Sunday, February 23, 2014


Pathology Demonstrated:
  • Pituitary adenoma may be demonstrated if involvement of the sella turcica is evident.

Technical Factors:
  • IR size - 18 x 24 cm (8 x 10 inches), lengthwise
  • Moving or stationary grid
  • 80 +- 5 kV range
  • Small focal spot
  • mAs 22

  • Shield patient's upper thoracic region.

Patient Position:
  • Remove all metal, plastic, or other removable objects from the patient's head.
  • Take radiograph with patient in erect or supine position.

Part Position:
  • Rest patient's posterior skull against table/Bucky surface.
  • Flex neck to bring IOML perpendicular to midline of the grid or table/Bucky surface.

Central Ray:
  • Angle CR 37° caudad if dorsum sallae and posterior clinoid processes are of primary interest.
  • Angle CR 30° caudad if anterior clinoids are of primary interest.
  • Center at midsagittal plane 1 1/2 inches (4 cm) above supercillary arch. (CR will exit the foramen magnum.)
  • Minimum SID is 40 inches (100 cm)

  • Callimate to a field size of approximately 4 inches (10 cm) square.

  • Suspend respiration during exposure.

Note: To obtain sharply detailed image of the dorsum sallae, use of a small focal spot and chose collimation is essential.

Radiographic Criteria:

Structure Shown:

  • Dorsum sallae, anterior and posterior clinoid processes (depending on CR angulation), foramen magnum, petrous ridges, and occipital bone are shown.

  • No rotation is evident, as indicated by symmetric petrous ridges and by equal distances from the midsagittal plane (which can be identified by the perpendicular plate) to each anterior clinoid process.
  • A correct position image will have the following features (CR angulation required depends on the structure of interest):
37° caudad angle: Dorsum sallae and posterior clinoid processes are projected within the foramen magnum.
30° caudad angle: Anterior clinoids are clearly visualized, adjacent to each petrous ridge, directly above the foramen magnum; dorsum sallae is projected above the foramen magnum, superimposing the occipital bone.

Collimation and CR:
  • A closely collimated image, with the dorsum sallae located in the center.

Exposure Criteria:
  • Density and contrast are sufficient to visualized the dorsum sallae to the adjacent skull structures.
  • Sharp bony margins indicate no motion.

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