(G) An older unit of flux density. The currently preferred SI unit is the tesla (T).
Definition: 1 gauss is defined as 1 line of flux per cm². The Earth's magnetic field is approximately one half gauss to one gauss, depending on location. For the large magnetic fields used by MRI, the unit gauss (G) has been replaced by the more practical unit tesla (T), where 1 T = 10 000 G.

This line specifies the perimeter around a MR scanner within which the static magnetic fields are higher than five gauss. Five gauss and below are considered 'safe' levels of static magnetic field exposure for the general public.
Portable devices requiring a separation distance between the device and the MR magnet, should not be considered 'MR Safe', 'MR Compatible', or intended for use in the MR environment. Typically the 5 gauss line is the only location where the static magnetic field strength is specified around a MR scanner. Therefore, labeling specifying a separation distance between the MR magnet and the device to ensure safe or proper operation of the device should be avoided.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'

The national regulatory boards decided to limit the threshold for access to MRI areas to 5 gauss.

It is of special interest for the observer of bureaucratic procedures that the 5 gauss safety limit is ten times higher than the average earth magnetic field, but lower than the magnetic field in electric trains such as subways (up to 7 gauss). For example, the fields measured on the surface of the receiver of a telephone are 35 gauss and of an audio headset 100 gauss.

Noise distributed in a normal (Gaussian) pattern. In such a distribution, approximately 65% of all points fall within one standard deviation (s) of the mean.

A line shape characterized by a bell-shaped form; proportional to exp (-(f - f0)2/Df2) where Df is a measure of the line width.