AP Dens (Fuchs) is a radiography positioning projection of the Spine. Supine, head extended, CR perpendicular. Alternate dens visualization. The centering point is located 1.5 inches below chin, with head extended.. The central ray is perpendicular to ir, 1.5 inches below chin.. Image-quality criteria include odontoid process clearly visualized without tooth obscuration., lateral borders of c1 symmetrically positioned.. Standard exposure ranges from 70 to 80 kVp, 10 to 15 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Odontoid (dens) of axis (C2).
- Lateral masses of atlas (C1).
- C1-C2 articulation relationship.
- Axis vertebral body.
- Upper cervical vertebral alignment.
Patient preparation
- Verify patient identity using two identifiers.
- Remove dentures, removable bridges, and neck metal.
- Supine on table, no rotation or tilt.
- Extend head backward gently.
- Jaw relaxed in neutral position.
Position & centering point
1.5 inches below chin, with head extended.
Central ray
Perpendicular to IR, 1.5 inches below chin.
Exposure / technique
- kVp
- 70–80
- mAs
- 10–15
- SID
- 40" (102 cm)
- Notes
- Used as alternative when open-mouth is contraindicated.
Image-quality criteria
- Odontoid process clearly visualized without tooth obscuration.
- Lateral borders of C1 symmetrically positioned.
- No head rotation or lateral flexion evident.
- Body of C2 inferior to dens shown.
- Structures sharp with no motion artifact.
Common errors / ARRT traps
- 1 Insufficient head extension closes the odontoid view.
- 2 Head rotation to either side tilts lateral masses off symmetry.
- 3 CR misalignment off chin prevents clear dens visualization.
- 4 Upper incisors may overlap odontoid if centration off.
Clinical indications
- Trauma screening when open-mouth position contraindicated.
- Suspected C2 odontoid fracture evaluation.
- Post-operative follow-up of odontoid fusion.
- Alternative method for limited mouth opening.
Aligned to the 2025 ARRT Content Specifications.