Graduate School of Health Sciences, Niigata University, 2-746 Asahimachi-Dori, Chuo-Ku, Niigata, 951-8518, Japan.
Department of Clinical Support, Niigata University Medical and Dental Hospital, 1-754 Asahimachi-Dori, Chuo-Ku, Niigata, 951-8520, Japan.
Radiol Phys Technol. 2023 Dec;16(4):471-477. doi: 10.1007/s12194-023-00733-2. Epub 2023 Jul 29.
This study aimed to evaluate the impact of region of interest (ROI) size on noise-power spectrum (NPS) measurement in computed tomography (CT) images and to propose a novel method for measuring NPS independent of ROI size. The NPS was measured using the conventional method with an ROI of size P × P pixels in a uniform region in the CT image; the NPS is referred to as NPS. NPSs were obtained and compared to assess their dependency on ROI size. In the proposed method, the true NPS was numerically modeled as an NPS, with adjustable parameters, and a noise image with the property of the NPS was generated. From the generated noise image, the NPS was measured using the conventional method with a P × P pixel ROI size; the obtained NPS was referred to as NPS'. The adjustable parameters of the NPS were optimized such that NPS' was most similar to NPS. When NPS' was almost equivalent to NPS, the NPS was considered the true NPS. NPSs obtained using the conventional method were dependent on the ROI size. Conversely, the NPSs (optimized NPSs) measured using the proposed method were not dependent on the ROI size, even when a much smaller ROI (P = 16 or 8) was used. The proposed method for NPS measurement was confirmed to be precise, independent of the ROI size, and useful for measuring local NPSs using a small ROI.
本研究旨在评估在 CT 图像中感兴趣区域（ROI）大小对噪声功率谱（NPS）测量的影响，并提出一种新的方法来测量与 ROI 大小无关的 NPS。使用常规方法，在 CT 图像的均匀区域中使用大小为 P×P 像素的 ROI 测量 NPS；该 NPS 称为 NPS。获得 NPS 并进行比较，以评估其对 ROI 大小的依赖性。在提出的方法中，将真实 NPS 数值建模为具有可调参数的 NPS，并生成具有 NPS 属性的噪声图像。从生成的噪声图像中，使用常规方法以 P×P 像素 ROI 大小测量 NPS；获得的 NPS 称为 NPS'。优化 NPS 的可调参数，以使 NPS'与 NPS 最相似。当 NPS'几乎等于 NPS 时，认为 NPS 是真实 NPS。使用常规方法获得的 NPS 取决于 ROI 大小。相反，使用所提出的方法测量的 NPS（优化的 NPS）与 ROI 大小无关，即使使用更小的 ROI（P=16 或 8）也是如此。所提出的 NPS 测量方法被证实是精确的，与 ROI 大小无关，并且对于使用小 ROI 测量局部 NPS 很有用。
