Semiquantitation of Axonal Injury in Traumatically Damaged Brains Using Color Deconvolution.

INTRODUCTION: In traumatic brain injury biomechanics, macroscale biomechanical events need to be correlated with microscale neuropathologic changes and improved quantitation of microscopic axonal injury is an essential component of lesion evaluation. OBJECTIVES: To develop a novel technique for automatically identifying injured amyloid precursor protein immunopositive axons and aggregating these observations over a macroscopic brain dissection. METHODS: A color deconvolution method was adapted into Matlab to identify clusters of pixels with colors typical of amyloid precursor protein positive tissue from large-scale brain dissection. RESULTS: The methodology is demonstrated in the brain of a sheep subjected to a controlled cortical indentation. CONCLUSIONS: The technique will be of interest to pathologists and bioengineers seeking to quantitate brain injury over macroscales.

The real-world safety potential of connected vehicle technology.

OBJECTIVE: This article estimates the safety potential of a current commercially available connected vehicle technology in real-world crashes. METHOD: Data from the Centre for Automotive Safety Research's at-scene in-depth crash investigations in South Australia were used to simulate the circumstances of real-world crashes. A total of 89 crashes were selected for inclusion in the study. The crashes were selected as representative of the most prevalent crash types for injury or fatal crashes and had potential to be mitigated by connected vehicle technology. The trajectory, speeds, braking, and impact configuration of the selected in-depth cases were replicated in a software package and converted to a file format allowing "replay" of the scenario in real time as input to 2 Cohda Wireless MK2 onboard units. The Cohda Wireless onboard units are a mature connected vehicle technology that has been used in both the German simTD field trial and the U.S. Department of Transport's Safety Pilot project and have been tuned for low false alarm rates when used in the real world. The crash replay was achieved by replacing each of the onboard unit Global Positioning System (GPS) inputs with the simulated data of each of the involved vehicles. The time at which the Cohda Wireless threat detection software issued an elevated warning was used to calculate a new impact speed using 3 different reaction scenarios and 2 levels of braking. RESULTS: It was found that between 37 and 86% of the simulated crashes could be avoided, with highest percentage due a fully autonomous system braking at 0.7 g. The same system also reduced the impact speed relative to the actual crash in all cases. Even when a human reaction time of 1.2 s and moderate braking of 0.4 g was assumed, the impact speed was reduced in 78% of the crashes. Crash types that proved difficult for the threat detection engine were head-on crashes where the approach angle was low and right turn-opposite crashes. CONCLUSIONS: These results indicate that connected vehicle technology can be greatly beneficial in real-world crash scenarios and that this benefit would be maximized by having the vehicle intervene autonomously with heavy braking. The crash types that proved difficult for the connected vehicle technology could be better addressed if controller area network (CAN) information is available, such as steering wheel angle, so that driver intent can be inferred sooner. More accurate positioning in the real world (e.g., combining satellite positioning and accelerometer data) would allow the technology to be more effective for near-collinear head-on and rear-end crashes, because the low approach angles that are common in such crashes are currently ignored in order to minimize false alarms due to positioning uncertainty.

Pedestrian headform testing: inferring performance at impact speeds and for headform masses not tested, and estimating average performance in a range of real-world conditions.

OBJECTIVE: Tests are routinely conducted where instrumented headforms are projected at the fronts of cars to assess pedestrian safety. Better information would be obtained by accounting for performance over the range of expected impact conditions in the field. Moreover, methods will be required to integrate the assessment of secondary safety performance with primary safety systems that reduce the speeds of impacts. Thus, we discuss how to estimate performance over a range of impact conditions from performance in one test and how this information can be combined with information on the probability of different impact speeds to provide a balanced assessment of pedestrian safety. METHOD: Theoretical consideration is given to 2 distinct aspects to impact safety performance: the test impact severity (measured by the head injury criterion, HIC) at a speed at which a structure does not bottom out and the speed at which bottoming out occurs. Further considerations are given to an injury risk function, the distribution of impact speeds likely in the field, and the effect of primary safety systems on impact speeds. These are used to calculate curves that estimate injuriousness for combinations of test HIC, bottoming out speed, and alternative distributions of impact speeds. RESULTS: The injuriousness of a structure that may be struck by the head of a pedestrian depends not only on the result of the impact test but also the bottoming out speed and the distribution of impact speeds. Example calculations indicate that the relationship between the test HIC and injuriousness extends over a larger range than is presently used by the European New Car Assessment Programme (Euro NCAP), that bottoming out at speeds only slightly higher than the test speed can significantly increase the injuriousness of an impact location and that effective primary safety systems that reduce impact speeds significantly modify the relationship between the test HIC and injuriousness. CONCLUSIONS: Present testing regimes do not take fully into account the relationship between impact severity and variations in impact conditions. Instead, they assess injury risk at a single impact speed. Hence, they may fail to differentiate risks due to the effects of bottoming out under different impact conditions. Because the level of injuriousness changes across a wide range of HIC values, even slight improvements to very stiff structures need to be encouraged through testing. Indications are that the potential of autonomous braking systems is substantial and needs to be weighted highly in vehicle safety assessments.

From crash test speed to performance in real world conditions: a conceptual model and its application to underhood clearance in pedestrian head tests.

Current safety testing protocols typically evaluate performance at a single test speed, which may have undesirable side effects if vehicles are optimised to perform at that speed without consideration to performance at other speeds. One way of overcoming this problem is by using an evaluation that incorporates the distribution of speeds that would be encountered in real crashes, the relationship between test speed and test performance, and the relationship between test performance and injury risk. Such an evaluation is presented in this paper and is applied to pedestrian headform testing. The applicable distribution of pedestrian impact speeds was compiled from in-depth crash data. Values of the Head Injury Criterion across the speed distribution were imputed from a single test result, taking into account the potential for 'bottoming out' on harder structures beneath the hood. Two different risk functions were used: skull fracture risk and fatal head injury risk. Eight example test locations were evaluated; each had an underhood clearance such that it would perform worse at higher speeds than suggested by its original test result. When the effect of bottoming out was included in the evaluation, the calculated average injury risk was generally higher than it was if bottoming out was ignored. The average risk of fatal head injury was more affected by the inclusion of bottoming out than the average skull fracture risk. The methodology presented in this paper may be extended to other forms of impact testing, although the input functions may be more difficult to derive for more complex tests.

An analysis of head impact severity in simulations of collisions between pedestrians and SUVs/work utility vehicles, and sedans.

OBJECTIVE: To describe the determinants of the severity of the head kinematics of a pedestrian when struck by common sport utility vehicles (SUV) and work utility vehicles (WUVs) to assess how effective assessment protocols are in assessing injury risk for SUVs and work utilities. METHODS: Three hundred twenty-four simulations of pedestrian collisions with SUVs, work utility vehicles, and sedans were performed using several vehicle geometries, pedestrian orientations, speeds, and braking levels. Contact stiffnesses in the models were based on impact test results with exemplar vehicle structures. A single contact characteristic was used for all head-to-hood contacts to allow the effects of other factors on head injury risk to be compared. Simulations of standard headform tests on the same hood characterized the structure from a subsystem test perspective. RESULTS: Head injury criterion values were higher in SUV/WUV simulations than sedan simulations because of high neck tension rather than through higher contact forces with the hood. In fact, the severity of the impact between the head and hood was slightly less in SUV/WUV simulations. Sedan and SUV/WUV simulations produced lower head injury criterion (HIC) values than did the subsystem tests. CONCLUSIONS: High bonnet leading edges led to increased neck loads in these simulations of pedestrian collisions. Neck loads were influential on head injury risk in the SUV/work utility simulations but not in sedan simulations. Subsystem impact tests may overestimate head impact risk from the hood itself but fail to capture a potentially important injury mechanism in collisions with vehicles with high leading edges and thus fail to differentiate completely risks posed by such vehicles. These results may have implications for the interpretation of pedestrian subsystem test results: a given HIC value in an SUV/WUV test may represent a relatively higher risk of injury than the same results recorded in a sedan test.

Using child age or weight in selecting type of in-vehicle restraint: implications for promotion and design.

A survey of motor vehicle child restraint use found around 28% of children under the age of six using weight-inappropriate restraints. Many parents did not know when a child was likely to outgrow a booster seat nor the weight of their child, but they did know the child's age. Anthropometric data show that, if advice on restraint transition, given solely in terms of age (6 months, 4 years, 8 years) were followed in Australia, incorrect restraint selection would occur in 5% of children under the age of six. Further analysis suggests how rewriting the Standard could reduce this number. We present an argument for placing age-based transitions at the heart of the strategy to improve child restraint compliance. This may be superior to one based on the child's weight or other anthropometric measurement. Our argument may be summarized as follows: 1 Age-based rules for selecting child restraints are simple, require less information to be retained, and might be more natural criteria for parents. They might have a greater chance of being adopted as norms, and of encouraging good peer cues. Anthropometric rules, on the other hand, assume that parents know the current dimensions of their children and have the tools at their disposal to measure these dimensions. 2 The consequences of age-based promotion for the proportion of children in a restraint suitable for their weight can be estimated for alternative regulatory frameworks. We will report such Calculations below and show that this rate can potentially be very high. The rate would be even higher if child restraint design standards were drafted with age-based transitions in mind. Age-based transitions imply restraint specifications (weight and height limits) that can be determined from anthropometric survey data. 3 Such standards would necessarily imply overlapping anthropometric ranges for the different types of restraint. However, we emphasize that these overlaps would exist to facilitate age-based transitions, not to feature in publicity advising on the correct selection of child restraints. Under such a regime, promotion is driven by what information is readily usable by parents, and ceases being consequential to the standards-setting process. In support of this argument we shall report a survey of restraint use among parents of pre-school and school aged children, and an analysis of the weights (or other dimensions) of children that provides a technique for estimating how well age-based transition could work. The remainder of this paper is divided into sections covering the survey and the anthropometric study. These are synthesized in a discussion of their implications for restraint promotions and standards setting.

Impact mechanics and axonal injury in a sheep model.

This paper describes a biomechanical study of axonal injury due to a blunt impact to the head. The aim of the experimental model was to produce axonal injury analogous to that seen in human trauma while measuring the dynamics of the impact and the subsequent kinematics of the head. These measurements were made in a way to facilitate the simulation of these experiments using the finite element method. Sheep were anaesthetised and ventilated, and subjected to a single impact to the lateral aspect of their skull. The impact force was measured throughout the duration of the impact and the kinematics of the head was measured using a novel implementation of a nine-accelerometer array. The axonal injury was identified using amyloid precursor protein (APP) as a marker, intensified using antigen retrieval techniques. Axonal injury was consistently produced in all animals. Commonly injured regions included the sub-cortical and deep white matter, and the periventricular white matter surrounding the lateral ventricles. The observed axonal injury was mapped and quantified on three coronal sections of each brain. The measure used to describe the injury severity correlated with the peak magnitude of the impact force and with peak values of kinematic parameters, particularly the peak change of linear and angular velocity.