[FieldTrip] Aligning electrodes to template head model (Wu, Jia)
RICHARDS, JOHN
RICHARDS at mailbox.sc.edu
Thu Sep 17 15:15:28 CEST 2015
If you need the standard model for some particular reason, the next part won’t help, but..
I have a database of average MRI templates (head or brain) for “20-24Year olds”, with segmented heads (e.g., 4 BEM compartments; or segmented for FEM), and average electrode positions. The average electrode positions are for the GSN or H-GSN and come from an electrode placement study with about 140 participants; I also have “virtual 10-10” positions. The electrode positions are already on the head surface so that “warping/transforming” is unnecessary, and if the head fiducials match the electrode fiducials the FT fit is perfect because the electrodes are already on the scalp. I have used the AC/PC/LPA/RPA alignment successfully. Also, there are stereotaxic atlases in the same format as the average MRI templates. I have managed for myself to get all these working in FT (spherical, BEM-CP, BEM-Dipoli, FEM-SImBio, and atlases with ROIs).
And, re average MRI templates, I have them for ages 4 through adults in steps of two years; with electrodes, segmented heads (and priors), atlases, etc.
See me www site for publications on the database (e.g., Richards, Sanchez et al, 2015), electrodes (Richards, Boswell et al, 2015), and atlases (for infants; Fillmore et al., 2015, Dev Neuroscience). I also am working on several papers that use FT for the source analysis.
John
***********************************************
John E. Richards Carolina Distinguished Professor
Department of Psychology
University of South Carolina
Columbia, SC 29208
Dept Phone: 803 777 2079
Fax: 803 777 9558
Email: richards-john at sc.edu
HTTP: jerlab.psych.sc.edu
***********************************************
On 9/17/15, 4:00 AM, "fieldtrip-bounces at science.ru.nl on behalf of fieldtrip-request at science.ru.nl" <fieldtrip-bounces at science.ru.nl on behalf of fieldtrip-request at science.ru.nl> wrote:
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>Today's Topics:
>
> 1. Re: Aligning electrodes to template head model (Wu, Jia)
> 2. Re: Aligning electrodes to template head model
> (m.goeldi at psychologie.uzh.ch)
> 3. Neighbors for Elekta Neuromag 306 gradiometers separately?
> (Darinka Tr?butschek)
> 4. Re: Leadfield of one condition with two different 'grad'
> structures (Sara Aurtenetxe)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Thu, 17 Sep 2015 02:13:57 +0000
>From: "Wu, Jia" <jia.wu at yale.edu>
>To: FieldTrip discussion list <fieldtrip at science.ru.nl>
>Subject: Re: [FieldTrip] Aligning electrodes to template head model
>Message-ID:
> <AA21F9F31911364596BE68CA1AAD8DA466E1FC44 at x10-mbx13.yu.yale.edu>
>Content-Type: text/plain; charset="iso-8859-1"
>
>Helen,
>Can you find the place where you downloaded the headmodel?
>-jia
>________________________________
>From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Helen Wieffering [helen.wieffering at gmail.com]
>Sent: Wednesday, September 16, 2015 8:20 PM
>To: FieldTrip discussion list
>Subject: Re: [FieldTrip] Aligning electrodes to template head model
>
>Hi again, Jia,
>I agree- something must be going wrong when I plot the head model, or maybe when I warp the fiducial coordinates from the mri, because the alignment is certainly worse off after I complete all the alignment steps than it was originally! But since all my steps draw from the standard_mri and standard_bem, I'm not sure what the problem could be.
>
>My best success has been simply from interactively aligning the electrodes and verifying it visually. I'm attaching a matlab figure of what it looks like just in case anyone has input - I think it looks accurately aligned, but this is my first time creating a head model in field trip so I have limited experience to draw upon.
>
>As always, thanks for your help.
>
>Best,
>Helen Wieffering
>Bowdoin College
>
>On Wed, Sep 16, 2015 at 3:50 PM, Helen Wieffering <helen.wieffering at gmail.com<mailto:helen.wieffering at gmail.com>> wrote:
>Hi Jia,
>Thanks so much for taking the time to help me. I'll try what you suggested and see how it goes!
>
>Best,
>Helen
>
>On Wed, Sep 16, 2015 at 11:59 AM, Wu, Jia <jia.wu at yale.edu<mailto:jia.wu at yale.edu>> wrote:
>Helen,
>I ran your code and it seemed to work with the mri and headmodel I have. I looked back at the picture you sent originally. It looks like the electrodes were aligned (before alignment, the tip of the head is facing upwards, after alignment with the mri provided by the wiki it points to the right), but the headmodel is not plotted correctly. The headmodel needs to be driven from mri. You can double check the headmodel, which is standard_bem in your code.
>-jia
>________________________________
>From: fieldtrip-bounces at science.ru.nl<mailto:fieldtrip-bounces at science.ru.nl> [fieldtrip-bounces at science.ru.nl<mailto:fieldtrip-bounces at science.ru.nl>] on behalf of Helen Wieffering [helen.wieffering at gmail.com<mailto:helen.wieffering at gmail.com>]
>Sent: Wednesday, September 16, 2015 10:00 AM
>To: FieldTrip discussion list
>Subject: Re: [FieldTrip] Aligning electrodes to template head model
>
>Hi Jia,
>Thanks so much for getting back to me. If you have a free moment, would you mind looking over my code? I have tried the tutorial steps many times, even having changed the label of the GSN fiducials to 'Nz', 'LPA', 'RPA', but seem to keep getting the same incorrect results.
>
>% ALIGN ELECTRODES TO STANDARD_BEM
>
>% read electrode coordinates
>elec = ft_read_sens('GSN-HydroCel-129.sfp');
>
>% convert units to mm to match units of headmodel
>elec = ft_convert_units(elec, 'mm');
>
>% change label of fiducials
>elec.label{1} = 'Nz';
>elec.label{2} = 'LPA'
>elec.label{3} = 'RPA';
>
>% create fiducial structure
>% draw fiducial coordinates from mri
>nas = standard_mri.hdr.fiducial.mri.nas;
>lpa = standard_mri.hdr.fiducial.mri.lpa;
>rpa = standard_mri.hdr.fiducial.mri.rpa;
>
>transm = standard_mri.transform;
>
>nas = ft_warp_apply(transm, nas, 'homogenous');
>lpa = ft_warp_apply(transm, lpa, 'homogenous');
>rpa = ft_warp_apply(transm, rpa, 'homogenous');
>
>% create a structure similar to a template set of electrodes
>fid.chanpos = [nas; lpa; rpa]; % mni-coordinates of fiducials
>fid.label = {'Nz','LPA','RPA'}; % same labels as in elec
>fid.unit = 'mm'; % same units as mri
>
>% alignment
>cfg = [];
>cfg.method = 'fiducial';
>cfg.template = fid; % see above
>cfg.elec = elec;
>cfg.fiducial = {'Nz', 'LPA', 'RPA'}; % labels of fiducials in fid and in elec
>elec_aligned = ft_electroderealign(cfg);
>
>% plot to check
>figure;
>ft_plot_mesh(standard_bem.bnd(1), 'edgecolor','none','facealpha',0.8,'facecolor',[0.6 0.6 0.8]);
>hold on;
>ft_plot_sens(elec_aligned,'style', 'sk');
>
>For reference, the coordinates I get in the structure fid are the following:
>fid =
>
> chanpos: [3x3 double]
> label: {'Nz' 'LPA' 'RPA'}
> unit: 'mm'
>
>fid.chanpos
>
>ans =
>
> 35 -36 0
> 118 -35 0
> -82 -35 0
>
>
>If those are different from yours, would you let me know? I'm trying to find out at which step I went wrong.
>Again, thank you very much!
>
>Best,
>Helen
>
>
>On Mon, Sep 14, 2015 at 11:00 PM, Wu, Jia <jia.wu at yale.edu<mailto:jia.wu at yale.edu>> wrote:
>Helen,
>
>What a coincident. I'm also working on source analysis on EEG data using GSN HydroCel 128. I had a post a couple weeks ago about later steps. But I did get the alignment to work. The picture you posted looked like the status before the alignment. So i suspect that alignment did not happen.
>
>I'm not sure whether you have noticed it, but the fiducial positions in elec location file were called 'FidNz', 'FidT9', 'FidT10', instead of 'Nz','LPA','RPA' as in the tutorial. So they need to be changed. Then the alignment should work.
>
>best,
>-jia
>
>________________________________
>From: fieldtrip-bounces at science.ru.nl<mailto:fieldtrip-bounces at science.ru.nl> [fieldtrip-bounces at science.ru.nl<mailto:fieldtrip-bounces at science.ru.nl>] on behalf of Helen Wieffering [helen.wieffering at gmail.com<mailto:helen.wieffering at gmail.com>]
>Sent: Monday, September 14, 2015 4:46 PM
>To: FieldTrip discussion list
>Subject: [FieldTrip] Aligning electrodes to template head model
>
>Hello all,
>
>I have a quick question on aligning electrodes to the standard_bem headmodel, which I downloaded from the FT server.
>
>Namely, are the standard_mri and the standard_bem in the same coordinate system? I assumed this would be so, since one was developed from the other. But when I try to align my electrodes to the standard_bem volume using fiducial positions from the standard_mri, I get very strange results: (image below and attached)
>
>[Inline image 1]
>
>I'm using a GSN HydroCel 128 Cap, and my elec structure contains the fiducial positions relative to the electrodes.
>I've been following the tutorial at http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.fieldtriptoolbox.org_tutorial_headmodel-5Feeg&d=AwMFaQ&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=9ehCplyXHP0-m9ayYv1FOg&m=wNRiA8CLR4Y1ZrEaTkTaIoVaUczL5TYuWIx6FyQDphg&s=LjU77qpw8I7LnSHIEQrNIB0R0YLrutfAEtjjOMjBys0&e=> and would like to follow the steps under 'Automatic Alignment', but as I said: pulling the fiducial positions from the standard_mri seems to not work with the tutorial steps.
>
>Any help is appreciated - thanks in advance!
>
>Helen Wieffering
>Bowdoin College
>
>_______________________________________________
>fieldtrip mailing list
>fieldtrip at donders.ru.nl<mailto:fieldtrip at donders.ru.nl>
>http://mailman.science.ru.nl/mailman/listinfo/fieldtrip<https://urldefense.proofpoint.com/v2/url?u=http-3A__mailman.science.ru.nl_mailman_listinfo_fieldtrip&d=AwMFaQ&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=9ehCplyXHP0-m9ayYv1FOg&m=kW18ZarjEMl0kcSTFdA9daM4KYcFZdGymg7wgboAsmc&s=9wDX5VD5t6xGdP84l_wit7DYMhK57vFlE5v1OkxjFgA&e=>
>
>
>_______________________________________________
>fieldtrip mailing list
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>
>
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>------------------------------
>
>Message: 2
>Date: Thu, 17 Sep 2015 08:36:34 +0200
>From: m.goeldi at psychologie.uzh.ch
>To: FieldTrip discussion list <fieldtrip at science.ru.nl>
>Subject: Re: [FieldTrip] Aligning electrodes to template head model
>Message-ID:
> <OFF1973E9E.C8345DDF-ONC1257EC3.0023A717-C1257EC3.00244EC6 at lotus.uzh.ch>
>
>Content-Type: text/plain; charset="utf-8"
>
>Hi Helen
>
>I also had problems using the file GSN-HydroCel-129.sfp electrode locations provided in fieldtrip.
>I ended up using the file provided in SPM12 (located in '\spm12\EEGtemplates\egi128_GSN_HydroCel.sfp').
>This seems to be the same file (it has the same electrodes) but slightly different locations that fit the headmodel much better.
>
>I hope that helps.
>Cheers
>Maurice
>
>
>-----fieldtrip-bounces at science.ru.nl schrieb: -----
>An: FieldTrip discussion list <fieldtrip at science.ru.nl>
>Von: Helen Wieffering
>Gesendet von: fieldtrip-bounces at science.ru.nl
>Datum: 17.09.2015 02:28
>Betreff: Re: [FieldTrip] Aligning electrodes to template head model
>
>Hi again, Jia,
>I agree- something must be going wrong when I plot the head model, or maybe when I warp the fiducial coordinates from the mri, because the alignment is certainly worse off after I complete all the alignment steps than it was originally! But since all my steps draw from the standard_mri and standard_bem, I'm not sure what the problem could be.
>
>My best success has been simply from interactively aligning the electrodes and verifying it visually. I'm attaching a matlab figure of what it looks like just in case anyone has input - I think it looks accurately aligned, but this is my first time creating a head model in field trip so I have limited experience to draw upon.
>
>As always, thanks for your help.
>
>Best,
>Helen Wieffering
>Bowdoin College
>
>On Wed, Sep 16, 2015 at 3:50 PM, Helen Wieffering <helen.wieffering at gmail.com> wrote:
>Hi Jia,
>Thanks so much for taking the time to help me. I'll try what you suggested and see how it goes!
>
>Best,
>Helen
>
>On Wed, Sep 16, 2015 at 11:59 AM, Wu, Jia <jia.wu at yale.edu> wrote:
>
>
>Helen,
>I ran your code and it seemed to work with the mri and headmodel I have. I looked back at the picture you sent originally. It looks like the electrodes were aligned (before alignment, the tip of the head is facing upwards, after alignment with the mri provided by the wiki it points to the right), but the headmodel is not plotted correctly. The headmodel needs to be driven from mri. You can double check the headmodel, which is?standard_bem in your code.
>-jia
>
>
>From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Helen Wieffering [helen.wieffering at gmail.com]
> Sent: Wednesday, September 16, 2015 10:00 AM
> To: FieldTrip discussion list
> Subject: Re: [FieldTrip] Aligning electrodes to template head model
>
>
>
>
>
>
>
>
>
>
>
>Hi Jia,
> Thanks so much for getting back to me. If you have a free moment, would you mind looking over my code? I have tried the tutorial steps many times, even having changed the label of the GSN fiducials to 'Nz', 'LPA', 'RPA',? but seem to keep getting the same incorrect results.
>
> % ALIGN ELECTRODES TO STANDARD_BEM
>
> % read electrode coordinates
> elec = ft_read_sens('GSN-HydroCel-129.sfp');
>
> % convert units to mm to match units of headmodel
> elec = ft_convert_units(elec, 'mm');
>
> % change label of fiducials
> elec.label{1} = 'Nz';
> elec.label{2} = 'LPA'
> elec.label{3} = 'RPA';
>
> % create fiducial structure
> % draw fiducial coordinates from mri
> nas = standard_mri.hdr.fiducial.mri.nas;
> lpa = standard_mri.hdr.fiducial.mri.lpa;
> rpa = standard_mri.hdr.fiducial.mri.rpa;
> ?
> transm = standard_mri.transform;
> ?
> nas = ft_warp_apply(transm, nas, 'homogenous');
> lpa = ft_warp_apply(transm, lpa, 'homogenous');
> rpa = ft_warp_apply(transm, rpa, 'homogenous');
>
> % create a structure similar to a template set of electrodes
> fid.chanpos = [nas; lpa; rpa]; % mni-coordinates of fiducials
> fid.label = {'Nz','LPA','RPA'}; % same labels as in elec
> fid.unit = 'mm'; % same units as mri
> ?
> % alignment
> cfg = [];
> cfg.method = 'fiducial';???????????
> cfg.template = fid; % see above
> cfg.elec = elec;
> cfg.fiducial = {'Nz', 'LPA', 'RPA'}; % labels of fiducials in fid and in elec
> elec_aligned = ft_electroderealign(cfg);
>
> % plot to check
> figure;
> ft_plot_mesh(standard_bem.bnd(1), 'edgecolor','none','facealpha',0.8,'facecolor',[0.6 0.6 0.8]);
> hold on;
> ft_plot_sens(elec_aligned,'style', 'sk');
>
> For reference, the coordinates I get in the structure fid are the following:
> fid =
>
> ??? chanpos: [3x3 double]
> ????? label: {'Nz'? 'LPA'? 'RPA'}
> ?????? unit: 'mm'
>
> fid.chanpos
>
> ans =
>
> ??? 35?? -36???? 0
> ?? 118?? -35???? 0
> ?? -82?? -35???? 0
>
>
> If those are different from yours, would you let me know? I'm trying to find out at which step I went wrong.
> Again, thank you very much!
>
> Best,
> Helen
>
>
>
>
>
>
>
>
>
>On Mon, Sep 14, 2015 at 11:00 PM, Wu, Jia <jia.wu at yale.edu> wrote:
>
>
>Helen,
>
>
>What a coincident. I'm also working on source analysis on EEG data using GSN HydroCel 128. I had a post a couple weeks ago about later steps. But I did get the alignment to work. The picture you posted looked like the status before the alignment. So i suspect that alignment did not happen.?
>
>
>I'm not sure whether you have noticed it, but the fiducial positions in elec location file were called 'FidNz', 'FidT9', 'FidT10', instead of?'Nz','LPA','RPA' as in the tutorial. So they need to be changed. Then the alignment should work.
>
>
>best,
>-jia
>
>
>
>From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Helen Wieffering [helen.wieffering at gmail.com]
> Sent: Monday, September 14, 2015 4:46 PM
> To: FieldTrip discussion list
> Subject: [FieldTrip] Aligning electrodes to template head model
>
>
>
>
>
>
>
>
>
>Hello all,
>
> I have a quick question on aligning electrodes to the standard_bem headmodel, which I downloaded from the FT server.
>
>
>Namely, are the standard_mri and the standard_bem in the same coordinate system? I assumed this would be so, since one was developed from the other. But when I try to align my electrodes to the standard_bem volume using fiducial positions from the standard_mri, I get very strange results: (image below and attached)
>
> ?
>
> I'm using a GSN HydroCel 128 Cap, and my elec structure contains the fiducial positions relative to the electrodes.
> I've been following the tutorial at http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg and would like to follow the steps under 'Automatic Alignment', but as I said: pulling the fiducial positions from the standard_mri seems to not work with the tutorial steps.
>
> Any help is appreciated - thanks in advance!
>
>
>
>
>Helen Wieffering
>
>Bowdoin College
>
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
>
>_______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
>
>
>_______________________________________________
>fieldtrip mailing list
>fieldtrip at donders.ru.nl
>http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
>[Anhang 'head model.fig' entfernt von Maurice G?ldi/at/UZH]
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>------------------------------
>
>Message: 3
>Date: Thu, 17 Sep 2015 09:43:49 +0200
>From: Darinka Tr?butschek <darinkat87 at gmail.com>
>To: fieldtrip at science.ru.nl
>Subject: [FieldTrip] Neighbors for Elekta Neuromag 306 gradiometers
> separately?
>Message-ID:
> <CAB8a2eJSvgt_MxU9JF4cqX0ML+QP7UWn3-Y7sL_3SnKFBCmdfQ at mail.gmail.com>
>Content-Type: text/plain; charset="utf-8"
>
>Dear Fieldtrip community,
>
>I am new to MEG/fieldtrip and have a question regarding the neighbor
>structure necessary for computing cluster-based statistics. I am currently
>analyzing data from a Neuromag 306 system (with 102 Mags and 204 Grads) and
>would like to look separately at Mags, Grad1, and Grad2.
>I assume that this means that I also need to compute the neighbors
>separately for the different channel types.
>
>My question therefore concerns fieldtrip's standard neighbor templates for
>Neuromag. Is there a specific reason (theoretical or methodological), why
>there are no separate templates for Grad1 and 2? All that I could find are
>separate templates for Mag (neuromag306mag_neighb.mat), the combined planar
>gradients (neuromag306cmb_neighb.mat), and the neuromag306planar_neighb.mat
>template, which, if I understand correctly, does not combine the Grads, but
>still lists sensors of one type as neighbors of sensors of another type
>(e.g., for sensor 0713 - a gradiometer measuring the derivative along the
>longitudinal component, the neighbors listed include 0432, 0723, but also
>sensors that, if I interpret it correctly, should measure the derivative
>along the latitudinal component, such as 0433, 0712, etc.) Is there a
>specific reason, why sometimes, for a given sensor position, both Grad1 and
>Grad2 are included in the neighbors (e.g., 0432 and 0433), but sometimes
>only one of the two (e.g., 0742)?
>
>Many thanks in advance for your help!
>
>Best,
>Darinka
>--
>Darinka Tr?butschek (PhD Candidate)
>
>Inserm-CEA Cognitive Neuroimaging Unit
>CEA/SAC/DSV/DRM/Neurospin
>B?t 145, Point Courier 156
>F-91191 Gif-sur-Yvette
>
>website: https://sites.google.com/site/dtruebutschek/
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>------------------------------
>
>Message: 4
>Date: Thu, 17 Sep 2015 10:09:11 +0200 (CEST)
>From: Sara Aurtenetxe <s.aurtenetxe at bcbl.eu>
>To: smoratti <smoratti at psi.ucm.es>
>Cc: FieldTrip discussion list <fieldtrip at science.ru.nl>
>Subject: Re: [FieldTrip] Leadfield of one condition with two different
> 'grad' structures
>Message-ID: <513570832.104914.1442477351857.JavaMail.zimbra at bcbl.eu>
>Content-Type: text/plain; charset=utf-8
>
>Dear Stephan,
>
>Thank you for your rapid answer.
>
>Indeed, I did measure the coils position.
>This approach seems the most suitable one so
>I will follow it and see how the results look like.
>
>Thank you!
>Best,
>
>Sara
>
>
>
>
>Sara Aurtenetxe
>
>----- Original Message -----
>From: "smoratti" <smoratti at psi.ucm.es>
>To: "FieldTrip discussion list" <fieldtrip at science.ru.nl>
>Cc: "Sara Aurtenetxe" <s.aurtenetxe at bcbl.eu>
>Sent: Wednesday, September 16, 2015 3:57:30 PM
>Subject: Re: [FieldTrip] Leadfield of one condition with two different 'grad' structures
>
>Dear Sara,
>
>Did you measure for each run the HPC coil position in order to determine the relative sensor position with respect to the head? If so, you could calculate the lead field for each run separately, source localize for each run and then collapse the runs after source localization.
>
>Best,
>
>Stephan
>
>
>________________________________________________________
>Stephan Moratti, PhD
>
>see: Stephan's research profile
>
>Universidad Complutense de Madrid
>Facultad de Psicolog?a
>Departamento de Psicolog?a B?sica I
>Campus de Somosaguas
>Despacho (Office) 1326-0
>28223 Pozuelo de Alarc?n (Madrid)
>Spain
>
>and
>
>Center for Biomedical Technology
>Laboratory for Cognitive and Computational Neuroscience
>Parque Cient?fico y Tecnol?gico de la Universidad Politecnica de Madrid
>Campus Montegancedo
>28223 Pozuelo de Alarc?n (Madrid)
>Spain
>
>
>email: smoratti at psi.ucm.es
>Tel.: +34 679219982
>
>El 16/09/2015, a las 15:21, Sara Aurtenetxe escribi?:
>
>> Dear all,
>>
>> I would appreciate to get some advice on the following.
>>
>> I am computing the leadfield (ft_prepare_leadfield) for the subsequent source analysis (ft_sourceanalysis) of ERF data acquired with Elekta Neuromag system.
>> My experiment is acquired in a unique run, including 3 randomized conditions for each participant normally.
>> Therefore, the unique 'cfg.grad' structure is used for the leadfield computation of each participant.
>>
>> However, due to a must, the experiment was recorded into two independent runs (splited) for one of the participants. Here comes the issue:
>> Given that the 'grad' structure is specific to each run, this participant turns to with two different 'grad' structures for the same condition.
>>
>> My question is: which is the most suitable approach to compute the leadfield of one condition when the data comes from two different runs, so when having two different 'grad' structures?
>>
>> I would say that I should compute the leadfield and the sourceanalysis for each run and condition separately, and then join the solutions of the same condition.
>> But I wonder if this is a correct approach and/or if there is any additional/more appropriate approach for that.
>>
>> Any comment will be very appreciated.
>>
>> Thank you in advance.
>> Best,
>>
>> Sara
>>
>>
>>
>>
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>End of fieldtrip Digest, Vol 58, Issue 17
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