Kemerink G J, Lamers R J, Thelissen G R, van Engelshoven J M
Department of Diagnostic Radiology, University Hospital Maastricht, The Netherlands.
Med Phys. 1995 Sep;22(9):1445-50. doi: 10.1118/1.597568.
A quantitative study was performed to assess the magnitude of the nonlinear partial volume effect (NLPVE) in computed tomography (CT) densitometry of polyethene foam and lung. This effect arises in materials having density variations on the scale of the sampling area of an individual CT-detector element. It causes a systematic underestimation of the density determined with CT. Foam samples and a resected lung of a goat were imaged with high resolution (20 lp/mm) using a mammography system, and the observed optical density variation in the images was converted into a distribution of pathlengths that x rays penetrate within the solid component of the cellular material. The obtained pathlength distribution was used to calculate the transmission, as seen by a single detector in computed tomography. Comparison with the transmission through homogeneous material of the same thickness gave an estimate of the NLPVE. For the foams studied, the CT-determined density was found to be too low by approximately 0.3%-0.5% due to this effect. Although these density errors are small, in calibrations of a CT scanner they may be of significance. For lung the underestimation of the density was less than 0.1%. These experimentally derived, NLPVE related CT-density errors are 32%-84% of those calculated from a simple model of a cellular solid.
进行了一项定量研究，以评估聚乙烯泡沫和肺部计算机断层扫描（CT）密度测定中非线性部分容积效应（NLPVE）的大小。这种效应出现在密度在单个CT探测器元件采样区域尺度上存在变化的材料中。它会导致CT测定的密度出现系统性低估。使用乳腺摄影系统对泡沫样本和山羊的切除肺进行高分辨率（20 lp/mm）成像，并将图像中观察到的光密度变化转换为X射线在细胞材料固体成分内穿透的路径长度分布。获得的路径长度分布用于计算CT中单个探测器所见的透射率。与通过相同厚度均匀材料的透射率进行比较，可估算NLPVE。对于所研究的泡沫，由于这种效应，发现CT测定的密度大约低了0.3% - 0.5%。尽管这些密度误差很小，但在CT扫描仪的校准中可能具有重要意义。对于肺部，密度的低估小于0.1%。这些通过实验得出的、与NLPVE相关的CT密度误差是根据细胞固体简单模型计算出的误差的32% - 84%。
