Department of Radiology, Mayo Clinic, Jacksonville, Florida, USA.
Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA.
Med Phys. 2022 Jun;49(6):3683-3691. doi: 10.1002/mp.15592. Epub 2022 Apr 21.
The purpose of this work is to evaluate the scaled computed tomography (CT) number accuracy of an artificial 120 kV reconstruction technique based on phantom experiments in the context of radiation therapy planning.
An abdomen-shaped electron density phantom was scanned on a clinical CT scanner capable of artificial 120 kV reconstruction using different tube potentials from 70 to 150 kV. A series of tissue-equivalent phantom inserts (lung, adipose, breast, solid water, liver, inner bone, 30%/50% CaCO , cortical bone) were placed inside the phantom. Images were reconstructed using a conventional quantitative reconstruction kernel as well as the artificial 120 kV reconstruction kernel. Scaled CT numbers of inserts were measured from images acquired at different kVs and compared with those acquired at 120 kV, which were deemed as the ground truth. The relative error was quantified as the percentage deviation of scaled CT numbers acquired at different tube potentials from their ground truth values acquired at 120 kV.
Scaled CT numbers measured from images reconstructed using the conventional reconstruction demonstrated a strong kV-dependence. The relative error in scaled CT numbers ranged from 0.6% (liver insert) to 31.1% (cortical bone insert). The artificial 120 kV reconstruction reduced the kV dependence, especially for bone tissues. The relative error in scaled CT number was reduced to 0.4% (liver insert) and 2.6% (30% CaCO insert) using this technique. When tube potential selection was limited to the range of 90 to 150 kV, the relative error was further restrained to <1.2% for all tissue types.
Phantom results demonstrated that using the artificial 120 kV technique, it was feasible to acquire raw projection data at the desired tube potential and then reconstruct images with scaled CT numbers comparable to those obtained directly at 120 kV. In radiotherapy applications, this technique may allow optimization of tube potential without complicating clinical workflow by eliminating the necessity of maintaining multiple sets of CT calibration curves.
本研究旨在评估基于体模实验的人工 120kV 重建技术的 CT 数缩放准确性，以便在放射治疗计划中使用。
使用可进行人工 120kV 重建的临床 CT 扫描仪对具有不同管电压（70-150kV）的腹部形状电子密度体模进行扫描。将一系列组织等效体模插件（肺、脂肪、乳腺、实心水、肝脏、内骨、30%/50%碳酸钙、皮质骨）置于体模内。使用常规定量重建核函数和人工 120kV 重建核函数对图像进行重建。从不同 kV 下获取的图像中测量插件的 CT 数缩放值，并与在 120kV 下获取的作为基准值的 CT 数缩放值进行比较。用不同管电压下获取的 CT 数缩放值与 120kV 下获取的基准值之间的百分比偏差来量化相对误差。
使用常规重建方法重建的图像中 CT 数缩放值具有很强的 kV 依赖性。在不同管电压下获取的 CT 数缩放值的相对误差范围为 0.6%（肝脏插件）至 31.1%（皮质骨插件）。人工 120kV 重建技术降低了 CT 数缩放值的 kV 依赖性，尤其是对骨组织。使用该技术，CT 数缩放值的相对误差降低至 0.4%（肝脏插件）和 2.6%（30%碳酸钙插件）。当管电压选择限制在 90-150kV 范围内时，所有组织类型的相对误差进一步限制在<1.2%。
体模结果表明，使用人工 120kV 技术，可以在所需管电压下获取原始投影数据，然后使用与直接在 120kV 下获得的 CT 数缩放值相当的图像进行重建。在放射治疗应用中，该技术可以在不增加临床工作流程复杂性的情况下优化管电压，而无需维持多组 CT 校准曲线。
