Jiang Hangyi, Chen Wei R, Liu Hong
Center for Bioengineering and School of Electrical Engineering, University of Oklahoma, Norman, OK 73019, USA.
IEEE Trans Biomed Eng. 2002 Nov;49(11):1270-8. doi: 10.1109/TBME.2002.804595.
Several techniques to increase the accuracy and to reduce the variance of the noise power spectrum (NPS) measurement for digital X-ray imaging systems are investigated. These techniques include: 1) averaging the outputs from subblocks of the entire image; 2) averaging the two-dimensional NPS data along a circular route centered on the origin of spectral domain; and 3) masking a window function on each subblock before Fourier transforms. Techniques 1) and 2) are used mainly to reduce the variance of the NPS measurement. Technique 3) serves to improve the accuracy of the final result. Experiments with two different charge-coupled device-based X-ray imaging systems demonstrated that the precision and accuracy of the NPS measurement could be significantly improved using these techniques. The impact of the image partition for averaging is discussed and the corresponding NPS estimations are presented for the number of subblocks ranging from 4 to 64. The effect of masking on the NPS is also studied using four different window functions.
研究了几种提高数字X射线成像系统噪声功率谱（NPS）测量精度和降低其方差的技术。这些技术包括：1）对整个图像子块的输出进行平均；2）沿以频谱域原点为中心的圆形路径对二维NPS数据进行平均；3）在傅里叶变换之前对每个子块应用窗函数进行掩蔽。技术1）和2）主要用于降低NPS测量的方差。技术3）用于提高最终结果的精度。使用两种不同的基于电荷耦合器件的X射线成像系统进行的实验表明，使用这些技术可以显著提高NPS测量的精度和准确性。讨论了用于平均的图像划分的影响，并给出了子块数量从4到64时相应的NPS估计。还使用四种不同的窗函数研究了掩蔽对NPS的影响。
