TBMLab, Dipartimento di Bioingegneria, Politecnico di Milano, Italy.
Acad Radiol. 2011 Oct;18(10):1277-84. doi: 10.1016/j.acra.2011.04.019. Epub 2011 Jul 12.
Emphysema is characterized by lung tissue destruction and trapped gas. On computed tomographic (CT) images, this may be expressed by widespread areas with high specific gas volume (SV(g)). SV(g) is highly sensitive to very low attenuation values, which frequently occur in the CT images of patients with severe emphysema. The purpose of the present work was to study if and how different reconstruction settings and different scanners significantly influence SV(g) distribution, particularly in the very low attenuation range.
Two sets of CT images taken from two different CT scanners at two different lung volumes in 10 healthy volunteers and 18 subjects with severe emphysema were analyzed. Images were reconstructed using two different settings of reconstruction parameters: (1) thin slice thickness and sharp filter and (2) thick slice thickness and smooth filter. For each set of images, average values of SV(g) and their variation (ΔSV(g)) from total lung capacity to residual volume were calculated in the whole lung.
Very low attenuation values are always present in CT images when reconstructed with thin slice thickness and a sharp filter and in very large numbers in patients with severe emphysema. SV(g) values were in general significantly higher in patients with emphysema than in healthy subjects, at both total lung capacity and residual volume (P < .001), and were significantly influenced by the reconstruction filter (P < .001) and CT scanner (P < .001). ΔSV(g) was lower in patients with emphysema than in healthy subjects (P < .001) and was significantly affected by the reconstruction setting but not by the CT scanner.
The disproportionate effect of low-attenuation pixels on SV(g) 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. ΔSV(g) is generally robust for quantifying the functional impairment of the lung in severe emphysema.
肺气肿的特征是肺组织破坏和气体被困。在计算机断层扫描（CT）图像上，这可能表现为具有高比气体体积（SV（g））的广泛区域。SV（g）对非常低的衰减值高度敏感，这些值经常出现在严重肺气肿患者的 CT 图像中。本研究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 SV（g）的分布，特别是在非常低的衰减范围内。
对 10 名健康志愿者和 18 名严重肺气肿患者的两组 CT 图像进行了分析，这些图像分别在两个不同的 CT 扫描仪上在两个不同的肺容积下拍摄。使用两种不同的重建参数设置对图像进行重建：（1）薄切片厚度和锐利滤波器，（2）厚切片厚度和平滑滤波器。对于每组图像，分别计算整个肺从肺总量到残气量的 SV（g）的平均值及其变化（ΔSV（g））。
当使用薄切片厚度和锐利滤波器进行重建时，CT 图像中始终存在非常低的衰减值，在严重肺气肿患者中则存在大量的非常低的衰减值。SV（g）值在肺气肿患者中一般显著高于健康受试者，在肺总量和残气量时均如此（P <.001），并且受重建滤波器（P <.001）和 CT 扫描仪（P <.001）的显著影响。ΔSV（g）在肺气肿患者中低于健康受试者（P <.001），并且受重建设置显著影响，但不受 CT 扫描仪影响。
低衰减像素对 SV（g）的不成比例影响可能导致对肺气肿和被困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，可以显著降低这种高估。ΔSV（g）通常对于量化严重肺气肿中的肺功能障碍是稳健的。
