CT-scan vs. 3D surface scanning of a skull: first considerations regarding reproducibility issues

Dimensional accuracy of structured light scans and 3D prints of various human skeletal elements

Three-dimensional (3D) structured light scanning is a beneficial documentation technique in forensic anthropology because such models facilitate continued analysis and data sharing; they can also be 3D printed for demonstrative purposes in legal proceedings and training, without risk of damage to the original skeletal material. As its application in forensic anthropology is relatively novel, the aim of the present study is to statistically evaluate the dimensional accuracy of 3D structured light scans and 3D prints for ten bone types, including the cranium, mandible, 2nd cervical vertebra (C2), clavicle, scapula, capitate, 2nd metacarpal, os coxae, femoral head, and patella. Standard linear measurements are acquired in each physical bone, 3D virtual model, and 3D print of the same bone specimen. Variances between measurements of physical, virtual, and printed bones are quantified using the technical error of measurement (TEM), relative TEM (rTEM), and coefficient of reliability (R). Measurements acquired in the virtual models and prints were found to be within ±2 mm average of the same measurements in the physical bones, with a tendency to underestimate true value. rTEM and R values for the virtual clavicle, capitate, scapula and C2, and rTEM for the printed clavicle and capitate, were comparatively less reliable than for other bone types; although all bones were reproduced to within acceptable anthropological error standards (rTEM≤5 %; R≥0.95). This study reaffirms the use of 3D structured light scanning and 3D printing to complement traditional skeletal documentation in forensic anthropology.

Forensic exploitation of patterned injuries: Promoting structured analysis as an early assessment for comparison process

Practice at our Center shows that approach using 3D surface imaging for morphometric comparison of patterned injuries does not always lead to accurate conclusions. We decided to evaluate whether a selection protocol focused on analysis phase could enable us to form an early assessment of the outcome of a comparison process, and then to select lesions likely to lead to a probative conclusion. 23 blunt objects were used to create 65 patterned injuries on an experimental model simulating human skin. A blinded analysis and a comparison were conducted on photographs and 3D models of the lesions. Statement of analysis phase was consistent with comparison results in most cases, enabling correct identification of the responsible object or at least keeping it as possibly responsible among 2 to 3 objects. Our protocol has been demonstrated to improve ability to exploit patterned injuries from surface imaging, despite certain limiting factors.

Evaluation of the accuracy of an augmented reality-based tumor-targeting guide for breast-conserving surgery

BACKGROUND AND OBJECTIVES

Although magnetic resonance imaging (MRI) is commonly used for breast tumor detection, significant challenges remain in determining and presenting the three-dimensional (3D) morphology of tumors to guide breast-conserving surgery. To address this challenge, we have developed the augmented reality-breast surgery guide (AR-BSG) and compared its performance with that of a traditional 3D-printed breast surgical guide (3DP-BSG).

METHODS

Based on the MRI results of a breast cancer patient, a breast phantom made of skin, body, and tumor was fabricated through 3D printing and silicone-casting. AR-BSG and 3DP-BSG were executed using surgical plans based on the breast phantom's computed tomography scan images. Three operators independently inserted a catheter into the phantom using each guide. Their targeting accuracy was then evaluated using Bland-Altman analysis with limits of agreement (LoA). Differences between the users of each guide were evaluated using the intraclass correlation coefficient (ICC).

RESULTS

The entry and end point errors associated with AR-BSG were -0.34±0.68 mm (LoA: -1.71-1.01 mm) and 0.81±1.88 mm (LoA: -4.60-3.00 mm), respectively, whereas 3DP-BSG was associated with entry and end point errors of -0.28±0.70 mm (LoA: -1.69-1.11 mm) and -0.62±1.24 mm (LoA: -3.00-1.80 mm), respectively. The AR-BSG's entry and end point ICC values were 0.99 and 0.97, respectively, whereas 3DP-BSG was associated with entry and end point ICC values of 0.99 and 0.99, respectively.

CONCLUSIONS

AR-BSG can consistently and accurately localize tumor margins for surgeons without inferior guiding accuracy AR-BSG can consistently and accurately localize tumor margins for surgeons without inferior guiding accuracy compared to 3DP-BSG. Additionally, when compared with 3DP-BSG, AR-BSG can offer better spatial perception and visualization, lower costs, and a shorter setup time.

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.

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

BACKGROUND

Computed tomography (CT) scans are a convenient means to study 3D reconstructions of bones. However, errors associated with the different nature of the observation, e.g. visual and tactile (on dry bone) versus visual only (on a screen) have not been thoroughly investigated.

MATERIALS AND METHODS

We quantified the errors between modalities for sex estimation protocols of nonmetric (categorical and ordinal) and metric data, using 200 dry pelves of archaeological origin and the CT reconstructions of the same bones. In addition, we 3D surface scanned a subsample of 39 pelves to compare observations with dry bone and CT data. We did not focus on the sex estimation accuracy but solely on the consistency of the scoring, hence, the interchangeability of the modalities.

RESULTS

Metric data yielded the most consistent results. Among the nonmetric protocols, ordinal data performed better than categorical data. We applied a slightly modified description for the trait with the highest errors and grouped the traits according to consistency and availability in good, intermediate, and poor.

DISCUSSION

The investigated modalities were interchangeable as long as the trait definition was not arbitrary. Dry bone (gold standard) performed well, and CT and 3D surface scans performed better. We recommend researchers test their affinity for using virtual modalities. Future studies could use our consistency analysis and combine the best traits, validating their accuracy on various modalities.

Hidden lesions: a case of burnt remains

One of the many challenging cases that forensic pathologists, anthropologists, and forensic imaging experts have to face are burnt human remains. Perpetrators frequently attempt to hide/destroy evidence and make the body unidentifiable by exposing it to fire. We present a case of a partially burnt body found in an apartment after an explosion. First, multidetector computed tomography (MDCT) images and the following autopsy revealed several lesions on the cranium. Forensic anthropologists were involved in order to specify the aetiology of the lesions observed on the cranium. Through an interdisciplinary approach bringing together MDCT scans, 3D surface scans, and anthropological analysis, it was possible to answer the questions raised during the autopsy. Analyses demonstrated that there were signs of blunt force trauma on the cranium vault that the perpetrator likely attempted to hide by exposing the body to fire. This case demonstrates the importance of close collaboration between forensic anthropologists, imaging experts, and forensic pathologists. This multidisciplinary approach allows for a better, more complete reconstitution of forensic cases.

Key points

The analyses of burnt human remains are one of the many challenging tasks that forensic pathologists and anthropologists have to face.We present an occurrence of a partially burnt body after an explosion and forensic anthropologists were asked whether the nature of the lesions observed on the cranium could be further specified.Anthropological analyses of the skull were consistent with the radiological and autopsy report. It was possible to reconstruct the various lesions on the dry bone.The case demonstrates the importance of an interdisciplinary approach and the close collaboration between forensic anthropologists, imaging experts, and forensic pathologists.

Forensic age estimation: comparison and validation of the Iscan method in 3D reconstructions using a surface scanner in a Spanish population

When investigating a death, post-mortem identification provides with results of great legal and humanitarian significance. The effectiveness of the methods used to estimate age depends on the reference population, considering variables such as sex and ancestry. The aim of this study was to validate the Iscan method to estimate age in a Spanish forensic population, comparing the estimates obtained in dry bones and 3D reconstructions created with a surface scanner. We carried out a cross-sectional study on 109 autopsied corpses (67% male), scanning the sternal end of the right fourth rib in a 3D mesh, using an EinScan-Pro® surface scanner (precision: 0.05 mm). Two observers estimated the phases in dry bones and 3D images according to the Iscan method and to the sex of the subject. The mean age was 57.73 years (SD = 19.12 years;18-93 years). The intra-observer agreement was almost perfect in bones (κ = 0.877-0.960) and 3D images (κ = 0.954), while the inter-observer agreement was almost perfect in bones (κ = 0.813) and substantial in 3D images (κ = 0.727). The correlation with the Iscan phases was very strong in bones (Rho = 0.794-0.820; p < 0.001) and strong in 3D images (Rho = 0.690-0.691; p < 0.001). Both sex-adjusted linear regression models were significant (dry bones: R2 = 0.65; SEE =  ± 11.264 years; 3D images: R2 = 0.50; SEE =  ± 13.537 years) from phase 4 onwards. An overestimation of age was observed in the first phases, and an underestimation in the later ones. Virtual analysis using a surface scanner in the fourth rib is a valid means of estimating age. However, the error values and confidence intervals were considerable, so the joint use of different methods and anatomical sites is recommended.

Identification parade in immersive virtual reality - A technical setup

Virtual Reality (VR) has sparked interest within the forensic community, where it is currently used for training purposes and in variety of forensic scenarios. In combination with efficient and user friendly full body 3-Dimensional (3D) documentation methods, VR visualisations present a viable tool for suspect witness identification. The well-known procedure of placing several persons in a room with a one-way-mirror, along with a witness on the other side of the mirror has practical disadvantages. The primary concern implicates the witness(s) and person(s) of interest coming face-to-face prior to the line-up, combined with finding sufficient persons to include within the line-up. Although image identification using printed paper partially resolved this problem, features such as body stature also marks an issue for the recognition and identification process. To test whether VR provides the technical capabilities to perform an identification parade, a total of 15 subjects were 3D documented using the multi-camera device "Photobox". From this group, one of the documented persons then interrupted a lecture, where consequently, the students were asked afterwards to identify the same person in VR and paper identification sets. It was found that the participating students were able to identify the "suspect" in both datasets. The results imply that VR technology allow users to identify persons. However, as this is a preliminary study the similarity problem was not analysed in this paper and requires further investigation to demonstrate the robustness of this approach.

Effect of the Segmentation Threshold on Computed Tomography-Based Reconstruction of Skull Bones with Reference Optical Three-Dimensional Scanning

BACKGROUND

A variety of applications related to neurosurgical procedures, education, and training require accurate reconstruction of the involved structures from the medical images such as computed tomography (CT). This study evaluates the quality of CT-based reconstruction of dry skull bones for advanced neurosurgical applications. The accuracy and precision of these models were examined with reference optical scanning.

METHODS

Three consecutive CT and optical scans of different skull bones were acquired and used to develop three-dimensional models. The accuracy of three-dimensional models was examined by manual inspection of the defined anatomical landmarks of the skull. Reproducibility was examined by deviation analysis of the models developed from repeated CT and optical scans.

RESULTS

Precision was excellent in both the techniques with less than 0.1 mm deviation error. On the interscan evaluation of the CT versus optical scan model, deviations of more than 0.1 mm were observed in 16 out of 21 instances. CT reconstruction using standard segmentation algorithms results in missing bone portions while using the default bone segmentation threshold. The segmentation threshold was varied to construct missing bone regions, and its effect on the iso-surface generation was evaluated. The threshold variation led to increased mean deviations of surfaces up to 0.6 mm.

CONCLUSIONS

The study reveals that bone structure, complexity, and segmentation threshold lead to CT reconstruction variability. The trade-off between the desirable model and accepted mean deviation should be considered as per traits of the desired application.

Accuracy of the Surface Contour of Three-Dimensional-Printed Canine Pelvic Replicas

OBJECTIVE

The aim of this study was to determine the differences in surface contour between models of native pelvic bones and their corresponding three-dimensional (3D)-printed replicas.

STUDY DESIGN

Digital 3D models of five cadaveric hemipelves and five live dogs with contralateral pelvic fractures were generated based on computed tomographic images and 3D printed. The 3D-printed replicas underwent 3D scanning and digital 3D models of the replicas were created. The digital 3D model of each replica was superimposed onto the model of the native hemipelvis. Errors in the replicas were determined by comparing the distances of 120,000 corresponding surface points between models. The medial surface, lateral surface and dorsal surface of the acetabulum (DSA) of each hemipelvis were selected for further analysis. The root mean square error (RMSE) was compared between various selected areas using a one-way repeated measures analysis of variance, followed by a Bonferroni post-hoc test.

RESULTS

The RMSE of the hemipelvis was 0.25 ± 0.05 mm. The RMSE significantly decreased from the medial surface (0.28 ± 0.06mm), to the lateral surface (0.23 ± 0.06mm), to the DSA (0.04 ± 0.02mm) (p < 0.001).

CONCLUSION

The 3D-printed replicas were adequate in serving as a template for the pre-contouring of bone plates in fracture repair of pelvic fractures, particularly those that demand accurate reduction such as acetabular fractures.

Precision of a Hand-Held 3D Surface Scanner in Dry and Wet Skeletal Surfaces: An Ex Vivo Study

Three-dimensional surface scans of skeletal structures have various clinical and research applications in medicine, anthropology, and other relevant fields. The aim of this study was to test the precision of a widely used hand-held surface scanner and the associated software's 3D model generation-error in both dry and wet skeletal surfaces. Ten human dry skulls and ten mandibles (dry and wet conditions) were scanned twice with an industrial scanner (Artec Space Spider) by one operator. Following a best-fit superimposition of corresponding surface model pairs, the mean absolute distance (MAD) between them was calculated on ten anatomical regions on the skulls and six on the mandibles. The software's 3D model generation process was repeated for the same scan of four dry skulls and four mandibles (wet and dry conditions), and the results were compared in a similar manner. The median scanner precision was 31 μm for the skulls and 25 μm for the mandibles in dry conditions, whereas in wet conditions it was slightly lower at 40 μm for the mandibles. The 3D model generation-error was negligible (range: 5-10 μm). The Artec Space Spider scanner exhibits very high precision in the scanning of dry and wet skeletal surfaces.

Comparability of skeletal fibulae surfaces generated by different source scanning (dual-energy CT scan vs. high resolution laser scanning) and 3D geometric morphometric validation

This work aims to test accuracy and comparability of 3D models of human skeletal fibulae generated by clinical CT and laser scanner virtual acquisitions. Mesh topology, segmentation and smoothing protocols were tested to assess variation among meshes generated with different scanning methods and procedures, and to evaluate meshes-interchangeability in 3D geometric morphometric analysis. A sample of 13 left human fibulae were scanned separately with Revolution Discovery CT dual energy (0.625 mm resolution) and ARTEC Space Spider 3D structured light laser scanner (0.1 mm resolution). Different segmentation methods, including half-maximum height (HMH) and MIA-clustering protocols, were compared to their high-resolution standard generated with laser-scanner by calculating topological surface deviations. Different smoothing algorithms were also evaluated, such as Laplacian and Taubin smoothing. A total of 142 semilandmarks were used to capture the shape of both proximal and distal fibular epiphyses. After Generalized Procrustes superimposition, the Procrustes coordinates of the proximal and distal fibular epiphyses were used separately to assess variation due to scanning methods and the operator error. Smoothing algorithms at low iteration do not provide significant variation among reconstructions, but segmentation protocol may influence final mesh quality (0.09-0.24 mm). Mean deviation among CT-generated meshes that were segmented with MIA-clustering protocol, and laser scanner-generated ones, is optimal (0.42 mm, ranging 0.35-0.56 mm). Principal component analysis reveals that homologous samples scanned with the two methods cluster together for both the proximal and distal fibular epiphyses. Similarly, Procrustes ANOVA reveals no shape differences between scanning methods and replicates, and only 1.38-1.43% of shape variation is due to scanning device. Topological similarities support the comparability of CT- and laser scanner-generated meshes and validate its simultaneous use in shape analysis with potential clinical relevance. We precautionarily suggest that dedicated trials should be performed in each study when merging different data sources prior to analyses.

The efficacy of computed tomography scanning versus surface scanning in 3D finite element analysis

Finite element analysis (FEA) is a commonly used application in biomechanical studies of both extant and fossil taxa to assess stress and strain in solid structures such as bone. FEA can be performed on 3D structures that are generated using various methods, including computed tomography (CT) scans and surface scans. While previous palaeobiological studies have used both CT scanned models and surface scanned models, little research has evaluated to what degree FE results may vary when CT scans and surface scans of the same object are compared. Surface scans do not preserve the internal geometries of 3D structures, which are typically preserved in CT scans. Here, we created 3D models from CT scans and surface scans of the same specimens (crania and mandibles of a Nile crocodile, a green sea turtle, and a monitor lizard) and performed FEA under identical loading parameters. It was found that once surface scanned models are solidified, they output stress and strain distributions and model deformations comparable to their CT scanned counterparts, though differing by notable stress and strain magnitudes in some cases, depending on morphology of the specimen and the degree of reconstruction applied. Despite similarities in overall mechanical behaviour, surface scanned models can differ in exterior shape compared to CT scanned models due to inaccuracies that can occur during scanning and reconstruction, resulting in local differences in stress distribution. Solid-fill surface scanned models generally output lower stresses compared to CT scanned models due to their compact interiors, which must be accounted for in studies that use both types of scans.

Cone-Beam Angle Dependency of 3D Models Computed from Cone-Beam CT Images

Cone-beam dental CT can provide high-precision 3D images of the teeth and surrounding bones. From the 3D CT images, 3D models, also called digital impressions, can be computed for CAD/CAM-based fabrication of dental restorations or orthodontic devices. However, the cone-beam angle-dependent artifacts, mostly caused by the incompleteness of the projection data acquired in the circular cone-beam scan geometry, can induce significant errors in the 3D models. Using a micro-CT, we acquired CT projection data of plaster cast models at several different cone-beam angles, and we investigated the dependency of the model errors on the cone-beam angle in comparison with the reference models obtained from the optical scanning of the plaster models. For the 3D CT image reconstruction, we used the conventional Feldkamp algorithm and the combined half-scan image reconstruction algorithm to investigate the dependency of the model errors on the image reconstruction algorithm. We analyzed the mean of positive deviations and the mean of negative deviations of the surface points on the CT-image-derived 3D models from the reference model, and we compared them between the two image reconstruction algorithms. It has been found that the model error increases as the cone-beam angle increases in both algorithms. However, the model errors are smaller in the combined half-scan image reconstruction when the cone-beam angle is as large as 10 degrees.

The big puzzle: A critical review of virtual re-association methods for fragmented human remains in a DVI context'

During a Disaster Victims Identification (DVI) mission, international protocols rely on interdisciplinary work, especially between specialists from forensic imaging and anthropology. In case of air crashes or explosions, DVI units may face thousands of fragmented human remains (FHRs). The physical re-association of FHRs and the identification process is very complex and challenging, and relies upon expensive and destructive DNA analysis. A virtual re-association (VRA) of these fragments, using Multidetector Computed Tomography (MDCT), could be a helpful tool in forensic anthropology analysis, as it could assist in reducing the number of DNA samples. However, there is no standardized protocol for including such an approach into a DVI procedure. The aim of this study was to summarize and analyze existing techniques through a systematic review and to develop a protocol for virtual re-association of FHRs, adapted to the DVI context. A keyword-based literature search was conducted, focusing on the VRA methods using MDCT imaging and 3D surface scan methodology. Reviews and primary articles, published between 2005 and 2020 in the fields of forensic anthropology, paleoanthropology, archeology, and fracture reduction surgery were sorted out. A total of 45 publications were selected and analyzed based on their content and relevance. The results show that research on the re-association of FHRs increased significantly during the last five years. Seven steps regarding the MDCT-based method for the virtual re-association of FHRs could be identified: acquisition of 3D-images, segmentation of the MDCT-data, post-processing and surface generation, identification of intact and fracture surfaces, identification and registration of matching fragments, and validation of the re-association. The literature is surprisingly sparse regarding the FHRs re-association as a forensic tool, and mainly consists in case reports, whereas validated methods were presented in archeology and surgery publications. However, we were able to adapt the MDCT-based approach for the virtual re-association of the FHRs and propose an innovative protocol for DVI missions. This protocol includes the needed details, from the acquisition of MDCT imaging to the virtual re-association of 3D models and its validation. Each step has to be fully tested, adapted and validated in future studies.

Explosion-related deaths: An overview on forensic evaluation and implications

Purpose

Explosion-related deaths are uncommon events which require expertise and confidence so that an appropriate death investigation can be performed. The present study aims to provide a detailed forensic analysis of the issues and implications arising in the event of an explosion.

Methods

A retrospective review of casualty data was conducted on electronic literature databases. Cases concerning deadly explosions registered at the Milan Institute of Legal Medicine were examined and analyzed altogether.

Results

Explosions may involve closed or open systems. A security assessment of the site is always necessary. Alterations of the site due to rescue procedures can occur; thus, on-site forensic investigation should be adapted to the environment. Then, a study protocol based on autopsy procedures is presented. Application of the postmortem radiology enforces forensic procedures both for the analysis of blast injuries and skeleton fractures, and for identification purposes. Blast injuries typically cause lacerations of the lungs, intestine and major vessels; moreover, hyoid fractures can be documented. Histopathology may help to define blast injuries effectively. Forensic chemistry, toxicology and ballistics provide useful investigative evidence as well as anthropology and genetics. Different forensic topics regarding explosions are discussed through five possible scenarios that forensic pathologists may come across. Scenarios include self-inflicted explosion deaths, domestic explosions, work-related explosions, terrorist events, and explosions caused by accidents involving heavy vehicles.

Conclusion

The scenarios presented offer a useful instrument to avoid misinterpretations and evaluation errors. Procedural notes and technical aspects are provided to the readers, with an insight on collaboration with other forensic experts.

Virtual anthropology? Reliability of three-dimensional photogrammetry as a forensic anthropology measurement and documentation technique

Osseous remains provide forensic anthropologists with morphological and osteometric information that can be used in building a biological profile. By conducting a visual and physical examination, an anthropologist can infer information such as the sex and age of the deceased. Traditionally, morphological and osteometric information is gathered by physically handling remains for analysis. With the advancement of digital technology, there has been a shift from direct to indirect methods of analysis by utilizing models generated from three-dimensional (3D) imaging, which includes computed tomography (CT) scanning and 3D photogrammetry. Although CT scanning is more common, photogrammetry has found application in a range of fields such as architecture, geography and road accident reconstruction. The application of modern-day photogrammetry for forensic anthropology purposes, however, has not been discussed extensively. The aim of this research was to validate the accuracy of 3D models generated by photogrammetry by comparing them to both 3D models generated by CT scanning and the actual physical models. In this study, six 3D models were created using photogrammetry (n = 3) and CT scanning (n = 3). The 3D models were generated from three different Bone Clone® human skulls. A mobile phone camera was used to capture images, which were then processed in Agisoft Metashape®. Intrarater, interrater, and intermethod reliability tests gave correlation coefficients of at least 0.9980, 0.9871, and 0.9862, respectively; rTEM results ranged from 0.250 to 6.55%; and an analysis of variance (ANOVA) yielded P values under 0.05 for all measurements except one. Statistical tests therefore showed photogrammetry to be a reliable and accurate alternative to more expensive CT scanning approaches.

Virtual anthropology: a preliminary test of macroscopic observation versus 3D surface scans and computed tomography (CT) scans

Virtual anthropology (VA) is based on applying anthropological methods currently used to analyse bones to 3D models of human remains. While great advances have been made in this endeavour in the past decade, several interrogations concerning how reliable these models are and what their proper use should be remain unanswered. In this research, a fundamental assumption of VA has been investigated: if the way we perceive and apply an anthropological method is truly similar when looking at bones macroscopically and through various 3D media. In order to answer, 10 skulls of known age and sex were scanned using a computed tomography (CT) scanner and a 3D surface scanner. Two observers separately applied a defined staging method to eight suture sites on these skulls, first looking at the bone macroscopically, then at the 3D surface scan, and finally on the CT scan. Two rounds of observation were carried out by each observer. Intra- and inter-observer error were evaluated, and two sample t-tests used to evaluate if the different types of medium used yielded significantly different observations. The results show a high degree of inter-observer error, and that data obtained from 3D surface scans differ from macroscopic observation (confidence level 95%, P ≤ 0.05). CT scans, in these settings, yielded results comparable to those obtained through macroscopic observations. These results offer many possibilities for future research, including indications on the kind of anthropological methods and anatomical landmarks that might be reliably transferable to the virtual environment. All current methods used in traditional anthropology should be tested, and if they prove unreliable, new techniques to analyse bones from virtual models should be developed.

Key points

Large discrepancies between observation on dry bones and computer-generated 3D models (surface scans or CT scans) could lead to the re-evaluation of the suitability of traditional anthropological methods for application on 3D models.

This preliminary study evaluates whether macroscopic, 3D surface scans, and CT scans viewings generate different observations.

The results indicate that the data are not always coherent across all three media of observation.

Explanations include the aspect given to the bone by the 3D software, differences between handling bones in real life versus on a computer, and level of expertise of the observers.

Effective approaches to three-dimensional digital reconstruction of fragmented human skeletal remains using laser surface scanning

The preservation and reconstruction of anthropological and archaeological remains has been given considerable attention in recent years, particularly within the fields of forensic science and palaeoanthropology. However, few studies have tapped the potential of using 3D technology to reconstruct, remodel and recontour remains and artefacts for the purpose of human identification. The aim of this study was to use 3D technology for the reconstruction and remodelling of fragmented and missing elements of skeletal remains. This project presents the application of three dimensional (3D) modalities to two different simulated forensic case scenarios where an attempt was made to remodel the missing element of the human cranium and reconstruction of fragmented replicated human mandible was performed. The accuracy of the reconstructed model was affirmed based on the anatomical features and digital analysis and methods for use in forensic practice are recommended.

Digital reconstruction of fragmented tooth remains in forensic context

Forensic odontology majorly focuses on the identification of victims through the analyses of oral and para–oral structures. Exposure to high temperatures and trauma can occur in mass disasters and may lead to the fracturing and fragmentation of teeth. These fragments may become very fragile and easily damaged while handling. Conventional methodologies such as the use of transparent nail polish, hair spray, cyanoacrylate or adhesives have been used to stabilize the fragmented pieces. This study introduces a new and innovative digital technique that utilizes three-dimensional surface scanning (3DSS) and rapid prototyping techniques to reconstruct fractured portions of the teeth. The results of qualitative congruency analysis suggest that over all variance of morphological error (0.0526 ± 0.05) mm. These results imply that the reconstructed 3D model can be used for various morphometric analyses.

Accuracy of an automated three-dimensional technique for the computation of femoral angles in dogs

AIMS

The purpose of the study was to evaluate the accuracy of a three-dimensional (3D) automated technique (computer-aided design (aCAD)) for the measurement of three canine femoral angles: anatomical lateral distal femoral angle (aLDFA), femoral neck angle (FNA) and femoral torsion angle.

METHODS

Twenty-eight femurs equally divided intotwo groups (normal and abnormal) were obtained from 14 dogs of different conformations (dolicomorphic and chondrodystrophicCT scans and 3D scanner acquisitions were used to create stereolithographic (STL) files , which were run in a CAD platform. Two blinded observers separately performed the measurements using the STL obtained from CT scans (CT aCAD) and 3D scanner (3D aCAD), which was considered the gold standard method. C orrelation coefficients were used to investigate the strength of the relationship between the two measurements.

RESULTS

A ccuracy of the aCAD computation was good, being always above the threshold of R² of greater than 80 per cent for all three angles assessed in both groups. a LDFA and FNA were the most accurate angles (accuracy >90 per cent).

CONCLUSIONS

The proposed 3D aCAD protocol can be considered a reliable technique to assess femoral angle measurements in canine femur. The developed algorithm automatically calculates the femoral angles in 3D, thus considering the subjective intrinsic femur morphology. The main benefit relies on a fast user-independent computation, which avoids user-related measurement variability. The accuracy of 3D details may be helpful for patellar luxation and femoral bone deformity correction, as well as for the design of patient- specific, custom-made hip prosthesis implants.