Some medical imaging equipment such as a Magnetic Resonance Imaging (MRI) employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. A radiofrequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field. When the radiofrequency field is turned off, the MRI sensors are able to detect the energy released as the protons realign with the magnetic field. The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released, changes depending on the environment and the chemical nature of the molecules. Physicians are able to tell the difference between various types of tissues based on these magnetic properties.

For optimum image quality the very strong magnetic field inside the MRI bore must be maintained to a very stable value throughout the scanning period.

Any object with carrying an electric current may create electromagnetic magnetic interference.  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 interference/fluctuations are produced by the DC current flow in moving metals, moving vehicles, subway or train passages, elevators, battery-based power systems, 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 welding equipment to structural steel during the construction.

AC magnetic interference/fluctuations are commonly occurring at extremely low frequency (ELF) or power frequency (60 HZ).  AC magnetic field interference are commonly contributed to the following sources: Elevated AC magnetic fields are present close to electrical equipment rooms and closets, utility station and transformer vaults, distribution bus ducts, and wire ducts and mechanical equipment.

Vibetech Consultants provides EMI testing using state-of-the-art instrumentation and techniques for a variety of applications.

Instrumentation

The measurement of EMI levels will be performed using Bartington Instruments Spectramag-6 system which is a six channel, 24-bit data acquisition system comprising of both hardware and software, and Mag-03MS1000 triaxial fluxgate magnetometers with field ranges from ±70(±0.7G) to ±1000uT (± 10G) with a resolution down to a few pT.