The MRI lumbar spine protocol encompasses a set of MRI sequences for the routine assessment of the lumbar spine.
Note: This article aims to frame a general concept of an MRI protocol for the assessment of the lumbar spine. Protocol specifics will vary depending on MRI scanner type, specific hardware and software, radiologist and perhaps referrer preference, patient factors e.g. implants, specific indications and time constraints.
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Indications
The most common indications include 1-3:
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disc herniation and radiculopathy
suspected spinal canal stenosis
spinal trauma and suspected lumbar spine fractures
spinal infections such as spondylodiscitis, epidural abscess etc.
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inflammatory/autoimmune conditions
acute inflammatory demyelinating polyradiculopathy (Guillain-Barré syndrome)
suspected complications of spinal surgery
congenital spinal malformations and spinal dysraphism
follow up of findings on other examinations
1.5 vs 3 tesla
Examinations of the spine are generally done on both 1.5 and 3.0 tesla. Postoperative examinations in patients with metallic implants, however, should be done on 1.5 tesla with a metal artifact reduction sequence (MARS). Some examinations might profit from the improved spatial and contrast resolution of 3 tesla.
Patient positioning
An MRI of the lumbar spine is usually conducted with the patient in the supine position.
A prone position can be considered in selected cases such as tethered cord syndrome.
Technical parameters
Coil
posterior coil
anterior coil
Scan geometry
in-plane spatial resolution: ≤0.7 x 0.7 mm
field of view (FOV): 300-380 (sagittal/coronal) 150-250 (axial)
slice thickness: (≤4 mm) 2,3 – better ≤3mm 4
Planning
A typical MRI of the lumbar spine might look as follows:
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sagittal images:
angulation: parallel to the lumbar spinal axis and spinous processes
volume: includes the whole vertebral bodies and the facet joints
slice thickness: ≤3 mm
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coronal images:
angulation: parallel to the lumbar spinal axis and transverse processes
volume: includes the whole vertebral body spinal canal and posterior laminae
slice thickness: ≤3 mm
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axial images (long stack):
angulation: perpendicular to the lumbar spine
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volume:
variable depends on the clinical question and/or the visible pathology
if clinical indication is generic, sufficient to include upper block (inferior half of L3 to superior half of L5) and lower block (inferior half of L5 to superior half of sacrum)
ensure slices intersect perpendicularly with nucleus pulposus
slice thickness: ≤3 mm
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axial images (short stacks)
angulation: parallel to the intervertebral discs in question
volume: variable depends on the clinical question and/or the visible pathology
slice thickness: ≤3 mm
Sequences
The mainstay in spinal imaging is T1 weighted and T2 weighted images 2. At least one T1-weighted sequence should be included to ease the assessment and interpretation of bone marrow and/or soft tissue lesions.
The majority of MRIs of the lumbar spine does not require any contrast media, the latter is usually administered in the setting of tumours, infection and postoperative imaging such as suspected complications of spinal surgery.
Standard sequences
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T1-weighted
purpose: bone and/or soft-tissue characterisation
technique: T1 fast spin echo
planes: sagittal, axial* (optional)
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T2-weighted
purpose: bone and/or soft-tissue characterisation, detailed anatomy, including ligament and tendon anatomy
technique: T2 Dixon / T2 fast spin echo
planes: coronal, sagittal, axial
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T2-weighted (fat-saturated)
purpose: bone and soft tissue characterisation, assessment of inflammatory changes, fractures
technique: T2 Dixon / STIR / T2 FS fast spin echo,
planes: coronal or sagittal, axial*
Optional sequences
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chemical shift imaging
purpose: bone and soft tissue characterisation, tumours
technique: T2 Dixon / T1 Dixon, T1 gradient-echo (GRE) in-phase (IP) and out-of-phase (OP)
planes: sagittal
Some indications might benefit from the application of contrast media such as e.g. inflammatory conditions, tumours, suspected complications of spinal surgery or the differentiation between epidural fibrosis/spinal nerve root scarring and recurrent disc herniation.
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T1-weighted C+ (fat-saturated)
purpose: for inflammatory conditions, suspected tumours
technique: T1 fast spin echo, T1 Dixon
planes: axial, sagittal
(*) indicates optional planes or sequences
Practical points
the protocol can and should be tailored to the specific indication or clinical question
as with joints and organs, the examination will benefit if three planes are imaged
a typical native protocol will consist of 4-5 sequences
nowadays fat saturation and in-and-out of phase imaging can be conveniently achieved by T2 Dixon images, which can save a separate acquisition
contrast administration is typically reserved for spinal tumours or vascular malformations