High-sensitive X-ray fluoroscopy using chalcogenide glasses: Degradation of X-ray images

非晶硒（a-Se）是可用于最近开发的用于医学成像的直接转换平板X射线图像检测器中的X射线光电导体之一。为了更好地理解非晶硒中的俘获和复合效应，我们研究了光和X射线在非晶硒薄膜中诱导的光电流。剩余的光电流，在X射线曝光后，减少在三明治电池，而它增加在共面电池。这些影响在数小时的时间尺度内恢复。我们表明，结果可以解释通过使用VAP（价交替对）型带电缺陷。a-Se为基础的X射线探测器已显示出一些下降的灵敏度（疲劳）作为累积的X射线曝光的结果。灵敏度降低是a-Se探测器的缺点之一，导致重影图像。术语重影是指来自先前X射线曝光的残留图像。在对重影的一些解释中，有人认为X射线照射会导致一般的重影。 ...更多信息 为了得到稳定的（和安全的）实时X射线图像（荧光透视），应该克服以下问题：（1）X射线图像随X射线曝光而退化（2）为了得到合适的图像，响应时间延迟约几十秒。X射线照射后，共面电池的光电流增加，而三明治电池的光电流减小。我们已经表明，共面和三明治电池有完全不同的特性，在X射线诱导的光电流的影响。在共面结构中，X射线产生的空穴的俘获改变了准费米能级，增加了光电流。在三明治结构中，当X射线诱导的电子被捕获在那里时，来自光生载流子的被捕获的空穴充当复合中心。已经证明，捕获的X射线感生电荷占主导地位的图像中的“重影”。有人建议，新的缺陷不会产生目前的X射线曝光条件。少

Amorphous selenium (a-Se) is one of the x-ray photoconductors that is available for use in recently developed direct conversion flat panel x-ray image detectors for medical imaging. To obtain a better understanding of trapping and recombination effects in a-Se, we have studied light and x-ray induced photocurrents in a-Se films. The residual photocurrent, after x-ray exposure, decreases in sandwich cells whereas it increases in coplanar cells. These effects are recovered over a time scale of hours. We show that the results can be interpreted by using VAP (valence alternation pair) type charged defects.a-Se based x-ray detectors have shown some decrease in the sensitivity (fatigue) as a result of accumulated x-ray exposure. Reduction of sensitivity is one of drawbacks of a-Se detectors, resulting in a ghosting images. The term ghosting means the residual image from previous x-ray exposure. In some explanation of ghosting it has been suggested that x-ray exposure should lead to the gener … More ation of new deep traps.To get stabilized (and safe) real-time X-ray image (fluoroscopy), the following problems should be overcome :(1) Degradation of X-ray images with exposing X-ray(2) Delay of the response time, around several ten seconds, for getting a proper image.X-ray induced effects on the photocurrent were observed in a-Se. After x-ray exposure, the photocurrent increases in coplanar and decreases in sandwich cells. We have shown that coplanar and sandwich cells have totally different characteristics in terms of x-ray induced effects on the photocurrent. In the coplanar structure, the trapping of x-ray generated holes modifies the quasi-Fermi level and increased the photocurrent. In the sandwich structure, the trapped holes from the photocarriers act as recombination centers, when the x-ray induced electrons are trapped there. It has been turned out that the trapping of X-ray induced charges dominate "ghosting" in the images. It is suggested that new defects are not created by the present x-ray exposure conditions. Less