Why are most structures captured twice in panoramic imaging?

• A. Because the x-ray source and receptor rotate around the patient
• B. Because the patient moves during exposure
• C. Because the receptor fails twice
• D. Because the image is captured twice with different exposure settings

Answer: (A)

Panoramic imaging uses a rotating X-ray source and receptor that move around the patient. As this gantry sweeps through its arc, every structure in the jaw passes through the beam twice—once during the forward part of the rotation and again during the return. Those two passes map to two different positions on the final image, so most structures are captured twice. This two-pass geometry is what makes a panoramic image possible in one exposure, but it also leads to dual appearances of structures (and sometimes ghost images) due to the opposite directions of the beam path.