Influence of CT reconstruction settings on extremely low attenuation values for specific gas volume calculation in severe emphysema.
Influence of CT reconstruction settings on extremely low attenuation values for specific gas volume calculation in severe emphysema.
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DOI：
10.1016/j.acra.2011.04.019
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发表时间：
2011-10
影响因子：
4.8
通讯作者：
Aliverti, Andrea
中科院分区：
文献类型：
--
作者：
Salito, Caterina;Woods, Jason C.;Aliverti, Andrea
肺气肿的特征是肺组织破坏和滞留气体。在CT图像上，这可以通过具有高比气体体积（SVg）的广泛区域来表示。SVg对严重肺气肿患者CT图像中经常出现的非常低的衰减值高度敏感。本工作的目的是研究不同的重建设置和不同的扫描仪是否以及如何显著影响SVg分布，特别是在非常低的衰减范围内。对10名健康志愿者和18名严重肺气肿受试者在两种不同的肺体积下从两种不同的CT扫描仪拍摄的两组CT图像进行了分析。使用两种不同的重建参数设置重建图像：薄层厚度/锐化滤波器和厚层厚度/平滑滤波器。对于每组图像的SVg平均值，计算其在整个肺中从TLC到RV的变化（ΔSVg）。当使用重建设置薄层/锐化重建滤波器时，CT图像中总是存在非常低的衰减值，并且在重度肺气肿受试者中存在非常大的数量。在TLC和RV下，肺气肿受试者的SVg值通常显著高于健康受试者（P<0.001），并且受重建滤波器（P<0.001）和CT扫描仪（P<0.001）的显著影响。肺气肿患者的ΔSVg低于健康受试者（P<0.001），并且受重建设置的影响显著，但不受CT扫描仪的影响。低衰减像素对SVg的不成比例的影响可能会导致对肺气肿和滞留气体严重程度的高估。然而，通过使用厚切片和平滑滤波器进行图像重建，可以显著减少这种情况。ΔSVg通常可用于定量重度肺气肿患者的肺功能损害。
Emphysema is characterized by lung tissue destruction and trapped gas. On CT images this may be expressed by widespread areas with high specific gas volume (SVg). SVg is highly sensitive to very low attenuation values which frequently occur in CT images of patients with severe emphysema. The purpose of the present work is to study if and how different reconstruction settings and different scanners significantly influence SVg distribution particularly in the very low attenuation range. Two sets of CT images taken from two different CT scanners at two different lung volumes on ten healthy volunteers and on eighteen subjects with severe emphysema were analyzed. Images were reconstructed using two different settings of reconstruction parameters: thin slice thickness/sharp filter and thick slice thickness /smooth filter. For each set of images average values of SVg, their variations (ΔSVg) from TLC to RV were calculated in the whole lung. Very low attenuation values are always present in CT images when the reconstruction setting thin slice/sharp reconstruction filter is used and in very large numbers in subjects with severe emphysema. SVg values were in general significantly higher in emphysematous subjects than in healthy subjects, both at TLC and RV (P<0.001), and were significantly influenced by the reconstruction filter (P<0.001) and CT scanner (P<0.001). ΔSVg was lower in emphysematous than in healthy (P<0.001) subjects and was significantly affected by the reconstruction setting but not by the CT scanner. The disproportionate effect of low-attenuation pixels on SVg likely causes overestimation of the severity of emphysema and trapped gas. This can be significantly reduced, however, by using thick slices and a smooth filter for image reconstruction. ΔSVg is generally robust for quantifying the functional impairment of the lung in severe emphysema.
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