Measurement of the detective quantum efficiency in digital detectors consistent with the IEC 62220-1 standard: Practical considerations regarding the choice of filter material.
Measurement of the detective quantum efficiency in digital detectors consistent with the IEC 62220-1 standard: Practical considerations regarding the choice of filter material.
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符合 IEC 62220-1 标准的数字探测器中探测量子效率的测量：有关过滤材料选择的实际考虑因素。
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
C. Ravin
中科院分区：
文献类型：
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作者：
N. Ranger;E. Samei;J. Dobbins;C. Ravin
作为一个更大的评估的一部分，我们试图测量的检测量子效率（DQE）的非晶硅平板探测器使用的方法中描述的国际电工委员会标准62220-1发表于2003年10月。为了达到标准中规定的射线照相光束条件，我们从一家知名的特种金属供应商处购买了厚度范围从0.1 mm到10.0 mm的科学级高纯铝（纯度99.999%，11999型合金）过滤器。在71 kV（RQA 5射束质量）下用21 mm高纯度铝过滤器获得的平场图像的定性评价表明，低频斑点是可再现的，并且当在74 kV（RQA 5射束质量）下用21 mm低纯度铝（99.0%纯度，1100型合金）过滤器重复测量时没有观察到。这一发现最终归因于高纯度铝金属的较大晶粒尺寸（约1-2 mm），这是一个众所周知的特性，特别是在厚度大于1 mm时。这种低频斑点的影响是显著高估了空间频率<0.2 mm-1处的噪声功率谱（SNR），这反过来又会导致低估该范围内的DQE。随后对从第二来源购买的高纯铝的评估表明，可以通过退火工艺实现晶粒尺寸的减小。使用该样品采集的图像显示了垂直条纹不均匀性，其归因于制造方法，并且似乎不会明显影响空间频率为0.5mm-1时的X射线衍射，但会导致空间频率为0.2mm-1时的x射线衍射和y射线衍射不对称。我们观察到的显着可见的不均匀性与高纯度铝过滤获得的图像表明，过滤材料的均匀性应仔细评估，并考虑到测量时的DQE。
As part of a larger evaluation we attempted to measure the detective quantum efficiency (DQE) of an amorphous silicon flat-panel detector using the method described in the International Electrotechnical Commission standard 62220-1 published in October 2003. To achieve the radiographic beam conditions specified in the standard, we purchased scientific-grade ultrahigh purity aluminum (99.999% purity, type-11999 alloy) filters in thicknesses ranging from 0.1 through 10.0 mm from a well-known, specialty metals supplier. Qualitative evaluation of flat field images acquired at 71 kV (RQA5 beam quality) with 21 mm of ultrahigh purity aluminum filtration demonstrated a low frequency mottle that was reproducible and was not observed when the measurement was repeated at 74 kV (RQA5 beam quality) with 21 mm of lower-purity aluminum (99.0% purity, type-1100 alloy) filtration. This finding was ultimately attributed to the larger grain size (approximately 1-2 mm) of high purity aluminum metal, which is a well-known characteristic, particularly in thicknesses greater than 1 mm. The impact of this low frequency mottle is to significantly overestimate the noise power spectrum (NPS) at spatial frequencies ⩽0.2mm-1, which in turn would cause an underestimation of the DQE in this range. A subsequent evaluation of ultrahigh purity aluminum, purchased from a second source, suggests, that reduced grain size can be achieved by the process of annealing. Images acquired with this sample demonstrated vertical striated nonuniformities that are attributed to the manufacturing method and which do not appear to appreciably impact the NPS at spatial frequencies ⩾0.5mm-1, but do result in an asymmetry in the x- and y-NPS at spatial frequencies ⩽0.2mm-1. Our observations of markedly visible nonuniformities in images acquired with high purity aluminum filtration suggest that the uniformity of filter materials should be carefully evaluated and taken into consideration when measuring the DQE.