Antonuk L E, El-Mohri Y, Siewerdsen J H, Yorkston J, Huang W, Scarpine V E, Street R A
Department of Radiation Oncology, University of Michigan Medical Center, Ann Arbor 48109, USA.
Med Phys. 1997 Jan;24(1):51-70. doi: 10.1118/1.597918.
Signal properties of the first large-area, high resolution, active matrix, flat-panel imager are reported. The imager is based on an array of 1536 x 1920 pixels with a pixel-to-pixel pitch of 127 microns. Each pixel consists of a discrete amorphous silicon n-i-p photodiode coupled to an amorphous silicon thin-film transistor. The imager detects incident x rays indirectly by means of an intensifying screen placed over the array. External acquisition electronics send control signals to the array and process analog imaging signals from the pixels. Considerations for operation of the imager in both fluoroscopic and radiographic modes are detailed and empirical signal performance data are presented with an emphasis on exploring similarities and differences between the two modes. Measurements which characterize the performance of the imager were performed as a function of operational parameters in the absence or presence of illumination from a light-emitting diode or x rays. These measurements include characterization of the drift and magnitude of the pixel dark signal, the size of the pixel switching transient, the temporal behavior of pixel sampling and the implied maximum frame rate, the dependence of relative pixel efficiency and pixel response on photodiode reverse bias voltage and operational mode, the degree of linearity of pixel response, and the trapping and release of charge from metastable states in the photodiodes. In addition, X-ray sensitivity as a function of energy for a variety of phosphor screens for both fluoroscopic and radiographic operation is reported. Example images of a line-pair pattern and an anthropomorphic phantom in each mode are presented along with a radiographic image of a human hand. General and specific improvements in imager design are described and anticipated developments are discussed. This represents the first systematic investigation of the operation and properties in both radiographic and fluoroscopic modes of an imager incorporating such an array.
报告了首个大面积、高分辨率、有源矩阵平板成像器的信号特性。该成像器基于一个1536×1920像素的阵列，像素间距为127微米。每个像素由一个离散的非晶硅n-i-p光电二极管与一个非晶硅薄膜晶体管耦合而成。成像器通过放置在阵列上方的增强屏间接检测入射的X射线。外部采集电子设备向阵列发送控制信号，并处理来自像素的模拟成像信号。详细介绍了成像器在荧光透视和射线照相模式下的操作注意事项，并给出了经验性的信号性能数据，重点是探索两种模式之间的异同。在有无发光二极管或X射线照明的情况下，根据操作参数对成像器性能进行了表征测量。这些测量包括像素暗信号的漂移和幅度、像素开关瞬态的大小、像素采样的时间行为和隐含的最大帧率、相对像素效率和像素响应与光电二极管反向偏置电压及操作模式的依赖性、像素响应的线性程度，以及光电二极管中亚稳态电荷的俘获和释放。此外，还报告了在荧光透视和射线照相操作中，各种磷光屏的X射线灵敏度与能量的函数关系。给出了每种模式下线对图案和人体模型的示例图像以及一只人手的射线照相图像。描述了成像器设计的一般和具体改进，并讨论了预期的发展。这是对包含这种阵列的成像器在射线照相和荧光透视模式下的操作和特性进行的首次系统研究。
