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

无定形硒（a-Se）是一种可用于最近开发的用于医学成像的直接转换平板x射线图像探测器的x射线光导体。为了更好地理解a- se中的捕获和复合效应，我们研究了a- se薄膜中的光和x射线诱导光电流。x射线照射后的剩余光电流在夹层细胞中减少，而在共面细胞中增加。这些影响需要几个小时的时间才能恢复。结果表明，可以用VAP（价交替对）型带电缺陷来解释。由于累积的x射线照射，基于a- se的x射线探测器的灵敏度（疲劳）有所下降。灵敏度降低是砷硒探测器的缺点之一，会导致图像的重影。术语“重影”是指以前x射线曝光后的残留图像。在对鬼影的某些解释中，有人提出x射线暴露会导致产生更多新的深圈闭。为了获得稳定（和安全）的实时x射线图像（透视），必须克服以下问题：(1)x射线曝光导致x射线图像退化(2)响应时间延迟，大约几十秒，以获得正确的图像。在a-Se中观察到x射线对光电流的诱导效应。x射线照射后，共面光电流增大，夹层光电流减小。我们已经证明了共面电池和夹层电池在x射线对光电流的诱导效应方面具有完全不同的特性。在共面结构中，x射线产生的空穴的捕获改变了准费米能级，增加了光电流。在夹层结构中，当x射线诱导的电子被困在那里时，来自光载流子的捕获空穴充当复合中心。已经证明，x射线诱导电荷的捕获主导了图像中的“重影”。认为现有的x射线曝光条件不会产生新的缺陷。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