MRI Safety Training Overview

Importance of Safety Regulations

• Accidents can occur in MRI systems if safety regulations are ignored.
• Safety training is mandatory for all personnel entering the MR environment to ensure safety for both personnel and patients.

Video Content Overview

• Basic Safety Precautions: Introduction to safety measures when using MRI systems.
• Understanding Magnets: Different types of magnets and their effects.
• Magnetic Field Strength: Demonstration of field strength and dangers with magnetic objects.
• Patient Preparation: Guidelines on how to prepare patients for the examination.
• Surface Coils Handling: Proper handling techniques for MRI coils.
• Emergency Examples: Illustrates potential accidents and appropriate response measures.
• This video supplements a more comprehensive safety training program.
• For detailed MR safety-related information, refer to the Siemens MR System and Operating Instruction Manuals.

Introduction to MRI

• Definition: MRI is a diagnostic method for generating cross-sectional images of the body.
• Principles of MRI: Based on interaction between the human body and externally generated magnetic fields.
• Comparison with CT: MRI does not use ionizing x-rays but employs static and varying magnetic fields.

Physical Principles of MRI

• Magnetic Field Generation: Patients are placed in a static magnetic field produced by a cylindrical magnet.
• Tesla Strength: Typical for human imaging: 0.2T to 3T; Earth’s magnetic field is ~0.00005T.
  • A 1.5T magnet's field is 30,000 times stronger than Earth’s.

Role of Protons in MRI

• Hydrogen Nuclei: The human body is approximately 75% water; therefore, hydrogen nuclei (protons) are the most used in MRI.
• Proton Alignment: Protons align with the main magnetic field and are disrupted by alternating magnetic fields.
• Frequency: For 1.5T field, the frequency is about 63 MHz (radio wave range).

MRI Signal Generation

• Transmitting Coil: Generates the alternating magnetic field in the examination area, exciting protons.
• Receiver Coils: Detect the emitted electromagnetic waves as protons return to equilibrium.
• Gradient Fields: Varying fields that help correlate MR signals to specific locations in the body.
• Computer Analysis: Generates images based on proton distribution.

Patient Experience during MRI

• Magnetic Fields Exposure: Patients are subjected to three types of fields:
  1. Static main magnetic field (aligns protons)
  2. High-frequency alternating fields (disrupts alignment)
  3. Pulse gradient fields (correlates MR signals to locations)
• Noise Levels: Generated by rapidly switched gradient fields; mitigated by audio comfort features. Hearing protection is recommended.
• Harmless Voltages: May be induced in peripheral nerves causing tingling; safety devices prevent excessive stimulation.
• Localized Warmth: RF energy absorbed by the body; controlled to prevent overheating (specific Absorption Rate - SAR).

Types of MRI Magnets

• Permanent Magnets: Always on, cannot be switched off in emergencies, limited field strength.
• Resistive Magnets: Can be turned off, generate heat requiring cooling; less common due to low field strengths.
• Superconducting Magnets: Common in clinical imaging, use liquid helium for cooling; can operate without external power once superconductivity is established.

Magnet Safety and Control Areas

• Fringe Field: Use of magnetizable objects near the MRI system is prohibited due to the attractive forces.
• Safety Zones: Control areas must be clearly marked; established based on the 0.5 mT fringe field line, which differs by system.
  • Example: A 1.5T system has its 0.5 mT line at 4m from the magnet center.