| 1. |
- Knudsen, Gitte M, et al.
(författare)
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Guidelines for the content and format of PET brain data in publications and archives : A consensus paper
- 2020
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Ingår i: Journal of Cerebral Blood Flow and Metabolism. - : SAGE Publications. - 0271-678X .- 1559-7016. ; 40:8, s. 1576-1585
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Tidskriftsartikel (refereegranskat)abstract
- It is a growing concern that outcomes of neuroimaging studies often cannot be replicated. To counteract this, the magnetic resonance (MR) neuroimaging community has promoted acquisition standards and created data sharing platforms, based on a consensus on how to organize and share MR neuroimaging data. Here, we take a similar approach to positron emission tomography (PET) data. To facilitate comparison of findings across studies, we first recommend publication standards for tracer characteristics, image acquisition, image preprocessing, and outcome estimation for PET neuroimaging data. The co-authors of this paper, representing more than 25 PET centers worldwide, voted to classify information as mandatory, recommended, or optional. Second, we describe a framework to facilitate data archiving and data sharing within and across centers. Because of the high cost of PET neuroimaging studies, sample sizes tend to be small and relatively few sites worldwide have the required multidisciplinary expertise to properly conduct and analyze PET studies. Data sharing will make it easier to combine datasets from different centers to achieve larger sample sizes and stronger statistical power to test hypotheses. The combining of datasets from different centers may be enhanced by adoption of a common set of best practices in data acquisition and analysis.
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| 2. |
- Aare, Magnus, et al.
(författare)
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Injury tolerances for oblique impact helmet testing
- 2004
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Ingår i: International Journal of Crashworthiness. - : Informa UK Limited. - 1358-8265 .- 1754-2111. ; 9:1, s. 15-23
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Tidskriftsartikel (refereegranskat)abstract
- The most frequently sustained severe injuries in motorcycle crashes are injuries to the head, and many of these are caused by rotational force. Rotational force is most commonly the result of oblique impacts to the head. Good testing methods for evaluating the effects of such impacts are currently lacking. There is also a need for improving our understanding of the effects of oblique impacts on the human head. Helmet standards currently in use today do not measure rotational effects in test dummy heads. However rotational force to the head results in large shear strains arising in the brain, which has been proposed as a cause of traumatic brain injuries like diffuse axonal injuries (DAI). This paper investigates a number of well-defined impacts, simulated using a detailed finite element (FE) model of the human head, an FE model of the Hybrid III dummy head and an FE model of a helmet. The same simulations were performed on both the FE human head model and the FE Hybrid III head model, both fitted with helmets. Simulations on both these heads were performed to describe the relationship between load levels in the FE Hybrid III head model and strains in the brain tissue in the FE human head model. In this study, the change in rotational velocity and the head injury criterion (HIC) value were chosen as appropriate measurements. It was concluded that both rotational and translational effects are important when predicting the strain levels in the human brain.
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| 3. |
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| 4. |
- Alvarez, Victor, et al.
(författare)
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Importance of neck muscle tonus in head kinematics during pedestrian accidents
- 2013
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Ingår i: 2013 IRCOBI Conference Proceedings - International Research Council on the Biomechanics of Injury. ; , s. 747-761
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Konferensbidrag (refereegranskat)abstract
- Unprotected pedestrians are an exposed group in the rural traffic and the most vulnerable human body region is the head which is the source of many fatal injuries. This study was performed to gain a better understanding of the influence that the neck muscle tonus has on head kinematics during pedestrian accidents. This was done using a detailed whole body FE model and a detailed FE vehicle model. To determine the influence of the muscle tonus a series of simulations were performed where the vehicle speed, pedestrian posture and muscle tonus were varied. Since the human reaction time for muscle activation is in the order of the collision time, the pedestrian was assumed to be prepared for the oncoming vehicle in order to augment the possible influence of muscle tonus. From the simulations performed, kinematic data such as head rotations, trajectory and velocities were extracted for the whole collision event, as well as velocity and accelerations at head impact. These results show that muscle tonus can influence the head rotation during a vehicle collision and therefore alter the head impact orientation. The level of influence on head rotation was in general lower than when altering the struck leg forward and backward, but in the same order of magnitude for some cases. The influence on head accelerations was higher due to muscle tonus than posture in all cases.
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| 5. |
- Alvarez, Victor, et al.
(författare)
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The Influence of Neck Muscle Tonus and Posture on Brain Tissue Strain in Pedestrian Head Impacts
- 2014
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 58, s. 63-101
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Tidskriftsartikel (refereegranskat)abstract
- Pedestrians are one of the least protected groups in urban traffic and frequently suffer fatal head injuries. An important boundary condition for the head is the cervical spine, and it has previously been demonstrated that neck muscle activation is important for head kinematics during inertial loading. It has also been shown in a recent numerical study that a tensed neck musculature also has some influence on head kinematics during a pedestrian impact situation. The aim of this study was to analyze the influence on head kinematics and injury metrics during the isolated time of head impact by comparing a pedestrian with relaxed neck and a pedestrian with increased tonus. The human body Finite Element model THUMS Version 1.4 was connected to head and neck models developed at KTH and used in pedestrian-to-vehicle impact simulations with a generalized hood, so that the head would impact a surface with an identical impact response in all simulations. In order to isolate the influence of muscle tonus, the model was activated shortly before head impact so the head would have the same initial position prior to impact among different tonus. A symmetric and asymmetric muscle activation scheme that used high level of activation was used in order to create two extremes to investigate. It was found that for the muscle tones used in this study, the influence on the strain in the brain was very minor, in general about 1-14% change. A relatively large increase was observed in a secondary peak in maximum strains in only one of the simulated cases.
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| 6. |
- Amann, Peter, et al.
(författare)
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The state of zinc in methanol synthesis over a Zn/ZnO/Cu(211) model catalyst
- 2022
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 376:6593, s. 603-608
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Tidskriftsartikel (refereegranskat)abstract
- The active chemical state of zinc (Zn) in a zinc-copper (Zn-Cu) catalyst during carbon dioxide/carbon monoxide (CO2/CO) hydrogenation has been debated to be Zn oxide (ZnO) nanoparticles, metallic Zn, or a Zn-Cu surface alloy. We used x-ray photoelectron spectroscopy at 180 to 500 millibar to probe the nature of Zn and reaction intermediates during CO2/CO hydrogenation over Zn/ZnO/Cu(211), where the temperature is sufficiently high for the reaction to rapidly turn over, thus creating an almost adsorbate-free surface. Tuning of the grazing incidence angle makes it possible to achieve either surface or bulk sensitivity. Hydrogenation of CO2 gives preference to ZnO in the form of clusters or nanoparticles, whereas in pure CO a surface Zn-Cu alloy becomes more prominent. The results reveal a specific role of CO in the formation of the Zn-Cu surface alloy as an active phase that facilitates efficient CO2 methanol synthesis.
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| 7. |
- Brinck, Tore, et al.
(författare)
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Local Electron Attachment Energy and Its Use for Predicting Nucleophilic Reactions and Halogen Bonding
- 2016
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Ingår i: JOURNAL OF PHYSICAL CHEMISTRY A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 120:50, s. 10023-10032
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Tidskriftsartikel (refereegranskat)abstract
- A new local property, the local electron attachment energy [E(r)], is introduced and is demonstrated to, be a useful guide to predict intermolecular interactions and chemical reactivity. The E(r) is analogous to the average local ionization energy but indicates susceptibility toward interactions with nucleophiles rather than electrophiles. The functional form E(r) is motivated based on Janak's theorem and the piecewise linear energy dependence of electron addition to atomic and molecular systems. Within the generalized Kohn-Sham method (GKS-DFT), only the virtual orbitals with negative eigenvalues contribute to E(r). In the, present study, E(r) has been computed from orbitals obtained from GKS-DFT computations with a hybrid exchange correlation functional. It is shown that E(r) computed on a molecular isodengty surface, E-S(r), reflects the regioselectivity and relative reactivity for nucleophilic aromatic substitution, nucleophilic addition to activated double bonds, and formation of halogen bonds. Good to excellent correlations between experimental or theoretical measures of interaction strengths and minima in E-S(r) (E-S,E-min) are demonstrated.
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| 8. |
- Brolin, Karin, et al.
(författare)
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Development of a finite element model of the upper cervical spine and a parameter study of ligament characteristics
- 2004
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Ingår i: Spine. - 0362-2436 .- 1528-1159. ; 29:4, s. 376-385
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Tidskriftsartikel (refereegranskat)abstract
- Study Design. Numeric techniques were used to study the upper cervical spine. Objectives. To develop and validate an anatomic detailed finite element model of the ligamentous upper cervical spine and to analyze the effect of material properties of the ligaments on spinal kinematics. Summary of Background Data. Cervical spinal injuries may be prevented with an increased knowledge of spinal behavior and injury mechanisms. The finite element method is tempting to use because stresses and strains in the different tissues can be studied during the course of loading. The authors know of no published results so far of validated finite element models that implement the complex geometry of the upper cervical spine. Methods. The finite element model was developed with anatomic detail from computed tomographic images of the occiput to the C3. The ligaments were modeled with nonlinear spring elements. The model was validated for axial rotation, flexion, extension, lateral bending, and tension for 1.5 Nm, 10 Nm, and 1500 N. A material property sensitivity study was conducted for the ligaments. Results. The model correlated with experimental data for all load cases. Moments of 1.5 Nm produced joint rotations of 3degrees to 23degrees depending on loading direction. The parameter study confirmed that the mechanical properties of the upper cervical ligaments play an important role in spinal kinematics. The capsular ligaments had the largest impact on spinal kinematics (40% change). Conclusions. The anatomic detailed finite element model of the upper cervical spine realistically simulates the complex kinematics of the craniocervical region. An injury that changes the material characteristics of any spinal ligament will influence the structural behavior of the upper cervical spine.
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| 9. |
- Brolin, Karin, et al.
(författare)
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The effect of muscle activation on neck response
- 2005
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Ingår i: Traffic Injury Prevention. - : Informa UK Limited. - 1538-9588 .- 1538-957X. ; 6:1, s. 67-76
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Tidskriftsartikel (refereegranskat)abstract
- Prevention of neck injuries due to complex loading, such as occurs in traffic accidents, requires knowledge of neck injury mechanisms and tolerances. The influence of muscle activation on outcome of the injuries is not clearly understood. Numerical simulations of neck injury accidents can contribute to increase the understanding of injury tolerances. The finite element (FE) method is suitable because it gives data on stress and strain of individual tissues that can be used to predict injuries based on tissue level criteria. The aim of this study was to improve and validate an anatomically detailed FE model of the human cervical spine by implement neck musculature with passive and active material properties. Further, the effect of activation time and force on the stresses and strains in the cervical tissues were studied for dynamic loading due to frontal and lateral impacts. The FE model used includes the seven cervical vertebrae, the spinal ligaments, the facet joints with cartilage, the intervertebral disc, the skull base connected to a rigid head, and a spring element representation of the neck musculature. The passive muscle properties were defined with bilinear force-deformation curves and the active properties were defined using a material model based on the Hill equation. The FE model's responses were compared to volunteer experiments for frontal and lateral impacts of 15 and 7 g. Then, the active muscle properties where varied to study their effect on the motion of the skull, the stress level of the cortical and trabecular bone, and the strain of the ligaments. The FE model had a good correlation to the experimental motion corridors when the muscles activation was implemented. For the frontal impact a suitable peak muscle force was 40 N/cm2 whereas 20 N/cm2 was appropriate for the side impact. The stress levels in the cortical and trabecular bone were influenced by the point forces introduced by the muscle spring elements; therefore a more detailed model of muscle insertion would be preferable. The deformation of each spinal ligament was normalized with an appropriate failure deformation to predict soft tissue injury. For the frontal impact, the muscle activation turned out to mainly protect the upper cervical spine ligaments, while the musculature shielded all the ligaments disregarding spinal level for lateral impacts. It is concluded that the neck musculature does not have the same protective properties during different impacts loadings.
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| 10. |
- Brolin, Karin, et al.
(författare)
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The importance of muscle tension on the outcome of impacts with a major vertical component
- 2008
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Ingår i: International Journal of Crashworthiness. - London : Taylor & Francis. - 1358-8265 .- 1754-2111. ; 13:5, s. 487-498
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Tidskriftsartikel (refereegranskat)abstract
- The hypothesis that muscle tension protects the spine from injuries in helicopter scenarios was tested using a finite-element model of the human head and neck. It was compared with cadaver crash sled experiment with good correlation. Then, simulations were performed with a sinusoidal velocity (5-22 G) applied at T1 60° to the horizontal plane. The model with relaxed muscle activation had delayed and decreased peak head rotation compared with passive properties only. Full muscle activation decreased the injury risk for the 13.5-22 G impacts. A sensitivity study of the impact angle showed a very slight variation of the resulting neck flexion, and 1° change affected all ligament injury predictions less than 4%. Finally, simulations with helmets resulted in increased ligament and disc strains with increasing helmet mass and with an anterior or inferior shift of the centre of gravity. It is concluded that the hypothesis seems to hold.
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