基于肺平均CT值的4D-CT图像重建方法研究

4D-CT reconstruction based on average CT value of the lungs

目的探讨基于肺平均CT值（ACV）在普通CT上实现4D—CT重建的可行性。方法根据CT值的定义和特性，本研究提出了“肺ACV原理”：在呼吸运动过程中，全肺的ACV将随呼吸运动而呈现周期性变化，据此可以确定进行Cine扫描时，肺部各CT图像的呼吸相位。然后，用VC＋＋语言开发了相应ACV 4D-CT重建系统。在自由呼吸状态下对患者进行多床位Cine模式扫描，每个床位持续扫描6s、共进行12次CT重建。扫描后，分别计算各CT图像中肺的ACV，按床位绘制肺ACV随重建时间变化的曲线，据此确定每层CT图像所处的呼吸相位，按相位对所有CT图像进行排序，可获得多个不同呼吸相位的CT系列，即4D-CT。结果利用商售RPM系统重建的4D—CT图像，证实了肺ACV原理；据此原理，对多床位Cine模式扫描CT图像进行排序，在普通CT上实现了满意的4D—CT重建。结论基于肺ACV原理，可实现简便、可靠的4D—CT重建，其重建过程不依赖于体外呼吸监测装置，具有普遍适用性。

Objective To investigate the feasibility of 4D-CT reconstruction based on average CT value （ACV） of the lungs on conventional CT. Methods According to the definition and characteristics of the CT values, a principle of pulmonary ACV was proposed ： the ACV of whole lung presents cyclic variation during respiration, which can determine each respiratory phase position in lung CT image during Cine scanning. In this study, 5 sets of reconstructed 4D-CT images based on commercial Real-time Position Management （RPM） system were selected to verify the ACV principle. Then, the corresponding ACV-based 4D-CT reconstruction system was developed by VC＋＋ language. Patients were scanned by multiple-bed Cine mode under the state of free breathing, with 6 seconds Cine duration for each bed and a total of 12 CT reconstructions. After scanning, the lung ACV in each CT image was calculated respectively, and the curve of lung ACV over the reconstruction time was drawn for each bed to determine the respiratory phase position in each layer of the CT image. All the CT images were sorted according to the phase position to obtain multiple different respiratory phase position of the CT set, ie the 4D-CT. Results The principle of lung ACV was verified by using the 4D-CT image reconstructed on commercial RPM system. And satisfactory 4D- CT reconstruction could be performed on conventional CT based on the ACV principle after sorting the scanned CT images by multiple- bed Cine mode. Conclusion Based on the lung ACV principle, convenient and reliable 4D- CT reconstruction can be accomplished without any external respiratory monitoring device during the reconstruction process, which may be widely practical.