Prospects for in vivo estimation of photon linear attenuation coefficients using postprocessing dual-energy CT imaging on a commercial scanner: comparison of analytic and polyenergetic statistical reconstruction algorithms.
Prospects for in vivo estimation of photon linear attenuation coefficients using postprocessing dual-energy CT imaging on a commercial scanner: comparison of analytic and polyenergetic statistical reconstruction algorithms.
复制标题
在商用扫描仪上使用后处理双能 CT 成像体内估计光子线性衰减系数的前景：分析和多能统计重建算法的比较。
DOI：
10.1118/1.4828787
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发表时间：
2013
期刊：
影响因子：
3.8
通讯作者：
Williamson,JeffreyF
中科院分区：
文献类型：
--
作者：
Evans,JoshuaD;Whiting,BruceR;O'Sullivan,JosephA;Politte,DavidG;Klahr,PaulH;Yu,Yaduo;Williamson,JeffreyF
目的：需要准确的患者特定光子截面信息，以支持医学中低能光子发射模式（如近距离放射治疗和千伏X射线成像程序）的更准确的基于模型的剂量计算。一个后处理双能CT（pDECT）技术的光子线性衰减系数的noninvasiveinvivoestimation已经实验上实现了商业CT扫描仪和其准确性评估在理想化的幻影geometrics.Methods：八个测试材料的已知成分和密度被用来比较pDECT估计的线性衰减系数NIST参考值的能量范围从10 keV到1 MeV。由于已证明统计图像重建（SIR）重建图像的随机误差和系统误差小于传统滤波反投影（FBP），因此使用内部多能SIR算法、交替最小化（AM）以及传统FBP重建算法实现了pDECT技术。还通过用额外的0.5 mm锡过滤高能束来研究增加光谱分离的改进。传播的不确定性的法律被用来评估的pDECT过程中重建images. Results误差的敏感性：平均pDECT-估计的线性衰减系数的8个测试材料同意在1%的NIST参考值的能量从1 MeV下降到30 keV，与平均误差上升到3%和6%之间，在10 keV，表明该方法是无偏的测量和校准体模几何形状匹配。使用FBP和AM算法重建的平均pDECT准确度相似。然而，在1 × 1 × 3 mm 3网格上重建的单体素pDECT估计值对重建图像的不确定性高度敏感;在某些情况下，pDECT衰减系数估计值的标准差约为平均值的20%。用统计AM算法重建导致标准偏差比FBP重建小大约40%至60%。高能射束的附加锡过滤表现出与未过滤射束相似的pDECT估计精度，即使在仅用25%的剂量扫描时也是如此。利用传播不确定性定律，发现低Z材料比高Z材料对图像重建误差更敏感。此外，据估计，重建CT图像的不确定性必须限制在0.25%以下，以实现28 keV时3%的目标线性衰减系数估计不确定性。结论：对于能量大于30 keV的情况，pDECT支持1%参考值的平均线性衰减系数测量精度，这是令人鼓舞的。然而，pDECT测量对重建CT图像中的噪声和系统误差的敏感性需要在更复杂的体模几何形状中进行进一步研究。调查统计重建算法，AM，减少随机测量不确定性相对于FBP由于改善噪声性能。这些早期结果也支持增加DE光谱分离的努力，这可以进一步降低pDECT对测量不确定性的灵敏度。
Purpose:Accurate patient‐specific photon cross‐section information is needed to support more accurate model‐based dose calculation for low energy photon‐emitting modalities in medicine such as brachytherapy and kilovoltage x‐ray imaging procedures. A postprocessing dual‐energy CT (pDECT) technique for noninvasivein vivoestimation of photon linear attenuation coefficients has been experimentally implemented on a commercial CT scanner and its accuracy assessed in idealized phantom geometries.Methods:Eight test materials of known composition and density were used to compare pDECT‐estimated linear attenuation coefficients to NIST reference values over an energy range from 10 keV to 1 MeV. As statistical image reconstruction (SIR) has been shown to reconstruct images with less random and systematic error than conventional filtered backprojection (FBP), the pDECT technique was implemented with both an in‐house polyenergetic SIR algorithm, alternating minimization (AM), as well as a conventional FBP reconstruction algorithm. Improvement from increased spectral separation was also investigated by filtering the high‐energy beam with an additional 0.5 mm of tin. The law of propagated uncertainty was employed to assess the sensitivity of the pDECT process to errors in reconstructed images.Results:Mean pDECT‐estimated linear attenuation coefficients for the eight test materials agreed within 1% of NIST reference values for energies from 1 MeV down to 30 keV, with mean errors rising to between 3% and 6% at 10 keV, indicating that the method is unbiased when measurement and calibration phantom geometries are matched. Reconstruction with FBP and AM algorithms conferred similar mean pDECT accuracy. However, single‐voxel pDECT estimates reconstructed on a 1 × 1 × 3 mm3grid are shown to be highly sensitive to reconstructed image uncertainty; in some cases pDECT attenuation coefficient estimates exhibited standard deviations on the order of 20% around the mean. Reconstruction with the statistical AM algorithm led to standard deviations roughly 40% to 60% less than FBP reconstruction. Additional tin filtration of the high energy beam exhibits similar pDECT estimation accuracy as the unfiltered beam, even when scanning with only 25% of the dose. Using the law of propagated uncertainty, low Z materials are found to be more sensitive to image reconstruction errors than high Z materials. Furthermore, it is estimated that reconstructed CT image uncertainty must be limited to less than 0.25% to achieve a target linear‐attenuation coefficient estimation uncertainty of 3% at 28 keV.Conclusions:That pDECT supports mean linear attenuation coefficient measurement accuracies of 1% of reference values for energies greater than 30 keV is encouraging. However, the sensitivity of the pDECT measurements to noise and systematic errors in reconstructed CT images warrants further investigation in more complex phantom geometries. The investigated statistical reconstruction algorithm, AM, reduced random measurement uncertainty relative to FBP owing to improved noise performance. These early results also support efforts to increase DE spectral separation, which can further reduce the pDECT sensitivity to measurement uncertainty.