Standardizing CT lung density measure across scanner manufacturers.
Standardizing CT lung density measure across scanner manufacturers.
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DOI：
10.1002/mp.12087
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发表时间：
2017-03
期刊：
影响因子：
3.8
通讯作者：
Fain SB
中科院分区：
文献类型：
--
作者：
Chen-Mayer HH;Fuld MK;Hoppel B;Judy PF;Sieren JP;Guo J;Lynch DA;Possolo A;Fain SB
以Hounsfield单位（HU）报告的肺部计算机断层扫描（CT）成像可以参数化为定量图像生物标志物，用于诊断和监测肺气肿（一种慢性阻塞性肺病（COPD））引起的肺密度变化。CT肺密度度量是基于肺CT数直方图的全局测量，并且通常是指定CT数低于阈值的体素的百分比或单个CT数的量，在该单个CT数之下，固定的相对肺体积、第n个百分位数福尔斯下降。为了减少CT衰减规定的密度指标的变异性，定量成像生物标志物联盟（QIBA）肺密度委员会组织了各种扫描仪模型中的体模研究，以建立基线，用于评估患者研究中归因于扫描仪校准和测量不确定性的变异性。数据来自四家制造商的CT扫描仪的体模研究，在不同的管电位电压（kVp）和曝光设置的几个协议。这些体模研究不存在生物学变异，仅由于机器校准和参考材料的不确定性，因此可评估平台间密度指标的准确度和精密度。本研究中使用的体模在肺密度区域有三个泡沫密度参考，在根据一套具有认证物理密度的标准参考材料（SRM）泡沫进行校准后，为每个机器协议建立了HU-电子密度关系。我们设计了一个5步校准程序结合一个简化的物理模型，使整个22个扫描仪协议设置报告的CT数的标准化到一个单一的能量（选择在80 keV）。在标准化前后，计算每种密度的总CT数的标准差，以及扫描仪和其他变量的标准差，作为变异性的度量。此外，使用线性混合效应模型评估扫描仪之间的异质性，并评估标准化前后平均CT数的95%置信区间。我们表明，在将标准化程序应用于体模数据后，参考泡沫的CT密度测量的仪器再现性提高了65%以上，如通过总体平均CT数的标准偏差所测量的。使用未参与校准的肺泡沫作为测试用例，混合效应模型分析显示，标准化前的95%置信区间为[-862.0 HU，-851.3 HU]，标准化至80 keV后为[-859.0 HU，-853.7 HU]。这与80 keV下-855.9 HU的预期CT数值基本一致，95% CI为[-857.4 HU，-854.5 HU]，基于SRM认证密度的校准和不确定性。本研究提供了CT肺密度测量中归因于非生物来源（如扫描仪校准和扫描仪X射线光谱和过滤）的预期变化的定量评估。通过从测量的CT数中去除扫描仪协议依赖性，可以实现定量CT测量的更高准确性和再现性。本研究所开发的标准化程序可用于CT肺密度临床数据。
Computed Tomography (CT) imaging of the lung, reported in Hounsfield Units (HU), can be parameterized as a quantitative image biomarker for the diagnosis and monitoring of lung density changes due to emphysema, a type of chronic obstructive pulmonary disease (COPD). CT lung density metrics are global measurements based on lung CT number histograms, and are typically a quantity specifying either the percentage of voxels with CT numbers below a threshold, or a single CT number below which a fixed relative lung volume, nth percentile, falls. To reduce variability in the density metrics specified by CT attenuation, the Quantitative Imaging Biomarkers Alliance (QIBA) Lung Density Committee has organized efforts to conduct phantom studies in a variety of scanner models to establish a baseline for assessing the variations in patient studies that can be attributed to scanner calibration and measurement uncertainty. Data were obtained from a phantom study on CT scanners from four manufacturers with several protocols at various tube potential voltage (kVp) and exposure settings. Free from biological variation, these phantom studies provide an assessment of the accuracy and precision of the density metrics across platforms solely due to machine calibration and uncertainty of the reference materials. The phantom used in this study has three foam density references in the lung density region, which, after calibration against a suite of Standard Reference Materials (SRM) foams with certified physical density, establishes a HU-electron density relationship for each machine-protocol. We devised a 5-step calibration procedure combined with a simplified physical model that enabled the standardization of the CT numbers reported across a total of 22 scanner-protocol settings to a single energy (chosen at 80 keV). A standard deviation was calculated for overall CT numbers for each density, as well as by scanner and other variables, as a measure of the variability, before and after the standardization. In addition, a linear mixed-effects model was used to assess the heterogeneity across scanners, and the 95% confidence interval of the mean CT number was evaluated before and after the standardization. We show that after applying the standardization procedures to the phantom data, the instrumental reproducibility of the CT density measurement of the reference foams improved by more than 65%, as measured by the standard deviation of the overall mean CT number. Using the lung foam that did not participate in the calibration as a test case, a mixed effects model analysis shows that the 95% confidence intervals are [–862.0 HU, –851.3 HU] before standardization, and [−859.0 HU, –853.7 HU] after standardization to 80 keV. This is in general agreement with the expected CT number value at 80 keV of –855.9 HU with 95% CI of [–857.4 HU, –854.5 HU] based on the calibration and the uncertainty in the SRM certified density. This study provides a quantitative assessment of the variations expected in CT lung density measures attributed to non-biological sources such as scanner calibration and scanner x-ray spectrum and filtration. By removing scanner-protocol dependence from the measured CT numbers, higher accuracy and reproducibility of quantitative CT measures were attainable. The standardization procedures developed in study may be explored for possible application in CT lung density clinical data.
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10.15326/jcopdf.1.1.2014.0111
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2014-05-01
影响因子：
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