PA Skull

Exposure Factors

70-75

Kilovoltage (kV)

20

Milliamperage (mAs)

Thick Focus

Focus Type

105-115 cm

Focus-Plate Distance

Equipment: With bucky. Position: Erect or prone decubitus.

Plate Size

24 × 30 cm

Longitudinally

Visible Anatomical Structures

Frontal Bone

Complete frontal region

Crista Galli

Ethmoidal process

Ethmoidal Cells

Posterior ethmoidal

Petrous Bones

Temporal petrous portion

Temporal Bones

Temporal bones

Frontal sinuses - Frontal sinus cavities
Eye orbits - Complete orbital borders
Optic foramina - When included
Cranial sutures - Coronal, sagittal, lambdoid
Diploe - Cranial spongy bone

Patient Positioning

Patient in erect or prone decubitus position

Rest forehead and nose on the bucky

Align MSP (mid-sagittal plane) with cassette midline

MSP perpendicular to cassette

The OML (orbitomeatal line) perpendicular to bucky

Both EAC (external auditory canals) equidistant to plate

Place hands on both sides of head for support

Head completely perpendicular to cassette

Central Ray Direction

Perpendicular to plate

⟂

PERPENDICULAR

Central ray emerges through the nasion

Entry point: Occiput

Exit point: Nasion (between eyebrows)

Centering: Cassette centered with central ray

No angulation - Direct 90°

Patient Instructions

"Hold your breath during exposure"

Maintain complete immobility - Do not move head during exposure

Technical Considerations

Critical Alignment

MSP perpendicular and OML perpendicular are essential to avoid rotation.

Image Quality

Perfect symmetry, sharp bone borders, visible diploe.

Comparison

Ideal for comparing both sides in asymmetric pathologies.

Clinical Indications

Cranial fractures

Bone tumors

Infections

Symmetry evaluation

PA Skull vs Caldwell

Angulation: 0° (perpendicular)

Visualization: Diploe, sutures

Indication: General bone study

CALDWELL

Angulation: 15° caudal

Visualization: Frontal sinuses, orbits

Indication: Facial trauma, sinuses

PA SKULL PROJECTION