Friday, December 23, 2011

Tangential Projection of the Carpal Bridge

X-ray examination of the carpal bridge with tangential projection, this is best demonstrate the lower part of the carpal bone. Remember: If patient has possible wrist trauma, do not attempt this position before routine wrist series has been completed and evaluated to rules out possible trauma of distal forearm and/or wrist
Pathology Demonstrated:
  • Calcification or other pathology of the dorsal aspect of the carpal bones is shown.

Technical Factor:
  • IR size - 18 x 24 cm (8 x 10 inches)
  • Detail screen, tabletop
  • Digital IR - use lead masking
  • 64 or add upto 6 kV range

  • Secure lead shield around waist to shield gonads.

Patient Position:
  • Have patient stand or sit at end of table and then lean over and place dorsal surface of hand, palm upward, on cassette.

Part Position:
  • Center dorsal aspect of carpals to IR.
  • Gently flex wrist as far as patient can tolerate, or until hand and forearm form as near 90degrees (right angle) as possible.
carpal bridge

Central Ray:
  • Angle the CR 45degrees to the long axis of the forearm.
  • Direct CR to a midpoint of the distal forearm about 4cm (1 1/2 inches) proximal to the wrist joint.
  • Minimum SID is 40 inches (100cm)

  • Collimate all four sides to area of interest.

Radiographic Criteria of Tangential View of the Carpal Bridge

Structure Shown:
  • A tangential view of the dorsal aspect of the scaphoid, lunate, and triquetrum is visible.
  • An outline of the capitate and trapezium superimposed is visible.
carpal bridge

  • Dorsal aspect of the carpal bones should be visualized clear of superimposition and centered to IR.

Collimation and CR:
  • Collimation should be visible on four sides of affected wrist
  • CR and center of the collimation should be to the area of dorsal carpal bones.

Exposure Criteria:
  • Optimal density and contrast with no motion should demonstrate the dorsal aspect of the carpal bones, with sharp borders and clear, sharp bony trabecular markings.
  • Outline of the proximal metacarpals should be visualized through superimposed structures without overexposure of the dorsal aspects of carpals seen in profile.

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