What are key differences in panoramic imaging compared to a real panoramic machine?

• A. The center of rotation is fixed, and the focal trough width is constant.
• B. The center of rotation moves, but focal trough width remains constant.
• C. The center of rotation moves, and the focal trough width varies.
• D. The center of rotation is fixed, and the focal trough width varies.

Answer: (C)

In panoramic imaging, the geometry isn’t a single fixed axis plus a uniform sharp zone. As the X-ray source and detector rotate around the head to sweep the curved dental arch, the effective center of rotation for the imaging plane shifts because the plane that best maps the anatomy changes with position. At the same time, the focal trough—the zone where structures are sharply imaged—is designed to follow that curved archaeology of the jaw, so its width isn’t constant. It must widen or narrow along the arch to keep different parts of the teeth in focus as the geometry changes. That combination—a moving center of rotation and a focal trough width that varies along the arch—is what differentiates panoramic imaging from a simple, fixed-geometry setup.