Department of Radiology, Mayo Clinic, 200 1st Street SW, Rochester, MN 55902, United States of America.
Phys Med Biol. 2019 Dec 13;64(24):245003. doi: 10.1088/1361-6560/ab55bf.
Compared to traditional multi-scan single-energy CT (SECT), one potential advantage of single-scan multi-energy CT (MECT) proposed for simultaneous imaging of multiple contrast agents is the radiation dose reduction. This phantom study aims to rigorously evaluate whether the radiation dose can truly be reduced in a single-scan MECT protocol (MECT_1s) in biphasic liver imaging with iodine and gadolinium, and small bowel imaging with iodine and bismuth, compared to traditional two-scan SECT protocols (SECT_2s). For MECT_1s, mixed iodine/gadolinium samples were prepared corresponding to late arterial/portal-venous phase for biphasic liver imaging. Mixed iodine/bismuth samples were prepared representing the arterial/enteric enhancement for small bowel imaging. For SECT_2s, separate contrast samples were prepared to mimic separate scans in arterial/venous phase and arterial/enteric enhancement. Samples were placed in a 35 cm wide water phantom and scanned by a research whole-body photon-counting-detector-CT (PCD-CT) system ('chess' mode). MECT images were acquired with optimized kV/threshold settings for each imaging task, and SECT images were acquired at 120 kV. Total CTDIvol was matched for the two protocols. Image-based three-material decomposition was employed in MECT_1s to determine the basis material concentration values, which were converted to CT numbers at 120 kV (i.e. virtual SECT images) to compare with the SECT images directly acquired with SECT_2s. The noise difference between the SECT and the virtual SECT images was compared to evaluate the dose efficiency of MECT_1s. Compared to SECT_2s, MECT_1s was not dose efficient for both imaging tasks. The amount of noise increase is highly task dependent, with noise increased by 203%/278% and 110%/82% in virtual SECT images for iodine/gadolinium and iodine/bismuth quantifications, respectively, corresponding to dose increase by 819%/1328% and 340%/230% in MECT_1s to achieve the same image noise level. MECT with the current PCD-CT technique requires higher radiation dose than SECT to achieve the same image quality.
与传统的多期单能 CT（SECT）相比，单期多能 CT（MECT）同时对多种对比剂成像的一个潜在优势是降低辐射剂量。这项体模研究旨在严格评估，在使用碘和钆进行双期肝脏成像，以及使用碘和铋进行小肠成像的情况下，与传统的两期 SECT 方案（SECT_2s）相比，单期 MECT 方案（MECT_1s）是否真的能降低辐射剂量。对于 MECT_1s，混合碘/钆样本是根据双期肝脏成像的晚期动脉/门静脉期制备的。混合碘/铋样本是根据小肠成像的动脉/肠期增强来制备的。对于 SECT_2s，分别制备了对比样本以模拟动脉/静脉期和动脉/肠期增强的单独扫描。样本放置在 35cm 宽的水模体中，并由研究用全身体光子计数探测器 CT（PCD-CT）系统（“棋盘”模式）进行扫描。为每个成像任务优化了 MECT 图像的 kV/阈值设置，SECT 图像在 120kV 下采集。两个方案的总 CTDIvol 相匹配。MECT_1s 中采用基于图像的三物质分解来确定基础物质浓度值，这些值被转换为 120kV 的 CT 值（即虚拟 SECT 图像），与直接使用 SECT_2s 采集的 SECT 图像进行比较。比较 SECT 图像和虚拟 SECT 图像之间的噪声差异，以评估 MECT_1s 的剂量效率。与 SECT_2s 相比，MECT_1s 对两种成像任务都没有剂量效率。噪声增加的量高度依赖于任务，碘/钆和碘/铋定量的虚拟 SECT 图像的噪声分别增加了 203%/278%和 110%/82%，相应的剂量增加了 819%/1328%和 340%/230%，在 MECT_1s 中达到相同的图像噪声水平。使用当前的 PCD-CT 技术进行 MECT 需要比 SECT 更高的辐射剂量才能达到相同的图像质量。
