Reducing intra plane blurring in dental panoramas

Dental imaging often requires to gather information from a curved plane that covers the upper and lower jaw. To acquire these data one may either use a CT scan followed by extracting the desired curved plane from the volumetric CT data, or one may decide to work at much lower dose levels and acquire a panoramic radiograph, which is also known as an orthopantomogram, or short as panorama. The panorama is acquired by moving the X-ray source and detector arrangement such that the X-ray cone intersects the curved plane in a preferably perpendicular way. Due to the small size of specialized panorama x-ray detectors, that often run in the so-called time-delayed integration (TDI) mode, the cone is collimated such that it is only a few millimeters wide in the fan direction. In this situation the fan angle is smaller than the cone angle. Assuming an imaging system based on a flat detector the panoramic imaging corresponds to digital X-ray tomosynthesis taken in a curved plane. Of course, panoramic imaging suffers from significant blurring between adjacent planes, as it is inherent to all tomosynthesis techniques. To reduce this intra plane blurring we propose an approach that uses a form filter to simultaneously acquire the data for a typical orthopantomogram and data with a significantly increased fan-angle, while the bow-tie takes care to reduce dose in that extended region to about 1 % compared to the dose in the central region. These data will be combined resulting in an orthopantomogram with improved image quality with reduced intra plane blurring. We conducted simulations to validate our approach. For that we use a volumetric CT data set of a patient´s head from which we generated raw data. The simulation results show that with our approach panoramic imaging with a flat detector offers the possibility to improve image quality without additional costs in patient dose.