Mark D. Barry

CAD/CAM-assisted breast reconstruction

The application of computer-aided design and manufacturing (CAD/CAM) techniques in the clinic is growing slowly but steadily. The ability to build patient-specific models based on medical imaging data offers major potential. In this work we report on the feasibility of employing laser scanning with CAD/CAM techniques to aid in breast reconstruction. A patient was imaged with laser scanning, an economical and facile method for creating an accurate digital representation of the breasts and surrounding tissues. The obtained model was used to fabricate a customized mould that was employed as an intra-operative aid for the surgeon performing autologous tissue reconstruction of the breast removed due to cancer. Furthermore, a solid breast model was derived from the imaged data and digitally processed for the fabrication of customized scaffolds for breast tissue engineering. To this end, a novel generic algorithm for creating porosity within a solid model was developed, using a finite element model as intermediate.

Modelling of infectious spreading in heterogeneous polymer oxidation I. Development of a stochastic model

The heterogeneous features of the oxidation of polypropylene in the amorphous region are consistent with infectious spreading from a small number of sites, such as catalyst residues. A stochastic model was developed for demonstrating the spatial and temporal development of oxidation from these sites. In this model, the probability of passing the infection from one site to an adjacent site could be used in place of conventional rate constants. The probability of spreading was assumed to be temperature dependent, and modelled with Arrhenius behaviour. Each site was given a predefined lifetime such that the maximum probability of spreading coincided with the maximum rate of oxidation at a particular site. This has enabled visualisation of the spatial development of oxidation within the amorphous region. The epidemiological fractions corresponding to the remaining (unoxidised) polymer, the dead (oxidised) polymer and the infectious (oxidising) polymer, were calculated and used to test the limitations of the simple epidemiological model.

Computational fluid dynamic analysis of intracranial aneurysmal bleb formation

BACKGROUND The management of unruptured aneurysms is controversial, with the decision to treat influenced by aneurysm characteristics including size and morphology. Aneurysmal bleb formation is thought to be associated with an increased risk of rupture. OBJECTIVE To correlate computational fluid dynamic (CFD) indices with bleb formation. METHODS Anatomic models were constructed from 3-dimensional rotational angiography data in 27 patients with cerebral aneurysms harboring a single bleb. Additional models representing the aneurysm before bleb formation were constructed by digitally removing the bleb. We characterized hemodynamic features of models both with and without the blebs using CFDs. Flow structure, wall shear stress (WSS), pressure, and oscillatory shear index (OSI) were analyzed. RESULTS There was a statistically significant association between bleb location at or adjacent to the point of maximal WSS (74%, P = .019), irrespective of rupture status. Aneurysmal blebs were related to the inflow or outflow jet in 89% of cases (P < .001), whereas 11% were unrelated. Maximal wall pressure and OSI were not significantly related to bleb location. The bleb region attained a lower WSS after its formation in 96% of cases (P < .001) and was also lower than the average aneurysm WSS in 86% of cases (P < .001). CONCLUSION Cerebral aneurysm blebs generally form at or adjacent to the point of maximal WSS and are aligned with major flow structures. Wall pressure and OSI do not contribute to determining bleb location. The measurement of WSS using CFD models may potentially predict bleb formation and thus improve the assessment of rupture risk in unruptured aneurysms.

Virtual reconstruction and morphological analysis of the cranium of an ancient Egyptian mummy

A mummy of an Egyptian priestess dating from the 22nd dynasty (c. 770 BC), completely enclosed in an anthropoid (human shaped) coffin, was scanned on a CT scanner. An accurate reconstruction of the cranium was generated from 115 × 2 mm CT images using AVS/Express on a SGI computer. Linear measurements were obtained from six orthogonal cranial views and used in a morphometric analysis software package (CRANID). The analyses carried out were both linear and nearest neighbour discriminant analysis. The results show that there is a 52.9% probability that the mummy is an Egyptian female, with a 24.5% probability that the mummy is an African female. Thus the technique confirms that the coffin contains an Egyptian female, which is consistent with the inscription on the coffin and the shape of the pelvic bones as revealed by plain X-rays. These results show that this technique has potential for analysing forensic cases where the bones are obscured by soft tissue and clothing. This technique may have an application in virtual autopsies.

Fit optimisation of a distal medial tibia plate

An iterative method for the fit optimisation of a pre-contoured fracture fixation plate for a given bone data set is presented. Both plate shape optimisation and plate fit quantification are conducted in a virtual environment utilising computer graphical methods and 3D bone and plate models. Two optimised shapes of the undersurface of an existing distal medial tibia plate were generated based on a dataset of 45 3D bone models reconstructed from computed tomography image data of Japanese tibiae. The existing plate shape achieved an anatomical fit on 13% of tibiae from the dataset. Modified plate 1 achieved an anatomical fit for 42% and modified plate 2 a fit for 67% of the bones. If either modified plate 1 or plate 2 is used, then the anatomical fit can be increased to 82% for the same dataset. Issues pertaining to any further improvement in plate fit/shape are discussed.

Modelling of infectious spreading in heterogeneous polymer oxidation II. Refinement of stochastic model and calibration using chemiluminescence of polypropylene

In the stochastic model for infectious spreading of oxidation in a polymer, the conventional view of a homogeneously oxidising polymer with associated rate parameters is replaced by a system consisting of localized zones of oxidation in a continuous unoxidised substrate (a 3-dimensional matrix) with the rate of degradation controlled by the probability of passing the infection to an adjacent site, and the infectious lifetime of the site. The populations in the epidemiological model for spreading of oxidation, p(i) (the infectious, oxidising fraction), p(r) (the remaining, unoxidised fraction) and P-d (the dead or oxidised fraction) are calculated for a particular site. Oxidation-time profiles are determined by calculating the sum of the component fractions over the entire matrix volume for different activities (i.e. temperatures). Profiles of the infectious fraction, p(i), at different activities were found to show features of an accumulating hydroperoxide fraction whereas the true infectious fraction should be more correctly represented by the reactive fraction of the hydroperoxides, p(i)*, at a particular temperature. This model has been tested by comparison with the reactive hydroperoxide profile as determined by chemiluminescence of polypropylene doped with 9,10-diphenyl anthracene to yield the infectious spreading parameters, their temperature dependence, as well as the profiles for the diffusion of the infectious species

Surface reconstruction of wheat leaf morphology from three-dimensional scanned data

Realistic virtual models of leaf surfaces are important for several applications in the plant sciences, such as modelling agrichemical spray droplet movement and spreading on the surface. In this context, the virtual surfaces are required to be smooth enough to facilitate the use of the mathematical equations that govern the motion of the droplet. Although an effective approach is to apply discrete smoothing D2-spline algorithms to reconstruct the leaf surfaces from three-dimensional scanned data, difficulties arise when dealing with wheat (Triticum aestivum L.) leaves, which tend to twist and bend. To overcome this topological difficulty, we develop a parameterisation technique that rotates and translates the original data, allowing the surface to be fitted using the discrete smoothing D2-spline methods in the new parameter space. Our algorithm uses finite element methods to represent the surface as a linear combination of compactly supported shape functions. Numerical results confirm that the parameterisation, along with the use of discrete smoothing D2-spline techniques, produces realistic virtual representations of wheat leaves.

Three-dimensional Lumbar Spine Postures Measured by Magnetic Resonance Imaging Reconstruction

Study Design. Investigation of method. Objective. This study presents a novel method of accurately determining relative bone position in vivo using magnetic resonance imaging (MRI). Summary of Background Data. Biomechanical modeling of the human body requires measurement of the relative positions of skeletal elements. Spinal orientation is particularly difficult to measure due to small joint movements, relative inaccessibility of the bones to direct measurement, and joint complexity. Methods. A process incorporating both positional and conventional MRI was used to measure the skeletal positions of the lumbar spine and pelvis. The method uses higher quality conventional MRI to determine bone geometries and then registers these with lower resolution, positional MRI images of various postures to determine the relative locations of the bones. Flexion/extension, lateral bend, and axial twist rotations were measured for each joint. Results. The results indicate good intrameasurer reliability, with a maximum rotational difference for all vertebral registrations of less than 1° and a maximum translational difference of less than 3 mm. While there did not appear to be significant patterns between the 2 Subjects, there were trends within each Subject as well as identifiable postural characteristics. Conclusions. Although processing times are currently lengthy, the data collected are 3-dimensional, and represent the anatomy and movement of a specific individual.

Standardized anthropological measurement of postcranial bones using three-dimensional models in CAD software

This study introduces a standardized protocol for conducting linear measurements of postcranial skeletal elements using three-dimensional (3D) models constructed from post-mortem computed tomography (PMCT) scans. Using femoral DICOM datasets, reference planes were generated and plane-to-plane measurements were conducted on 3D surface rendered models. Bicondylar length, epicondylar breadth, anterior-posterior (AP) diameter, medial-lateral (ML) diameter and cortical area at the midshaft were measured by four observers to test the measurement error variance and observer agreement of the protocol (n=6). Intra-observer error resulted in a mean relative technical error of measurement (%TEM) of 0.11 and an intraclass correlation coefficient (ICC) of 0.999 (CI=0.998-1.000); inter-observer error resulted in a mean %TEM of 0.54 and ICC of 0.996 (CI=0.979-1.000) for bicondylar length. Epicondylar breadth, AP diameter, ML diameter and cortical area also yielded minimal error. Precision testing demonstrated that the approach is highly repeatable and is recommended for implementation in anthropological investigation and research. This study exploits the benefits of virtual anthropology, introducing an innovative, standardized alternative to dry bone osteometric measurements.

Bayesian modeling predicts age and sex are not required for accurate stature estimation from femoral length

Despite the recognized flaws in applying traditional stature estimation equations such as those of Trotter and Gleser (1952) [5] to a contemporary population, there are currently no available alternatives for stature estimation in Australia that address these limitations. Post mortem computed tomography (PMCT) DICOM scans of the left and right femora were acquired from 76 Australian deceased individuals aged 17-76 years for metric analysis. Femoral bicondylar length, femoral epicondylar breadth and anterior-posterior (AP) diameter, medial-lateral (ML) diameter, circumference and cortical area at the femoral midshaft were measured on three-dimensional (3D) models to build statistical models for estimating stature. In addition, Australian individuals aged 16-63 years (n=111) were measured in standing and supine positions to aid in the adjustment of supine stature of deceased individuals utilized in this study to standing stature. The results of this preliminary evaluation strongly indicate that the optimal model for estimating stature includes bicondylar femoral length and epicondylar breadth, that the effect of sex as an independent variable is very low, and there is limited practical benefit in including age in the estimation of stature. Our study indicates that the Australian population sampled represents a small yet significant shift in stature from the original Trotter and Gleser sample. Additionally, in the case of fragmentary remains, it was found that epicondylar breadth and AP diameter had the highest probability of accurate stature estimation in the absence of bicondylar femoral length. As stature forms a significant component of a biological profile and therefore aids in the personal identification of human remains, it is important that forensic anthropologists utilize the most accurate methodologies available. Stature estimation of Australian individuals is therefore achieved with higher accuracy through utilizing the femoral equations proposed in this study.