Ohkubo Masaki, Wada Shinichi, Kanai Satoshi, Ishikawa Kazuhiro, Marasinghe Janaka C, Matsumoto Toru
Graduate School of Health Sciences, Niigata University, 2-746 Asahimachi-dohri, Chuo-ku, Niigata 951-8518, Japan.
Radiol Phys Technol. 2013 Jul;6(2):492-9. doi: 10.1007/s12194-013-0225-2. Epub 2013 Jun 9.
For the wide dissemination of lung cancer screening by low-dose computed tomography (CT), it is important to determine the optimal conditions for scan and image reconstruction based on objective standards of evaluation. Our aim in this study was to propose a quantitative index of nodule detectability without an observer test. It was essential to determine the apparent size and density of nodules visible on CT images for developing the nodule-detectability index based on a statistical observer-independent method. Therefore, we introduced a computer simulation technique for CT images based on the spatial resolution of the system to evaluate the size and density accurately. By use of scan/reconstruction parameter settings as employed for low-dose CT screening, a detectability index was obtained for target nodules (ideal spheres) of various sizes and with varying contrast (ΔCT) between nodule density and background density. The index was compared with the qualitative results of observer tests of nodule detectability. As the target nodule diameter or ΔCT was increased, the index value increased, implying improved nodule visibility. According to the index, the detection limits for nodules with ΔCTs of 70, 100, or 150 Hounsfield units were approximately 6, 5, and 4 mm in diameter, respectively. Index values were well correlated with nodule detectability as assessed by four observers. The proposed index was effective for quantifying nodule detectability, and its validity was confirmed by an observer test. This index has potential use in the determination of optimal scan/reconstruction parameters for lung cancer screening by low-dose CT without observer test.
为了通过低剂量计算机断层扫描（CT）广泛开展肺癌筛查，依据客观评估标准确定扫描和图像重建的最佳条件至关重要。本研究的目的是提出一种无需观察者测试的结节可检测性定量指标。基于一种与观察者无关的统计方法开发结节可检测性指标时，确定CT图像上可见结节的表观大小和密度至关重要。因此，我们引入了一种基于系统空间分辨率的CT图像计算机模拟技术，以准确评估大小和密度。利用低剂量CT筛查所采用的扫描/重建参数设置，获得了各种大小且结节密度与背景密度之间对比度（ΔCT）不同的目标结节（理想球体）的可检测性指标。将该指标与结节可检测性观察者测试的定性结果进行了比较。随着目标结节直径或ΔCT的增加，指标值升高，这意味着结节可见性提高。根据该指标，对于ΔCT分别为70、100或150亨氏单位的结节，检测限直径分别约为6、5和4毫米。指标值与四名观察者评估的结节可检测性密切相关。所提出的指标对于量化结节可检测性有效，并且其有效性通过观察者测试得到了证实。该指标在无需观察者测试的情况下确定低剂量CT肺癌筛查的最佳扫描/重建参数方面具有潜在用途。
