MRI Image Contrast & Advanced Sequences

Vocabulary flashcards reviewing MRI image contrast fundamentals, pulse sequences, fat-suppression methods, diffusion and susceptibility imaging, key parameters, artifacts and useful mnemonics.

Image Contrast (MRI)

Visual differences between tissues produced by varying T1 and T2 relaxation, proton density, diffusion, susceptibility, flow, perfusion and related factors.

T1-Weighted Image

MRI sequence with short TR/TE where fat and white matter appear bright, CSF dark; best for anatomy and post-contrast studies.

T2-Weighted Image

Sequence with long TR/TE where CSF and fluid are bright, white matter dark; preferred for detecting pathology.

Proton Density (PD)-Weighted Image

Long TR + short TE sequence emphasising hydrogen concentration; useful for white-matter lesions and MSK imaging.

FLAIR (Fluid-Attenuated Inversion Recovery)

Inversion-recovery sequence that nulls CSF, making lesions adjacent to fluid more conspicuous.

Fat Saturation (FS)

Generic term for techniques that suppress fat signal to enhance lesion conspicuity or reduce artifacts.

Spin Echo (SE)

Pulse sequence using 90° excitation plus 180° refocusing to generate true T2 contrast and correct inhomogeneity effects.

Gradient Echo (GE)

Sequence with <90° excitation and gradient reversal instead of 180° pulse, producing T2* contrast and rapid scans.

Echo Time (TE)

Interval from RF excitation to the centre of the measured echo; controls the degree of T2/T2* weighting.

Repetition Time (TR)

Time between successive excitations of the same slice; key determinant of T1 weighting.

Flip Angle

Degree to which magnetisation is tipped from B0; determined by RF pulse duration and power.

Turbo Spin Echo (TSE)

SE variant that uses multiple 180° refocusing pulses per TR to acquire several echoes, shortening scan time.

Echo Train Length (ETL)

Number of echoes collected per TR in a turbo spin-echo sequence; longer ETL means faster acquisition.

T2* Weighting

Contrast sensitive to both T2 decay and magnetic field inhomogeneity; obtained with gradient-echo techniques.

Magnetic Susceptibility

Property describing how a material becomes magnetised; basis for SWI and blooming artifacts.

Susceptibility-Weighted Imaging (SWI)

High-resolution 3D gradient-echo technique combining magnitude and phase to accentuate paramagnetic substances like blood products.

Diffusion-Weighted Imaging (DWI)

Spin-echo EPI sequence sensitive to Brownian motion of water; crucial for acute stroke detection.

b-Value

Numeric description of gradient strength, duration and spacing in DWI; higher values increase diffusion sensitivity.

Apparent Diffusion Coefficient (ADC)

Quantitative map derived from multiple b-values, representing true diffusion independent of T2 shine-through.

Diffusion Gradient

Pair of equal-but-opposite gradients applied to encode molecular motion, causing signal loss in moving spins.

Inversion Recovery (IR)

Sequence beginning with a 180° prep pulse followed by TI delay, 90° excitation, and 180° refocusing to enhance contrast.

STIR (Short Tau Inversion Recovery)

IR technique with TI ≈ 200–300 ms that nulls fat signal; robust to field inhomogeneity but unusable post-contrast.

CHESS (Chemical Shift Selective) Fat Sat

Frequency-selective RF pulse that saturates fat protons; fastest but needs homogeneous field.

SPAIR (Spectral Adiabatic Inversion Recovery)

Hybrid method applying an adiabatic 180° pulse to fat only, combining IR robustness with chemical shift selectivity.

DIXON Technique

Method acquiring in-phase and out-of-phase echoes to mathematically separate fat and water images; good for large FOV and post-contrast.

Ernst Angle

Optimal flip angle in gradient-echo imaging that maximises signal for a given tissue at a particular TR.

J-Coupling Effect

Interaction causing fat to appear bright on turbo spin-echo T2 images despite its short T2.

Magnetic Field Inhomogeneity

Spatial variation in B0 that dephases spins and creates artifacts; corrected by 180° pulse in SE but amplified in GE.

Blooming Artifact

Exaggeration of hypointense foci on T2* or SWI caused by strong local susceptibility differences.

Motion Artifact

Ghosting or blurring arising from patient movement during acquisition.

Wrap-Around (Aliasing)

Artifact where anatomy outside the FOV is mapped onto the opposite side of the image.

Free Induction Decay (FID)

Rapid exponential signal loss immediately after RF excitation due to dephasing of spins.

Echo Planar Imaging (EPI)

Ultra-fast technique that captures an entire image after a single excitation; backbone of DWI.

Multidirectional DWI (MDDW)

Acquisition using diffusion gradients in multiple orthogonal directions, enabling tractography.

Orthogonal Diffusion Mode

Setting where gradients are applied along x, y and z axes to sample diffusion anisotropy.

Turbo Gradient Echo (GRE)

Rapid GRE variant using multiple gradient reversals per TR for faster 3D acquisitions (e.g., SWI).

WGFFC Mnemonic

When Girls Fight For Colleges – checklist for image evaluation: White matter, Grey matter, Fluid, Fat, Contrast.

WW2 Mnemonic

Water is White on T2 – quick reminder that CSF appears bright on T2-weighted images.

Field-of-View & Fat Sat Choice

Large FOV or metal: choose STIR or DIXON; small homogeneous FOV: CHESS is acceptable.