Jani Ashesh B, Irick John-Stockton, Pelizzari Charles
Department of Radiation and Cellular Oncology, University of Chicago Hospitals, 5758 S. Maryland Avenue, MC 9006, Chicago, IL 60637, USA.
Acad Radiol. 2005 Jun;12(6):761-70. doi: 10.1016/j.acra.2005.03.054.
The selection of an opacity transfer function is essential for volume visualization. Computed tomography (CT) scans of the pelvis were used to determine an optimal opacity transfer function for use in radiotherapy.
On sample datasets (a mathematical phantom and a patient pelvis CT scan), standard viewing orientations were selected to render the prostate. Opacity functions were selected via (1) trapezoidal manual selection, (2) trapezoidal semiautomatic selection, and (3) histogram volume-based selection. Using an established metric, the errors using each of these methods were computed.
Trapezoidal manual opacity function optimization resulted in visually acceptable images, but the errors were considerable (6.3-9.1 voxel units). These errors could be reduced with the use of trapezoidal semiautomatic selection (4.9-6.2 voxel units) or with histogram volume-based selection (4.8-7.9 voxel units). As each visualization algorithm focused on enhancing the boundary of the prostate using a different approach, the scene information was considerably different using the three techniques.
Improved volume visualization of soft tissue interfaces was achieved using automated optimal opacity function determination, compared with manual selection.
不透明度传递函数的选择对于容积可视化至关重要。使用骨盆的计算机断层扫描（CT）来确定用于放射治疗的最佳不透明度传递函数。
在样本数据集（一个数学模型和一名患者的骨盆CT扫描）上，选择标准的观察方向来呈现前列腺。通过以下方式选择不透明度函数：（1）梯形手动选择，（2）梯形半自动选择，以及（3）基于直方图体积的选择。使用既定的指标，计算使用这些方法中的每一种方法时的误差。
梯形手动不透明度函数优化产生了视觉上可接受的图像，但误差相当大（6.3 - 9.1体素单位）。使用梯形半自动选择（4.9 - 6.2体素单位）或基于直方图体积的选择（4.8 - 7.9体素单位）可以减少这些误差。由于每种可视化算法都采用不同的方法来增强前列腺的边界，因此使用这三种技术时场景信息有很大差异。
与手动选择相比，使用自动最佳不透明度函数确定可实现软组织界面更好的容积可视化。
