Sex determination with morphological characteristics of the skull by using 3D modeling techniques in computerized tomography

What we see is what we touch? Sex estimation on the skull in virtual anthropology

BACKGROUND

The increased use of virtual bone images in forensic anthropology requires a comprehensive study on the observational errors between dry bones and CT reconstructions. Here, we focus on the consistency of nonmetric sex estimation traits on the human skull.

MATERIALS AND METHODS

We scored nine nonmetric traits on dry crania and mandibles (n = 223) of archaeological origin and their CT reconstructions. Additionally, we 3D surface scanned a subsample (n = 50) and repeated our observations. Due to the intricate anatomy of the mental eminence, we split it into two separate traits: the bilateral mental tubercles and the midsagittal mental protuberance. We provide illustrations and descriptions for both these traits.

RESULTS

We obtained supreme consistency values between the CT and 3D surface modalities. The most consistent cranial traits were the glabella and the supraorbital margin, followed by the nuchal crest, zygomatic extension, mental tubercles, mental protuberance, mental eminence, mastoid process and ramus flexure, in descending order. The mental tubercles show higher consistency scores than the mental eminence and the mental protuberance.

DISCUSSION

The increased interchangeability of the virtual modalities with each other as compared to the dry bone modality could be due to the lack of tactility on both the CT and surface scans. Moreover, tactility appears less essential with experience than a precise trait description. Future studies could revolve around the most consistent cranial traits, combining them with pelvic traits from a previous study, to test for accuracy.

Validating the use of clinical MSCT scans for cranial nonmetric sex estimation in a contemporary Indonesian population

There is renewed interest in Asia for the development of forensic anthropological standards, partly due to the need for population-specific models to maintain high classification accuracies. At present, there are no known studies utilising morphoscopic standards specific to the Indonesian population. Craniometric analyses can often be time-consuming; morphoscopic assessments are quicker and are also known to be reliable and accurate. One of the most utilised morphoscopic standards for the estimation of skeletal sex is that of Walker (2008). Its application across population groups demonstrated reduced accuracies outside of the United States; population-specific predictive models would thus serve to improve the identification process of unknown skeletal remains. Digital imaging also allows for the validation of standards on a contemporary population and is an appropriate proxy to physical skeletal material.The present study quantifies the applicability of the Walker standard to a contemporary Indonesian population. A total of 200 cranial MSCT scans from a hospital in Makassar were analysed using OsiriX®. Scoring was performed in accordance with the Walker standard. Five univariate and nine multivariate predictive models were derived using single trait and multi-trait combinations. The best performing univariate model included the glabella, with a total classification accuracy of 82.0% and a sex bias of 14.6%. Classification accuracy with all traits considered was at 95.2% for females and 82.8% for males with a sex bias of 12.5%. These results provide forensic practitioners in Indonesia with an appropriate morphoscopic sex estimation standard, strengthening their capabilities in the field and improving judicial outcomes.

Morphometric analysis of the palatine triangle in adult human skulls: a potential aid for anthropologists and intraoral bone grafts

Morphometrics of the hard palate is an important aspect of forensic anthropology and odontology. Palatine triangle is a triangular area in the hard palate formed by the palatine processes of the maxillae, which can aid intraoral bone grafts. We present the osteological measurements of the palatine triangle (maxillary palate) based on sex, compare it with other hard palate parameters, and establish the correlation between them. Seventy-seven male skulls and 36 female skulls were examined. Various morphometric measurements of the hard palate and palatine triangle were performed meticulously. Mean and standard deviation of each parameter were computed for groups using SPSS 16.0. Relationships between all parameters were analyzed using Pearson's rank correlation test. The mean palatine length was 38.84 ± 3.75 mm in males and 37.22 ± 4.12 mm in females; the mean palatine breadth was 31.36 ± 2.61 mm in males and 29.78 ± 3.07 mm in females. The mean area of the palatine triangle was 600.88 ± 80.16 mm2 in male skulls and 547.96 ± 94.28 mm2 in the female skulls. Statistically significant difference in various measurements of the palatine triangle and hard palate between the male and female skulls was noted. Leptostaphyline (narrow palate) was the most prominent type of palate. The area of the palatine triangle showed a strong positive correlation between the total length and breadth of the palate for both male and female skulls. A strong positive correlation was also observed between the palate length and the palatine triangle length. Palatine index and palate breadth had a statistically significant moderate linear relationship. The maxillary palate length, breadth, and area of the palatine triangle were higher in males when compared to females in South Indian origin skulls. Most of the skulls had a narrow palate. The results of this metric analysis of the palatine triangle may lead to a new concept of anatomical research into studying the hard palate, which can be used for sexual dimorphism.

Comparative study of sex estimates in adult skulls using direct measurement and tomographic image reconstruction

Sex estimation is an important procedure in forensic anthropology for human identification. The development of new technologies, such as three-dimensional computed tomography (CT), has provided excellent alternatives for this purpose. This study examined and compared a morphological method for sex estimation using two different approaches - direct measurement of physical structures and tomographic analysis using 3D images. A total of 111 skulls from the Museum of Human Anatomy at the University of São Paulo (MAH-USP) were used, (60 males and 51 females). All specimens were scanned by Philips Brilliance 64 CT scanner equipment and their corresponding images were reconstructed in three-dimensional (3D) models. The morphological characteristics of the skulls were analyzed by an observer who was blinded to the sex of the specimens. Five cranial structures were analyzed: external occipital crest, mastoid process, supraorbital margin, glabella, and mental eminence. The structures were scored 1 to 5 according to Buikstra and Ubelaker and validated by Walker. The success rates of the sex estimates obtained through direct measurement of the dry skulls ranged from 67.4% to 70.4% as compared to 60.2% to 68.1% for CT reconstruction. When analyzed separately, the maximum accuracy of the method was 68.33% in males and 88.24% in females in the physical analysis of structures. The glabella and mastoid process were the most effective structures to estimate sex through both techniques, respectively. Our results show that 3D CT images can be accurately used in the morphological analysis for sex estimation, representing a viable alternative in forensic anthropology.

Sex estimation from virtual models: exploring the potential of stereolithic 3D crania models for morphoscopic trait scoring

Modern computed tomography (CT) databases are becoming an accepted resource for the practice and development of identification methods in forensic anthropology. However, the utility of 3D models created using free and open-source visualization software such as 3D Slicer has not yet been thoroughly assessed for morphoscopic biological profiling methods where virtual methods of analysis are becoming more common. This paper presents a study that builds on the initial findings from Robles et al. (2020) to determine the feasibility of estimating sex on stereolithic (STL) 3D cranial models produced from CT scans from a modern, living UK population (n = 80) using equation 2 from the Walker's (2008) morphoscopic method. Kendall's coefficients of concordance (KCC) indicated substantial agreement using cranial features scores in an inter-observer test and a video-inter-observer test. Fleiss' Kappa scores showed moderate agreement (0.50) overall between inter-observer sex estimations, and for observer sex estimations in comparison to recorded sexes (0.56). It was found that novice users could virtually employ morphoscopic sex estimation methods effectively on STL 3D cranial models from modern individuals. This study also highlights the potential that digital databases of modern living populations can offer forensic anthropology.

Key points

First example of Walker's (2008) method applied to a living UK population.Open-source software is a valuable resource for crime reconstruction approaches.Male scoring bias was observed in method application.Forensic anthropologists would benefit from virtual anthropology training to use and interpret 3D models.Digital databases offer more ethical, diverse, modern populations for future research.

Developmental changes of the facial skeleton from birth to 18 years within a South African cohort (A computed tomography study)

Skeletal remains are often found on a crime scene in which a forensic anthropologist is then consulted to create a biological profile, which includes the estimation of age, sex, ancestry and stature. The viscerocranium plays an important role in the formation of a biological profile. However, to utilise the viscerocranium for age estimation, population specific normative data and knowledge of the development of the viscerocranium is required. Therefore, this study aimed to investigate the developmental changes from birth to 18 years of age of the facial skeleton of individuals from a South African cohort. This study comprised of 239 computed tomography (CT) scans (128 males; 111 females). The viscerocranium was subdivided into five regions viz.: orbital, nasal, midfacial, maxillary and mandibular. The linear parameters in each region were correlated to age to identify the developmental growth patterns of the viscerocranial regions according to male and female. The measurements which displayed the highest correlations with age were used to develop formulas which could be used for age estimation. The results of this study showed that the measurements in the orbital, midfacial, maxillary and mandibular regions experienced rapid growth between 0 and 5 years of age, with the nasal region increasing steadily over time. It was noted that males displayed overall larger measurements than females except for the anterior interorbital distance and both right and left zygomatic arch lengths (ZAL). Although only the left orbital height, nasal aperture height and mandible width displayed statistically significant size differences according to sex (p ≤ 0.05). The measurements which showed the highest correlations to age were the zygomatic arch distance (r = 0.8842, p < 0.001), ZAL (right: r = 0.8929, p < 0.001; left: r = 0.8656, p < 0.001) and the mandible width (r = 0.8444, p < 0.001). Formulas were derived for the measurements that could be used to forensically estimate age within a subadult cohort.

Data mining for sex estimation based on cranial measurements

The aim of the present study is to develop effective and understandable classification models for sex estimation and to identify the most dimorphic linear measurements in adult crania by means of data mining techniques. Furthermore, machine learning models and models developed through logistic regression analysis are compared in terms of performance. Computed tomography scans of 393 adult individuals were used in the study. A landmark-based approach was applied to collect the metric data. The three-dimensional coordinates of 47 landmarks were acquired and used for calculation of linear measurements. Two datasets of cranial measurements were assembled, including 37standard measurements and 1081 interlandmark distances, respectively. Three data mining algorithms were applied: the rule induction algorithms JRIP and Ridor, and the decision tree algorithm J48. Two advanced attribute selection methods (Weka BestFirst and Weka GeneticSearch) were also used. The best accuracy result (91.9 %) was achieved by a set of rules learnt by the JRIP algorithm from the dataset constructed by application of the GeneticSearch selection algorithm to the dataset of standard cranial measurements. The set consisted of five rules including seven cranial measurements. Its accuracy was even better than the classification rates achieved by the logistic regression models. Concerning the second dataset of nonstandard measurements, the best accuracy (88.3 %) was obtained by using classification models learnt by two algorithms - JRIP with a dataset preprocessed by the BestFirst selection algorithm and Ridor with preprocessing by the GeneticSearch selection algorithm. Our experiments show that for the two datasets mentioned above the rule-based models contain smaller sets of rules with shorter lists of measurements and achieve better classification accuracy results in comparison with decision tree-based models.