Lu Xiaomei, Lu Zaiming, Yin Jiandong, Gao Yuying, Chen Xingbiao, Guo Qiyong
Department of Radiology, Shengjing Hospital of China Medical University, Shenyang 110004, China.
Division of Biomedical Engineering, China Medical University, Shenyang 110001, China.
Quant Imaging Med Surg. 2019 Feb;9(2):188-200. doi: 10.21037/qims.2018.11.12.
The purpose of this study is to investigate the accuracy of iodine quantification and virtual monochromatic CT numbers obtained with the dual-layer spectral CT (DLCT) using a phantom at different radiation dose levels and spectral iterative reconstruction (IR) levels.
An abdomen phantom with seven iodine inserts (2.0, 2.5, 5.0, 7.5, 10.0, 15.0, 20.0 mg/mL) was imaged using a DLCT scanner. Five repeated scans were performed at computed tomography dose index volume (CTDI) levels of 5, 10, 15, 20, 25 mGy at tube voltages of 120 and 140 kVp, respectively. Spectral-based images were reconstructed using four spectral IR levels (spectral level of 0, 2, 4, 6). Iodine density images and virtual monochromatic images (VMI) at energy levels of 50, 70 and 120 keV were created. The absolute percentage bias (APB) of the measured iodine concentration and the true iodine concentration, and the measured VMI CT numbers and the theoretical VMI CT numbers were compared to determine the difference of radiation dose levels and different spectral IR levels.
At CTDI levels of 25, 20, 15, 10 mGy, radiation dose levels had no effect on the accuracy of iodine quantitation; at CTDI level of 5 mGy, the accuracy of iodine quantification was the poorest, with the mean APB of 4.33% (P<0.05). There was no significant difference in the accuracy of iodine quantitation between 120 and 140 kVp (P=0.648). At energy levels of 50, 70 and 120 keV, there was no significant difference in the accuracy of the VMI CT numbers among the CTDI levels of 25, 20 and 15 mGy. However, the accuracy of VMI CT numbers was significantly degraded at the CTDI levels of 10 and 5 mGy (P<0.05). At energy level of 50 keV, the accuracy of VMI CT numbers was not affected by tube voltages (kVps) used (P=0.125). At the energy levels of 70 and 120 keV, 140 kVp produced a smaller bias than 120 kVp, with the mean APB at 120 and 140 kVp being of 3.62% 2.99% for 70 keV (P<0.01), and 11.65% 9.28% for 120 keV (P<0.01), respectively. Spectral IR levels did not affect the accuracy of iodine quantification and VMI CT numbers (P=0.998, P=0.963).
The accuracy of iodine quantification and VMI CT numbers was only affected by very low radiation dose levels. At the clinically applied radiation dose levels of >10 mGy, the accuracy of both iodine quantification and VMI CT numbers is relatively stable and high.
本研究的目的是使用体模在不同辐射剂量水平和光谱迭代重建（IR）水平下，研究双层光谱CT（DLCT）获得的碘定量和虚拟单色CT值的准确性。
使用DLCT扫描仪对具有七个碘插入物（2.0、2.5、5.0、7.5、10.0、15.0、20.0 mg/mL）的腹部体模进行成像。分别在120 kVp和140 kVp管电压下，在计算机断层扫描剂量指数容积（CTDI）水平为5、10、15、20、25 mGy时进行五次重复扫描。使用四个光谱IR水平（光谱水平0、2、4、6）重建基于光谱的图像。创建了50、70和120 keV能量水平下的碘密度图像和虚拟单色图像（VMI）。比较测量的碘浓度与真实碘浓度的绝对百分比偏差（APB），以及测量的VMI CT值与理论VMI CT值，以确定辐射剂量水平和不同光谱IR水平的差异。
在CTDI水平为25、20、15、10 mGy时，辐射剂量水平对碘定量的准确性没有影响；在CTDI水平为5 mGy时，碘定量的准确性最差，平均APB为4.33%（P<0.05）。120 kVp和140 kVp之间碘定量的准确性没有显著差异（P=0.648）。在50、70和120 keV能量水平下，25、20和15 mGy的CTDI水平之间VMI CT值的准确性没有显著差异。然而，在CTDI水平为10和5 mGy时，VMI CT值的准确性显著降低（P<0.05）。在50 keV能量水平下，VMI CT值的准确性不受使用的管电压（kVp）影响（P=0.125）。在70和120 keV能量水平下，140 kVp产生的偏差小于120 kVp，70 keV时120 kVp和140 kVp的平均APB分别为3.62%和2.99%（P<0.01），120 keV时分别为11.65%和9.28%（P<0.01）。光谱IR水平不影响碘定量和VMI CT值的准确性（P=0.998，P=0.963）。
碘定量和VMI CT值的准确性仅受极低辐射剂量水平的影响。在临床应用的辐射剂量水平>10 mGy时，碘定量和VMI CT值的准确性相对稳定且较高。
