The role of focal block (trough/plane) in panoramic radiography: Why do some structures appear blurred out on these images?

Panoramic radiographs are commonly used in dental practice. The challenge with panoramic radiography is overlapping structures, ghost and air shadows. The area of interest can appear blurred especially in the anterior region. The focal block is a virtual space in which the dentition should be perfectly placed when acquiring the radiograph. Anatomical structures that are within this focal block appear focused and in perfect geometric accuracy on the final image. Structures outside this focal block appear blurred, and distorted. Accurate positioning of the patient will help in placing the region of interest within in the focal block and as a result minimising artefacts, ghost and air shadows. We utilise cone beam computed tomography (CBCT) software to explain this principle.