The characteristics of flat-panel detectors (FPD) are degraded by exposure to radiation. Degradation in a FPD progresses locally and has a nonlinear relationship to the radiation dose. In order to manage FPD systems properly, one must perform quality control (QC) such as evaluation of image degradation. However, no evaluation method for degradation has been established. In this paper, we first review the structure and degradation mechanism of FPDs, and then we propose a daily QC system for FPDs. To evaluate the degradation of FPDs, we investigated the number of defective pixels and lines, as well as the offset level of the pixel output. Furthermore, we developed daily QC software for FPD that can evaluate the image quality and is operationally simple. In the experiments, an indirect-conversion type FPD was evaluated by our proposed system. The offset level of FPD increased exponentially with X-ray exposure; no trends were seen for the number of defective pixels and defective lines. The required time for the evaluation of an FPD was about 1 min, and no special skills were needed for the analysis. These results indicate that our system may be useful for daily QC of FPDs.
We discussed the slice thickness of pr 。 丘1e of two different machines which could be grouped into 180°t w 。 − slice scanner (head sc 註 nner) and 360D ・ne −slibe scanner (wh ・ 1e b ・dy scanne ・) . The results as follows: 1. The slice thickness of 180°two ・ slice scanner was not same in the horizontal and the vertical plane 、 The slice thickness was thicker 1 . 5ti 卑 es on the periphery than in the eenter and alsD thinner on the tube side than on the detector side . The two slice profiles of 360°one − slice scanner were sym 皿 etric and the distri − bution of CT numbers was even . The slice thickness was thicker ユ. 2times on the periphery than in the center . 2. We investigated the infiuence of the ten kinds of weighting functiohs gn the slice thickness , The close relationship between the s ! ice thickness and weighting function was clearly demonstrated . Thus , it is necessary for us to measure slice thickness more precisely uti [ izing重he raw data obtained from the cross −section of a phantom . 1. 緒
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