Ebert M A, Lambert J, Greer P B
Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, Australia.
Australas Phys Eng Sci Med. 2008 Jun;31(2):154-9. doi: 10.1007/BF03178591.
The influence of tube voltage (kV) and current (mA) on the resulting relationship of computed tomography number to electron density (CT-ED) was investigated for a wide-bore GE scanner. The influence of kV and mA scan settings were examined in combination with a 16-bit image reconstruction algorithm made available via the scanner software and which allowed resolution of CT numbers for high density materials. By using titanium and stainless steel inserts in an electron density phantom, mA variation was found to have minimal impact on the CT-ED relationship, whereas variation in kV led to significant differences in CT number for the high density materials. The scanner is also equipped with automatic tube-current modulation capabilities. The influence of automatic tube-current modulation on CT number was investigated for a range of materials in a phantom geometry. It was found that tube current modulation has negligible effect on CT number, though the changing dimension of the phantom did influence CT number of an aluminium insert for scans undertaken with both fixed and modulated tube currents. In light of evidence from other studies examining the influence of CT number on dose calculation, it is recommended that scanner settings and specific CT-ED look-up tables be considered when calculations will be required with high-density materials present.
对于一台大孔径通用电气扫描仪，研究了管电压（kV）和电流（mA）对计算机断层扫描数值与电子密度（CT-ED）之间所得关系的影响。结合通过扫描仪软件提供的16位图像重建算法，研究了kV和mA扫描设置的影响，该算法可解析高密度材料的CT数值。通过在电子密度体模中使用钛和不锈钢插入物，发现mA变化对CT-ED关系的影响最小，而kV变化会导致高密度材料的CT数值出现显著差异。该扫描仪还具备自动管电流调制功能。针对体模几何形状中的一系列材料，研究了自动管电流调制对CT数值的影响。结果发现，管电流调制对CT数值的影响可忽略不计，不过体模尺寸的变化确实会影响在固定管电流和调制管电流扫描下铝插入物的CT数值。鉴于其他研究中有关CT数值对剂量计算影响的证据，建议在存在高密度材料需要进行计算时，考虑扫描仪设置和特定的CT-ED查找表。
