Li Guang, Wei Jie, Kadbi Mo, Moody Jason, Sun August, Zhang Shirong, Markova Svetlana, Zakian Kristen, Hunt Margie, Deasy Joseph O
Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York.
Department of Computer Science, City College of New York, New York, New York.
Int J Radiat Oncol Biol Phys. 2017 Jun 1;98(2):454-462. doi: 10.1016/j.ijrobp.2017.02.016. Epub 2017 Feb 17.
To develop and evaluate a super-resolution approach to reconstruct time-resolved 4-dimensional magnetic resonance imaging (TR-4DMRI) with a high spatiotemporal resolution for multi-breathing cycle motion assessment.
A super-resolution approach was developed to combine fast 3-dimensional (3D) cine MRI with low resolution during free breathing (FB) and high-resolution 3D static MRI during breath hold (BH) using deformable image registration. A T1-weighted, turbo field echo sequence, coronal 3D cine acquisition, partial Fourier approximation, and SENSitivity Encoding parallel acceleration were used. The same MRI pulse sequence, field of view, and acceleration techniques were applied in both FB and BH acquisitions; the intensity-based Demons deformable image registration method was used. Under an institutional review board-approved protocol, 7 volunteers were studied with 3D cine FB scan (voxel size: 5 × 5 × 5 mm) at 2 Hz for 40 seconds and a 3D static BH scan (2 × 2 × 2 mm). To examine the image fidelity of 3D cine and super-resolution TR-4DMRI, a mobile gel phantom with multi-internal targets was scanned at 3 speeds and compared with the 3D static image. Image similarity among 3D cine, 4DMRI, and 3D static was evaluated visually using difference image and quantitatively using voxel intensity correlation and Dice index (phantom only). Multi-breathing-cycle waveforms were extracted and compared in both phantom and volunteer images using the 3D cine as the references.
Mild imaging artifacts were found in the 3D cine and TR-4DMRI of the mobile gel phantom with a Dice index of >0.95. Among 7 volunteers, the super-resolution TR-4DMRI yielded high voxel-intensity correlation (0.92 ± 0.05) and low voxel-intensity difference (<0.05). The detected motion differences between TR-4DMRI and 3D cine were -0.2 ± 0.5 mm (phantom) and -0.2 ± 1.9 mm (diaphragms).
Super-resolution TR-4DMRI has been reconstructed with adequate temporal (2 Hz) and spatial (2 × 2 × 2 mm) resolutions. Further TR-4DMRI characterization and improvement are necessary before clinical applications. Multi-breathing cycles can be examined, providing patient-specific breathing irregularities and motion statistics for future 4D radiation therapy.
开发并评估一种超分辨率方法，用于重建具有高时空分辨率的时间分辨四维磁共振成像（TR-4DMRI），以进行多呼吸周期运动评估。
开发了一种超分辨率方法，通过使用可变形图像配准，将自由呼吸（FB）期间的快速三维（3D）电影MRI与低分辨率图像以及屏气（BH）期间的高分辨率3D静态MRI相结合。使用了T1加权、涡轮场回波序列、冠状面3D电影采集、部分傅里叶近似和灵敏度编码并行加速技术。在FB和BH采集中应用相同的MRI脉冲序列、视野和加速技术；使用基于强度的Demons可变形图像配准方法。在机构审查委员会批准的方案下，对7名志愿者进行了研究，以2Hz的频率进行40秒的3D电影FB扫描（体素大小：5×5×5mm）和3D静态BH扫描（2×2×2mm）。为了检查3D电影和超分辨率TR-4DMRI的图像保真度，以3种速度对带有多个内部目标的移动凝胶体模进行扫描，并与3D静态图像进行比较。使用差异图像对3D电影、4DMRI和3D静态图像之间的图像相似性进行视觉评估，并使用体素强度相关性和Dice指数（仅针对体模）进行定量评估。以3D电影为参考，在体模和志愿者图像中提取并比较多呼吸周期波形。
在移动凝胶体模的3D电影和TR-4DMRI中发现了轻度成像伪影，Dice指数>0.95。在7名志愿者中，超分辨率TR-4DMRI产生了高体素强度相关性（0.92±0.05）和低体素强度差异（<0.05）。TR-4DMRI和3D电影之间检测到的运动差异在体模中为-0.2±0.5mm，在横膈膜中为-0.2±1.9mm。
已重建出具有足够时间分辨率（2Hz）和空间分辨率（2×2×2mm）的超分辨率TR-4DMRI。在临床应用之前，有必要对TR-4DMRI进行进一步的特性研究和改进。可以检查多呼吸周期，为未来的四维放射治疗提供患者特定的呼吸不规则性和运动统计数据。
