Safety for Human MR Scanners at 7T

Area of Science:

• Medical Imaging
• Biophysics
• Neuroscience

Background:

• 7 tesla (7T) Magnetic Resonance Imaging (MRI) systems have been pivotal in human MR research for over two decades.
• Two 7T MRI models are approved for clinical use in the U.S.A., with approximately 100 systems globally.

Purpose of the Study:

• To review the safety aspects of 7T MRI systems for clinical applications.
• To discuss potential bioeffects, radiofrequency (RF) exposure, and considerations for metallic implants.

Main Methods:

• Review of existing large-scale studies on bioeffects associated with 7T MRI.
• Analysis of safety concerns related to static magnetic fields, RF excitation, specific absorption rate (SAR), and metallic implants.

Main Results:

• Reported bioeffects include vertigo, dizziness, motion disturbances, and nausea in subjects, and potentially in MR workers.
• Challenges in RF pulse excitation necessitate multi-channel parallel transmit (pTx) systems, which can create hotspots affecting SAR estimation.
• Stronger magnetic fields pose risks with metallic implants due to displacement and heating, generally precluding their use at 7T.

Conclusions:

• Understanding and mitigating adverse effects from static magnetic fields, scan sound, SAR, and metal implants are crucial for reducing safety risks.
• Adherence to safety guidelines and criteria is essential for the responsible implementation of 7T MRI in clinical settings.