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首页> 外文期刊>Medical Physics >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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Measurement of the detective quantum efficiency in digital detectors consistent with the IEC 62220-1 standard: practical considerations regarding the choice of filter material.

机译：在符合IEC 62220-1标准的数字探测器中测量探测量子效率：有关选择过滤材料的实际考虑。

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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 < or = 0.2 mm(-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 > or = 0.5 mm(-1), but do result in an asymmetry in the x- and y-NPS at spatial frequencies < or = 0.2 mm(-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.
机译：作为较大评估的一部分，我们尝试使用2003年10月发布的国际电工委员会标准62220-1中描述的方法测量非晶硅平板探测器的检测量子效率（DQE）。为了达到规定的射线照相条件在标准中，我们从著名的特种金属供应商处购买了科学级的超高纯铝（99.999％纯度，-11999型合金）过滤器，其厚度范围从0.1到10.0 mm。在21毫米超高纯铝过滤条件下以71 kV（RQA5光束质量）采集的平场图像的定性评估表明，低频斑点可重现，在21 kV（74 kV）（RQA5光束质量）重复测量时未观察到毫米的低纯度铝（99.0％纯度，1100型合金）过滤。该发现最终归因于高纯度铝金属的较大晶粒尺寸（约1-2 mm），这是众所周知的特性，特别是厚度大于1 mm时。这种低频斑点的影响是大大高估了空间频率<或= 0.2 mm（-1）时的噪声功率谱（NPS），这反过来又会导致对该范围内DQE的低估。从第二来源购买的超高纯铝的后续评估表明，可以通过退火工艺实现减小的晶粒尺寸。用该样品采集的图像显示出垂直条纹的不均匀性，该不均匀性归因于制造方法，在空间频率>或= 0.5 mm（-1）时，似乎不会明显影响NPS，但确实导致x和y-NPS在空间频率<或= 0.2 mm（-1）时。我们对高纯铝过滤所采集图像中明显可见的不均匀性的观察表明，在测量DQE时应仔细评估过滤器材料的均匀性并加以考虑。

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