Ghosting caused by bulk charge trapping in direct conversion flat-panel detectors using amorphous selenium
Ghosting caused by bulk charge trapping in direct conversion flat-panel detectors using amorphous selenium
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DOI：
10.1118/1.1843353
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发表时间：
2005-02-01
期刊：
影响因子：
3.8
通讯作者：
Rowlands, JA
中科院分区：
文献类型：
--
作者：
Zhao, W;DeCrescenzo, G;Rowlands, JA
使用非晶硒（a-Se） x射线光导体的直接平板探测器正获得广泛的临床应用。我们研究的目的是了解造成重影的物理机制，即x射线引起的灵敏度变化导致图像持久性，以便可以使用这些知识来一致地减少a-Se平板探测器中的重影伪影。在本文中，我们将讨论在a-Se中电荷捕获对x射线灵敏度的影响，这是a-Se平板探测器中重影的主要来源。我们的方法是通过“飞行时间”（TOF）方法将电极a-Se探测器中的重影与捕获电荷浓度联系起来。在E-Se = 5和10 V / mum的电场强度下，所有的测量都是作为高达20 R的辐射暴露X的函数进行的。结果表明，随着E-Se的增加，X射线灵敏度随X的变化而降低，重影量随E-Se的增加而减少。由于辐照，TOF曲线的形状发生了变化，表明在大量的a- se中捕获了电子。捕获电子的密度随着x的增加而增加。我们开发了一种方法，通过TOF测量来确定a- se体中n(t)的值，并预测相应的x射线灵敏度变化。我们的结果表明，复合系数与Langevin预测的结果一致，在计算和测量的x射线灵敏度变化之间有很好的一致性。由此可以得出结论，电子在a-Se体中的捕获及其随后与x射线产生的自由空穴的复合是a-Se中重影的主要机制。(C) 2005年美国医学物理学家协会。
Direct flat-panel detectors using amorphous selenium (a-Se) x-ray photoconductors are gaining wide-spread clinical use. The goal of our investigation is to understand the physical mechanisms responsible for ghosting, i.e., x-ray induced change in sensitivity that results in image persistence, so that the knowledge can be used to consistently minimize ghosting artifacts in a-Se flat-panel detectors. In this paper we will discuss the effect on x-ray sensitivity of charge trapping in a-Se, which is the dominant source for ghosting in a-Se flat-panel detectors. Our approach is to correlate ghosting in electroded a-Se detectors with the trapped charge concentration measured by the "time-of-flight" (TOF) method. All measurements were performed as a function of radiation exposure X of up to similar to20 R at electric field strengths of E-Se = 5 and 10 V / mum. The results showed that the x-ray sensitivity decreased as a function of X and the amount of ghosting decreased with increasing E-Se. The shape of the TOF curves changed as a result of irradiation in a manner indicating trapped electrons in the bulk of a-Se. The density of trapped electrons it, increases as a function of X. A method was developed to determine the values of n(t) in the bulk of a-Se from the TOF measurements, and to predict the corresponding change in x-ray sensitivity. Our results showed that a recombination coefficient consistent with that predicted by Langevin produced good agreement between calculated and measured x-ray sensitivity changes. Thus it can be concluded that the trapping of electrons in the bulk of a-Se and their subsequent recombination with x-ray generated free holes is the dominant mechanism for ghosting in a-Se. (C) 2005 American Association of Physicists in Medicine.