Thoracoabdominal Organ Volumes for Small Women

<div><p><b>Objective:</b> Thoracoabdominal injuries commonly occur as a result of motor vehicle crashes. In order to design occupant protection systems that reduce risk of injury, researchers are using a variety of tools, including computational human body models. Though research has been conducted to provide morphological and volumetric data for the thoracoabdominal cavity of the average male, there is currently an interest in developing models for a wider range of occupants. One particular cohort of interest is the small female by stature and weight because of their use in restraint system development. Geometric data on thoracoabdominal organs are needed to construct accurate representations of female occupants. This study aimed to gather information on organ volumes from clinical medical imaging studies of small females.</p><p><b>Methods:</b> Anonymized clinical computed tomography (CT) and magnetic resonance images were used to segment organs relevant to crash-induced injuries: namely, the liver, spleen, left kidney, right kidney, pancreas, gallbladder, lungs, and heart. Segmentations were conducted using semi-automatic techniques. Additionally, diametric measurements of the vena cava, aorta, trachea, and colon were obtained from the medical images at discrete locations using linear measurement tools.</p><p><b>Results:</b> A total of 14 adult scans were selected with stature and weight ranges of 145.0 to 162.6 cm and 43.7 to 65.5 kg, respectively. The following are the average thoracoabdominal organ volumes: liver (1,224.5 ± 220.7 mL), spleen (151.6 ± 42.1 mL), left kidney (123.7 ± 20.1 mL), right kidney (115.4 ± 20.9 mL), heart (417.8 ± 36.6 mL), pancreas (54.1 ± 11.8 mL), and gallbladder (20.6 ± 13.4 mL). The average diameters were 19.7 ± 3.2 mm and 17.7 ± 5.1 mm for the vena cava and aorta, respectively. The colon had an average diameter of 37.9 ± 7.1 mm.</p><p><b>Conclusion:</b> Data characterizing the small female are important to validate the geometries used in computational models, including models derived from scaling techniques and those developed using subject-specific medical imaging. The goal of this study was to use a sample of subjects anthropometrically representative of small females to evaluate the average volume for organs commonly injured in motor vehicle crashes. Based on these data, the right and left lungs were strongly correlated with stature and the heart was strongly correlated with weight. Ultimately, these measurements will be useful for the validation of computational models of the small female.</p></div

Modular use of human body models of varying levels of complexity: Validation of head kinematics

<p><b>Objective</b>: The significant computational resources required to execute detailed human body finite-element models has motivated the development of faster running, simplified models (e.g., GHBMC M50-OS). Previous studies have demonstrated the ability to modularly incorporate the validated GHBMC M50-O brain model into the simplified model (GHBMC M50-OS+B), which allows for localized analysis of the brain in a fraction of the computation time required for the detailed model. The objective of this study is to validate the head and neck kinematics of the GHBMC M50-O and M50-OS (detailed and simplified versions of the same model) against human volunteer test data in frontal and lateral loading. Furthermore, the effect of modular insertion of the detailed brain model into the M50-OS is quantified.</p> <p><b>Methods</b>: Data from the Navy Biodynamics Laboratory (NBDL) human volunteer studies, including a 15<i>g</i> frontal, 8<i>g</i> frontal, and 7<i>g</i> lateral impact, were reconstructed and simulated using LS-DYNA. A five-point restraint system was used for all simulations, and initial positions of the models were matched with volunteer data using settling and positioning techniques. Both the frontal and lateral simulations were run with the M50-O, M50-OS, and M50-OS+B with active musculature for a total of nine runs.</p> <p><b>Results</b>: Normalized run times for the various models used in this study were 8.4 min/ms for the M50-O, 0.26 min/ms for the M50-OS, and 0.97 min/ms for the M50-OS+B, a 32- and 9-fold reduction in run time, respectively. Corridors were reanalyzed for head and T1 kinematics from the NBDL studies. Qualitative evaluation of head rotational accelerations and linear resultant acceleration, as well as linear resultant T1 acceleration, showed reasonable results between all models and the experimental data. Objective evaluation of the results for head center of gravity (CG) accelerations was completed via ISO TS 18571, and indicated scores of 0.673 (M50-O), 0.638 (M50-OS), and 0.656 (M50-OS+B) for the 15<i>g</i> frontal impact. Scores at lower <i>g</i> levels yielded similar results, 0.667 (M50-O), 0.675 (M50-OS), and 0.710 (M50-OS+B) for the 8<i>g</i> frontal impact. The 7<i>g</i> lateral simulations also compared fairly with an average ISO score of 0.565 for the M50-O, 0.634 for the M50-OS, and 0.606 for the M50-OS+B. The three HBMs experienced similar head and neck motion in the frontal simulations, but the M50-O predicted significantly greater head rotation in the lateral simulation.</p> <p><b>Conclusion</b>: The greatest departure from the detailed occupant models were noted in lateral flexion, potentially indicating the need for further study. Precise modeling of the belt system however was limited by available data. A sensitivity study of these parameters in the frontal condition showed that belt slack and muscle activation have a modest effect on the ISO score. The reduction in computation time of the M50-OS+B reduces the burden of high computational requirements when handling detailed HBMs. Future work will focus on harmonizing the lateral head response of the models and studying localized injury criteria within the brain from the M50-O and M50-OS+B.</p

Development of a Computationally Efficient Full Human Body Finite Element Model

<div><p><b>Introduction:</b> A simplified and computationally efficient human body finite element model is presented. The model complements the Global Human Body Models Consortium (GHBMC) detailed 50th percentile occupant (M50-O) by providing kinematic and kinetic data with a significantly reduced run time using the same body habitus.</p><p><b>Methods:</b> The simplified occupant model (M50-OS) was developed using the same source geometry as the M50-O. Though some meshed components were preserved, the total element count was reduced by remeshing, homogenizing, or in some cases omitting structures that are explicitly contained in the M50-O. Bones are included as rigid bodies, with the exception of the ribs, which are deformable but were remeshed to a coarser element density than the M50-O. Material models for all deformable components were drawn from the biomechanics literature. Kinematic joints were implemented at major articulations (shoulder, elbow, wrist, hip, knee, and ankle) with moment vs. angle relationships from the literature included for the knee and ankle. The brain of the detailed model was inserted within the skull of the simplified model, and kinematics and strain patterns are compared.</p><p><b>Results:</b> The M50-OS model has 11 contacts and 354,000 elements; in contrast, the M50-O model has 447 contacts and 2.2 million elements. The model can be repositioned without requiring simulation. Thirteen validation and robustness simulations were completed. This included denuded rib compression at 7 discrete sites, 5 rigid body impacts, and one sled simulation. Denuded tests showed a good match to the experimental data of force vs. deflection slopes. The frontal rigid chest impact simulation produced a peak force and deflection within the corridor of 4.63 kN and 31.2%, respectively. Similar results vs. experimental data (peak forces of 5.19 and 8.71 kN) were found for an abdominal bar impact and lateral sled test, respectively. A lateral plate impact at 12 m/s exhibited a peak of roughly 20 kN (due to stiff foam used around the shoulder) but a more biofidelic response immediately afterward, plateauing at 9 kN at 12 ms. Results from a frontal sled simulation showed that reaction forces and kinematic trends matched experimental results well. The robustness test demonstrated that peak femur loads were nearly identical to the M50-O model. Use of the detailed model brain within the simplified model demonstrated a paradigm for using the M50-OS to leverage aspects of the M50-O. Strain patterns for the 2 models showed consistent patterns but greater strains in the detailed model, with deviations thought to be the result of slightly different kinematics between models. The M50-OS with the deformable skull and brain exhibited a run time 4.75 faster than the M50-O on the same hardware.</p><p><b>Conclusions:</b> The simplified GHBMC model is intended to complement rather than replace the detailed M50-O model. It exhibited, on average, a 35-fold reduction in run time for a set of rigid impacts. The model can be used in a modular fashion with the M50-O and more broadly can be used as a platform for parametric studies or studies focused on specific body regions.</p></div