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Fringe (stray) Field
•
Scanner ‘footprint’
Credit cards erased at 10 G
Safety limit is ‘five gauss line’
•
7 Tesla scanner has 23 m
5 G line
> 30 G Stainless steel, non-
ferromagnetic objects
< 30 G ECG monitors,
unrestrained
ferromagnetic objects
< 10 G Credit cards, x-ray tubes
Passive & Active shielding
•
Radial & axial components
Typically axial 1.6 times larger
•
May be measured with
handheld gaussmeter
< 5 G Pacemakers, general
public
< 3 G Moving cars etc
< 1 G TVs, CT & PET scanners
< 0.5 G Railways, gamma
cameras