A pencil beam approach to proton computed tomography.
A pencil beam approach to proton computed tomography.
复制标题
质子计算机断层扫描的笔形束方法。
DOI：
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
D. Brasse
中科院分区：
文献类型：
--
作者：
R. Rescigno;C. Bopp;M. Rousseau;D. Brasse
目的
提出了一种新的质子计算机断层扫描（pCT）方法。在这种方法中，质子不是一个接一个地跟踪，而是考虑粒子束。在这种新方法的基础上重新定义了pCT重建问题的要素（剩余能量和路径）。本文还提出了一种适用于这种情况的解析图像重建算法。
方法
利用推广的Fermi-Eyges理论对笔形束及其在物质中的传播进行了模拟，并考虑了多次库仑散射。该模型被集成到pCT重建问题中，允许定义与单粒子方法中使用的最可能路径（MLP）相似的平均射束路径概念。对模型进行了数值验证。将滤波反投影沿着MLP算法应用于逐波束方法。模拟了一个完美的质子扫描的采集，并将数据用于用单质子和逐束方法重建体模的相对阻止本领的图像。以定性的方式比较所得图像。
结果
将建模PB的参数（平均值和分布）与Monte Carlo结果进行比较，以验证模型。对于水的目标，发现良好的协议的平均值的分布。就扩散而言，深度依赖的差异高达2%-3%，对于异质体模，分布扩散的差异范围为6%-8%。与用经典方法重建的图像相比，用逐束方法重建的图像显示出高水平的噪声。
结论
质子成像的PB方法可以允许克服当前逐个质子方法所施加的技术挑战。在此框架下，提出了一种分析算法。进一步的工作将涉及详细研究这种方法在图像质量方面的性能和局限性。本文展示了如何占MCS在重建步骤与这种新的方法时，使用的分析重建算法。
PURPOSE
A new approach to proton computed tomography (pCT) is presented. In this approach, protons are not tracked one-by-one but a beam of particles is considered instead. The elements of the pCT reconstruction problem (residual energy and path) are redefined on the basis of this new approach. An analytical image reconstruction algorithm applicable to this scenario is also proposed.
METHODS
The pencil beam (PB) and its propagation in matter were modeled by making use of the generalization of the Fermi-Eyges theory to account for multiple Coulomb scattering (MCS). This model was integrated into the pCT reconstruction problem, allowing the definition of the mean beam path concept similar to the most likely path (MLP) used in the single-particle approach. A numerical validation of the model was performed. The algorithm of filtered backprojection along MLPs was adapted to the beam-by-beam approach. The acquisition of a perfect proton scan was simulated and the data were used to reconstruct images of the relative stopping power of the phantom with the single-proton and beam-by-beam approaches. The resulting images were compared in a qualitative way.
RESULTS
The parameters of the modeled PB (mean and spread) were compared to Monte Carlo results in order to validate the model. For a water target, good agreement was found for the mean value of the distributions. As far as the spread is concerned, depth-dependent discrepancies as large as 2%-3% were found. For a heterogeneous phantom, discrepancies in the distribution spread ranged from 6% to 8%. The image reconstructed with the beam-by-beam approach showed a high level of noise compared to the one reconstructed with the classical approach.
CONCLUSIONS
The PB approach to proton imaging may allow technical challenges imposed by the current proton-by-proton method to be overcome. In this framework, an analytical algorithm is proposed. Further work will involve a detailed study of the performances and limitations of this approach in terms of image quality. The paper shows how to account for the MCS in the reconstruction step with this new approach when an analytical reconstruction algorithm is used.
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