Magnetic Shielding

Magnetic shielding may be necessary to limit the fringe field of the MRI magnet at certain sites or to comply with health and safety regulations.

For the safety of people in the general vicinity of an MRI magnet, a controlled area is usually declared as defined by the 0.5 mT (5 Gauss) line. Magnetic fields higher than 0.5 mT should not be exceeded in a public area. Barriers, access control doors, warning signs and facilities for the safe keeping of watches, credit cards and other magnetically sensitive objects must be provided.

Further reduction of the fringe fields to 0.1 mT or even 0.05 mT (less than 1 Gauss) may be necessary to safeguard the performance of sensitive equipment such as computer monitors, image amplifiers and other medical equipment, etc. or to satisfy local regulations. For comparison, the magnetic field strength of the earth is approximately 0.04 mT (0.4 Gauss).

IMEDCO has experience in calculating, simulating, designing, producing and installing magnetic shields up to 600 tons of iron mass.

IMEDCO has developed a special technique for magnetic shielding. The shielding necessary for a particular project is designed at the works and the parts are prefabricated. On site, the sheet metal shielding panels are mounted on a strip metal frame on the walls or the concrete ceiling. This procedure shortens the installation time and achieves an accurately assembled shield. The required thickness is built up by fitting several layers of panels which are rolled and also overlap in the direction of the flux. The overlapping of the panels and the pressure applied at the points of contacts ensure a homogeneous shielding effect which has a positive influence on the homogeneity of the MRI field.

We develop and manufacture magnetic shielding for special applications such as attenuating fields generated by the 50/60 Hz public power supply or DC or 16 ⅔ Hz railway supply systems etc. Nickel-iron alloys are used where the maximum attenuation in a wide frequency range is required.

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