AP Lumbar is a radiography positioning projection of the Spine. Supine, knees flexed, CR perpendicular to the iliac crest (L4-5) on a large IR. Grid required. The centering point is located at the level of the iliac crests (L4-L5), at midline. The central ray is perpendicular to the IR at the level of the iliac crest (L4-L5), midline. Image-quality criteria include all lumbar vertebrae L1-L5 clearly visualized, intervertebral disc spaces symmetrically open. A sample technique is 90 kVp with DR 10 or CR 20 mAs, at an SID of 40 inches (102 cm).
Watch the setup
All steps (4)
- Supine on the table, arms at the sides, head on a pillow.
- Align the midsagittal plane to the CR and the midline of the table.
- Flex the knees and hips, feet flat on the table, to flatten the lumbar spine onto the table.
- No rotation of the thorax or pelvis.
3D anatomy: BodyParts3D, © The Database Center for Life Science. Posed, rendered and labelled by RadTechPrepper. These animations are licensed CC BY-SA 4.0. Credits
Anatomy demonstrated
- Lumbar vertebral bodies L1-L5.
- Intervertebral disc spaces.
- Lumbar spinous processes.
- Transverse processes of the lumbar vertebrae.
- Spinous processes in the midline of the vertebral column.
Patient preparation
- WARNING: with possible spinal injury or severe trauma, do not attempt to move the patient (Bontrager). A physician reviews the horizontal-beam lateral before this AP (Bontrager, Merrill's).
- Verify patient identity using two identifiers.
- Remove jewelry, belt, and radiopaque objects.
- Supine on the table, arms at the sides, head on a pillow.
- Align the midsagittal plane to the CR and the midline of the table.
- Flex the knees and hips, feet flat on the table, to flatten the lumbar spine onto the table.
- No rotation of the thorax or pelvis.
Position & centering point
At the level of the iliac crests (L4-L5), at midline.
Central ray
Perpendicular to the IR at the level of the iliac crest (L4-L5), midline.
Exposure / technique
- kVp
- 90
- mAs
- DR 10 / CR 20
- SID
- 40" (102 cm)
- Notes
- Grid required. Knees flexed to reduce lumbar lordosis. Sample technique: DR 10 / CR 20 mAs at 90 kVp, 40 in SID, for a 21 cm part (Merrill's sample chart). Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- All lumbar vertebrae L1-L5 clearly visualized.
- Intervertebral disc spaces symmetrically open.
- Spinous processes aligned midline.
- No rotation evidenced by symmetric transverse processes.
- Lumbar vertebrae, SI joints and sacrum shown: about T11 to the distal sacrum on a 35 x 43 cm IR, T12 to S1 on a 30 x 35 cm IR.
Common errors
- 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-L5) clips the upper lumbar spine or sacrum.
- 4 Pelvic rotation tilts vertebral alignment.
- 5 Body rotation shifts the transverse processes off symmetry.
- 6 CR not centered for the IR size clips the upper lumbar spine or sacrum.
- 7 Pelvic rotation: SI joints no longer equidistant from the spinous processes.
Clinical indications
- Pathology of the lumbar vertebrae, including fractures, scoliosis and neoplastic processes.
- Suspected compression fracture assessment.