Biomedical subjects

John G Clement

Publications and source records attributed to John G Clement.

14 recordsLinked to original sources

PubMed2007

Age-dependent change in the 3D structure of cortical porosity at the human femoral midshaft.

Microstructural change associated with cortical bone remodeling has been extensively explored with 2D techniques. However, relatively little is known regarding the 3D dynamic microstructure of cortical bone. Therefore, we employed micro-CT imaging to investigate 3D remodeling-related change in the structure of cortical bone porosity across the human lifespan. Anterior femoral midshaft specimens (n=51 male, 28 female) spanning 18 to 92 years of age were scanned with 7 mum nominal isotropic resolution. Canal volume fraction (Ca.V/TV), mean diameter (Ca.Dm), mean separation (Ca.Sp), degree of anisotropy (DA), connectivity density (Ca.ConnD), and number (Ca.N) were calculated for subperiosteal cylindrical regions of interest. Ca.N was calculated in 2D (Ca.N(2D)) and 3D (Ca.N(3D)). Regression was used to examine the relation between the structural parameters and age. Additionally, the impact of sex, height, and weight were investigated collectively (MANCOVA) and individually (ANCOVA). For all analyses, Ca.V/TV and Ca.Dm were inverted (Ca.V/TV(-1), Ca.Dm(-1)) to establish normality and linear relations with age. Ca.N values (2D and 3D) were non-linearly (quadratic) related to age, increasing until the 6th decade then decreasing. This relation was only significant for the pooled sexes Ca.N(3D) values (p=0.012). Ca.ConnD was positively related to age (p<0.05), while all remaining 3D parameters, except DA for males (p=0.070), were negatively related (p<0.05). In all cases, the relation with age was strongest for females. MANCOVA revealed that age was the only significant (p<0.001) covariate overall. Univariate ANCOVA indicated significant differences between the sexes for Ca.V/TV(-1) and Ca.Dm(-1) (p=0.018 and 0.010, respectively). Relative to males, females had lower values for these parameters, translating into larger mean canal diameter and overall porosity. Body weight had a significant (p=0.043) positive relation with Ca.Dm(-1), indicating lower weight was also associated with increased mean canal diameter. Therefore, while age was the most important factor, sex and body size were found to play a role in parameters related to canal size and the overall level of porosity. This study is unique in that changes in cortical bone microstructure were examined across the adult human lifespan in three rather than two dimensions.

Adolescent↗

PubMed2006

Three-dimensional microcomputed tomography imaging of basic multicellular unit-related resorption spaces in human cortical bone.

This study employed microcomputed tomography (micro-CT) as a novel means for visualizing the morphology and quantifying the range (length) of basic multicellular unit (BMU)-related resorption spaces in human cortical bone. We tested the hypotheses that the density and range of spaces vary with age and sex. The sample included 82 human (18-92 years) anterior femoral midshaft samples. The morphology of the spaces (n = 99) was varied, including unidirectional, bidirectional, branched, and even highly clustered forms. The density of resorption spaces was negatively correlated with age for the combined sexes and females, with Spearman's rho values of -0.355 (P < 0.001) and -0.522 (P = 0.002), respectively. The density of spaces did not differ significantly between the sexes (P = 0.735). Mean range +/- SD for the combined sexes, females, and males was 2,706 +/- 1,177, 2,681 +/- 1,247, and 2,718 +/- 1,150 microm, respectively. Numerical simulation of the effect of the 7,000 microm scan field of view suggested that the actual mean range of the spaces for the pooled sample was actually on the order of 3,770 microm. Range did not correlate significantly with age for the combined sexes (P = 0.587) or females (P = 0.345) and males (P = 0.896) considered separately and was not significantly different (P = 0.883) between the sexes. These results suggest that the range of BMUs is not affected by age. The age-dependent decrease in resorption space density for the females and pooled sexes was most likely a consequence of cortical rarefaction, leading to difficulty detecting resorption spaces with micro-CT, rather than a decrease in overall remodeling activity.

Adolescent↗

PubMed2006

Increase in pore area, and not pore density, is the main determinant in the development of porosity in human cortical bone.

This study investigated the relative contributions of pore size and pore density (number of pores per mm2) to porosity in the midshaft of the human femur. Cross-sections were obtained from 168 individuals from a modern Australian population (mostly Anglo-Celtic). The study group comprised 73 females and 95 males, aged from 20 to 97 years. Microradiographs were made of 100-microm sections and porosity, pore areas and pore densities determined using image processing software. The cortex was divided into three rings radially and into octants circumferentially, and the porosity, pore area and pore density of each segment were calculated. Results show that 81% of the variance in porosity can be explained by changes in mean pore area with only a further 12-16% explained by changes in pore density. These effects were found to be constant across all areas of the cortex and in both sexes. These results are significant in their consistency and ordered gradation and indicate a well-regulated and systematic process of bone removal with ageing. The results show a regular progression from less porous to more porous bone; this is a uniform process that occurs in all individuals, and factors such as sex and rate of ageing determine where on this continuum any individual is at a particular time.

Adult↗

PubMed2005

A new retrieval system for a database of 3D facial images.

A new retrieval system for a 3D facial image database was designed and its reliability was experimentally examined. This system has two steps, firstly to automatically adjust the orientation of all 3D facial images in a database to that of the 2D facial image of a target person, and then to identify the facial image of the target person from the adjusted 3D facial images in the database using a graph-matching method. From the experimental study [M. Yoshino, K. Imaizumi, T. Tanijiri, J.G. Clement, Automatic adjustment of facial orientation in 3D face image database, Jpn. J. Sci. Tech. Iden. 8 (2003) 41-47], it is concluded that the software developed for the first step will be applicable to the automatic adjustment of facial orientation in the 3D facial image database. In 28 out of 110 sets (25.5%), the 3D image of the target person was chosen as the best match (from a database of 132 3D facial images) according to the similarity of the facial image characteristics based on the graph matching. The 3D facial image of the target person was ranked in the top of 10 of the database in 75 out of 110 sets (68.2%). These results suggest that this system is inadequate for the identification level, but may be feasible for screening method in a small database. It will be necessary to further pursue the possibility of realization of a facial image retrieval system for a large database such as suspects' facial images in future.

Adult↗

PubMed2005

Regional variation of intracortical porosity in the midshaft of the human femur: age and sex differences.

This study investigated age and sex differences in patterns of porosity distribution in the midshaft of the human femur. Cross-sections were obtained from 168 individuals from a modern Australian population. The sample comprised 73 females and 95 males, aged between 20 and 97 years. Microradiographs were made of 100-microm sections and pore and bone areas were determined using image processing software. Initially the sample was divided by age: young (20-44 years), middle (45-64 years) and old (65+ years), but it was found that analysis on the basis of the ratio of medullary area to total subperiosteal area gave clearer results. The cortex was divided into three rings radially and into octants circumferentially and the porosity of each segment was calculated. Results showed that a pattern with raised porosity in the posterior and anterolateral regions, and with greater porosity in the inner parts of the cortex, becomes more pronounced with age. In males this pattern develops steadily; in females there are much greater differences between the middle and older groups than earlier in life. The patterns observed are consistent with progressive bone loss occurring along a neutral axis of the cortex where bending stress is lowest and the mechanical advantage of the bone is least.

Adult↗

PubMed2004

Detecting hemifacial asymmetries in emotional expression with three-dimensional computerized image analysis.

Emotions are expressed more clearly on the left side of the face than the right: an asymmetry that probably stems from right hemisphere dominance for emotional expression (right hemisphere model). More controversially, it has been suggested that the left hemiface bias is stronger for negative emotions and weaker or reversed for positive emotions (valence model). We examined the veracity of the right hemisphere and valence models by measuring asymmetries in: (i) movement of the face; and (ii) observer's rating of emotionality. The study uses a precise three-dimensional (3D) imaging technique to measure facial movement and to provide images that simultaneously capture the left or right hemifaces. Models (n = 16) with happy, sad and neutral expressions were digitally captured and manipulated. Comparison of the neutral and happy or sad images revealed greater movement of the left hemiface, regardless of the valence of the emotion, supporting the right hemisphere model. There was a trend, however, for left-sided movement to be more pronounced for negative than positive emotions. Participants (n = 357) reported that portraits rotated so that the left hemiface was featured, were more expressive of negative emotions whereas right hemiface portraits were more expressive for positive emotions, supporting the valence model. The effect of valence was moderated when the images were mirror-reversed. The data demonstrate that relatively small rotations of the head have a dramatic effect on the expression of positive and negative emotions. The fact that the effect of valence was not captured by the movement analysis demonstrates that subtle movements can have a strong effect on the expression of emotion.

Adolescent↗

PubMed2004

A new rig for standardized craniofacial photography put to the test.

This article describes and tests a photography rig that has been built at the University of Melbourne, Australia, specifically for the purpose of taking rapid and highly standardized craniofacial photographs, in simultaneous views of front and profile. The rig uses a novel projected light range-finding system that has been designed for easy and accurate positioning of subjects, in the natural head position, at precise distances from the frontal camera. Results of experiments examining the intraobserver error of multiple photographs taken on the rig indicate that high-quality, repeatable photographs can be taken after a reasonably large amount of time has lapsed between photography sessions (e.g., 30 days). This study also indicates that some variability remains between photographs even when highly standardized protocols are followed. Consequently, it is expected that the variation between photographs with limited standardization is much larger and more likely to cause significant errors in any comparisons.

Equipment Design↗

PubMed2004

Delineation of facial archetypes by 3d averaging.

The objective of this study was to investigate the feasibility of creating archetypal 3D faces through computerized 3D facial averaging. A 3D surface scanner Fiore and its software were used to acquire the 3D scans of the faces while 3D Rugle3 and locally-developed software generated the holistic facial averages. 3D facial averages were created from two ethnic groups; European and Japanese and from children with three previous genetic disorders; Williams syndrome, achondroplasia and Sotos syndrome as well as the normal control group. The method included averaging the corresponding depth (z) coordinates of the 3D facial scans. Compared with other face averaging techniques there was not any warping or filling in the spaces by interpolation; however, this facial average lacked colour information. The results showed that as few as 14 faces were sufficient to create an archetypal facial average. In turn this would make it practical to use face averaging as an identification tool in cases where it would be difficult to recruit a larger number of participants. In generating the average, correcting for size differences among faces was shown to adjust the average outlines of the facial features. It is assumed that 3D facial averaging would help in the identification of the ethnic status of persons whose identity may not be known with certainty. In clinical medicine, it would have a great potential for the diagnosis of syndromes with distinctive facial features. The system would also assist in the education of clinicians in the recognition and identification of such syndromes.

Adolescent↗

PubMed2003

A Japanese computer-assisted facial identification system successfully identifies non-Japanese faces.

The method developed by Yoshino et al. in [Forensic Sci. Int. 109 (2000) 225 and Jpn. J. Sci. Tech. Iden. 5 (2000) 9] and already being applied in Japan utilizes a three-dimensional (3D) physiognomic rangefinder combined with a computer-assisted superimposition system. Facial outlines can be compared between two-dimensional (2D) surveillance images and data extracted from 3D images obtained from the rangefinder. Also, the loci of potentially concordant features can be compared and differences measured. The method is largely objective and gives statistics for false positive/false negative findings. This recently developed method by Yoshino et al. is currently being introduced to the Japanese courts. To enable courts outside Japan to assess the admissibility of this new method, studies of non-Japanese faces have been undertaken and shown to produce similar low error rates. The present authors, therefore, consider the Yoshino method to be applicable in a non-Japanese context. As part of this study a comparison of morphological features between two ethnic groups has been undertaken using 3D measurements for the first time and will serve as the foundation for an anthropological database in the future.

Adult↗

PubMed2003

Lateral facial soft-tissue prediction model: analysis using Fourier shape descriptors and traditional cephalometric methods.

This study was designed to investigate the relationship between traditional skeletal cephalometric measurement and Fourier analysis of the lateral soft-tissue profile. A random sample of 121 untreated subjects of European descent, with wide ranges of malocclusions and underlying facial patterns, was selected in the Orthodontic Unit at the University of Melbourne. Lateral cephalograms were available for all subjects. Both traditional lateral cephalometric analysis and Fourier soft-tissue profile analysis were carried out. Multivariate statistical analysis among 11 hard-tissue cephalometric measurements and the first 50 Fourier harmonics was then performed. This analysis formed the basis for a subsequently proposed soft-tissue prediction model. From this model, 50 predicted x- and y-harmonics were generated for each subject in the total sample. Calculation of Pearson's correlation coefficients between the actual and predicted harmonics revealed strong relationships for many of the lower-order harmonics. To further test the model, the prediction-coefficients derived from all 121 subjects were then used to make predictions for the first 50 x- and y-harmonics for a subgroup of 10 independent test subjects. Once again, Pearson's correlations between the actual and predicted harmonics of the test model in the lower-order harmonics revealed strong associations. Superimposition of the actual and predicted soft-tissue outlines, however, revealed that much actual detail in the region between the nose and the chin was still lost using the predicted Fourier harmonics. This suggests that soft-tissue prediction based on this Fourier test model, while already useful in Forensic facial reconstruction, may not yet be appropriate for useful diagnosis and planning in clinical disciplines.

Adolescent↗

PubMed2003

Preferred collagen fiber orientation in the human mid-shaft femur.

Collagen fiber orientation is one aspect of the microstructure of bone that influences its mechanical properties. While the spatial distribution of preferentially oriented collagen is hypothesized to reflect the effects of loading during the process of aging, its variability in a modern human sample is essentially unknown. In a large sample (n = 67) of autopsied adults, the variability of collagen fiber orientation in the mid-shaft femur was examined in relation to age and sex. Montaged images of entire 100 microm thick cross-sections were obtained using circularly polarized light microscopy (CPLM) under standardized illuminating conditions. An automated image-analyzing routine divided images into 48 segments according to anatomical position. Average gray values (varying with orientation) were quantified for each segment, and one-way ANOVA with Tukey HSD post hoc tests were applied to assess differences between segments. Collagen fiber orientation appeared to be nonrandomly distributed across the mid-shaft femur sample; however, no single "human" pattern was identified. Individual variation, unexplainable by age, sex, or body size, exceeded population-level trends. Differences between age and sex groups suggest there is a strong correspondence between collagen fiber orientation and tissue-type distributions. The minimal consistencies demonstrated here may reflect mechanical forces induced at the femoral mid-shaft. However, the myriad of other factors that may influence collagen fiber orientation patterning, including growth trajectories, metabolic and nutritional status, and disease states, must be explored further. Only then, in conjunction with studies of other structural and material properties of bone, will we be able to elucidate the linkages between microstructure and functional adaptation in the human mid-shaft femur.

Adult↗

PubMed2003

Description of a photoelastic coating technique to describe surface strain of a dog skull loaded in vitro.

There are several methods of determining strain in the facial skeleton on loading in vitro. This article describes an alternative photoelastic coating technique adapted from the commonly accepted method used by engineers to study surface strains in objects. In applying this method to the stomatognathic system, because the masticatory apparatus is loaded by muscular contraction an opposite reaction load should be distributed throughout the skeletal structure. This load distribution should slightly deform the bones to which the muscles of mastication are attached. An understanding of the resulting strain generated in the facial skeleton is important because strain distribution on loading reflects how the loads applied during mastication are partially dissipated. Preliminary descriptive results are presented, suggesting that anatomic structures influence the distribution of strain on loading. The technique described should allow in vitro investigation of the mechanical environment into which osseointegrated implants are placed and may aid in understanding their behavior.

Animals↗

PubMed2002

Individual identification of disguised faces by morphometrical matching.

The reliability of a morphometrical matching method for identifying disguised faces was examined experimentally using a computer-assisted facial image identification system. The 2D right oblique facial images of three target persons disguised with sunglasses, cap and gauze mask were each compared with each of the 3D facial images of 100 subjects, yielding 900 face-to-face superimpositions. The average perpendicular distance between the facial outlines and the average point-to-point distance of the corresponding landmarks in the 2D image of the disguised face and the 3D facial image, were calculated. As a matching criterion, the sum of the values of the average perpendicular difference of the facial outlines and the average point-to-point difference between the corresponding landmarks was used (abbreviation: average difference). The range of the average difference was 2.3-2.8mm for the same person (a match) and 4.0-14.6mm for different (non-matching) people, respectively. The ranges for matching and non-matching faces did not overlap. Even the 3D facial images of the non-matching person showing the closest value of average difference to the average difference for the matching person could be excluded easily. It was concluded that the morphometrical matching method can reliably identify disguised faces and the results produced by this method could be easily understandable by a court of law.

Adult↗

PubMedDate not supplied

Relation between age, femoral neck cortical stability, and hip fracture risk.

BACKGROUND: Hip fracture risk rises 100 to 1000-fold over 60 years of ageing. Loss of resistance to bending is not a major feature of normal ageing of the femoral neck. Another cause of fragility is local buckling or elastic instability. Bones adapt to their local experience of mechanical loading. The suggestion that bipedalism allows thinning of the underloaded superolateral femoral neck cortex arises from the failure of walking to transmit much mechanical load to this region. We aimed to measure whether elastic instability increases greatly with age since it might trigger hip fracture in a sideways fall. METHODS: We measured with computed tomography the distribution of bone in the mid-femoral neck of 77 proximal femurs from people who died suddenly aged 20-95 years. We then calculated the critical stress, from the geometric properties and density of the cortical zone most highly loaded in a sideways fall, as a threshold for elastic instability. FINDINGS: With normal ageing, this thin cortical zone in the upper femoral neck became substantially thinner. Relative to mean values at age 60 years, female cortical thickness declined by 6.4% (SD 1.1) per decade (p<0.0001), and critical stress by 13.2% (4.3) per decade (p=0.004) in the superoposterior octant compressed most in a sideways fall. Similar, but significantly smaller, effects were evident in men (p=0.004). This thinning compromised the capacity of the femur to absorb energy independently of osteoporosis. Patients with hip fracture had further reduced stability. INTERPRETATION: As women age, hip fragility increases because underloading of the superolateral cortex leads to atrophic thinning. Because walking does not sufficiently load the upper femoral neck, the fragile zones in healthy bones may need strengthening, for example with more well targeted exercise.

Absorptiometry, Photon↗