Skull SMV (Cranial Base) is a radiography positioning projection of the Skull. Vertex on IR. IOML parallel to IR. CR perpendicular to IOML. The centering point is located midway between the angles of the mandible, perpendicular to ioml. ioml parallel to ir.. The central ray is perpendicular to ioml. centered 3/4 inch anterior to the eam.. Image-quality criteria include entire cranial base visible, mandibular symphysis over the frontal bone., mandibular condyles anterior to the petrous pyramids.. Standard exposure ranges from 80 to 90 kVp, 40 to 60 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Cranial base and foramen magnum.
- Sphenoid sinus and foramina at the base.
- Mastoid processes and petrous pyramids.
- Mandible projected anteriorly over the frontal bone.
- Bony nasal septum and maxillary sinuses.
- Zygomatic arches.
Patient preparation
- Verify patient identity.
- Remove glasses, earrings, dentures, and hairpins.
- Position patient supine or upright with head fully extended.
- Rest vertex of head against the IR.
- IOML (infraorbitomeatal line) parallel to IR.
- MSP perpendicular to IR with no rotation.
- Suspend respiration during exposure.
Position & centering point
Midway between the angles of the mandible, perpendicular to IOML. IOML parallel to IR.
Central ray
Perpendicular to IOML. Centered 3/4 inch anterior to the EAM.
Exposure / technique
- kVp
- 80–90
- mAs
- 40–60
- SID
- 40" (102 cm)
- Notes
- Grid required. Head extension critical for IOML parallel to IR.
Image-quality criteria
- Entire cranial base visible, mandibular symphysis over the frontal bone.
- Mandibular condyles anterior to the petrous pyramids.
- No rotation: distance from mandibular ramus to lateral skull equal.
- Symmetric appearance of petrous pyramids and mastoids.
- Sphenoid sinus and foramen ovale visible.
- IOML parallel to IR confirmed by symmetric anatomy.
Common errors / ARRT traps
- 1 Inadequate head extension foreshortens the cranial base.
- 2 Rotation: mandible asymmetric relative to skull margins.
- 3 IOML not parallel: petrous pyramids displaced anteriorly or posteriorly.
- 4 Underexposure obscures the cranial base detail.
Clinical indications
- Evaluation of basal skull fracture.
- Assessment of sphenoid sinus pathology.
- Detection of mastoid air cell disease.
- Localization of intracranial foreign bodies.
- Pre-operative cranial base evaluation.
Aligned to the 2025 ARRT Content Specifications.