Skull Positioning
Five Common Positioning Errors
1.Rotation 2.Tilt 3.Excessive flexion (C-spine) 4.Excessive extension (C-spine) 5.Incorrect CR angle
Glabella
A single bony prominence of the frontal bone located between the superciliary arches in the inferior part of the frontal bone above the root of the nose.
Interpupilary line
An imaginary horizontal line drawn between the centers of the pupils of the eyes. The length of the line is the interpupillary distance.
AP Axial (Towne Method)
Basic Patient: Supine MSP centered to midline and perpendicular OML or IOML perpendicular
AP Axial (Towne Method) CR interseption
CR 2 ½ inches above the glabella
AP Axial (Towne Method) CR Angle:
CR Angle: 30° caudad to OML or 37° to IOML
Skull Positioning and Technical Considerations
Erect vs. recumbent kV range: Analog: 65-85 Digital: 75-90 SID minimum 40 in Small focal spot Shielding of radiosensitive organs
Acanthiomeatal line (AML)
From acanthion to EAM
Glabellomeatal line (GML)
From glabella to EAM
Infraorbitomeatal line (IOML)
From infraorbital margin to EAM
Mentomeatal line (MML)
From mental point (center of chin) to EAM
Orbitomeatal line (OML)
From outer canthus to EAM
Hyposthenic/asthenic patients usually need support at chest to elevate cervical spine (C-spine).
Helps prevent downward tilt of MSP
Hypersthenic patients require radiolucent support at head.
Helps prevent upward tilt of MSP
Skull Classifications
Mesocephalic: Average shaped Head Brachycephalic: Short (front to back) Broad (side to side) Dolichocephalic: Long (front to back) Narrow (side to side)
Acanthion
Midline point at the junction of the upper lip & nasal septum (where nose & upper lip meet)
Interpupillary line (IPL)
Perpendicular line between pupils of eyes
Dolichocephalic skull
Petrous pyramids project anteriorly and medially at 40-degree angle from MSP * Long from front to back, narrow from side to side, and deep from vertex to base
Typical skull = Mesocephalic
Petrous pyramids project anteriorly and medially at 47-degree angle from midsagittal plane (MSP)
Brachycephalic skull
Petrous pyramids project anteriorly and medially at 54-degree angle from MSP * Short from front to back, broad from side to side, and shallow from vertex to base
Mesocephalic skull
Skull of average shape Width 75% to 80% of length
Inner canthus
The corner of the eye where the upper and lower eyelids meet
Angle of mandible (gonion)
The forensic term for the midpoint of the mandibular angle is the gonion.
Infraorbital margin
The infraorbital margin is the lower margin of the eye socket. It consists of the zygomatic bone and the maxilla, on which it separates the anterior and the orbital surface of the body of the maxilla.
Nasion
The nasion (also known as bridge of the nose) is the midline bony depression between the eyes where the frontal and two nasal bones meet, just below the glabella.
Mental point
Tip of chin
Recumbent position
Trauma
Outer canthus
Where eyelids meet on the outside of the eye
Skull Routine Basic
•AP axial (Towne) •Lateral both sides •PA 15° (Caldwell), PA 25° to 30° or PA 0°
Erect position
•Air-fluid levels shown •Easier for hypertension patients
Evaluation Criteria: AP Axial (Towne)
•Dorsum sellae projected within foramen magnum •Entire skull visualized •Occipital Bone in Profile •No rotation or tilt •Petrous ridges symmetric •Optimal exposure factors
Skull Special views
•PA axial (Haas) •SMV (submentovertex)
