Ullman Gustaf, Sandborg Michael, Dance David R, Hunt Roger, Alm Carlsson Gudrun
Department of Radiation Physics, Linköping University, SE-581 85 Linköping, Sweden.
Radiat Prot Dosimetry. 2005;114(1-3):355-8. doi: 10.1093/rpd/nch530.
The aim of this work was to calculate distributions of scatter-to-primary ratios (epsilon(s)/epsilon(p)) and signal-to-noise ratios per pixel (SNRp) in chest images. Such distributions may provide useful information on how physical image quality (contrast, SNR) is distributed over the posterior/anterior (PA) chest image. A Monte Carlo computer program was used for the calculations, including a model of both the patient (voxel phantom) and the imaging system (X-ray tube, anti-scatter grid and image detector). The calculations were performed for three PA thicknesses 20, 24 and 28 cm. For a 24 cm patient, the epsilon(s)/epsilon(p) varies between 0.5 in the lung to 2.5 behind the spine and heart. The corresponding variation of the SNRp is a factor of 3, with the highest values in the lung. Increasing the patient thickness from 20 to 28 cm increases the epsilon(s)/epsilon(p) by a factor of 2.2 behind the spine and heart.
这项工作的目的是计算胸部图像中散射与原发射线比率（ε(s)/ε(p)）以及每像素信噪比（SNRp）的分布情况。这样的分布可能会提供有关物理图像质量（对比度、信噪比）如何在胸部后前位（PA）图像上分布的有用信息。使用了一个蒙特卡洛计算机程序进行计算，该程序包括患者模型（体素模型）和成像系统模型（X射线管、防散射格栅和图像探测器）。针对三种PA厚度20厘米、24厘米和28厘米进行了计算。对于一名厚度为24厘米的患者，ε(s)/ε(p)在肺部为0.5，在脊柱和心脏后方为2.5。SNRp的相应变化为3倍，在肺部的值最高。将患者厚度从20厘米增加到28厘米，会使脊柱和心脏后方的ε(s)/ε(p)增加2.2倍。
