A maximum likelihood method for high resolution proton radiography/proton CT
A maximum likelihood method for high resolution proton radiography/proton CT
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DOI：
10.1088/0031-9155/61/23/8232
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发表时间：
2016-11-03
影响因子：
3.5
通讯作者：
Seco, Joao
中科院分区：
文献类型：
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作者：
Collins-Fekete, Charles-Antoine;Brousmiche, Sebastien;Seco, Joao
多重库仑散射(MCS)是造成质子成像模糊的最大因素。在这项工作中，我们开发了一种最大似然最小二乘估计器来提高质子照相的空间分辨率。通过从源到探测器像素的投影估算了水当量厚度(湿)，以使穿过体积的每个质子的能量损失的可能性最大化。通过优化的三次样条线路径估计来计算每个投影所花费的长度。质子射线照相是使用Geant4模拟产生的。这里研究了三个体模：测量2D空间分辨率的水箱中的倾斜立方体，用于临床性能评估的体素化头部体模以及用于3D空间分辨率的参数Catphan体模(CTP528)。使用了两种质子束配置：平行和圆锥束。模拟了200 MeV和330 MeV的质子束，以获得射线照相。在200 MeV束流中，空间分辨率从2.44 LP cm(-1)提高到4.53 LP cm(-1)；在330 MeV束流中，空间分辨率从3.49 LP cm(-1)提高到5.76 LP cm(-1)。在平行束(3.49lp cm(-1)至5.76lp cm(-1))和圆锥束(3.49lp cm(-1)至5.56lp cm(-1))所采集的X线片之间，光束配置不影响重建的空间分辨率。然后，将改进后的图像用作光子断层成像算法的输入。Catphan体模的质子CT重建显示出高的空间分辨率(平行束的空间分辨率为2.79~5.55lp cm(-1)，圆锥束的空间分辨率为3.03~5.15lp cm(-1))，头部体模的重建虽然定性，但在梯度区显示高对比度。提出的优化公式显示出极大的潜力来提高质子射线成像的空间分辨率(提高65%)，并极大地加速质子CT重建。
Multiple Coulomb scattering (MCS) is the largest contributor to blurring in proton imaging. In this work, we developed a maximum likelihood least squares estimator that improves proton radiography's spatial resolution. The water equivalent thickness (WET) through projections defined from the source to the detector pixels were estimated such that they maximizes the likelihood of the energy loss of every proton crossing the volume. The length spent in each projection was calculated through the optimized cubic spline path estimate. The proton radiographies were produced using Geant4 simulations. Three phantoms were studied here: a slanted cube in a tank of water to measure 2D spatial resolution, a voxelized head phantom for clinical performance evaluation as well as a parametric Catphan phantom (CTP528) for 3D spatial resolution. Two proton beam configurations were used: a parallel and a conical beam. Proton beams of 200 and 330 MeV were simulated to acquire the radiography. Spatial resolution is increased from 2.44 lp cm(-1) to 4.53 lp cm(-1) in the 200 MeV beam and from 3.49 lp cm(-1) to 5.76 lp cm(-1) in the 330 MeV beam. Beam configurations do not affect the reconstructed spatial resolution as investigated between a radiography acquired with the parallel (3.49 lp cm(-1) to 5.76 lp cm(-1)) or conical beam (from 3.49 lp cm(-1) to 5.56 lp cm(-1)). The improved images were then used as input in a photon tomography algorithm. The proton CT reconstruction of the Catphan phantom shows high spatial resolution (from 2.79 to 5.55 lp cm(-1) for the parallel beam and from 3.03 to 5.15 lp cm(-1) for the conical beam) and the reconstruction of the head phantom, although qualitative, shows high contrast in the gradient region. The proposed formulation of the optimization demonstrates serious potential to increase the spatial resolution (up by 65%) in proton radiography and greatly accelerate proton computed tomography reconstruction.