Evaluation of an anthropometric shape model of the human scalp

Intra-rater and inter-rater reliability of 3D facial measurements

Three-dimensional (3D) body scanning technology has applications for obtaining anthropometric data in human-centered and product development fields. The reliability of 3D measurements gathered from 3D scans must be assessed to understand the degree to which this technology is appropriate for use in place of manual anthropometric methods. The intra- and inter-rater reliabilities of 3D facial measurements were assessed among four novice raters using 3D landmarking. Intraclass correlation coefficient (ICC) statistics were calculated for the 3D measurement data collected in three phases to assess baseline reliabilities and improvements in reliabilities as the result of additional training and experience. Based on the results of this study, the researchers found that the collection of 3D measurement data, by multiple raters and using 3D landmarking methods, yielded a high percentage of ICC statistics in the good to excellent (>0.75 ICC) reliability range. Rater training and experience were important considerations in improving intra- and inter-rater reliabilities.

Thoughts and perspectives on biomechanical numerical models under impacts: Are women forgotten from research?

The present paper explores a series of articles in the literature which deal with impact biomechanics of the head and thorax/abdomen segments, investigating the "sex specific properties/data" used in the studies. Statements in these studies are analyzed and point out, the use of male or female subjects for the developments of finite element models and their validation against experimental data. The present analysis raises the question about "androcentrism," and how biomechanical engineering findings and the design of the derived protecting devices are focused on male subjects.

Modeling 3D geometric growth patterns and variations of Children's heads

To design high-quality head/face-related products for children, it is essential to be able to construct 3D geometric models of their head growth patterns and variations. However, compared to 3D anthropometric analysis of adults' heads, this is still an underexplored research area. This study developed a framework for modeling the 3D geometric growth patterns and sex-specific variations of children's heads. To analyze these variations, the entire heads of 793 children (395 females and 398 males) ages 5-17 were scanned, and one global and two sex-specific statistical shape models (SSMs) were constructed. The first principal component in these SSMs, contributing more than 65% to the total explained variations, was highly related to overall head sizes. To model growth patterns, expected average heads for different ages and per-vertex growth rates were computed. Our results showed that the entire female head basically reaches its mature size at age 13-14, whereas in males it continues to increase until age 16-17. This study therefore provides valuable references for children's head/face-related product design, including the development of a more accurate sizing system and improvements in product fit and function.

A modelling framework for local thermal comfort assessment related to bicycle helmet use

Thermal discomfort due to accumulated sweat increasing head skin wettedness may contribute to low wearing rates of bicycle helmets. Using curated data on human head sweating and helmet thermal properties, a modelling framework for the thermal comfort assessment of bicycle helmet use is proposed. Local sweat rates (LSR) at the head were predicted as the ratio to the gross sweat rate (GSR) of the whole body or by sudomotor sensitivity (SUD), the change in LSR per change in body core temperature (Δt_re). Combining those local models with Δt_re and GSR output from thermoregulation models, we simulated head sweating depending on the characteristics of the thermal environment, clothing, activity, and exposure duration. Local thermal comfort thresholds for head skin wettedness were derived in relation to thermal properties of bicycle helmets. The modelling framework was supplemented by regression equations predicting the wind-related reductions in thermal insulation and evaporative resistance of the headgear and boundary air layer, respectively. Comparing the predictions of local models coupled with different thermoregulation models to LSR measured at the frontal, lateral and medial head under bicycle helmet use revealed a large spread in LSR predictions predominantly determined by the local models and the considered head region. SUD tended to overestimate frontal LSR but performed better for lateral and medial head regions, whereas predictions by LSR/GSR ratios were lower and agreed better with measured frontal LSR. However, even for the best models root mean squared prediction errors exceeded experimental SD by 18-30%. From the high correlation (R > 0.9) of skin wettedness comfort thresholds with local sweating sensitivity reported for different body regions, we derived a threshold value of 0.37 for head skin wettedness. We illustrate the application of the modelling framework using a commuter-cycling scenario, and discuss its potential as well as the needs for further research.

Pressure sensitivity for head, face and neck in relation to soft tissue

Pressure sensitivity research on the head, face, and neck is critical to develop ways to reduce discomfort caused by pressure in head-related products. The aim of this paper is to provide information for designers to be able to reduce the pressure discomfort by studying the relation between pressure sensitivity and soft tissue in the head, face and neck. We collected pressure discomfort threshold (PDT) and pressure pain threshold (PPT) from 119 landmarks (unilateral) for 36 Chinese subjects. Moreover, soft tissue thickness data on the head, face and neck regions of 50 Chinese people was obtained through CT scanning while tissue deformation data under the PDT and PPT states was obtained from literature. The results of the three-elements correlation analysis revealed that soft tissue thickness is positively correlated with deformation but not an important factor in pressure sensitivity. Our high-precision pressure sensitivity maps confirm earlier findings of more rough pressure sensitivity studies, while also revealing additional fine scale sensitivity differences. Finally, based on the findings, a high-precision "recommended map" of the optimal stress-bearing area of the head, face and neck was generated.

A parametric head geometry model accounting for variation among adolescent and young adult populations

BACKGROUND AND OBJECTIVE

Modeling the size and shape of human skull and scalp is essential for head injury assessment, design of helmets and head-borne equipment, and many other safety applications. Finite element (FE) head models are important tools to assess injury risks and design personal protective equipment. However, current FE head models are mainly developed based on the midsize male, failing to account for the significant morphological variation that exists in the skull and brain. The objective of this study was to develop a statistical head geometry model that accounts for size and shape variations among the adolescent and young adult population.

METHODS

To represent subject-specific geometry using a homologous mesh, threshold-based segmentation of head CT scans of 101 subjects between 14 and 25 years of age was performed, followed by landmarking, mesh morphing, and projection. Skull and scalp statistical geometry models were then developed as functions of age, sex, stature, BMI, head length, head breadth, and tragion-to-top of head using generalized Procrustes analysis (GPA), principal component analysis (PCA) and multivariate regression analysis.

RESULTS

The statistical geometry models account for a high percentage of morphological variations in scalp geometry (R²=0.63), outer skull geometry (R²=0.66), inner skull geometry (R²=0.55), and skull thickness (error < 1 mm) CONCLUSIONS: Skull and scalp statistical geometry models accounts for size and shape variations among the adolescent and young adult population were developed as functions of subject covariates. These models may serve as the geometric basis to develop individualized head FE models for injury assessment and design of head-borne equipment.

Comfort and fit perception based on 3D anthropometry for ear-related product design

Anthropometry and human perception lie at the core of the ergonomic design process. Until now, relevant studies have been quite restricted, being unable to provide a holistic view of the perceived comfort and fit for ear-related products. The study examined the perceived comfort and fit using factor analysis and established a linkage between anthropometry and human perception for design uses. A total of 30 participants (15 male, 15 female) were recruited in the within-subject experiment. The results showed that ear symmetry, gender, concha length, and cavum concha width had either insignificant or weak correlation with the perception scores. Use condition and product size significantly influenced the perceived comfort and fit for ear-related products. Users preferred a larger product size in the dynamic condition than in the static condition. Moreover, the study proposed a novel method to quantify the relationship between anthropometric data and human perception for the ear-related product. For an in-the-ear product, trendlines were generated to link the product size based on 3D anthropometry with the comfort and fit scores.

Establishment of a finite element model based on craniofacial soft tissue thickness measurements and stress analysis of medical goggles

In this study, an accurate finite element (FE) stress analysis of head-mounted products for Chinese users was performed. Using craniofacial computed tomography scans of 280 Chinese individuals, the total soft tissue thickness and thickness of the fat and muscle layers for 41 landmarks were measured. The data were used to construct FE head models (FEH). An FE stress test was conducted to analyse the wearing of medical goggles using two FE models based on one-layer (FEH 1) and three-layer (FEH 3) soft tissue material parameters. When compared with the experimental results, the modelling results for FEH 3 were more realistic than those for FEH 1. Wearing medical goggles led to stress concentration over five landmark areas, A: upper medial forehead, B: temporal, C: zygion, D: infraorbital fossa and E: rhinion, of which B, C and D caused the most discomfort during long-term goggle wear. Practitioner summary: A precise FE head model can reflect the complex contact pressure of a head-related product. Two FE models based on one- and three-layer soft tissue material parameters were established and tested separately with medical goggles. The model can be used to improve the comfort of head-related products. Abbreviations: FE: finite element; FEH: FE head models; FEH 1: FE models based on one-layer; FEH 3: FE models based on three-layer; VR: virtual reality; AR: augmented reality; 3D: three-dimensional; WSU: Wayne State University; WSUBIM: Wayne State University Brain Injury Model; CT: computed tomography; MRI: magnetic resonance imaging; CFSTT: craniofacial soft tissue thickness; FSR: force sensing resistor; NURBS: non-uniform rational basis spline; SPSS: statistical product and service solutions; STL: stereolithography; STP: standard for the exchange of product model data; BDF: glyph bitmap distribution format; EEG: electroencephalogram.

The Variation in 3D Face Shapes of Dutch Children for Mask Design

The use of 3D anthropometric data of children’s heads and faces has great potential in the development of protective gear and medical products that need to provide a close fit in order to function well. Given the lack of detailed data of this kind, the aim of this study is to map the size and shape variation of Dutch children’s heads and faces and investigate possible implications for the design of a ventilation mask. In this study, a dataset of heads and faces of 303 Dutch children aged six months to seven years consisting of traditional measurements and 3D scans were analysed. A principal component analysis (PCA) of facial measurements was performed to map the variation of the children’s face shapes. The first principal component describes the overall size, whilst the second principal component captures the more width related variation of the face. After establishing a homology between the 3D scanned face shapes, a second principal component analysis was done on the point coordinates, revealing the most prominent variations in 3D shape within the sample.

Age- and Sex-Related Measurements of Total Craniofacial Soft Tissue Thickness and Fat in a Central Chinese Population

ABSTRACT

In this study, data related to the total soft tissue thickness and fat layer thickness of 41 anatomical landmarks were extracted from the craniofacial computerized tomography data of 280 Chinese individuals (160 males and 120 females). The measurements were assessed according to the following factors: a. sex, b. age, and c. sex × age. Descriptive statistics and a differential analysis were carried out in each group to analyze both the total soft tissue thickness and fat layer thickness. The results showed the following. 1. The results showed that the greater the total thickness of the soft tissue, the thicker the fat layer. 2. The thicknesses of the head and face soft tissues are strongly affected by sex. The total thickness of all landmark points in the men, except for the zygomatic points, was on average greater than that in the women. In contrast to the total thickness, the fat layer, except for the point of rhinion, in the women was larger than that in the men. 3. In the comparison of the 4 age groups, most feature points did not show an evident increasing or decreasing trend with age in the total thickness of the soft tissue. However, regarding the thickness of fat, the thickness at the other points, except for the feature infraorbital fossa point, decreased with age. 4. In the analysis of the sex × age group, no statistically significant differences were found at any landmark points. This paper is significant for facial reconstruction and cosmetic surgery in the Chinese population.

Sex-based differences in helmet performance in bicycle trauma

OBJECTIVES

To determine the existence of sex-based differences in the protective effects of helmets against common injuries in bicycle trauma.

METHODS

In a retrospective cohort study, we identified patients 18 years or older in the 2017 National Trauma Database presenting after bicycle crash. Sex-disaggregated and sex-combined multivariable logistic regression models were calculated for short-term outcomes that included age, involvement with motor vehicle collision, anticoagulant use, bleeding disorder and helmet use. The sex-combined model included an interaction term for sex and helmet use. The resulting exponentiated model parameter yields an adjusted OR ratio of the effects of helmet use for females compared with males.

RESULTS

In total, 18 604 patients of average age 48.1 were identified, and 18% were female. Helmet use was greater in females than males (48.0% vs 34.2%, p<0.001). Compared with helmeted males, helmeted females had greater rates of serious head injury (37.7% vs 29.9%, p<0.001) despite less injury overall. In sex-disaggregated models, helmet use reduced odds of intracranial haemorrhage and death in males (p<0.001) but not females. In sex-combined models, helmets conferred to females significantly less odds reduction for severe head injury (p=0.002), intracranial bleeding (p<0.001), skull fractures (p=0.001), cranial surgery (p=0.006) and death (p=0.017). There was no difference for cervical spine fracture.

CONCLUSIONS

Bicycle helmets may offer less protection to females compared with males. The cause of this sex or gender-based difference is uncertain, but there may be intrinsic incompatibility between available helmets and female anatomy and/or sex disparity in helmet testing standards.

A three-dimensional parametric adult head model with representation of scalp shape variability under hair

Modeling the shape of the scalp and face is essential for the design of protective helmets and other head-borne equipment. However, head anthropometry studies using optical scanning rarely capture scalp shape because of hair interference. Data on scalp shape is available from bald men, but female data are generally not available. To address this issue, scalp shape was digitized in an ethnically diverse sample of 100 adult women, age 18-59, under a protocol that included whole head surface scanning and scalp measurement using a three-dimensional (3D) coordinate digitizer. A combined male and female sample was created by adding 3D surface scans of a similarly diverse sample of 80 bald men. A statistical head shape model was created by standardizing the head scan data. A total of 58 anatomical head landmarks and 12 head dimensions were obtained from each scan and processed along with the scans. A parametric model accounting for the variability of the head shape under the hair as a function of selected head dimensions was developed. The full-variable model has a mean shape error of 3.8 mm; the 95th percentile error was 7.4 mm, which were measured at the vertices. The model will be particularly useful for generating a series of representing a target population as well as for generating subject-specific head shapes along with predicted landmarks and dimensions. The model is publicly available online at http://humanshape.org/head/.

Customized designs of short thumb orthoses using 3D hand parametric models

This research achieved its purposes of producing a 3D hand parametric hand model in a functional position, using the 3D hand parametric model as a template to generate an individualized approximate 3D hand model, constructing a 3D printed short thumb orthosis with a seamless structural design and ductile materials based on the individualized approximate 3D hand model, and reporting a case study on the usability. In experiment one, 3D hand parametric models were generated using anthropometric data collected with a scanning device from 120 Taiwanese adults. Experiment two examined the feasibility of constructing 3D-printed orthoses from the 3D hand parametric models through a case report on one client. The 19 values of the parameters measured from the client were imported into the 3D hand parametric models. An individual 3D hand mesh model approximating the client's hand was synthesized. The orthosis was precisely sketched and then printed. In usability testing, scores on the Quebec User Evaluation of Satisfaction with Assistive Technology were mostly high. The orthosis provided greater flexibility of hand movement and stronger support than the traditional, manually-formed orthosis. The results indicated the feasibility of using a hand parametric model to optimize the reverse engineering of a short thumb orthosis.

Aortic root sizing for transcatheter aortic valve implantation using a shape model parameterisation

During a transcatheter aortic valve implantation, an axisymmetric implant is placed in an irregularly shaped aortic root. Implanting an incorrect size can cause complications such as leakage of blood alongside or through the implant. The aim of this study was to construct a method that determines the optimal size of the implant based on the three-dimensional shape of the aortic root. Based on the pre-interventional computed tomography scan of 89 patients, a statistical shape model of their aortic root was constructed. The weights associated with the principal components and the volume of calcification in the aortic valve were used as parameters in a classification algorithm. The classification algorithm was trained using the patients with no or mild leakage after their intervention. Subsequently, the algorithms were applied to the patients with moderate to severe leakage. Cross validation showed that a random forest classifier assigned the same size in 65 ± 7% of the training cases, while 57 ± 8% of the patients with moderate to severe leakage were assigned a different size. This initial study showed that this semi-automatic method has the potential to correctly assign an implant size. Further research is required to assess whether the different size implants would improve the outcome of those patients.

Technical Report on the Modification of 3-Dimensional Non-contact Human Body Laser Scanner for the Measurement of Anthropometric Dimensions: Verification of its Accuracy and Precision

Introduction: Three-dimensional (3D) scanners are widely used in medicine. One of the applications of 3D scanners is the acquisition of anthropometric dimensions for ergonomics and the creation of an anthropometry data bank. The aim of this study was to evaluate the precision and accuracy of a modified 3D scanner fabricated in this study. Methods: In this work, a 3D scan of the human body was obtained using DAVID Laser Scanner software and its calibration background, a linear low-power laser, and one advanced webcam. After the 3D scans were imported to the Geomagic software, 10 anthropometric dimensions of 10 subjects were obtained. The measurements of the 3D scanner were compared to the measurements of the same dimensions by a direct anthropometric method. The precision and accuracy of the measurements of the 3D scanner were then evaluated. The obtained data were analyzed using an independent sample t test with the SPSS software. Results: The minimum and maximum measurement differences from three consecutive scans by the 3D scanner were 0.03 mm and 18 mm, respectively. The differences between the measurements by the direct anthropometry method and the 3D scanner were not statistically significant. Therefore, the accuracy of the 3D scanner is acceptable. Conclusion: Future studies will need to focus on the improvement of the scanning speed and the quality of the scanned image.

Analysis of the three-dimensional anatomical variance of the distal radius using 3D shape models

BACKGROUND

Various medical fields rely on detailed anatomical knowledge of the distal radius. Current studies are limited to two-dimensional analysis and biased by varying measurement locations. The aims were to 1) generate 3D shape models of the distal radius and investigate variations in the 3D shape, 2) generate and assess morphometrics in standardized cut planes, and 3) test the model's classification accuracy.

METHODS

The local radiographic database was screened for CT-scans of intact radii. 1) The data sets were segmented and 3D surface models generated. Statistical 3D shape models were computed (overall, gender and side separate) and the 3D shape variation assessed by evaluating the number of modes. 2) Anatomical landmarks were assigned and used to define three standardized cross-sectional cut planes perpendicular to the main axis. Cut planes were generated for the mean shape models and each individual radius. For each cut plane, the following morphometric parameters were calculated and compared: maximum width and depth, perimeter and area. 3) The overall shape model was utilized to evaluate the predictive value (leave one out cross validation) for gender and side identification within the study population.

RESULTS

Eighty-six radii (45 left, 44% female, 40 ± 18 years) were included. 1) Overall, side and gender specific statistical 3D models were successfully generated. The first mode explained 37% of the overall variance. Left radii had a higher shape variance (number of modes: 20 female / 23 male) compared to right radii (number of modes: 6 female / 6 male). 2) Standardized cut planes could be defined using anatomical landmarks. All morphometric parameters decreased from distal to proximal. Male radii were larger than female radii with no significant side difference. 3) The overall shape model had a combined median classification probability for side and gender of 80%.

CONCLUSIONS

Statistical 3D shape models of the distal radius can be generated using clinical CT-data sets. These models can be used to assess overall bone variance, define and analyze standardized cut-planes, and identify the gender of an unknown sample. These data highlight the potential of shape models to assess the 3D anatomy and anatomical variance of human bones.

Ergonomic design of an EEG headset using 3D anthropometry

Although EEG experiments over the past decades have shown numerous applications for brain-computer interfacing (BCI), there is a need for user-friendly BCI devices that can be used in real-world situations. 3D anthropometry and statistical shape modeling have been shown to improve the fit of devices such as helmets and respirators, and thus they might also be suitable to design BCI headgear that better fits the size and shape variation of the human head. In this paper, a new design method for BCI devices is proposed and evaluated. A one-size-fits-all BCI headset frame is designed on the basis of three digital mannequins derived from a shape model of the human head. To verify the design, the geometric fit, stability and repeatability of the prototype were compared to an EEG cap and a commercial BCI headset in a preliminary experiment. Most design specifications were met, and all the results were found to be similar to those of the commercial headset. Therefore, the suggested design method is a feasible alternative to traditional anthropometric design for BCI headsets and similar headgear.

The Helmet Fit Index--An intelligent tool for fit assessment and design customisation

Helmet safety benefits are reduced if the headgear is poorly fitted on the wearer's head. At present, there are no industry standards available to assess objectively how a specific protective helmet fits a particular person. A proper fit is typically defined as a small and uniform distance between the helmet liner and the wearer's head shape, with a broad coverage of the head area. This paper presents a novel method to investigate and compare fitting accuracy of helmets based on 3D anthropometry, reverse engineering techniques and computational analysis. The Helmet Fit Index (HFI) that provides a fit score on a scale from 0 (excessively poor fit) to 100 (perfect fit) was compared with subjective fit assessments of surveyed cyclists. Results in this study showed that quantitative (HFI) and qualitative (participants' feelings) data were related when comparing three commercially available bicycle helmets. Findings also demonstrated that females and Asian people have lower fit scores than males and Caucasians, respectively. The HFI could provide detailed understanding of helmet efficiency regarding fit and could be used during helmet design and development phases.