Liu Yilin, Yin Fang-Fang, Rhee DongJoo, Cai Jing
Medical Physics Graduate Program, Duke University, Durham, North Carolina 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710.
Dongnam Institute of Radiological and Medical Sciences, Gijang-gun, Busan 619-953, South Korea.
Med Phys. 2016 Jan;43(1):179. doi: 10.1118/1.4938066.
The authors have recently developed a cine-mode T2*/T1-weighted 4D-MRI technique and a sequential-mode T2-weighted 4D-MRI technique for imaging respiratory motion. This study aims at investigating which 4D-MRI image acquisition mode, cine or sequential, provides more accurate measurement of organ motion during respiration.
A 4D digital extended cardiac-torso (XCAT) human phantom with a hypothesized tumor was used to simulate the image acquisition and the 4D-MRI reconstruction. The respiratory motion was controlled by the given breathing signal profiles. The tumor was manipulated to move continuously with the surrounding tissue. The motion trajectories were measured from both sequential- and cine-mode 4D-MRI images. The measured trajectories were compared with the average trajectory calculated from the input profiles, which was used as references. The error in 4D-MRI tumor motion trajectory (E) was determined. In addition, the corresponding respiratory motion amplitudes of all the selected 2D images for 4D reconstruction were recorded. Each of the amplitude was compared with the amplitude of its associated bin on the average breathing curve. The mean differences from the average breathing curve across all slice positions (D) were calculated. A total of 500 simulated respiratory profiles with a wide range of irregularity (Ir) were used to investigate the relationship between D and Ir. Furthermore, statistical analysis of E and D using XCAT controlled by 20 cancer patients' breathing profiles was conducted. Wilcoxon Signed Rank test was conducted to compare two modes.
D increased faster for cine-mode (D = 1.17 × Ir + 0.23) than sequential-mode (D = 0.47 × Ir + 0.23) as irregularity increased. For the XCAT study using 20 cancer patients' breathing profiles, the median E values were significantly different: 0.12 and 0.10 cm for cine- and sequential-modes, respectively, with a p-value of 0.02. The median D values were significantly different: 0.47 and 0.24 cm for cine- and sequential-modes, respectively, with a p-value < 0.001.
Respiratory motion measurement may be more accurate and less susceptible to breathing irregularity in sequential-mode 4D-MRI than that in cine-mode 4D-MRI.
作者最近开发了一种电影模式的T2*/T1加权4D-MRI技术和一种序列模式的T2加权4D-MRI技术用于成像呼吸运动。本研究旨在调查哪种4D-MRI图像采集模式，即电影模式或序列模式，在呼吸过程中能更准确地测量器官运动。
使用带有假设肿瘤的4D数字扩展心脏-躯干（XCAT）人体模型来模拟图像采集和4D-MRI重建。呼吸运动由给定的呼吸信号曲线控制。肿瘤被操纵以与周围组织一起连续移动。从序列模式和电影模式的4D-MRI图像中测量运动轨迹。将测量的轨迹与根据输入曲线计算的平均轨迹进行比较，该平均轨迹用作参考。确定4D-MRI肿瘤运动轨迹中的误差（E）。此外，记录用于4D重建的所有选定2D图像的相应呼吸运动幅度。将每个幅度与其在平均呼吸曲线上相关联的区间的幅度进行比较。计算所有切片位置上与平均呼吸曲线的平均差异（D）。总共使用500个具有广泛不规则性（Ir）的模拟呼吸曲线来研究D和Ir之间的关系。此外，使用由20名癌症患者的呼吸曲线控制的XCAT对E和D进行统计分析。进行Wilcoxon符号秩检验以比较两种模式。
随着不规则性增加，电影模式（D = 1.17×Ir + 0.23）的D比序列模式（D = 0.47×Ir + 0.23）增加得更快。对于使用20名癌症患者呼吸曲线的XCAT研究，中位数E值有显著差异：电影模式和序列模式分别为0.12和0.10 cm，p值为0.02。中位数D值有显著差异：电影模式和序列模式分别为0.47和0.24 cm，p值<0.001。
在序列模式4D-MRI中，呼吸运动测量可能比电影模式4D-MRI更准确且更不易受呼吸不规则性的影响。
