[visionlist] Shielded display for MR environment

[Alex Wade]

A while ago I asked for suggestions on building a shielded display 
screen for displaying video stimuli to subjects in an MRI scanner. Many 
thanks to everyone who responded.

We have completed this project and are very happy with the final 
product. I thought that the vision community might be interested in the 
device we finally ended up with - particularly as the machine shop that 
built it for us has offered to make more at a reasonable cost.

The display is built around a commercial 32" Westinghouse LCD device 
available at BestBuy :

http://www.bestbuy.com/site/olspage.jsp?skuId=6998396&type=product&id=1110265591303

It can be driven by a VGA signal as well as composite video and DVI. The 
nominal refresh rate is 60Hz. We measure a full contrast rise time of 
about 10ms and a fall time of about 16ms. We have not yet measured the 
homogeneity of the screen in a precise manner but it appears 'flat' to 
the naked eye and to spot measurements with a photometer. There are no 
'gun additivity' errors:  the luminance of a white patch is equal to the 
sum of the luminances of the individual red, green and blue components 
in isolation.

The device is enclosed in a custom-built aluminum enclosure. I/O happens 
through two shielded conduits at the back: shielded cables can be coiled 
around a spiral 'maze' before entering the box which reduces RF noise 
leakage. The front of the box is made of conductive glass.

We have tested the display in an MR environment (3T GE Signa scanner) 
and it generates no detectable noise.

Photos are available here:
http://darwin.ski.org/misc/box1.jpg
http://darwin.ski.org/misc/box2.jpg
http://darwin.ski.org/misc/box3.jpg

If you would like more details, please contact me and I can put you in 
touch with the supplier.

Best wishes


Alex

A.R. Wade Ph.D.
Associate Scientist
Brain Imaging Center
The Smith-Kettlewell Eye Research Institute
2318 Fillmore Street
San Francisco, CA 94115

tel. 415 345 2083
fax. 309 416 6533