Summary

There are three main components of an MR scanner, the main magnet, gradient coils and RF coils. The magnetic fields generated by these components are essential in creating an MR image but they also have certain safety implications.

The main magnet creates a strong static magnetic field, i.e. B0 field, which aligns spins in our body with itself. B0 field effects SNR, resolution and imaging speed. The main safety risk associated with the main magnet is the projectile effect.

Gradient coils create linearly varying gradient fields in three axes. These gradient fields enable spatial encoding and effect image resolution and minimum echo time. The main safety risks associated with gradient coils are nerve stimulation and hearing damage.

Radiofrequency or RF coils transmit and receive RF waves. They enable spin excitation and signal reception and affect flip angle, SAR, SNR and coverage. The main safety risk associated with RF transmit coils is tissue heating.

Implants can pose additional safety risks due to their interaction with all three magnetic fields. These risks include translational and rotational forces applied by the B0 field, increased nerve stimulation, implant malfunction and heating and vibration of the implant due to gradient fields and increased tissue heating due to RF fields. However, several patients with implants can be scanned under stricter safety regulations than usual.

Acknowledgements

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References

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