Xiaomian Xie, Duchun Tao, Siping Chen, Shangkai Gao, Yalei Bi
Department of Biomedical Engineering, Tsinghua University, Beijing 100084, China.
Comput Med Imaging Graph. 2006 Sep-Oct;30(6-7):383-9. doi: 10.1016/j.compmedimag.2006.09.006. Epub 2006 Nov 7.
Navigation is important in Computed Tomography Virtual Endoscopy (CTVE) functions. Existing navigation methods involve planning and pre-calculating of a fixed path before the viewpoint flight inside the targeted organs. This includes path construction, centering, smoothing and multi-branch processing. This paper proposes a 3D navigation method which was achieved by utilizing the compatibility of the 3D navigation and the ray casting 3D rendering method, without the necessity of planning and pre-calculating a fixed path, eliminating the multi-branch problems. In our 3D navigation method, the viewpoint direction and location are tracked in real time when the viewpoint is inside the organs. At the same time it presents and controls the direction changes and location changes of the viewpoint in x, y, z dimensions. With interactive control of the viewpoint, it can fly in any direction in 3D, not only along a fixed path, thus eliminating multi-branch problems. The viewpoint locations and directions will change smoothly and will be used to calculate the current scene of CTVE. Accelerated ray casting is used to render 3D scenes, which is compatible with the 3D navigation method. In Minimum Intensity Projection (MinIP) applications, if the conventional MinIP reconstruction method is used, realistic results cannot be achieved when they are rotated in multi-directions because the Computed Tomography (CT) images always contain empty regions surrounding the tissue regions. The conventional MinIP reconstruction algorithm always chalks up a minimum intensity voxel which relates to the empty regions instead of the tissue regions. To solve such valid voxel searching problems, seed-filling algorithms are used to fill the empty regions of each slice automatically. The empty voxels are labeled automatically and are avoided in MinIP calculation to gain correct results in all directions.
导航在计算机断层扫描虚拟内窥镜检查（CTVE）功能中很重要。现有的导航方法包括在目标器官内进行视点飞行之前规划和预先计算固定路径。这包括路径构建、居中、平滑和多分支处理。本文提出了一种三维导航方法，该方法利用三维导航与光线投射三维渲染方法的兼容性来实现，无需规划和预先计算固定路径，从而消除了多分支问题。在我们的三维导航方法中，当视点在器官内部时，实时跟踪视点方向和位置。同时，它呈现并控制视点在x、y、z维度上的方向变化和位置变化。通过对视点的交互式控制，它可以在三维空间中沿任何方向飞行，而不仅仅是沿着固定路径，从而消除了多分支问题。视点的位置和方向将平滑变化，并用于计算CTVE的当前场景。使用加速光线投射来渲染三维场景，这与三维导航方法兼容。在最小强度投影（MinIP）应用中，如果使用传统的MinIP重建方法，当在多方向旋转时无法获得逼真的结果，因为计算机断层扫描（CT）图像总是在组织区域周围包含空白区域。传统的MinIP重建算法总是找出与空白区域而非组织区域相关的最小强度体素。为了解决这种有效体素搜索问题，使用种子填充算法自动填充每个切片的空白区域。空白体素会自动标记，并在MinIP计算中被避免，以便在所有方向上获得正确结果。
