Sacrum AP Axial is a radiography positioning projection of the Pelvis. Axial view of sacrum. CR 15° cephalad. SID 40". The centering point is located midline, 2 inches superior to the pubic symphysis (approximately midway between asis and symphysis).. The central ray is 15° cephalad along the midline, entering 2 inches superior to the pubic symphysis.. Image-quality criteria include sacral ala shown symmetrically without rotation., sacral foramina visible on both sides.. Standard exposure ranges from 75 to 85 kVp, 15 to 25 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Entire sacrum from base to apex.
- Sacral ala bilaterally.
- Anterior sacral foramina.
- Coccyx in relation to sacral apex.
- Sacroiliac joint articulation.
- Lumbosacral junction region.
Patient preparation
- Verify patient identity.
- Position patient supine on the table.
- Remove all radiopaque objects from pelvis and lower spine.
- Flex hips and knees slightly to relax lumbar spine.
- Place sandbag or pillow under knees if needed for comfort.
- Suspend respiration during exposure.
Position & centering point
Midline, 2 inches superior to the pubic symphysis (approximately midway between ASIS and symphysis).
Central ray
15° cephalad along the midline, entering 2 inches superior to the pubic symphysis.
Exposure / technique
- kVp
- 75–85
- mAs
- 15–25
- SID
- 40" (102 cm)
- Notes
- Use moderate exposure for good visualization of sacral foramina.
Image-quality criteria
- Sacral ala shown symmetrically without rotation.
- Sacral foramina visible on both sides.
- Coccyx shown in relation to sacrum.
- Sacrum centered on IR.
- No superimposition of pubic symphysis over sacrum.
- Sacral apex and foramina clearly demonstrated.
Common errors / ARRT traps
- 1 CR angled insufficient (less than 15°) shows unclear foramina.
- 2 Patient rotation obscures symmetry of sacral ala.
- 3 Pubic symphysis superimposed over sacral base.
- 4 Excessive kVp reduces visualization of foraminal detail.
- 5 IR not centered to midline allows lateral cutoff of ala.
Clinical indications
- Suspected sacral fracture from trauma.
- Evaluation of sacroiliitis or SI joint pathology.
- Assessment of sacral anatomy prior to fusion surgery.
- Chronic sacral or coccygeal pain investigation.
Aligned to the 2025 ARRT Content Specifications.