Dear Jukka et al.,
Very rarely, we experience the following problem with files recorded with continuous HPI on our Triux (see attached image).
On a few channels (in this case just the one shown in figure: 0322), turning the HPI on induces a strong oscillation. In this case the oscillation is at ~7 Hz, i.e., visible with the default 40 Hz lowpass setting. Needless to say, MaxFilter does not deal well with this...
I would like to hear if you have a suggestion as to what might be going wrong here? The data was collected with 60 EEG channels turned on, but no cap was attached due to large head size (user forgot to disable the EEG channels, which are set active by default). I've seen this clearly once before (oscillations at ~33 Hz): In this case the cap was attached, but only 19/60 electrodes attached (all recorded, due to an interface-issue with Curry). Most recordings, however, work out just fine even with the 19/60 setup. We use standard coil frequencies, sampling rate (1 kHz) and anti-aliasing filter cutoff (330 Hz).
I hope you can help me debug this problem! I've placed an example data file at:
http://dl.dropbox.com/u/14937634/Elekta/Session1.tar.gz
Let me know if there are any tests I can/should run.
Best,
Chris
[cid:B139421A-6046-4F2C-A3FF-76C2ED6F5C2A@akh06.auh.dk]
--
Christopher Bailey, MSc
MEG Engineer, MINDLab Core Experimental Facility
Center of Functionally Integrative Neuroscience (CFIN)
Aarhus University, Denmark
tel. cell: +45-2674-9927
tel. office: +45-7846-9944
|