References

MRI Sequences: Vendor-Neutral Nomenclature — Master Reference Dossier

1. Rationale and Scope

MRI sequence nomenclature represents one of the most persistent sources of confusion in clinical radiology, medical education, and scientific literature. Each major hardware vendor — Siemens Healthineers, GE HealthCare, Philips MR, Canon Medical, Hitachi/Fujifilm — has independently developed proprietary acronyms for sequences that are, in many cases, physically and mathematically equivalent or near-equivalent. This fragmentation creates avoidable barriers to:

• Cross-institutional protocol harmonization
• Multi-vendor research reproducibility

• Clinical education across training environments
• Guideline implementation independent of scanner brand
• Scientific communication in peer-reviewed literature

The vendor-neutral nomenclature framework adopted on MRINinja follows the conventions established by the International Society for Magnetic Resonance in Medicine (ISMRM), the European Society of Radiology (ESR), and the foundational MR physics literature. The principle is: the physics defines the sequence; the brand defines only the label.

This document constitutes the authoritative cross-reference layer for all MRINinja protocol pages. Wherever a vendor acronym appears in clinical practice, it maps back to a vendor-neutral term used as the canonical identifier throughout the site.

2. Pulse Sequence Taxonomy — Overview

All clinical MRI pulse sequences derive from a limited set of fundamental physical mechanisms. The primary classification axis is the type of signal excitation and refocusing:

Primary Family Signal Formation Mechanism Core Physics

Spin Echo (SE) RF refocusing pulse (180°) T1/T2 contrast via RF

Gradient Echo (GRE) Gradient reversal — no RF T1/T2*/susceptibility refocusing For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page Gradient Echo (GRE/FLASH) Sequence.

Inversion Recovery (IR) Inversion pre-pulse + SE or GRE Null point contrast selection readout

Echo Planar Imaging         Rapid oscillating gradients —        Speed;
 (EPI)                       single/multishot                     diffusion/BOLD/perfusion

Steady-State Free           Balanced gradient moment —           T2/T1 ratio contrast
 Precession (SSFP)           coherent steady state

Diffusion-Weighted          Motion-sensitizing gradient pairs    Brownian motion of water
 (DWI)                       (Stejskal-Tanner)

Perfusion DSC, DCE, or ASL mechanisms Microcirculatory blood flow

MR Angiography TOF, PC, or CE-MRA Vascular signal mechanisms

Spectroscopy (MRS) Chemical shift encoding Metabolite quantification

A secondary classification axis concerns k-space filling strategy:

• Sequential (line-by-line): conventional SE and GRE
• Segmented / multi-shot: fast SE variants, segmented EPI
• Single-shot: ss-EPI, ss-TSE
• Radial: UTE, VIBE with radial readout, Golden-angle acquisitions
• Spiral: less common clinically; used in cardiac/fMRI research
• 3D volumetric: 3D-GRE, 3D-TSE, 3D-SSFP

3. Spin Echo Family

3.1 Conventional Spin Echo (SE) For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page Conventional Spin Echo (SE) Sequence.

Vendor-neutral name:Spin Echo (SE)

Physics:90° excitation RF pulse followed by a 180° refocusing RF pulse, producing a spin echo at time TE. The 180° pulse corrects for static magnetic field inhomogeneities (B0), yielding true T2 contrast — independent of susceptibility effects. This is the fundamental distinction from GRE sequences.

Contrast profiles:

• T1-weighted SE: short TR (300–700 ms), short TE (10–30 ms)
• T2-weighted SE: long TR (>2000 ms), long TE (80–120 ms)
• Proton Density (PD) SE: long TR, short TE

Clinical status:Largely replaced by TSE/FSE in routine practice due to long acquisition times. Still considered the gold standard for T2 measurement accuracy and used in specific phantoms and relaxometry studies. Retains a niche role in musculoskeletal imaging where ETL-related T2 blurring of TSE is problematic.

Vendor equivalents:

Vendor Acronym

Siemen SE s

GE SE

Philips SE

Canon SE

Hitachi SE

(Conventional SE is one of the few sequences where all vendors use the same label.)

3.2 Turbo Spin Echo / Fast Spin Echo (TSE / FSE)

Vendor-neutral name:Turbo Spin Echo (TSE) — also known as Fast Spin Echo (FSE) and RARE (Rapid Acquisition with Relaxation Enhancement) For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page Turbo Spin Echo (TSE/FSE) Sequence.

Physics:Extension of SE using a train of 180° refocusing pulses (echo train) following a single 90° excitation. Each echo in the train fills a different k-space line, multiplying acquisition speed by the Echo Train Length (ETL), also called the Turbo Factor. Originally described by Hennig et al. (1986) as RARE.

Key parameters:

• Echo Train Length (ETL) / Turbo Factor: number of echoes per TR; directly determines speed increase
• Effective TE: the TE of the echo placed at the center of k-space (determines dominant contrast)
• Echo Spacing (ESP): time between consecutive echoes in the train
• Refocusing flip angle: may be reduced from 180° (variable flip angle TSE — see 3.4)

Contrast implications of ETL:

• Longer ETL → faster acquisition but increased T2 blurring (fat and fluid appear bright due to J-coupling effects on fat signal)
• SAR increases substantially with long ETLs at high field strength

Clinical ubiquity:TSE/FSE is the dominant T2-weighted sequence in all anatomical regions. Practically every T2-weighted sequence in routine clinical MRI is a TSE/FSE variant.

Vendor equivalents:

Vendor Acronym Full Name

Siemen TSE Turbo Spin Echo s

GE FSE Fast Spin Echo

Philips TSE Turbo Spin Echo

Canon FSE Fast Spin Echo

Hitachi FSE Fast Spin Echo

3.3 Single-Shot Turbo Spin Echo (ss-TSE / HASTE)

Vendor-neutral name:Single-Shot Turbo Spin Echo (ss-TSE) / Half-Fourier Acquisition Single-shot Turbo Spin Echo

Physics:All k-space lines acquired in a single TR following one excitation pulse, using an extended echo train. Combined with Half-Fourier acquisition (approximately 60% of k-space acquired; remainder synthesized by conjugate symmetry), enabling image acquisition in ~200–400 ms. Eliminates motion artifacts from breathing but introduces T2 blurring with long echo trains.

Clinical role:

• Abdomen / pelvis in non-cooperative patients
• MRCP (ss-TSE with very long TE for fluid-only signal)
• Fetal MRI
• Quick survey sequences

Vendor equivalents:

Vendor Acronym Full Name

Siemen HASTE Half-Fourier Acquisition Single-shot Turbo Spin Echo s

GE SSFSE Single-Shot Fast Spin Echo

Philips SS-TSE Single-Shot Turbo Spin Echo

Canon FASE Fast Advanced Spin Echo

Hitachi SS-FSE Single-Shot Fast Spin Echo

3.4 Variable Flip Angle TSE (3D-TSE with Variable Refocusing)

Vendor-neutral name:Variable Flip Angle Turbo Spin Echo (VFA-TSE) / 3D Turbo Spin Echo

Physics:3D TSE acquisition using a variable (reduced) refocusing flip angle train (hyperecho or pseudo-steady-state approach). Reduces SAR substantially at 3T while maintaining SNR through stimulated echo contributions. Allows isotropic or near-isotropic 3D acquisition with T2

or mixed contrast. Key conceptual innovation by Hennig (hyperecho) and Mugler (SPACE concept).

Contrast notes:At long TR and moderate flip angles, contrast has a mixed T1/T2 component. Specific optimization needed for pure T2 contrast (CAIPI sampling, flip angle modulation).

Clinical applications:

• 3D T2-weighted brain (white matter lesion detection, hippocampal volumetry)
• 3D FLAIR brain
• 3D MR myelography / cisternography
• 3D inner ear / cranial nerve imaging
• 3D musculoskeletal (cartilage)

Vendor equivalents:

Vendor Acronym Clinical Label Notes

Siemen     SPACE        Sampling Perfection with Application-optimized         T2, FLAIR, PD
 s                       Contrasts using different flip-angle Evolution         variants

GE CUBE — T2, FLAIR, PD variants

Philips VISTA Volume ISotropic TSE Acquisition T2, FLAIR variants

Canon PHASE — —

Hitachi isoFSE — —

4. Gradient Echo Family

4.1 Spoiled Gradient Echo (SPGR)

Vendor-neutral name:Spoiled Gradient Recalled Echo (SPGR) / T1-weighted GRE

Physics:Gradient echo sequence in which transverse magnetization is deliberately destroyed (spoiled) at the end of each TR using either RF spoiling (phase-cycling of RF pulses) or gradient spoiling. This prevents steady-state buildup of transverse coherence, yielding T1-weighted contrast. The Ernst angle determines optimal flip angle for maximum SNR at a given T1 and TR.

Key parameters:

• TR: typically 4–15 ms (3D); longer for 2D
• TE: short (1–5 ms at 3T) to minimize T2* effects
• Flip angle: 5–20° for 3D volumetric; higher for 2D
• Fat saturation options: chemical shift selective (CHESS), Dixon

Clinical role:

• 3D T1-weighted brain: gold standard for structural MRI (cortical thickness, morphometry, volumetry)
• Post-contrast imaging (pre/post Gd)
• Dynamic contrast-enhanced sequences (DCE-MRI)
• MR angiography (CE-MRA)
• Liver lesion characterization (dynamic phases)

Vendor equivalents:

Vendor Acronym Full Name

Siemen FLASH Fast Low Angle Shot s

GE SPGR Spoiled GRE; also MP-RAGE uses IR-prepped FLASH

Philips T1-FFE T1-weighted Fast Field Echo

Canon FastFE —

Hitachi RSSG RF-Spoiled SARGE (Steady-state Acquisition Rewound GRE)

3D variants with inversion prep:

Vendor Acronym Notes

Siemen     MPRAGE               Magnetization Prepared Rapid Gradient Echo — gold
 s                               standard 3D T1 brain

GE IR-FSPGR / Inversion Recovery Fast SPGR BRAVO

Philips TFE / 3D-TFE Turbo Field Echo

Canon 3D-QUICK —

Hitachi MPRAGE — For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page MPRAGE / 3D T1 Magnetisation-Prepared GRE Sequence.

4.2 Steady-State Gradient Echo — Coherent (SSFP-FID)

Vendor-neutral name:Steady-State Free Precession — Free Induction Decay readout (SSFP-FID) / Coherent GRE

Physics:Short TR GRE without spoiling, allowing transverse magnetization to persist and contribute to signal. The FID (Free Induction Decay) component is sampled before the echo. Contrast has both T1 and T2* dependence. Less commonly used than FISP or PSIF.

Vendor equivalents:

Vendor Acronym

Siemen FISP (FID variant) s

GE GRE (coherent)

Philips FFE

Canon SSFP

4.3 Steady-State Free Precession — Refocused (True FISP / bSSFP)

Vendor-neutral name:Balanced Steady-State Free Precession (bSSFP) For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page Balanced Steady-State Free Precession (bSSFP) Sequence.

Physics:All three gradient axes are fully balanced (net zero first moment) within each TR. This allows maximum transverse steady-state signal, yielding contrast proportional to T2/T1 ratio — unique among GRE sequences. Produces very high SNR in fluids and tissues with high T2/T1 ratio. Sensitive to off-resonance banding artifacts (addressed by frequency scouting or phase-cycling).

Clinical role:

• Cardiac MRI (cine imaging) — primary sequence
• Fetal MRI (rapid acquisition)
• MR myelography
• Inner ear / vestibulocochlear anatomy
• Coronary artery MRA
• Abdominal survey in neonates

Vendor equivalents:

Vendor Acronym Full Name

Siemen TrueFISP True Fast Imaging with Steady-state Precession s

GE FIESTA Fast Imaging Employing Steady-state Acquisition

Philips b-FFE Balanced Fast Field Echo

Canon True SSFP —

Hitachi Balanced SARGE —

4.4 Steady-State Free Precession — Echo (PSIF / T2-SSFP)

Vendor-neutral name:Reversed FISP (PSIF) / T2-weighted SSFP

Physics:Asymmetric SSFP variant reading the steady-state echo (rather than FID). Contrast is predominantly T2-weighted. Used less frequently than bSSFP.

Vendor equivalents:

Vendor Acronym

Siemen PSIF s

GE SSFP

Philips T2-FFE

Canon PSIF

4.5 Multi-Echo GRE / Dixon Methods

Vendor-neutral name:Multi-Echo Gradient Echo / Dixon Fat-Water Separation

Physics:Acquisition at multiple TEs exploiting the chemical shift between water (4.7 ppm) and fat (1.3 ppm — predominantly methylene). In/out-of-phase acquisitions at 1.15 ms intervals (at 3T) enable algebraic separation of water and fat images. Advanced Dixon methods (2-point, 3-point, IDEAL) also provide fat fraction quantification (proton density fat fraction — PDFF) and R2* mapping.

Clinical role:

• Liver fat quantification (NAFLD/NASH)

• Adrenal adenoma characterization
• Lipid-containing lesion identification
• Bone marrow infiltration assessment
• Muscle disease (fat replacement)

Vendor equivalents:

Vendor Acronym Notes

Siemen VIBE-Dixon / mDixon Often combined with VIBE 3D acquisition s

GE IDEAL / LAVA-Flex Iterative Decomposition of water and fat with Echo Asymmetry

Philips mDixon / mDixon Quant Multi-point Dixon

Canon WFS / Water Fat — Separation

Hitachi FatSep —

4.6 Susceptibility-Weighted Imaging (SWI)

Vendor-neutral name:Susceptibility-Weighted Imaging (SWI)

Physics:High-resolution 3D spoiled GRE with long TE, exploiting T2* sensitivity to local magnetic field perturbations caused by paramagnetic/diamagnetic substances. Phase images processed with high-pass filtering to remove background phase, then multiplied with magnitude image (phase mask) to enhance susceptibility contrast. Produces minimum intensity projections (mIP) for vascular and microbleed mapping.

Detectable substances:Deoxyhemoglobin, hemosiderin, ferritin, calcium (diamagnetic — opposite phase), melanin, air, contrast agents.

Clinical role:

• Cerebral microbleed detection (cerebral amyloid angiopathy, hypertensive vasculopathy)
• Cavernous malformation characterization
• Traumatic axonal injury (DAI) — hemorrhagic shearing lesions
• Venous malformation mapping
• Tumor microvasculature (BOLD venography)
• Iron deposition quantification (emerging: quantitative susceptibility mapping — QSM)

Vendor equivalents:

Vendor Acronym Full Name

Siemen SWI / SWAN (GRE-based) Susceptibility Weighted Imaging s For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page Susceptibility Weighted Imaging (SWI) Sequence.

GE SWAN Susceptibility Weighted Angiography

Philips SWI / Venous BOLD —

Canon FSBB Field Strength Banding Based

Hitachi BSI Brain susceptibility imaging

5. Inversion Recovery Family

5.1 Inversion Recovery Spin Echo (IR-SE)

Vendor-neutral name:Inversion Recovery (IR)

Physics:A 180° inversion pre-pulse precedes the standard SE readout by an inversion time (TI). At TI, tissue longitudinal magnetization passes through zero — the null point for a given T1 is TI = T1 × ln(2). Signal nulling at specific TI values is the basis for fat suppression (STIR) and fluid suppression (FLAIR). For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page STIR Sequence.

General IR equation:Signal ∝ |1 − 2·e^(−TI/T1) + e^(−TR/T1)|

5.2 Short TI Inversion Recovery (STIR)

Vendor-neutral name:Short Tau Inversion Recovery (STIR)

Physics:IR sequence with short TI (approximately 150–175 ms at 1.5T; ~130 ms at 3T) chosen to null fat signal (fat T1 ≈ 250 ms at 1.5T). Combined with TSE readout in modern practice. Fat suppression is T1-based and therefore field-strength independent and insensitive to B0 inhomogeneity — critical advantage over chemical shift fat saturation.

Critical distinction from fat-saturated T2:STIR suppresses any short-T1 tissue (not only fat), including gadolinium-enhanced tissue — STIR must not be used post-contrast as enhancing lesions may be suppressed.

Clinical role:

• Musculoskeletal (bone marrow edema, soft tissue pathology)

• Peripheral nerve imaging (neurography)
• Lymph node assessment
• Whole-body MRI
• Spine (marrow infiltration, discoligamentous injury)
• Breast MRI (background suppression)

Vendor equivalents:

Vendor Acronym

Siemen STIR s

GE STIR

Philips STIR

Canon STIR

Hitachi STIR

(STIR is universally used across all vendors without proprietary renaming.)

5.3 Fluid-Attenuated Inversion Recovery (FLAIR)

Vendor-neutral name:Fluid-Attenuated Inversion Recovery (FLAIR) For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page FLAIR Sequence.

Physics:IR sequence with long TI (typically 2200–2500 ms at 1.5T; ~2400 ms at 3T) chosen to null free water signal (CSF T1 ≈ 4500 ms at 1.5T). Combined with TSE readout. Reveals periventricular and cortical lesions that would be obscured by CSF signal on conventional T2. The 3D variant (3D-FLAIR) offers higher resolution and reformatting capability.

Artifacts to recognize:

• FLAIR CSF pulsation artifact: incomplete CSF suppression in posterior fossa / foramen of Monro
• FLAIR shine-through: T2-very-long-T1 structures (cysts, CSF) may not fully suppress
• Gadolinium effect on FLAIR TI: post-contrast FLAIR — T1 shortening of CSF by meningeal Gd — can cause CSF to appear bright (leptomeningeal enhancement detection)

Vendor equivalents:

Vendor Acronym 3D Variant

Siemen FLAIR / Dark Fluid 3D FLAIR (SPACE FLAIR) s

GE FLAIR 3D FLAIR (CUBE FLAIR)

Philips FLAIR 3D FLAIR (VISTA FLAIR)

Canon FLAIR 3D FLAIR

Hitachi FLAIR 3D isoFSE FLAIR

5.4 Magnetization Transfer + Inversion Recovery Combinations

Vendor-neutral name:MT-FLAIR / DIR (Double Inversion Recovery)

Double Inversion Recovery (DIR): Two sequential inversion pulses — one to null CSF, one to null white matter — yielding cortical gray matter-selective contrast. Increases sensitivity for cortical demyelinating lesions in MS.

Vendor equivalents (DIR):

Vendor Acronym

Siemen DIR s

GE DIR

Philips DIR

Canon DIR

6. Echo Planar Imaging Family

6.1 Echo Planar Imaging — General For sequence-level protocol optimisation, vendor terminology and artefact management, see the dedicated MRIninja page Echo Planar Imaging (EPI) Sequence.

Vendor-neutral name:Echo Planar Imaging (EPI)

Physics:Introduced by Mansfield (1977). EPI acquires all k-space lines within a single TR following one excitation by rapidly oscillating frequency-encoding gradients (flyback or blipped). Single-shot EPI acquires the entire k-space in ~50–100 ms — the fastest conventional MRI technique. This speed enables:

• Diffusion-weighted imaging (DWI)
• Functional MRI (fMRI / BOLD)
• Perfusion imaging (DSC)
• Real-time cardiac imaging

EPI-specific artifacts:

• Geometric distortion (N/2 ghost / Nyquist ghost): from off-resonance at fat-water interface; addressed by B0 field maps and fat saturation
• Susceptibility distortion: EPI k-space traversal in phase direction is slow; B0 inhomogeneities accumulate, causing geometric warping (most severe at air-tissue interfaces)
• T2 blurring:* long effective TE → blurring along phase-encode direction
• Chemical shift in phase-encode direction (large — fat must always be suppressed in EPI)

Readout variants:

• Single-shot EPI (ss-EPI): all k-space in one shot — fastest, most distorted
• Multi-shot / Segmented EPI: k-space divided across multiple shots — reduced distortion, slower, requires motion correction
• Simultaneous Multi-Slice (SMS) EPI / Multiband: multiple slices excited and acquired simultaneously using CAIPIRINHA — 2–8× acceleration in slice dimension

6.2 Diffusion-Weighted EPI (DW-EPI)

(See Section 7 for full DWI treatment — this entry addresses the EPI readout component specifically.)

The dominant readout for DWI in clinical practice is ss-EPI due to motion insensitivity. The Stejskal-Tanner diffusion-encoding gradient pair is applied around the 180° refocusing pulse in a spin-echo EPI sequence.

6.3 BOLD fMRI (Blood Oxygen Level Dependent)

Vendor-neutral name:BOLD fMRI / GRE-EPI for fMRI

Physics:T2*-weighted GRE-EPI exploiting the difference in magnetic susceptibility between oxygenated (oxyhemoglobin — diamagnetic) and deoxygenated (deoxyhemoglobin — paramagnetic) hemoglobin. Neural activity → local increase in cerebral blood flow → relative decrease in deoxyhemoglobin → increase in T2* signal (BOLD response). Neurovascular coupling introduces 4–6 s hemodynamic lag.

Technical considerations:

• Whole-brain coverage with TR ≈ 1–2 s (conventional); sub-second with SMS/Multiband
• TE optimized to approximately T2* of gray matter (~30 ms at 3T, ~50 ms at 1.5T)
• Temporal SNR (tSNR) is critical — > 100 preferred for robust activation detection
• Motion is the dominant confound — 6-parameter rigid-body realignment mandatory

7. Diffusion-Weighted Imaging Family

7.1 Diffusion-Weighted Imaging (DWI)

Vendor-neutral name:Diffusion-Weighted Imaging (DWI)

Physics:Based on Stejskal-Tanner (1965) pulsed gradient spin echo. Pairs of motion-sensitizing diffusion gradients applied symmetrically around a 180° refocusing pulse. Spins undergoing diffusion (random Brownian motion) experience incomplete rephasing → signal attenuation. The degree of signal attenuation is characterized by the b-value (gradient strength, duration, separation):

b = γ² G² δ² (Δ − δ/3)

where G = gradient amplitude, δ = gradient duration, Δ = time between gradient pulses, γ = gyromagnetic ratio.

ADC (Apparent Diffusion Coefficient):Quantitative measure derived from signal decay across b-values: S(b) = S(0) × e^(−b × ADC)

Standard b-values:

• b=0: T2-weighted reference (no diffusion weighting)
• b=500–1000 s/mm²: routine clinical DWI
• b=1500–3000 s/mm²: high b-value DWI (prostate, brain tumor, restricted diffusion accentuation)

DWI vs ADC map interpretation:

• Restricted diffusion = high DWI signal + low ADC → ischemia, abscess, hypercellular tumor, epidermoid
• T2 shine-through = high DWI signal + high ADC → high T2 lesion, NOT true restriction
• T2 blackout = low DWI + low ADC → hemorrhage (T2* susceptibility)

Vendor equivalents:DWI is universally labeled as DWI across all vendors. Vendor differences exist primarily in:

• Readout (EPI vs non-EPI)
• Fat suppression method
• Distortion correction algorithms
• Multi-slice acceleration (SMS/Multiband labeling)

7.2 Diffusion Tensor Imaging (DTI)

Vendor-neutral name:Diffusion Tensor Imaging (DTI)

Physics:Extension of DWI applying diffusion gradients in ≥6 non-collinear directions to reconstruct the full diffusion tensor (3×3 symmetric matrix). Eigenvalues (λ1 ≥ λ2 ≥ λ3) characterize diffusion magnitude and directionality:

• Mean Diffusivity (MD): mean of eigenvalues — overall diffusion magnitude
• Fractional Anisotropy (FA): normalized variance of eigenvalues — 0 (isotropic) to 1 (fully anisotropic); reflects white matter tract integrity
• Axial Diffusivity (AD): λ1 — along principal axis
• Radial Diffusivity (RD): mean of λ2, λ3 — perpendicular to principal axis

Tractography:FA maps and eigenvector fields seed fiber tracking algorithms (deterministic or probabilistic).

Clinical role:

• White matter tract integrity assessment (TBI, MS, neurodegenerative disease)
• Presurgical eloquent cortex / tract mapping
• Developmental neuroscience
• Research biomarker (FA reduction in neurodegeneration)

Minimum directions for clinical use:15–30 directions (≥6 mandatory for tensor; ≥30 recommended for tractography).

7.3 Diffusion Kurtosis Imaging (DKI)

Vendor-neutral name:Diffusion Kurtosis Imaging (DKI)

Physics:Extension of DTI addressing non-Gaussian diffusion in biological tissue using higher b-values (up to b=2000–3000 s/mm²). Quantifies kurtosis tensor K — a measure of deviation from Gaussian diffusion related to tissue microstructural complexity. Requires ≥3 b-values and ≥15 directions.

Clinical role:Primarily research; emerging clinical role in tumor grading, prostate cancer, neonatal brain.

7.4 Intravoxel Incoherent Motion (IVIM)

Vendor-neutral name:Intravoxel Incoherent Motion (IVIM)

Physics:Le Bihan model (1988) separating diffusion signal contributions from true molecular diffusion (D) and pseudo-diffusion from blood flowing in capillaries (D*, perfusion fraction f). Requires multiple low b-values (b=0–200 s/mm²) for accurate f and D* estimation. Biexponential signal model:

S(b)/S(0) = f·e^(−b·D*) + (1−f)·e^(−b·D)

Clinical role:Liver lesion characterization, tumor perfusion, renal cortex assessment — vendor-agnostic acquisition but model fitting varies by platform.

8. Perfusion Imaging Family

8.1 Dynamic Susceptibility Contrast (DSC) Perfusion

Vendor-neutral name:Dynamic Susceptibility Contrast MRI (DSC-MRI) / T2*-PWI

Physics:Rapid T2* (or T2)-weighted GRE-EPI (or SE-EPI) imaging during first-pass bolus of gadolinium-based contrast agent (GBCA). Paramagnetic Gd causes local T2*/T2 shortening → signal drop. Deconvolution of concentration-time curve with arterial input function (AIF) yields perfusion maps:

• rCBV (relative Cerebral Blood Volume)
• rCBF (relative Cerebral Blood Flow)
• MTT (Mean Transit Time)
• Tmax / TTP (Time-to-Peak)

Clinical role:

• Stroke penumbra imaging (Tmax > 6s threshold)
• Brain tumor grading and treatment response (rCBV)
• CNS vasculopathy assessment

Vendor implementations:All vendors provide DSC-PWI packages. Post-processing and AIF selection vary.

8.2 Dynamic Contrast Enhancement (DCE) Perfusion

Vendor-neutral name:Dynamic Contrast-Enhanced MRI (DCE-MRI) / T1-DCE

Physics:Serial T1-weighted (spoiled GRE) imaging before, during, and after GBCA injection. Signal enhancement curve reflects tissue perfusion and permeability via Tofts model or extended Tofts model:

• Ktrans: volume transfer constant (permeability × surface area product)
• ve: extravascular extracellular space volume fraction
• vp: plasma volume fraction
• kep: efflux rate constant = Ktrans/ve

Clinical role:

• Breast MRI (lesion characterization, kinetic curves)
• Prostate MRI (PI-RADS v2.1 — perfusion complementary role)
• Brain tumor response assessment
• Liver, kidney, musculoskeletal tumor characterization

8.3 Arterial Spin Labeling (ASL)

Vendor-neutral name:Arterial Spin Labeling (ASL)

Physics:Non-contrast perfusion technique. Endogenous water protons in arterial blood are magnetically labeled (inverted) using RF pulses proximal to the imaging region. Labeled water protons flow into tissue and exchange with tissue water, reducing signal relative to a control acquisition (no labeling). Subtraction of labeled from control image yields perfusion-weighted map. Quantitative CBF in mL/100g/min.

ASL variants:

• CASL (Continuous ASL): continuous RF irradiation of labeling plane
• PASL (Pulsed ASL): single inversion pulse over slab (e.g., EPISTAR, FAIR)
• pCASL (pseudo-Continuous ASL): series of discrete RF pulses mimicking CASL; current recommended standard (ISMRM/ESMRMB Consensus 2015)
• Velocity-selective ASL (VS-ASL): labels based on velocity rather than spatial position; useful in cerebrovascular disease

Vendor equivalents:

Vendor ASL Implementation

Siemen pCASL (syngo.via) s

GE pCASL (3D ASL)

Philips pCASL (3D TRAK / QUASAR)

Canon pCASL

Hitachi pCASL

9. MR Angiography Family

9.1 Time-of-Flight MRA (TOF-MRA)

Vendor-neutral name:Time-of-Flight MRA (TOF-MRA)

Physics:Non-contrast technique exploiting flow-related enhancement. Stationary tissue within the imaging slab is progressively saturated by repeated RF pulses (short TR). Unsaturated spins flowing into the slab from outside carry full longitudinal magnetization → appear bright against suppressed background. GRE sequence with short TR and moderate flip angle.

2D vs 3D TOF:

• 2D TOF: sequential thin slabs, high sensitivity to slow flow, longer scan time; used for peripheral vessels, veins
• 3D TOF: entire volume excited simultaneously; superior spatial resolution and SNR; standard for intracranial arteries; saturation bands suppress venous signal

Limitations:Slow or in-plane flow signal loss; tortuous vessel segment dropout; overestimation of stenosis.

Clinical role:

• Intracranial artery imaging (aneurysm screening, vascular anomalies)
• Carotid/vertebral artery assessment
• Renal artery (2D TOF)
• Peripheral MRA (2D TOF)

9.2 Phase Contrast MRA (PC-MRA)

Vendor-neutral name:Phase Contrast MRA (PC-MRA)

Physics:Flow velocity encoded in the phase of the MR signal using bipolar velocity-encoding gradients. Background phase (stationary tissue) subtracted from flow-encoded phase. Velocity encoding (VENC) parameter must be set to exceed maximum expected velocity to avoid aliasing. Provides both morphological and quantitative velocity / flow volume information.

Clinical role:

• Intracranial venous sinus evaluation (dural sinus thrombosis)
• CSF flow quantification (aqueductal stenosis, normal pressure hydrocephalus)
• Cardiac flow quantification (valve assessment)
• Pre/post-surgical vascular assessment

9.3 Contrast-Enhanced MRA (CE-MRA)

Vendor-neutral name:Contrast-Enhanced MRA (CE-MRA)

Physics:Rapid 3D spoiled GRE (ultrashort TR/TE) timed to arterial phase of GBCA bolus. T1 shortening of blood by gadolinium provides very high vessel-to-background contrast independent of flow velocity — overcoming TOF limitations. Timing critical: test bolus, automated bolus detection (e.g., CARE bolus), or fluoroscopic triggering.

Clinical role:

• Aorta, peripheral arteries
• Renal arteries
• Pulmonary MRA
• Mesenteric vasculature
• Carotid / arch vessels

9.4 Non-Contrast MRA Techniques

Vendor-neutral name:Non-Contrast MRA (NCE-MRA)

Multiple physical mechanisms employed:

Technique Physics Basis Vendor Examples

Fresh Blood          ECG-gated 3D TSE exploiting           Canon: FBI; Siemens: Native
 Imaging (FBI)        systolic/diastolic flow difference    SPACE; GE: InFlow IR

TRANCE / QISS Quiescent-interval single-shot bSSFP GE: QISS; Siemens: Native SPACE

VIPR / TWIST Radial k-space sampling Siemens: TWIST; GE: TRICKS time-resolved

bSSFP-based        b-SSFP high T2/T1 ratio for           TrueFISP/FIESTA angiography
 NCE-MRA            vessel-to-background

10. MR Spectroscopy

10.1 Single-Voxel Spectroscopy (SVS)

Vendor-neutral name:Single-Voxel Spectroscopy (SVS)

Physics:Two primary localization techniques:

• PRESS (Point-Resolved Spectroscopy): three selective 90°-180°-180° pulses defining voxel intersection; TE selectable (short ≈30 ms for broad metabolite profile; long ≈135/270 ms for lactate editing); standard clinical technique
• STEAM (Stimulated Echo Acquisition Mode): three 90° pulses; shorter minimum TE; lower SNR due to stimulated echo signal loss (50% compared to PRESS); useful for very short TE and diffusion spectroscopy

Key brain metabolites:

• NAA (N-acetylaspartate, 2.0 ppm): neuronal marker; reduced in neurodegeneration, tumor infiltration
• Cho (Choline, 3.2 ppm): membrane turnover; elevated in tumors, demyelination
• Cr (Creatine, 3.0 ppm): energy metabolism; relatively stable internal reference
• Lac (Lactate, 1.3 ppm — doublet): anaerobic metabolism; elevated in ischemia, necrotic tumor, mitochondrial disease
• Lip (Lipids, 0.9/1.3 ppm): necrosis, glioblastoma
• mI (Myo-inositol, 3.5 ppm): glial marker; elevated in gliosis and dementia
• Glx (Glutamate/Glutamine, 2.1–2.4 ppm): excitatory neurotransmitter pool

Vendor equivalents:

Vendor PRESS label STEAM label

Siemen PRESS STEAM s

GE PROBE-P PROBE-S

Philips PRESS STEAM

Canon PRESS STEAM

10.2 Multi-Voxel Spectroscopy / Chemical Shift Imaging (CSI)

Vendor-neutral name:Chemical Shift Imaging (CSI) / MR Spectroscopic Imaging (MRSI)

Physics:Phase-encoding in one, two, or three spatial dimensions to obtain spectral information from multiple voxels simultaneously. 2D-CSI or 3D-CSI provides metabolite maps over a defined slice or volume. Post-processing intensive; longer acquisition times.

Vendor equivalents:

Vendor Acronym

Siemen CSI / MRSI s

GE PROSE / CSI

Philips CSI

Canon CSI

11. Special and Advanced Sequences

11.1 Magnetization Transfer Imaging (MT)

Vendor-neutral name:Magnetization Transfer (MT) / Magnetization Transfer Contrast (MTC)

Physics:Off-resonance RF pulse saturates semi-solid (bound) proton pool (macromolecules, myelin). Saturation transfers to free water pool via chemical exchange → signal reduction. Tissues with abundant macromolecular content (myelin, muscle) show greater MT effect. Magnetization Transfer Ratio (MTR) quantifies effect: MTR = (M0 − Msat)/M0 × 100%.

Advanced variant — qMT (quantitative MT) and ihMT (inhomogeneous MT):emerging research techniques for myelin quantification.

Clinical role:

• MS lesion detection (MT-enhanced FLAIR/GRE)
• Post-contrast CE-MRA (background suppression)
• Cartilage assessment
• Research: myelin water imaging

11.2 Ultrashort Echo Time (UTE) and Zero Echo Time (ZTE)

Vendor-neutral name:Ultrashort Echo Time (UTE) / Zero Echo Time (ZTE)

Physics:Conventional MRI cannot image tissues with very short T2 (cortical bone, tendons, ligaments, lung parenchyma, myelin — T2 < 1 ms) as signal decays before readout. UTE acquires signal within 8–100 μs using radial k-space trajectories and gradient switching during RF pulse. ZTE begins acquisition during the RF pulse itself (TE ≈ 0).

Clinical role:

• Cortical bone imaging
• Lung parenchyma (UTE-MRI as radiation-free alternative to CT)
• Tendon and ligament (Achilles, ACL)
• Cartilage deep zone
• Implant-adjacent imaging

Vendor equivalents:

Vendor UTE Acronym ZTE Acronym

Siemen UTE — s

GE UTE SILENZ (Silent ZTE)

Philips UTE —

Canon UTE —

11.3 Synthetic MRI

Vendor-neutral name:Synthetic MRI / Quantitative MRI (qMRI)

Physics:Single scan acquisition (typically multi-echo, multi-delay sequence) enabling simultaneous extraction of quantitative tissue relaxation parameters: T1, T2, PD (proton density). From these maps, any conventional contrast-weighted image can be synthesized retrospectively. Reduces total scan time for multi-contrast protocols.

Vendor implementations:

Vendor Acronym / Product

Siemen MAGiC (partnership with SyntheticMR) s

GE MAGIC / SyMRI

Philips SyMRI / AxT1ρ

11.4 MR Fingerprinting (MRF)

Vendor-neutral name:MR Fingerprinting (MRF)

Physics:Introduced by Ma et al. (Nature, 2013). Pseudorandom variation of acquisition parameters (TR, flip angle, TE) generates unique signal evolution "fingerprints" per tissue. Pattern matching against a precomputed dictionary yields simultaneous T1, T2, and other parameter maps in a single acquisition.

Status:Research → transitioning to clinical implementation. Vendor implementations available (Siemens, GE, Philips) but not yet universally standardized.

11.5 Quantitative Susceptibility Mapping (QSM)

Vendor-neutral name:Quantitative Susceptibility Mapping (QSM)

Physics:Extension of SWI. Phase images from multi-echo GRE processed to remove background phase, then dipole deconvolution applied to convert local phase to susceptibility distribution (χ in ppm). Directly quantifies iron, calcium, myelin, and GBCA concentration in tissue. More accurate than SWI for lesion characterization (can distinguish calcification from hemorrhage by sign of susceptibility).

Clinical role:

• Deep gray matter iron quantification (Parkinson's, MSA, PSP)
• Multiple sclerosis lesion characterization (central vein sign, paramagnetic rim lesions)
• Quantitative GBCA pharmacokinetics
• Neurodegeneration biomarker

11.6 MR Elastography (MRE)

Vendor-neutral name:MR Elastography (MRE)

Physics:Mechanical waves (40–80 Hz) propagated through tissue using a pneumatic or electromechanical actuator. Phase-contrast MRI encodes the resulting tissue displacement. Wave propagation characteristics yield viscoelastic stiffness maps (elastogram). Stiffer tissue propagates waves faster.

Clinical role:

• Liver fibrosis staging (non-invasive alternative to biopsy — Grade F0–F4)
• Brain stiffness in neurodegeneration
• Breast lesion characterization
• Spleen stiffness in portal hypertension

11.7 Chemical Exchange Saturation Transfer (CEST)

Vendor-neutral name:CEST MRI / APT (Amide Proton Transfer)

Physics:RF saturation of exchangeable protons in specific molecular groups (e.g., amide protons at +3.5 ppm from water) with saturation transfer to bulk water. Enables indirect detection of low-concentration molecules at water sensitivity. APT (Amide Proton Transfer) imaging specifically probes amide proton pool — elevated in malignant tumors (increased mobile proteins) and reduced in ischemia.

Clinical role:

• Glioma grading and treatment response (APT-CEST)
• Ischemia assessment
• Research: glycosaminoglycan imaging (gagCEST), glucose imaging (glucoCEST)

12. Master Cross-Vendor Equivalence Table

13. Evidence-Based References

A. Guidelines / Consensus / Recommendations

B. Systematic Reviews / Meta-analyses

C. Prospective / Original Important Studies

D. Technical MRI Papers

E. Landmark Historical References