Skull PA axial (Caldwell) is a radiography positioning projection of the Skull. PA axial / Caldwell. Frontal bone, frontal & ethmoid sinuses. CR 15° caudad to OML. The centering point is located cr exits at the nasion. forehead and nose touching the ir; oml perpendicular to ir.. The central ray is cr 15° caudad to oml. exits at the nasion. (some protocols: 25° caudad for orbital rims.). Image-quality criteria include petrous ridges fill the lower one-third of the orbits (15° caudad cr)., frontal bone clearly demonstrated.. Standard exposure ranges from 75 to 85 kVp, 20 to 40 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Frontal bone.
- Greater and lesser wings of the sphenoid.
- Superior orbital fissures within the orbits.
- Frontal and anterior ethmoid sinuses.
- Supraorbital margins.
- Crista galli.
Patient preparation
- Verify patient identity.
- Remove glasses, earrings, hairpins, dentures.
- Position patient prone or upright facing the IR.
- Forehead and tip of nose touching the IR.
- OML perpendicular to IR (chin slightly tucked).
- Suspend respiration.
Position & centering point
CR exits at the nasion. Forehead and nose touching the IR; OML perpendicular to IR.
Central ray
CR 15° caudad to OML. Exits at the nasion. (Some protocols: 25° caudad for orbital rims.)
Exposure / technique
- kVp
- 75–85
- mAs
- 20–40
- SID
- 40" (102 cm)
Image-quality criteria
- Petrous ridges fill the lower one-third of the orbits (15° caudad CR).
- Frontal bone clearly demonstrated.
- Frontal and ethmoid sinuses well-visualized through the orbits.
- No rotation: equal distance from lateral border of skull to lateral border of orbit bilaterally.
- Crista galli, internal auditory canals visible.
Common errors / ARRT traps
- 1 Rotation: unequal distance from each midlateral orbital margin to the lateral cranial cortex.
- 2 At 15 degrees caudad the petrous pyramids should fill the lower third of the orbits.
- 3 At 25 to 30 degrees caudad they should project at or below the inferior orbital margin.
- 4 Tilt, where the MSP is not perpendicular to the image receptor.
- 5 Incorrect neck extension misaligns the OML and shifts the petrous ridges.
Clinical indications
- Frontal bone fracture or pathology.
- Frontal and ethmoid sinusitis evaluation.
- Anterior cranial fossa workup.
- Orbital floor and superior orbital fissure (with 25° caudad variant).
Aligned to the current ARRT Radiography Content Specifications.