CT thoracic spine (protocol)

The CT thoracic spine or T-spine protocol serves as an examination for the assessment of the thoracic spine. As a separate examination, it is often performed as a non-contrast study. It might be combined or simultaneously acquired with a CT chest or CT chest-abdomen-pelvis as part of a trauma or staging protocol and also forms a part of a polytrauma CT. It might be acquired as dual-energy CT or rarely 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 thoracic 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. 

Contrast doses apply for CT examinations in adults.

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

Indications

Typical indications include the following ^1-8:

• thoracic or thoracolumbar injury

  • thoracic spine fracture-dislocation

  • thoracolumbar spine fracture

• thoracic spine implants and complications

• congenital anomalies

• spinal tumors and/or vertebral metastasis

• if MRI is contraindicated

  • inflammatory arthritis or spondylodiscitis

  • degenerative disc disease

• thoracic spine interventions (e.g. CT guided biopsy)

• CT myelography  (if MRI is contraindicated or metallic implants are present)

  • spinal cord compression

Purpose

The purpose of a CT of the thoracic spine in the setting of a traumatic injury is the timely diagnosis or exclusion of thoracic spine injuries as well as their classification and characterization ^1-3.

Dual-energy CT can aid in the detection of bone marrow edema and improved identification of vertebral compression fractures or differentiation from old fractures ⁴.

The evaluation of the spinal canal and the intervertebral foramina is another important objective of spinal imaging in general and is a purpose in the setting of spinal tumors, spinal infections, degenerative disc disease or in a postoperative setting, where metallic implants are present ^5-7.

Technique

• patient position

  • supine position 

  • both arms elevated

• tube voltage

  • ≤120 (140) kVp

• tube current

  • as suggested by the automated current adjustment mode 

• scout

  • lower neck to the iliac crest

• scan extent

  • varies with regard to the clinical question, and might be more limited or more extensive

  • the whole thoracic spine includes the area from C7 to L1

• 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 tissues

• contrast injection considerations

  • usually non-contrast, optionally with contrast

  • contrast volume: 70-100ml (0.1 mL/kg) with 30-40 mL saline chaser at 2-3 mL/s

  • scan delay: 65-80 seconds

• multiplanar reconstructions

  • 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 thoracic spine with the 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 before scanning might reduce and facilitate multiplanar reconstructions

• dual-energy CT might aid in the identification of compression fractures

• dose optimization

  • use iterative reconstruction algorithms if available

  • reconstructions from the raw data set or reformations from the stored thin slice data of a recent thoracic CT or CT CAP is a valid option

• imaging of implants ¹

  • use metal artifact reduction (MAR) algorithms

  • use monochromatic reconstructions in dual-energy CT scans

  • use additional wide window setting

  • might require a higher tube voltage