How many degrees and in what direction should the tube be angled for an AP axial projection of the cervical spine?

Citation, DOI & article data

Citation:

Nguyen, M., Murphy, A. Cervical spine (AP view). Reference article, Radiopaedia.org. (accessed on 08 Sep 2022) https://doi.org/10.53347/rID-51498

The anteroposterior (AP) cervical spine projection is part of the cervical spine series.

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This projection helps to visualize pathology relating to C3-C7 in the anatomical position, demonstrating any compression fractures, clay-shoveler fractures and herniated nucleus pulposus (HNP) 1.

• patient positioned erect in AP position (unless trauma when the patient will be supine)
• patient shoulders should be at equal distances from the image receptor to avoid rotation
• chin should be raised to align the lower margin of the upper incisors to the mastoid tips/base of the skull (unless trauma when the patient is placed in a cervical collar)

• anterior-posterior projection
• centering point
  • the central ray is midline centered at the level of C4 to enter immediately below the hyoid bone
  • 15° cephalad 2
• collimation
  • laterally to include the entire cervical spine
  • superiorly to include C2 and inferiorly to include T2
• orientation
  • portrait 
• detector size
  • 18 cm x 24 cm
• exposure
  • 65-75 kVp
  • 8-12 mAs
• SID
  • 100 cm 
• grid
  • yes

• cervical spine intervertebral disk spaces should be open 2
• spinous processes should be midline, equidistant to the pedicles, indicating that there is no rotation

• make sure that any removable artifacts such as earrings, glasses or metal dentures are removed to avoid obscuring the anatomy of interest

Correcting rotational errors

Rotation can be detected by looking at the spinous processes in relation to the pedicles. The spinous process should be midline of the vertebral body, equidistant from both pedicles 3. Any deviation from the midline indicates rotation is present. The spinous process will rotate toward the pedicle of the side farther from the image receptor 3.

Correcting tube angle errors and head tilt errors

A lordotic curvature exists in the cervical spine. For this reason, a cephalic angle is required to project through the long axis of the vertebral column. This angle can and will vary between 5-20° depending on the position of the head. To project the intervertebral disc spaces open, the central ray should be directed perpendicular to the long axis of the vertebral column 3, 4. An excessive or insufficient angle can distort these disc spaces.

To achieve the best angle, the central ray should be directed at an angle that parallels the plane of the mandible and then directed to just below the hyoid bone. This allows for discrepancies in the tilt of the head (flexion/extension of the cervical spine).

Quiz questions

References

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