[Eeglablist] CTF MEG data import

[Darren Weber]

Hi Andrey,

I have taken responsibility to develop the ctf matlab functions, available in the ctf module of the cvs repository at eeg.sf.net.  These functions are the CTF plugin for EEGLAB.

http://eeg.sourceforge.net/
http://cvs.sourceforge.net/viewcvs.py/eeg/ctf/#dirlist

In this instance, the ctf_read_res4 function can read the reference sensor coefficients.  Sarang Dalal programmed this functionality; he is a PhD student at UCSF, working with Srikantan Nagarajan, and he develops the nutmeg toolbox.  We should consult with Sarang on this issue. As I understand it, these coefficients are being used to calculate the forward solution (or lead field) for nutmeg.  However, we have always used the ctf software to first apply synthetic gradient corrections (2nd, 3rd order gradients).  In the system at UCSF, there are 275 radial gradiometers and about 32 reference channels (about 20+ cm from the head sensors).  The ctf matlab functions should provide easy ways to select channels, see

http://cvs.sourceforge.net/viewcvs.py/eeg/ctf/ctf_channel_select.m?rev=1.9&view=log

So, the short answer to your question is:

The functions do not calculate higher-order synthetic gradiometer corrections.  It should be possible to program this, but time is not on my side :-(  Please follow-up with myself and Sarang and we can discuss options for your work.  If you have or you can get the ctf LINUX programs, I recommend you take a look at newDs and the process.cfg file inside the *.ds/ folders.

Take care, Darren


On Wed, 14 Dec 2005 18:34:03 +0200
 zhdanova at post.tau.ac.il wrote:
>Hi everybody.
>I am working on MEG data from CTF machine recorded at another facility (we do
>not have our own MEG :-(. I am not familiar with all the details of MEG
>acquisition process, but as far as I know there are a couple of external
>sensors located throughout the MEG room that record environment noise for the
>purpose of noise cancellation in the MEG signal.
>
>I use CTF_READ to read the MEG data. My question is whether the values returned
>by CTF_READ are already corrected for the environment noise measured by these
>external sensors? Does this have anything to do with the COEFS parameter?
>Thanks,
>
>Andrey Zhdanov,
>Research Student,
>Wohl Advanced Imaging Institute,
>Tel Aviv Sourasky Medical Center
>
>
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