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首页> 美国卫生研究院文献>Medical Physics >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
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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

机译：在商用扫描仪上使用后处理双能CT成像在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

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>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 noninvasive in vivo estimation 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 mm3 grid 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.
机译：>目的：需要准确的患者特定光子横截面信息，以支持更精确的基于模型的剂量计算，以实现药物的低能光子发射方式（例如近距离放射疗法和千伏X射线成像程序）。在商用CT扫描仪上实验性地采用了一种后处理双能CT（pDECT）技术，用于无创体内估计光子线性衰减系数，并在理想的幻像几何体中评估了其准确性。>方法：在10 keV至1 MeV的能量范围内，使用已知成分和密度的PbECT估计值将pDECT估计的线性衰减系数与NIST参考值进行比较。由于统计图像重建（SIR）已显示出比传统的滤波反投影（FBP）重建的图像具有更少的随机性和系统性误差，因此，pDECT技术既可以通过内部多能SIR算法实现，也可以采用交替最小化（AM）来实现作为常规FBP重建算法。还通过用额外的0.5毫米锡过滤高能束来研究增加光谱分离带来的改善。 >结果：八种测试材料的平均pDECT估计线性衰减系数在NIST参考值的1％之内达成一致对于从1 MeV到30 keV的能量，平均误差在10 keV时上升到3％至6％之间，表明当测量和校准体模几何形状匹配时，该方法是无偏见的。用FBP和AM算法进行重构可得到相似的平均pDECT精度。然而，在1×1×3 mm 3 网格上重建的单体素pDECT估计值对重建的图像不确定性高度敏感；在某些情况下，pDECT衰减系数估计值的标准偏差约为平均值的20％。使用统计AM算法进行重建，导致标准偏差比FBP重建小40％至60％。即使仅以剂量的25％进行扫描，高能束的其他锡过滤也表现出与未过滤束类似的pDECT估算精度。使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，估计重建的CT图像不确定度必须限制在0.25％以下，以使目标线性衰减系数估计不确定度在28 keV时达到3％。>结论： pDECT支持平均线性衰减对于大于30 keV的能量，系数测量精度达到参考值的1％是令人鼓舞的。但是，pDECT测量对重建的CT图像中的噪声和系统误差的敏感性值得在更复杂的幻像几何体中进行进一步研究。由于改善了噪声性能，因此研究的统计重建算法AM相对于FBP减少了随机测量的不确定性。这些早期结果还支持增加DE光谱分离的努力，这可以进一步降低pDECT对测量不确定性的敏感性。

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