Department of Medical Biophysics, University of Toronto, Ontario, Canada.
Med Phys. 2012 Feb;39(2):801-10. doi: 10.1118/1.3676740.
Power spectral analysis in radiographic images is conventionally performed using a windowed overlapping averaging periodogram. This study describes an alternative approach using a multitaper technique and compares its performance with that of the standard method. This tool will be valuable in power spectrum estimation of images, whose content deviates significantly from uniform white noise. The performance of the multitaper approach will be evaluated in terms of spectral stability, variance reduction, bias, and frequency precision. The ultimate goal is the development of a useful tool for image quality assurance.
A multitaper approach uses successive data windows of increasing order. This mitigates spectral leakage allowing one to calculate a reduced-variance power spectrum. The multitaper approach will be compared with the conventional power spectrum method in several typical situations, including the noise power spectra (NPS) measurements of simulated projection images of a uniform phantom, NPS measurement of real detector images of a uniform phantom for two clinical digital mammography systems, and the estimation of the anatomic noise in mammographic images (simulated images and clinical mammograms).
Examination of spectrum variance versus frequency resolution and bias indicates that the multitaper approach is superior to the conventional single taper methods in the prevention of spectrum leakage and variance reduction. More than four times finer frequency precision can be achieved with equivalent or less variance and bias.
Without any shortening of the image data length, the bias is smaller and the frequency resolution is higher with the multitaper method, and the need to compromise in the choice of regions of interest size to balance between the reduction of variance and the loss of frequency resolution is largely eliminated.
在射线影像中，功率谱分析通常使用带窗的重叠平均周期图法进行。本研究描述了一种使用多谱线技术的替代方法，并将其性能与标准方法进行了比较。这种工具将在功率谱估计图像中非常有用，这些图像的内容与均匀白噪声有很大的差异。将从谱稳定性、方差减少、偏差和频率精度等方面评估多谱线方法的性能。最终目标是开发一种用于图像质量保证的有用工具。
多谱线方法使用递增阶数的数据窗口。这减轻了谱泄漏，允许计算具有较小方差的功率谱。将在几种典型情况下将多谱线方法与传统功率谱方法进行比较，包括均匀体模模拟投影图像的噪声功率谱（NPS）测量、两种临床数字乳腺摄影系统的均匀体模实际探测器图像的 NPS 测量，以及对乳腺图像（模拟图像和临床乳腺 X 线照片）中解剖噪声的估计。
对谱方差与频率分辨率和偏差的研究表明，与传统的单谱线方法相比，多谱线方法在防止谱泄漏和减少方差方面具有优越性。在具有等效或更小方差和偏差的情况下，可以实现超过四倍的更精细的频率精度。
在不缩短图像数据长度的情况下，多谱线方法的偏差较小，频率分辨率较高，并且在选择感兴趣区域大小以平衡方差减少和频率分辨率损失之间的关系时，需要进行妥协的情况大大减少。
