Department of Imaging and Pathology, Division of Nuclear Medicine and Molecular Imaging, KU Leuven, B-3000 Leuven, Belgium.
Phys Med Biol. 2020 Jul 8;65(13):135010. doi: 10.1088/1361-6560/ab8953.
In computed tomography (CT)-imaging an optimal compromise between the radiation burden and the image quality for the imaging task is needed. Lower-dose CT is desirable, however, lowering the dose results in a lower signal-to-noise ratio and therefore in a reduced image quality. In this research, we aim to develop a tool to simulate lower-dose scans from an existing standard-dose scan. The main application of this tool is to determine the lowest possible radiation dose that still produces sufficient clinical information. The x-ray tube current reduction is modeled by estimating the noise equivalent number of photons in the high exposure scan and applying a thinning technique to reduce that number. The proposed method accounts for the bowtie filter, for the electronic system noise, for the noise correlation between neighboring detector elements, for the beam hardening effect, and for the non-linear smoothing filter in very low-dose scans. Several phantom studies with different acquisition protocols were performed to evaluate the accuracy of the proposed framework. The results demonstrate a close agreement between the noise magnitude and texture of the measured and the simulated lower-dose scans. For instance, the standard deviation of noise in the simulation of lower-dose scans with 90% tube current reduction matches the reconstructions from the real scans with less than 1% and 3% error for sequential and helical scans, respectively. The noise texture was also assessed by analyzing the noise power spectrum of the simulated lower-dose images which matches those from the real scans. Furthermore, the relation between the measured and predicted noise in projection domain is very close to the line of identity which confirms the accuracy of the model.
在计算机断层扫描（CT）成像中，需要在辐射负担和成像任务的图像质量之间找到一个最佳的折衷方案。较低剂量的 CT 是理想的，但是降低剂量会导致信噪比降低，从而降低图像质量。在这项研究中，我们旨在开发一种工具，从现有的标准剂量扫描中模拟低剂量扫描。该工具的主要应用是确定能够提供足够临床信息的最低辐射剂量。通过估计高曝光扫描中的噪声等效光子数，并应用细化技术来减少该数量，从而对 X 射线管电流进行建模。所提出的方法考虑了蝶形滤波器、电子系统噪声、相邻探测器元件之间的噪声相关性、束硬化效应以及非常低剂量扫描中的非线性平滑滤波器。进行了多项具有不同采集协议的体模研究，以评估所提出框架的准确性。结果表明，所测量和模拟的低剂量扫描的噪声幅度和纹理之间存在紧密的一致性。例如，对于管电流降低 90%的低剂量扫描的模拟，噪声的标准偏差与真实扫描的重建结果非常吻合，对于顺序扫描和螺旋扫描，误差分别小于 1%和 3%。通过分析模拟低剂量图像的噪声功率谱，还评估了噪声纹理，与真实扫描的噪声功率谱相匹配。此外，测量和预测的投影域中的噪声之间的关系非常接近身份线，这证实了模型的准确性。
