What happens to structures inside vs outside the focal trough?

• A. Structures inside the focal trough are sharp; structures farther away become progressively blurred.
• B. Structures inside are blurred; outside are sharp.
• C. All structures are equally sharp.
• D. Only structures within a narrow band are captured.

Answer: (A)

In panoramic imaging, there is a curved zone called the focal trough where structures come into its best focus as the machine rotates. Structures that lie inside this trough stay aligned with the rotating beam and detector, so their edges appear sharp. Structures that sit outside the trough are out of the optimal focusing plane, so they are projected with blur and distortion—the farther they are from the trough, the more blurred they become. This is why positioning the patient so the teeth and other anatomy sit within the trough is crucial for a sharp image.