Monday, September 29, 2014

Pathology Demonstrated:

  • Spondylolisthesis involving L4 to L5 or L5 to S1 and other L5 to S1 pathologies is demonstrated.

Technical Factors:

  • IR size - 18 x 24 cm (8 x 10 inches), lengthwise
  • Moving or stationary grid.
  • 95 to 100 kV range
  • Lead mat on tabletop behind patient
  • mAs 50


  • Shield gonads without obscuring area of interest.

Patient Position:

  • Patient should be in the lateral recumbent position, with a pillow for head and knees flexed. Provide support between knees and ankles to better maintain a true lateral position and ensure patient comfort.

Part Position:

  • Align midcoronal plane to CR and midline of table or grid.
  • Flex knees.
  • Place radiolucent support under waist. see note
  • Ensure that pelvis and torso are in true lateral position.

Central Ray:

  • Direct CR perpendicular to image receptor with sufficient waist support or angles 5° to 8° caudad with less support. see note
  • Center CR 1.5 inches or 4 cm inferior to iliac crest and 2 inches 5 cm posterior to ASIS. Center IR to CR.
  • Minimum SID is 40 inches or 100 cm.


  • Close four-sided collimation to area of interest.


  • Suspend breathing

Note: If waist is not supported sufficiently, resulting in sagging of the vertebral column, the CR must be angled 5° to 8° caudad to be parallel to the interiliac plane (imaginary line between iliac crest)
High amounts of secondary or scatter radiation are generated as the result of the part thickness. Close collimation  is essential, along with placement of lead mat on tabletop behind patient. (This is especially important with digital imaging.)

Radiographic Criteria:

Structure Shown:

  • Open L4 to L5 and L5 to S1 joint space.

Proper Patient Position:

  • No rotation of the patient is evidenced by superimposed AP dimensions of greater sciatic notches of posterior pelvis and superimposed posterior borders of the vertebral bodies.
  • Correct alignment of the vertebral column and the IR and CR is indicated by open L4 to L5 and L5 to S1 joint spaces.

Collimation and CR:

  • L5 to S1 joint space in center of closely collimated field / IR.

Exposure Criteria:

  • Optimal contrast and density should clearly demonstrated the L5 to S1 joint space through the superimposed ilia of the pelvis.
  • Sharp bony margins indicate no motion.

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