[Eeglablist] Antw: Re: Question about helium-pump artifact of EEG

[Gregor Volberg]

Dear Helen,
 
indeed we switched off the pump manually. The system at our scanner constantly monitors the temperature and would stop scanning if it gets critical, so there were no safety concerns during scanning. The important thing is that you do not forget to switch on the pump again _after_ scanning in order to avoid damage to the machine. Our Siemens partner told us that even 24 hours without cooling would be OK with our system, but it is of course necessary to check this point with the local  technician at your place, and with the technical support team of your scanner manufacturer.
 
Best regards,
Gregor  

 
-- 
Dr. rer. nat. Gregor Volberg <gregor.volberg at psychologie.uni-regensburg.de> ( mailto:gregor.volberg at psychologie.uni-regensburg.de )
University of Regensburg
Institute for Experimental Psychology
93040 Regensburg, Germany
Tel: +49 941 943 3862 
Fax: +49 941 943 3233
http://www.psychologie.uni-regensburg.de/Greenlee/team/volberg/volberg.html
>>> Helen Juan Zhou <zhoujuan227 at gmail.com> 16.01.2013 04:02 >>>
Dear Gregor,
Thank you very much for your reply. It is helpful to know that you can turn it off. We did not do it due to safety concerns. May I know how your team manage it, any additional measures to make sure the helium pump been turned on in time?
Thanks a lot!
Best regards,
Helen

On Wed, Jan 16, 2013 at 5:11 AM, Gregor Volberg <Gregor.Volberg at psychologie.uni-regensburg.de> wrote:


Dear Helen,
this will not be of much help for your current data set I fear, but this is how we did it: On a Siemens Allegra 3T, we simply turned off the helium pump during the EEG acquisition. We could leave it off for 1.5 hours without doing harm to the scanner. Of course, we checked this beforehand with the Siemens technician...
This was the only way to avoid the pump artifact. At least at our system, the pump works with a heat sensor. Thus, the pump interval and the load is not constant and produces an artifact that is not well defined in terms of frequency or amplitude. 
Best wishes for your data analysis, anyway. Gregor




-- 
Dr. rer. nat. Gregor Volberg <gregor.volberg at psychologie.uni-regensburg.de> ( mailto:gregor.volberg at psychologie.uni-regensburg.de )
University of Regensburg
Institute for Experimental Psychology
93040 Regensburg, Germany
Tel: +49 941 943 3862 ( tel:%2B49%20941%20943%203862 ) 
Fax: +49 941 943 3233 ( tel:%2B49%20941%20943%203233 )
http://www.psychologie.uni-regensburg.de/Greenlee/team/volberg/volberg.html
>>> Helen Juan Zhou <zhoujuan227 at gmail.com> 15.01.2013 10:06 >>>
Dear All,

My group is working on some eeg data recorded simultaneously during fMRI
scanning and it has been contaminated with helium pump (HP) artifacts. 
The HP noise in our data has a significant peak around 35 Hz in power
spectrum, however, its harmonics have also contaminated the eeg signal
in other frequencies. Anyone know how to remove the HP artifacts from EEG effectively?

We have tried to remove this noise using ICA, however, most of ICs seem to contain HP
harmonics pattern (based on visual inspection of ICs power spectrum). Therefore, I have a concern that removing all of these ICs (with peak around 35 Hz) may lose other informative part of data.


Appreciate any advice, comment or suggestions.

Thank you and best regards,
Helen Juan Zhou

Helen Juan Zhou, Ph.D.
Assistant Professor/Principal Investigator
Neuroscience and Behavioral Disorders Program
Duke-NUS Graduate Medical School, Singapore
8 College Road, #06-33, Singapore 169857 Tel: (65) 66012392 Fax: (65) 62218685
Email: helen.zhou at duke-nus.edu.sg ( https://mail.google.com/mail/u/0/html/compose/static_files/helen.zhou@duke-nus.edu.sg ) Website:https://sites.google.com/site/mneuroimaginglab/ <https://sites.google.com/site/mneuroimaginglab/> 






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