Multi-volume visualization for interactive therapy planning

During the past decade, various volume visualization techniques have been developed for different purposes, and many of them, such as direct volume rendering, maximum intensity projection and non-photorealistic rendering, have been implemented on consumer graphics hardware for real time visualization. However, effective multi-volume visualization, a way to establish the visual connections between two or more types of data, has not been adequately addressed even though it has wide applications in medical imaging and numerical simulation based on 3D physical model. In this paper, we aim to develop an effective GPU-based system for multi-volume visualization which is able to reveal both the connections and distinctions among multiple volume data. To address the main challenge for multi-volume visualization on how to establish the visual correspondences while maintaining the distinctive information among multiple volumes, a multi-level distinction mechanism is developed including 2D transfer function, mixed rendering modes, and volume clipping. Taking advantage of the fast hardware-supported processing capabilities, the system is implemented based on the GPU programming. Several advanced volume rendering techniques based on segmented volume are also implemented. The resulting visualization is a highly interactive image fusion system with high quality image and three-level volume distinction. We demonstrate the effectiveness of our system with a case study in which the heat effect on brain tumor, represented as a temperature volume resulting from high intensity focused ultrasound beam exposure over time, is visualized in the context of a MRI head volume.