J. Anat.

(2007)

211

, pp399–406 doi: 10.1111/j.1469-7580.2007.00770.x

© 2007 The Authors Journal compilation © 2007 Anatomical Society of Great Britain and Ireland

Blackwell Publishing Ltd

METHODS

Volume rendering based on magnetic resonance imaging: advances in understanding the three-dimensional anatomy of the human knee

Giuseppe Anastasi,

1

Placido Bramanti,

2

Paolo Di Bella,

2

Angelo Favaloro,

1

Fabio Trimarchi,

1

Ludovico Magaudda,

1

Michele Gaeta,

3

Emanuele Scribano,

3

Daniele Bruschetta

1

and Demetrio Milardi

1

1

Department of Biomorphology and Biotechnologies, School of Medicine, University of Messina, Italy

2

IRCCS Centro Neurolesi ‘Bonino-Pulejo’, Messina, Italy

3

Department of Radiology, School of Medicine, University of Messina, Italy

Abstract

The choice of medical imaging techniques, for the purpose of the present work aimed at studying the anatomy ofthe knee, derives from the increasing use of images in diagnostics, research and teaching, and the subsequentimportance that these methods are gaining within the scientific community. Medical systems using virtual realitytechniques also offer a good alternative to traditional methods, and are considered among the most importanttools in the areas of research and teaching. In our work we have shown some possible uses of three-dimensionalimaging for the study of the morphology of the normal human knee, and its clinical applications. We used thedirect volume rendering technique, and created a data set of images and animations to allow us to visualize thesingle structures of the human knee in three dimensions. Direct volume rendering makes use of specific algorithmsto transform conventional two-dimensional magnetic resonance imaging sets of slices into see-through volumedata set images. It is a technique which does not require the construction of intermediate geometric representations,and has the advantage of allowing the visualization of a single image of the full data set, using semi-transparentmapping. Digital images of human structures, and in particular of the knee, offer important information aboutanatomical structures and their relationships, and are of great value in the planning of surgical procedures. On thisbasis we studied seven volunteers with an average age of 25 years, who underwent magnetic resonance imaging.After elaboration of the data through post-processing, we analysed the structure of the knee in detail. The aim ofour investigation was the three-dimensional image, in order to comprehend better the interactions betweenanatomical structures. We believe that these results, applied to living subjects, widen the frontiers in the areas ofteaching, diagnostics, therapy and scientific research.

Key words

direct volume rendering; knee; MRI.

Introduction

The two last decades have seen great advances in medicalsystems for the acquisition of images of organs and innerstructures, and for their elaboration in three dimensions(Higgins et al. 1998; Ratib et al. 2000), with application tovarious clinical and surgical disciplines. For example,digital processing in three dimensions can be used insurgical simulations (Vannier et al. 1984; Nilsson et al. 2004),e.g. the virtual reality (VR) arthroscopic knee simulator

(Mabrey et al. 2002), and in anatomical studies of livingsubjects (Fishman et al. 1988; Spitzer & Whitlock, 1998),e.g. QuickTime VR features that can be used to producephotorealistic, interactive ‘non-linear movies’ of anatomicalstructures ranging in size from microscopic to grossanatomic (Trelease et al. 2000). A further example isrepresented by a mechatronic system that provides visual,acoustic and haptic (force) feedback so that it allows a userto touch and move a virtual shank, bones or muscleswithin the leg, and simultaneously observe the generatedmovement (Riener et al. 2001), without the need to usecadavers for dissection, with all the related legal problemsthat concern this practice. Using these techniques todaywe are able to extract images with better detail thancan be seen on images derived using more traditionalmethods, and this can help specialists to reach a correct

Correspondence

Dr G. Anastasi, Department of Biomorphology and Biotechnologies, School of Medicine, University of Messina, Italy. E: demil74@alice.it

Accepted for publication

3 April 2007

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diagnosis and to plan surgical operations better. Three-dimensional (3D) volume rendering has the potential tosimplify standard radiological study (Fishman et al. 1987).In fact, although a two-dimensional (2D) image seriesallows a radiologist of moderate skill to draw all thenecessary conclusions, 3D visualization has many advant-ages. Three-dimensional volume rendering immediately(in real time) generates accurate images from the full dataset, allowing radiologists and clinicians to make a correctdiagnosis. In our work we apply a texture-based volumerendering approach that achieves the image quality ofthe best post-shading approaches with fewer slices, providinghigh-quality images even with low-resolution volume dataand non-linear transfer functions with high frequencies. Itis especially useful for the representation of volumetriceffects, and particularly in professional scientific volumevisualization. With the volume rendering of the kneepresented here, we wish to highlight the capabilities ofthis new technique, demonstrating that the images obtainedby 3D volume-based methods appear more realistic, withhigh-quality detail and without the common limitations ofother graphical reconstruction techniques. Indeed, thisnew technique has fewer limitations than surface rendering,in which, during the reconstruction procedure, specklesproduce artefacts due to the loss of information. Further-more, with surface rendering and binary voxels, it is notpossible to visualize small, ill-defined elements because abinary classification of data is performed prior to surfacerendering. In conclusion, 3D computed tomography (CT)acquisition produces higher noise and lower-grade 3Drenderings than 3D magnetic resonance imaging (MRI)renderings that are based on less noisy standard reconstruc-tion algorithms (Pelc & Beaulieu, 2001). Today it is possibleto utilize a modern method that uses a normalizedcross-correlation (NCC) algorithm to register serial MRimages of the knee joint with subvoxel precision. Thismethod would be useful for a precise assessment oftherapeutic response and the monitoring of knee jointdiseases (Takao et al. 2005). We used high-quality 3Dgraphic software that is able to give both voxel opacityand colour properties (colourmap) relative to the tissueexamined. This integrated system is proving to be anextremely useful tool in highlighting anatomical morpho-logies and correlated diseases. The original MRI data wereconverted and interpolated, and 3D regions of interestwere cropped for further visualization on a normalcomputer screen, with the possibility of zooming in andout, translating and rotating (Fishman et al. 1987). Theaim of the study was to highlight not only the knee jointbut all the fine details of the structures that compose it,giving us the opportunity to find pathological elementsthat are not usually visualized with a normal MRI; of greatimportance is the attribution of colours resembling thenatural anatomical appearance as seen, for example,during surgery. We have modified the parameters of the

graphics software, obtaining fine details of the images,in order to pursue our aim of applying this technique tothe human brain, although it is necessary to calibrate theparameters further based on our initial results. For medicalstudents it is important to study anatomy not only fromthe large variety of available textbooks and atlases butalso on real corpses, which is often difficult, including atour faculty, due to legal and logistical problems. For theabove reasons volume rendering should be used to com-plement the knowledge gained from dissection; further-more, it is an irreplaceable method for learning structuralrelationships in three dimensions. We have already startedto teach anatomy using 3D volume rendering and studentparticipation is growing, with students paying moreattention during class. Moreover, this method could be away of presenting volumetric data and may enable non-invasive diagnostic endoscopy to be used as an alternativemethod for analysing volumetric imaging data for prelimi-nary diagnosis (Rubin et al. 1996). With the collaboration ofother hospitals it is possible to create a collection of all theimages of the human body, creating a human atlas data setthat can be used for the comparison of pathologicalimages. In the future, with the evolution of computerhardware and software, and with the adaptation ofcolour, opacity, depth, weight parameters, etc., of theimages, we will be able to provide higher quality descriptivedetails, as we have recently done with the brain, highlighting,for example, the lateral ventricles, which have not beensuccessfully picked out by any other graphic techniqueuntil now. Other authors have just created a prototype ofan interactive digital brain atlas using the Visible HumanProject data set. Their atlas, as a graphical user interface,allows user interaction with 3D representations of thewhole brain, displaying multiple images simultaneously(Toh et al. 1996). We are also creating a data set of high-quality digital images of the entire human body. Thereconstructions created using volume rendering are moreaccurate and easier to calculate than those based onsurface rendering. Virtual endoscopy, for example (in thetransparent mode), permits visualization of hard-to-reachstructures outside the ventricular system, such as the basilarartery tip. Transparent 3D images of the ventricles providea good overview of the exemplified structures, not includingthe performance overhead caused by rendering additionalslices, also being useful to neurosurgical interventionalendoscopy. Virtual MR endoscopy can be employed forpreoperative use, simplifying endoscopy planning with afine visualization of the anatomical structures (Lemkeet al. 2004).

Materials and methods

Seven healthy 20- to 35-year-old volunteers (five male,two female with no medical history of pathologies) signedconsent forms and underwent MRI of the knee using a

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Siemens Sonata magnet of 1.5 T (Magnetom Sonata,Siemens, Erlangen, Germany). For examination of thecartilage we used a Sonata Siemens magnet, obtaining 3DDESS (three-dimensional double-echo steady state)sequences; sagittal, coronal, transverse and oblique coronalmultiplanar reconstruction images were reformatted fromMRI and acquired by 1 SLAB with 1.50-mm slices. Thesequence is characterized by a TR of 17.81 ms, a TE of5.11 ms, flip angle 25%, slice thickness 1.5 mm, voxel size0.6

×

0.6

×

1.5 mm, and distance factor 20%.The volumedata set was 10.3 MB and the base resolution of thesequence is 256 d.p.i. For the other images of the knee weused TSE-T2 weighted (turbo-spin-echo images) in 512 d.p.i.(volume data set: 13.6 MB); voxel size, 0.6

×

0.3

×

4 mm;echo train length, 11; section thickness, 1.5 mm; field ofview, 12.75 cm; image matrix, 384

×

384; bandwidth,75.8 kHz; section-selection and refocusing-pulse duration,2 ms; signal acquisition, 2; total acquisition time, 21 min.The digital MRI data were acquired in pixel resolutions ofeither 256

×

256 or 512

×

512 in 16 bits of grey, convertedin 8 bits of grey TIFF files and imported into the volumerendering software for further processing. For the renderingprocess we used Volview 2.0 graphic software (KitwareInc., USA); this is a volume rendering system that enablesresearchers to visualize data from a variety of imagingmodalities including CT, MRI, fMRI and confocal microscopy,and it can be interfaced with a variety of hardware andsoftware systems, including accelerated OpenGL texturing,on a workstation equipped with a real-time 3D volumerendering board (RTViz VolumePro 500, Real Time Visuali-zation, MA, USA) offering multi-threaded parallel renderingsupport for a variety of data file formats such as BITMAP,PNM, TIFF, basic DICOM, RAW data and volume formats.We modified the parameter for visualization, modulating– with the use of the above-mentioned software – thesefunctions: scalar opacity mapping, scalar colour mappingand gradient colour mapping, associating each voxel witha colour and partial opacity and blending them.

Results

Applying our volume rendering algorithm, we obtainedimages that allowed us to study all the structures of theknee region. In particular, in order to examine the struc-ture of the subcutaneous tissues of the medial side of thetested region first, we applied parameters that enable thesuperficial regions to be highlighted, e.g. the superficialvessels such as the great saphenous vein, which runs up themedial side of the front of the thigh (Fig. 1). By cropping,rotating and changing the transparency of the 3D image,we can highlight the femur, tibia and fibula and alsovisualize the nearby muscles as well as the adipose tissue.

With regard to the femur, it is possible to show clearlythe surface of the distal extremity, which articulates withthe head of the tibia (Fig. 2, see supplementary Animation

S1 online). In addition, in the context of the femur, thearticular cartilage is shown. We were also able to visualizethe adipose tissue and the quadriceps femoris in front ofthe femur. In sagittal view, we modified the parameters in

Fig. 1 Computerized three-dimensional reconstruction of the right knee region of a human female (34 years old) with direct volume rendering from sagittal MRI: shading parameters, weighting of the various components and colour and opacity properties have been applied for visualizing the great saphenous vein and other superficial vessels.

Fig. 2 Computerized three-dimensional reconstruction of the left knee region of a human male (28 years old) with direct volume rendering from sagittal MRI: the femur, tibia and fibula have been highlighted.

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order to highlight different anatomical structures of theknee joint (Fig. 3). In particular, on the anterior surface ofthe knee we observed the skin, which is thinner where itsurrounds the patella, whereas it is thicker above andbelow it. It is possible to observe the same behaviour forthe subcutaneous tissue. Depth detail showed the patellaand patellar ligament, which appeared as a thick lamina,which is stretched between the patella and tuberosity ofthe tibia. In more detail still, it is possible to show theposterior cruciate ligament, and the articular capsule. Inthis image we also visualized the superficial and deepprepatellaris bursae of the knee joint. With regard to muscle,it is possible to observe, with these parameters and in thissection, the medial head of the gastrocnemius, on theback of the femur, and the biceps femoris above it. Thevascular structures are also visible in this image. In particular,it is possible to illustrate the popliteal artery, which runsthrough the popliteal fossa. In Fig. 4 we highlight thetopography of the insertion tendon of the semitendinosus,which can br better distinguished in a more superficialsection. It originates from the medial margin and dorsalsurface of the tibia. The popliteal tendon bursa is evident

behind this tendon. Furthermore, the medial meniscus andthe articular capsule around the distal extremity of thefemur are visualized. Coming down in depth and removingthe closer structures, it is possible to highlight the anteriorcruciate ligament (Fig. 5a). An ulterior sagittal projectionreveals the entire extension of the posterior cruciateligament (Fig. 5b). Furthermore, we extracted an imagefrom a DESS (steady state) sequence of an MRI analysis ina sagittal section (Fig. 6) to demonstrate the morphologyof the articular cartilage in a single section only, which alsohighlights the quadriceps tendon, the patellar articularcartilage, Hoffa’s fat pad, the patella and gastrocnemiusmuscle. Applying the 3D volume rendering on the DESSsequence of the MRI, we are able to show articular cartilagein 3D total view, as the bone structures of the distalextremity of the femur were transparent through the

Fig. 3 Highlighting of the left knee of a human male (28 years old) showing anatomical detail.

Fig. 5 The anterior cruciate ligament (a) and extension of posterior cruciate ligament (b) of the left knee of a human male (29 years old).

Fig. 4 With the same technique parameters we are able to visualize the tendon of insertion of the semitendinosus of the left knee of a human male (29 years old). This begins on the medial margin and dorsal surface of the muscle and curves forward of the femur to be inserted into the proximal part of the medial surface of the tibia.

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modification of the algorithm. Thus, it is possible to showclearly the large cartilage-covered surface, on the distalextremity of the femur (Fig. 7). In particular, the cartilageis more evident and takes the form of rollers, not exactlyparallel but diverging posteriorly and inferiorly. Thesagittal curves change gradually from an anterior circle oflarger radius to one of smaller posterior radius, giving aspiral curve. From a superior view, we were able to see the

menisci of the knee joint (Fig. 8). The medial meniscus isshown as a segment of a larger circle compared with thelateral one, and has an outline which is more oval thancircular. It is possible to denote that the posterior horn isfixed by a broad insertion in an anteroposterior line alongthe medial side of the posterior intercondyloid fossa. Thelateral meniscus is nearly circular in form and is less firmlyfixed than the medial. Its anterior horn is attached to anarrow depression along the lateral articular surface. Inour first animation, proceeding in a medial–lateral direction,all the structures of the knee joint are removed, extractingand highlighting the articular cartilage, surrounded byseveral voxels due to residues of muscles, ligaments andbone. In the second animation, proceeding in the sameway and tilting the frames 45

°

, we highlighted the menisciwith their broad insertion, using also a transparency filterfor the final image.

Discussion and conclusions

Common CT and MR images still have a relatively lowtemporal and spatial resolution and can be used only formacrostructural analysis (Udupa, 1999). With volumerendering we are able to obtain images with a higherresolution, which permits us to carry out a microstructuralanalysis, too. This integrated system is proving to be anextremely useful tool in highlighting anatomical characters.Interpolation and extraction of the volume region ofinterest from our data sets enabled us to visualize the 3Dimages on a computer screen, with the possibility of makingenlargements or reductions, translations and rotations(Udupa, 1999). In particular, using volume rendering, the3D images (voxels) of a living human knee can be visualizedon the monitor screen through a 2D projection surface,

Fig. 6 Right knee of a 30-year-old man; image extracted from DESS (double echo steady-state) sequence of MRI analysis, in sagittal section. In this way, the morphology of the articular cartilage can be shown in a single section only. Quadriceps tendon, the patellar articular cartilage, Hoffa’s fat pad, the patella and gastrocnemius muscle have been evidenced.

Fig. 7 Applying the 3D volume rendering on the DESS sequence of MRI of the right knee of a human male (30 years old), we are able to show articular cartilage in 3D total view, as the bone structures of the distal extremity of the femur were transparent through the modification of the algorithm. Thus, it is possible to show clearly, on the distal extremity of the femur, the large cartilage-covered surface.

Fig. 8 Axial scans of MRI: the entire meniscal structures of right knee of a human female (23 years old) are highlighted.

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composed of very small picture elements (pixels). In fact,all 3D rendering techniques rely on mathematical formulasto determine, for each pixel, what portion of the datamemorized should be displayed on the screen and howthat portion should be weighed to represent spatialrelationships better. Voxel selection is usually accomplishedby projecting lines (rays) through the data set cor-responding to the pixel matrix of the desired 2D image.Differences in the images produced with various 3Drendering techniques are the result of variations in therelative selected and weighed voxels (Calhoun et al. 1999).On this basis we studied the morphology of volume-rendered knees of living humans along arbitrarily positionedcutting planes. Using this technique, every single part ofthe joint can be virtually removed in order to analyse theinner structures better (Adam et al. 1989). In order toobtain our images, the necessary steps to be performed areas follows: data acquisition, interpretation of the resultswith re-sampling and editing (which requires filtering),segmentation, classification and 3D reconstruction(Calhoun et al. 1999). The image is acquired through normaldiagnostic instruments, as magnetic resonance, and then is‘purified’ by filtering systems. In particular, in this report,to study the knee structures, we used acquisition techniquessuch as DESS and turbo spin-echo (TSE-T2 weighted) thatcan be utilized with good results in post-processing.However, for the reconstruction of articular cartilageimages, the three-dimensional spoiled gradient-recalled(3D-SPGR) can also be used, giving good results in the post-processing phase and allowing for the visualization ofhigh-quality images, but it has the disadvantage of requir-ing a long scan time with the consequence of producingpatient motion artefacts (Kornaat et al. 2005). 3D-SPGRrepresents an imaging method for identifying and charac-terizing physeal growth arrest following physeal plateaggression (Sailhan et al. 2004). Fluctuating equilibriumMR imaging can also be used for the evaluation of thearticular cartilage in the knee as it provides highest cartilagesignal-to-noise ratio (SNR) and contrast-to-noise ratioefficiencies although it has worst fat suppression (Goldet al. 2006). Recently there has been renewed interest inSNR-efficient imaging sequences for imaging cartilage,including various forms of steady-state free-precession(FS-SSFP, LCSSFP and FEMR) as well as driven-equilibriumimaging; the comparison of several of these sequenceswith existing methods (FSE, T

2

-weighted FSE and T

1

-SPGR)showed that the new steady-state methods increase SNRefficiency by as much as 30% and improve cartilage–syno-vial fluid contrast by a factor of three (Hargreaves et al.2003). A new way has been represented by 3DSS-SPGRimaging, which is a promising method for evaluating car-tilage pathology in patients with osteoarthritis of the kneeand has the potential to replace fat-suppressed 3D SPGRimaging (Yoshioka et al. 2003). Furthermore, an MR-basedtechnique that permits identification of the specific role of

surface size, curvature and incongruity as potential riskfactors for osteoarthritis has been developed (Hohe et al.2002). The next step is segmentation, which consists ofsubdividing the image into homogenous areas followed bycataloguing and incorporation every single area. A new setof texture features based on phase information that providesa very good discrimination between bone and surroundingtissues was applied by Bourgeat et al. (2005) for segmen-tation of knee bones. After filtration, segmentation andclassification of the images we move on to their elaborationin order to obtain 3D visualization. The latter phase gener-ates the final images, associating each voxel with a colourand partial opacity, and blending them. The ultimate goalof this study is to render the image in such a way that its3D nature can be perceived. Indeed, thanks to the greaterpower and greater programmability of modern graphicsprocessors, the new technology can use sophisticated toolssuch as stereo glasses with ultrasound sensor and virtualdevices like the ‘head mounted display or the boom’, whichallows us to dip directly into the obtained data (Zorcoloet al. 1997) and navigate inside the human body with thebest possible definition. In order to understand better thereal structure and morphology of the knee in living humans,we studied the knee joint with a volume rendering technique,making a comparison with anatomical structures of dissectiontables. Our findings revealed the real anatomical morphologyof the knee, evidencing bone structures, ligaments, musclesand vessels. We were also able to show other inner structuresof the joint, such as the menisci and the articular cartilage.In our images, for example, it is possible to visualize theorigin and insertion of posterior and anterior cruciateligament, the exact relationship between femur andtibia, clearly differentiating each articular structure.

Modulating the parameters of the algorithms andcreating video frames, we can also show all structures ofthe knee isolating every single element, e.g. articularcartilage and meninsci (see see supplementary AnimationsS1 and S2). Although this study is mainly focused on creatinga database of 3D high-quality images, it provides a substantialcontribution to medicine, opening several scenarios indidactics, research, diagnostics and the surgical field.

Regarding the didactic value of our data set, we intendto create a database of digital images similar to materialthat has been published on the internet as the outcome ofthe Visible Human Project (Jastrow & Vollrath, 2003; http://www.nlm.nih.gov/research/visible/applications.html). Thiscould lead to a different method of studying anatomy(Reidenberg & Laitman, 2002), no longer on dissectedcorpses but, indirectly, on living humans. There is an opendebate on whether or not real dissections are necessary forstudent training. In many places, unfortunately, educationis of marginal interest only as professors of anatomy betterperform high-end molecular biology research to gainpositions, reputation and grants over the personal care ofstudents at dissection tables. Considerable costs and time

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may be saved when education in anatomy is modified byreducing (or completely abolishing) the time spent in realcadaver dissection (Collins et al. 1994). However, providinga good anatomical education of our students is of paramountimportance to give them a reliable basis for their futurework as doctors on real patients. Thus, we find it necessaryto provide true dissections accomplished by virtual materialfor a better 3D understanding of the human body. There-fore, the course in macroscopic anatomy at our facultyruns from September to May. It includes 120 h of dissectionroom applications with anatomical pieces, demonstrationsof 3D volume-rendered structures, lectures and laboratorywork. Our histology and embryology courses are conductedin parallel with gross anatomy, though as separate entities.We have many students in our clinical faculty; and today,with this new methodology, more students can participatein the study of anatomy, fully appreciating 3D volumerendering, although their training must be completedthrough dissection. In the training of medical students it isessential to correlate anatomical structures of the humanbody with rendering. The 3D images can be integrated inpractical studies, seminars and lectures. We have demon-strated that the anatomy of the knee can be studied bycomparing our virtual images with those of atlases ofhuman anatomy and real preparations. Another applicationof the present results is the creation of a direct internetresource or printouts of the images, permitting studentsto continue learning at home. For this reason we haveactually developed an internet site that allows studentsand colleagues to learn about the latest evolution ofour work and to access its results, i.e. images and anima-tions (http://ww2.unime.it/biomorfologiabiotecnologie).Unfortunately, high-quality anatomy software is oftenexpensive for students, so we can offer them the possibilityto improve anatomy studies using our workstations situatedin specialized computer rooms. As far as diagnostics andthe surgical field are concerned, this method can be usedto supply surgeons with a valid support in planningoperations. Volume visualization is becoming an ever moreimportant tool in engineering and in medicine. One ofthe main reasons for this increased interest is that theacquisition devices and calculation techniques that pro-duce sets of volumetric data are increasingly being used. Inparticular, in medicine, the acquisition of groups of scalarvolume data, through the use of non-invasive techniques,is growing in importance, especially in the fields of therapyplanning and diagnostics. Doctors were once forced todraw up images in their mind from various points ofview, in order to construct a mental 3D model, making analready difficult operation even harder. The creation ofa virtual environment for the analysis of volumetric data,directly in three dimensions, resolves these problems.For this purpose, our results demonstrate that the use ofvolume rendering allows specialists to approach thestudy of the knee with a non-invasive method, without

the aid of invasive techniques such as arthroscopy, whichentailed a high level of risk, for diagnosis or presurgeryplanning (Heng et al. 2006). It also offers young surgeonsthe opportunity to gain experience, using preoperativeanalysis systems. In this way young surgeons gain moreconfidence and more experienced surgeons have a com-plete picture of the pathology and can plan operationswith greater accuracy (Perrone et al. 2003), with a morerealistic evaluation of the risks involved (Pelizzari et al. 1996).A virtual reality knee simulator for training orthopaedicresidents in arthroscopic surgery before live-patient oper-ating room experience has been developed by Cannonet al. (2006) using data from the visible human project.Their validation study is currently running, but it mayalready be assumed that trained participants will completediagnostic arthroscopy on an actual patient in less timewith greater accuracy, less iteration of movement of thearthroscope, and less damage to the patient’s tissue ascompared with untrained residents. Further models usedin arthroscopic knee surgeon training were constructed fromthe Visible Human Project and Chinese Visible Human datasets by Heng et al. (2004, 2006). These models simulate thereal-time deformation of soft tissue with topologicalchange using finite element analysis and offer a realistictactile feedback. Our findings reveal that volume renderingcan be applied to all parts of the human living body. Forexample, it is intriguing to study the real morphologyand alterations of the central nervous system, consideringthat all evidence, at present, is based on dissection studies.For this purpose, through this technique, it will be possibleto study empty structures, such as cerebral ventricles. It is alsointeresting to apply this method on ultrastructural images,obtained by confocal laser scanning microscopy, in orderbetter to define the real relationship between proteinsconstituting human skeletal muscle and better to under-stand their interactions. Finally, our findings from

in vivo

3D rendering derived from MRI digital formats may be ableto help direct more focused anatomical studies of severalbody regions. Such correlative imaging studies will be criticalfor the definition of the future role of anatomy in medicine.Our study on the knee demonstrates how medical imagingcan be applied at present and how much still remains tobe done in terms of technology development in order toachieve what was once considered only fantasy.

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Supplementary material

The following supplementary material is available for thisarticle:

Animation S1 Right knee of a human male (30 years old).Marching through a stack of reconstructed images whichhighlight the articular cartilage separated from the entireknee structures.

Animation S2 Right knee of a human female (23 yearsold). Three dimensional frames in AVI extension with high-lighting of the menisci with broad insertion.

This material is available as part of the online articlefrom: http://www.blackwell-synergy.com/doi/abs/10.1111/j.1469-7580.2007.00770.x (this link will take you to thearticle abstract).

Please note: Blackwell Publishing is not responsible for thecontent or functionality of any supplementary materialssupplied by the authors. Any queries (other than missingmaterial) should be directed to the corresponding authorfor the article.