Medical professionals rely on medical imaging to help diagnose and treat patients. It is therefore important for them to be able to see all the details captured in the images. Often the use of contrast enhancement or noise reduction techniques are used to help improve the image quality. This paper introduces a real-time implementation of 3D Contrast Limited Adaptive Histogram Equalization (CLAHE) to enhance 3D medical image stacks, or volumes. This algorithm can be used interactively by medical doctors to help visualize the 3D medical volumes and prepare for surgery. It also introduces two novel extensions to the algorithm to allow a user to interactively decide on what region to focus the enhancement: Focused CLAHE and Masked CLAHE. Focused CLAHE applies the 3D CLAHE algorithm to a specified block of the entire medical volume and Masked CLAHE applies the algorithm to a selected organ or organs. These three contributions can be used, to not only help improve the visualization of 3D medical image stacks, but also to provide that contrast enhancement in real-time.