Robert,
we built a wooden box covered with copper foil, with the top and one side
covered with copper mesh. the projector lens projects through a bazooka of
copper mesh attached to the front of the box. We split the VGA signal at the
point of the penetration panel into 5 coax lines, and then run those back into
the box through BNC connections. Our initial testing has not shown any RF
artifacts on our EPI images, whereas the projector without a shield resulted in
significant artifacts. You should be sure to use an RF-filtered power line
feedthrough on the box as well.
Some people have encountered artifacts even after enclosing their projector in
a box like I have described. if that happens, the next solution is to move to
fiber optical transmission of the VGA signal. That's substantially more costly
but will eliminate artifacts (which probably occur because the bandwidth of
1024X768 video signal is very near the sampling frequency of a 1.5T MR
scanner).
cheers,
russ
"Ogg, Robert" wrote:
> We are presenting visual stimuli during fMRI with an lcd projector. With
> the projector in the 'room', we get a lot of interference with the scanner
> (Siemens Vision, iron shielding). Can anyone provide design details for a
> projector enclosure that provides adequate rf shielding with minimal optical
> interference?
>
> Thanks,
>
> Robert J. Ogg, Ph.D.
> St. Jude Children's Research Hospital
> tel: 901-495-2502 fax: 901-495-4398
> email: [log in to unmask]
--
Russell A. Poldrack, Ph. D.
Assistant Professor of Radiology, Harvard Medical School
MGH-NMR Center
Building 149, 13th St.
Charlestown, MA 02129
Phone: 617-726-4060
FAX: 617-726-7422
Email: [log in to unmask]
Web Page: http://www.nmr.mgh.harvard.edu/~poldrack
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