AP or PA Projection in Lumbar Spine X-ray

Sunday, September 28, 2014

Pathology Demonstrated:

  • Pathology of the lumbar vertebrae, including fractures, scoliosis, and neoplastic processes, is demonstrated in this projection.

Technical Factor:

  • IR size - 35 x 43 cm (14 x 17 inches), lengthwise, or 30 x 35 cm (11 x 14 inches)
  • Moving or stationary grid
  • 75 to 80 kV range (or 80 to 92 kV and reduce of mAs and dose.)
  • if in AP position at 80 kV mAs is 15
  • if in AP Position at 92 kV mAs is 8
  • and if in PA at 92 kV mAs is 8.

Patient Shielding:

lumbar spine x ray
AP Lumbar Spine
  • Place the gonadal shielding in the gonads area without obscuring the part or area of interest.
  • When using a female ovarian shielding it obscures portions of sacrum and coccyx.

Patient Position:

  • Let patient in supine and slightly flex the knee and put pillow on head for patient comfortability. It may also be done in prone or standing position. see note.

Part Position:

  • Midsagital plane is align to central ray and in the midline of table or bucky.
  • Put arm on chest or at the side.
  • Ensure that no rotation of torso or pelvis exist.

Central Ray:

  • Direct the central ray perpendicular to image receptor to following:
  • If large image receptor used (35 x 43): Center to level of illiac crest between L4-L5 interspace. This large image receptor will include the lumbar vetebrae, sacrum, and possibly coccyx.
  • If smaller image receptor 30 x 35: Center central ray to level of L3, it can be palpated to the local costal margin ( 1 1/2 inches or 4 cm above the iliac crest.) Small image receptor will include primary the five lumbar vertebrae.
  • Minimum SID is 40 inches or 100 cm.


  • Four-sided collimation with superior and inferior borders to near IR margins.

Patient Respiration:

  • Let patient suspend breathing on expiration when exposing.

Note: Partial flexion of knees as shown straighten the spine, which help to open intervertebral disk spaces.
Radiograph may done prone as a PA projection, which places the intervetebral spaces more closely parallel to the diverging rays.
The erect position may be useful for demonstrating the natural weight bearing stance of the spine.

Radiographic Criteria:

Structure Shown:

  • Lumbar vertebral bodies, intervertebral joints, spinous and transverse processes, SI joints, and sacrum are shown.
  • 35 x 43 cm or 14 x 17 inches film. Approximately T11 to the distal sacrum should be included.
  • 30 x 35 cm or 11 x 14 inches film. T12 to S1 should be included.
lumbar spine radiograph

Patient Positon:

  • No patient rotation is indicated by the following:
  • SI joint id equidistant from spinous processes.
  • Spinous processes in midline of vertibral column.
  • R and L transverse processes in equal in length.

Collimation and Central Ray:

  • The vertebral column should be centered to the IR / collimated field, at the approximate level of L3 - L4.
  • Lateral margins of collimated field should include the SI joints and psoas muscles.

Exposure Criteria:

  • Optimal density and contrast should demonstate the lumbar vertebral bodies, intervertebral disk spaces, transverse processes, and psoas muscle.
  • Sharp bony margins indicate no motion.

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