Threshold of the skull injury for blunt force impacts under free and constraint boundary conditions.

The formation of skull fractures is an important topic in legal medicine. In particular, the influence of boundary conditions is controversially discussed in the literature. A study focusing solely on this aspect was missing. This study aimed to investigate the influence of boundary conditions on the energy threshold for head fractures. Because of the great variability of biological tissue of real skulls, we opted for a head model made from a polyurethane sphere filled with gelatin. Furthermore, we decided to investigate two opposite situations: A fixed configuration where a model was placed on a rigid surface and a (quasi) free boundary configuration where the head model was held at a force of 5 N compensating for gravity. For both configurations, we determined the acceleration signal of the impactor, the force, and the energy threshold for head fracture. It turned out that the fracture forces for both configurations were the same whereas the energy threshold was 11.0 J for the fixed and 13.6 J for the free boundary. The difference seems to be negligible if compared to the effect of varying structural mechanical properties of real human heads. This means that in a forensic case, the two situations most probably cannot be distinguished. To investigate the influence of the impactor mass, we developed a mathematical model and fitted the experimental data. As a result, we found that in the free configuration, a larger mass increases the energy threshold for head fracture. So that in principle, the two configurations are distinguishable.

Influence of a soft tissue layer covering the kidney upon blunt impact.

Blunt abdominal organ injury is an abundant and relevant topic in forensic medicine, yet comparatively few experimental studies have been performed to quantify organ injury threshold parameters. The goal of this study was to relate an impact to a kidney injury determining an energy threshold while taking account of the influence of the overlaying soft tissue thickness. A model consisting of ballistic gelatin with an embedded filled porcine kidney was made such that a gelatin layer of 2 or 4 cm thickness covered the organ. An impactor was dropped on this model from different heights and the resulting organ damage was categorized according to the abbreviated injury scale (AIS). The 50% energy threshold for damage and the 50% energy threshold causing injuries ≥ AIS 3 were determined for the two protecting soft layers to be 22 J and 32 J and 27 J and 36 J, respectively. A finite element model was created to determine the strain energy densities at the depth of the organ's surface for these energies. The strain energy densities for the 50% damage thresholds were 88.9 mJ/cm3 and 86.7 mJ/cm3 for 2 and 4 cm and for the injuries ≥ AIS 3104.2 mJ/cm3 and 98.7 mJ/cm3. For forensic cases, this means that the thickness of the abdominal layers must be taken into account when the severity of an injury is used to draw conclusions about the applied impact strength.

Impact energy of everyday items used for assault.

Blunt force is a frequently used type of violence especially because it can be performed with basically every object of our daily lives or with bare hands or feet. The injuries and medical consequences have been widely examined, whereas the forces and especially the energies acting on impact have rarely been analyzed. The aim of the present study is to provide the impact energy and its ranges of four longish everyday items with different characteristics for male and female offenders. Additionally, the moment of inertia (MOI) for all the objects was calculated and its influence on the energy determined. A combination wrench, aluminum pipe, golf club, and spade were chosen as representatives of the four categories short, medium length with the center of mass (COM) in the middle, medium length with the COM close to the hitting point, and long and heavy. A total of 880 strikes have been performed by 11 volunteers. The results show the mean energy values of wrench, pipe, golf club, and spade for men of 51.1, 74.4, 93.5, and 166.7 J. For women, the results are 33.0, 41.0, 56.5, and 76.8 J. Knowing the energy thresholds for certain fractures and injuries, these results help to assess whether a claimed hit may have caused the fracture or injury or not.

Stabbing energy and force required for pocket-knives to pierce ribs.

PURPOSE: In addition to reconstructing the course of events, the medical examiner will often have to answer questions regarding the force necessary to inflict a certain injury in stabbing incidents. Several groups have examined the force needed to penetrate soft-tissue and clothing; however, no studies addressing the energy needed for penetrating ribs exist. Therefore, we decided to investigate this force on an animal model. METHOD: Ribs from healthy, 8 to 10-month-old pigs were used as a substitute for human ribs. These ribs were then stabbed either transversely or longitudinally with two different pocket-knife blades, namely a Swiss Army pocket knife and a sturdier pocket knife (Classic Schnitzmesser, Herbertz Solingen) dropped from a drop-tower at defined heights and therefore defined energies. RESULTS: Longitudinally orientated stabs showed complete piercing of the ribs at approximately 11 Joules (J) or with a stabbing force in excess of 906 Newton (N) for both blade types. Transversely orientated stabs, however, displayed complete piercing between 11 and 16 J, or in excess of 1198 N, with the sturdy pocket knife tending to require a little more energy than the Swiss army pocket knife. CONCLUSIONS: Young adult porcine ribs are completely pierced by pocket knife blades at energies between 11 and 16 J. Assuming the porcine ribs are comparable to those ribs of young adult humans, our results indicate that a complete penetration of the chest wall through the ribs by stabbing with a pocket knife is rather easily achieved.

The influence of striking object characteristics on the impact energy.

A common form of violence investigated in legal medicine is blunt trauma caused by striking with different objects. The injuries and medical consequences have been widely examined, whereas the forces and especially the energies acting on impact have rarely been analyzed. This study focuses on how the impact energy of different striking objects depends on their characteristics. A total of 1170 measurements of horizontal strikes against a static and relatively heavy pendulum have been acquired with 13 volunteers. The main focus was laid on how the weight, the length, and the center of mass of the different striking objects influenced the striking energy. The results show average impact energies in the range of 67.3 up to 311.5 J for men with an optimum weight of about 1.3 kg with its center of mass in the far end quarter for a 1-m-long striking object. The average values for women range from 30 to 202.6 J, with an optimum weight between 1.65 and 2.2 kg and similar settings for the center of mass as the men. Also, the impact energies are getting higher with shorter object lengths and reach a maximum at a length of about 0.3 to 0.4 m. The male volunteers' impact energy was on average by 84.2% higher than the values of the female volunteers, where the impact masses were very similar and the impact velocities played the key role.

Sex determination from os sacrum by postmortem CT.

Sex determination in forensic practice is performed mostly on sexually dimorphic bones, including pelvic bones such as the os sacrum. Postmortem CT scan provides an easy and fast method for depicting and measuring bone structures prior to elaborate autopsy preparations. To develop a simple and objective method for sex determination in postmortem CT, metric data were evaluated from CT images of the pelvic-associated os sacrum of 95 corpses (49 men and 46 women) from the Canton of Bern, Switzerland. Discriminant function analysis of the data showed that the best accuracy in determining sex was 76.8% and 78.9% with two different observers. It is concluded that measuring the os sacrumin postmortem CT for sex determination has moderate accuracy and should only be applied in combination with other methods.

The influence of body temperature on image contrast in post mortem MRI.

OBJECTIVE: To assess the temperature dependency of tissue contrast on post mortem magnetic resonance (PMMR) images both objectively and subjectively; and to visually demonstrate the changes of image contrast at various temperatures. MATERIALS AND METHODS: The study was approved by the responsible justice department and the ethics committee. The contrast of water, fat, and muscle was measured using regions of interest (ROI) in the orbit of 41 human corpses to assess how body temperature (range 2.1-39.8 °C) relates to image contrast of T1-weighted (T1W) and T2-weighted (T2W) sequences on PMMR. Regressions were calculated using the method of least squares. Three readers judged visible changes of image contrast subjectively by consensus. RESULTS: There was a positive relationship between temperature and contrast on T1-weighted (T1W) images and between temperature and the contrast of fat/muscle on T2-weighted (T2W) images. There was a negative relationship between temperature and the contrast of water/fat and water/muscle on T2W images. Subjectively, the influence of temperature became visible below 20 °C on T2W images, and below 10 °C on T1W images. CONCLUSION: Image contrast on PMMR depends on the temperature of a corpse. Radiologists involved in post mortem imaging must be aware of temperature-related changes in MR image contrast. To preserve technical quality, scanning corpses below 10 °C should be avoided.

[Aiming at the chest, but hitting the back]. / Auf die Brust gezielt--in den Rücken getroffen.

Gunshot injuries in the back may suggest the unjustified use of firearms. A wound in the back inflicted by a firearm should not automatically imply that the shooter aimed at the back. A previous study demonstrated that it is possible for men to turn their trunk faster than it takes for a shooter to fire or throw a hand-operated weapon. With a high speed motion camera the authors were able to demonstrate that it is also possible for women to turn their trunk fast enough, so that a shot in the back could have been aimed at the front of the body. This conclusion is also likely to apply to hand-operated or thrown weapons, since the velocity of their projectiles is considerably lower than that of firearms.

Reduction of background in optoacoustic image sequences obtained under tissue deformation.

For real-time optoacoustic imaging of the human body, a linear array transducer and reflection mode optical irradiation is preferably used. Experimental outcomes however revealed that such a setup results in significant image background, which prevents imaging structures at the ultimate depth limited only by the optical attenuation of the irradiating light and the signal noise level. Various sources of image background, such as bulk tissue absorption, reconstruction artifacts, and backscattered ultrasound, could be identified. To overcome these limitations, we developed a novel method that results in significantly reduced background and increased imaging depth. For this purpose, we acquire, in parallel, a series of optoacoustic and echo-ultrasound images while the tissue sample is gradually deformed by an externally applied force. Optoacoustic signals and background signals are differently affected by the deformation and can thus be distinguished by image processing. This method takes advantage of a combined optoacoustic/echo-ultrasound device and has a strong potential for improving real-time optoacoustic imaging of deep tissue structures.