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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 or a DVT 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 much smaller than the cone angle.
Assuming an imaging system based on flat detectors 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 low-dose data with a significantly increased fan-angle, sufficient to perform a low-dose FDK reconstruction. The bow-tie takes care to reduce dose in that extended region to about 1% compared to the dose in the central region. The total dose remains constant. These data will be combined resulting in an orthopantomogram with improved image quality due to reduced intra plane blurring as one is able to subtract the unwanted background structures arising from off focus objects as for example the cervical vertebrae. 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 rawdata.
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.
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