CT lumbar spine (protocol)

The CT lumbar spine or L-spine protocol serves as an examination for the assessment of the lumbar spine. As a separate examination, it is most often performed as a non-contrast study. It might be combined or simultaneously acquired with a CT abdomen. It also forms a part of a polytrauma CT or might rarely be done as a CT myelogram in situations where MRI is contraindicated.

Note: This article aims to frame a general concept of a CT protocol for the assessment of the lumbar spine. Protocol specifics will vary depending on CT scanner type, specific hardware and software, radiologist and perhaps referrer preference, patient factors e.g. implants, specific indications.

A typical CT of the lumbar spine might look like as follows:

Indications

Typical indications include the following ^1-5:

• lumbar spine fractures
• seat belt injury
• lumbar spine implants and complications
• if MRI is contraindicated
  • spinal tumors and/or vertebral metastasis
  • spondylodiscitis or inflammatory arthritis 
  • degenerative disc disease
• spondylolisthesis/spondylolysis
• lumbar spine interventions (e.g. lumbar spinal epidural injections)
• CT myelography (if MRI is contraindicated or metallic implants are present)
  • cauda equina syndrome

Purpose

The purpose of a CT of the lumbar spine in the setting of a traumatic injury is the timely diagnosis and classification or exclusion of lumbar spine fractures and/or discoligamentous injuries. 

The evaluation of the spinal canal and the intervertebral foramina is another important objective of spinal imaging in general.

In the setting of vertebral metastasis or spinal tumors, CT can help in the evaluation of the fracture risk e.g. with the spinal instability neoplastic score (SINS).

The purpose of a CT in the setting of interventions is image guidance and in this setting, the scan extent will be reduced to the segment of the intervention ^3-5.

Technique

• patient position
  • supine position 
  • both arms elevated
• tube voltage
  • 120 (140) kVp
• tube current
  • as suggested by the automated current adjustment mode 
• scout
  • diaphragm to hip
• scan extent
  • might vary with regard to the clinical question
  • should include TH12 and S1
• scan direction
  • craniocaudal
• scan geometry
  • field of view (FOV): 120-200 mm (should be adjusted to increase in-plane resolution)
  • slice thickness: ≤0.625 mm, interval: ≤0.5 mm
  • reconstruction algorithm: bone, soft tissue
• contrast injection considerations
  • usually non-contrast, optionally with contrast
  • contrast volume: 70-100 mL (0.1 mL/kg) at 2-3 mL/s
  • scan delay: 65-80 seconds
• multiplanar reconstructions/reformats
  • sagittal images: sagittal aligned through the center of the vertebral bodies and spinal processes
  • coronal images: coronal aligned to the transverse processes
  • axial images: perpendicular to the lumbar spine with a separate reconstruction of several blocks
  • curved reformats might be helpful
  • slice thickness: bone ≤2 mm, soft tissue ≤3 mm, overlap 50%

Practical points

• patient positioning prior to scanning might reduce and facilitate multiplanar reconstructions
• dose optimization ^6-9
  • use iterative reconstruction algorithms if available
  • reconstructions from the raw data set or reformations from the stored thin slice data of a recent abdominal CT might be a valid option ⁹
• imaging of implants ¹
  • use metal artifact reduction algorithms
  • use monochromatic reconstructions in dual-energy CT scans
  • use additional wide window setting
  • might require a higher tube voltage