Why put a pad under the knees for a lumbar MRI?

The lumbar spine curves forward and lifts away from the table coil. Flexing the hips over a knee pad flattens the spine against the coil, which raises signal-to-noise, opens the disc spaces and makes it easier for the patient to lie still.

Why does each disc get its own axial stack?

The lumbar spine is curved, so every disc sits at a different angle; one straight block cannot be parallel to all of them and cuts the end discs obliquely, faking a bulge. A short stack parallel to each disc shows every level true.

How do you avoid operating on the wrong level?

Count from a fixed landmark (down from C2 on a whole-spine scout, or up from the sacrum) and document any transitional vertebra (e.g. LSTV) with your counting reference, so the surgeon and radiologist agree on numbering.

Why phase-encode head-to-foot on lumbar sagittals?

With anterior–posterior phase, pulsation from the aorta ghosts directly over the spinal canal. Head-to-foot phase moves that motion artefact along the spine instead of across the pathology.

Lumbar spine MRI protocol

The most common spine exam you will run. The questions are specific (a herniated disc causing sciatica, stenosis squeezing the cauda equina, a fracture), and the answers hinge on flattening the spine and counting levels correctly.

By the ScanFlo Editorial Team · Updated 12 October 2026

In this section · Protocols

Protocols/Spine

Video language

When this study is used

Back pain, sciatica or radiculopathy.
Suspected disc herniation, spinal stenosis or cauda equina syndrome.
Suspected fracture, metastasis or spondylolysis.

Patient & coil positioning

Head-first supine, straight on the spine coil, arms by the sides and clear of the field of view (cross them on the chest if they would wrap into it).
A pad or wedge under the knees. Flexing the hips flattens the lordosis against the coil, which lifts signal, opens the disc spaces and lets the patient lie still.
Centre the laser about 10 cm above the iliac crest, so the conus and the sacrum both sit in the coil.

Localizer

Three-plane localizer. The sagittal must show the conus medullaris (usually T12–L1) at the top and the sacrum below. Miss the conus and you miss tumours.

Sequence planning

For each sequence below you get the reference line the slice group follows, how much it covers, and why the sequence is in the protocol at all. Plan against the localizer, not by eye.

Sagittal T2 TSE

Sagittal

Planning: On the coronal, parallel to the spinal cord and canal. On the axial, along the line from the centre of the vertebral body to the spinous process, so the slices fall on the midline. Cover from one transverse process to the other; the FoV runs from T11 to the coccyx. Phase head-to-foot so aortic ghosts miss the canal.

Why: Myelogram effect (bright CSF and disc water, dark nerves); best for compression.

Sagittal T1 TSE

Sagittal

Planning: Copy the T2 sagittal's slices (Copy Parameter → Slices) so both stacks fall in the same place slice for slice.

Why: Anatomical map; marrow signal for cancer or fracture (fat and marrow bright, CSF dark).

Axial T2 TSE (one stack per disc)

Axial

Planning: A separate stack for each disc from L1–L2 to L5–S1, each parallel to its own disc on the sagittal. The L5–S1 disc next to the sacrum is the steepest and needs the biggest tilt. 3–5 slices per disc, centred on the nucleus, with no overlap in the canal.

Why: Disc, canal and nerve-root assessment at each level.

Coronal STIR (T2 TIRM)

Coronal

Planning: On the sagittal, parallel to the spine, covering the vertebral bodies and the canal from front to back; shim on the spine, excluding bowel gas.

Why: Marrow oedema and fluid: acute fracture, metastasis, infection and paraspinal collections.

In the video

The video scans a ScanFlo Lumbar Spine case. The angles are that patient's, so follow the landmarks, not the numbers.
Sagittal T2: 13 slices, 4 mm, 10% gap, FoV 300 mm, TR 3000 / TE 103 ms; tilted about 3° on the coronal because this spine is slightly tilted. The T1 sagittal (TR 500 / TE 8 ms) copies it with Copy Parameter → Slices.
Axial T2: five per-disc slice groups, L1–L2 to L5–S1 (18 slices, 4 mm), TR 4250 / TE 101 ms; L5–S1 tilts about 8° on the sagittal and L4–L5 about 4°.
Coronal STIR: 15 slices, 4 mm, 20% gap.
The queue takes about 5½ minutes; the video shows the scan as a time-lapse.

Representative parameters

Treat these as ranges. Field strength, coil and vendor all move the numbers. What must not move is understanding why each sits where it does.

Sequence	Field	Matrix / FOV	Notes
T2 TSE sagittal	1.5–3 T	320 / 28–32 cm	Phase H–F to avoid aortic ghost
T1 TSE sagittal	1.5–3 T	320 / 28–32 cm	Marrow, anatomy
T2 axial	1.5–3 T	256–320 / 18–22 cm	One stack per disc; thin for roots
STIR coronal	1.5–3 T	256 / 30–34 cm	Fracture, metastasis, infection

Artifacts & how to fix them

Artifact	Typical cause	Mitigation
CSF pulsation ghost	Turbulent CSF, aortic pulsation	Anterior sat band over the aorta; flow compensation
Inhomogeneous STIR	Large FOV and bowel gas	Shim on the spine only, excluding the belly
Blurry nerve roots	Partial-volume on thick axials	Drop to 3 mm; raise matrix
Phase wrap	Arms in the FOV	Arms crossed on chest; oversampling

What am I looking at?

You are not reporting the study, but recognising pathology helps you keep it in the field of view and know when to add a sequence or contrast. How the common findings read on the console:

Finding	Sequence to check	How it reads
Stenosis	Axial T2	Round thecal sac squeezed to a trefoil or slit
Cauda equina syndrome	Sagittal/axial T2	Canal filled with grey disc, no bright fluid; surgical emergency, flag it
Pars defect	Sagittal / parasagittal T1	Dark break in the neck of the bone between the facets
Metastasis / fracture	Coronal STIR + sagittal T1	Bright oedema on STIR; dark marrow replacement or fracture line on T1

Review checklist

Conus medullaris and the whole sacrum included on the sagittal.
T1 sagittal copied from the T2, slice for slice.
Axial stacks angled per disc, L5–S1 tilted to match its slope, none overlapping in the canal.
STIR fat suppression uniform along the spine.
Any cauda-equina compression escalated immediately.

Mistakes that cost repeats

Flat positioning leaving the lordosis lifted off the coil, dropping signal.
A straight axial block cutting the steep L5–S1 disc obliquely.
Overlapping per-disc stacks in the canal, so the slices saturate each other (cross-talk).
Miscounting levels in transitional anatomy. Document the counting reference.
AP phase direction letting aortic ghosts streak over the canal.

Common questions

Why put a pad under the knees for a lumbar MRI?: The lumbar spine curves forward and lifts away from the table coil. Flexing the hips over a knee pad flattens the spine against the coil, which raises signal-to-noise, opens the disc spaces and makes it easier for the patient to lie still.
Why does each disc get its own axial stack?: The lumbar spine is curved, so every disc sits at a different angle; one straight block cannot be parallel to all of them and cuts the end discs obliquely, faking a bulge. A short stack parallel to each disc shows every level true.
How do you avoid operating on the wrong level?: Count from a fixed landmark (down from C2 on a whole-spine scout, or up from the sacrum) and document any transitional vertebra (e.g. LSTV) with your counting reference, so the surgeon and radiologist agree on numbering.
Why phase-encode head-to-foot on lumbar sagittals?: With anterior–posterior phase, pulsation from the aorta ghosts directly over the spinal canal. Head-to-foot phase moves that motion artefact along the spine instead of across the pathology.

Try it in ScanFlo: Plan a lumbar sagittal with the knees flat, then re-plan after adding a knee wedge, and compare the disc spaces and signal. The flattened lordosis is the difference between a grainy scan and a crisp one. See ScanFlo MRI →

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