MRI Instrumentation

MRI Instrumentation

GE MRI System Components

  • Magneto

    • Aligns the nuclei of atoms inside the magnetic field.

    • Causes nuclear magnetic resonance (NMR).

  • Gradient Coils

    • Precisely positioned conductive coils that deliberately vary the magnetic field.

  • Radio Frequency Coil

    • Transmits and receives radiofrequency (RF) signals in the body.

  • System Process

    • High performance electronics and computer.

  • Patient Table

    • Supports and transfers patient for imaging examination.

Introduction to MRI

Basics of Magnetism

  • Content Overview

    • Fringe field, Shim coil, Gradient coil, Radiofrequency coil.

    • Types of RF-coil, MR computer systems, and the user interface.

Magnetic Resonance Imaging (MRI)

  • MRI is a non-invasive imaging technique producing diagnostic images without ionizing radiation.

  • The scanner is essentially a large, strong magnet.

  • RF signals are transmitted to and received from the body to generate images.

  • Any body part can be imaged using various planes.

MRI Process Breakdown

Key Processes in MRI

  1. Nuclear Alignment

  2. Radio Frequency Excitation

  3. Spatial Encoding

  4. Image Formation

Required Hardware

  • MRI Scanner

  • Gradient Magnets

  • Transceiver

  • Radiofrequency Coils

  • Computer System for image processing and user interface.

Magnetic Properties of Matter

Types of Magnetic Susceptibility

  • Diamagnetism

    • Pair of electrons; no net magnetic moment.

    • Substances: Lead, Copper, Water.

  • Paramagnetism

    • Unpaired electrons create a small magnetic moment.

    • Substances: Tungsten, Gadolinium chelates.

  • Superparamagnetism

    • Intermediate positive magnetic susceptibility.

    • Example: Iron oxide particles.

  • Ferromagnetism

    • Half-filled electron shells lead to strong attraction and alignment in a magnetic field.

    • Materials: Iron, Steel.

Magnetic Field and Shielding

Inhomogeneity and Homogeneity

  • A homogenous magnetic field is essential for uniform proton response.

  • Inhomogeneity can cause image distortions.

Magnetic Shielding

  1. Passive Shielding

  • Surrounds the magnet with steel plates to maintain field integrity.

  1. Active Shielding

  • Uses additional solenoid electromagnets to reduce fringe field size.

Gradient Coils

Functions of Gradient Coils

  • Enhances imaging capabilities by creating secondary magnetic fields that allow localization of images.

  • Helps with slice selection, phase encoding, and frequency encoding.

Types of Gradient Coils

  • Z-gradient (Maxwell coil configuration)

  • Y-gradient (double-saddle configuration)

Radiofrequency (RF) Coils

Types

  • Surface Coil

    • Positioned closely over specific areas; limited area of sensitivity.

  • Volume Coil

    • Transmit and receives MR signals, covering entire regions.

  • Phased Array Coil

    • Consists of multiple coils for improved SNR and coverage.

Functions of RF Coils

  • RF transmitters create RF pulses which excite nuclei, allowing imaging.

  • RF receivers detect the MR signal, converting it for image formation.

MRI Computer Systems

Components

  • Consist of a minicomputer with expansion capabilities, pulse control units, image processors, and operator console.

Conclusion

  • MRI relies on a complex integration of hardware components to produce detailed images safely and effectively.