Chest digital tomosynthesis (chest DTS) has been recently introduced to overcome the limitations for high patient dose of conventional X-ray radiography and of a cone-beam computed tomography (CBCT) in studies of overlap of anatomical structures. In the present study, we constructed chest DTS system with amorphous-silicon (a-Si) digital flat-panel detector with pixel pitch of 143 × 143 µm 2 based upon filtered backprojection (FBP) reconstruction methods We performed both experiments and systematic simulations using our chest DTS system. The image performances were evaluated by means of root-mean-square error (RMSE) and signal difference-to-noise ratio (SDNR) with respect to scan angles such as ±5 • , ±10 • , ±15 • , and ±20 • . We also performed experiments using our chest DTS system. According to the results, the image performances obtained from chest DTS are improved by using our wide scan angle approach The chest DTS slices showed an improvement in the depth resolution with increasing scan angle. It was found that the optimized filter with a Hanning window to limit the high-frequency components improves image performance because of noise reduction. The chest DTS slices showed an improvement in the depth resolution with increasing scan angle. Both simulation and experimental results showed the same tendency when image performances quantitatively compared. Based on our results, we successfully obtained chest DTS reconstruction images by using a FBP method and promising to application to field of medical imaging. KEYWORDS: Detector design and construction technologies and materials; Medical-image reconstruction methods and algorithms, computer-aided diagnosis; X-ray radiography and digital radiography (DR)

A: Chest digital tomosynthesis (CDT) is a promising new modality that provides 3D information by reconstructing limited projection views. CDT systems have been developed to improve the limitations of conventional radiography such as image degradation and low sensitivity. However, the development of reconstruction methods is challenging because of the limited projection views within various angular ranges. Optimization of reconstruction parameters for various reconsturction methods in CDT system also is needed. The purpose of this study was to investigate the feasibility of algebraic reconstruction technique (ART) method, and to evaluate the effect of the reconstruction parameters for our newly developed CDT system. We designed ART method with 41 projection views over an angular range of ±20°. To investigate the effect of reconstruction parameters, we measured the contrast-to-noise ratio (CNR), artifact spread function (ASF), and quality factor (QF) using LUNGMAN phantom included tumors. We found that the proper choice of reconstruction parameters such as relaxation parameter, initial guess, and number of iterations improved the quality of reconstructed images from the same projection views. Optimal values of ART relaxation parameter with uniform (UI) and back-projection (BP) initial guesses were 0.4 and 0.6, respectively. BP initial guess improved image quality in comparison with UI initial guess, in terms of providing a higher CNR and QF values with a faster speed. CNR and QF values improved with increasing number of iteration. Particularly, ART method with BP initial guess (when β = 0.6) after 3-terations provide satisfactory reconstructed image. In conclusion, the use of ART method with proper reconstruction parameters provided better image quality than FBP method as well as conventional radiography. These results indicated that the ART method with optimal reconstruction parameters could improve image quality for nodule detection using the CDT system. K: Image reconstruction in medical imaging; Computerized Tomography (CT) and Computed Radiography (CR)

The pixelated semiconductor based on cadmium zinc telluride (CZT) is a promising imaging device that provides many benefits compared with conventional scintillation detectors. By using a high-resolution square parallel-hole collimator with a pixelated semiconductor detector, we were able to improve both sensitivity and spatial resolution. Here, we present a simulation of a CZT pixleated semiconductor single-photon emission computed tomography (SPECT) system with a high-resolution square parallel-hole collimator using various geometric designs of 0.5, 1.0, 1.5, and 2.0 mm X-axis hole size. We performed a simulation study of the eValuator-2500 (eV Microelectronics Inc., Saxonburg, PA, U.S.A.) CZT pixelated semiconductor detector using a Geant4 Application for Tomographic Emission (GATE). To evaluate the performances of these systems, the sensitivity and spatial resolution was evaluated. Moreover, to evaluate the overall performance of the imaging system, a hot-rod phantom was designed. Our results showed that the average sensitivity of the 2.0 mm collimator X-axis hole size was 1.34, 1.95, and 3.92 times higher than that of the 1.5, 1.0, and 0.5 mm collimator X-axis hole size, respectively. Also, the average spatial resolution of the 0.5 mm collimator X-axis hole size was 28.69, 44.65, and 55.73% better than that of the 1.0, 1.5, and 2.0 mm collimator X-axis hole size, respectively. We discuss the high-resolution square parallel-hole collimator of various collimator geometric designs and our evaluations. In conclusion, we have successfully designed a high-resolution square parallel-hole collimator with a CZT pixelated semiconductor SPECT system.