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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.