2, for EEG is 3
> cfg.grid.resolution = 0.5;   % use a 3-D grid with a 0.5 cm resolution
> cfg.grid.unit       = 'cm';
> cfg.grid.tight      = 'yes';
> [grid] = ft_prepare_leadfield(cfg);
>
> % source analysis
> cfg              = [];
> cfg.channel      = elec.label;
> cfg.method       = 'dics';
> cfg.frequency    = SourceFrequency;
> cfg.grid         = grid;
> cfg.headmodel    = headmodel;
> cfg.elec         = elec;
> cfg.senstype     = 'EEG';
> cfg.dics.keepfilter   = 'yes'; % We wish to use the calculated filter
> later on
> cfg.dics.projectnoise = 'yes';
> cfg.dics.lambda  = '0.3%';
> source_raw = ft_sourceanalysis(cfg, powcsd_all);
>
>
> I played with a couple of parameters like cfg.dics.lambda, but without
> success.
>
> Do you have ideas how to improve our localization results ?
>
> Thank you,
>
> Matthias
>
>
>
> UNIVERSITÄTSKLINIKUM FREIBURG
> Epileptologie
> Breisacher Str. 64 · 79106 Freiburg
> Telefon: +49 761 270-52410
> matthias.duempelmann at uniklinik-freiburg.de
>
> www.uniklinik-freiburg.de
>
>
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