For a PA axial oblique projection with RAO position of the cervical spine, what is the appropriate angulation of the central ray?

• A. 15-20 degree cephalad
• B. 15-20 degree caudal
• C. 0 degrees
• D. 25-30 degrees caudal

Answer: (B)

When you want to visualize the cervical zygapophyseal joints in a PA axial oblique with an RAO position, the central ray should be angled caudally about 15–20 degrees. This caudal tilt aligns the beam with the oblique plane of the cervical joints, helping to open the joint spaces and reduce superimposition by surrounding structures like the vertebral bodies and occiput. Zero angulation wouldn’t separate the joints, a cephalad angle would misalign the beam and can obscure or distort the joints, and a much larger caudal angle (25–30 degrees) would over-project and distort the anatomy. The 15–20 degree caudal angle is the balanced value that best demonstrates the cervical zygapophyseal joints in this projection.