The geometrical precision of virtual bone models derived from clinical computed tomography data for forensic anthropology

Estimation of population affinity using proximal femoral measurements based on computed tomographic images in the Japanese and western Australian populations

The present study analyzes morphological differences femora of contemporary Japanese and Western Australian individuals and investigates the feasibility of population affinity estimation based on computed tomographic (CT) data. The latter is deemed to be of practical importance because most anthropological methods rely on the assessment of aspects of skull morphology, which when damaged and/or unavailable, often hampers attempts to estimate population affinity. The study sample comprised CT scans of 297 (146 females; 151 males) Japanese and 330 (145 females; 185 males) Western Australian adult individuals. A total of 10 measurements were acquired in two-dimensional CT images of the left and right femora; two machine learning methods (random forest modeling [RFM]) and support vector machine [SVM]) were then applied for population affinity classification. The accuracy of the two-way (sex-specific and sex-mixed) model was between 71.38 and 82.07% and 76.09-86.09% for RFM and SVM, respectively. Sex-specific (female and male) models were slightly more accurate compared to the sex-mixed models; there were no considerable differences in the correct classification rates between the female- and male-specific models. All the classification accuracies were higher in the Western Australian population, except for the male model using SVM. The four-way sex and population affinity model had an overall classification accuracy of 74.96% and 79.11% for RFM and SVM, respectively. The Western Australian females had the lowest correct classification rate followed by the Japanese males. Our data indicate that femoral measurements may be particularly useful for classification of Japanese and Western Australian individuals.

Minimal but potentially clinically relevant anteroinferior position of the humeral head following traumatic anterior shoulder dislocations: A 3D-CT analysis

In unstable shoulders, excessive anteroinferior position of the humeral head relative to the glenoid can lead to a dislocation. Measuring humeral head position could therefore be valuable in quantifying shoulder laxity. The aim of this study was to measure (1) position of the humeral head relative to the glenoid and (2) joint space thickness during passive motion in unstable shoulders caused by traumatic anterior dislocations and in contralateral uninjured shoulders. A prospective cross-sectional CT-study was performed in patients with unilateral anterior shoulder instability. Patients underwent CT scanning of both injured and uninjured side in supine position (0° abduction and 0° external rotation) and in 60°, 90°, and 120° of abduction with 90° of external rotation without an external load. Subsequently, 3D virtual models were created of the humerus and the scapula to create a glenoid coordinate system to identify poster-anterior, inferior-superior, and lateral-medial position of the humeral head relative to the glenoid. Joint space thickness was defined as the average distance between the subchondral bone surfaces of the humeral head and glenoid. Fifteen consecutive patients were included. In supine position, the humeral head was positioned more anteriorly (p = 0.004), inferiorly (p = 0.019), and laterally (p = 0.021) in the injured compared to the uninjured shoulder. No differences were observed in any of the other positions. A joint-space thickness map, showing the bone-to-bone distances, identified the Hill-Sachs lesion footprint on the glenoid surface in external rotation and abduction, but no differences on average joint space thickness were observed in any position.

Demonstrating the empirical effect of population specificity of anthropological standards in a contemporary Australian population

The ability to differentiate individuals based on their biological sex is essential for the creation of an accurate anthropological assessment; it is therefore crucial that the standards that facilitate this are likewise accurate. Given the relative paucity of population-specific anthropological standards formulated specifically for application in the contemporary Australian population, forensic anthropological assessments have historically relied on the application of established methods developed using population geographically and/or temporally disparate. The aim of the present paper is, therefore, to assess the accuracy and reliability of established cranial sex estimation methods, developed from geographically distinct populations, as applied to the contemporary Australian population. Comparison between the original stated accuracy and sex bias values (where applicable) and those achieved after application to the Australian population provides insight into the importance of having anthropological standards optimised for application in specific jurisdictions. The sample analysed comprised computed tomographic (CT) cranial scans of 771 (385 female and 386 male) individuals collected from five Australian states/territories. Cranial CT scans were visualised as three-dimensional volume-rendered reconstructions using OsiriX®. On each cranium, 76 cranial landmarks were acquired, and 36 linear inter-landmark measurements were calculated using MorphDB. A total of 35 predictive models taken from Giles and Elliot (1963), Iscan et al. (1995), Ogawa et al. (2013), Steyn and İşcan (1998) and Kranioti et al. (2008) were tested. Application to the Australian population resulted in an average decrease in accuracy of 21.2%, with an associated sex bias range between - 64.0 and 99.7% (average sex bias value of 29.6%), relative to the original studies. The present investigation has highlighted the inherent inaccuracies of applying models derived from geographically and/or temporally disparate populations. It is, therefore, imperative that statistical models developed from a population consistent with the decedent be used for the estimation of sex in forensic casework.

Measuring pelvises in 3D surface scans and in MDCT generated virtual environment: Considerations for applications in the forensic context

Virtual Anthropology (VA) transposes the traditional methods of physical anthropology to virtual environments using imaging techniques and exploits imaging technologies to devise new methodological protocols. In this research, we investigate whether the measurements used in the Diagnose Sexuelle Probabiliste (DSP) and Ischio-Pubic Index (IPI) differ significantly when 3D models of a bone are generated using 3D surface scans (3DSS) and Multidetector Computed Tomography (MDCT) scans. Thirty pelvises were selected from the SIMON identified skeletal collection. An equal ratio of females to males was sought, as well as a good preservation of the bones. The pelvises were scanned using an MDCT scanner and a 3D surface scanner. The measurements of the DSP and IPI methods on the dry bones (referred to as macroscopic measurements here), and then to the 3D models. The intra- and interobserver, using the Technical Error of Measurement (TEM) and relative Technical Error of Measurement (rTEM) error was assessed, and we aimed to observe if the measurements made on the MDCT and 3DSS generated models were significantly different from those taken on the dry bones. Additionally, the normality of the data was tested (Shapiro-Wilk test) and the differences in measurements was evaluated using parametric (Student t-tests) and non-parametric (Wilcoxon) tests. The TEM and rTEM calculations show high intra and interobserver consistency in general. However, some measurements present insufficient inter- and intraobserver agreement. Student t and Wilcoxon tests indicate potentially significant differences of some measurements between the different environments. The results show that especially in the virtual environment, it is not easy to find the right angle for some of the DSP measurements, However, when comparing the measurement differences between dry and virtual bones, the results show that most of the differences are less than or equal to 2.5 mm. Considering the IPI, the landmarks are already difficult to determine on the dry bone, but they are even more difficult to locate in the virtual environment. Nevertheless, this study shows that quantitative methods may be better suited for application in the virtual environment, but further research using different methods is needed.

Estimating age at death by Hausdorff distance analyses of the fourth lumbar vertebral bodies using 3D postmortem CT images

The existing methods for determining adult age from human skeletons are mostly qualitative. However, a shift in quantifying age-related skeletal morphology on a quantitative scale is emerging. This study describes an intuitive variable extraction technique and quantifies skeletal morphology in continuous data to understand their aging pattern. A total of 200 postmortem CT images from the deceased aged 25-99 years (130 males, 70 females) who underwent forensic death investigations were used in the study. The 3D volume of the fourth lumbar vertebral body was segmented, smoothed, and post-processed using the open-source software ITK-SNAP and MeshLab, respectively. To measure the extent of 3D shape deformity due to aging, the Hausdorff distance (HD) analysis was performed. In our context, the maximum Hausdorff distance (maxHD) was chosen as a metric, which was subsequently studied for its correlation with age at death. A strong statistically significant positive correlation (P < 0.001) between maxHD and age at death was observed in both sexes (Spearman's rho = 0.742, male; Spearman's rho = 0.729, female). In simple linear regression analyses, the regression equations obtained yielded the standard error of estimates of 12.5 years and 13.1 years for males and females, respectively. Our study demonstrated that age-related vertebral morphology could be described using the HD method. Moreover, it encourages further studies with larger sample sizes and on other population backgrounds to validate the methodology.

Testing different 3D techniques using geometric morphometrics: Implications for cranial fluctuating asymmetry in humans

This study aimed to test the performance of 3D digitizer, CT scanner, and surface scanner in detecting cranial fluctuating asymmetry. Sets of 32 landmarks (6 in the midline and 13 bilateral) were acquired from 14 archeological crania using a 3D digitizer, and from 3D models generated from a CT scanner and surface scanner using Viewbox 4. Levels of shape variation were analyzed in MorphoJ using Procrustes analysis of variance and Principal component analysis. Intra-observer error accounted for 1.7%, 1.8%, and 4.5% of total shape variation for 3D digitizer, CT scanner, and surface scanner respectively. Fluctuating asymmetry accounted for 15%-16% of total shape variation. Variation between techniques accounted for 18% of total shape variation. We found a higher level of missing landmarks in our surface scan data than for both 3D digitizer and CT scanner data, and both 3D model-based techniques sometimes obscured taphonomic damage. All three 3D techniques are appropriate for measuring cranial fluctuating asymmetry. We advise against combining data collected with different techniques.

3D-3D Superimposition of Pubic Bones: Expanding the Anthropological Toolkit for the Pair-Matching of Commingled Skeletal Remains

Virtual anthropology (VA) has recently produced an additional tool for the analysis of commingled remains and is based on the distance analysis between three-dimensional (3D) models of bones. To date, the pair-matching of the innominate bone through a 3D approach remains partially unexplored. Here, 44 abdominal CT scans (22 males and 22 females) were selected from a hospital database, and the pubic bones were segmented through ITK-SNAP software. The models were hollowed with Viewbox4 to minimize the amount of trabecular bone. The left pubic bones were mirrored and superimposed on the right ones, according to the smallest point-to-point difference between the two surfaces through VAM software. RMS distances between models were calculated through VAM, producing RMS values for 20 matches and 420 mismatches for each sex group. Differences in RMS distance values between matches and mismatches were investigated through Mann−Whitney tests (p < 0.05); the repeatability of the procedure was assessed through absolute and relative technical error measurement (TEM and rTEM). RMS distance values of matches and mismatches were significantly different (p < 0.01) in both groups. The method yielded optimal results with high sensitivity (100.0%) and specificity (99.8% in males, 98.8% in females) rates according to the chosen threshold. This project contributes to the research field of VA with a valuable adjunct that may bolster and strengthen the results of the current visual and osteometric methods through a multidisciplinary approach.

Performance of the supervised learning algorithms in sex estimation of the proximal femur: A comparative study in contemporary Egyptian and Turkish samples

Sex estimation standards are population specific however, we argue that machine learning techniques (ML) may enhance the biological sex determination on trans-population application. Linear discriminant analysis (LDA) versus nine ML including quadratic discriminant analysis (QDA), support vector machine (SVM), Decision Tree (DT), Gaussian process (GPC), Naïve Bayesian (NBC), K-Nearest Neighbor (KNN), Random Forest (RFM) and Adaptive boosting (Adaboost) were compared. The experiments involve two contemporary populations: Turkish (n = 300) and Egyptian populations (n = 100) for training and validation, respectively. Base models were calibrated using isotonic and sigmoid calibration schemes. Results were analyzed at posterior probabilities (pp) thresholds >0.95 and >0.80. At pp = 0.5, ML algorithms yielded comparable accuracies in the training (90% to 97%) and test sets (81% to 88%) which are not modified after employing the calibration techniques. At pp >0.95, the raw RFM, LDA, QDA, and SVM models have shown the best performance however, calibration techniques improved the performance of various classifier especially NBC and Adaboost. By contrast, the performance of GPC, KNN, QDA models worsened by calibration. RFM has shown the best performance among all models at both thresholds whereas LDA benefited the best from using both calibration methods at pp >0.80. Complex ML models are not necessarily achieving better performance metrics. LDA and QDA remain the fastest and simplest classifiers. We demonstrated the capability of enhancing sex estimation using ML on an independent population sample however, differences in the underlying probability distribution generated by models were detected which warranted more cautious application by forensic practitioners.

Difference in orientation of the talar articular facets between healthy ankle joints and ankle joints with chronic instability

Since both the talocrural and subtalar joints can be involved in chronic ankle instability, the present study assessed the talar morphology as this bone is the key player between both joint levels. The 3D orientation and curvature of the superior and the posteroinferior facet between subjects with chronic ankle instability and healthy controls were compared. Hereto, the talus was segmented in the computed tomography images of a control group and a chronic ankle instability group, after which they were reconstructed to 3D surface models. A cylinder was fitted to the subchondral articulating surfaces. The axis of a cylinder represented the facet orientation, which was expressed by an inclination and deviation angle in a coordinate system based on the cylinder of the superior talar facet and the geometric principal axes of the subject's talus. The curvature of the surface was expressed as the radius of the cylinder. The results demonstrated no significant differences in the radius or deviation angle. However, the inclination angle of the posteroinferior talar facet was significantly more plantarly orientated (by 3.5°) in the chronic instability group (14.7 ± 3.1°) compared to the control group (11.2 ± 4.9°) (p < 0.05). In the coronal plane this corresponds to a valgus orientation of the posteroinferior talar facet relative to the talar dome. In conclusion, a more plantarly and valgus orientated posteroinferior talar facet may be associated to chronic ankle instability.

Use of deep learning in forensic sex estimation of virtual pelvic models from the Han population

Accurate sex estimation is crucial to determine the identity of human skeletal remains effectively. Here, we developed convolutional neural network (CNN) models for sex estimation on virtual hemi-pelvic regions, including the ventral pubis (VP), dorsal pubis (DP), greater sciatic notch (GSN), pelvic inlet (PI), ischium, and acetabulum from the Han population and compared these models with two experienced forensic anthropologists using morphological methods. A Computed Tomography (CT) dataset of 862 individuals was divided into the subgroups of training, validation, and testing, respectively. The CT-based virtual hemi-pelvises from the training and validation groups were used to calibrate sex estimation models; and then a testing dataset was used to evaluate the performance of the trained models and two human experts on the sex estimation of specific pelvic regions in terms of overall accuracy, sensitivity, specificity, F1 score, and receiver operating characteristic (ROC) curve. Except for the ischium and acetabulum, the CNN models trained with the VP, DP, GSN, and PI images achieved excellent results with all the prediction metrics over 0.9. All accuracies were superior to those of the two forensic anthropologists in the independent testing. Notably, the heatmap results confirmed that the trained CNN models were focused on traditional sexual anatomic traits for sex classification. This study demonstrates the potential of AI techniques based on the radiological dataset in sex estimation of virtual pelvic models. The excellent sex estimation performance obtained by the CNN models indicates that this method is valuable to proceed with in prospective forensic trials.

An exploration of sacral morphology using geometric morphometrics and three-dimensionally derived interlandmark distances

INTRODUCTION

Accurate sex estimation is an important component of a biological profile in forensic anthropology. The pelvis is widely accepted as the most dimorphic osseous structure, and thus, this dimorphism is also reflected by the sacrum.

AIM

This study aimed to explore sacral morphology and to derive a practically applicable discriminant function formula for sex estimation.

MATERIALS

A total of 20 three-dimensional landmarks were digitised on a sample of 200 sacra from a sample of South Africans of African descent (Black South Africans) with ages ranging between 20 and 90 years, equally distributed for sex.

METHODS

Geometric morphometric methods were used to analyse sacral morphology and sexual dimorphism as it captures size-independent shape variation and three-dimensional morphology.

RESULTS

Size-independent shape analysis revealed four sacral structures and metrics that account for most of its shape variation. When these were compared between the sexes, we found that sacral curvature pattern, rather than depth, differed between sexes and that males have greater anterior sacral heights. Females have larger alae relative to the body of S1. In addition, the anterior posterior breadth of the sacral canal is larger in males, as is the relative size and projection of the superior articular processes. Discriminant analyses of these data produced average accuracies of only 72.5%, but this improved to 84.5% when using novel interlandmark distances derived from the raw coordinate data.

CONCLUSION

Our results demonstrate that landmark-based techniques allow for a more nuanced understanding of structural variation. In addition, accuracies were achieved that surpass traditional metrics using an equal number of variables. These results contribute to our understanding of sacral dimorphism and will assist in forensic casework.

A potential method for sex estimation of human skeletons using deep learning and three-dimensional surface scanning

Deep learning based on radiological methods has attracted considerable attention in forensic anthropology because of its superior classification capacities over human experts. However, radiological instruments are limited in their nature of high cost and immobility. Here, we integrated a deep learning algorithm and three-dimensional (3D) surface scanning technique into a portable system for pelvic sex estimation. Briefly, the images of the ventral pubis (VP), dorsal pubis (DP), and greater sciatic notch (GSN) were cropped from virtual pelvic samples reconstructed from CT scans of 1000 individuals; 80% of them were used to train and internally evaluate convolutional neural networks (CNNs) that were then evaluated externally with the remaining samples. An additional 105 real pelvises were documented virtually with a handheld 3D surface scanner, and the corresponding snapshots of the VP, DP, and GSN were predicted by the trained CNN models. The CNN models achieved excellent performance in the external testing using CT-based images, with accuracies of 98.0%, 98.5%, and 94.0% for VP, DP, and GSN, respectively. When the CT-based models were applied to 3D scanning images, they obtained satisfactory accuracies above 95% on the VP and DP images compared to the GSN with 73.3%. In a single-blind trial, a multiple design that combined the three CNN models yielded a superior accuracy of 97.1% with 3D surface scanning images over two anthropologists. Our study demonstrates the great potential of deep learning and 3D surface scanning for rapid and accurate sex estimation of skeletal remains.

Age estimation based on the acetabulum using global illumination rendering with computed tomography

INTRODUCTION

The acetabulum has been reported as a reliable age estimation marker. However, analyzing its morphological changes can be challenging using computed tomography (CT) imaging. Newly introduced global illumination rendering (GIR) applied to CT can improve the visualization of the fine details and thus the method's performance. This study aimed to analyze age estimation using morphological features of the acetabulum using GIR applied to CT.

METHODS

We collected 200 postmortem CT scans. A segmentation of the acetabular joint was initially done. Then, three-dimensional (3D) reconstruction of the images was performed using GIR. These images were saved and then analyzed by two operators based on the three morphological criteria described in the Rougé-Maillart method. Reproducibility was assessed by intraclass correlation (ICC). Age estimation was assessed by multiple linear regression.

RESULTS

The sample was composed of 155 males and 45 females, with a mean age of 50 ± 18.3 years old. We observed high agreement in both the inter-observer and intra-observer reproducibility for the three variables (ICC of 75.6 to 90.8% and 89.3 to 95.8%, respectively) and the total score (ICC of 93.5% and 95%, respectively). The three variables, as well as the total score, were significantly correlated with age groups. The total score showed a prediction rate higher than 85% for ages under 40 and over 70 years old. We identified three models with two validated models with an adjusted R² of 85.6% and 84.8%, respectively; a standard error of 0.688 and 0.706, respectively; and a good correlation of all variables and no inter-correlation. The first validated model included the three morphological criteria scores, and the second model was based on the total score.

CONCLUSION

GIR applied to CT provides photorealistic images that can be useful for forensic imaging intended for age estimation based on morphological methods.

Shape morphing technique can accurately predict pelvic bone landmarks

Diffeomorphic shape registration allows for the seamless geometric alignment of shapes. In this study, we demonstrated the use of a registration algorithm to automatically seed anthropological landmarks on the CT images of the pelvis. We found a high correlation between manually and automatically seeded landmarks. The registration algorithm makes it possible to achieve a high degree of automation with the potential to reduce operator errors in the seeding of anthropological landmarks. The results of this study represent a promising step forward in effectively defining the anthropological measures of the human skeleton.

Standardizing ordinal subadult age indicators: Testing for observer agreement and consistency across modalities

Skeletal and dental data for subadult analyses obtained from dry bones or various types of medical images, such as computed tomography (CT) scans or conventional radiographs/x-rays, should be consistent and repeatable to ensure method applicability across modalities and support combining study samples. The present study evaluates observer agreement of epiphyseal fusion and dental development stages obtained on CT scans of a U.S. sample and the consistency of epiphyseal fusion stages between CT scans and projected scan radiographs/scout images (U.S. CT sample), and between dry bones and conventional x-rays (Colombian osteological sample). Results show that both intra- and interobserver agreements of scores on CT scans were high (intra: mean Cohen's kappa=0.757-0.939, inter: mean Cohen's kappa=0.773-0.836). Agreements were lower for dental data (intra: mean Cohen's kappa=0.757, inter: mean Cohen's kappa=0.773-0.0.820) compared to epiphyseal fusion data (intra: mean Cohen's kappa=0.939, inter: mean Cohen's kappa=0.807-0.836). Consistency of epiphyseal fusion stages was higher between dry bones and conventional x-rays than between CT scans and scout images (mean Cohen's kappa=0.708-0.824 and 0.726-0.738, respectively). Differences rarely surpassed a one-stage value between observers or modalities. The complexity of some ossification patterns and superimposition had a greater negative impact on agreement and consistency rates than observer experience. Results suggest ordinal subadult skeletal data can be collected and combined across modalities.

A comparison of subadult skeletal and dental development based on living and deceased samples

OBJECTIVES

A fundamental assumption in biological anthropology is that living individuals will present with different growth than non-survivors of the same population. The aim is to address the question of whether growth and development data of non-survivors are reflective of the biological consequences of selective mortality and/or stress.

MATERIALS AND METHODS

The study compares dental development and skeletal growth collected from radiographic images of contemporary samples of living and deceased individuals from the United States (birth to 20 years) and South Africa (birth to 12 years). Further evaluation of deceased individuals is used to explore differential patterns among manners of death (MOD).

RESULTS

Results do not show any significant differences in skeletal growth or dental development between living and deceased individuals. However, in the South African deceased sample the youngest individuals exhibited substantially smaller diaphyseal lengths than the living sample, but by 2 years of age the differences were negligible. In the US sample, neither significant nor substantial differences were found in dental development or diaphyseal length according to MOD and age (>2 years of age), though some long bones in individuals <2 years of age did show significant differences. No significant differences were noted in diaphyseal length according to MOD and age in the SA sample.

DISCUSSION

The current findings refute the idea that contemporary deceased and living individuals would present with differential growth and development patterns through all of ontogeny as well as the assumptions linking short stature, poor environments, and MOD.

Forensic sex estimation using the vertebrae: an evaluation on two European populations

Sex estimation is one of the primary steps for constructing the biological profile of skeletal remains leading to their identification in the forensic context. While the pelvis is the most sex diagnostic bone, the cranium and other post-cranial elements have been extensively studied. Earlier research has also focused on the vertebral column with varying results regarding its sex classification accuracy as well as the underlying population specificity. The present study focuses on three easily identifiable vertebrae, namely T1, T12, and L1, and utilizes two modern European populations, a Greek and a Danish, to evaluate their forensic utility in sex identification. To this end, 865 vertebrae from 339 individuals have been analyzed for sexual dimorphism by further evaluating the effects of age-at-death and population affinity on its expression. Our results show that T1 is the best sex diagnostic vertebra for both populations reaching cross-validated accuracy of almost 90%, while age-at-death has limited effect on its sexual dimorphism. On the contrary, T12 and L1 produced varying results ranging from 75 to 83% accuracy with the Greek population exhibiting distinctively more pronounced sexual dimorphism. Additionally, age-at-death had significant effect on sexual dimorphism of T12 and L1 and especially in the Greek female and Danish male groups. Our results on inter-population comparison suggest that vertebral sex discriminant functions, and especially those utilizing multiple measurements, are highly population specific and optimally suitable only for their targeted population. An open-source software tool to facilitate classifying new cases based on our results is made freely available to forensic researchers.

Pitfalls of Computed Tomography 3D Reconstruction Models in Cranial Nonmetric Analysis

Many studies in the literature have highlighted the utility of virtual 3D databanks as a substitute for real skeletal collections and the important application of radiological records in personal identification. However, none have investigated the accuracy of virtual material compared to skeletal remains in nonmetric variant analysis using 3D models. The present study investigates the accuracy of 20 computed tomography (CT) 3D reconstruction models compared to the real crania, focusing on the quality of the reproduction of the real crania and the possibility to detect 29 dental/cranial morphological variations in 3D images. An interobserver analysis was performed to evaluate trait identification, number, position, and shape. Results demonstrate a false bone loss in 3D models in some cranial regions, specifically the maxillary and occipital bones in 85% and 20% of the samples. Additional analyses revealed several difficulties in the detection of cranial nonmetric traits in 3D models, resulting in incorrect identification in circa 70% of the traits. In particular, pitfalls included the detection of erroneous position, error in presence/absence rates, in number, and in shape. The lowest percentages of correct evaluations were found in traits localized in the lateral side of the cranium and for the infraorbital suture, mastoid foramen, and crenulation. The present study highlights important pitfalls in CT scan when compared with the real crania for nonmetric analysis. This may have crucial consequences in cases where 3D databanks are used as a source of reference population data for nonmetric traits and pathologies and during bone-CT comparisons for identification purposes.

Virtual forensic anthropology: The accuracy of osteometric analysis of 3D bone models derived from clinical computed tomography (CT) scans

Clinical radiology is increasingly used as a source of data to test or develop forensic anthropological methods, especially in countries where contemporary skeletal collections are not available. Naturally, this requires analysis of the error that is a result of low accuracy of the modality (i.e. accuracy of the segmentation) and the error that arises due to difficulties in landmark recognition in virtual models. The cumulative effect of these errors ultimately determines whether virtual and dry bone measurements can be used interchangeably. To test the interchangeability of virtual and dry bone measurements, 13 male and 14 female intact cadavers from the body donation program of the Amsterdam UMC were CT scanned using a standard patient scanning protocol and processed to obtain the dry os coxae. These were again CT scanned using the same scanning protocol. All CT scans were segmented to create 3D virtual bone models of the os coxae ('dry' CT models and 'clinical' CT models). An Artec Spider 3D optical scanner was used to produce gold standard 'optical 3D models' of ten dry os coxae. The deviation of the surfaces of the 3D virtual bone models compared to the gold standard was used to calculate the accuracy of the CT models, both for the overall os coxae and for selected landmarks. Landmark recognition was studied by comparing the TEM and %TEM of nine traditional inter-landmark distances (ILDs). The percentage difference for the various ILDs between modalities was used to gauge the practical implications of both errors combined. Results showed that 'dry' CT models were 0.36-0.45mm larger than the 'optical 3D models' (deviations -0.27mm to 2.86mm). 'Clinical' CT models were 0.64-0.88mm larger than the 'optical 3D models' (deviations -4.99mm to 5.00mm). The accuracies of the ROIs were variable and larger for 'clinical' CT models than for 'dry' CT models. TEM and %TEM were generally in the acceptable ranges for all ILDs whilst no single modality was obviously more or less reliable than the others. For almost all ILDs, the average percentage difference between modalities was substantially larger than the average percentage difference between observers in 'dry bone' measurements only. Our results show that the combined error of segmentation- and landmark recognition error can be substantial, which may preclude the usage of 'clinical' CT scans as an alternative source for forensic anthropological reference data.

Measurement error in μCT-based three-dimensional geometric morphometrics introduced by surface generation and landmark data acquisition

Computed-tomography-derived (CT-derived) polymesh surfaces are widely used in geometric morphometric studies. This approach is inevitably associated with decisions on scanning parameters, resolution, and segmentation strategies. Although the underlying processing steps have been shown to potentially contribute artefactual variance to three-dimensional landmark coordinates, their effects on measurement error have rarely been assessed systematically in CT-based geometric morphometric studies. The present study systematically assessed artefactual variance in landmark data introduced by the use of different voxel sizes, segmentation strategies, surface simplification degrees, and by inter- and intra-observer differences, and compared their magnitude to true biological variation. Multiple CT-derived surface variants of the anuran (Amphibia: Anura) pectoral girdle were generated by systematic changes in the factors that potentially influence the surface geometries. Twenty-four landmarks were repeatedly acquired by different observers. The contribution of all factors to the total variance in the landmark data was assessed using random-factor nested permanovas. Selected sets of Euclidean distances between landmark sets served further to compare the variance among factor levels. Landmark precision was assessed by landmark standard deviation and compared among observers and days. Results showed that all factors, except for voxel size, significantly contributed to measurement error in at least some of the analyses performed. In total, 6.75% of the variance in landmark data that mimicked a realistic biological study was caused by measurement error. In this landmark dataset, intra-observer error was the major source of artefactual variance followed by inter-observer error; the factor segmentation contributed < 1% and slight surface simplification had no significant effect. Inter-observer error clearly exceeded intra-observer error in a different landmark dataset acquired by six partly inexperienced observers. The results suggest that intra-observer error can potentially be reduced by including a training period prior to the actual landmark acquisition task and by acquiring landmarks in as few sessions as possible. Additionally, the application of moderate and careful surface simplification and, potentially, also the use of case-specific optimal combinations of automatic local thresholding algorithms and parameters for segmentation can help reduce intra-observer error. If landmark data are to be acquired by several observers, it is important to ensure that all observers are consistent in landmark identification. Despite the significant amount of artefactual variance, we have shown that landmark data acquired from microCT-derived surfaces are precise enough to study the shape of anuran pectoral girdles. Yet, a systematic assessment of measurement error is advisable for all geometric morphometric studies.

A novel method for analyzing long bone diaphyseal cross-sectional geometry. A GNU Octave CSG Toolkit

The diaphyseal cross-sectional geometric properties of the humerus, femur and tibia have been extensively used for studying their adaptation to mechanical loading. To date common practices for such studies involve either computed tomography or the latex cast method in conjunction with image analysis for calculating such properties. With the advent of modern laser scanning and photogrammetry technologies in biological anthropology, the computation of the cross-sectional geometric properties directly from 3D models is a viable and sensible alternative. Nevertheless, such method has not been properly implemented as yet. A dedicated toolkit, named long-bone-diaphyseal-CSG-Toolkit, comprising a set of functions for the GNU Octave programming language, is presented here. Offering a robust analytical implementation and an easy to follow application either for a single bone or in batch-processing mode, the toolkit requires minimum user intervention and also provides functionality for graphical representation of the calculated periosteal contours and their respective cross-sectional geometric properties. Finally, the long-bone-diaphyseal-CSG-Toolkit utilizes advanced optimization algorithms, which eliminate intra- and inter-observer error by reliably orienting the cross-sectional contours to a well-defined orientation and close to the bone's true anatomical position, which provides a significant advantage over the latex cast method.

The accuracy of 3D virtual bone models of the pelvis for morphological sex estimation

It is currently unknown whether morphological sex estimation traits are accurately portrayed on virtual bone models, and this hampers the use of virtual bone models as an alternative source of contemporary skeletal reference data. This study determines whether commonly used morphological sex estimation traits can be accurately scored on virtual 3D pelvic bone elements. Twenty-seven intact cadavers from the body donation program of the Amsterdam UMC, University of Amsterdam, were CT scanned; this data was used to produce virtual bone models. Thereafter, the dry bones were obtained. Three traits by Klales (2012) and five traits from the Workshop of European Anthropologists (WEA) (1980) were scored on the virtual bone models and their dry skeletal counterparts. Intra- and inter-observer agreement and the agreement between the scores for each virtual bone model-dry bone pair were calculated using weighted Cohen’s kappa (K). For all Klales (2012) traits, intra- and inter-observer agreement was substantial to almost perfect for the virtual- and dry bones (K = 0.62–0.90). The agreement in scores in the virtual-dry bone pairs ranged from moderate to almost perfect (K = 0.58–0.82). For the WEA (1980) traits, intra-observer agreement was substantial to almost perfect (K = 0.64–0.91), but results were less unambiguous for inter-observer agreement (K = 0.24–0.88). Comparison of the scores between the virtual bone models and the dry bones yielded kappa values of 0.42–0.87. On one hand, clinical CT data is a promising source for contemporary forensic anthropological reference data, but the interchangeability of forensic anthropological methods between virtual bone models and dry skeletal elements needs to be tested further.

The role of forensic anthropology in disaster victim identification (DVI): recent developments and future prospects

Forensic anthropological knowledge has been used in disaster victim identification (DVI) for over a century, but over the past decades, there have been a number of disaster events which have seen an increasing role for the forensic anthropologist. The experiences gained from some of the latest DVI operations have provided valuable lessons that have had an effect on the role and perceived value of the forensic anthropologist as part of the team managing the DVI process. This paper provides an overview of the ways in which forensic anthropologists may contribute to DVI with emphasis on how recent experiences and developments in forensic anthropology have augmented these contributions. Consequently, this paper reviews the value of forensic anthropological expertise at the disaster scene and in the mortuary, and discusses the way in which forensic anthropologists may use imaging in DVI efforts. Tissue-sampling strategies for DNA analysis, especially in the case of disasters with a large amount of fragmented remains, are also discussed. Additionally, consideration is given to the identification of survivors; the statistical basis of identification; the challenges related to some specific disaster scenarios; and education and training. Although forensic anthropologists can play a valuable role in different phases of a DVI operation, they never practice in isolation. The DVI process requires a multidisciplinary approach and, therefore, has a close collaboration with a range of forensic specialists.

Determination of sex on the basis of hyoid bone measurements in a Japanese population using multidetector computed tomography

Sex determination for unidentified human remains is important because the determined sex is usually used as a foundation for the estimation of other biological profiles. This study investigated the sexual dimorphism of the adult hyoid bone and developed discriminant equations to accurately estimate sex in a contemporary Japanese population using measurements on two-dimensional computed tomography (CT) images. The study sample comprised 280 cadavers (140 males, 140 females) of known age and sex that underwent postmortem CT and subsequent forensic autopsy. In accordance with previous studies, seven measurements were performed using two-dimensional CT reconstructed images. Most measurements of males were significantly greater than those of females. The perpendicular length from the most anterior edge of the hyoid body to the line that connects the most distal points of the greater horns of the hyoid and the linear distance between the most lateral edges of the hyoid body most significantly contributed to sex determination. This study demonstrated that discriminant functions on the basis of three measurements provided higher rates of accurate sex classification (93.3-94.6%) than univariate functions. Therefore, the hyoid bone is highly sexually dimorphic in the contemporary Japanese population and may be useful in forensic contexts for sex determination with a high level of accuracy.