Accuracies of the synthesized monochromatic CT numbers and effective atomic numbers obtained with a rapid kVp switching dual energy CT scanner
Accuracies of the synthesized monochromatic CT numbers and effective atomic numbers obtained with a rapid kVp switching dual energy CT scanner
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DOI：
10.1118/1.3567509
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发表时间：
2011-04-01
期刊：
影响因子：
3.8
通讯作者：
Larson, Sandra C.
中科院分区：
文献类型：
--
作者：
Goodsitt, Mitchell M.;Christodoulou, Emmanuel G.;Larson, Sandra C.
目的：本研究是进行调查的合成单色图像和有效的原子序数地图获得的准确性与新的GE发现CT 750 HD CT scanners.Methods：一个Gammex-RMI模型467组织定征体模和CT数线性部分的一个Phantom实验室Catphan 600体模扫描使用双能量（DE）功能的GE CT 750 HD扫描仪。合成的单色图像在40和120千电子伏之间的各种能量和有效原子序数（Z（eff））的地图生成。将感兴趣区域放置在这些图像/标测图内，以测量这些体模内材料的平均单色CT数和平均Z（eff）。真实Z（eff）值由体模制造商提供或使用Mayneord方程计算。使用NIST XCOM程序计算真实CT数的线性衰减系数，输入制造商提供的元素组成和密度。还研究了假定的材料真密度的小变化的影响。最后，使用带有和不带有外部脂肪模拟环的定制腰椎节段体模，研究了身体尺寸对合成单色CT数准确性的影响。除了组织定征体模中模拟肺插入物的Z（eff）（无法通过DECT测量）外，组织定征和Catphan体模中所有其他材料的Z（eff）值精确到15%。两种体模中材料的合成单色CT数的准确性因能量和材料而异。对于40-120 keV范围，当使用标称塑料密度计算真实CT数时，Catphan中测量的CT数和真实CT数之间的RMS误差为8-25 HU。对于标称密度+/-0.02 g/cc范围内的假定真密度，这些RMS误差改善到3-12 HU。在40-120 keV范围内，组织表征体模中组织模拟材料的测量CT数与真实CT数之间的RMS误差在约6 HU-248 HU之间变化，并且在假设的真实密度变化很小的情况下没有显著改善。然而，合成的单色CT数可能非常不准确，特别是对于低能量下的致密组织模仿材料。此外，材料的合成单色CT数仍然取决于周围组织的量，特别是在低keV下，这表明这些数不是真正单色的。需要进一步的研究来开发DE方法，以产生更准确的合成单色CT数。(C)2011年美国医学物理学家协会。[DOI 10.1118/1.3567509]
Purpose: This study was performed to investigate the accuracies of the synthesized monochromatic images and effective atomic number maps obtained with the new GE Discovery CT750 HD CT scanner.Methods: A Gammex-RMI model 467 tissue characterization phantom and the CT number linearity section of a Phantom Laboratory Catphan 600 phantom were scanned using the dual energy (DE) feature on the GE CT750 HD scanner. Synthesized monochromatic images at various energies between 40 and 120 keV and effective atomic number (Z(eff)) maps were generated. Regions of interest were placed within these images/maps to measure the average monochromatic CT numbers and average Z(eff) of the materials within these phantoms. The true Z(eff) values were either supplied by the phantom manufacturer or computed using Mayneord's equation. The linear attenuation coefficients for the true CT numbers were computed using the NIST XCOM program with the input of manufacturer supplied elemental compositions and densities. The effects of small variations in the assumed true densities of the materials were also investigated. Finally, the effect of body size on the accuracies of the synthesized monochromatic CT numbers was investigated using a custom lumbar section phantom with and without an external fat-mimicking ring.Results: Other than the Z(eff) of the simulated lung inserts in the tissue characterization phantom, which could not be measured by DECT, the Z(eff) values of all of the other materials in the tissue characterization and Catphan phantoms were accurate to 15%. The accuracies of the synthesized monochromatic CT numbers of the materials in both phantoms varied with energy and material. For the 40-120 keV range, RMS errors between the measured and true CT numbers in the Catphan are 8-25 HU when the true CT numbers were computed using the nominal plastic densities. These RMS errors improve to 3-12 HU for assumed true densities within the nominal density +/-0.02 g/cc range. The RMS errors between the measured and true CT numbers of the tissue mimicking materials in the tissue characterization phantom over the 40-120 keV range varied from about 6 HU-248 HU and did not improve as dramatically with small changes in assumed true density.Conclusions: Initial tests indicate that the Z(eff) values computed with DECT on this scanner are reasonably accurate; however, the synthesized monochromatic CT numbers can be very inaccurate, especially for dense tissue mimicking materials at low energies. Furthermore, the synthesized monochromatic CT numbers of materials still depend on the amount of the surrounding tissues especially at low keV, demonstrating that the numbers are not truly monochromatic. Further research is needed to develop DE methods that produce more accurate synthesized monochromatic CT numbers. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3567509]