Which statement about real and ghost images is correct?

• A. Real images occur outside the focal trough; ghost images occur outside it
• B. Real images occur inside the focal trough; ghost images occur inside it
• C. Both real and ghost images occur inside the focal trough
• D. Real images occur inside the focal trough; ghost images occur outside it

Answer: (D)

In panoramic imaging, the focal trough is the curved zone where structures are represented most sharply. Objects that lie within this trough produce sharp, real images on the film. Ghost images are artifacts created by dense structures on one side of the head projecting onto the opposite side due to the geometry of the rotating X-ray source and sensor; these ghost projections appear outside the focal trough. So the best statement is that real images occur inside the focal trough and ghost images occur outside it.