Direct volumetric visualization of medical datasets has important application in areas such as minimally-invasive therapies and surgical simulation. In popular fixed-slice-distance hardware-based volume rendering algorithms, such as 2D and 3D texture mapping, the non-isotropic nature of the volumetric medical images and the constantly changed viewing rays make it difficult to render medical datasets without disturbing or slicing artifacts during volume rotation. We have developed a hardware accelerated 3D medical image visualization system based on a commodity graphics unit, in which a viewing-direction based dynamic texture slice resampling scheme is descirbed and implemented on an Nvidia graphics processing unit (GPU). In our algorithm, we utilize graphics hardware to dynamically slice the volume texture according to the viewing directions during the rendering process, in which the slice number can be dynamically changed without consuming additional video memory. Near-uniform effective slice spacing can be achieved in real-time and updated as the viewing angles change, so improved uniform visual quality is achieved with high rendering performance. To further improve rendering efficiency, we have implemented a multi-resolution scheme within our rendering system, which offers the user the option to highlight the volume of interest (VOI) and render it with higher resolution than the surrounding structures. This system also incorporates a fragment-level interactive post-classification algorithm that modifies the texture directly within the texture unit on graphics card, making it possible to interactively change transfer function parameters and navigate medical datasets in real-time during the 3D medical image visualization process.