Patent Application: US-81228309-A

Abstract:
a new conceptual biomedical method is presented for designing scaffold - based bone implants and using these implants in treating deteriorated bones . these implants have micro - architectural bone structures that are capable of mimicking the stochastic micro - structure as in natural bone bio - mineral structures . moreover , they can be adapted as specific tailor - made compatible bone - repair mediator implants to be used as effective substitutes for natural damaged bone fracture structures .

Description:
some embodiments of the invention are herein described , by way of example only , with reference to the accompanying drawings . with specific reference to the drawings in detail , it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only . these particulars are presented for the purpose of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention . in this regard , no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention . the description , together with the drawings , makes it apparent to those skilled in the art how the several forms of the invention may be embodied in practice . the scaffold - based implant structure is defined by applying volumetric hole in - filling to diseased cavities of the bone micro - structure . these scaffold - based implants can be designed and produced in advance before they are used . some embodiments of the present invention offer new and unique methods for detecting and characterizing damaged cavities by applying a 3d imaging technique before hole in - filling . diseased bone cavities are not straightforward due to the porous and deformed nature of the bone micro - structure . some embodiments of the present invention use a 3d computational modeling method that is based on a 3d texture synthesis technique . this method is an extension of the 2d method to three dimensions to achieve the desired outcome of volumetric micro - cavity hole in - filling . this new method can be used to reproduce the micro - structural architecture in a sample of fractured bone , thus providing the designer and engineer with a bone scaffold - based implant required for better bone growth and improved healing . two modeling methods have been extended and implemented : voxel - by - voxel and block - wise texture syntheses . in the 3d images produced by computational modeling , the resulting topology is much more complex than in the 2d case . moreover , the bone has a 3d stochastic texture structure which has no exact pattern repetitions . some embodiments of the present invention present a novel method for modeling natural scaffold - based implants to fill in cavities ( holes ) in cancellous bone caused by bone diseases . as mentioned herein before , this type of bone is characterized by a complex micro - structure composed mainly of trabecula modeled as thin cylindrical rods and plates . cavities in the 3d micro - structure are identified by measuring the cavity volumes and comparing them to a specified threshold . the present invention provides a novel method for seamless in - filling of these holes using deformed elements consistent with the 3d neighborhood of a given hole , and therefore provides highly improved implants . the hole in - filling is based on a 3d pattern - growing scheme , a 3d texture synthesis that takes into account the exerted forces so that the global directionality of the micro - structure is preserved . furthermore , another goal of some embodiments of the present invention is to optimize the scaffold according to the mechanical properties of the bone . this scheme can take the exerted forces into account so that the global directionality of the micro - structure is preserved . a main contribution of this invention is the development of customized micro - implants according to given bone micro - structures . some embodiments of the present invention describe a novel method for modeling scaffold - based implants that have the stochastic structure of bone and can be customized according to given bone structures . the method for designing these implants is based on applying a 3d texture synthesis technique that can create a scaffold to be inserted to the damaged cavities of a given bone . these scaffold - based implants can replace the diseased cavities in the cancellous bone . reference is made to fig1 a and 1 b , depicting two views of bone growth over a scaffold ( prior art ). in the figures , bone tissues grow over a standard implant that forms a scaffold for healing fractured bones . one of the main features of the present invention is a structure called a scaffold that is placed onto the bone so the bone can grow in areas where its micro - structure has been corrupted . the scaffold has two purposes : ( a ) its structure facilitates the growth of the bone around it , and ( b ) the material forming the scaffold is consumed by the bone and eventually degrades over the years as new healthy bone replaces the scaffold material . the inventors of the present invention have shown that the resulting bone structure resembles the scaffold structure ; therefore , its shape is critical from the point of view of functionality . detecting 3d holes in the cancellous bone sample . developing 3d texture synthesis for stochastic pattern of bone scaffold - based implants . developing topology optimization of the implants , based on mechanical constraints . merging the scaffold - based implant with its bone local neighborhood . the present invention has evolved a process for 3d in - filling of holes in a volumetric micro - structure . some implementations of the present invention work on deformed 3d volumetric bone textures , such as the trabecular bone micro - structure , rather than on segments and their topological relations . the present invention shows that the texture synthesis approach is more natural for bone micro - structures . reference is now made to fig2 , which shows a block diagram of steps taken in implementing the method of generating a scaffold in accordance with a referred embodiment of the present invention . the method involves scanning a medical model from μct / μmri and extracting its micro - structure 3d image ( 3d computerized model ). initially , the medical condition of the bone fractures is acquired either from μct or μmri images , where the input is digitized slice by slice , with each slice constituting a 2d image . a 3d model is extracted from the set of 2d slices , and 3d diagnostic methods are then applied . 3d texture synthesis is performed for 3d hole - filling of the deformed texture . the development of the method includes the following operations : 3d micro - structure meshing — reconstructing a 3d triangular mesh out of the set of 2d images . mesh analysis — performing mesh analysis to evaluate the quality of the mesh . extracting 3d holes from bone micro - structure — identifying the cavities representing the holes . this operation is not straightforward , since the structure of the bone is cancellous and is thus characterized by many hole - like patterns , forming a model of high genus . the criterion is size . if the volume of a cavity is larger than a certain threshold , it is defined as a hole . determining the 3d sampled patterns based on geometric and topological criteria — analyzing the surroundings of the hole and selecting a sample pattern that best fits the hole identified . this analysis takes both geometric and topological aspects into consideration . adaptive fitting of 3d sampled patterns to the 3d holes — applying a 3d texture synthesis - based method for bone structure . this method is based on seamlessly in - filling the hole according to the sample , so that the resulting mesh will appear as a single continuous 3d structure . texture optimization — texture optimization according to mechanical criteria . the present invention makes use of a voxel - by - voxel approach since this approach has more degrees of freedom when choosing a new pixel value . optionally , a patch - wise approach can be used which preserves the bone features better . texture synthesis for 3d hole in - filling is described as a texture synthesis process in 3d space . the following operations are needed : in this stage , a volumetric cavity in the mesh that represents a hole in the bone structure is identified . this volume is characterized by sparse and relatively thin trabeculae . in this stage , an appropriate pattern in the mesh is searched , wherein this pattern best fits the hole found in the previous stage . the match of such a pattern is determined by applying geometric analysis both on the pattern and on the hole . in this stage , an appropriate pattern in the mesh is searched , wherein this pattern fits the hole previously found . here , the match of the pattern is determined by applying topological analysis both on the pattern and on the hole . in this stage , holes are filled in using samples found in the prior two stages . the hole is filled in by applying a volumetric texture synthesis scheme , given the volume to be filled and the sample pattern . this is performed under the assumption that the bone pattern containing the hole also has regions with a normal , uncorrupted structure . moreover , in certain cases where features in the resulting model should be preserved , a feature extraction method for hinting at and assisting the growth process can be applied , as for example in lefebvre , et al ., 2006 . the algorithm applied in the preferred implementation of the present invention is based on the pixel - by - pixel approach introduced by efros , et al ., 1999 . the following steps illustrate a 3d extension of the 2d case : get a cubic region reg i from the synthesized mesh , centered at v i . this region may contain original voxels taken from the sample , synthesized ones and invalid ones ( that were not initialized ). get a cubic region reg j from the sample mesh , centered at v j . define a distance measure d ij , between reg i and reg j , such that d ij = d ( reg i , reg j ). create the set { reg j } that has a good correlation with reg . select reg j with the highest correlation from the set { reg j } and assign its center voxel value v j to the voxel v i in the synthesized mesh . optionally , the synthesized patterns are improved by integrating a mask that contains the main geometric features and shape characteristic in high contrast . this integration can be implemented via a weighting process . creating the features mask can optionally involve segmentation and feature detection . optionally , 3d texture synthesis based on the patch - wise approach ( block by block ) can be applied . the stages are described as follows : the input : a cubic region reg i from the synthesized mesh that defines a hole , centered at v i . this region can contain original voxels taken from the sample , synthesized ones and invalid ones ( that were not initialized ). get a cubic region reg j from the sample mesh ( the sampled window ), centered at v j . define a distance measure d ij , between reg i and reg j , such that d ij = d ( reg i , reg j ). create the set { reg j } that has a good correlation with reg i . select reg j with the highest correlation from the set { reg j } and copy it entirely to the synthesized mesh . optionally , this approach can be improved by introducing a minimal cut optimization scheme between adjacent patches . optionally , the method of the present invention as described herein can be improved by adding parameters of bone density and directionality . thus , a block can be added according to shape correlation and density threshold and according to the directionality of the surroundings volume of that block . evaluation of the correlation between the sample and the 3d synthesized meshes . evaluation of the correlation between an average 3d pattern in the sample and the 3d synthesized mesh . comparison of the averaged area / volume of the holes within a selected region in the sample , assuming the region is the same size as the sample image . comparison of the number of holes within a selected region ( density of holes ) with the number of holes in the sample , assuming the region is the same size as the sample image . reference is now made to fig3 depicting the following analysis : ( a ) original model , with ( b ) artificially generated hole , ( c ) micro - structure synthesized in accordance with a preferred embodiment of the present invention and ( d ) symmetric scaffold where r is approximately 10 units (˜ 350μ ). the results illustrate the reconstruction of a bone that models a scaffold - based implant using the proposed 3d texture synthesis method . the results are compared with other bone models that were filled in by standard scaffold - based implants . the stresses acting upon the structure are illustrated , with the entire implant illustrated on the left side and a cross - sectional view of the implant shown for clarity purposes on the right side . the color scaling ranges from blue ( minimal stress ) through green ( average stresses ) up to red ( maximal stresses ). as seen in the figure , the stress distribution for the micro - structure synthesized model of the proposed method is almost the same as for the original sample of the healthy bone structure . moreover , the standard scaffold - based implant bears minimal stress distribution , reducing the risk that the surrounding healthy bone structure might be harmed due to incorrect load exertion to it . almeida h . a ., bartolo p . j . and ferreira j . c . mechanical behavior and vascularisation of tissue engineering scaffolds [ conference ]// 3rd international conference on advanced research in virtual and rapid prototyping .— 2008 . bhat pravin , ingram stephen and turk greg geometric texture synthesis by example [ conference ]// sgp &# 39 ; 04 : proceedings of the 2004 eurographics / acm siggraph symposium on geometry processing .— nice : acm press , 2004 .- pp . 41 - 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