AP AXIAL L5 TO S1 PROJECTION: LUMBAR SPINE

Pathology Demonstrated:

• Pathology of L5 to S1 and the sacroiliac joints is demonstrated.

Technical Factors:

• IR size 18 x 24 cm (8 x 10 inches), crosswise
• Moving or stationary grid
• 80 to 85 kV range
• mAs 20

Shielding:

• Shield gonads without obscuring area of interest. Female ovarian shielding obscures a portion of sacroiliac joints.

Patient Position:

• Patient should be supine, with pillow for head and legs, extended, with support under knees for comfort.

Part Position:

• Place arms at side or on chest.
• Align midsagittal plane to CR and midline of table / grid.
• Ensure that no rotation of torso or pelvis exist.

Central Ray:

• Angle CR cephalad, 30° for males to 35°for females.
• CR should enter at the level of the ASIS centered to the midline of the body.
• Center IR to projected CR.
• Minimum SID is 40 inches (100 cm)

Collimation:

• Close four-sided collimation to area of interest.

Respiration:

• Suspend breathing during exposure.

Note: Angled AP projection opens L5 to S1 joint.
Lateral view of L5-S1 generally provides more information than the AP projection.
This projection may also be performed prone with caudad angle of CR (increase OID.)

Radiographic Criteria on AP AXIAL L5 to S1 LUMBAR SPINE X-RAY:

Structure Shown:

• L5 to S1 joint space and sacroiliac joints in AP projection.

Position:

• Sacroiliac joints demonstrate equal distance from spine, indicating no pelvic rotation.
• Correct alignment of CR and L5 to S1 is evidenced by an open joint space.

Collimation and CR:

• L5 to S1 joint demonstrates in the center of a well-collimated field/IR.

Exposure Criteria:

• Optimal density and contrast demonstrate the L5 to S1 region and sacroiliac joints.
• Sharp bony margins indicate no motion.