MRI Sequence Types: The Full Catalogue
Every major sequence family and named technique you will meet on the console and in reports, grouped by how they generate signal, with the physical principle, the clinical job it does, and the equivalent name on each vendor. For the parameter physics behind these families (TR/TE/flip, k-space), see the Sequence Physics Explainer; for tuning them, see the Sequence Optimiser.
On this page
Master comparisonSpin-echo familyInversion-recovery familyGradient-echo familyEcho-planar (EPI) readoutDiffusion, perfusion & advanced contrastVascular & flow: MRA and MRVFat–water separation & suppressionVendor name Rosetta tableSequence decision guide: choosing between close alternativesSources- Spin echo’s 180° refocusing pulse cancels static field inhomogeneity, so spin echo is robust to it; gradient echo replaces the 180° with a gradient reversal, so it is very fast but susceptibility-sensitive.
- In inversion recovery, STIR nulls fat and FLAIR nulls CSF; do not use STIR after gadolinium, because it can also null enhancing tissue.
- Always read DWI with the ADC map: restricted water stays bright on DWI, and the ADC map removes T2 shine-through.
- Vendors give the same physics different names: fast spin echo is TSE on Siemens and Philips but FSE on GE and Canon.
- When renal function rules out gadolinium, use non-contrast MRA (TOF, phase contrast, QISS or FBI); phase contrast also answers questions about flow direction or velocity.
Explain it simply
- Spin echo scans use an extra radio pulse that cancels uneven magnetism, so they resist the faults it causes. Gradient echo scans skip it: much faster, but more easily disturbed by small magnetic differences.
- STIR scans make fat go dark and FLAIR scans make the fluid around the brain and spine go dark. Do not use STIR after contrast: it can also darken the parts the contrast lights up.
- Diffusion scans (DWI) show water that cannot move freely as bright. Always read them with the matching ADC map, which removes a misleading brightness called T2 shine-through.
- Scanner makers give the same type of scan different brand names. The same fast spin echo scan is called TSE on Siemens and Philips scanners and FSE on GE and Canon ones.
- Blood vessels can be scanned without a contrast injection when kidney problems rule out the dye. One method, phase contrast, can also show which way and how fast blood flows.
A guide only: follow your departmental protocols and regional requirements.
1 · Master comparison
The 20-second orientation. Detailed cards for each follow below.
| Family | Core mechanism | Typical weighting/output | Bread-and-butter use |
|---|---|---|---|
| Spin echo (SE / FSE·TSE) | 90° then 180° refocusing pulse(s) | T1, PD, T2: the reference standard | Almost everything; robust to field inhomogeneity |
| Inversion recovery (STIR, FLAIR, PSIR, MP-RAGE) | 180° inversion + tailored TI to null a tissue | Fat-null, fluid-null, or high-contrast T1 3D | Oedema, MS plaques, fat suppression, volumetric brain |
| Gradient echo: spoiled (FLASH/SPGR/T1-FFE) | Gradient reversal, no 180°, spoiled residual signal | T1 / T2* fast imaging | Breath-hold T1, dynamic post-contrast, 3D VIBE |
| Gradient echo: balanced SSFP (TrueFISP/FIESTA/bFFE) | Fully rewound gradients, coherent steady state | High-SNR T2/T1 ratio, bright fluid & blood | Cardiac cine, fetal, MRCP, inner ear |
| Echo-planar (EPI) | Single/multi-shot readout of whole k-space per excitation | Very fast; carries DWI, perfusion, BOLD | Diffusion, DSC perfusion, functional MRI |
| Diffusion / functional | Motion-probing gradients or physiologic contrast | DWI/ADC, DTI, ASL, BOLD, SWI, MRS | Stroke, tractography, tumour, microbleeds, spectra |
| Vascular / flow (MRA·MRV) | Inflow, phase shift, or contrast bolus | Arteriograms, venograms, flow quantification | Circle of Willis, carotids, aorta, DVT/sinus thrombosis |
| Fat–water / suppression | Chemical-shift separation or selective saturation | Fat-only, water-only, in/out-of-phase | Adrenal/liver fat, marrow, uniform fat-sat |
2 · Spin-echo family
A 90° excitation followed by one or more 180° refocusing pulses. The 180° cancels static field inhomogeneity, so SE is the family most resistant to susceptibility and field-inhomogeneity artefact and the benchmark for tissue contrast.
Conventional SE
- Principle
- One 180° refocus per TR. True T1, PD or T2 depending on TR/TE.
- Use
- Reference T1 (short TR/TE). Largely replaced by FSE for T2/PD because it is slow.
▲ Clean contrast, low artefact · ▼ Long acquisition
Fast / Turbo SE (FSE · TSE)
- Principle
- An echo train: multiple 180° pulses per TR fill several k-space lines (echo-train length/turbo factor), cutting scan time in proportion.
- Use
- The workhorse for T2 and PD everywhere. Fat stays brighter than on true SE (reduced J-coupling), so often paired with fat-sat.
Vendor: Siemens TSE · GE FSE · Philips TSE · Canon FSE
Single-shot FSE (SSFSE · HASTE)
- Principle
- All (or half, with half-Fourier) k-space lines in one very long echo train: a whole slice in under a second.
- Use
- Motion-insensitive T2: fetal, uncooperative patients, MRCP, myelography.
Vendor: Siemens HASTE · GE SSFSE · Philips SSh-TSE · Canon FASE
3D FSE volumetric (SPACE·CUBE·VISTA)
- Principle
- 3D FSE with variable-flip refocusing pulses to sustain a long echo train; isotropic sub-mm volume, reformat in any plane.
- Use
- 3D T2/FLAIR/STIR of brain, spine, MSK; one acquisition reformatted instead of three 2D stacks.
Vendor: Siemens SPACE · GE CUBE · Philips VISTA · Canon 3D MVOX
3 · Inversion-recovery family
A 180° inversion pulse precedes the imaging readout. By choosing the inversion time (TI), the signal from one tissue is caught at its null (zero crossing) and disappears. See the TI-to-null calculator for the numbers.
STIR (Short TI IR)
- Principle
- Short TI (~150–170 ms at 1.5T) nulls fat by its short T1. Suppression is B0/B1-insensitive, so it works where chemical fat-sat fails.
- Use
- Marrow/soft-tissue oedema, MSK, whole-body. Do not use with gadolinium; it can also null enhancing tissue.
FLAIR (Fluid-Attenuated IR)
- Principle
- Long TI (~2000–2500 ms) nulls CSF while keeping heavy T2 weighting: bright lesions on a dark-fluid background.
- Use
- Periventricular MS plaques, gliosis, SAH detection. 3D FLAIR (SPACE/CUBE) for small cortical/juxtacortical lesions.
PSIR (Phase-Sensitive IR)
- Principle
- Recovers the sign of the inverted signal, doubling the effective T1 dynamic range and giving crisp grey–white contrast.
- Use
- Cortical/spinal-cord MS lesions, late-gadolinium cardiac viability imaging.
MP-RAGE / 3D IR-SPGR
- Principle
- A single inversion prepares magnetisation, then a fast spoiled-GRE readout: isotropic, high grey–white-contrast T1 volume.
- Use
- Volumetric brain, neuro-navigation, volumetry. MP2RAGE variant removes B1 bias for quantitative T1.
Vendor: Siemens MPRAGE · GE BRAVO/3D IR-SPGR · Philips 3D TFE · Canon 3D FFE
DIR (Double IR)
- Principle
- Two inversion pulses null two tissues at once (e.g. CSF and white matter).
- Use
- Cortical/juxtacortical MS lesions; black-blood cardiac and vessel-wall imaging.
4 · Gradient-echo family
A gradient reversal replaces the 180°, so flip angles are small and TR/TE short; it is very fast, but sensitive to susceptibility (T2*). Two branches: spoiled (residual transverse signal destroyed each TR) and balanced steady-state (residual signal preserved and reused).
Spoiled GRE (FLASH·SPGR·T1-FFE)
- Principle
- RF or gradient spoiling removes leftover transverse magnetisation → clean T1 (or PD/T2* by TE).
- Use
- Breath-hold T1, dynamic contrast, angio source images.
Vendor: Siemens FLASH · GE SPGR · Philips T1-FFE · Canon FastFE
3D fat-sat spoiled GRE (VIBE·LAVA·THRIVE)
- Principle
- 3D spoiled GRE with Dixon/spectral fat-sat: thin isotropic T1 volume in a breath-hold.
- Use
- Dynamic liver, pre/post-contrast abdomen & pelvis, breast.
Vendor: Siemens VIBE · GE LAVA · Philips THRIVE · Canon Quick3D/LAVA-like
Balanced SSFP (TrueFISP·FIESTA·bFFE)
- Principle
- All gradients rewound each TR → coherent steady state with very high SNR and a T2/T1 contrast; fluid and flowing blood are bright.
- Use
- Cardiac cine, fetal, MRCP, cranial nerves/inner ear, bowel. Prone to dark banding artefact at field inhomogeneity (needs good shim/short TR).
Vendor: Siemens TrueFISP · GE FIESTA · Philips Balanced-FFE · Canon True SSFP
Coherent/steady-state variants (FISP·GRASS · PSIF·SSFP-echo · DESS·MERGE)
- Principle
- Partially rewound (FISP/GRASS) or time-reversed (PSIF) steady states; DESS/MEDIC combine both for T2*-like cartilage contrast.
- Use
- Cartilage (DESS), spine/nerve (MEDIC/MERGE), flow-tolerant fast imaging.
Vendor: Siemens FISP/PSIF/DESS/MEDIC · GE GRASS/SSFP/MERGE · Philips FFE/T2-FFE
5 · Echo-planar (EPI) readout
Not a contrast in itself but an ultra-fast readout: an oscillating gradient traverses much or all of k-space after a single excitation. It is the delivery vehicle for diffusion, perfusion and BOLD, at the cost of geometric distortion and susceptibility drop-out near air/bone.
Single-shot EPI
- Principle
- Whole slice in one shot (~50–100 ms). Freezes motion but distorts at air interfaces.
- Use
- Standard DWI, DSC perfusion, fMRI.
Multi-shot / readout-segmented EPI
- Principle
- k-space split across shots (e.g. RESOLVE) → less distortion, higher resolution.
- Use
- High-resolution DWI of orbit, skull base, spine, breast.
Vendor: Siemens RESOLVE · GE MUSE · Philips multi-shot DWI
6 · Diffusion, perfusion & advanced contrast
Sequences whose contrast comes from tissue physiology or microstructure rather than plain T1/T2.
DWI + ADC
- Principle
- Paired motion-probing gradients dephase moving water; restricted water stays bright. Acquire ≥2 b-values → ADC map removes T2 shine-through.
- Use
- Hyperacute stroke, abscess vs necrosis, cellular tumour, cholesteatoma. Always read DWI with the ADC map.
DTI / DKI / tractography
- Principle
- Diffusion sampled in ≥6 directions → anisotropy (FA) and fibre orientation; DKI adds non-Gaussian kurtosis.
- Use
- White-matter tract mapping for surgical planning, microstructural research.
DSC perfusion
- Principle
- Dynamic T2*-EPI tracks a gadolinium bolus first pass → CBV, CBF, MTT.
- Use
- Tumour grading, recurrence vs radiation necrosis, stroke penumbra.
DCE perfusion
- Principle
- Dynamic T1 spoiled-GRE tracks contrast leakage → permeability (Ktrans).
- Use
- Prostate (mpMRI), breast, tumour angiogenesis.
ASL (Arterial Spin Labelling)
- Principle
- Magnetically labels arterial blood water as an endogenous tracer (no contrast agent).
- Use
- Cerebral perfusion in children/renal-impaired patients, tumour, ischaemia.
BOLD fMRI
- Principle
- T2*-EPI detects deoxy/oxy-haemoglobin ratio changes with neuronal activity.
- Use
- Pre-surgical eloquent-cortex mapping, research.
SWI / SWAN / T2*-GRE
- Principle
- Flow-compensated 3D spoiled GRE combining magnitude + phase to amplify susceptibility from blood products, iron, calcium.
- Use
- Microbleeds, DAI, cavernomas, mineralisation, vein mapping.
Vendor: Siemens SWI · GE SWAN · Philips SWIp · Canon SWI/FSBB
MRS (single-voxel / CSI)
- Principle
- Resolves metabolite chemical shifts (NAA, choline, creatine, lactate, lipid) instead of an image.
- Use
- Tumour vs necrosis, metabolic disease, prostate.
7 · Vascular & flow: MRA and MRV
Three physical routes to a vessel image: inflow (TOF), velocity-encoded phase (PC), and contrast bolus (CE-MRA), plus time-resolved and non-contrast variants built on them. Venography (MRV) uses the same physics tuned to slow venous flow.
Show the full section
Time-of-Flight MRA (2D & 3D TOF)
- Principle
- Stationary tissue is saturated by rapid RF; fresh unsaturated blood flowing in is bright. No contrast. A travelling saturation band suppresses either arteries or veins by inflow direction.
- Use
- 3D TOF for Circle of Willis/intracranial arteries; 2D TOF for slower/longer runs (carotids, peripheral, and TOF venography).
▲ No contrast, great for COW · ▼ Slow flow saturates, in-plane flow lost, overestimates stenosis
Phase-Contrast MRA (PC)
- Principle
- Bipolar gradients give moving spins a phase shift proportional to velocity. You set a VENC (encoding velocity); aliasing occurs if true velocity exceeds it.
- Use
- Directional & quantitative flow, slow venous flow (PC-MRV, dural sinuses), CSF flow, distinguishing thrombus from slow flow.
▲ Quantitative, direction-encoded, background fully suppressed · ▼ Slow; VENC must match expected velocity
Contrast-Enhanced MRA (CE-MRA)
- Principle
- Fast 3D spoiled GRE during a timed gadolinium bolus shortens blood T1 directly; signal comes from contrast, not flow, so flow artefacts largely vanish. Timed by test-bolus or bolus-tracking (SmartPrep/CARE-Bolus/BolusTrak).
- Use
- Aorta, renal, carotid, run-off/peripheral, pulmonary arteries.
▲ Fast, large FOV, few flow artefacts · ▼ Needs gadolinium & correct bolus timing (venous contamination if late)
Time-resolved CE-MRA (TWIST·TRICKS·4D-TRAK·DISCO)
- Principle
- Repeatedly under-samples k-space (sampling the centre often, the periphery sparsely) to make a rapid 3D dynamic series that captures arterial → venous phases. Removes the need for precise bolus timing and adds temporal information.
- Use
- AVMs/fistulae, distal run-off, hand/foot, congenital and dialysis-access vessels where flow dynamics matter.
Vendor: Siemens TWIST · GE TRICKS · Philips 4D-TRAK · Canon DISCO-like/Freeze-Frame
4D flow MRI (PC-VIPR)
- Principle
- Time-resolved 3-directional velocity encoding over a 3D volume: flow through the whole territory across the cardiac cycle.
- Use
- Aortic & congenital-heart haemodynamics, wall shear stress, shunt/valve quantification (research → clinical).
Non-contrast MRA: ECG-gated FSE (FBI/NATIVE-SPACE)
- Principle
- 3D FSE subtraction of bright-artery systolic and dark-artery diastolic images (fresh-blood imaging). No gadolinium.
- Use
- Peripheral run-off in renal-impaired patients (NSF avoidance).
Vendor: Canon FBI · Siemens NATIVE SPACE · Philips TRANCE · GE Delta Flow
QISS (Quiescent-Interval Single-Shot MRA)
- Principle
- 2D single-shot balanced-SSFP acquired station-by-station, triggered off the cardiac cycle, either ECG-gated (leads on the chest) or peripheral-pulse-gated (a finger/toe pulse-oximetry trigger), the latter often more reliable at distal stations or when ECG signal is degraded by gradient/RF noise or an irregular rhythm. A slice-selective saturation pulse is followed by a “quiescent interval” (~150–200 ms, timed to diastole) that lets fresh unsaturated arterial blood flow into the section while a travelling venous saturation band keeps veins dark: bright artery on a suppressed background, no contrast.
- Use
- Peripheral run-off (aorta to foot); the best-validated non-contrast option for lower-extremity peripheral arterial disease, particularly when gadolinium is contraindicated (severe renal impairment / NSF risk).
▲ No contrast, robust venous suppression, station-by-station coverage, gating flexible (ECG or pulse) · ▼ Slower than CE-MRA; needs a regular, reliably detected cardiac trigger; arrhythmia, poor pulse signal, or a mistimed saturation band degrades quality
Other inflow / labelling non-contrast MRA (NATIVE TrueFISP · Inhance · Time-SLIP)
- Principle
- Balanced-SSFP inflow techniques (NATIVE TrueFISP, Inhance) brighten arterial inflow the same way as QISS. Time-SLIP instead uses a spatially selective ASL-style tag placed proximal or distal to the target vessel; imaging after a chosen delay shows only the labelled blood that has flowed into the region: a selective, direction-controlled single-vessel “roadmap” angiogram.
- Use
- Renal arteries, portal/hepatic and other abdominal vessels, paediatric imaging, and any renal-impaired patient where gadolinium should be avoided.
Vendor: Siemens NATIVE TrueFISP · GE Inhance · Philips TRANCE/b-TRANCE · Canon Time-SLIP
MR venography (MRV)
- Principle
- Same three routes, tuned to slow venous flow: 2D TOF venography (dural sinuses/legs), PC-MRV (direction & quantification, thrombus vs slow flow), and CE-MRV (large-territory venous mapping).
- Use
- Cerebral venous sinus thrombosis, DVT, venous mapping. SWI complements MRV for slow/occluded veins.
8 · Fat–water separation & suppression
Not standalone families but techniques layered onto SE/GRE to control fat signal; a frequent source of confusion, so grouped here.
In-/opposed-phase GRE (chemical shift)
- Principle
- Two TEs where fat & water are in phase vs opposed; voxels with both drop signal on opposed-phase.
- Use
- Adrenal adenoma, hepatic steatosis, marrow.
Dixon (multi-echo)
- Principle
- Acquires multiple echoes and computes four sets (in-phase, opposed-phase, water-only, fat-only) in one pass. Robust uniform fat-sat + fat-fraction maps.
- Use
- Uniform fat suppression over large/off-isocentre FOV, PDFF quantification.
Vendor: Siemens Dixon · GE IDEAL · Philips mDixon · Canon WFS/Dixon
SPAIR · SPIR · fat-sat · water excitation
- Principle
- Frequency-selective pulses saturate (SPIR) or invert-and-null (SPAIR) fat, or excite only water. SPAIR is more B1-robust than plain fat-sat.
- Use
- Post-contrast fat-sat (unlike STIR, compatible with gadolinium), cartilage, breast.
9 · Vendor name Rosetta table
Same physics, different marketing. Read across the row.
| Generic | Siemens | GE | Philips | Canon |
|---|---|---|---|---|
| Fast/Turbo SE | TSE | FSE | TSE | FSE |
| Single-shot FSE | HASTE | SSFSE | SSh-TSE | FASE |
| 3D FSE volume | SPACE | CUBE | VISTA | 3D MVOX |
| Spoiled GRE T1 | FLASH | SPGR | T1-FFE | FastFE |
| 3D fat-sat spoiled GRE | VIBE | LAVA | THRIVE | 3D Quick |
| Balanced SSFP | TrueFISP | FIESTA | bFFE | True SSFP |
| 3D IR T1 (volumetric brain) | MPRAGE | BRAVO | 3D TFE | 3D FFE |
| Susceptibility-weighted | SWI | SWAN | SWIp | SWI/FSBB |
| Time-resolved CE-MRA | TWIST | TRICKS | 4D-TRAK | Freeze-Frame/DISCO-like |
| Non-contrast inflow MRA (QISS-type) | NATIVE TrueFISP | Inhance | TRANCE/b-TRANCE | Time-SLIP |
| Dixon fat-water | Dixon | IDEAL | mDixon | WFS/Dixon |
Sequence decision guide: choosing between close alternatives
Practical “this vs that” calls that come up when building or tuning protocols: what each option buys you, what it costs, and when to pick which. Educational reference; always validate against your local protocol and radiologist preference.
1 · T1 MPRAGE brain post-contrast: fat-sat vs non-fat-sat
Post-gadolinium 3D T1 MPRAGE of the brain can be run with or without fat suppression. The choice depends on what you’re looking for and where.
| Non-fat-sat MPRAGE | Fat-sat MPRAGE | |
|---|---|---|
| Best for | Parenchymal / intra-axial enhancement, general post-Gd brain, volumetrics | Skull base, orbits, cavernous sinus, IACs, scalp/calvarium, post-op beds, and anywhere marrow/orbital fat masks enhancement |
| Why | Bright T1 fat is a familiar anatomical backdrop; maximal SNR & grey–white contrast for brain | Suppressing bright fat unmasks subtly enhancing lesions next to fat (dural tails, perineural spread, orbital/skull-base disease) that would otherwise be iso-intense to fat |
| Cost | Enhancement adjacent to fat can be hidden | Lower SNR; fat-sat failure/inhomogeneity at skull base & air interfaces; slightly longer |
2 · Whole-spine imaging: MSK vs neuro emphasis, and FS vs non-FS post-contrast
“Whole spine” means different things to a neuro service (cord, canal, leptomeninges) and an MSK/oncology service (marrow, bones, soft tissue). That drives sequence weighting and fat-sat choice.
| Neuro emphasis | MSK / marrow emphasis | |
|---|---|---|
| Question | Cord signal, compression, MS/myelitis, leptomeningeal/drop mets, CSF | Marrow infiltration, mets, discitis-osteomyelitis, fractures, soft-tissue mass |
| Core sequences | Sag T2 & T1, STIR, axials through lesions; post-Gd T1 for tumour/infection/inflammation | Sag T1 (marrow), STIR/T2 fat-sat (oedema), Dixon; post-Gd T1 fat-sat |
| Post-contrast fat-sat? | Yes, generally fat-sat: spine marrow & epidural fat are bright on T1; unsuppressed, enhancing leptomeningeal/epidural/marrow disease blends into fat. Fat-sat (or subtraction) makes enhancement conspicuous | Yes, fat-sat: essential to see marrow & soft-tissue enhancement against bright fatty marrow |
| When non-fat-sat T1 post-Gd helps | As an anatomical companion, or via subtraction (pre/post non-fat-sat) where fat-sat is inhomogeneous over a long FOV | Rarely alone; pairs with pre-contrast T1 for subtraction |
3 · Black-blood imaging: pre- vs post-contrast
Black-blood techniques (double/triple inversion recovery, or T1 SPACE/CUBE/VISTA with flow-suppression) null flowing blood so the vessel wall, meninges or myocardium stand out against a dark lumen.
| Pre-contrast black-blood | Post-contrast black-blood | |
|---|---|---|
| Shows | Baseline wall thickness, morphology, intramural haematoma/plaque, oedema | Wall/leptomeningeal/plaque enhancement, the key marker of active inflammation, vulnerable plaque, or leptomeningeal/dural disease |
| Role | Reference for comparison; without it you can’t call enhancement | The diagnostic series in vessel-wall imaging, black-blood brain-met detection & leptomeningeal disease |
- Vessel-wall MRI (intracranial vasculitis, dissection, plaque): pre and post black-blood T1 are both needed; enhancement is only meaningful against the matched pre-contrast image.
- Black-blood post-Gd T1 for brain metastases / leptomeningeal disease: suppressing bright vascular signal stops small enhancing vessels mimicking or hiding tiny enhancing mets and improves small-lesion conspicuity vs bright-blood post-Gd.
4 · T2 SPACE (3D TSE) vs conventional 2D T2 TSE
SPACE (Siemens) / CUBE (GE) / VISTA (Philips) / 3D MVOX (Canon) is a single-slab 3D turbo-spin-echo with a long, variable-flip echo train. How it compares to standard 2D T2 TSE:
| 2D T2 TSE | T2 SPACE / 3D TSE | |
|---|---|---|
| Resolution | Good in-plane; thick slices with gaps | Isotropic sub-mm: reformat in any plane from one acquisition |
| Coverage/planes | One plane per acquisition; repeat for each | One slab → axial/sag/cor reformats; replaces several 2D series |
| SNR per voxel | Higher per voxel (thicker slices) | Lower per (tiny) voxel, offset by 3D averaging & thin slices |
| Blurring/contrast | Crisp; conventional T2 contrast | Variable-flip train → some T2 blurring & slightly altered contrast; excellent for CSF/fluid & small structures |
| Time & motion | Fast per plane; robust | Longer single acquisition; more motion-sensitive (whole slab degrades) |
| Flow/pulsation | Can have CSF flow artefact | Better flow suppression; good for cisternal nerves, internal auditory canal, spine canal |
5 · STEALTH T1 MPRAGE neuronavigation: 0.9 mm vs 1.0 mm isotropic
For a StealthStation / neuronavigation 3D T1 (typically post-contrast MPRAGE covering the whole head), the isotropic voxel choice trades registration/detail against SNR and time.
| 1.0 mm isotropic | 0.9 mm isotropic | |
|---|---|---|
| Detail | Standard for navigation; adequate for most cranial cases | ~30% smaller voxel volume → finer surface/lesion detail, marginally better small-target localisation |
| SNR | Higher per voxel (voxel is ~37% larger) | Lower SNR per voxel; needs recovering (averages, BW, DL-recon) or images look noisier |
| Time | Shorter | Longer (more encoding steps for full-head coverage) |
| Navigation upload | Universally accepted; whole-head coverage & contiguous slices matter more than 0.1 mm | Accepted; benefit is real only if SNR is maintained and the patient holds still for the longer scan |
6 · T1 MPRAGE: axial vs sagittal acquisition
Because MPRAGE is a 3D isotropic acquisition, you can reformat any plane afterwards, so the acquired plane matters less for viewing and more for artefact direction, wrap and motion behaviour.
| Sagittal-acquired MPRAGE | Axial-acquired MPRAGE | |
|---|---|---|
| Typical use | The common default: efficient whole-head slab, natural for midline structures (corpus callosum, brainstem, ventricles), volumetrics | Chosen when axial is the primary read plane or to orient wrap/phase artefact away from a region of interest |
| Coverage efficiency | Fewer slices to cover the head L–R; often fastest for whole brain | More slices to cover vertex–foramen; can be longer |
| Wrap/fold | Phase wrap tends to be S–I or A–P depending on setup; midline geometry clean | Wrap can come off shoulders/neck; watch phase direction |
| Reformats | Isotropic → axial & coronal reformats are equivalent in quality | Isotropic → sagittal & coronal reformats equivalent |
7 · “True axial” vs “normal axial”
These terms describe how the slice/plane is aligned relative to the patient’s true anatomical axes versus the scanner/table axes.
- True axial (orthogonal to the anatomy): the slice is angled to the patient’s actual anatomical planes, e.g. perpendicular to the long axis of the structure or aligned to a defined anatomical landmark line (AC–PC for brain, disc space for spine, the specific joint axis for MSK). It corrects for how the patient is actually lying or how the structure is oriented.
- Normal / straight axial (orthogonal to the scanner): the slice is aligned to the magnet’s z-axis / table: straight transverse “as the patient lies,” without angling to anatomy.
| True axial | Normal axial | |
|---|---|---|
| Aligned to | Patient anatomy / a defined landmark line | Scanner/table (straight transverse) |
| Pros | Symmetric, reproducible planes; correct comparison L vs R; matches reporting conventions & prior studies; essential for AC–PC brain, orbits, IACs, cardiac, angled joints | Fast to prescribe; fine when the patient is well-positioned and the structure is already aligned to the bore |
| Cons | Takes a moment more to plan off the localiser | Asymmetric/oblique through the target if the patient is rotated or the structure is angled → harder to compare sides & to priors |
8 · Contrast-enhanced vs non-contrast MRA/MRV: when to skip gadolinium
Both arteriography and venography can be built on a contrast platform (CE-MRA / CE-MRV) or a non-contrast one (TOF, PC, QISS, FBI/NATIVE-SPACE). The choice turns on renal function, the vascular territory, and whether the question is anatomy alone or flow direction/quantification too.
| Contrast-enhanced (CE-MRA / CE-MRV) | Non-contrast (TOF · PC · QISS · FBI) | |
|---|---|---|
| Signal source | Shortened blood T1 from a timed gadolinium bolus, independent of flow pattern | Flow itself: inflow saturation (TOF/QISS), velocity-induced phase shift (PC), or ECG-gated subtraction (FBI); signal depends on flow velocity, direction and rhythm |
| Best for | Large-territory, single fast-acquisition coverage: aorta, renal, carotid, pulmonary, run-off; time-resolved variants (TWIST/TRICKS) for AVMs and dynamic arterial→venous filling | Renal impairment / NSF risk, paediatric or contrast-averse patients, screening exams, and any case where flow direction or velocity is itself the answer (PC) |
| Flow-pattern sensitivity | Largely avoided; the vessel is bright from contrast regardless of flow pattern, so slow, turbulent or in-plane flow is not a problem | A real limitation: TOF saturates slow flow and can overestimate stenosis; PC needs a correctly chosen VENC; QISS/FBI need a regular, reliably detected cardiac trigger (ECG or peripheral pulse) |
| Venous side | CE-MRV maps large venous territories quickly but needs correct bolus timing to avoid arterial contamination | 2D TOF and PC-MRV are the default for dural-sinus thrombosis / DVT screening without contrast; PC-MRV additionally distinguishes thrombus from slow flow by direction |
| Main cost | Gadolinium exposure and bolus-timing risk (too early = arterial-only, too late = venous contamination); agent and time cost | Longer acquisition; more sensitive to motion, arrhythmia and technique; less forgiving of a poorly planned saturation band or VENC |
See the full sequence catalogue above for the underlying families (MPRAGE, SPACE/3D TSE, IR, black-blood, MRA/MRV) and the Sequence & Protocol Optimiser for how to defend SNR when you push resolution.
Teaching reference. Parameter ranges, vendor implementations and clinical indications vary by scanner, field strength and local protocol; always confirm against your site’s protocols and manufacturer documentation.
Related on High Yield Imaging: Sequence Physics Explainer (TR/TE/flip & k-space) · Sequence Optimiser (problem-solving & tuning) · Protocols & Parameters explorer · MR Calculators (VENC, TI-to-null, Ernst angle).
Sources
Key references: Bitar R et al. MR pulse sequences: what every radiologist wants to know but is afraid to ask. RadioGraphics 2006. · Hartung MP et al. Magnetic resonance angiography: current status and future directions. J Cardiovasc Magn Reson 2011. · Miyazaki M, Lee VS. Nonenhanced MR angiography. Radiology 2008. · Edelman RR et al. Quiescent-interval single-shot unenhanced magnetic resonance angiography of peripheral vascular disease. AJR 2010. · Markl M et al. 4D flow MRI. JMRI 2012. · Haacke EM et al. Susceptibility-weighted imaging. AJNR 2009. · ISMRM/ACR white papers & manufacturer sequence documentation.