Image processing algorithms, CAD-CAM tools and rapid prototyping (RP) techniques are able to produce complex lumen artery replicas. This work presents a system for manufacturing the lumen of human carotid from computed tomography acquisition. The pipe-line of manufacturing process of a human carotid lumen replication is presented. Each stage of the pipe-line is brieﬂy discussed. Technical details of the 3D surface

reconstruction phase, based on the Open Cascade geometric modelling software, and the RP manufaturing process based on Fused Deposition Modelling are presented

Franzoni, Gregorio

Murgia, Fabrizio

Pusceddu, Gabriella

P-arch

Eurographics Italian Chapter July 11-12- 2002OPEN CASCADE AND RAPID PROTOTYPINGIN HUMAN CAROTID LUMEN RECONSTRUCTIONFabrizio MurgiaCRS4   - EIP- GEMMSVI Strada OVEST Z.I. Macchiareddu, C.P. 94, 09010 UTA (CA - Italy)ph +39 0702796321, fax +39 0702796216, e-mail: fmurgia@crs4.itGabriella PuscedduCRS4 - EIP - GEMMS VI Strada OVEST Z.I. Macchiareddu, C.P. 94, 09010 UTA (CA - Italy)ph +39 0702796321, fax +39 0702796216, e-mail: gabri@crs4.itGregorio FranzoniCRS4 - EIP - GEMMS VI Strada OVEST Z.I. Macchiareddu, C.P. 94, 09010 UTA (CA - Italy)ph +39 0702796347, fax +39 0702796216, e-mail: franz@crs4.itAbstract:Image processing algorithms, CAD-CAM tools and rapid prototyping (RP) techniques are able to producecomplex lumen artery replicas. This work presents a system for manufacturing the lumen of human carotidfrom computed tomography acquisition. The pipe-line of manufacturing process of a human carotid lumenreplication is presented. Each stage of the pipe-line is briefly discussed. Technical details of the 3D surfacereconstruction phase, based on the Open Cascade geometric modelling software, and the RP manufaturingprocess based on Fused Deposition Modelling are presented.Keywords: Rapid Prototyping, Geometric Modelling, Medical Imag-ing1 IntroductionRapid Prototyping (RP) is an emerging technique used in industry for manufacturing prototypes[11]. RP can be considered a new imaging technique. Its capability to physically reproducegeometrical complex shapes is getting increasing interest in medicine [5]. Stereolithographicbiomodelling has already been used in craniofacial surgery for management of deformities, trau-mas and tumours. Accurate analysis of Computed Tomography (CT) and Magnetic ResonanceImaging (MRI) data of a patient is a common practice in vascular surgery. Surgeons try to men-tally reconstruct a virtual 3D surgical anatomy model. Physical models can help in this importanttask providing the physician with a visual and tactile support [8], [4]. Physical replicas can alsofacilitate experimental studies of computational vascular fluid dynamics [3]; they also permit invitro reproductions of flows in living subjects before and after surgery.The CT data are transmitted from the acquisition clinical apparatus to the graphics worksta-tion. The replica manufacturing process starts with making a segmentation step. It is necessaryto extract the set of points (curves) which represents the lumen. This step is a semi-automaticCenter for Advanced Studies, Research and Development in SardiniaEnergy and Process EngineeringGeometric Modelling and Monte Carlo Simulations1Eurographics Italian Chapter July 11-12- 2002process aided by an image processing tool. These points are linked together, by using commer-cial CAD-CAM systems to build 3D surfaces. This step is called the geometric reconstruction.BSpline are used to define the geometry of curves and surfaces . The last stage of the pipelineis Rapid Prototyping. At this point the surfaces are tessellated to obtain the mesh of trianglesin STL format which is the input format for the RP device; RP device builds the object using alayer-by-layer manufacturing process.Pentecost group [10] used a digital photomicrograph (10 micrometers section thickness) appa-ratus to reconstruct the cardiac blood space of human embryonic heart (approximately the greatestdimension of the embryo is 	 ). The curves representing the lumen were manually tracedfrom the photos and reconstructed in surfaces by using Maya software (http://www.aliaswavefront.-com/). The replicas were built using a Stereo Lithographic Apparatus (SLA) with layers thicknessof 	 .Lermusiaux work [7] reports the use of CT scan acquisition (the reconstruction interval of	 every  and a pitch of  ) with contrast liquid and without cardiac synchronisationduring the acquisition procedure. An unspecified semi-automatic image processing tool, drivenby the operator, is used to generate a structured points cloud and to compute the interpolatedsurfaces from adjacent sections. The STL model is sliced in  cross sections. SLA 250 (3DSystems Corp. Valencia, CA) is used to build the physical replicas in epoxy resin. The systemwas developed to reconstruct abdominal aortic aneurysm (AAA). Three days were required toproduce the final replica.Renaudin group [2] used MRI apparatus (a 3D MR angiograph 	ﬁﬀ and static MR imagingecho setting with  pixel size dimension) to develop a complete phantom of the coronaryarteries dedicated to 2D or 3D angiographic imaging. The system can also be used to constructa realistic phantom of stenoses of the coronary arteries. The CAD Euclid system (from Matra-Renault http://www.matra-datavision.com/) was used to build 3-D anthropomorphic phantoms.The segmentation was done by using parametric curves (B-Spline) starting from center lines ofthe vessels manually computed by an expert operator. Phantoms were built using a SLA technique(manufacturing precision is under  that can be improved till ﬂ ). The phantom canalso be used for testing 3D reconstruction of vessels.Friedman [1] used a slightly different approach to manufacturing vascular replicas that canbe used for testing in vitro reproduction of flows in living subjects: a MRI acquisition apparatus(1.5 T GE). 3D time-of-flight imaging sequence is used to produce sixty sections 	 thickwith a pixel size of ﬃ !" . Points were Fourier interpolated to ﬃ #ﬃ has beenused. He used an ad-hoc image processing routine manually driven by the operator to define 120points for each lumen curves. These points were equally spaced around the perimeter of each axialsection. A CAD system was used to interpolate these points in BSpline surfaces. These surfaceswere transferred (by using IGES format) to the powerful commercial CAD-CAM system Catia(http://www.catia.com). Both, two mold parting planes and the tool path for numerical controlledprocess were created in CATIA. A replica of real artery was milled out by a machinable plasticdevice. The distance between each final step of the cutter was ﬂ$ producing scallopsﬃ high. The run time was 	 h.Our study follows a previous work made at CRS4 on the development of the ViVa system[3]. In this work we have investigated the applicability of RP technique in the vascular surgeryfield. We focused on applying RP technique to the carotid lumen reconstruction of a human arteryacquired through Computed Tomography (CT).2Eurographics Italian Chapter July 11-12- 20022 Materials and methods2.1 Data acquisitionDigital data were obtained by spiral CT on a patient affected by carotid aneurysm. The examina-tion was performed using a Picker scanner at the Brotzu Hospital in Cagliari. Data was transferredto our workstation by using DICOM3 (http://medical.nema.org) standard protocol. We consid-ered 48 CT images for this case. The distance between slides (derived from CT acquisition) is .2.2 SegmentationThe picture segmentation is asemi-automatic process driven by theend user (operator).In this stage each CT image is fil-tered to extract points belonging tothe lumen boundary.Figure 1 shows a typical CT im-age after filtering. The lumen to bereconstructed is the boundary layerwhich separates dark pixels (insidelumen) from grey pixels (intima).For the segmentation we usedgsnake (http://www.cs.wisc.edu/com-puter-vision/projects/gsnake.html) li-brary. The segmentation processFigure 1: Acquisition and segmentation steps. The leftimage shows the filtered CT image of a carotid (2.1).The right image shows the results obtained applyingthe segmentation step and interpolating the points by aBSpline curve (see 2.2).starts opening a CT image, selecting the region of interest (ROI) on the image and positioninga contour of 3-D points inside the lumen region. At this point, an iteration loop starts movingpoints to lumen regions.When all points reach the lumen boundary the evolving process stops and the cartesian coordinatesof each point is stored in an indexed vector of 3D vertices. This stage is costantly monitored by theoperator that fixes the number of iterations and some other parameters. This vector represents thegeometric constraints for requested interpolation curve. This segmentation procedure is repeatedsemi-automatically for each CT image. This procedure generates 24 slides, each one storing $ﬃ3D vertices (Fig. 1).2.3 Geometric reconstructionThe lumen reconstruction is realised using the Open CASCADE (OC) (http://www.opencascade.-com) software. OC is a powerful 3D modelling application development platform. It consists inreusable C++ object libraries and development tools that are available as Open Source.OC is used to create domain specific 3D graphic applications such as: Computer Aided Engi-neering (CAE), Architecture Engineering Construction (AEC) and Geographic Information Sys-tem (GIS), CAD-CAM.We use the OC’s Boundary Representation (BRep) scheme [6] to manage the model re-3Eurographics Italian Chapter July 11-12- 2002construction of the lumen and to convert it in STL format. In fact, the topological li-brary supported by this program allows us to build the valid topological data structure of theartery.The set of parameterized points produced by the segmentation and stored in a file, are dividedin horizontal planes. These points are stored into an array of gp Pnt (OC data structure). We in-terpolate points belonging to the same plane by a BSpline curve using the Geom Api Interpolateclass of OC. We use Bspline because such a representation presents a local control fea-ture. This means that modifying one control point (vertex) only affects the part of the curvenear that control point (Figure 1).In order to obtain a valid Brep ob-ject of the OC class TopoDS Solid,we compute the previous interpo-lation algorithm for each slide byBRep Builder API MakeShell andBRep Builder API MakeSolid clas-ses.The left image in Figure 2 shows theBspline surfaces obtained interpo-lating two adjacent Bspline curves.The inner surface represents the re-quested artery lumen. This surfaceFigure 2: Reconstruction step. The image on the leftshows two Bspline curves obtained in the geometric re-construction and segmentation steps (2.3).has continuity C2. The outer surface represents an offset surface necessary to give the right man-ufacturing thickness to the physical replica. The inner and the outer surfaces are capped on the top(right image) and on the bottom by holed plane dishes in order to compute a valid BRep schemewith OpenCascade (2.3)This solution is obtained overcoming both, numerical problems due to the BSpline curves/surfacecomputation and problems due to topological aspects in the definition of the BRep (ex: orientationof computed surfaces). At this point, the solid model is completed and its BRep represents a valid3D solid [6]. Last step is the tessellation of the BRep with triangles by Stl API Writer class ofOC. This class produces the mesh of triangle that is stored in a output file using the STL format(Fig. 3)The number of triangles produced by Stl API Writer class is kept low (setting tessellationparameters of OC) because the FDM apparatus defines an upper bound limit on the number oftriangles. Because the STL file has been generated from a valid BRep representation no manualoperation is needed from the RP operator to fix it. Surface model of the carotid lumen in eachof the above specimens was converted to STL format in the previous step and transmitted to ourprototyping center Proto21. Proto21 uses a RP machine with FDM technology. FDM meansFused Deposition Modelling, and is a technique whereby digital surface models are converted toscale models of resin or wax. It works by means of a moving head which is driven on the XY planeby the coordinates data in the 3D wireframe surface model. While moving, this head extrudes afused wire of material which solidifies producing a thin layer (0.178 to 0.5 mm) of the object.2.4 Rapid PrototypingThen the workplane moves down along Z-axis of exactly the thickness of the layer created,4Eurographics Italian Chapter July 11-12- 2002and another layer is built up over the previous. The process goes on layer by layer, and createsa pretty accurate solid resin model.In our case, resin was ABS and themachine was a Stratasys FDM 2000[9]. The manufacturing orientationis shown in Figure 3. This positionhas been chosen in order to have themaximum manufacturing resolutionalong the lumen axis. This mesh isobtained from Open CASCADE bythe tessellation process and stored inSTL format during the geometric re-construction step (see 2.3).Figure 3: Rapid Prototyping. The mesh of triangles po-sitioned in the manufacturing Stratasys FDM 2000 po-sition is shown on the left. The right image shows themachining path of the FDM disposal (SSL format) ona manufacturing cross section (see 2.4).3 Discussion and conclusionsLumen replicas can help vascular surgeons in diagnosy and therapy of particular carotid diseases.In order to be able to plane the operation, vascular surgeons need to know, with great accuracy, theanatomy of the part. The physical model provides a visual and a tactile support that can improvethe communication quality between surgeon and surgical equipe between surgeon and the patient.Replicas are also important for training scope. Lumen replicas of human carotid offers a mean tovisualise internal anatomic features difficult to see otherwise.The first production of the lumen replica is shown in Figure 4. The FDM technique is fairlycheap. Its cost is continuously decreasing and depends of the height of the artery to be manu-factured. The building process for the lumen replica was rather fast, it took four hours to builda complete 3D lumen replica. For future models we are planning to use transparent materials(silicone) instead of ABS. We are also planning to include markings to distinguish pathologicalareas from healthy ones.Figure 4: This image show the physical re-construction of the carotid in FDM. Theprinting stage is about 30 minutes.The system developed so far is a prototype.It is a part of undergoing research project: Lab-oratory for Advanced Planning and Simulations(http://www.crs4.it/ % laps/).Preliminary results presented herein demon-strate mainly how to use the Open Cascadelibrary and FDM technique to build a lumenreplica. It provides a software environmentwhere we can verify different interpolation andblending surface algorithms supported by OC.We have also checked the capability of OC togenerate correct tessellated geometries which canautomatically be sent to the FDM device withoutany further intervention of the RP operator. Next phase of this study will be devoted to segmentcomplex carotid CT data to automatically extract complex geometric and topological features(reconstruction of the carotid bifurcation). This technique, developed in collaboration with the5Eurographics Italian Chapter July 11-12- 2002Radiology Dept. and the Vascular Surgery Dept. of the Ospedale Brotzu of Cagliari, will beused, in the next stage of the project, to reconstruct the carotid replicas of 10 patients with differ-ent carotid pathologies in order to study applicability of this technique to a minimum number ofcases.4 AcknowledgementsThis research was supported by the Italian Government - MIUR - inside the project LAPS (Lab-oratory for Advanced Planning and Simulation). The medical data sets were provided by theRadiology and Vascular Surgery Dept. of the Ospedale Brotzu of Cagliari, Italy. The authorsalso acknowledge Dr. Andrea Giachetti and Dr. Alan Scheinine for their technical assistance insegmentation techniques and MD. Massimiliano Tuveri (AB/MIDA-CRS4) and Dr. Piero Pili fortheir support.References[1] M.H. FRIEDMAN — D.B. KUBAN — P.SCHMALBROCK — K. SMITH — T. ALTAN.Fabrication of vascular replicas from magnetic resonance images. Journal of BiomedicalEngineering, pages 364–365, August 1995.[2] C.P. RENAUDIN — B. BARBIER — R. RORIZ — D. REVEL — M. AMIEL. Coronaryarteries: New design for three-dimensional arterial phantom. Radiology, pages 579–582,Mars 1994.[3] G. ABDULAEEV et al. Viva: the virtual vascular project. Information Technology inBiomedicine, pages 268–273, December 1988.[4] M.H. FRIEDMAN. Arteriosclerosis research using vacular flow models: From 2-d branchesto compliant replicas. ASME Journal of BIOMECHANICS ENGINEERING, 3:595–601,1993.[5] D.P. MAHONEY. Rapid prototyping in medicine. Computer Graphics World, pages 42–48,February 1995.[6] M. MANTYLA. Solid Modelling. Computer Science Press, 1995.[7] P. LERMUSIAUX — C. LEROUX — J.C. TASSE — L.CASTELLANI — R. MARTINEZ.Aortic aneurysm: Construction of a life-size model by rapid prototyping. Annals of VascularSurgery, pages 131–135, Mars 2001.[8] M.H. FRIEDMAN HACKER V.A. — JAMES B.F. — KUBAN B.D. — QIN and SCHAL-BROCK P. Mri measurement of arterial branch geometry. 1991 Biomechanics Symposium,pages 45–48, 1991.[9] Fused Deposition Modeling Technique. http://www.stratasys.com/.6Eurographics Italian Chapter July 11-12- 2002[10] J.O. PENTECOST — D.J. SAHN — B.L. THORNBURG — M. GHARIB — A. BAP-TISTA — K.L. THORNBURG. Graphical and stereolithographics models of the develop-ing human heart lumen. Computerized Medical Imaging and Graphics, pages 459–463,December 2001.[11] T. WOHLERS. Wohlers Report 2001, Rapid Prototyping and Tooling State of the IndustryAnnual Worldwide Progress Report. Wohlers associates, 2001.7

Open CASCADE and rapid prototyping in human carotid lumen reconstruction

http://www.p-arch.it/bitstream/handle/11050/720/5944_0.pdf?sequence=1&isAllowed=y

Open CASCADE and rapid prototyping in human carotid lumen reconstruction

Abstract

Similar works

Full text

Available Versions

P-arch