Skull PA is a radiography positioning projection of the Skull. Forehead and nose on IR. OML perpendicular. CR exits nasion. The centering point is located nasion. oml and msp perpendicular to ir.. The central ray is perpendicular to ir, exiting at the nasion.. Image-quality criteria include entire cranium with no rotation or tilt., equal distance from lateral orbital rims to lateral skull margins.. Standard exposure ranges from 75 to 85 kVp, 25 to 40 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Frontal bone and frontal sinuses.
- Petrous ridges filling the orbits.
- Crista galli in the midline.
- Dorsum sellae within the foramen magnum.
- Orbital rims and superior orbital fissures.
- Greater wings of the sphenoid.
Patient preparation
- Verify patient identity using two identifiers.
- Remove glasses, earrings, dentures, and hairpins.
- Position patient prone or upright facing the IR.
- Rest forehead and nose against the receptor.
- OML perpendicular to the IR.
- MSP perpendicular to the IR (no rotation or tilt).
- Suspend respiration during exposure.
Position & centering point
Nasion. OML and MSP perpendicular to IR.
Central ray
Perpendicular to IR, exiting at the nasion.
Exposure / technique
- kVp
- 75–85
- mAs
- 25–40
- SID
- 40" (102 cm)
- Notes
- Grid required. 10"x12" IR lengthwise.
Image-quality criteria
- Entire cranium with no rotation or tilt.
- Equal distance from lateral orbital rims to lateral skull margins.
- Petrous ridges fill the orbits symmetrically.
- Dorsum sellae projected above the foramen magnum.
- Crista galli centered along the midline.
- No tilt: superior orbital margins level.
Common errors / ARRT traps
- 1 Rotation of the head: unequal distance from orbital rims to skull.
- 2 Tilt of the head: superior orbital margins not level.
- 3 OML not perpendicular: petrous ridges projected above or below orbits.
- 4 Incorrect CR angle distorts orbital and sellar landmarks.
Clinical indications
- Evaluation of frontal bone fracture or pathology.
- Skull series for trauma or post-operative assessment.
- Assessment of frontal sinus disease.
- Detection of cranial lesions or calcifications.
Aligned to the 2025 ARRT Content Specifications.