X-ray quantum limited portal imaging using amorphous silicon flat-panel arrays
X-ray quantum limited portal imaging using amorphous silicon flat-panel arrays
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DOI：
10.1118/1.598252
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发表时间：
1998-05-01
期刊：
影响因子：
3.8
通讯作者：
Bouius, DC
中科院分区：
文献类型：
--
作者：
Munro, P;Bouius, DC
我们测量了基于非晶硅平板阵列的电子射野成像设备（EPID）的线性度、空间分辨率（MTF）、噪声（SNR）和信噪比（DQE）。该阵列具有128 x128像素矩阵，每个像素的尺寸为0.75x0.75 mm（2），因此阵列覆盖96 x96 mm（2）的区域。该阵列就像一个大面积的光传感器，并记录在金属板/荧光屏X射线检测器中产生的光信号时，检测器被兆伏级X射线束照射。此外，总信号的大约0.5%是由非光学过程产生的。噪声测量结果表明，该设备是量子噪声限制与噪声功率产生的x射线量子是高达100倍以上的外部读出电子和平板光传感器本身添加的噪声。然而，平板光传感器确实降低了空间分辨率（与具有无限小像素尺寸的完美光学传感器相比），因为其中等像素尺寸，并且因为光学扩散可能发生在用于将荧光屏附接到平板光传感器的透明胶中。该传感器的响应是非常线性的，不遭受与基于电视摄像机的EPID相关的眩光现象，这表明非晶硅EPID将非常适合于运输剂量测定的特性。然而，在这些设备可以用于临床之前，需要克服一些限制。这些包括开发更大的帽面板光传感器，消除具有高暗信号的“噪声”像素，以及提高传感器的均匀灵敏度。最后一项要求仅适用于运输剂量测定应用，在这些应用中，它将大大简化设备的校准。此外，必须开发图像采集方案以消除由线性加速器产生的脉冲X射线束产生的伪影。尽管有这些局限性，我们的研究表明，非晶硅EPID非常适合于射野成像。(C)1998年美国医学物理学家协会。
We have measured the linearity, spatial resolution (MTF), noise (NPS), and Signal-to-noise characteristics (DQE) of an electronic portal imaging device (EPID) based on an amorphous silicon fiat-panel array. The array has a 128x128-pixel matrix and each pixel is 0.75x0.75 mm(2) in dimension so the array covers an area of 96x96 mm(2). The array acts like a large area light sensor and records the optical signals generated in a metal plate/phosphor screen x-ray detector when the detector is irradiated by a megavoltage x-ray beam. In addition, approximately 0.5% of the total signal is generated by nonoptical processes. The noise measurements show that the device is quantum noise limited with the noise power generated by the x-ray quanta being up to 100 times greater than the noise added by the external readout electronics and flat-panel light sensor itself. However, the flat-panel light sensor does reduce the spatial resolution (compared to a perfect optical sensor with infinitesimal pixel size) because of its moderate pixel size and because optical spread can occur in the transparent glues used to attach the phosphor screen to the flat-panel light sensor. The response of the sensor is very linear and does not suffer from the glare phenomenon associated with TV camera-based EPIDs-characteristics which suggest that the amorphous silicon EPID will be well suited to transit dosimetry. Nevertheless, some limitations need to be overcome before these devices can be used clinically. These include developing larger hat-panel light sensors, the elimination of "noisy" pixels with high dark signal, and improvements in the uniform sensitivity of the sensors. This last requirement is only needed for transit dosimetry applications where it would greatly simplify calibration of the device. In addition, an image acquisition scheme must be developed to eliminate artifacts created by the pulsed x-ray beam generated by linear accelerators. Despite these limitations, our studies suggest that the amorphous silicon EPIDs are very well suited to portal imaging. (C) 1998 American Association of Physicists in Medicine.