Direct volume rendering is a key technique for the visualization of medical image data. It allows to display the image data as acquired by a CT or MRI in a three dimensional rendering without the need for segmentation and mesh creation. Since it displays all the available data in the volumetric data depending on a transfer function, it offers more context than mesh based visualization. Advanced techniques, such as Path Tracing, allow to simulate realistic lighting and shadowing, but often suffer from low frame rates, image noise or other restrictions with regard to interactive changes of the camera, clipping planes, or the transfer function.