[en] We report the physical imaging properties of a flat panel detector (FPD) designed for radiographic imaging applications (Revolution XQ/i digital chest imaging system, G.E. Medical Systems). The imaging properties of the detector were evaluated through measurements of the characteristic curve, modulation transfer function (MTF), and Wiener spectrum. The digital characteristic curves of the FPD system were measured for the two tube voltages (80 kV and 120 kV). They showed that the correlation between the pixel values of FPD and the incident exposure to the FPD was a linear correlation. The dynamic range of characteristic curves had a range from about 0.003 to 2μC/kg at the exposure. The presampling MTFs for different tube voltage were almost the same, when we measured the MTFs at 80 kV and 120 kV. And also, there was no significant difference between the MTFs measured with the slit in the direction parallel to the horizontal direction and with the slit in the perpendicular direction. The relative resolution of the FPD system was a 46% higher than that of ST-V imaging plate of FCR (Fuji Computed Radiography) system at 2 cycles/mm. The digital Wiener spectrum of the FPD system was about 1/10 lower than that of the CR system. Thus the FPD system can provide superior imaging performance due to both high resolution and low noise. (author)

[en] The influence of the numbers of projection of single photon emission computed tomography (SPECT) exerting on a re-constructed image cannot be strictly evaluated by phantom studies. Therefore, we compared re-constructed images of the filtered back projection (FBP) method and the maximum likelihood-expectation maximization (ML-EM) method by using simulation data. Simulation data was entered in the image processing software, and the projection data that changed the numbers of projection was made. Afterwards, reconstructed images of the FBP and the ML-EM methods were compared with respect to contrast, %COV, and the normalized mean square error (NMSE) value. When the numbers of projection of the FBP and the ML-EM method were decreased, all of the contrast, %COV, and the NMSE value were more deteriorated than that of the ideal image. Therefore, the image quality of SPECT improves with both FBP and ML-EM methods when there are many numbers of projection. Moreover, the FBP method was excellent in a cold contrast, and the ML-EM method was uniformly excellent. Therefore, an understanding of features and their inspection are effective for the selection of each image reconstruction method. (author)