We present a volumetric dental tomography method that compensates for insufficient projection views obtained from limited-angle scans. The reconstruction algorithm is based on the backprojection filtering method which employs apodizing filters that reduce out-of-plane blur artifacts and suppress high-frequency noise. In order to accompolish this volumetric imaging two volume-reconstructed datasets are synthesized. These individual datasets provide two different limited-angle scans performed at orthogonal angles. The obtained reconstructed images, using less than 15% of the number of projection views needed for a full skull phantom scan, demonstrate the potential use of the proposed method in dental imaging applications. This method enables a much smaller radiation dose for the patient compared to conventional dental tomography. KEYWORDS: Computerized Tomography (CT) and Computed Radiography (CR); Medical-image reconstruction methods and algorithms, computer-aided so; X-ray radiography and digital radiography (DR) 3 Results 4 Discussion and conclusion 5

In radiology, image quality excellence is a balance between system performance and patient dose, hence x-ray systems must be designed to ensure the maximum image quality is obtained for the lowest consistent dose. The concept of detective quantum efficiency (DQE) is widely used to quantify, understand, measure, and predict the performance of x-ray detectors and imaging systems. Cascaded linear-systems theory can be used to estimate DQE based on the system design parameters and this theoretical DQE can be utilized for determining the impact of various physical processes, such as secondary quantum sinks, noise aliasing, reabsorption noise, and others. However, the prediction of DQE usually requires tremendous efforts to determine each parameter consisting of the cascaded linear-systems model. In this paper, practical DQE formalisms assessing both the photoconductor-and scintillator-based flat-panel detectors under quantum-noise-limited operation are described. The developed formalisms are experimentally validated and discussed for their limits. The formalisms described in this paper would be helpful for the rapid prediction of the DQE performances of developing systems as well as the optimal design of systems. KEYWORDS: Detector modelling and simulations I (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc); X-ray detectors; Detector design and c onstruction technologies and materials

In digital X-ray imaging systems, X-ray imaging detectors based on scintillating screens with electronic devices such as charge-coupled devices (CCDs), thin-film transistors (TFT), complementary metal oxide semiconductor (CMOS) flat panel imagers have been introduced for general radiography, dental, mammography and non-destructive testing (NDT) applications. Recently, a large-area CMOS active-pixel sensor (APS) in combination with scintillation films has been widely used in a variety of digital X-ray imaging applications. We employed a scintillatorbased CMOS APS image sensor for high-resolution mammography. In this work, both powder-type Gd 2 O 2 S:Tb and a columnar structured CsI:Tl scintillation screens with various thicknesses were fabricated and used as materials to convert X-ray into visible light. These scintillating screens were directly coupled to a CMOS flat panel imager with a 25 × 50 mm 2 active area and a 48 µm pixel pitch for high spatial resolution acquisition. We used a W/Al mammographic X-ray source with a 30 kVp energy condition. The imaging characterization of the X-ray detector was measured and analyzed in terms of linearity in incident X-ray dose, modulation transfer function (MTF), noise-power spectrum (NPS) and detective quantum efficiency (DQE). KEYWORDS: X-ray detectors; Scintillators, scintillation and light emission processes (solid, gas and liquid scintillators); Scintillators and scintillating fibres and light guides; X-ray radiography and digital radiography (DR)

We theoretically characterize the imaging performance of a hypothetical mercuric iodide (HgI 2 ) photoconductor prepared by a screen printing method in terms of the spatial-frequencydependent detective quantum efficiency (DQE) using the cascaded-systems analysis. In the DQE model, we use the "photon-interaction process" in order to represent both the selection of interacting photons and subsequent conversion gain as a single process because both processes are not statistically independent but their probabilities are determined by the photon energy. We further include the thermal generation process of leakage current charges and the incomplete chargecollection process in the DQE model. Theoretical imaging performances of the hypothetical HgI 2 photoconductor sample are compared with those of a 0.2-mm thick amorphous selenium (a-Se) under mammographic imaging conditions. It is shown that the hypothetical HgI 2 with a smaller value of the average ionization energy than a-Se gives a better DQE performance at lower exposure levels, which suggests that a HgI 2 -based photoconductor may have the potential to reduce the 1 Corresponding author.

We are developing a silicon microstrip-array detector, which is operated in photoncounting mode, for line-scanned digital mammography. To enhance the x-ray interaction efficiency, the x-ray beam is oriented toward the edge of microstrips, known as the edge-on geometry. To predict the fundamental signal and noise performances induced by x-ray interactions, we performed Monte Carlo simulations. Absorbed energy distribtuions were obtained for various tilting angles (5 to 85 degrees) in the edge-on detector geometry for a wide range of incident energies from 1 to 50 keV. Based on the energy-moments theory with the obtained absorbed energy distributions, we estimated various physical performance parameters such as the quantum absorption efficiency, the average energy deposition per interaction, and the Swank noise factor. In addition, relative accuracy and imprecision in photon-energy measurements were estimated. These analyses were extended to the typical poly-energetic mammography x-ray spectra from various target materials