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From CAD User Mechanical Magazine  Vol 20 No 12 - JANUARY 2008

David Chadwick explains how Simpleware's 3D imaging, model and mesh generation and CAD integration tools transform the development of medical implants - and solve many other complex multi-part and multi-segmented issues

I haven't a clue why the company calls itself Simpleware - for simple it certainly ain't! Furthermore, they supplied me with so much material about the software and the applications in which it is being used, that I got a bit lost reading up about 'the simulation of salt diffusion in a pork (bacon) side using 3D imaging', when I should have been reading about how it is used with CAD software to solve some complex modelling issues!

Perhaps the most interesting of these more complex applications is the software’s ability to create a 3D image of the pelvic region of someone about to receive a hip implant - and to add a 3D model of the implant itself, creating volumetric meshes from the imported image and, together with the implant, building a complete FEA model for analysis of the interaction between the pelvis and the implant.
Such a complex solution to a pressing medical problem begs a lot of questions that can only be answered by describing the software that can handle it. Simpleware is a series of tools that convert 3D images into CAD, rapid prototyping and finite element models.

It comes in three parts - ScanIP, which handles all of the image processing, taking in scan data from a wide range of imaging devices, +ScanFE, which can convert 3D image data into multi-part volumetric models with unique meshing capabilities, and +ScanCAD, which allows users to import and place CAD models with image data.

ScanIP
ScanIP comes with lots of image processing tools to enable it to handle all kinds of images, including those with complex internal architectures - such as the human body, engine blocks to produce transparent 3D images (fig 1), and even composite materials, or materials with arbitrary complexity, such as foam! It uses the tools to visualise, segment and generate multi-part CAD models, making it ideal for non-destructive reverse-engineering and the analysis of biological structures.
ScanIP can take in 3D image data from MRI, CT and microCT scanners, and can import numerous data formats including DICOM (a medical imaging format), ACR-NEMA etc., and even stacks of 2D JPGs or TIFFs, with which it can create 3D images!
It also comes with a long list of image processing tools, from noise reduction, smoothing and metal artifact filters, to flood and cavity fills, thresholding, multi-part anti-aliasing and mesh decimation - plus many others. All are designed to produce watertight models with low distortion high quality mesh surfaces, whose accuracy is contingent purely on image quality. Output consists either of multi-part surface meshes or STL file data.

Creating FEA/CFD models
The next step is to turn the data into something usable, and for that Simpleware has provided +ScanFE and +ScanCAD. The former, meshing, module converts the segmented 3D image into multi-part volumetric models, using the company's proprietary technology, and providing 3D image based models of unparalleled accuracy and sophistication (Fig 2).
+ScanFE uses the data from ScanIP to generate volume and surface meshes, contact surfaces and material properties from segmented data, which can then be imported directly into FE and CFD packages - material properties being established through signal strength.
Multiple structures, or regions of interest can be meshed together, and contact surfaces between them established - best explained by going back to the side of bacon (I knew it would be relevant!).
A CT scan of the side of bacon picked up, basically, bone, fat and muscle (meat), all with different densities. To analyse the absorption of salt through the joint, the different areas with different absorption properties have to be defined. Using thresholding tools in the imaging software - ScanIP - minimum and maximum signal strengths from the scan were used to identify the different components of the joint, assisted by Floodfill and Level Set Methods to semi-automate segmentation of the joint.
In this particular case, simulation of the salt absorption in the multi-part joint of meat was passed to COMSOL's Multiphysics because of the complex nature of the analysis.
+ScanFE is a fast and accurate tool for building analytical models, taking just a few minutes after importing raw image processing data, making it a practical tool for many engineering and non-destructive testing applications. Again, the topological, or morphological accuracy is governed by the image quality, and the volumetric meshes can be exported to all leading analysis packages - including Abaqus, Ansys, MSC. Patran Neutral, Fluent, and STL - and also for multi-physics simulations (fig. 3).
The software can also be used for rapid prototyping, with RP models exact geometric replicas of FE mesh - an opportunity which has prompted many users in biological sciences to create exact replicas, sometimes scaled up dramatically, from scans of both living and extinct creatures (one case study used the skull of an extinct dinsoaur to check its 'bite power'!).

3D Images and CAD
As we approach the Medical Devices exhibition at NEC, and considering other medical applications in this issue, the use of Simpleware software to model hip implants is very apt (fig. 4). The tool that combines the 3D image from ScanIP with the 3D CAD model of the implant (called Stryker, in case your hips are feeling the strain) is +ScanCAD. This allows CAD models to be positioned within image data, and the combined results to be exported as multi-part CAD models for further modelling of the implant, or, using +ScanFE, to be converted automatically into multi-part FEA or CFD meshes.
3D models can be imported from most major CAD applications, or using IGES, STEP or STL formats, and can be positioned interactively, or using the keyboard in the 3D image, and supplied with constrained motion along user-defined vectors.
The benefits for medical or dentistry problems can easily be seen, but the software can also be used in commercial environments, a typical example being the incorporation of mobile phone designs into MRI head models to explore EM exposure, or just comfort and fit in the ear.

Ease-of-Use
Simpleware does not, obviously, reflect on the complex issues being solved using very advanced image processing, volumetric meshing and complex model generation with multi-part analysis capabilities, but on the ease with which the different tools can be accessed and used. The background to all modules is a user-customisable graphical interface with both 2D and 3D views, the automation of many functions - such as the one-click operation of multi-part smoothing in ScanIP, and the improved visualisation of complex data sets.
In +ScanCAD the exact placing of 3D models is made simple using an intuitive positioning widget, and FEA and CFD meshing is automatic. Multiple structures can be meshed simultaneously in +ScanFE.

“four!”
The last image (fig 5) represents a very painful collision between a golf ball and a human eye. The simulation process, carried out by ARUP and the University of Exeter, involved an MRI scan, which was segmented into five structures - the globe, optic nerve, bony orbit, extra-oracular muscles, eyelids and facial soft tissue. The golf ball was introduced for impact analysis. All six structures were meshed simultaneously, and impact analysis was carried out in LS-Dyna.
What it cannot do is explain why standing behind the golfer as he tees off does not eliminate such a possibility!
www.simpleware.com

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