Li Sha, Huang Xinrui, Li Guozhen, Zhang Yibao, Li Zhaotong, Liu Liangyou, Gao Song
Department of Medical Physics, Institute of Medical Humanities, Peking University, Beijing, PR China.
Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Radiation Oncology, Peking University Cancer Hospital & Institute, Beijing Cancer Hospital & Institute, Beijing, PR China.
Acta Radiol. 2020 Jun;61(6):760-767. doi: 10.1177/0284185119877797. Epub 2019 Sep 30.
Short T2 tissues can be directly visualized by dual-echo ultrashort echo time imaging with weighted subtraction. As a type of post-processing method, exponential subtraction of ultrashort echo time images with an optimal exponential factor is expected to provide improved positive short T2 contrast.
To test the feasibility and effectiveness of exponential subtraction in three-dimensional ultrashort echo time imaging and to determine the optimal exponential factor.
A dual-echo three-dimensional ultrashort echo time sequence was implemented on a 3-T MRI system. Exponential subtraction was performed on dual three-dimensional ultrashort echo time images of the tibia of seven healthy volunteers with exponential factors in the range of 1.00-3.00 in increments of 0.01. The regions of interest, including cortical bone, marrow, and muscle, were depicted on subtracted images of different exponential factors. Contrast-to-noise ratio values were calculated from these regions of interest and then used to assess the optimal exponential factor. To determine intra-observer agreement regarding region of interest selection, paired intra-observer measurements of regions of interest in all direct subtraction images were conducted with a one-week interval and the paired measurements were assessed using Bland-Altman analysis and paired-samples t-test.
Cortical bone can be better visualized by using exponential subtraction in three-dimensional ultrashort echo time imaging; the suggested optimal exponential factor is 1.99-2.03 in the tibia. Paired measurements showed excellent intra-observer agreement.
It is feasible to visualize cortical bone of the tibia using exponential subtraction in three-dimensional ultrashort echo time imaging. Compared with weighted subtraction images, exponential subtraction images with an optimal exponential factor provide enhanced visualization of short T2 tissues.
短T2组织可通过加权减法的双回波超短回波时间成像直接可视化。作为一种后处理方法，采用最佳指数因子对超短回波时间图像进行指数减法有望改善正性短T2对比度。
测试指数减法在三维超短回波时间成像中的可行性和有效性，并确定最佳指数因子。
在3-T MRI系统上实施双回波三维超短回波时间序列。对7名健康志愿者胫骨的双三维超短回波时间图像进行指数减法，指数因子范围为1.00 - 3.00，增量为0.01。在不同指数因子的减法图像上描绘包括皮质骨、骨髓和肌肉在内的感兴趣区域。从这些感兴趣区域计算对比度噪声比值，然后用于评估最佳指数因子。为确定观察者间在感兴趣区域选择方面的一致性，对所有直接减法图像中的感兴趣区域进行观察者内配对测量，间隔一周，并使用Bland-Altman分析和配对样本t检验评估配对测量结果。
在三维超短回波时间成像中使用指数减法可更好地显示皮质骨；胫骨的建议最佳指数因子为1.99 - 2.03。配对测量显示观察者内一致性极佳。
在三维超短回波时间成像中使用指数减法可视化胫骨皮质骨是可行的。与加权减法图像相比，具有最佳指数因子的指数减法图像能增强短T2组织的可视化效果。
