Magnetic Resonance Imaging Terms and Concepts

These flashcards cover key terms and concepts in Magnetic Resonance Imaging, focusing on definitions essential for understanding the subject.

Magnetic Resonance Imaging (MRI)

A non-invasive imaging technology that produces three-dimensional detailed anatomical images.

Tesla (T)

The unit of measurement for magnetic field strength.

Free-Induction Decay (FID)

The signal emitted by tissue after an RF pulse has excited the nuclear spins of that tissue at resonance.

Gradient Magnetic Field

A change in the intensity of a magnetic field in space.

Specific Absorption Rate (SAR)

The power absorbed by tissue during RF irradiation.

Pulse Sequence

A series of radiowave pulses designed to excite nuclei in a way that their energy release has varying contributions from T1 or T2 processes.

Gating

A technique used to synchronize imaging processes with the patient’s physiological cycles.

Voxel

A 3D volumetric portion of an image where the viewing face is the pixel and whose depth is the third dimension.

Spin Echo (SE)

An MRI sequence that uses a 90° excitation pulse followed by a 180° refocusing pulse to generate echoes.

T1 Relaxation Time

The time required for net magnetization to return to its initial maximum value parallel to the main magnetic field.

T2 Relaxation Time

The time required for the interaction between nuclear spins and adjacent spins to return to normal following RF excitation.

Aliasing

An artificial wraparound image caused by misregistration of higher frequency components posted in lower frequency areas.

Contrast Resolution

The ability of an imaging process to distinguish adjacent soft tissues from one another; a principal advantage of MRI.

Spin Density (SD)

The concentration of nuclei in tissue that contributes to the MRI signal.

Fat Suppression

Techniques used to reduce or eliminate the signal from fat in MRI images to improve visibility of other tissues.

Dixon Method

An MRI sequence that exploits the chemical shift difference between water and fat protons.

Helmholtz Coil

A device consisting of two identical circular coils placed symmetrically to create a nearly uniform magnetic field.

Signal-to-Noise Ratio (SNR)

A measure used to quantify how much a signal has been corrupted by noise, crucial for image quality in MRI.

Gradient Coils

Coils that produce a gradient magnetic field within the MRI system, essential for spatial encoding and slice selection.

Gradient Echo (GRE)

An MRI sequence that relies on gradients for imaging, allowing for faster imaging compared to spin echo sequences.

Aliasing

An artifact in imaging that occurs when a signal is sampled at a frequency lower than twice its highest frequency.

Contrast Agent

A substance used to enhance the contrast of structures or fluids within the body in medical imaging.

Nuclear Magnetic Resonance (NMR) Spectrum

A plot that results from a Fourier transformation of the FID, showing the different frequencies and intensities of the signals detected.

Fringe Field

The portion of the magnetic field that extends away from the confines of the magnet, which can affect nearby equipment or personnel.