AP Lumbar is a radiography positioning projection of the Spine. Supine, knees flexed, CR perpendicular to the iliac crest (L4). Grid required. The centering point is located at the level of the iliac crest (l4), at midline.. The central ray is perpendicular to ir at the level of the iliac crest (l4).. Image-quality criteria include all lumbar vertebrae l1-l5 clearly visualized., intervertebral disc spaces symmetrically open.. Standard exposure ranges from 80 to 90 kVp, 30 to 50 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Lumbar vertebral bodies L1-L5.
- Intervertebral disc spaces.
- Lumbar spinous processes.
- Lateral processes and facet joints.
- Lumbar lordotic curve.
Patient preparation
- Verify patient identity using two identifiers.
- Remove jewelry, belt, and radiopaque objects.
- Supine on table, no rotation or tilt.
- Knees flexed with feet flat on table.
- Hips and shoulders aligned symmetrically.
Position & centering point
At the level of the iliac crest (L4), at midline.
Central ray
Perpendicular to IR at the level of the iliac crest (L4).
Exposure / technique
- kVp
- 80–90
- mAs
- 30–50
- SID
- 40" (102 cm)
- Notes
- Grid required. Knees flexed to reduce lumbar lordosis.
Image-quality criteria
- All lumbar vertebrae L1-L5 clearly visualized.
- Intervertebral disc spaces symmetrically open.
- Spinous processes aligned midline.
- No rotation evidenced by symmetric lateral processes.
- Entire lumbar region and sacrum base included.
Common errors / ARRT traps
- 1 Body rotation shifts lateral processes off symmetry.
- 2 Extended legs increase lumbar lordosis, closes disc spaces.
- 3 CR not centered to the iliac crest (L4) clips the upper lumbar spine or sacrum.
- 4 Pelvic rotation tilts vertebral alignment.
Clinical indications
- Lumbar spine trauma survey in supine patient.
- Evaluation of spondylosis or disc degeneration.
- Suspected compression fracture assessment.
- Post-operative lumbar fusion follow-up.
Aligned to the 2025 ARRT Content Specifications.