Morphometric sex estimation from 3D computed tomography os coxae model and its validation in skeletal remains

Sex estimation from skull measurements of a contemporary Japanese population using three-dimensional computed tomography images

In this study, we assessed the sexual dimorphism of the contemporary Japanese skull and established sex discriminant function equations based on cranial measurements using three-dimensional (3D) computed tomography (CT) images. The CT images of 263 corpses (142 males, 121 females) that underwent postmortem CT scanning and subsequent forensic autopsy were evaluated. Twenty-one cranial measurements were obtained from 3D CT reconstructed images, which extracted only bone data. We performed descriptive statistics and discriminant function analyses for the measurements. Nineteen measurements were significantly larger in males, suggesting sexual dimorphism of the Japanese skulls. Univariate discriminant function analyses using these measurements showed a sex classification accuracy of 57.8-88.2%, and bizygomatic breadth provided the highest correct prediction rate. Multivariate discriminant function analyses offered the most accurate model using seven variables with an estimation rate of 93.9%. Our results suggest that cranial measurements based on 3D CT images may help in the sex estimation of unidentified bodies in a contemporary Japanese population.

Population affinity estimation using pelvic measurements based on computed tomographic data acquired from Japanese and Western Australian populations

The present study analyzes morphological differences in the pelvis of Japanese and Western Australian individuals and investigates the feasibility of population affinity classification based on computed tomography (CT) data. The Japanese and Western Australian samples comprise CT scans of 207 (103 females; 104 males) and 158 (78 females; 80 males) adult individuals, respectively. Following volumetric reconstruction, a total of 19 pelvic landmarks were obtained on each sample, and 11 measurements, including two angles, were calculated. Machine learning methods (random forest modeling [RFM] and support vector machine [SVM]) were used to classify population affinity. Classification accuracy of the two-way models was approximately 80% for RFM: the two-way sex-specific and sex-mixed models for SVM achieved > 90% and > 85%, respectively. The sex-specific models had higher accurate classification rates than the sex-mixed models, except for the Japanese male sample. The classification accuracy of the four-way sex and population affinity model had an overall classification accuracy of 76.71% for RFM and 87.67% for SVM. All the correct classification rates were higher in the Japanese relative to the Western Australian sample. Our data suggest that pelvic morphology is sufficiently distinct between Japanese and Western Australian individuals to facilitate the accurate classification of population affinity based on measurements acquired in CT images. To the best of our knowledge, this is the first study investigating the feasibility of population affinity estimation based on CT images of the pelvis, which appears as a viable supplement to traditional approaches based on cranio-facial morphology.

The influence of age on greater sciatic notch morphology: testing the Walker method in an Australian population

Sex estimation is an integral aspect of a forensic biological profile. The pelvis, being the most dimorphic part of the skeleton, has been studied in considerable detail relative to morphological and metric variation. However, empirical data on the effect of age on pelvic morphology relative to sex-specific morphological variation is limited, especially in regard to the estimation of skeletal sex. This study assesses whether there are age-related differences in the distribution of the Walker (2005) morphological scores for the greater sciatic notch (GSN) in an Australian population. Three-dimensional volumetric reconstructions derived from multi-detector computed tomography (MDCT) scans of 567 pelves of 258 females and 309 males aged 18 to 96 years were scored following Walker (2005). Differences in score distributions and means by sex and age group were tested using Pearson's chi-squared test and ANOVA, respectively. The accuracy of sex estimates derived from logistic regression equations was explored using leave-one-out cross-validation. Significant differences were found in score distribution and means among age groups in females, but not in males. There was a tendency toward higher scores in older females. The overall sex estimation accuracy was 87.5%. When comparing age groups 18-49 and 70 + years, estimation accuracy decreased in females (99% vs. 91%), while the opposite was found for males (79% vs. 87%). These findings suggest that age affects GSN morphology. Higher mean scores in older females imply that, on average, the GSN becomes narrower with increasing age. It is thus recommended due consideration of estimated age when assessing sex based on the GSN in unidentified human remains.

Population affinity estimation on a Spanish sample: Testing the validity and accuracy of cranium and mandible online software methods

Population affinity estimation is an important step in the identification of unknown individuals. To ensure accurate results, validation studies of newly developed methods must be performed using different target populations and skeletal elements. This research aimed to determine the accuracy and reliability of population affinity estimation on a modern Spanish sample using two online software applications. The sample consisted of 114 adult individuals (51 males, 63 females) using 38 measurements and one angle from the skull and mandible. AncesTrees was used for craniometric measurements and (hu)MANid for mandibular variables with different classification models and probability thresholds being evaluated. The required parameters were inputted for each individual and statistics were generated to assess the accuracy of the estimation. AncesTrees performed with the greatest accuracy as the program correctly classified the sample as Southwestern European or European, with highest accuracies being 54.56% (trial 1), 86.05% (trial 2), 82.61% (trial 3), 34.55% (trial 4) and 100% (trial 5). (hu)MANid correctly classified the sample as being from white origin with accuracies ranging from 70.59% to 80% without considering correct sex estimation, while accuracy ranged between 62.75% and 80% accounting for estimated sex. Population affinity estimation may determine subsequent methods used in the construction of the biological profile. Our results demonstrated varying accuracy rates depending on the element and method, offering a critical view in relation to software applicability and validity. Reference populations and intrinsic and extrinsic factors can potentially influence the method accuracy and reliability. Future research should focus on the inclusion of underrepresented groups.

The usability of the ratio of bi-humerus breadth to maximum pelvic breadth in sex estimation

BACKGROUND

Although sex can be determined with high accuracy in forensic anthropology, additional parameters are still required.

AIM

To estimate with known simple statistical methods, the usability of the bi-humerus/maximum pelvic breadth ratio in sex estimation.

SUBJECTS AND METHODS

Bi-humerus breadth and maximum pelvic breadth were measured using the topogram images (196 males, 171 females), the ratio between them was calculated. We examined the usability of the ratio of the distance between the lateral edges of the right and left humeral heads to the maximum distance between the two most lateral parts of the iliac crests in sex estimation.

RESULTS

There was significant difference in the bi-humerus breadth and "bi-humerus breadth/maximum pelvic breadth" according to sex. The greatest breadth of the pelvis was higher in females, yet the difference was not statistically significant. The ratio yielded 80.6%-90.3% accuracy for females and 73.6%-74.7% for males, depending on arm position.

CONCLUSIONS

The obtained data may contribute to the development of formulas created with metric measurements used in sex estimation. This can be used as a parameter to help in estimating the sex of skeletal remains found as a whole or excavated without losing their integrity, and also in the reconstruction of body structure.

Investigating metacarpi of Hamdani sheep via different measurement and modelling methods: A methodological study

The aim of the study was to perform the morphometric analyses on metacarpi of Hamdani sheep via different measurement methods and to compare the methods. Thus, metacarpal bones of 15 females and 15 males were used in the study. Measurements were taken from the measurement points determined on metacarpus via four methods, and their statistical analyses were performed. When both male and female metacarpal bones were examined in the De parameter in the comparison with the methods, it was observed that the four measurement methods were different from one another (p < 0.01). When DEM and DEL measurement parameters were examined in male metacarpus, the highest value was measured in ImageJ and the smallest value was measured in 3D Slicer software; however, it was found that the statistical difference was not significant when compared numerically (p > 0.05). As a result, while it was observed that the measurements made by using digital calliper measurements, photometric analysis, and 3D software were similar in some of the parameters but there was no statistically significant difference; whereas, Statistical difference was detected in some parameters.

Three-dimensional geometric morphometric sex determination of the whole and modeled fragmentary human pubic bone

Sex determination of the human pelvis has traditionally been done through visual analyses of morphoscopic traits and there are limited metric methods available to forensic anthropologists to add metric credibility to these analyses. The goal of this research was to create an improved metric method using three-dimensional geometric morphometrics to determine sex from both whole and modeled fragmented human pubic bones. The sample consisted of n = 378 pubic bones from the University of New Mexico’s Maxwell Museum Documented Skeletal Collection and eight landmarks were collected from each bone. Statistical analyses and machine learning algorithms were used to predict the accuracy of the method’s ability to classify a bone as male or female on both whole and simulated fragmented remains; this included tests run on each possible landmark combination of three or more landmarks to simulate fragmented bones (218 combinations). The results of the whole bone analysis resulted in 95.35% testing accuracy. The results of the modeled fragmentary analysis consisted of 164 combinations which exhibit a 90% or higher accuracy in sex prediction; and twelve combinations which exhibit 96% or higher accuracy in sex prediction. In particular, two landmarks clustered around the ventral arc of the pubic bone performed the best, indicating this is the most sexually dimorphic portion of the bone. These results indicate that three-dimensional geometric morphometrics is a valid method to be applied to sex determination in forensic anthropology.

Sex classification using the human sacrum: Geometric morphometrics versus conventional approaches

The human pelvis shows marked sexual dimorphism that stems from the conflicting selective pressures of bipedal locomotion and parturition. The sacrum is thought to reflect this dimorphism as it makes up a significant portion of the pelvic girdle. However, reported sexual classification accuracies vary considerably depending on the method and reference sample (54%-98%). We aim to explore this inconsistency by quantifying sexual dimorphism and sex classification accuracies in a geographically heterogeneous sample by comparing 3D geometric morphometrics with the more commonly employed linear metric and qualitative assessments. Our sample included 164 modern humans from Africa, Europe, Asia, and America. The geometric morphometric analysis was based on 44 landmarks and 56 semilandmarks. Linear dimensions included sacral width, corpus depth and width, and the corresponding indices. The qualitative inspection relied on traditional macroscopic features such as proportions between the corpus of the first sacral vertebrae and the alae, and sagittal and coronal curvature of the sacrum. Classification accuracy was determined using linear discriminant function analysis for the entire sample and for the largest subsamples (i.e., Europeans and Africans). Male and female sacral shapes extensively overlapped in the geometric morphometric investigation, leading to a classification accuracy of 72%. Anteroposterior corpus depth was the most powerful discriminating linear parameter (83%), followed by the corpus-area index (78%). Qualitative inspection yielded lower accuracies (64-76%). Classification accuracy was higher for the Central European subsample and diminished with increasing geographical heterogeneity of the subgroups. Although the sacrum forms an integral part of the birth canal, our results suggest that its sex-related variation is surprisingly low. Morphological variation thus seems to be driven also by other factors, including body size, and sacrum shape is therefore likely under stronger biomechanical rather than obstetric selection.

Sex estimation from the greater sciatic notch: a comparison of classical statistical models and machine learning algorithms

The greater sciatic notch (GSN) is a useful element for sex estimation because it is quite resistant to damage, and thus it can often be assessed even in poorly preserved skeletons. This study aimed to develop statistical models for sex estimation based on visual and metric analyses of the GSN, and additional variables linked to the GSN. A total of 60 left coxal bones (30 males and 30 females) were analysed. Fifteen variables were measured, and one was a morphologic variable. These 16 variables were used for the comparison of six statistical models: linear discriminant analysis (LDA), regularized discriminant analysis (RDA), penalized logistic regression (PLR) and flexible discriminant analysis (FDA), and two machine learning algorithms, support vector machine (SVM) and artificial neural network (ANN). The statistical models were built in two steps: firstly, only with the GSN variables (group 1), and secondly, with the whole variables (group 2), in order to see if the models including all the variables performed better. The overall accuracy of the models was very close, ranging from 0.92 to 0.97 using specific GSN variables. When additional variables starting from the deepest point of GSN are available, it is worth to use them, because the accuracy increases. PLR (after optimization of parameters) stands out from other statistical models. The position of the deepest point of GSN (Fig. 2) probably plays a crucial role for the sexual dimorphism, as stated by the good performance of the visual assessment of this point and the fact that the A2 angle (posterior angle with the deepest point of the GSN as the apex) is included in all models.

Testing the validity of population-specific sex estimation equations: An evaluation based on talus and patella measurements

Sex estimation is essential for forensic scientists to identify human skeletal remains. However, the most sexually dimorphic elements like pelvis or skull are not always assessable. Osteometric analyses have proven useful in sex estimation, but also to be population specific. The main purpose of this study was to test the validity of contemporary Greek and Spanish discriminant functions for the talus and the patella, respectively, on a Swiss skeletal sample and to quantify the utility of the measurements as a novel approach in osteometric sex assessment. Four talus and three patella measurements on dry bone were obtained from 234 individuals of the modern cemetery SIMON Identified Skeletal Collection. The previously derived discriminant functions were applied, accuracies determined, the utility of the different measurements was assessed and new multivariable equations constructed. Accuracies varied between 67% and 86% for talus and 63% and 84% for patella, similar to those reported by the original studies. Multivariable equations should be preferred over equations based on single measurements and combining the most significant measurements rather than using several variables obtained the best possible accuracy. The new discriminant functions did not provide a substantial improvement to the original ones. The overall utility of talus and patella is limited, allowing sex estimation with sufficient certainty only in a small proportion of individuals. Discriminant functions developed in contemporary Greek or Spanish populations are in principle applicable also to Swiss contemporary populations. We recommend that at present existent studies of this type should be validated and tested rather than developing new formulas.

Sex estimation of the subadult ilium prior to acetabular fusion

Previous studies evaluating sexual dimorphism in subadult pelvic features present variable, and at times conflicting, conclusions. As a result, there is yet to be a consensus on whether the subadult pelvis can be used in sex estimation methods. This study aims to assess the forensic utility of ilium shape and greater sciatic notch morphology in sexing subadult pelves prior to acetabular fusion. A sample of 397 modern U.S. individuals with unfused acetabula (i.e., tri-radiate cartilages) aged birth to 14 years was queried from a larger sample of postmortem computed tomography scans. Elliptical Fourier analyses were performed on ilium and greater sciatic notch outlines and resultant PCs were evaluated for significant effects of sex and age. Greater sciatic notch metrics were also collected. Stepwise linear discriminant function analyses with leave-one-out cross-validation were performed on the PCs and metric variables. Analyses were performed on pooled samples, on age-specific cohort samples, and on samples that iteratively removed the youngest one-year cohort. Cross-validated correct classification rates ranged from 57% to 65% and no patterns were observed to support an appearance and/or consistent expression of sexually diagnostic traits. Based on the results, sex estimation using these features is not recommended in pelvic remains prior to acetabular fusion, although the sample sizes of individuals over 5 years of age were limited in this study. Future studies should focus on the sexually diagnostic ability of pelvic traits in subadult samples post-fusion of the acetabulum.

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.

Virtual anthropology - a brief review of the literature and history of computed tomography

Computed tomography (CT) has influenced numerous fields since its inception in the 1970s. The field of palaeoanthropology significantly benefited from this efficient and non-invasive medium in terms of the conservation, reconstruction and analysis of fossil human remains. Over the past decade, there has been a steady increase in the number of forensic anthropological studies incorporating virtual osteological analyses. Because of the increasing importance of these modern cross-sectional imaging techniques and the requirement for standardized parameters in forensic science, we deemed it important to outline the history and development of CT applications in these related academic areas. The present paper outlines the history of “virtual anthropology” and osteological multi-detector CT in the context of palaeoanthropology and forensic anthropology.

Sexual determination based on multidetector computed tomographic measurements of the second cervical vertebra in a contemporary Japanese population

Accurate sex estimation is important in forensic investigation to determine the identity of unknown individuals. The aim of this study was to investigate the accuracy of sex assessment based on measurements of the second cervical vertebra (C2) using computed tomographic (CT) images in a Japanese population and to develop discriminant function formulae. The data were collected from 224 Japanese cadavers (112 male subjects, 112 female subjects) on which postmortem CT scanning and subsequent forensic autopsy were performed. Nine CT measurements of the C2 were performed for CT images of each subject. The measurements were assessed using descriptive statistics and discriminant function analyses (DFA). All of the measurements demonstrated significant sexual dimorphism. Multiple DFA with stepwise variable selection resulted in multivariable models; a five-variable model reached an accuracy rate of 92.9%. Our results suggest that metric analysis based on CT images of the C2 can accurately determine the sex from the human skeletal remains in a contemporary Japanese population and may be useful for sex estimation in forensic anthropology.

Sex estimation based on scapula analysis in a Japanese population using multidetector computed tomography

Accurate sex estimation based on measurements of dimorphic dimensions in human unknown remains is important as the first step toward making individual identification. The purpose of this study was to assess the sexual dimorphism of the scapula and to quantify the accuracy of sex estimation in a contemporary Japanese forensic sample using scapular measurements based on three-dimensional (3D) computed tomographic (CT) images. A total of 218 cadavers (109 males, 109 females) that underwent postmortem CT and subsequent forensic autopsy were used. Ten scapular measurements were performed on 3D CT reconstructed images that extracted only bone data, and were analyzed using descriptive statistics and discriminant function analyses (DFA). All measurements were dimorphic in terms of sex differences. Univariate DFA provided sex classification accuracy rates of 75.7-91.3%. Stepwise DFA yielded sex prediction accuracy rates of 93.1-94.5%. In conclusion, the scapular measurements using 3D CT images of a contemporary Japanese population may be useful for the estimation of skeletal sex in the field of forensic anthropology.

Possible application of CT morphometry of the calcaneus and talus in forensic anthropological identification

Computed tomography (CT) data provide information for volumetric and radiographic density analysis. The present study investigated the application of virtual CT volumetry of the tarsal bones to estimation of the sex, stature, and body weight using postmortem CT (PMCT) data of forensic autopsy cases. Three-dimensional (3D) images of the bilateral foot bones of intact Japanese subjects after adolescence (age ≥ 15 years, n = 179, 100 males and 79 females) were reconstructed on an automated CT image analyzer system. Measured parameters were mass volume, mean CT value (HU), and total CT value of the talus and calcaneus. Mean CT values of these bones showed age-dependent decreases in elderly subjects over 60 years of age for both sexes, with significant sex-related differences especially in the elderly. The mass volumes and total CT values of the talus and calcaneus showed significant sex-related differences, and also moderate correlations with body height and weight for bilateral bones in all cases (r = 0.58-0.78, p < 0.0001); however, the correlations of these parameters of the female talus with body weight were insufficient (r = 0.41-0.61, p < 0.0001). These observations indicate the applicability of virtual CT morphometry of the talus and calcaneus using an automated analyzer to estimate the sex and stature in forensic identification; however, greater variations should be considered in body weight estimations of females.