Lee J S, Jani A B, Pelizzari C A, Haraf D J, Vokes E E, Weichselbaum R R, Chen G T
Department of Radiation and Cellular Oncology, University of Chicago, IL 60637-9006, USA.
Int J Radiat Oncol Biol Phys. 1999 Jun 1;44(3):693-703. doi: 10.1016/s0360-3016(99)00042-5.
To demonstrate the utility of volume rendering, an alternative visualization technique to surface rendering, in the practice of CT based radiotherapy planning for the head and neck.
Rendo-avs, a volume visualization tool developed at the University of Chicago, was used to volume render head and neck CT scans from two cases. Rendo-avs is a volume rendering tool operating within the graphical user interface environment of AVS (Application Visualization System). Users adjust the opacity of various tissues by defining the opacity transfer function (OTF), a function which preclassifies voxels by opacity prior to rendering. By defining the opacity map (OTF), the user selectively enhances and suppresses structures of various intensity. Additional graphics tools are available within the AVS network, allowing for the manipulation of perspective, field of view, data orientation. Users may draw directly on volume rendered images, create a partial surface, and thereby correlate objects in the 3D scene to points on original axial slices. Information in volume rendered images is mapped into the original CT slices via a Z buffer, which contains the depth information (Z coordinate) for each pixel in the rendered view. Locally developed software was used to project conventionally designed GTV contours onto volume rendered images.
The lymph nodes, salivary glands, vessels, and airway are visualized in detail without prior manual segmentation. Volume rendering can be used to explore the finer anatomic structures that appear on consecutive axial slices as "points." Rendo-avs allowed for acceptable interactivity, with a processing time of approximately 5 seconds per 256 x 256 pixel output image.
Volume rendering is a useful alternative to surface rendering, offering high-quality visualization, 3D anatomic delineation, and time savings to the user, due to the elimination of manual segmentation as a preprocessing step. Volume rendered images can be merged with conventional treatment planning images to add anatomic information to the treatment planning process.
展示体绘制（一种与面绘制不同的可视化技术）在基于CT的头颈部放射治疗计划实践中的效用。
使用在芝加哥大学开发的体可视化工具Rendo-avs对头颈部CT扫描的两个病例进行体绘制。Rendo-avs是一个在AVS（应用可视化系统）的图形用户界面环境中运行的体绘制工具。用户通过定义不透明度传递函数（OTF）来调整各种组织的不透明度，该函数在渲染前按不透明度对体素进行预分类。通过定义不透明度映射（OTF），用户可以有选择地增强和抑制不同强度的结构。AVS网络中还提供了其他图形工具，可用于操作视角、视野、数据方向。用户可以直接在体绘制图像上绘图，创建局部表面，从而将3D场景中的物体与原始轴向切片上的点相关联。体绘制图像中的信息通过Z缓冲区映射到原始CT切片上，Z缓冲区包含渲染视图中每个像素的深度信息（Z坐标）。使用本地开发的软件将传统设计的GTV轮廓投影到体绘制图像上。
无需事先手动分割即可详细显示淋巴结、唾液腺、血管和气道。体绘制可用于探索在连续轴向切片上显示为“点”的更精细的解剖结构。Rendo-avs具有可接受的交互性，每256×256像素输出图像的处理时间约为5秒。
体绘制是面绘制的一种有用替代方法，由于无需将手动分割作为预处理步骤，可为用户提供高质量的可视化、3D解剖描绘并节省时间。体绘制图像可与传统治疗计划图像合并，为治疗计划过程添加解剖信息。
