Filtered back-projection reconstruction for attenuation proton CT along most likely paths
Filtered back-projection reconstruction for attenuation proton CT along most likely paths
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DOI：
10.1088/0031-9155/61/9/3258
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发表时间：
2016-05-07
影响因子：
3.5
通讯作者：
Rit, S.
中科院分区：
文献类型：
--
作者：
Quinones, C. T.;Letang, J. M.;Rit, S.
这项工作研究了质子束的衰减，以重建材料的线性衰减系数图，这主要是由质子与物质的非弹性相互作用引起的。衰减质子计算机层析成像(PCT)与传统的能量损失PCT类似，由于物质中质子的多次库仑散射(MCS)，导致其空间分辨率较低。因此，我们沿着能量损失PCT的质子的最可能路径(MLP)(RIT等人2013)将最近的过滤反投影算法修改为衰减PCT，假设PCT扫描器可以跟踪被扫描物体之前和之后的质子的位置和方向。使用Geant4(Via Gate)对密度和空间分辨率模体的PCT采集进行了蒙特卡罗模拟，以表征新算法。衰减PCT假定为能量无关的非弹性截面，当剩余能量低于100 MeV时，低于100 MeV的非弹性截面的能量依赖性的影响显示出封顶伪影。用解析的方法确定了统计极限，发现在200 MeV和300 MeV剂量下，衰减PCT图像的噪声分别是能量损失PCT图像噪声的411倍和278倍。衰减PCT图像的空间分辨率与传统的直线路径入库的比较表明，在重建过程中结合MLP估计提高了衰减PCT的空间分辨率。此外，不考虑衰减PCT图像中的显著噪声，由于MCS和被称为West-Sherwood效应的衰减的相互作用，在所研究的某些情况下，衰减PCT的空间分辨率要好于传统的能量损失PCT。
This work investigates the attenuation of a proton beam to reconstruct the map of the linear attenuation coefficient of a material which is mainly caused by the inelastic interactions of protons with matter. Attenuation proton computed tomography (pCT) suffers from a poor spatial resolution due to multiple Coulomb scattering (MCS) of protons in matter, similarly to the conventional energy-loss pCT. We therefore adapted a recent filtered back-projection algorithm along the most likely path (MLP) of protons for energy-loss pCT (Rit et al 2013) to attenuation pCT assuming a pCT scanner that can track the position and the direction of protons before and after the scanned object. Monte Carlo simulations of pCT acquisitions of density and spatial resolution phantoms were performed to characterize the new algorithm using Geant4 (via Gate). Attenuation pCT assumes an energy-independent inelastic cross-section, and the impact of the energy dependence of the inelastic crosssection below 100 MeV showed a capping artifact when the residual energy was below 100 MeV behind the object. The statistical limitation has been determined analytically and it was found that the noise in attenuation pCT images is 411 times and 278 times higher than the noise in energy-loss pCT images for the same imaging dose at 200 MeV and 300 MeV, respectively. Comparison of the spatial resolution of attenuation pCT images with a conventional straight-line path binning showed that incorporating the MLP estimates during reconstruction improves the spatial resolution of attenuation pCT. Moreover, regardless of the significant noise in attenuation pCT images, the spatial resolution of attenuation pCT was better than that of conventional energy-loss pCT in some studied situations thanks to the interplay of MCS and attenuation known as the West-Sherwood effect.