Novel reconstruction method of angle-limited backprojection (ALBP) for low-dose dental panoramic X-ray imaging

Abstract

Panoramic radiography is a popular two-dimensional X-ray imaging modality in dentistry. It produces a single image of the overall facial view, including the maxillary and mandibular arches and supporting structures. Panoramic images are typically reconstructed using the shift-and-add (SAA) algorithm, in which only structures within a certain image layer are in focus, and others are out of focus on the panoramic image. As the clinical use of panoramic radiography has grown rapidly, radiologists are continuously seeking ways to reduce the radiation dose to patients. This study proposes a novel panoramic reconstruction method called the angle-limited backprojection (ALBP) algorithm for low-dose panoramic X-ray imaging. In ALBP, X-rays that meet the angular criterion established in this study are selected from the measured panoramic projection data and then backprojected onto the spherical voxels placed along the dental arch, as in a typical computed tomography reconstruction. The angular criterion selects X-rays that pass through a given spherical voxel and simultaneously have directional vectors within a prespecified angular range concerning the directional vector at the corresponding source position. To validate the efficacy of the proposed reconstruction method, we conducted a numerical simulation and experiment and investigated the image characteristics. Panoramic images were reconstructed using the SAA and ALBP algorithms with full and half (i.e., half radiation dose) panoramic projections, and their image quality was quantitatively evaluated using the intensity profile and universal quality index (UQI). The image quality of the ALBP with half projections was similar to that of the SAA with full projections, indicating the efficacy of the proposed method. Accordingly, our results demonstrated the potential for radiation dose reduction in panoramic X-ray imaging.