Skull AP is a radiography positioning projection of the Skull. Trauma AP cranium. SID 40". CR parallel to OML, centered to glabella. The centering point is located glabella (Bontrager), the smooth prominence between the eyebrows. Merrill's AP, for a patient who cannot be positioned for a PA, is perpendicular with the OML perpendicular to the IR. Its AP axial (reverse Caldwell) is 15 degrees cephalad to the nasion. The central ray is parallel to the OML, centered to the glabella (Bontrager). The head is not moved (in a cervical collar this often occurs about 10 to 15 degrees caudad, varying by patient). Merrill's: OML perpendicular to the IR with a perpendicular CR. Image-quality criteria include midsagittal plane perpendicular to IR (no tilt or rotation), petrous ridges fill the orbits symmetrically. A sample technique is 85 kVp with DR 6.3 or CR 12 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Frontal bones and frontal sinuses.
- Orbital cavities and orbital margins.
- Crista galli.
- Dorsum sellae.
- Petrous portions of temporal bones.
- Orbits magnified compared with the PA (Merrill's).
Patient preparation
- Cervical spine fractures and subluxations or dislocations must be ruled out before moving or manipulating the head or neck.
- Verify patient identity.
- Remove glasses, earrings, hairpins, dentures, hearing aids.
- Position patient supine with head on table.
- Do not move the head to set a line: angle the CR parallel to the OML (Bontrager). With a cleared neck, Merrill's sets the OML perpendicular to the IR.
- Align the MSP perpendicular to the midline of the grid or table.
- Center the CR to the glabella, then center the IR to the projected CR.
- Suspend respiration during exposure.
Position & centering point
Glabella (Bontrager), the smooth prominence between the eyebrows. Merrill's AP, for a patient who cannot be positioned for a PA, is perpendicular with the OML perpendicular to the IR. Its AP axial (reverse Caldwell) is 15 degrees cephalad to the nasion.
Central ray
Parallel to the OML, centered to the glabella (Bontrager). The head is not moved (in a cervical collar this often occurs about 10 to 15 degrees caudad, varying by patient). Merrill's: OML perpendicular to the IR with a perpendicular CR.
Exposure / technique
- kVp
- 85
- mAs
- DR 6.3 / CR 12
- SID
- 40" (102 cm)
- Notes
- ARRT lists this as trauma AP in both the 2022 and 2027 outlines. The trauma AP axial (reverse Caldwell) line is on the 2022 outline only, and leaves on March 1, 2027. Use small focal spot for cranial suture detail. Sample technique: DR 6.3 / CR 12 mAs at 85 kVp, 40 in SID, for a 20 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Midsagittal plane perpendicular to IR (no tilt or rotation).
- Petrous ridges fill the orbits symmetrically.
- Orbits symmetric without rotation.
- Equal distance from the lateral skull borders to the lateral orbital borders on both sides (Merrill's).
- Bony detail of the frontal bone and surrounding soft tissues.
- Cranium centered on IR with 1" margin all around.
Common errors
- 1 Moving the head or neck before the cervical spine has been cleared.
- 2 15 degrees cephalad on a plain AP: pyramids in the lower third of orbits, not filling them (Merrill's).
- 3 Head rotation asymmetrically demonstrates orbits.
Clinical indications
- Calvarial fractures, including the frontal bone.
- Penetrating injuries.
- Radiopaque foreign bodies.