Department of Radiology, Stanford University, Stanford, CA, USA.
Phys Med Biol. 2012 Oct 7;57(19):6193-210. doi: 10.1088/0031-9155/57/19/6193. Epub 2012 Sep 14.
Many scientists in the field of x-ray imaging rely on the simulation of x-ray images. As the phantom models become more and more realistic, their projection requires high computational effort. Since x-ray images are based on transmission, many standard graphics acceleration algorithms cannot be applied to this task. However, if adapted properly, the simulation speed can be increased dramatically using state-of-the-art graphics hardware. A custom graphics pipeline that simulates transmission projections for tomographic reconstruction was implemented based on moving spline surface models. All steps from tessellation of the splines, projection onto the detector and drawing are implemented in OpenCL. We introduced a special append buffer for increased performance in order to store the intersections with the scene for every ray. Intersections are then sorted and resolved to materials. Lastly, an absorption model is evaluated to yield an absorption value for each projection pixel. Projection of a moving spline structure is fast and accurate. Projections of size 640 × 480 can be generated within 254 ms. Reconstructions using the projections show errors below 1 HU with a sharp reconstruction kernel. Traditional GPU-based acceleration schemes are not suitable for our reconstruction task. Even in the absence of noise, they result in errors up to 9 HU on average, although projection images appear to be correct under visual examination. Projections generated with our new method are suitable for the validation of novel CT reconstruction algorithms. For complex simulations, such as the evaluation of motion-compensated reconstruction algorithms, this kind of x-ray simulation will reduce the computation time dramatically.
许多从事 X 射线成像研究的科学家都依赖于 X 射线图像的模拟。随着体模模型变得越来越逼真，它们的投影需要大量的计算。由于 X 射线图像基于透射，许多标准的图形加速算法不能应用于这项任务。然而，如果适当调整，使用最先进的图形硬件可以显著提高模拟速度。本文基于移动样条曲面模型实现了一个用于层析重建的传输投影模拟的定制图形管道。样条细分、探测器投影和绘制的所有步骤都在 OpenCL 中实现。为了提高性能，我们引入了一个特殊的附加缓冲区，以便为每条光线存储与场景的交点。然后对交点进行排序并解析为材料。最后，评估吸收模型以给出每个投影像素的吸收值。移动样条结构的投影既快速又准确。可以在 254 毫秒内生成大小为 640×480 的投影。使用这些投影进行重建显示出的误差低于 1 HU，重建核锐利。传统的基于 GPU 的加速方案不适合我们的重建任务。即使没有噪声，它们的平均误差也高达 9 HU，尽管从视觉检查来看，投影图像似乎是正确的。我们的新方法生成的投影适用于验证新的 CT 重建算法。对于复杂的模拟，如运动补偿重建算法的评估，这种 X 射线模拟将大大减少计算时间。
