For an AP lumbar projection, where is the CR directed?

For an AP lumbar projection, where is the CR directed?

• A. L3–L4
• B. L1–L2
• C. L5–S1
• D. T12–L1

Answer: (A)

Center the beam at the L3–L4 interspace, about 2 inches (5 cm) above the iliac crests. This spot places the central ray roughly in the middle of the lumbar spine and ensures the image includes from roughly L1 down to S1. The iliac crest sits at the L4–L5 region, so lifting the CR about 2 inches brings you to L3–L4, which is ideal for a single AP lumbar view. If the CR were directed higher, you’d risk not including the lower lumbar and sacrum; if directed lower, you’d miss the upper lumbar.

Center the beam at the L3–L4 interspace, about 2 inches (5 cm) above the iliac crests. This spot places the central ray roughly in the middle of the lumbar spine and ensures the image includes from roughly L1 down to S1. The iliac crest sits at the L4–L5 region, so lifting the CR about 2 inches brings you to L3–L4, which is ideal for a single AP lumbar view. If the CR were directed higher, you’d risk not including the lower lumbar and sacrum; if directed lower, you’d miss the upper lumbar.