A novel method for measuring the direction and angle of central ray and predicting rotation centre via panorama phantom.

The aim of this study is to propose and evaluate a novel method for measuring the central ray direction and detecting the rotation centre of panoramic radiography using the panorama phantom. To determine the central ray direction, 2 points passing through the same x-coordinate in a panoramic radiograph were identified and connected. The angles formed by the central ray with the midline and the angle to the arch form were measured using mathematical calculations. Further, by analysing the continuous changes in the central ray obtained in this manner, the movement of the rotation centre was detected and visualized. The angle between the central ray and the midline exhibited a progressive decrease from the anterior to the posterior direction. With regards to the arch form, the angle of the central ray exhibited an increasing pattern as it moved from the anterior to the posterior direction, culminating in its peak value at the lower second premolar cusp region, followed by a consistent decrease. The rotation centre approximately started from the distolateral aspect of the coronoid process and then anteromedially moved to the midline in a curved line passing between the mandibular notch and coronoid process. By using the panorama phantom, we successfully obtained the central ray direction and detected the rotation centre of the panoramic radiography.