Wang Chao, Jung Hyunuk, Yang Ming, Shen Chenyang, Jia Xun
Innovative Technology of Radiotherapy Computation and Hardware (iTORCH) Laboratory, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, United States.
Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, United States.
Front Oncol. 2022 Feb 1;12:827136. doi: 10.3389/fonc.2022.827136. eCollection 2022.
Iodine contrast agent is widely used in liver cancer radiotherapy at CT simulation stage to enhance detectability of tumor. However, its application in cone beam CT (CBCT) for image guidance before treatment delivery is still limited because of poor image quality and excessive dose of contrast agent during multiple treatment fractions. We previously developed a multienergy element-resolved (MEER) CBCT framework that included x-ray projection data acquisition on a conventional CBCT platform in a kVp-switching model and a dictionary-based image reconstruction algorithm that simultaneously reconstructed x-ray attenuation images at each kilovoltage peak (kVp), an electron density image, and elemental composition images. In this study, we investigated feasibility using MEER-CBCT for low-concentration iodine contrast agent visualization. We performed simulation and experimental studies using a phantom with inserts containing water and different concentrations of iodine solution and the MEER-CBCT scan with 600 projections in a full gantry rotation, in which the kVp level sequentially changed among 80, 100, and 120 kVps. We included iodine material in the dictionary of the reconstruction algorithm. We analyzed iodine detectability as quantified by contrast-to-noise ratio (CNR) and compared results with those of CBCT images reconstructed by the standard filter back projection (FBP) method with 600 projections. MEER-CBCT achieved similar contrast enhancement as FBP method but significantly higher CNR. At 2.5% iodine solution concentration, FBP method achieved 170 HU enhancement and CNR of 2.0, considered the standard CNR for successful tumor visualization. MEER-CBCT achieved the same CNR but at ~6.3 times lower iodine concentration of 0.4%.
碘造影剂在肝癌CT模拟放疗阶段被广泛应用，以提高肿瘤的可检测性。然而，由于图像质量差以及多次治疗分次过程中造影剂剂量过大，其在治疗前图像引导的锥形束CT（CBCT）中的应用仍然有限。我们之前开发了一种多能量元素分辨（MEER）CBCT框架，该框架包括在kVp切换模式下于传统CBCT平台上采集X射线投影数据，以及一种基于字典的图像重建算法，该算法可同时重建每个千伏峰值（kVp）下的X射线衰减图像、电子密度图像和元素组成图像。在本研究中，我们调查了使用MEER-CBCT可视化低浓度碘造影剂的可行性。我们使用了一个含有水和不同浓度碘溶液插入物的体模进行模拟和实验研究，并在全机架旋转中进行了600次投影的MEER-CBCT扫描，其中kVp水平在80、100和120 kVps之间依次变化。我们在重建算法的字典中纳入了碘物质。我们分析了以对比度噪声比（CNR）量化的碘可检测性，并将结果与通过标准滤波反投影（FBP）方法重建的600次投影的CBCT图像结果进行比较。MEER-CBCT实现了与FBP方法相似的对比度增强，但CNR显著更高。在2.5%碘溶液浓度下，FBP方法实现了170 HU的增强和2.0的CNR，这被认为是成功进行肿瘤可视化的标准CNR。MEER-CBCT实现了相同的CNR，但碘浓度低约6.3倍，为0.4%。
