Amato Carlo, Klein Laura, Wehrse Eckhard, Rotkopf Lukas T, Sawall Stefan, Maier Joscha, Ziener Christian H, Schlemmer Heinz-Peter, Kachelrieß Marc
Division of X-Ray Imaging and Computed Tomography, German Cancer Research Center (DKFZ), Heidelberg, 69120, Germany.
Medical Faculty, Ruprecht-Karls-University, Heidelberg, 69120, Germany.
Med Phys. 2020 Dec;47(12):6179-6190. doi: 10.1002/mp.14519. Epub 2020 Nov 1.
In clinics, only iodine- and barium-based contrast agents are currently used for contrast-enhanced x-ray computed tomography (CT). Recently, the introduction of new photon-counting (PC) detectors increased the interest in developing new contrast agents based on heavier elements. These elements may provide more contrast and spectral information compared to iodine and barium thanks to their k-edges at higher energies. In this paper, the potential of high-Z elements in contrast-enhanced CT was evaluated for different patient sizes and x-ray spectra using a PC detector.
An adult liver phantom with five high-Z element solutions (iodine, gadolinium, ytterbium, tungsten, and bismuth) was scanned with a whole-body photon-counting computed tomography (PCCT) prototype. For each element, the contrast-to-noise ratio at unit concentration and at unit dose (CNRCD) was evaluated in low threshold images ( ) as function of the tube voltage (80, 100, 120, and 140 kV) and in bin images (tube voltage = 120 kV) as function of the higher threshold ( and ). Simulations were performed for validation with measurements and to investigate more elements (cerium and gold), different patient sizes (infant, adult, and obese), and spectrum filtration (with and without 0.4-mm tin filter). The dose reductions associated with the CNRCD improvements over iodine were quantified as well.
CNRCD improvements and dose reductions depend on the investigated scenario. For the infant phantom, dose reductions around 30% were reached using cerium or gadolinium in combination with the tin filter. For the adult and obese phantom, reductions around 50% were provided by gadolinium or ytterbium in combination with the tin filter. Independently of the high-Z element, the CNRCD of two optimally combined bin images was higher than the CNRCD of the low threshold image. Good agreement was found between measurements and simulations.
Between the investigated elements, gadolinium resulted to have the highest potential as novel contrast agent in PCCT, providing significant dose reductions for all patient sizes. Compared to the other elements, the implementation of gadolinium as CT contrast agent may be facilitated since it is already deployed as contrast agents for magnetic resonance imaging.
在临床上，目前仅碘基和钡基造影剂用于增强型X射线计算机断层扫描（CT）。最近，新型光子计数（PC）探测器的引入增加了人们对开发基于重元素的新型造影剂的兴趣。由于这些元素在更高能量处的K边，与碘和钡相比，它们可能提供更多的对比度和光谱信息。在本文中，使用PC探测器针对不同患者体型和X射线光谱评估了高Z元素在增强CT中的潜力。
使用全身光子计数计算机断层扫描（PCCT）原型对含有五种高Z元素溶液（碘、钆、镱、钨和铋）的成人肝脏模型进行扫描。对于每种元素，在低阈值图像（ ）中，将单位浓度和单位剂量下的对比度噪声比（CNRCD）评估为管电压（80、100、120和140 kV）的函数，在bin图像（管电压 = 120 kV）中评估为较高阈值（ 和 ）的函数。进行模拟以验证测量结果，并研究更多元素（铈和金）、不同患者体型（婴儿、成人和肥胖者）以及光谱过滤（有和没有0.4毫米锡滤过器）的情况。还对与碘相比CNRCD改善相关的剂量降低进行了量化。
CNRCD的改善和剂量降低取决于所研究的情况。对于婴儿模型，使用铈或钆并结合锡滤过器可实现约30%的剂量降低。对于成人和肥胖模型，钆或镱结合锡滤过器可提供约50%的剂量降低。与高Z元素无关，两个最佳组合的bin图像的CNRCD高于低阈值图像的CNRCD。测量结果与模拟结果吻合良好。
在所研究的元素中，钆作为PCCT中的新型造影剂具有最高潜力，可为所有患者体型显著降低剂量。与其他元素相比，钆作为CT造影剂的应用可能更容易，因为它已被用作磁共振成像的造影剂。
