For a lateral lumbar spine radiograph, where should the central ray enter?

• A. Midcoronal plane
• B. Midline at the level of L3
• C. 2 inches posterior to the ASIS
• D. 2 inches inferior to the iliac crest

Answer: (A)

Centering the beam on the midcoronal plane is essential for a true lateral lumbar spine image. When the central ray enters through the midcoronal plane, the beam passes through the center of the spinal column and the vertebral bodies are superimposed without rotation. This alignment keeps the anatomy of interest in the center of the image and minimizes distortion or clipping of structures on either side. The vertical level is chosen to include the lumbar region, but the key principle is that the entry point is at the body’s midline so the spine remains truly lateral. Entering the beam at a fixed anterior or posterior offset or at a specific vertebral landmark that isn’t the midline can shift the image laterally, create rotation, and compromise the visualization of the lumbar anatomy.