OBLIQUES PROJECTION | ANTERIOR OR POSTERIOR OBLIQUE : LUMBAR SPINE

Pathology Demonstrated:

• Detects of the pars interarticularis like spondylolysis are demonstrated.
• Both right and left obliques obtained.

Technical Factors:

• Image receptor size - two 30 x 35 cm or (11 x 14 inches), lengthwise or 24 x 30 cm (10 x 12 inches)
• Moving or stationary grid
• 75 to 85 kV range (or 85 to 90 kV and reduction of mAs and dose.)
• mAs 15 for both anterior and posterior oblique

Shielding:

• Place contact shield over gonads without obscuring area of interest.

AP Oblique - RPO

Patient Position:

• Patient should be semisupine (RPO and LPO or semiprone (RAO and LAO)

Part Position:

• Rotate body 45° to place spinal column directly over midline of table/grid, aligned to CR.
• Flex knee to stability and comfort.
• Support lower back and pelvis with radiolucent sponge to maintain position. (This support is strongly recommended to prevent patients from grasping the edge of the table, which may result in their fingers being pinched.)

Cental Ray:

• Direct CR perpendicular to image receptor.
• Center to L3 at the level of the lower costal margins (4 cm or 1.5 inches above iliac crest.
• Center 2 inches or 5 cm medial to upside ASIS.
• Center IR to central ray.
• SID is 40 inches or 100 cm.

Collimation:

• Four-sided collimation to area of interest.

Respiration:

• Suspend breathing on expiration.
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• Note: A 50° oblique from plane of tabletop best visualizes the zygapophyseal joint at L1 to L2, and 30 degree for L5 to S1.

Radiographic Criteria:

Structure Shown:

AP Oblique - Scottie Dogs

• Zygapophyseal joints are visible. (RPO and LPO show downside; RAO and LAO show upside.
• Scottie dogs should be visualized, and zygapophyseal joint should appear open.

Proper Patient Positioning:

• Correct 45° patient rotation results in the pedicle (the eye of scottie dog) near the center of the vertebral body on the image.
• The pedicle demonstrated posteriorly on the vertebral body indicates overrotation, and the pedicle demonstrated anteriorly on the vertebral body indicates underrotation.

Collimation and Central Ray:

• The vertebral column should be in the midline of the collimated field / IR, which is centered to L3.

Exposure Criteria:

• Optimal density and contrast clearly demonstrate zygapophyseal joint from L1 to L5.
• Sharp bony margins indicate no motion.