Magnetic
Resonance Imaging relies upon the excitation and detection of resonances at radio
frequencies of atomic nuclei within the cells of the human body. For optimum image
quality this is performed in a very strong magnetic field which must be maintained
to a very stable value -throughout the scanning period. Any object with carrying
an electric current create magnetic fields. Depending on the source of the field,
a magnetic field’s strength and direction can be static (direct current, DC) or
alternating (alternating current, AC).
DC magnetic fields are produced by the:
• Earth total magnetic field as a background DC field
• DC current flow in moving metals, vehicles, subways, trains, and elevators
• Powerful magnets associated with MRI and NMR units
• Structural and reinforcing steel which may have been magnetized by presence of
permanent magnets inside the building or exposed to strong DC currents during the
construction, such as by grounding the welding equipment to structural steel during
the construction
AC magnetic fields, commonly occuring at
extremely low frequency (ELF) or power frequency (60 HZ) are contributed to the
following sources:
• Elevated AC magnetic fields are present near electrical equipment rooms,
utility station and transformer vaults, distribution bus and wire ducts.
• Transmission and distribution lines passing near the exterior of a building
• Wiring errors such as improper ground to neutral connections, in a building’s
AC power system, can cause substantial ELF magnetic field conditions to exist in
large areas of the building.
Vibetech Consultants provide Electromagnetic Interference (EMI) testing using state-of-the-art
instrumentation and techniques. EMI test results are used to determine whether EMI
levels are acceptable
for installation of different types of MRI systems.
Vibetech Consultants staff has successfully completed more than 100 EMI testing
projects in the United States.
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