Vedam S S, Keall P J, Kini V R, Mostafavi H, Shukla H P, Mohan R
Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA.
Phys Med Biol. 2003 Jan 7;48(1):45-62. doi: 10.1088/0031-9155/48/1/304.
Four-dimensional (4D) methods strive to achieve highly conformal radiotherapy, particularly for lung and breast tumours, in the presence of respiratory-induced motion of tumours and normal tissues. Four-dimensional radiotherapy accounts for respiratory motion during imaging, planning and radiation delivery, and requires a 4D CT image in which the internal anatomy motion as a function of the respiratory cycle can be quantified. The aims of our research were (a) to develop a method to acquire 4D CT images from a spiral CT scan using an external respiratory signal and (b) to examine the potential utility of 4D CT imaging. A commercially available respiratory motion monitoring system provided an 'external' tracking signal of the patient's breathing. Simultaneous recording of a TTL 'X-Ray ON' signal from the CT scanner indicated the start time of CT image acquisition, thus facilitating time stamping of all subsequent images. An over-sampled spiral CT scan was acquired using a pitch of 0.5 and scanner rotation time of 1.5 s. Each image from such a scan was sorted into an image bin that corresponded with the phase of the respiratory cycle in which the image was acquired. The complete set of such image bins accumulated over a respiratory cycle constitutes a 4D CT dataset. Four-dimensional CT datasets of a mechanical oscillator phantom and a patient undergoing lung radiotherapy were acquired. Motion artefacts were significantly reduced in the images in the 4D CT dataset compared to the three-dimensional (3D) images, for which respiratory motion was not accounted. Accounting for respiratory motion using 4D CT imaging is feasible and yields images with less distortion than 3D images. 4D images also contain respiratory motion information not available in a 3D CT image.
在肿瘤和正常组织存在呼吸诱导运动的情况下，四维（4D）方法致力于实现高度适形放疗，尤其是对于肺部和乳腺肿瘤。四维放疗在成像、计划和放疗过程中考虑了呼吸运动，并且需要一个四维CT图像，其中内部解剖结构的运动作为呼吸周期的函数可以被量化。我们研究的目的是（a）开发一种使用外部呼吸信号从螺旋CT扫描获取四维CT图像的方法，以及（b）研究四维CT成像的潜在效用。一个商用呼吸运动监测系统提供患者呼吸的“外部”跟踪信号。同时记录来自CT扫描仪的TTL“X射线开启”信号指示CT图像采集的开始时间，从而便于对所有后续图像进行时间标记。使用0.5的螺距和1.5秒的扫描仪旋转时间进行过采样螺旋CT扫描。来自这种扫描的每个图像被分类到一个图像仓中，该图像仓与采集该图像时的呼吸周期阶段相对应。在一个呼吸周期内积累的完整的此类图像仓集构成一个四维CT数据集。获取了机械振荡器体模和一名接受肺部放疗患者的四维CT数据集。与未考虑呼吸运动的三维（3D）图像相比，四维CT数据集中的图像中的运动伪影明显减少。使用四维CT成像考虑呼吸运动是可行的，并且产生的图像比三维图像的失真更小。四维图像还包含三维CT图像中不可用的呼吸运动信息。
