United States Patent [191
`D’Urso
`
`[54] STEREOLITHOGRAPHIC ANATOMICAL
`MODELLING PROCESS
`
`[75] Inventor:
`
`Paul Steven D’Urso, Coorparoo,
`Australia
`
`[73] Assignee: The University of Queensland, St.
`Lucia, Australia
`[21] Appl. N0.:
`596,237
`Sep. 12, 1994
`[22] PCI‘ Filed:
`PCT/AU94/00536
`[86] PCI‘ N0.:
`Apr. 25, 1996
`§37l Date:
`§ 102(e) Date: Apr. 25, 1996
`[87] PCT Pub. N0.: WO95/07509
`
`PCP Pub. Date: Mar. 16, 1995
`Foreign Application Priority Data
`
`[30]
`
`Sep.10,1993 [AU]
`
`Australia .............................. .. PM1195
`
`A61F 2/00; G06F 15/42
`[51] Int. Cl.6 ..... ..
`[52] US. Cl. ........................ .. 600/407; 128/922; 128/898;
`623/901; 378/901; 395/120
`[58] Field of Search ............................... .. 128/653.1. 920,
`128/922, 898; 623/16, 66, 901; 378/4, 34,
`901; 395/120, 121, 124, 125; 356/376,
`379, 380
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,436,684
`3/1984 White .................................... .. 264/138
`4,589,882
`5/1986 Uny ........................................ .. 623/11
`4,902,290
`2/1990 Fleckenstein et a1. .
`6/1990 Walker et a1. .
`4,936,862
`8/1990 Crawford ......................... .. 364/413.18
`4,953,087
`4,976,737 12/1990 Leake ...................................... .. 623/16
`5,127,037
`6/1992 Bynum.
`5,217,653
`6/1993
`5,231,470
`7/1993
`5,299,288
`3/1994 Glassman et a1. .
`5,357,429 10/1994 Levy.
`
`SUENTNER
`
`[AB
`
`US005741215A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,741,215
`Apr. 21, 1998
`
`5,358,935 10/1994 Smith et al. .
`5,373,860 1211994 Catone .
`5,443,510
`8/1995 Shetty et a1, .
`5,452,407
`9/1995 Crook .
`5,454,383 10/1995 Niblolon .
`5,487,012
`l/l996 Topholm et al. .
`5,554,190
`9/1996 Draenert.
`5,612,885
`3/1997 Love .
`
`FOREIGN PATENT DOCUMENTS
`
`European Pat. OE. .
`
`0 574 099 12/1993
`89/10801 11/1989
`91/06378
`5/1991
`92/08200 5/ 1992
`
`OTHER PUBLICATIONS
`
`Pediatr. Radiol. (1992), 22: 45 8-460, “Pediatric craniofacial
`surgery: comparison of milling and stereolithography for 3D
`model manufacturing”, H. M. Klein et a1.
`
`(List continued on next page.)
`
`Primary Examiner—-Marvin M. Lateef
`Assistant Examiner—Shawna J. Shaw
`Attorney, Agent, or Firm-—Gri?in, Butler, Whisenhunt &
`SZipl
`[57]
`
`ABSTRACT
`
`A method for stereolithographic construction of models
`including prostheses and anatomical pathology wherein CT
`scan data is computed to construct a plurality of two
`dimensional cross sectional images along one axis and the
`two dimensional image data is computed to create three
`dimensional coordinate data sets for the article to be mod
`elled. The three dimensional data sets are then computed to
`obtain spaced parallel two dimensional image data sets in a
`second plane of the article and the reconstructed two dimen
`sional image data sets are employed in a stereolithographic
`modelling apparatus to produce a three dimensional model
`of the article or part thereof. A prosthetic implant shaped to
`correct a defect in an anatomical part as well as a method for
`surgically implanting the implant using the stereolitho
`graphic method is also disclosed.
`-
`
`19 Claims, 4 Drawing Sheets
`
`SLA
`COMPUTER
`
`o
`
`20 IMAGE
`SEGMENTATION
`
`30 MODEL
`GENERATION
`
`20 SLIEE
`GENERATION
`
`SLA
`BUILD FILE
`
`;
`
`HATCH FILE
`VECTORS
`
`-1-
`
`Smith & Nephew Ex. 1038
`IPR Petition - USP 7,534,263
`
`

`
`5,741,215
`Page 2
`
`OTHER PUBLICATIONS
`SPIE, vol. 1444, Image Capture. Formatting, and Display
`(1991), Solid models for CI‘lMR image display: accuracy
`and utility in surgical planning, Nicholas J. Mankovich et al
`(pp. 2-8).
`Orthopaedic Clinics of North America, vol. 17, N0. 4, Oct
`1986, Computer-Aided Simulation, Analysis, and Design
`
`Orthopedic Surgery, Stephen B. Murphy, MD. et al (pp.
`637-649).
`Australasian Physical & Engineering Sciences in Medicine,
`vol. 14, N0. 1, 1991, “A Software System For Interactive
`and Quantitative Visualization of Multidimensional Bio
`medical Images”, R. A. Robb et al (pp. 9-30).
`
`-2-
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`

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`US. Patent
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`Apr. 21, 1998
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`Sheet 1 of 4
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`5,741,215
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`US. Patent
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`Apr. 21, 1998
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`Sheet 2 of 4
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`5,741,215
`
`F162
`
`FIGS
`
`FIGA
`
`1
`
`@1
`1 X
`9;? y
`Y
`
`(3/3 2
`
`-
`
`A
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`

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`US. Patent
`U.S. Patent
`
`Apr. 21, 1998
`Apr. 21, 1993
`
`Sheet 3 of 4
`Sheet 3 of 4
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`5,741,215
`5,741,215
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`FIG 7
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`/
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`8b
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`FIG 8
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`US. Patent
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`Apr. 21, 1998
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`Sheet 4 0f 4
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`5,741,215
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`1
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`FIGS
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`-6-
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`

`
`1
`STEREOLITHOGRAPHIC ANATOMICAL
`MODELLING PROCESS
`
`FIELD OF INVENTION
`
`THIS INVENTION is concerned primarily, but not
`exclusively, with methods and apparatus for forming
`implantable prostheses and method for use thereof.
`
`BACKGROUND ARI‘
`A variety of methods and apparatus for three dimensional
`modelling of articles including prosthetic implants are
`known. Many of these techniques employ digitised infor
`mation from CAD-CAM design systems or data captured
`and/or reconstructed from a variety of re?ection and/or
`transmission scanning devices.
`Such scanning devices include laser and acoustic re?ec
`tion apparatus and various types of transmission apparatus
`including X-ray, magnetic resonance imaging (MRI), mag
`netic resonance angiography (MRA), positron emission
`(PET) as well as ultrasonic radiation. Typically, data is
`captured by scanning a series of spaced parallel planes
`which may then be combined by computer tomography (CT)
`techniques to reconstruct a two or three dimensional pro
`jection of the article so scanned.
`Modelling of anatomical pathology using computed
`tomography data is well known for pro-operative planning
`and rehearsal of procedures and in the manufacture of
`prosthetic devices.
`U.S. Pat. No. 4436684 describes a non invasive method
`for forming prostheses of skeletal structures for use in
`reconstructive surgery. Three dimensional coordinate data is
`obtained directly from the digital data generated by the
`computed tomographic information. The three dimensional
`coordinate data is then utilised to generate three dimensional
`cylindrical coordinates which are speci?ed relative to an
`origin which is coincident with the origin of a coordinate
`system used in a sculpting tool apparatus to specify the
`spatial location of a cutting tool relative to a workpiece
`rotating on a turntable.
`Due to dif?culties in supporting the workpiece however it
`is generally not possible to sculpt an entire three dimen
`sional model of an article, rather. this system is employed to
`construct models of portions of skeletal structures to act as
`male or female mould surfaces for construction of prosthetic
`inlays or onlays.
`This apparatus and system however cannot construct a
`hollow model having faithfully reproduced external and
`internal surfaces and structural features.
`U.S. Pat. No. 4976737 describes a method of forming a
`prosthetic device by employing the apparatus and method
`described in U.S. Pat. No. 4436684 to form a template which
`may be used directly or indirectly to create a mould surface
`for moulding a polyurethane impregnated Dacron (Trade
`Mark) prosthesis. This document describes in detail a “mir
`ror imaging” technique to generate digital data for recon
`struction of a missing. damaged or deformed portion of a
`skeletal structure by transferring image data from one side of
`an axis of symmetry to another.
`stereolithographic modelling of engineering components
`from UV sensitive cross-linkable acrylic polymers using
`CAD/CAM digital data is known. Of more recent times. the
`use of stereolithography for creation of three dimensional
`models of bony structures has been reported.
`stereolithographic modelling of anatomical pathology to
`provide a far more accurate means for physicians and
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`surgeons to examine the condition of a patient for the
`purposes of diagnosis and for surgical procedures. Rather
`than rely upon say a solid model representing external
`features alone (as with U.S. Pat. No. 4436684), with or
`without two dimensional tomographic images, stereolitho
`graphically reproduced representations of anatomical
`pathology provide an almost exact replica of both internal
`and external features of a region under consideration.
`Moreover, such stereolithographically reproduced models
`permit surgical procedures to be pre-planned and rehearsed
`with a great deal of precision to minimise risks and trauma
`and should enable a means for preparing accurate prostheses
`for surgical repair of defects or in reconstructive surgery.
`One of the dif?culties in reconstructing three dimensional
`co-ordinate data from X-ray tomographic scans is that in
`order to minimise the amount of radiation to which a patient
`is exposed, the tomographic “slices” are relatively widely
`spaced and complex computer programmes are required to
`reconstruct this scanning data. Typically a “slice” is about
`1.5 mmin thickness and “slice” data is obtained at about 1.0
`mm intervals. A scan of an adult human skull may thus
`comprise ‘70-80 tomographic “slices”.
`A comparison of three dimensional CT image reconstruc
`tions using a destructive mechanical milling process and a
`constructive stereolithographic modelling process is
`described in “Paediatric craniofacial surgery: Comparison of
`milling and stereolithography for 3D model manufacturing”,
`Pediatr: Radiol. (1992) 22: 458-460. This article addresses
`the limitations of the milling process and concludes that
`while stereolithography is extremely expensive by
`comparison, ‘The slice oriented construction of the model
`corresponds well with the cross-sectional imaging methods
`and promises (sic) for the future a direct transfer from image
`slice to object slice.”
`Similar mechanical and stereolithographic modelling pro
`cesses are described respectively in “Computed-Aided
`Simulation, Analysis, and Design in Orthopaedic Surgery”,
`Orthopaedic Clinics of North America—Vol 17, No. 4,
`October 1986 and “Solid models for CI‘IMR image display:
`accuracy and utility in surgical planning”. ISPIE Vol 1444
`Image Capture, Formatting and Display (1991): 2-8.
`Both of the references referred to immediately above
`describe in detail a computed tomography slice processing
`technique utilising proprietary software to trace all bone
`boundaries in the image volume after empirically determin
`ing the threshold for cortical bone. The algorithm, after
`exhaustively searching each image, locates the inner and
`outer edges of cortical bone objects and generates a contour
`volume data set. This data set is passed to a reformat
`program to generate the SLA build ?le containing informa
`tion necessary to operate the stereolithography apparatus.
`In both of these references, the technique requires that the
`exhaustive contour descriptions must be replicated four
`times to provide a ?nished layer of 0.25 mm in thickness.
`This repetition is necessary to reconstruct the CI‘ axial
`resolution as one CI‘ slice equals four SLA layers.
`In transforming contour data to CAD data, a number of
`algorithms are available. A simple algorithm uses simple
`thresholded segmentation to produce voxel faces as paired
`triangles. A more complex technique uses the “Marching
`Orbes” algorithm which interpolates slices to yield a surface
`composed of sub-voxel polygons. The “Marching Cubes”
`algorithm is described in “Two algorithms for the three
`dimensional reconstruction of tomograms”. Med Phys.
`15(3): 320-7, and “Marching Cubes: a high resolution 3D
`surface construction algorithm” Computer Graphics.
`21:163-169.
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`from tubular sections of varying diameters intraoperatively
`as is the case at present.
`
`SU'NIMARY OF THE INVENTION
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`In order to control the stereolithography apparatus for
`model construction contour information determined from
`tomograms this may be introduced into a CAD system to
`generate surface models composed of triangular approxima
`tions which is the standard interface between a CAD system
`and the stereolithography apparatus.
`In addition to contour construction, the region between
`the inner and outer boundaries must be de?ned by hatch
`vectors to enable the solid region to be formed by cross
`linking of monomer in a prede?ned region in the monomer
`bath. By generating not only the contours. but also hatchings
`with different densities it is possible to produce different
`structures to represent cortical and trabecula bone.
`Of more recent times however, there has been reported a
`more direct technique in “Medical Applications of Rapid
`Prototyping Techniques” :201-216.
`This system addresses both the support generation and
`interpolation problems of earlier systems and is able to
`create directly from the CI‘ scans the SLA ?les of both the
`model and its support structures in a much shorter time.
`While it may be advantageous to utilise direct layer
`interfacing such that the most accurate directions of the
`input data in the scanning plane are produced on the most
`accurate directions of the stereolithography apparatus, the
`lack of true three dimensional data requires. as with the prior
`art systems, that the orientation of the part in the stere
`olithography apparatus should be the same as the orientation
`during the patient scanning operation.
`There are a number of serious disadvantages associated
`with conventional manufacture of stereolithographic models
`in the same orientation as conventional patient scanning
`orientation.
`As models are built up from successive 0.25 mm layers of
`polymerised resin. an upright model will take substantially
`longer to manufacture than a horizontally orientated model.
`For example. a 50 mm diameter cranial defect would require
`about 200 layers of polymerised material when in an upright
`position as against about 10-20 layers when the model is
`built in a horizontal orientation. Costs of model production
`could therefore be substantially reduced if manufacturing
`time could be reduced by selective orientation of models on
`the support platform in the monomer bath of the stere
`olithography apparatus.
`Moreover. selective orientation of models during manu
`facture would permit a plurality of objects to be simulta
`neously modelled and orientated in the most e?icient man
`ner.
`A further disadvantage is that with model construction
`limited to a single orientation. it is not possible to selectively
`orientate the model for construction to minimise the extent
`of support structure which must subsequently be removed
`from the completed model.
`In all prosthetic implant surgery it is essential that a very
`close ?t is obtained between the prosthesis and the tissue to
`which it is attached if an effective bond is to be obtained
`from tissue growth. Accordingly. there is a need for a much
`more accurate method for construction of prosthetic
`implants. both for hard and soft tissue regions. to ensure an
`initial accurate ?t and accurate contour to avoid intraopera
`tive delays while adjustments. contour changes or prolonged
`attachment procedures are undertaken.
`It would also be advantageous in arterial and vascular
`surgery to provide complex branched prostheses which
`require attachment to blood vessels at the free ends of the
`prosthesis rather than having to construct the prostheses
`
`It is an aim of the present invention no provide an
`improved method for the construction of prosthetic implants
`and/or models of anatomical pathology.
`It is another aim of the present invention to provide
`improved implantable prostheses.
`It is yet a further aim of the invention to provide an
`improved method for implantation of prostheses.
`According to one aspect of the invention there is provided
`a method for stereolithographic construction of implantable
`surgical prosthesis and/or an anatomical pathology model,
`said method comprising the steps of:
`inputting into a data storage means scanning data relating
`to internal and/or external surfaces of anatomical
`pathology;
`computing the stored scanning data according to a pre
`determined algorithm to reconstruct a plurality of two
`dimensional cross-sectional images of the anatomical
`pathology;
`computing said plurality of two dimensional cross
`sectional images according to a predetermined algo
`rithm to generate a three dimensional coordinate data
`set for the anatomical pathology;
`and generating a three dimensional representation of said
`anatomical pathology by stereolithographic modelling
`’ of a cross linkable liquid polymer using selected
`sequential two dimensional coordinate data sets com
`puted in preselected planes from said three dimensional
`coordinate data set.
`Suitably said scanning data comprises digitised X-ray,
`MRI. MRA, PET acoustic or other computed tomographic
`data.
`If required the stored scanning data may be computed to
`reconstruct a plurality of two dimensional cross sectional
`images of an existing anatomical pathology.
`Alternatively the stored scanning data may be computed
`to reconstruct a plurality of two dimensional cross-sectional
`images of an anatomical defect in a region of the pathology
`scanned.
`If required. the two dimensional images of said defect
`may be generated by direct computation of image data
`obtained from a corresponding region on an opposite side of
`a symmetrical axis of a reconstructed two dimensional
`image.
`Alternatively said two dimensional images of said defect
`may be generated by overlaying. in the defect region. an
`image obtained from an opposite side of a symmetrical axis
`of a reconstructed two dimensional image, assigning respec
`tive values to the image data obtained from opposite sides of
`said symmetrical axis and adding or subtracting the assigned
`Values to obtain two dimension image data for the defect
`only.
`If required, the two dimensional data obtained for the
`defect may be manipulated to obtain a best ?t or enhanced
`fit with the defect region.
`Preferably said method includes the step of simulta
`neously modelling a ?rst portion of an anatomical pathology
`with an aperture de?ning the boundary of a defect and a
`second portion of said anatomical pathology complementary
`to said defect.
`If required said second portion may be modelled with a
`peripheral boundary slightly larger than the peripheral
`boundary of said aperture.
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`The anatomical prosthesis may be constructed directly
`from a cross linkable polymer by stereolithographic mod
`elling.
`Preferably the liquid polymer is comprised of a biocom
`patible material. at least when cross linked.
`Alternatively the prosthesis may be constructed indirectly
`by forming a mould from the stereolithographically formed
`anatomical pathology representation.
`Preferably however the prosthesis may be constructed
`indirectly by manipulation of the scanned data. the recon
`structed two dimensional images or the three dimensional
`coordinate data set to form a mould or mould surface from
`which the prosthesis may be moulded or otherwise formed
`According to another aspect of the invention there is
`provided a prosthetic implant whenever made in accordance
`with the aforesaid method.
`The prosthetic implant may be comprised of an indirectly
`formed biocompatible metal such as titanium or the like.
`The prosthetic implant may be constructed directly or
`indirectly from a biocompatible or bio-inert polymeric
`organic compound such as acrylic polymers and
`co-polymers, polyesters, polyole?ns, polyurethanes, silicon
`polymers and co-polymers, vinyl polymers and
`co-polymers. halogenated hydrocarbons such as Te?on
`(Trade Mark), nylons etc. or even proteinaceous materials.
`Preferably the prosthetic implant is constructed directly
`by stereolithographic modelling of a polymerisable or cross
`linkable proteinaceous material.
`If required the prosthetic implant may be constructed
`indirectly from an inorganic compound such as
`hydroxyapatite, ceramics or like materials.
`Suitably the prosthetic implant is porous or comprises
`porous regions to permit bonding by tissue migration.
`If required the prosthetic implant may be impregnated
`with tissue growth stimulation factors such as bone mor
`phogenetic protein or the like.
`The prosthetic implant may include mounting or attach
`ment means to facilitate attachment to adjacent anatomical
`pathology.
`According to yet another aspect of the invention, there is
`provided a method for the surgical implantation of a pros
`thesis comprising the steps of:
`tomographically scanning a region of anatomical pathol
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`inputting scanning data so obtained into a data storage
`means;
`computing the stored scanning data according to a pre
`determined algorithm to reconstruct a plurality of two
`dimensional cross-sectional images of the anatomical
`pathology;
`computing said plurality of two dimensional cross
`sectional images according to a predetermined algo
`rithm to generate a three dimensional coordinate data
`set for the anatomical pathology;
`and generating a three dimensional representation of said
`anatomical pathology or a mould surface therefor by
`stereolithographic modelling of a cross linkable liquid
`polymer using selected sequential two dimensional
`coordinate data sets computed in preselected planes
`from said three dimensional coordinate data set; and
`surgically implanting in a patient a prosthesis obtained
`directly or indirectly therefrom. said prosthesis being
`characterised in having a close ?t with connective
`tissue and contours appropriate for the implant site.
`Preferably said three dimensional representation includes
`a region of anatomical pathology surrounding or adjacent to
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`the region of anatomical pathology being modelled, said
`surrounding region providing a template for accurate ?t of a
`prosthesis so obtained.
`
`BRIEF DESCRIPTION OF THE INVENTION
`
`In order that the various aspects of the invention may be
`more fully understood and put into practice, reference will
`now be made to various preferred embodiments illustrated in
`the drawings in which:
`FIG. 1 shows schematically a data ?ow chart from capture
`through to operation of the SLA apparatus.
`FIG. 2 shows a cranial defect and a prosthesis therefor.
`FIG. 3 shows a cross sectional view of a cranio-plastic
`implantation according to one method.
`FIG. 4 shows a variation on the method of FIG. 2.
`FIG. 5 shows a variation in the means of attachment of the
`cranio-plastic implant of FIGS. 2-4.
`FIG. 6 shows a prosthetic replacement for an aortic
`junction aneurysm.
`FIG. 7 shows an alternative method of production of a
`cranioplastic model.
`FIG. 8 shows alternative methods of orientation of a
`model in an SLA monomer bath.
`
`DETAILED DESCRIPTION
`
`In FIG. 1 CT scan data is obtained conventionally from an
`X Ray. MRI. MRA, PET scanner and is processed by
`conventional software to produce. initially, two dimensional
`boundary images of say, a bony structure for each tomo
`graphic slice.
`The segmented data is then further processed by conven
`tional contour or voxel methods to produce a three dimen
`sional data set for the anatomical pathology scanned. The
`three dimensional data set may be manipulated by conven
`tional CAD software if so required.
`The three dimensional data set is then further processed to
`produce parallel two dimensional slice image data sets.
`which can also be manipulated by the CAD software, before
`creation of the SLA build ?les required to operate the SLA
`apparatus.
`Once the three dimensional data set is established. two
`dimensional slice data may be obtained at a selected spacing,
`suitably 0.25 mm to correspond to the model build layer
`thickness of the SLA apparatus.
`For reasons which will be described in greater detail later,
`an operator is able to chose the planar orientation of the two
`dimensional slice data to optimise the SLA modelling opera
`tion rather than be constrained to generation of SLA build
`?le data representing two dimensional data sets only in
`planes parallel to the tomography scan data as with prior art
`systems.
`Hatch ?le vectors may be computed from the initial two
`dimensional segmented image data but preferably hatch ?le
`vectors are computed from the reconstructed two dimen
`sional image data sets for the planar orientation chosen. This
`avoids the need for interpolation by repetition to create SLA
`build slices as with prior art systems. Moreover. the hatch
`?le vectors are a more accurate representation of the solid
`structure for each individual SLA build slice.
`FIG. 2 shows a human skull 1 with a cranial defect 2.
`An ideal cranio-plastic implant 3 comprises a body of
`bio-compatible material which is shaped such that its thick
`ness and contours are substantially identical to the bone
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`which previously occupied the craniotomy defect. The
`peripheral shape is substantially identical to the peripheral
`shape of the defect aperture to permit a very close ?t.
`Accordingly. in a cranioplasty procedure, the previously
`manufactured cranio-plastic implant is able to be ?tted
`directly to the defect and secured therein with acrylic
`cement. wires or screws. During such a procedure the
`operating time is minimised and the inherent risk of infec
`tion substantially reduced as little, if any. adjustments are
`necessary to adapt the implant to ?t the defect.
`Moreover the very close ?t of the implant into the defect
`aperture minimises the degree of bone tissue growth
`required to bond with the implant to regain maximum
`structural integrity of the cranial structure.
`The “ideal” cranio-plastic implant described with refer
`ence to FIG. 2 is obtained by a stereolithographic method in
`accordance with one aspect of the invention.
`Initially. part or all of the cranial structure of a patient is
`scanned to obtain X-ray or MRI computed tomography data
`of spaced cross sections in a coronal or axial plane trans
`verse to the long axis of the body due to the physical
`constraints of the scanning apparatus.
`Using conventional computer software. the scanning data
`is segmented according to tissue type to de?ne tissue bound
`aries and the segmented data is then reconstructed as two
`dimensional images in the same coronal plane.
`Again. using conventional computer software the data
`relating to the reconstructed two dimensional images is
`computed and interpolated by voxel or contour means to
`generate three dimensional coordinate data sets which may
`be employed to display or print out two dimensional images
`of the three dimensional representation.
`The three dimensional coordinate data sets may then be
`computed to generate two dimensional image data sets at
`much closer intervals than those representing the original
`coronal scan planes. Moreover, these two dimensional
`image data sets may be generated in any desired plane eg.
`sagittal, medial, coronal or other planes oblique to the main
`orthogonal planes.
`.
`Accordingly depending upon the position of the defec ,
`two dimensional coordinate data sets may be established in
`one or more planes and the data sets may be combined to
`provide highly accurate three dimensional contour and shape
`de?nition in the region of the defect, particularly its bound
`aries.
`FIG. 3 shows one method for generating two dimensional
`coordinate data sets to construct three dimensional coordi
`nate data sets for a cranio-plastic implant to be accommo
`dated in the defect region 2.
`From the closely spaced two dimensional images recon
`structed from the computed three dimensional coordinate
`data sets. a two dimensional image may be drawn with a
`light pen or the like to ?t the defect aperture. In so doing the
`drawn image follows a visual “best ?t” mode in terms of
`thickness and contour. This procedure is repeated over a
`series of spaced parallel planes from the top of the defect to
`the bottom or vice versa.
`The process may be repeated in a medial plane orthogonal
`to the ?rst coronal plane to eliminate inaccuracies in say the
`upper and lower regions of the reconstructed image of the
`defect.
`The combined image data representing three dimensional
`coordinate data for a cranio-plastic implant is assigned a
`numerical value as is the data representing the surrounding
`bone tissue. By appropriate allocation of respective values
`
`8
`and then adding or subtracting those values, a three dimen
`sional coordinate data set is obtained only for a structure -
`representing a cranio-plastic implant.
`The data so obtained is then employed with a stereolitho
`graphic apparatus to construct a model of an implantable
`prosthesis from a cross-linkable acrylic polymer.
`FIG. 4 shows an alternative method for construction of
`three dimensional coordinate data sets of a cranio-plastic
`implant.
`In this method, two dimensional images are reconstructed
`from the three dimensional coordinate data sets at required
`planar spacings as with the method described above.
`An axis of symmetry 4 is established relative to the two
`dimensional image and the bone tissue regions on each side
`of the axis are assigned arbitrary values of say +1 for the left
`side and —l for the right side.
`A mirror image of the left side is then superimposed on
`the right side image and the numerical values of the bone
`tissue regions are summed. The values for the intact portions
`of the cranial structure are nulli?ed leaving an image 5
`having a valve of +1 and representing a two dimensional
`cross sectional image of a plane in the region of the defect.
`As most human cranial structures are not perfectly sym
`metrical there may be some misalignment of the mirror
`image object with the defect aperture. Using suitable graph
`ics manipulation software or perhaps simply a light pen,
`corrections may be made as appropriate to align the super
`imposed image.
`FIG. 5 shows yet another embodiment of the invention.
`Using a graphics manipulation program. light pen or the
`like. the thickness of the three dimensional coordinate data
`for the implant may be increased, at least toward the
`peripheral edges. In this manner it is possible to build a
`smoothly tapered ?ange 6 around the periphery of the
`implant 3 to provide a more secure means of attachment to
`the surrounding bone tissue and otherwise permit a greater
`area for tissue bonding.
`Suitably, the implant shown in FIG. 5 is constructed of a
`somewhat porous hydroxyapatite material and is impreg
`nated in the region of ?ange 6 with bone morphogenetic
`protein to stimulate penetration of bone tissue into the
`implant.
`'
`FIG. 6 illustrates a prosthetic implant 17 to replace an
`aortic junction. damaged for example by atherosclerosis
`and/or an aneurysm.
`Using scanning data obtained from say MRI computed
`tomography. a complex hollow branched structure may be
`created directly using a ?exible cross-linkable polymeric
`material in a stereolithographic apparatus. Where a region of
`wall thickness in the patient’s aortic junction is reduced or
`damaged by the aneurism, this can be corrected or compen
`sated for by manipulating the initial or reconstructed two
`dimensional scan images in a manner similar to that
`described with reference to FIGS. 3 and 4.
`Alternatively the implant may be created indirectly by
`creating a female mould by a stereolithographic process, the
`mould having an internal surface corresponding to the
`external dimensions and contours of a computed three
`dimensional representation. The implant may be formed in
`the mould by. say. rotational casting of a thermoplastic
`material or a cross-linkable liquid polymer.
`Arterial and vascular implants constructed in accordance
`with the invention have the advantage that operation time is
`substantially reduced. the number of sutured joins. sutures
`and suturing time is also substantially reduced and the free
`
`35
`
`50
`
`55
`
`65
`
`-10-
`
`

`
`5,741,215
`
`15
`
`20
`
`25
`
`35
`
`ends of the implant are substantially identical in diameter to
`the artery or vein to which they are to be attached
`FIG. 7 illustrates a most preferred method of creating a
`defect prosthesis such as a cranioplastic implant.
`After establishing a three dimensional coordinate data set
`for a region 7 surrounding the defect 2, two dimensional
`image date is then reconstructed in spaced parallel planes
`generally perpendicular to the notional “surface” of region 7.
`By orienting the reconstructed two dimensional images in
`this manner highly accurate boundary de?nitions are obtain
`able for the edge of the effect aperture as well as the cross
`sectional contours of region 7.
`A prosthetic model for the defect is