A multidimensional image navigation and display software was designed for display and interpretation of large sets of multidimensional and multimodality images such as combined PET-CT studies. The software is developed in Objective-C on a Macintosh platform under the MacOS X operating system using the GNUstep development environment. It also benefits from the extremely fast and optimized 3D graphic capabilities of the OpenGL graphic standard widely used for computer games optimized for taking advantage of any hardware graphic accelerator boards available. In the design of the software special attention was given to adapt the user interface to the specific and complex tasks of navigating through large sets of image data. An interactive jog-wheel device widely used in the video and movie industry was implemented to allow users to navigate in the different dimensions of an image set much faster than with a traditional mouse or on-screen cursors and sliders. The program can easily be adapted for very specific tasks that require a limited number of functions, by adding and removing tools from the program's toolbar and avoiding an overwhelming number of unnecessary tools and functions. The processing and image rendering tools of the software are based on the open-source libraries ITK and VTK. This ensures that all new developments in image processing that could emerge from other academic institutions using these libraries can be directly ported to the OsiriX program. OsiriX is provided free of charge under the GNU open-source licensing agreement at http://homepage.mac.com/rossetantoine/osirix.

The display and interpretation of images obtained by combining three-dimensional data acquired with two different modalities (eg, positron emission tomography and computed tomography) in the same subject require complex software tools that allow the user to adjust the image parameters. With the current fast imaging systems, it is possible to acquire dynamic images of the beating heart, which add a fourth dimension of visual information-the temporal dimension. Moreover, images acquired at different points during the transit of a contrast agent or during different functional phases add a fifth dimension-functional data. To facilitate real-time image navigation in the resultant large multidimensional image data sets, the authors developed a Digital Imaging and Communications in Medicine-compliant software program. The open-source software, called OsiriX, allows the user to navigate through multidimensional image series while adjusting the blending of images from different modalities, image contrast and intensity, and the rate of cine display of dynamic images. The software is available for free download at http://homepage.mac.com/rossetantoine/osirix.

The field of medicine is often cited as an area for which content-based visual retrieval holds considerable promise. To date, very few visual image retrieval systems have been used in clinical practice; the first applications of image retrieval systems in medicine are currently being developed to complement conventional text-based searches. An image retrieval system was developed and integrated into a radiology teaching file system, and the performance of the retrieval system was evaluated, with use of query topics that represent the teaching database well, against a standard of reference generated by a radiologist. The results of this evaluation indicate that content-based image retrieval has the potential to become an important technology for the field of radiology, not only in research, but in teaching and diagnostics as well. However, acceptance of this technology in the clinical domain will require identification and implementation of clinical applications that use content-based access mechanisms, necessitating close cooperation between medical practitioners and medical computer scientists. Nevertheless, content-based image retrieval has the potential to become an important technology for radiology practice.

Purpose Open source software (oss) development for medical imaging enables collaboration of individuals and groups to produce high-quality tools that meet user needs. This process is reviewed and illustrated with OsiriX, a fast DICOM viewer program for the Apple Macintosh. Materials and methods OsiriX is an oss for the Apple Macintosh under Mac OS X v10.4 or higher specifically designed for navigation and visualization of multimodality and multidimensional images: 2D Viewer, 3D Viewer, 4D Viewer (3D series with temporal dimension, for example: Cardiac-CT) and 5D Viewer (3D series with temporal and functional dimensions, for example: Cardiac-PET-CT). The 3D Viewer offers all modern rendering modes: multiplanar reconstruction, surface rendering, volume rendering and maximum Intensity projection. All these modes support 4D data and are able to produce image fusion between two different series (for example: PET-CT). OsiriX was developed using the Apple Xcode development environment and Cocoa framework as both a DICOM PACS workstation for medical imaging and an image processing software package for medical research (radiology and nuclear imaging), functional imaging, 3D imaging, confocal microscopy and molecular imaging. ResultsOsiriX is an open source program by Antoine Rosset, a radiologist and software developer, was designed specifically for the needs of advanced imaging modalities. The software program turns an Apple

Advances in anatomical informatics, three-dimensional (3D) modeling, and virtual reality (VR) methods have made computer-based structural visualization a practical tool for education. In this article, the authors describe streamlined methods for producing VR "learning objects," standardized interactive software modules for anatomical sciences education, from newer high-resolution clinical imaging systems data. The key program is OsiriX, a free radiological image processing workstation software capable of directly reformatting and rendering volumetric 3D images. The transformed image arrays are then directly loaded into a commercial VR program to produce a variety of learning objects. Multiple types or "dimensions" of anatomical information can be embedded in these objects to provide different kinds of functions, including interactive atlases, examination questions, and complex, multistructure presentations. The use of clinical imaging data and workstation software speeds up the production of VR simulations, compared with reconstruction-based modeling from segmented cadaver cross-sections, while providing useful examples of normal structural variation and pathological anatomy.