Haba Tomonobu, Kondo Shimpei, Hayashi Daiki, Koyama Shuji
Department of Radiological Technology, Graduate School of Medicine, Nagoya University, 1-1-20 Daiko-Minami, Higashi-ku, Nagoya, Japan.
Radiol Phys Technol. 2013 Jul;6(2):423-30. doi: 10.1007/s12194-013-0215-4. Epub 2013 May 7.
Detective quantum efficiency (DQE) is widely used as a comprehensive metric for X-ray image evaluation in digital X-ray units. The incident photon fluence per air kerma (SNR²(in)) is necessary for calculating the DQE. The International Electrotechnical Commission (IEC) reports the SNR²(in) under conditions of standard radiation quality, but this SNR²(in) might not be accurate as calculated from the X-ray spectra emitted by an actual X-ray tube. In this study, we evaluated the error range of the SNR²(in) presented by the IEC62220-1 report. We measured the X-ray spectra emitted by an X-ray tube under conditions of standard radiation quality of RQA5. The spectral photon fluence at each energy bin was multiplied by the photon energy and the mass energy absorption coefficient of air; then the air kerma spectrum was derived. The air kerma spectrum was integrated over the whole photon energy range to yield the total air kerma. The total photon number was then divided by the total air kerma. This value is the SNR²(in). These calculations were performed for various measurement parameters and X-ray units. The percent difference between the calculated value and the standard value of RQA5 was up to 2.9%. The error range was not negligibly small. Therefore, it is better to use the new SNR²(in) of 30694 (1/(mm(2) μGy)) than the current [Formula: see text] of 30174 (1/(mm(2) μGy)).
探测量子效率（DQE）被广泛用作数字X射线设备中X射线图像评估的综合指标。计算DQE需要每空气比释动能的入射光子注量（SNR²(in)）。国际电工委员会（IEC）报告了标准辐射质量条件下的SNR²(in)，但根据实际X射线管发射的X射线光谱计算得出的该SNR²(in)可能不准确。在本研究中，我们评估了IEC62220 - 1报告中给出的SNR²(in)的误差范围。我们在RQA5标准辐射质量条件下测量了X射线管发射的X射线光谱。将每个能量区间的光谱光子注量乘以光子能量和空气的质量能量吸收系数，从而得出空气比释动能谱。对空气比释动能谱在整个光子能量范围内进行积分，得到总空气比释动能。然后将总光子数除以总空气比释动能。该值即为SNR²(in)。针对各种测量参数和X射线设备进行了这些计算。计算值与RQA5标准值之间的百分比差异高达2.9%。误差范围并非小到可以忽略不计。因此，使用新的SNR²(in)值30694（1/(mm² μGy)）比当前的30174（1/(mm² μGy)）更好。
