Transient noise characterization and filtration in CCD cameras exposed to stray radiation from a medical linear accelerator
Transient noise characterization and filtration in CCD cameras exposed to stray radiation from a medical linear accelerator
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DOI：
10.1118/1.2975147
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发表时间：
2008-10-01
期刊：
影响因子：
3.8
通讯作者：
Beddar, Sam
中科院分区：
文献类型：
--
作者：
Archambault, Louis;Briere, Tina Marie;Beddar, Sam
电荷耦合器件(CCDs)越来越多地被用于放射治疗的剂量学目的。然而，ccd对杂散辐射很敏感。这种效应会产生暂态噪声。辐射引起的噪声强烈地改变了图像，因此限制了其定量分析。这项工作的目的是表征辐射引起的噪声，并开发滤波算法来恢复图像质量。两种型号的ccd被用来在医用直线加速器附近进行测量。首先对瞬时噪声的结构进行了表征。然后，比较了四种噪声滤除方法：相同图像时间序列的中值滤波、单幅图像的均匀中值滤波、带切换机制的自适应滤波和改进的自适应切换滤波。两台摄像机中噪声像素的强度分布相似。然而，噪声的空间分布是不同的：U2000和LUCA的平均噪声簇大小分别为1.2+/-0.6和3.2+/-2.7像素。时间序列图像的中值可以得到最好的滤波效果和最小的图像失真。对于时间序列不切实际的应用，必须使用自适应切换滤波器来减少图像失真。我们的改进版本的开关过滤器可用于处理非孤立的噪声像素组。(C)2008年美国医学物理学家协会。
Charge coupled devices (CCDs) are being increasingly used in radiation therapy for dosimetric purposes. However, CCDs are sensitive to stray radiation. This effect induces transient noise. Radiation-induced noise strongly alters the image and therefore limits its quantitative analysis. The purpose of this work is to characterize the radiation-induced noise and to develop filtration algorithms to restore image quality. Two models of CCD were used for measurements close to a medical linac. The structure of the transient noise was first characterized. Then, four methods of noise filtration were compared: median filtering of a time series of identical images, uniform median filtering of single images, an adaptive filter with switching mechanism, and a modified version of the adaptive switch filter. The intensity distribution of noisy pixels was similar in both cameras. However, the spatial distribution of the noise was different: The average noise cluster size was 1.2 +/- 0.6 and 3.2 +/- 2.7 pixels for the U2000 and the Luca, respectively. The median of a time series of images resulted in the best filtration and minimal image distortion. For applications where time series is impractical, the adaptive switch filter must be used to reduce image distortion. Our modified version of the switch filter can be used in order to handle nonisolated groups of noisy pixels. (C) 2008 American Association of Physicists in Medicine.