Odontoid (peg) view X-ray positioning (open mouth)
An extra C-spine view, used when a routine one is not enough. The patient lies on their back, the beam passes front to back (AP), tilted 10° towards the head, and the centring point is the centre of the open mouth.
By the ScanFlo Editorial Team · Updated
In this section · X-ray positioning
- X-ray positioning guides
- Skull positioning
- Face & sinuses positioning
- Soft tissue neck positioning
- C-spine positioning
- Chest positioning
- Shoulder positioning
- Humerus positioning
- Elbow positioning
- Forearm positioning
- Wrist positioning
- Hand positioning
- T-spine positioning
- Abdomen positioning
- L-spine positioning
- Sacrum & SI joints positioning
- Pelvis positioning
- Hip positioning
- Femur positioning
- Knee positioning
- Tibia & fibula positioning
- Ankle positioning
- Foot positioning
Still being checked: a radiographer is reviewing this guide. If your department does it differently, follow your department.
Patient position
Supine. Supine, mouth wide open (a soft wedge between the teeth if needed), the occlusal plane and mastoid tips aligned.
Centring & collimation
Central ray
APCentre: the centre of the open mouth.
Beam: AP, angled 10° cephalad.
Collimate: C1 and C2
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 18 × 24 cm | portrait |
| Placement | Table bucky | Grid in |
| Angulation | 10° | cephalad |
Marker & breathing
- Marker: R or L marker on the side nearest the detector
- Breathing: Suspend respiration.
Exposure by patient size
Treat these as a starting point. Your detector, your generator and the patient in front of you will all move the numbers.
| Patient size | kV | mAs (chart) | mAs (DR default) |
|---|---|---|---|
| XS | 70 | 5 | 2 |
| S | 70 | 8 | 3.2 |
| M | 70 | 10 | 4 |
| L | 70 | 16 | 6.3 |
These start from a classic film-screen chart (70 kV, 20 mAs at 140 cm) and are adjusted for a digital detector at 100 cm. The DR column is what ScanFlo's console suggests; each step up or down changes the mAs by about a quarter.
Image quality checklist
- The dens is seen through the open mouth.
- Lateral masses of C1 symmetric about the dens.
- The anatomical side marker is visible, correct and clear of the anatomy.
- Collimation borders are visible on all sides, no wider than the area requested.
Faults & how to fix them
| Fault | Cause | Fix |
|---|---|---|
| Teeth over the dens | Head flexed | Align occlusal plane and mastoid tips. |
Common questions
- Where do you centre for an odontoid (open mouth) X-ray?
- The centring point is the centre of the open mouth.
- What distance and beam angle does an odontoid (open mouth) need?
- 100 cm from the tube to the receptor. The beam passes front to back (AP), tilted 10° towards the head.
- What size receptor, and do you need a grid?
- Use an 18 × 24 cm receptor, portrait, in the table bucky. A grid is needed.
- What should the patient do with their breathing?
- Ask them to stop breathing for the moment of the exposure.
- What goes wrong most often on an odontoid (open mouth)?
- Teeth over the dens. Usual cause: head flexed. The fix: align occlusal plane and mastoid tips.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a odontoid (open mouth) in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.