Direct volume rendering has become an essential tool to explore and analyse 3D medical images. Despite several advances in the field, it remains a challenge to produce an image that highlights the anatomy of interest, avoids occlusion of important structures, provides an intuitive perception of shape and depth while retaining sufficient contextual information. Although the computer graphics community has proposed several solutions to address specific visualization problems, the medical imaging community still lacks a general volume rendering implementation that can address a wide variety of visualization use cases while avoiding complexity. In this paper, we propose a new open source framework called the Programmable Ray Integration Shading Model, or PRISM, that implements a complete GPU ray-casting solution where critical parts of the ray integration algorithm can be replaced to produce new volume rendering effects. A graphical user interface allows clinical users to easily experiment with pre-existing rendering effect building blocks drawn from an open database. For programmers, the interface enables real-time editing of the code inside the blocks. We show that in its default mode, the PRISM framework produces images very similar to those produced by a widely-adopted direct volume rendering implementation in VTK at comparable frame rates. More importantly, we demonstrate the flexibility of the framework by showing how several volume rendering techniques can be implemented in PRISM with no more than a few lines of code. Finally, we demonstrate the simplicity of our system in a usability study with 5 medical imaging expert subjects who have none or little experience with volume rendering. The PRISM framework has the potential to greatly accelerate development of volume rendering for medical applications by promoting sharing and enabling faster development iterations and easier collaboration between engineers and clinical personnel.
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机译：直接体积渲染已成为探索和分析3D医学图像的重要工具。尽管在该领域取得了一些进展，但要产生突出感兴趣的解剖结构，避免重要结构的遮挡，提供形状和深度的直观感知并同时保留足够的上下文信息的图像仍然是一个挑战。尽管计算机图形学界已经提出了解决特定可视化问题的几种解决方案，但是医学影像学界仍然缺乏一种通用的体绘制方法，该实现可以解决各种各样的可视化用例，同时又避免了复杂性。在本文中，我们提出了一个名为Programmable Ray Integration Shading Model（PRISM）的新开源框架，该框架实现了完整的GPU射线投射解决方案，在该解决方案中，可以替换射线整合算法的关键部分以产生新的体绘制效果。图形用户界面使临床用户可以轻松地尝试从开放数据库中提取的渲染效果构建块。对于程序员而言，该接口可对块内的代码进行实时编辑。我们显示，在其默认模式下，PRISM框架以可比的帧速率生成的图像与VTK中广泛采用的直接体积渲染实现所产生的图像非常相似。更重要的是，我们通过展示如何用不超过几行代码的方式在PRISM中实现几种体积渲染技术来展示该框架的灵活性。最后，我们在可用性研究中展示了我们系统的简单性，该研究由5位没有或几乎没有体绘制经验的医学影像专家组成。 PRISM框架通过促进共享并实现更快的开发迭代和工程师与临床人员之间更轻松的协作，具有极大地加速医疗应用体绘制的开发的潜力。
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