MRIcroGL is a simple program for rendering Analyze and NIfTI format images. The program can open Analyze-style images (.hdr and .img pairs, common with SPM users) as well NIfTI .nii and compressed NIfTI .nii.gz files (common with FSL users). This program is open source freeware, but is not intended for professional use. Click here to download the program, sample images and source code (if you want to compile your own version, you will need Delphi and GLScene).

Watch the sample video.

• You can rotate the object by clicking and dragging on the image.
• To adjust contrast right-drag over the image.
• The menus also allow you to adjust the rendering. Here are some of the shortcuts for menu commands and their function:
• Ctrl-O opens an Analyze or NIfTI format image (or simply drag-and-drop).
• Ctrl-F shows or hides the surrounding frame (shown as red-green cube in some images shown on below).
• Ctrl-B Adjusts the background color.
• Ctrl-X shows the Cutout window that allows you to remove a sector.
• Ctrl-A shows top axial view (Ctrl-Alt-A shows bottom axial view).
• Ctrl-C shows anterior coronal view (Ctrl-Alt-C shows posterior coronal view view).
• Ctrl-S shows left Sagittal view (Ctrl-Alt-S shows right Sagittal view).
• Ctrl-R Begins clockwise rotation animation (Ctrl-Alt-R shows counter-clockwise rotation). Click on the screen or press Control-R again to stop the animation.
• Ctrl-Z Zooms-in to enlarge the object (Ctrl-Alt-Z zooms-out).
• Ctrl-I opens the illumination window that allows you to interactively adjust image contrast, brightness and transparency.

• This software requires the OpenGL GL_TEXTURE_3D extension. Typically, the level of OpenGL support is limited by your graphics card. Some laptop computers allow you to switch between two graphics cards - for example with some Sony laptops MRIcroGL will run on 'Speed' mode but not on 'Stamina' mode. The speed of volume rendering is largely determined by the number of texture units. For comparison, a GeForce 8400M GS provides ~6 frames per second, a GeForce 8500 GT yields 17 fps, while the GeForce 9800 GTX and Radeon HD 4850 both offer ~65 fps. To determine the number of texture units, check the Wikipedia pages for Radeon, GeForce, and Intel Graphics Media Accelerator cards. One disadvantage of Radeon cards (relative to GeForce cards) is that they are much faster at rendering some views than others, so during realtime animations the rotation speed may appear to speed up and slow down (see Weiskopf et al., IEEE CGI (2004), 604-607) .

• License: Chris Rorden's MRIcroGL, copyright 2008, all rights reserved. Redistribution and use in binary forms, with or without modification, are permitted provided inclusion of the copyright notice, this list of conditions and the following disclaimer is provided with the distribution: Neither the name of the copyright owner nor the name of this project (MRIcroGL) may be used to endorse or promote products derived from this software without specific prior written permission.This software is provided by the copyright holder "as is" and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. In no event shall the copyright owner be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.
• The download includes versions for Windows (mricrogl.exe) and 32-bit Linux (with the files mricrogl_gtk and mricrogl_gtk2 requiring GTK1 and GTK2, respectively). The Linux versions may also work on 64-bit Linux systems if you install ia32libs. I hope to support OSX in the future.
• My rendering web page includes sample Analyze format images, links to other images and links to other volume rendering applications.
• MRIcroGL comes with a few sample images. There is a volume from the visible human project, as distributed with Ogle. The fMRI example uses the MCBI the single subject T1 image with activation maps from my lab, the CT is from the Chapel Hill Volume Rendering Test Dataset, and the T1, T2 and MRA are from my lab (courtesy of the McCausland Center for Brain Imaging .
• The quality of MRIcroGL's renderings are somewhat inferior to my MRIcron. I would be happy to hear any hints for improving the quality of the OpenGL renderings.
• This application is an extension of the GLscene Texture3D Demo, written by Jürgen Abel. His free MVE - Medical Volume Explorer also uses GLScene, but is much more sophisticated. His project inspired me.
• Most NIfTI programs can only read images where there is a single value per voxel (image intensity), in contrast MRIcroGL can read these images as well as RGB images which store red, green and blue intensities for every voxel. Other programs that can read RGB data are ImageJ, Jimmy Shen's Matlab NIfTI viewer and recent versions of MRIcron for Windows. However, only the latter program can read the compressed .nii.gz sample images that come with my software (you can drag-and-drop the images onto dcm2niigui to uncompress them).
• You can create RGB overlays that show activation maps by using recent versions of MRIcron for Windows. Simple load you you background scan using File/Open and then load your statistical maps using Overlay/Add. Then adjust the brightness and color schmemes and finally export the image using the Drawing/Advanced/ExportAsRGB command (if you do not see the 'Draw' menu, click Help/Preferences and check the 'Show drawing menu and tools' option). The resulting image can be viewed with MRIcroGL.