Magnetic Resonance Imaging Final Review

Vocabulary flashcards to help review key concepts and terms related to Magnetic Resonance Imaging.

Magnetic Field

Region around a magnet or electric current where magnetic forces are observable.

Free-Induction Decay (FID)

Signal emitted by tissue after an RF pulse has excited the nuclear spins of that tissue.

Specific Absorption Rate (SAR)

Power absorbed by tissue during RF irradiation.

Gradient Magnetic Field

Change in the intensity of a magnetic field in space.

Magnetization

Large scale macroscopic magnetic moment resulting from many nuclear magnetic moments.

Pulse Sequence

Series of radiowave pulses designed to excite nuclei in a specific manner.

Spin Density

Concentration of nuclei in tissue precessing at the Larmor frequency contributing to the MRI signal.

T1 Relaxation Time

Time required for the interaction between nuclear spins and the tissue lattice to return to normal after RF excitation.

T2 Relaxation Time

Time required for the interaction between nuclear spins to return to normal following RF excitation.

Voxel

3D volumetric portion of an image where viewing face is the pixel.

Contrast Resolution

Ability of an imaging process to distinguish adjacent soft tissues from one another.

Aliasing

Artificial wraparound image caused by misregistration of a higher frequency component.

Spin Echo (SE)

Technique using a 90° excitation pulse followed by a 180° refocusing pulse to generate echoes.

Gradient Echo (GRE)

Technique relying on gradients to form echoes instead of 180° refocusing pulses.

Fringe Field

Portion of the magnetic field extending away from the confines of the magnet.

Gating

Technique to synchronize imaging with physiological cycles like heartbeats or breathing.

Dixon Technique

MRI sequence exploiting the chemical shift difference between water and fat protons.

Shimming

Process of making the magnetic field homogeneous.

Surface Coils

Type of receive-only RF coil used in MRI for localized body regions.

Spin Density Weighted Scan

Scan where signal change comes from differences in the amount of available spins.

Fourier Transform

Mathematical operation relating number and positions of spatial features to their occurrence frequency.