MRI Lecture Notes Flashcards

Underlying Physical Principles of MRI

• Signal Generation:
  • The MRI system generates signals using a combination of magnetic fields and radiofrequency pulses.
  • These signals are primarily produced from hydrogen nuclei in the body’s water molecules.
• Introduction to Weightings:
  • Different sequences and settings affect image contrast based on T1, T2, and Proton Density (PD).
  • T1-weighted images show fat as bright and water as dark, while T2-weighted images depict water as bright and fat as dark.

Basics of MRI Equipment

• Core Components:
  • Magnet: Establishes a static magnetic field (B0).
  • Radiofrequency (RF) Coil: Used for transmitting and receiving RF signals.
  • Gradient Coils: Adjust the magnetic field to localize signals spatially.
• Safety Precautions:
  • Training is essential for handling equipment and ensuring patient safety.

MRI Signal Detection

• Gradients:
  • Variations in magnetic field strength (B0) allow for spatial localization of signals.
  • Three types of gradient coils based on imaging axis: X, Y, and Z.
• Slice Selection:
  • Uses RF excitation pulses targeted at specific areas, defined by RF amplitude and bandwidth.

Image Reconstruction in K-Space

• K-Space:
  • Matrix storing raw data from MRI, used to reconstruct images via Fourier transformation.
  • Center of k-space holds information on tissue contrast; periphery contains spatial resolution details.
• Echo Events:
  • Signals acquired during imaging cycles are encoded in terms of frequency and phase.

Pulse Sequences

• Fundamental Types:
  • Spin Echo and Gradient Echo are the primary pulse sequences used in MRI to acquire images.
• TR (Repetition Time) and TE (Echo Time):
  • Adjusting these parameters alters contrast, e.g., short vs. long TR or TE influences T1 and T2 contrast.

Relaxation Time and Image Contrast

• T1 and T2 Relaxation:
  • T1: Time for longitudinal magnetization recovery after RF pulse.
  • T2: Time for transverse magnetization decay.
• Adjusting TR and TE:
  • Short TR emphasizes T1 effects, while long TE focuses on T2 effects.

MRI Safety

• Hazards:
  • Direct (e.g., projectile effects of ferromagnetic objects) and indirect hazards (e.g., RF radiation).
  • Proper labelling and training are essential to mitigate risks associated with MRI operation.
• Control Measures:
  • Authorized personnel and routine safety checks are necessary within MRI environments.

Equipment and Patient Management

• Clinical Protocols:
  • MRI operators should conduct thorough screening of patients, particularly those with implanted medical devices.
  • Emergency procedures need to be established for quick patient removal if necessary.

Legislation and Guidelines

• Safety Regulations:
  • There are various guidelines provided by bodies such as the MHRA, ICNIRP, and IEC, which focus on the safety of MRI environments and equipment handling.