MAGNETIC-RESONANCE-IMAGING-3-1

Magnetic Resonance Imaging

A medical imaging technique that uses strong magnetic fields, magnetic field gradients, and radio waves to generate detailed images of the organs and tissues in the body.

Historical Development of Magnetic Resonance Imaging

The timeline of key events and discoveries leading to the invention and advancement of MRI technology, including the contributions of notable figures like Raymond Damadian and Paul C. Lauterbur.

Magnet

A material or object that produces a magnetic field, exerting a force on other ferromagnetic materials and attracting or repelling other magnets.

Magnetic Field

A vector field describing the magnetic influence on moving electric charges, electric currents, and magnetic materials, created by electric currents and varying electric fields.

Atomic Nucleus

The small, dense region at the center of an atom consisting of protons and neutrons, discovered by Ernest Rutherford in 1911.

Proton Spin

A quantum-mechanical property of protons, akin to angular momentum, with a spin of ħ/2.

Radiofrequency

A medical procedure involving the ablation of tissue using heat generated from medium-frequency alternating current.

Types of Magnets Used in MRI

Permanent magnets, resistive magnets, and superconducting magnets, each with specific characteristics and applications in MRI technology.

T2 Relaxation Time

The time constant determining the rate at which excited protons reach equilibrium or lose phase coherence in MRI.

Gyromagnetic Ratio

The ratio of magnetic momentum to angular momentum in a particle, crucial in NMR and MRI technology.

Magnetic Momentum

A measure of the torque exerted on a magnetic system in a magnetic field, related to the distance between poles and pole strength.

Angular Momentum

The velocity of rotation around an axis, important in stabilizing rotational movement in systems like gyroscopes.

Resonance

A phenomenon where a body vibrates with amplitude when an externally applied periodic force matches its natural frequency.

Radiofrequency Fields

Critical for nuclear excitation and signal reception in MRI, playing a key role in the imaging process.

Larmor Frequency

The frequency at which a nucleus precesses in the magnetic field. Unit:MHz

Net Magnetization

The large-scale macroscopic magnetic moment resulting from many nuclear magnetic moments.

Antenna

Device for transmitting or receiving radio waves.

Artifacts

Spurious finding in or distortion of an image.

Attenuation

Reduction in energy or amount of a beam of radiation when it passes through tissue or other substances.

Coil

Single or multiple loops of wire designed to produce a magnetic field from the current flowing through the wire.

Cryogenic

Relating to extremely low temperature.

Diffusion

Spontaneous random motion of molecules in a medium.

Fat Suppressed Images

Fat tissue in the image is made to be of lower, darker signal intensity.

Free Induction Decay

Signal emitted by tissue after RF excitation.

Gating

Technique used in reducing motion artifacts.

Gradient Echo

Fast pulse sequence often used with 3D imaging to generate T2 weighted images.

Gradient Magnetic Field

A change in the intensity of a magnetic field in space. Unit:mT/cm

Gyromagnetic Ratio

A constant, specific ratio for each nucleus. Unit:MHz/T

Inverse Recovery

Standard pulse sequence available in most MRI imagers used for T1-weighted images.

Magnetic Moment

A force is created when the magnetic dipole is in a magnetic field. Unit:T

Magnetization

The large-scale macroscopic magnetic moment resulting from many nuclear magnetic moments.

Perfusion

Flow of blood through vessels of an organ or anatomic structure.

Precession

The wobble of the rotational axis of a spinning body about a stationary axis.

Radiofrequency (RF)

Electromagnetic radiation with frequencies from 8.3kHz to 300 GHz. RF range in MRI:1-100 MHz.

Relaxation

Returning to equilibrium.

Relaxation Time

The time required for return.

Resonance

Transfer of vibrating energy from one system to another.

Specific Absorption Rate (SAR)

The power absorbed during RF irradiation. Unit:W/kg

Spin Density (SD)

Concentration of hydrogen nuclei in tissue, principal determinants of MRI signal.

T1 Relaxation Time

Longitudinal relaxation time, decrease in signal:63% of maximum value.

T2 Relaxation Time

Transverse relaxation time, decrease in signal:37% of saturated fat.

Image Quality

Brightness, hyperintense, hypointense, isointense. Factors affecting image quality:Field Strength, Section Thickness, Imaging Parameters, Motion (temporal resolution), Spatial Resolution, Signal-to-Noise Ratio (S/N).

Gadolinium

Metal with a paramagnetic effect, used as a contrast medium in MRI scans.

Teslascan

A new manganese-based paramagnetic liver contrast agent used for imaging liver lesions.

Feridex

An iron oxide mixture used as a contrast agent to detect and diagnose liver lesions.

Gating

Technique used in MRI to organize the signal, improve image quality, and reduce motion artifacts.

Proton Density

Quantity of resonating spins in tissue, affecting image contrast in MRI.

T1 Spin-Lattice Relaxation Time

Time required for magnetic moments to realign after RF excitation in MRI.

T2 Spin-Spin Relaxation Time

Time for precessing spins to lose coherence in MRI.

Repetition Time (TR)

Time interval between pulse sequences in MRI.

Echo Time (TE)

Time between a 90° pulse and the echo in MRI.

Inversion Time (TI)

Time in an inversion recovery pulse sequence in MRI.

Flip Angle (FA)

Angle of inclination from the longitudinal axis in MRI.

Image Artifact

Structure not normally present visible due to hardware limitations or malfunctions.

Magic Angle Artifact

Bright signal in tendons due to a specific angle to the main magnetic field.

Partial Volume Artifact

Loss of contrast between adjacent tissues due to insufficient resolution.

Metal Artifact

Signal dropouts and spatial distortion due to metal in MRI.

Motion Artifact

Blurring and ghosting in images due to movement of the imaged object.

Herringbone Artifact

Static on the image due to electromagnetic emissions.

RF Overflow/Data Clipping Artifact

Image non-uniformity due to intense signal in MRI.

Shading Artifact

Localized inhomogeneous brightness in MRI images.

Slice Overlap Artifact

Loss of signal due to overlapping slices in MRI.

Staircase Artifact

Staircase-like nuance in images due to thick slices or lack of overlap.

Aliasing Artifact

Image wrapping around due to anatomy extending out of the field of view in MRI.

MRI Contraindications

List of conditions or devices that are contraindicated for MRI scans.

MRI vs Conventional Radiography

Comparison of MRI and conventional radiography in terms of imaging capabilities.