CT neck (protocol)

The CT neck protocol serves as a radiological examination of the head and neck. This protocol is usually performed as a contrast study and might be acquired separately or combined with a CT chest or CT chest-abdomen-pelvis. On rare occasions, it will be performed as a non-contrast study. Depending on the clinical question it might be acquired as double acquisition with a CT angiogram or as a single acquisition e.g with a mono- or biphasic technique.

Note: This article aims to frame a general concept of a CT protocol for the assessment of the head and neck. 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 neck might look like as follows:

Indications

Typical indications include the following ^1-5:

• inflammatory or infectious processes
• head and neck neoplasms
• head and neck cancer therapy response and follow up
• head and neck trauma
• vascular malformations
• bleeding/epistaxis
• congenital anomalies
• foreign bodies
• thyroid disease

Purpose

In the setting of inflammatory or neoplastic processes, the purpose of a CT neck is the localisation and characterisation of the respective process its extent and its relation to the adjacent tissues as well as the detection of potential complications.

The search for a foreign body requires its localisation. Because contrast material may pose a confounding factor the examination should be performed as a non-contrast study ¹.

In the setting of head and neck trauma, the evaluation includes the detection and characterisation of maxillofacial fractures, laryngotracheal injuries, and fractures to the skull base and cervical spine ^2,3.

In the setting of thyroid disease, a CT of the neck is usually performed as a non-contrast study and should demonstrate the retrosternal or full extent of the thyroid gland.

Technique

• patient position
  • supine position 
  • both arms next to the body, shoulders pulled down
• tube voltage
  • ≤120 kVp
• tube current
  • as suggested by the automated current adjustment mode 
• scout
  • mid-chest to vertex
• scan extent
  • frontal sinus to the aortic arch
  • depending on the clinical question might exclude the orbit to save radiation on the eye lens
• scan direction
  • craniocaudal
• scan geometry
  • field of view (FOV): 140-200 mm (should be adjusted to increase in-plane resolution)
  • slice thickness: ≤0.75 mm, interval: ≤0.5 mm
  • reconstruction kernel: soft tissue kernel (e.g. I40), high-resolution kernel (e.g. I70)
• contrast injection considerations
• non-contrast (e.g. foreign body, thyroid disease)
• contrast volume:  70-100 mL
• biphasic injection technique (inflammatory conditions)
  • 50-60 ml contrast media at 1-2 mL/s
  • 40-50 ml contrast media followed by 30-50 ml saline chaser at 2-3 mL/s starting after 60 seconds
  • scan delay: 80-100 seconds
• monophasic injection technique (parotid tumours)
  • 70-100ml followed by 30-50 ml saline chaser at 2-3 mL/s
  • scan delay: 40-50 seconds
• respiration phase
  • single breath-hold: inspiration
• multiplanar reconstructions
  • sagittal images: sagittal aligned through the centre of the vertebral bodies and the chin
  • coronal images: coronal aligned to the transverse processes and the mandibula
  • axial images:perpendicular to the head-neck axis
  • slice thickness: soft tissue ≤3 mm, overlap >30%, bone ≤2 mm

Practical points

• patient positioning before scanning might reduce and facilitate multiplanar reconstructions
• reconstructions in both standard kernel and high-resolution kernels
• in the setting of trauma separate reconstructions of the cervical spine should be obtained from the raw data set
• place markers in the setting of palpable lumps and bumps
• depending on the exact indication the scan might require an extension of the scan field
• dose optimisation
  • use iterative reconstruction algorithms if available
  • try to minimize acquisitions (e.g with a biphasic injection protocol)
• imaging in the setting of implants
  • use metal artifact reduction algorithms
  • use monochromatic reconstructions in dual-energy CT scans
  • use additional wide window setting