Lumbar spine protocol (MRI)

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.

Indications

The most common indications include ^1-3:

• low back pain (red and yellow flags)
• degenerative disc disease
  • disc herniation and radiculopathy
  • suspected spinal canal stenosis
  • cauda equina syndrome
• spinal trauma and suspected lumbar spine fractures
• spinal tumors and/or vertebral metastasis
• spinal infections such as spondylodiscitis, epidural abscess etc. 
• inflammatory/autoimmune conditions
  • inflammatory arthritis
  • acute inflammatory demyelinating polyradiculopathy (Guillain-Barre syndrome)
  • chronic inflammatory demyelinating polyradiculopathy
• 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 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:

• 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
• 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
• axial images (long stack):
  • angulation: perpendicular to the lumbar spine
  • volume: variable depends on the clinical question and/or the visible pathology
  • slice thickness: ≤3 mm
• 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 do not require any contrast media, the latter is usually administered in the setting of tumors, infection and postoperative imaging such as suspected complications of spinal surgery.

Standard sequences

• T1-weighted
  • purpose: bone and/or soft-tissue characterization
  • technique:  T1 fast spin echo
  • planes: sagittal, axial* (optional)
• T2-weighted
  • purpose: bone and/or soft-tissue characterization, detailed anatomy, including ligament and tendon anatomy
  • technique: T2 Dixon / T2 fast spin echo
  • planes: coronal, sagittal, axial
• T2-weighted (fat-saturated)
  • purpose: bone and soft tissue characterization, assessment of inflammatory changes, fractures
  • technique: T2 Dixon / STIR / T2 FS fast spin echo,
  • planes: coronal or sagittal, axial*

Optional sequences

• chemical shift imaging
  • purpose: bone and soft tissue characterization, tumors
  • technique: 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, tumors, suspected complications of spinal surgery or the differentiation between epidural fibrosis/spinal nerve root scarring and recurrent disc herniation.

• T1-weighted C+ (fat-saturated)
  • purpose: for inflammatory  conditions, suspected tumors
  • 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 can be conveniently achieved by T2 Dixon images, which can save a separate acquisition
• contrast administration is typically reserved for spinal tumors or vascular malformations

See also

• investigating cauda equina syndrome
• red and yellow flags for guiding imaging of lower back pain