Thoracic spine protocol (MRI)

The MRI thoracic spine protocol encompasses a set of MRI sequences for the routine assessment of the thoracic spine.

Note: This article aims to frame a general concept of an MRI protocol for the assessment of the thoracic spine. An MR thoracic spine protocol might be combined with a cervical spine or lumbar spine protocol, and if not the scout should be extended to the craniocervical junction or lumbosacral junction to account for proper vertebral labeling .

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:

• inflammatory/autoimmune conditions
  • multiple sclerosis
  • acute disseminated encephalomyelitis
  • inflammatory arthritis
• spinal infections such as spondylodiscitis, vertebral osteomyelitis, spinal epidural abscess etc. 
• spinal tumors and/or vertebral metastasis
• spinal vascular malformations
• spinal cord infarction
• spinal trauma and suspected thoracolumbar spine fractures
• degenerative disc disease and suspected spinal canal stenosis
• spinal cord herniation
• syringohydromyelia
• congenital spinal malformations and spinal dysraphism
• suspected complications of spinal surgery
• follow up of findings on other examinations

1.5 vs 3 tesla

Examinations of the spine are generally performed on both 1.5 and 3.0 tesla systems. Postoperative examinations in patients with metallic implants, however, should be done on 1.5 tesla with metal artifact reduction sequence (MARS) (MARS). Some examinations may profit from the improved spatial and contrast resolution of 3 tesla.

Patient positioning

An MRI of the cervical spine is usually conducted with the patient in the supine position.

Technical parameters

Coil

• posterior coil/anterior coil
• spine coil

Scan geometry

• in-plane spatial resolution: ≤0.7 x 0.7 mm
• field of view (FOV): 320-400 (sagittal/coronal) 150-240 (axial)
• slice thickness: ≤4mm ¹ (≤3mm is preferred ^2-4)

Planning

A typical MRI of the thoracic spine might look as follows:

• sagittal images
  • angulation: parallel to the thoracic spine axis and the spinous processes
  • volume: includes the whole vertebral bodies and the facet joints
  • slice thickness: ≤3 mm
• axial images (long stack)
  • angulation: perpendicular to the thoracic spine, 
  • volume: variable depends on the clinical question and/or the visible pathology
  • slice thickness: ≤3 mm
• coronal images*            
  • angulation: parallel to the thoracic spinal axis and the costovertebral joints
  • volume: includes the whole vertebral body and the spinous process
  • slice thickness: ≤3 mm
• axial images (short stacks)*
  • angulation: perpendicular to the thoracic spine parallel to the intervertebral discs
  • 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. At least one T1-weighted sequence should be included to ease assessing and interpreting bone marrow and/or soft tissue lesions.

Contrast media is usually administered in the setting of tumors, infection and postoperative imaging such as suspected complications of spinal surgery. Depending on the exact indication the examination can be supplemented by several adjuncts ^1-4.

Standard sequences

• T1-weighted
  • purpose: bone and/or soft-tissue characterization
  • technique: T1 fast spin echo
  • planes: sagittal, axial
• T2-weighted
  • purpose: bone and/or soft-tissue characterization, detailed anatomy
  • technique: T2 Dixon / T2 fast spin echo
  • planes: 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: sagittal or coronal* ^4,5

Optional sequences

• chemical shift imaging*
  • purpose: tissue characterization of bone tumors, differentiation
  • technique: T2 Dixon or T1 Dixon, T1 gradient-echo (GRE) in-phase (IP) and out-of-phase (OP) 
  • planes: sagittal
• phase-sensitive inversion recovery*
  • purpose: might improve detection of cord lesions in multiple sclerosis ^1,7
  • technique: 3D PSIR 
  • planes: sagittal
• diffusion-weighted imaging*
  • purpose: evaluation of spinal ischemia, differentiation spondylodiscitis vs degenerative changes ^3,8
  • technique: DWI/DTI - b800 or b500 ⁶
  • planes: sagittal

Some indications might benefit from the application of contrast media. Such indications include inflammatory conditions, tumors, and suspected complications of spinal surgery.

• T1-weighted C+ (fat-saturated)
  • purpose: for inflammatory  conditions, suspected tumors
  • technique: T1 Dixon, T1 fast spin echo
  • planes: axial, sagittal
• MR Perfusion*
  • purpose: evaluation of tumors with respect to their vascularization
  • technique: T1 GRE (DCE)
  • planes: sagittal or axial

(*) indicates optional planes or sequences

Practical points

• the protocol can and should be tailored to the specific indication or clinical question
• a typical native protocol will consist of 4 sequences
• nowadays fat saturation can be conveniently achieved by Dixon images
• contrast administration is typically reserved for spinal tumors or vascular malformations