A ghost story: Spatio-temporal response characteristics of an indirect-detection flat-panel imager
A ghost story: Spatio-temporal response characteristics of an indirect-detection flat-panel imager
复制标题
DOI：
10.1118/1.598657
复制
发表时间：
1999-08-01
期刊：
影响因子：
3.8
通讯作者：
Jaffray, DA
中科院分区：
文献类型：
--
作者：
Siewerdsen, JH;Jaffray, DA
研究了非晶硅平板成像器（FPI）的空间和时间成像特性，这些成像特性与此类器械在锥形束计算机断层扫描（CBCT）和其他X射线成像模式（包括普通X线摄影、荧光透视、断层摄影、放射治疗射野成像和无损检测）中的应用相关。具体而言，图像滞后（包括幅度，空间均匀性，时间-频率特性，以及对曝光和帧时间的依赖性）和长期图像持久性（“重影”）的问题进行了研究。作为FPI的基本表征的一部分，还测量了像素暗信号和噪声（幅度、时间稳定性和空间均匀性）以及辐射响应（信号大小、线性度、增益和互易性）。图像滞后作为帧时间和入射曝光的函数进行了分析。第一帧滞后（即，在曝光读出后的第一帧中的相对残留信号）类似于2- 10%，这取决于入射曝光，并且在FPI上在空间上不均匀到轻微的程度;第二、第三和第四帧滞后分别类似于0.7%、0.4%和0.3%（在25%传感器饱和度下）。图像滞后也进行了分析，从辐射响应的时间频率相关的传递函数，允许系统组件的定量描述有助于滞后。最后，测量了物体在曝光后随时间变化的对比度，以检查长期图像持久性（“重影”）。幽灵被发现持续长达30分钟或更长时间，这取决于曝光和帧时间。测试了两种降低重影图像的明显对比度的方法：（i）以最大帧速率快速扫描EPI，以及（ii）FPI的泛场曝光;两者都不完全令人满意。这些结果为FPI在CBCT以及其他X射线成像模式中的应用提出了重要的考虑因素。例如，在CBCT中，图像滞后的幅度使得如果不采用策略来减小或校正连续投影之间的滞后（例如，分别在投影之间快速扫描或迭代校正算法）。类似地，长期的图像持久性可能需要频繁地重新校准偏移校正。(C)1999年美国医学物理学家协会。[S0094-2405（99）00608-2]。
Spatial and temporal imaging characteristics of an amorphous silicon flat-panel imager (FPI) were investigated in terms relevant to the application of such devices in cone-beam computed tomography (CBCT) and other x-ray imaging modalities, including general radiography, fluoroscopy, tomogramography, radiotherapy portal imaging, and nondestructive testing. Specifically, issues of image lag (including the magnitude, spatial uniformity, temporal-frequency characteristics, and dependence upon exposure and frame time) and long-term image persistence (''ghosts'') were investigated. As part of the basic characterization of the FPI, pixel dark signal and noise (magnitude, temporal stability, and spatial uniformity) as well as radiation response (signal size, linearity, gain, and reciprocity) were also measured. Image lag was analyzed as a function of frame time and incident exposure. First-frame lag (i.e., the relative residual signal in the first frame following readout of an exposure) was similar to 2-10%, depending upon incident exposure and was spatially nonuniform to a slight degree across the FPI; second-, third-, and fourth-frame lag were similar to 0.7%, 0.4%, and 0.3%, respectively (at 25% sensor saturation). Image lag was also analyzed in terms of the temporal-frequency-dependent transfer function derived from the radiation response, allowing a quantitative description of system components contributing to lag. Finally, the contrast of objects as a function of time following an exposure was measured in order to examine long-term image persistence (''ghosts''). Ghosts were found to persist up to 30 min or longer, depending upon the exposure and frame time. Two means of reducing the apparent contrast of ghost images were tested: (i) rapid scanning of the EPI at maximum frame rate, and (ii) flood-field exposure of the FPI; neither was entirely satisfactory. These results pose important considerations for application of FPIs in CBCT as well as other x-ray imaging modalities. For example in CBCT, the magnitude of image lag is such that significant artifacts in tomographic reconstructions may result if strategies are not adopted either to reduce or correct the lag between successive projections (e.g., rapid scanning between projections or iterative correction algorithms, respectively). Similarly, long-term image persistence may necessitate frequent recalibration of offset corrections. (C) 1999 American Association of Physicists in Medicine. [S0094-2405 (99)00608-2].