We tested a novel approach for the quantitative remote analysis of abdominal aortic aneurysms by reconstructing  their 3D geometry and topological structure (i.e. centereline path) and put them on the web as VRML97 models including specialized code enabling the user to perform guided inspection and measurements useful for surgical planning

Giachetti, Andrea

Piccinini, E.

Tuveri, Massimiliano

Zanetti, Gianluigi

P-arch

1Web based 3D quantitative measurements of Abdominal AortiAneurysmsA. Giahetti, M.Tuveri, G.Zanettiaand E. PiininibaBMA Area - CRS4Sesta Strada Ovest, Z.I. MahiaredduI09010 Uta(CA)bUnita Operativa Chirurgia Vasolare ed Endovasolare Dipartimento ChirurgiaPresidio Ospedaliero di Ravenna ASL, viale Randi, I48100 Ravenna.We tested a novel approah for the quantitative remote analysis of Abdominal aortiAneurysm by reonstruting their 3D geometry and topologial struture (i.e. enterlinepath) and put them on the web as VRML97 models inluding speialized ode enablingthe user to perform guided inspetion and measurements useful for surgial planning.1. Methods1.1. Image retrievalA DICOM server based on the Mallinkrodt CTN have been used to reeive and storethe CT data reeived from the diagnosti enter.1.2. SegmentationDeformable models have been used for segmentation: we developed a software toolwith an user friendly interfae that an be used to ontrol two dierent segmentationproedures used to reover the geometrial struture of the aorta. The rst methodonsists of generating single vessel branhes from series of 2D ontours arbitrarily orientedin the 3D spae and then joining them with basi operations. Contours are extrated from2D slies using region growing or balloon snakes [7,8℄ algorithms, and an be modied andontrolled through the user interfae. Vessel surfaes are nally built in the following way:rst point orrespondene on suessive ontours is found, then a triangulated surfae isgenerated and a enterline (a spline joining the enters of mass of the ontours) is alsobuilt. The operations introdued to join the ontours are three: simple joint, anastomosisand bifuration. The rst onnets two segments at their extrema, the seond joins twointerseting vessels, the third joins three dierent branhes in a bifuration struture.The same proedure of the balloon evolution, an be performed diretly in 3D startingfrom a small sphere rst put inside the vessel region in the data set and then making itgrow driven by an internal pressure, regularizing fores and voxel based fores. We founda good 3D geometrial struture to be used as a basis to implement the balloon in theSimplex Meshes [9℄. Simplex Meshes are very simple surfae meshes where eah node isonneted exatly to three neighbors. This makes very easy to write the ode for the2dynamis and the algorithms obtained are simple and fast. This method an be moreaurate near bifurations, but it is less easy to ontrol when, for example, the preseneof plaques or loal strutures makes onvenient to orret loally the reonstrution or totune the segmentation parameters. Furthermore it requires the use of another algorithmto reover the vessel enterline (we implemented a voxel oding method [10℄. In anyase, the nal result is still a le inluding both the surfae of the arterial lumen and itsenterline. The same tehniques an be obviously used also to extrat other interestingstrutures, suh as the external surfae of the thromboti region. Geometri operationsand the le struture is based on the XOX Shapes Mirotopology library [14℄.1.3. Web-based measurable models generationVRML97 and ECMA sripting are used to obtain 3D models that are not only viewablefrom any VRML97 enabled browser, but that also allow users to interat with them, tonavigate along the vessel lumen and to perform guided measurements of distanes andangles. The segmented data are automatially onverted in VRML97 worlds hiding sript-ing ode that enables the measurement of the geometrial parameters relevant for surgialplanning diretly from standard web browsers. The onversion tool has been realized as aperl sript and generates the geometri objet nodes, several viewpoints, an user interfaewith likable buttons, guided navigation paths, an image display and the measurementsupport. Using ECMA sripting we implemented methods to measure parameters of sur-gial interest. The rst gives the 3D oordinates and the distane from the enterline foran arbitrary point on the surfae seleted with the mouse. A plane perpendiular to theenterline is also shown. Another one onsists of measuring the distane traveled by apoint moving along the enterline between two user seleted referene points. This is anextremely useful value, sine usual measurements of vessel length done with 2D imagingor endosopy are often wrong due to the eet of vessel urvature [11℄. Furthermore, it ispossible to measure angles dened seleting three points on the enterline. Other optionsintrodued in the VRML97 worlds are introdued to perform a guided navigation insidethe vessel lumen ("Virtual endosopy") or to perform a test to verify if a probe of givenradius an be inserted through the vessel lumen. During the measurement phase, imagesorresponding to a setion of the CT dataset passing through the liked point of thesurfae and perpendiular to the vessel enterline are also represented inside the browserinterfae. Images have been obtained from the CT data by seleting planes perpendiularto the enterline in sampled points and using linear interpolation to ompute the pixelvalues. These images are saved as gif les and used as texture of a plane in the VRMLmodel.Using these tools the end user an performmany useful omputations on realisti modelsthat an be distributed worldwide a few hours after the image aquisition and an beaessed and analyzed in the same moment by dierent onsulting enters just usinga standard web browser. This means that, one fully validated, this tehnology ouldbe used by speialized servie enters to provide, in a ost-eetive way, surgial supportthrough 3D based measurements. Fig. 1 shows the expeted servie model: the diagnostienter an send DICOM3 datasets through the net to the elaboration enter, and aftera few hours, the surgeons an browse, from their standard PC, the resulting VRML97model and perform guided measurements. Dierently from other similar servies urrently3available [1℄, this new system is based on open standards, does not require speializedsoftware on the lient side and it is speially designed to operate within Internet.Figure 1. The VRML97 measurable model servie: a diagnosti enter an send imagesto the reonstrution enter, and a few hours after, a 3D model with guided measurementsupport is available on the net.2. Abdominal Aorti AneurysmsTo test on a really useful appliation the idea desribed in the previous setions, weapplied our method to measure the geometrial parameters desribing aorti aneurysms.The aorti aneurysm is a progressive, pathologial dilation of the aorta. The fate ofall aneurysms is the rupture. This ondition is almost always fatal. Thus aggressivesurgial approah is warranted. Therapeuti approahes inlude open surgery and/orendovasular exlusion. The latest proedure involves the endovasular plaement ofa omplex prosthesis. A orret geometrial evaluation of the aneurysm struture isfundamental to have a suessful implant. Moreover, [11℄ knowledge of the true aneurysmdiameter, proximal aorti nek diameter and its distane from renal arteries is neessaryin order to evaluate the surgial risk. CT is the most aurate tehnique [12℄ to evaluateabdominal aorti aneurysm. The useful measures to plan the endovasal proedures areoften performed on the volumetri data. However, this is usually done with empirialtehniques: seleting some sliing planes and making ad ho orretions to measuresperformed on the 2D projetions. If the parameters are estimated from these projetionsor from the trajetory of a atether a large amount of error due to the urvilinear strutureof the vessel is introdued both in diameter and length measurements.3. ResultsEight ases of Aorti Aneurysms already treated with the plaement of an endovasularstent by our vasular surgeons have been aquired by the CRS4 PACS. Vasular geometri-4al strutures have been reonstruted using the ontour based method and VRML modelshave been generated. Two trained vasular surgeons performed blind measurements onthe model using a simple web browser with the Cosmo Player 2.1 plugin, as if he had tohoose the design of the stent and to plan the proedure. The aneurysm nek,length andsa diameter has been measured. Partiular attention has been paid to the presene ofalied plaques at the level of the bifuration and ilia arteries. Operators omputed alsothe intra-aorti angle and the aorti-ilia angles. The results obtained were always om-patible with the previous values used by the surgeons who planned the intervention, whohad to reover the parameters from 2D images and orret them with ad ho methods.Figure 2. The VRML97 model an be inspeted, navigated and measured from any pwith a web browser and a plugin. Here a \virtual endosopy" with radius measurementis shown.4. ConlusionThe results obtained show that the system desribed here an be eetively useful toobtain reliable measurements and support for ollaborative work. The same method anbe applied also for other linial appliations, i.e. olonosopy, where measurements of 3Dstrutures and a ollaborative diagnosis an be extremely helpful for a orret diagnosis.5A BFigure 3. Measurement of enterline distanes (A) and angles (B): the user an plae thetwo or three referene points just by liking with the mouse on the enterline, and thedistane or angle is automatially shown.We plan to improve the quality of the reonstrutions and the funtionality of the systemin the near future, espeially with regards to the support of ollaborative work.REFERENCES1. Medial Media Systems, http://www.medialmedia.om2. N.W. John, N. Philips, R. Vawda, J. Perrin, \A VRML simulator for VentriularCatheterisation" in Proeedings of the Eurographis UK onferene, Cambridge, UK,April 19993. J.C. Parodi, J.C. Palmaz, H.D. Barone, \ Transfemoral intraluminal graft implanta-tion for abdominal aorti aneurysms. \ Ann Vas Surg 1991;5:491-499.4. J.S. Milner et al. \Hemodynamis of human arotid artery bifurations: omputa-tional studies with models reonstruted from magneti resonane of normal subjets." J. of Vasular Surgery, 07/1998, pp.143{1565. M. Fillinger, \New Imaging Tehnologies in Endovasular Surgery" Surgial Clinisof North Ameria 79: 3 (1999)6. K. Krissian et al. \Model Based Multisale Detetion and Reonstrution of 3D ves-sels" INRIA Sophie Antipolis Report n.3442 (1998)7. A. Kass, A. Witkin and D. Terzopoulos, \Snakes: Ative ontour models," Int. J. ofComp. Vision 1, 321{331 (1988).8. L.D. Cohen and I. Cohen, \A nite element method applied to new ative ontourmodels and 3D reonstrutions from ross-setions" Pro. of 3rd Int. Conf. on Comp.Vision, pp. 587{591 (1990).9. H. Delingette, \Simplex meshes: a general representation for 3d shape reonstru-tion", in CVPR94, pp. 856{859, 1994.10. Y. Zhou and A. W. Toga, \EÆient skeletonization of volumetri objets", TVCG,6Figure 4. Testing the insertion of a probe of xed size inside the vessel.vol. 5, 1999.11. K. M. Baskin et al., \Volumetri Analysis of Abdominal Aorti Aneurysm", Medi-al Imaging 1996: Physiology and Funtion from Multidimensional Images, Eri A.Homan, Editor, Pro. SPIE 2709, p. 323-337 (1996).12. J.D. Santilli and S. M. Santilli, \Diagnosis and treatment of Abdominal AortiAneurysms" Amerian Family Physiian 56:4 (1997)13. Cosmo software, http://www.ai.om/osmo/14. XOX Corporation, http://www.xox.om

Web based 3D quantitative measurements of abdominal aortic aneurysms

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Web based 3D quantitative measurements of abdominal aortic aneurysms

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