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Complex Anatomies in Medical Rapid Prototyping
Abstract
The complex anatomy of the nasal airways is an anatomy that is difficult to understand from conventional twodimensional anatomy
images. The objective of the present study was to establish the methods and parameters necessary to provide three-dimensional
triangulated models for Rapid Prototyping. Anatomical data derive from scanned medical images made with computerized tomography.
Different data sets of nasal airway structures were segmented and 3D reconstructed. With high-resolution scans, accurate segmentation
of the structures was possible. The reconstructed and triangulated models were evaluated in order to determine triangulation
parameters that are needed for Rapid Prototyping models. Gaining insight in the interplay of parameters necessary for modeling
complex anatomies for Rapid Prototyping enables to provide accurate Rapid Prototyping models for biomedical engineering applications.
... Digital bone surface meshes of the trapezia and first metacarpals were generated from the CT data via semi-automated, density-based threshold segmentation, followed by manual editing (Mimics v12-20, Materialise, Leuven, Belgium). Segmentation masks of each bone were exported as closed triangular meshes without triangle refinement and with minimal smoothing (single iteration, smoothing factor 0.030) (Bardyn et al., 2010;Mallepree and Bergers, 2009;Taubin et al., 1992). For consistent analysis, all left-hand scans were mathematically mirrored. ...
Background
Thumb carpometacarpal osteoarthritis is characterized by osteophyte growth and changes in the curvature of the articular surfaces of the trapezium and first metacarpal. The aim of this longitudinal study was to quantify in-vivo bone morphology changes with osteoarthritis progression.
Methods
The study analyzed an observational dataset of 86 subjects with early thumb osteoarthritis and 22 age-matched asymptomatic controls. CT scans of subjects' affected hands were acquired at enrollment (year 0), and at 1.5, 3, 4.5, and 6-year follow-up visits. Osteoarthritic subjects were classified into stable and progressive groups, as defined by osteophyte volume and the rate of osteophyte growth. Trapezium height, width, and volar facet recession, along with first metacarpal volar beak recession and recession angle, were quantified.
Findings
Mean trapezium width increased 12% over six years in the progressive osteoarthritis group. Trapezium volar recession of the progressive osteoarthritis group was significantly greater than stable at enrollment (P < 0.0001) and year 6 (P < 0.0001). The first metacarpal volar beak of the progressive osteoarthritis group recessed significantly faster than stable (P = 0.0004) and control (P = 0.0003). In year 6, volar beak surfaces in subjects with progressive osteoarthritis were flatter with reduced curvature, measuring −8.7 ± 4.0 degrees, compared to the stable osteoarthritis (P < 0.0001) and control groups (P = 0.0003), which maintained nominal curvatures, measuring 0.7 ± 2.5 and 0.2 ± 3.2 degrees, respectively.
Interpretation
Our results demonstrate significant recession and reduction in the angle of the first metacarpal volar beak in progressive osteoarthritis. Flattening of the first metacarpal volar beak may have important associations with carpometacarpal joint contact and loading migrations, further propagating osteophyte formation and bony remodeling. This work highlights the volar beak of the first metacarpal as a region of morphology change with disease.
... Digital bone surface meshes of the trapezia and first metacarpals were generated from the CT data via semi-automated, density-based threshold segmentation, followed by manual editing (Mimics v12-20, Materialise, Leuven, Belgium). Segmentation masks of each bone were exported as closed triangular meshes without triangle refinement and with minimal smoothing (single iteration, smoothing factor 0.030) (Bardyn et al., 2010;Mallepree and Bergers, 2009;Taubin et al., 1992). For consistent analysis, all left-hand scans were mathematically mirrored. ...
... The CT scan files were recorded in Digital Imaging and Communications in Medicine (DICOM) format. The details of importing CT scan files to the reconstruction software package (MIMICS 3D, Materialise, MI, USA) are explained in more detail elsewhere (Inthavong et al., 2010a,b;Mallepree & Bergers, 2009). Briefly, by selecting a threshold setting defined by a higher and lower bound (min: À 1024 and max: À250 in the Hounsfield scale), the airway passage was extracted from the Table 1 Summary of child subject information and airway diameters of child replicas. ...
The principal role of medical imaging is to provide valuable data for diagnoses. However, imaging systems have been exhibiting certain weaknesses regarding the generated visual representation and the further utilization of the acquired data. Computer-aided design (CAD) is, nowadays, widely used for the design of various implants and, in general, for the development of medical devices. However, traditionally, there has been no direct, effective method to design based on real anatomical data. Similarly, finite element analysis (FEA), an established numerical simulation method, has been shown to be applicable to numerous biomechanical applications for studying the function of anatomical systems. Nevertheless, although medical images can provide important information regarding the geometry and the material properties of various tissues, the communication of such information between various image modalities and the FEA software has been quite demanding. Additive manufacturing (AM), a fast and accurate method of constructing the physical counterparts of CAD virtual models, has enormous potential in medical applications, for manufacturing anatomical replicas, product prototypes, or even actual implants, provided that it can also utilize the geometrical information of anatomical data. The effective integration of medical imaging with digital engineering, namely, CAD, FEA, and AM, can provide a powerful method for the realistic modeling and simulation of various body structures, the design and development of implants, tools, and medical devices, and the diagnosis and treatment of various pathologies. For this purpose, the imaging principles, dose, protocols, and accuracy relevant to maxillofacial practice as well as the overall process for modeling the anatomy are described in this chapter.
Osteophytes are associated with later‐stage osteoarthritis and are most commonly described using semi‐quantitative radiographic grading systems. A detailed understanding of osteophyte formation is, in part, limited by the ability to quantify bone pathology. Osteophytes can be quantified relative to pre‐osteoarthritic bone, or to the contralateral bone if it is healthy; however, in many cases, neither are available as references. We present a method for computing three‐dimensional osteophyte models using a library of healthy control bones. An existing dataset containing the computed tomography scans of 90 patients with first carpometacarpal osteoarthritis (OA) and 46 healthy subjects was utilized. A healthy bone that best‐fit each OA subject's bone was determined using a dissimilarity‐excluding Procrustes registration technique (DEP) that minimized the influence of dissimilar features (i.e., osteophytes). The osteophyte model was then computed through Boolean subtraction of the reference bone model from the OA bone model. DEP reference bones conformed significantly better to the OA bones (p < 0.0001) than by finite difference iterative closest point registration (root mean squared distances 0.33mm ± 0.05mm and 0.41mm ± 0.16mm, respectively). The effect of library size on dissimilarity measure was investigated by leave‐k‐out cross‐validation randomly reducing k from 46 to 1. A library of n >= 31 resulted in less than 10% difference from the theoretical minimum value. The proposed method enables quantification of osteophytes when the disease‐free bone or the healthy contralateral bone are not available for any three‐dimensional dataset. Quantifying osteophyte formation and growth may aid in understating the associated mechanisms in osteoarthritis. This article is protected by copyright. All rights reserved.
Purpose
Aims to investigate medical rapid prototyping (medical RP) technology applications and methods based on reverse engineering (RE) and medical imaging data.
Design/methodology/approach
Medical image processing and RE are applied to construct three‐dimensional models of anatomical structures, from which custom‐made (personalized) medical applications are developed.
Findings
The investigated methods were successfully used for design and manufacturing of biomodels, surgical aid tools, implants, medical devices and surgical training models. More than 40 medical RP applications were implemented in Europe and Asia since 1999.
Research limitations/implications
Medical RP is a multi‐discipline area. It involves in many human resources and requires high skills and know‐how in both engineering and medicine. In addition, medical RP applications are expensive, especially for low‐income countries. These practically limit its benefits and applications in hospitals.
Practical implications
In order to transfer medical RP into hospitals successfully, a good link and close collaboration between medical and engineering sites should be established. Moreover, new medical applications should be developed in the way that does not change the traditional approaches that medical doctors (MD) were trained, but provides solutions to improve the diagnosis and treatment quality.
Originality/value
The presented state‐of‐the‐art medical RP is applied for diagnosis and treatment in the following medical areas: cranio‐maxillofacial and dental surgery, neurosurgery, orthopedics, orthosis and tissue engineering. The paper is useful for MD (radiologists and surgeons), biomedical and RP/CAD/CAM engineers.
Additive fabrication (AF) and rapid prototyping (RP) technologies are mostly associated with applications in the product development
and the design process as well as with small batch manufacturing. Due to their relatively high speed and flexibility, however,
they have also been employed in various non-manufacturing applications. A field that attracts increasingly more attention
by the scientific community is related to the application of AF technologies in medicine and health care. The associated research
is focused both on the development of specifically modified or new methods and systems based on AF principles, as well as
on the applications of existing systems assisting health care services. In this paper, representative case studies and research
efforts from the field of AF medical applications are presented and discussed in detail. The case studies included cover applications
like the fabrication of custom implants and scaffolds for rehabilitation, models for pre-operating surgical planning, anatomical
models for the mechanical testing and investigation of human bones or of new medical techniques, drug delivery devices fabrication,
as well as the development of new AF techniques specifically designed for medical applications.
Transparent stereolithographic rapid prototyping (RP) technology has already demonstrated in literature to be a practical model construction tool for optical flow measurements such as digital particle image velocimetry (DPIV), laser doppler velocimetry (LDV), and flow visualization. Here, we employ recently available transparent RP resins and eliminate time-consuming casting and chemical curing steps from the traditional approach. This note details our methodology with relevant material properties and highlights its advantages. Stereolithographic model printing with our procedure is now a direct single-step process, enabling faster geometric replication of complex computational fluid dynamics (CFD) models for exact experimental validation studies. This methodology is specifically applied to the in vitro flow modeling of patient-specific total cavopulmonary connection (TCPC) morphologies. The effect of RP machining grooves, surface quality, and hydrodynamic performance measurements as compared with the smooth glass models are also quantified.
Purpose
This paper aims to illustrate a number of instances where RP and associated technology has been successfully used for medical applications.
Design/methodology/approach
A number of medical case studies are presented, illustrating different uses of RP technology. These studies have been analysed in terms of how the technology has been applied in order to solve related medical problems.
Findings
It was found that RP has been helpful in a number of ways to solve medical problems. However, the technology has numerous limitations that have been analysed in order to establish how the technology should develop in the future.
Practical implications
RP can help solve medical problems, but must evolve if it is to be used more widespread in this field.
Originality/value
This paper has shown a number of new applications for RP, providing a holistic understanding how the technology can solve medical problems. It also identifies a number of ways in which the technology can improve in order to better solve such problems.
Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering.
Using RP to fabricate custom implants and prosthesis for surgical planning and education is now an important area of research.
Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current
CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help
designers exploit the expanded opportunities offered by RP technology. Medical data cannot be input into these CAD systems
directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling
and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In Part 1 of two papers, a
new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is
developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits
advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit
the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. This
paper, Part 2, deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through
volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently.
Software development and case studies are also given.
Stereolithographic (SL) biomodelling is a new technology that allows three-dimensional (3-D) computed tomography (CT) data to be used to manufacture solid plastic replicas of anatomical structures (biomodels). A prospective trial with the objective of assessing the utility of biomodelling in complex surgery has been performed. Forty-five patients with craniofacial, maxillofacial, skull base cervical spinal pathology were selected. 3-D CT or MR scanning was performed and the data of interest were edited and converted into a form acceptable to the rapid prototyping technology SL. The data were used to guide a laser to selectively polymerize photosensitive resin to manufacture biomodels. The biomodels were used by surgeons for patient education, diagnosis and operative planning. An assessment protocol was used to test the hypothesis that 'biomodels in addition to standard imaging had greater utility in the surgery performed than the standard imaging alone'. Biomodels significantly improved operative planning (images 44.09%, images with biomodel 82.21%, P < .01) and diagnosis (images 65.63%, images with biomodel 95.23%, P < .01). Biomodels were found to improve measurement accuracy significantly (image measurement error 44.14%, biomodel measurement error 7.91%, P < .05). Surgeons estimated that the use of biomodels reduced operating time by a mean of 17.63% and were cost effective at a mean price of $1031 AUS. Patients found the biomodels to be helpful for informed consent (images 63.53%, biomodels 88.54%, P < .001). Biomodelling is an intuitive, user-friendly technology that facilitated diagnosis and operative planning. Biomodels allowed surgeons to rehearse procedures readily and improved communication between colleagues and patients.
Medical rapid prototyping applications and methods
- L C Hieu
- N Zlatov
- J Vander Sloten
- L.C. Hieu