OsiriX: An Open-Source Software for Navigating in MultidimensionalDICOM Images

Antoine Rosset, MD, Luca Spadola, MD, and Osman Ratib, MD, PhD

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 soft-

ware is developed in Objective-C on a Macintosh

platform under the MacOS X operating system using

the GNUstep development environment. It also ben-

efits from the extremely fast and optimized 3D gra-

phic 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 func-

tions, by adding and removing tools from the pro-

grams 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 por-

ted to the OsiriX program. OsiriX is provided free of

charge under the GNU open-source licensing agree-

ment at http://homepage.mac.com/rossetantoine/

osirix.

KEY WORDS: DICOM viewer, 3D, image fusion, dy-

namic series, open-source software

THE RAPID EVOLUTION of digitalimaging techniques and the increasingnumber of multidimensional and multimodalitystudies constitute a challenge for PACS work-stations and image display programs. With the

improvement of spatial resolution of multi-detectors CT scanners and the emergence ofmultimodality exams like PET-CT1 or Cardiac-CT,2 traditional two-dimensional image viewersand image display programs are becomingunsuitable for interpretation of these large setsof images. For most tomographic imagingtechniques such as magnetic resonance imaging(MRI) and CT, the traditional 2D acquisitiontechnique of cross-sectional slices is evolvinginto 3D volume acquisitions with isotropic vo-xel sizes resulting in very large data sets. Theconventional way of reviewing these imagesslice-by-slice is too cumbersome for interpretingthe 800 to 1,000 slices that can be acquired withmulti-detector CT scanners. These large sets ofimages require additional image processing andreformatting to make them suitable for efcientand rapid image navigation and image inter-pretation. In most cases this can only beachieved on high-end dedicated 3D worksta-tions that can provide thick-slab maximumintensity projections (MIP), orthogonal andoblique multiplanar reformatting (MPR), and3D volume and surface rendering.3 These recentchanges in the acquisition modalities requireradiologists to use expensive dedicated 3D

From the Department of Radiology, University of Cali-

fornia Los Angeles, Los Angeles, California.

Correspondence to: Antoine Rosset, MD, UCLA -

Department of Radiology, David Geffen School of Medicine

at UCLA, B2-165 CHS, Mail code 172115, 10833 Le Conte

Avenue, Los Angeles, CA, 90095-1721, USA; e-mail: rosse-

tantoine@bluewin.ch

Copyright 2004 by SCAR (Society for ComputerApplications in Radiology)

Online publication 29 June 2004

doi: 10.1007/s10278-004-1014-6

Journal of Digital Imaging, Vol 17, No 3 (September), 2004: pp 205-216 205

processing workstations to properly interpretthese exams.4 Furthermore, access to thesevisualization and rendering tools is usuallylimited to high-end users in a radiologydepartment, preventing referring physicians,surgeons, and other care providers to benetfrom the extraordinary value of the multidi-mensional imaging techniques for decisionmaking and patient management In most casesstatic snapshots and preselected movie clipsmust be exported from the 3D processingworkstations to be distributed to other usersoutside of a radiology department.The goal of our project is to develop a com-

pletely new software platform that will allowusers to eciently and conveniently navigatethrough large sets of multidimentional datawithout the need for high-end expensive hard-ware or software. We also elected to developour system on new open-source software li-braries, thus by allowing the system to be easilyadaptable to a variety of hardware platforms.We also benet from our experience severalyears ago of having developed one of the rstfree DICOM viewers, OSIRIS, running onMacintosh and Windows personal comput-ers.5,6 The success and wide adoption of theOSIRIS software has encouraged us to extendour effort into a completely new program moresuitable for navigating through large multidi-mensional data sets. The name given to the newsoftware, OsiriX, marks the transition to acompletely new platform with the added Xindicating the migration to the new Macintoshoperating system version 10, also called MacOSX. The X also indicates the compatibility withunderlying Unix platform and the adoption ofthe open-source paradigm.In our design we also wanted to take

advantage of the signicant progress in perfor-mance and exibility of 3D animation on per-sonal computers mostly driven by the computergraphics and game industry. Most video gamestoday are developed on OpenGL14 graphic li-braries that benet from hardware accelerationand processing capabilities of todays ultra-fastvideo cards. Also, OpenGL, because it is anindustry standard, adapts automatically to anyhardware conguration and take advantage ofany hardware accelerator that is provided forvideo display of 2D and 3D data.

In the scientic community, new open-sourcelibraries have emerged for the visualization ofmultidimensional data. The VisualizationToolkit or VTK7 is a well-recognized andwidely adopted software library that runs onmultiple platforms and has been used fornumerous scientic and medical applications sofar. The recent adjunction of the Insight Seg-mentation and Registration Toolkit or ITK,8

mostly funded by the US National Library ofMedicine as part of the Visible Human Project,9

adds a wealth of additional rendering and im-age processing tools for medical applications.These new open-source software toolkits offerpowerful functions to do complex imagesmanipulations, and great performance for real-time 3D image visualization.With the introduction of more advanced im-

age processing and visualization functions,imaging software applications tend to becomemore complex and usually include numerousprocessing functions that are not necessarilyuseful for all users. Depending on the type ofimages being evaluated and the interpretationtask to be performed, most users would onlyuse a fraction of the tools or features of a typ-ical image processing and 3D visualizationprogram. The purpose of our project was toexplore new techniques that would allow easycustomization of the program for dierent usersand applications. Each user should be able tocustomize the software to include only thefunctions and tools needed for their specicpurposes.

METHODS, TECHNIQUES, AND RESULTS

The Open-Source Paradigm

The OsiriX software program is developed asa stand-alone application for the MacOS Xoperating system. It includes an image databasethat is updated automatically when new imagesare downloaded to a specic directory (Fig. 1).Images can either be pushed from the PACSusing a DICOM store function or they can bepulled by a DICOM query-retrieve functionof the program. Image les can also be manu-ally copied from off-line media or from othernetwork sources. The OsiriX software wasdeveloped based on an open architecture built

206 ROSSET ET AL

on existing open-source components as de-scribed in Figure 2. The main components arethese:

1. GNUstep / Cocoa10,11: an object-orientedand cross-platform framework for the devel-opment of the graphical user interface. Thisframework allows the user to quickly designand develop complex graphic user interfaces.It is distributed in open-source format underthe name of GNUstep. Cocoa is the namegiven by Apple Computer in the MacOS Xenvironment. It is developed in Objective-C

language.12 Objective-C is an object-orientedlanguage that has the benets of C++ butwithout its complexity. Objective-C languagealso provides powerful memory manage-ment: it uses a retain/release scheme. Itallows the user to automatically retain orrelease memory blocks. This prevents anyundesired memory hugs and memory over-ows (memory leaks) of the type that oftenoccur in the development of graphic pro-grams that manipulate large sets of imagedata. The open-source and cross-platformcompiler GNU Compiler Collection

Fig 1. Main window of the OsiriX program providing a listing of available images in the database (upper left corner) and sets of

thumbnail images of the different series (right panel), as well as a preview window of any selected sets of images (lower left

corner).

Fig 2. General architecture of the

OsiriX program showing some of

the open-source components and

libraries that were used.

OSIRIX 207

(GCC)13 is used to compile this Objective-Cframework.

2. OpenGL14: an industry standard graphiclibrary for 3D image visualization functions.OpenGL was originally developed by SGI(Silicon Graphics) under the name of IrixGLand was only available to high-end dedicatedUnix workstations that came with extremelyhigh price tags. With the evolution of the 3Dgames market, OpenGL has been adapted bygraphic boards manufacturers for the per-sonal computing market, dominated by twomain manufacturers: NVIDIA15 and ATI.16

All their graphic video boards are OpenGLcompatible. OpenGL allows the user to takeadvantage of hardware acceleration by 3Dgraphic cards when available. It is the onlytruly cross-platform 3D library availablethat is designed for hardware acceleration.It is currently available for Linux, IRIX,Windows, and MacOS X; there is even anOpenGL version for the Palm operatingsystem. OpenGL has been developed for3D rendering, but it also performs extremelywell in 2D rendering functions. On mostoperating systems 2D images are displayedfaster through OpenGL than by using thestandard graphic functions of the nativeoperating system. By adopting OpenGL,large sets of over 1000 CT slices can bedisplayed in a few seconds.

3. The Visualization Toolkit (VTK)7: anobject-oriented open-source and cross-plat-form library for 3D image processing andvisualization that is widely adopted in thescientic community. This toolkit offers alarge number of functions for the manipula-tion and display of 3D data sets. It is builtover OpenGL to ensure hardware acceler-ated rendering on different platforms. VTKoffers a complete set of functions for themanipulation and display of 3D data sets:multiplanar reconstruction (MPR), maxi-mum intensity projection (MIP), volumerendering with transparency, and surfacerendering with 2D or 3D texturing. VTKalso offers a complete set of function todisplay and modify 3D vectorial graphics: itallows the display and modication ofregion-of-interest as well as other measuresin 3D data sets. Finally, it fully supports all

the blending functions of OpenGL to easilycreate 3D image fusion between two differ-ent data sets. VTK is actually the only truecross-platform and hardware accelerated 3Drendering library for personal computers.Under open-source licensing, VTK is usedand developed by a large number of users,allowing its fast and robust evolution.

4. The Insight Segmentation and RegistrationToolkit (ITK)8 is an extended set oflibraries for specic medical image process-ing. It is an extension of the VTK library andis based on the same framework. It wasdeveloped to solve some of todays problemsin medical imaging such as image segmenta-tion and multimodality image registration. Itprovides a full set of 2D and 3D processingalgorithms adapted for these tasks. Thedifferent library components allow develop-ers to easily add image fusion and organssegmentation in image processing softwareprograms. This library is, like VTK, underactive open-source licensing and benetsfrom updates and improvements providedby a large number of users.

5. Papyrus toolkit17 for DICOM les man-agement (Fig. 1): This public domain librarydeveloped at the University of Geneva offersall the necessary functions to read and writeDICOM les including all meta-data. Thislibrary is distributed with the entire ANSIC18 source code, easily adaptable to anyplatform. It provides a complete set offunctions to manage the complex and cum-bersome DICOM image le format. It allowsfor the extraction of image data but also forall numeric and textual meta-data associatedto a DICOM le. The Papyrus toolkit is aconvenient extension to VTK and ITKlibraries.

6. DICOM Ofs19 for DICOM networkfunctions: This cross-platform library sup-ports the DICOM communication protocolsthat make it possible to query, send, retrieve,and receive DICOM images within a PACSnetwork. The complete C++ source code isalso available. This library provides a com-plete set of functions that greatly facilitatethe management and implementation of theextremely complex and convoluted DICOMnetwork protocol.

208 ROSSET ET AL

7. Altivec of PowerPC20 is a low-level assem-bly function for accelerating digital signalprocessing (DSP) functions. Because ourgoal is to provide the maximum level ofacceptability and adoption by the users, wehave emphasized the need for high perfor-mance and real time interaction. To achievethe best performance, we adopted Altivec asthe only platform-specic and non-open-source technology that is available only forPowerPC platforms. We used this assemblylanguage feature in very limited portions ofour program to accelerate key features suchas convolutions, image projections, andcomplex mathematical data conversions.We also wrote these functions in standardANSI C18 in order to compile the project onnon-PowerPC platforms. Altivec is a SingleInstruction, Multiple Data (SIMD) unit ofPowerPC processors. A SIMD system packsmultiple data elements into a single registerand performs the same calculation in all ofthem at the same time. It offers greatperformance when manipulating large setsof data such as 3D volume data. Onedisadvantage is the complexity of softwaredevelopment restricted to 128 bit registersfor all operations. However, the advantage isthe acceleration in performance of somefunctions by a factor of 10 or 20.

8. Quicktime21 for exchange of multimediaimage le formats. Many commercial DI-COM viewers or 3D workstations allow theusers to see and manipulate images, but theylack a convenient way to export the images tostandard multimedia le formats. This limitsthe ability to communicate the resultingimages to other users and applications. Tosupport the maximum possible number ofexisting image and graphic le formats inOsiriX, the cross-platform Quicktime librarywas used. It allows the export of any imagedata toall standardmultimedia image formatssuch as TIFF, Photoshop, JPEG, JPEG2000,andBMP22 and any image sequence tomoviesle formats such as AVI, MPEG, andMPEG4. Furthermore we also used theQuickTime library to enable importing ofnon-DICOM images into OsiriX, therebyallowing users to benet from the displayand processing tools provided in OsiriX.

An important and challenging aspect of thedevelopment of this project was to integrate allof these technologies. OpenGL, VTK, ITK,DICOM Os, Papyrus, and Quicktime are C/C++ cross-platform toolkits. These compo-nents were not designed to be fully compatible,and some inconsistencies and incompatibilitiesbetween header les or compiler ags made theintegration somewhat dicult and laborious.Once past the steep learning curve in assessingthe structure of the various components, themajor advantage of the integrated product isthe wealth of functions and features that areinvaluable for any software developer of medi-cal imaging applications.The most important aspect of the project is

that all the components function togetherwithin a simple and user-friendly graphic userinterface. To achieve the best possible userinterface design, we chose to develop the OsiriXprogram on a Macintosh platform to benetfrom its well-known user interface features andconvenience and ease of use. Additionally, thelatest development environment provided byApple greatly facilitates the rapid developmentof interactive graphic applications. The rstversion of OsiriX was developed in less than 6months including complex 2D and 3D func-tions, DICOM les, and network managementand multimedia le formats management. Oneof the key features of the latest Macintoshgraphic user interface is the ability to interac-tively add or delete some of the software fea-tures by simply dragging icons from aretractable palette (Fig. 3) to and from a win-dow toolbar. Each icon can represent a simpleprogram function or a complex processing tool.This feature alone offers a major advantageover other computer platforms, allowing easycustomization of the program adaptable todifferent users needs.

From Parallel Processing toGrid Computing

The OsiriX program oers all the basic imagemanipulation functions of zoom, pan, intensityadjustment, and ltering with real-time perfor-mance. Additional functions such as multipla-nar projection, convolution lters, variable slicethickness adjustments, volume rendering, min-

OSIRIX 209

imum and maximum intensity projections, andsurface rendering are also accessible in quasi-real-time, depending on the hardware used, aswell as on the number of slices to reconstruct.For example, on a dual-GS 2 GHz PowerMaccomputer, OsiriX can to render two images persecond of a 400 CT slices set in volume-ren-dering mode. All these basic functions beinghandled by the OpenGL library essentially relyon the processing capabilities of the videohardware and require very minimal processingfrom the central processor unit (CPU). In es-sence the most basic image manipulations areprocessed in parallel by the video graphic pro-cessor unit (GPU), and the performance there-fore does not depend on the computer processorunit (CPU).The program enables the rapid review of very

large sets of images and does not rely on pre-loading of the images from the disk to memorybefore review. As soon as an images serie isselected, images will automatically be displayed

on the screen in a cine loop using a streamingtechnique, enabling direct display of the imagesat a very rapid pace. For example, on a G41 GHz mobile PowerBook computer, OsiriX isable to completely load a 355 CT images seriesin less than 10 seconds (loading rate: 35 imagesper second) while displaying the rst image onthe screen in less than 1 second. This streamingtechnique allows for an unlimited number ofimage series to be displayed simultaneously inseparate windows. The software architecturewas tested on very large image series consistingof thousands of images without any limitations.The OsiriX program was developed and mainlytested on the following standard o-the-shelfcomputers: PowerPC G4 laptop from AppleComputer, running at 1.25 GHz with 768 MBof RAM, with a built-in original 64 MB graphicboard from ATI (ATI Mobility Radeon). Evenon this standard laptop, the basic imagemanipulations were extremely fast and per-formed in real time without noticeable delays in

Fig 3. Example of user interface customization allowing the user to drag and drop tools and functions represented by a list of

icons that can be added and removed from the tool bar.

210 ROSSET ET AL

response. For performance comparisons, wealso implemented the software on a PowerPCdual G5 processors desktop computer fromApple Computer, running at 2 GHz with 1 GBof RAM and with a 128 MB graphic boardfrom ATI (ATI Radeon 9600 Pro): perfor-mance was signicantly better on the dualprocessor unit, with sometimes up to a factor of610 faster performance for computer intensivetasks such as MIP and volume rendering,mostly due to the faster graphic board and dualprocessor architecture. The other basic func-tions of image manipulation and display such asintensity and contrast, zoom and pan, andnavigation through large image sets were notnoticeably dierent, as they are already fast inreal time on the standard laptop computer. Theprogram was also tested on lower end com-puters such as older generation laptops basedon 800 MHz G4 PowerPC and 512 Mb ofRAM, as well as a desktop 1.2 GHz G4 with1 Gb of memory. No perceivable dierence inperformance could be identied except formoderately-slower 3D rendering and maximumintensity projection functions. The OsiriX soft-ware is designed to be multithreading compli-ant, taking advantage of parallel processingcapabilities of multiprocessors when available.In particular, all graphics manipulations andrendering functions are tilled in separatethreads and distributed to each available pro-cessor when possible. The support of multi-processor architecture is seamless, performingparticularly well on the new generation of dualprocessor G5 computers: the HyperTransporttechnology developed by Apple23 greatlyaccelerates memory transfers from RAM toprocessors (up to 12.8 gigabytes/second). TheRAM to processor transfer is particularly crit-ical for all 3D medical imaging rendering tech-niques, and signicant improvement inperformance can be perceived on multiproces-sor platforms.Another potential improvement in perfor-

mance could be expected for very computa-tional-intensive image processing and renderingtechniques by using Grid Computing technol-ogy federating several networked computers.Grid Computing technology would allow mul-tiple computers to be networked to performcomplex processing tasks such as high-resolu-

tion volume rendering and surface rendering ofvery large data sets.

Navigating the Fifth Dimension

The development of this new DICOM viewerwas motivated by the necessity to a have a toolmore suitable for multidimensional and mul-timodality imaging studies such as PET-CT andultra-fast multidetector Cardiac-CT.24 Essen-tially these new imaging techniques provideimage data that are beyond the traditional 3Danatomical data. The combined PET-CT adds anew dimension to the data that represent themetabolic activity of the tracer, and blendingthis functional parameter represents a fourthdimension that the users need in order to nav-igate. The ultrafast multidetector CT scannerscan add a temporal dimension to the data bysequentially acquiring images over time to dis-play temporal behavior such as a beating heartor transit of a tracer or contrast agent across avascular tree or an organ. The newer generationof PET-CT scanners can now provide data setsthat represent all ve dimensions for cardiacPET-CT studies. We therefore designed oursoftware to allow users to interactively navigatein the ve dimensions.Although the software does not yet support

any realignment technique for images obtainedfrom dierent modalities, it does provide a verysimple and very intuitive way to generate fusedimages by blending two image sets that areprealigned. For image fusion, the user needs toselect and adjust a color scale for one of theimage sets that will be overlaid over anotherimage set. Both sets must be open at the sametime on the screen, and the fusion can be initi-ated simply by dragging and dropping the titlebar of the window containing the overlay image(PET for example) over the window of the basicimages (CT for example) as shown in Figure 4.The program will automatically generate a setof fused images by color blending the two imagesets. This new set is still fully synchronized withthe original images, and any changes in contrastor intensity in either of the two sets will be re-ected in the fused image set, allowing the userto adjust the best rendering setting of the fusedimage. The fused image set can also be manip-ulated like any other image data set, and image

OSIRIX 211

processing functions such as MIP rendering orMPR can be applied to the four-dimensionaldata (Fig 5).To facilitate and improve the navigation and

image manipulation functions in ve-dimensionexams, we explored innovative solutions usingadvanced joystick and multidimensional navi-gation devices that can be used in conjunctionwith the standard mouse and keyboard func-tions. We elected to use a special multipurposevideo editing jog-wheel device (Fig 6) that iswidely used by professional video editors. Thisallows rapid navigation in multiple data setsand multiple dimensions with a single hand.The addition of this low-cost pointing deviceincreases the ability of the user to navigate

rapidly and to switch among different functionsin real time.By using this jog-wheel device we were able to

develop an interactive graphic user interfacethat allows navigation in these ve dimensionsin all rendering modes: the classic 2D viewer,but also in MPR or volume rendering modes(Fig 7). The user is able at any time to move inany of the ve dimensions: for example it ispossible to modify the dynamic and the fusionparameters while navigating in a 3DMPR view.

DISCUSSION AND CONCLUSIONS

Radiology imaging modalities are evolvingfrom conventional sets of 2D tomographic sli-

Fig 4. Diagram showing the simple process used for image fusion. (1) The overlay image (PET image) is selected and (2) a color

scale is applied. (3) The image fusion is initiated by drag-and-drop of the PET window title bar over the CT window resulting in (4) a

fused image set obtained by color blending of the two original sets. The image fusion is instantaneous and the user can continue

to navigate through the whole set of fused images and apply any of the processing tools such as intensity and contrast adjust-

ment, slice thickness adjustment, MIP and MPR.

212 ROSSET ET AL

ces to 3D volumetric acquisition extending to afourth or fth dimension with temporal andfunctional data that can be acquired withultrafast CT and MR scanners with combinedPET/CT scanners. To allow radiologists andclinicians to conveniently and eciently inter-pret these large exam sets, traditional imageviewers have to be re-designed and tailored to anew paradigm of multidimensional image nav-igation visualization, and manipulation. Bycombining the performance of new hardwarecomponents and the wealth of existing open-source image processing and manipulationtools, it is now possible to develop a new gen-eration of high-performance multidimensionalimage viewers for o-the-shelf personal com-puters. These advanced navigation and visuali-zation tools were traditionally only accessibleon expensive dedicated 3D workstations,

thereby restricting their use to specialist radi-ologists. With easier access to these multidi-mensional navigation and visualization tools instandard personal computers, they should soonbecome complementary tools for routine inter-pretation of complex diagnostic studies.One of the key features of the OsiriX soft-

ware is its exible user interface allowing usersto customize the program by adding andremoving tools and functions from the tool barand menus of the program. This also allowsthe creation of customized versions of theprogram for specic groups of users. Userswho are not computer experts can adopt sim-pler versions of the software containing only alimited number of essential tools. Specializedversions of the program could be easily cus-tomized for specic medical specialties or forspecic clinical applications without the need

Fig 5. Example of maximum in-

tensity projection rendering of 4-

dimensional data obtained by fusion

of PET and CT image sets.

OSIRIX 213

for any additional programming or softwaredevelopment.The multithreading ability of the software

that allows OsiriX to take full advantage ofmultiprocessor computers ensures a scalabilityof performance that can be expected from fu-ture generation computers. The same softwarearchitecture will also allow a migration towardthe emerging technology of Grid Computing.With Grid Computing technology

, 26 it is pos-sible to signicantly enhance image processingperformance by using clusters of computers.The grid technology is already used for large 3Dvirtual reality software applications to greatlyaccelerate the rendering time. In the computeranimation movie industry, including PIXAR27

and other industry leaders, Grid Computingtechnology has taken a prominent role. Most of

the rendering is performed based on clusters ofcomputers. Grid Computing is also usedextensively in large multicentric bioinformaticprojects for genome analysis.

, 29 We anticipatethat Grid Computing technology could signi-cantly improve the performance of 3D medicalimaging rendering techniques. The VTK libraryalready supports Grid Computing renderingthrough the open-source and cross-platformstandard Message Passing Interface (MPI).30

Apple Computer recently announced a newtechnology, X-Grid,31 that will facilitate themanagement and conguration of large clustersof computers. With the X-Grid technology itwill be easy to connect all computers of aradiology department to share complex pro-cessing and rendering tasks during processoridle time. In large academic radiology depart-

Fig 6. Integration of a video-editing jog wheel device allowing the users to rapidly navigate through multidimensional data sets.

The upper buttons above the jog wheel are used to select the data dimension of the navigation function that the jog wheel applies

to. The user can therefore rapidly change from 3D navigation to slice thickness adjustment to contrast and intensity adjustment

without having to use on screen cursors or sliders.

214 ROSSET ET AL

ments it is common to have a relatively largenumber of computers that are only partiallyused and remain idle for signicant amounts oftime. The Grid Computing technology makes itpossible to take advantage of idle computertime for performing computational intensivetasks needed for 3D rendering applicationsacross the network. By adopting the X-Gridtechnology, OsiriX, which is already multi-thread compliant, could benet from a signi-cant improvement in performance if used in anetwork of multiple computers.OsiriX is distributed freely as open-source

software under the GNU licensing scheme atthe following Web site: http://homepage.mac.com/rossetantoine/osirix.

REFERENCES

1. Voge, WV, Oyen, WJ, Barentsz, JO, et al: PET/CT:

panacea, redundancy, or something in between? J Nucl Med

45(Suppl 1):15S-24S, 2004

2. Flohr, T, Ohnesorge, B, Bruder, H, et al: Image recon-

struction and performance evaluation for ECG-gated spiral

scanningwitha16-sliceCTsystem.MedPhys. 30:2650-2662, 2003

3. Salgado, R, Mulkens, T, Bellinck, P, et al: Volume

rendering in clinical practice, a pictorial review. JBR-BTR

86(4):215-220, 2003

4. Kirchgeorg, MA, Prokop, M: Increasing spiral CT

benets with postprocessing applications. Review. Eur J

Radiol 28:39-54, 1998

5. Ligier, Y, Funk, M, Ratib, O, et al: The OSIRIS user

interface for manipulating medical images In: Spring-Ver-

lag. Picture archiving and communication system (PACS) in

medicine. Evian: NATO ASI Series Springer-Verlag, Berlin,

Heidelberg, 1991, pp 395-399

Fig 7. Example of three dimensional multiplanar reformatting (MPR) showing the real-time navigation panel on the right

allowing the user to easily navigate and position the selected reformatted slice shown in the main window. The example here

shows 4-dimensional data obtained by fusion of PET and CT data.

OSIRIX 215

6. Ratib, O, Ligier, Y, Mascarini, C, et al: Multimedia

image and data navigation workstation. RadioGraphics

17:515-521, 1997

7. The Visualization Toolkit (VTK): http://public.kit-

ware.com/VTK/, Accessed February 20, 2004

8. The Insight Segmentation and Registration Toolkit

(ITK): http://itk.org/, Accessed February 20, 2004

9. Ackerman, MJ, Yoo, TS: The Visible Human Data

Sets (VHD) and Insight Toolkit (ITK): Experiments in

Open Source Software. Proc AMIA Symp. 773, 2003

10. GNUstep Framework: http://www.gnustep.org/, Ac-

cessed February 20, 2004

11. Cocoa Framework: http://developer.apple.com/, Ac-

cessed February 20, 2004

12. Objective-C language; http://theory.uwinnipeg.ca/

gnu/libobjects/objective-c_toc.html, Accessed February 20,

2004

13. GNU GCC Compiler. http://gcc.gnu.org, Accessed

February 20, 2004

14. OpenGL: http://opengl.org, Accessed February 20,

2004

15. NVIDIA, Inc., Company: http://www.nvidia.com,

Accessed February 20, 2004

16. ATI, Inc., Company; http://www.ati.com, Accessed

February 20, 2004

17. Papyrus Toolkit, Digital Imaging Unit, Geneva

University Hospital: http://www.expasy.ch/UIN/html1/

projects/papyrus/papyrus.html, Accessed January 10, 2004

18. ANSI C: American National Standard for Informa-

tion. http://www.lysator.liu.se/c/rat/title.html, Accessed

January 10, 2004

19. DICOM Ofs Toolkit: http://dicom.ofs.de, Ac-

cessed January 10, 2004

20. Altivec / PowerPC: http://www.ibm.com/powerpc,

Accessed January 10, 2004

21. Quicktime. Apple Computer: http://www.quick-

time.com, Accessed February 20, 2004

22. Wiggins, RH, Davidson, C, Harnsberger, R: Image

File Formats: Past, Present, and Future. Radiographics

21:789-798, 2001

23. HyperTransport: http://www.hypertransport.org/,

Accessed February 20, 2004

24. Saito, K, Saito, M, Komatu, S, et al: Real-time four-

dimensional imaging of the heart with multi-detector row

CT. Radiographics 23:E8-8, 2003

25. Grid Computing: http://www.gridcomputing.com/,

Accessed February 20, 2004

26. Avery, P: Data grids: a new computational infra-

structure for data-intensive science. Philos Transact Ser A

Math Phys Eng Sci 15;360:1191-1209, 2002

27. Pixar Company: http://www.pixar.com, Accessed

February 20, 2004

28. Rowe, A, Kalaitzopoulos, D, Osmond, M, et al: The

discovery net system for high throughput bioinformatics.

Bioinformatics 19(Suppl 1):1225-1231, 2003

29. Cummings, L, Riley, L, Black, L, et al: Genomic

BLAST: custom-dened virtual databases for complete and

unnishedgenomes.FEMSMicrobiolLett 216:133-138, 2002

30. Message Passing Interface: http://www.lam-mpi.org/,

Accessed February 20, 2004

31. X-Grid: http://www.apple.com/acg/xgrid, Accessed

February 20, 2004

216 ROSSET ET AL