A Benchmark Environment for Neuromorphic Stereo Vision.

Without neuromorphic hardware, artificial stereo vision suffers from high resource demands and processing times impeding real-time capability. This is mainly caused by high frame rates, a quality feature for conventional cameras, generating large amounts of redundant data. Neuromorphic visual sensors generate less redundant and more relevant data solving the issue of over- and undersampling at the same time. However, they require a rethinking of processing as established techniques in conventional stereo vision do not exploit the potential of their event-based operation principle. Many alternatives have been recently proposed which have yet to be evaluated on a common data basis. We propose a benchmark environment offering the methods and tools to compare different algorithms for depth reconstruction from two event-based sensors. To this end, an experimental setup consisting of two event-based and one depth sensor as well as a framework enabling synchronized, calibrated data recording is presented. Furthermore, we define metrics enabling a meaningful comparison of the examined algorithms, covering aspects such as performance, precision and applicability. To evaluate the benchmark, a stereo matching algorithm was implemented as a testing candidate and multiple experiments with different settings and camera parameters have been carried out. This work is a foundation for a robust and flexible evaluation of the multitude of new techniques for event-based stereo vision, allowing a meaningful comparison.

OpenHELP (Heidelberg laparoscopy phantom): development of an open-source surgical evaluation and training tool.

BACKGROUND: Apart from animal testing and clinical trials, surgical research and laparoscopic training mainly rely on phantoms. The aim of this project was to design a phantom with realistic anatomy and haptic characteristics, modular design and easy reproducibility. The phantom was named open-source Heidelberg laparoscopic phantom (OpenHELP) and serves as an open-source platform. METHODS: The phantom was based on an anonymized CT scan of a male patient. The anatomical structures were segmented to obtain digital three-dimensional models of the torso and the organs. The digital models were materialized via rapid prototyping. One flexible, using an elastic abdominal wall, and one rigid method, using a plastic shell, to simulate pneumoperitoneum were developed. Artificial organ production was carried out sequentially starting from raw gypsum models to silicone molds to final silicone casts. The reproduction accuracy was exemplarily evaluated for ten silicone rectum models by comparing the digital 3D surface of the original rectum with CT scan by calculating the root mean square error of surface variations. Haptic realism was also evaluated to find the most realistic silicone compositions on a visual analog scale (VAS, 0-10). RESULTS: The rigid and durable plastic torso and soft silicone organs of the abdominal cavity were successfully produced. A simulation of pneumoperitoneum could be created successfully by both methods. The reproduction accuracy of ten silicone rectum models showed an average root mean square error of 2.26 (0-11.48) mm. Haptic realism revealed an average value on a VAS of 7.25 (5.2-9.6) for the most realistic rectum. CONCLUSION: The OpenHELP phantom proved to be feasible and accurate. The phantom was consecutively applied frequently in the field of computer-assisted surgery at our institutions and is accessible as an open-source project at www.open-cas.org for the academic community.

Kinematic Bézier Maps.

The kinematics of a robot with many degrees of freedom is a very complex function. Learning this function for a large workspace with a good precision requires a huge number of training samples, i.e., robot movements. In this paper, we introduce the Kinematic Bézier Map (KB-Map), a parameterizable model without the generality of other systems but whose structure readily incorporates some of the geometric constraints of a kinematic function. In this way, the number of training samples required is drastically reduced. Moreover, the simplicity of the model reduces learning to solving a linear least squares problem. Systematic experiments have been carried out showing the excellent interpolation and extrapolation capabilities of KB-Maps and their relatively low sensitivity to noise.

[Expanded reality in head surgery]. / Erweiterte Realitat in der Kopfchirurgie.

The preoperative planning of complex craniofacial surgical interventions is increasingly realized with the aid of appropriate planning systems in order to achieve high precision, minimal invasion and protection of risk areas. But the most important step from the planning to the actual intervention consists of providing the planning data intraoperatively in a reasonable and easy to handle way. In this regard, augmented reality is one of the most challenging and promising techniques to solve this problem. In this paper we present two different systems based on see-through glasses resp. a common video projector to directly visualize the planning data in the surgeon's field of view. The work is funded by the 'Deutsche Forschungsgemeinschaft (DFG)' and Stryker Leibinger Freiburg/Germany.

Symmetry considerations for volumetric implant-planning.

Symmetry Considerations can be used not only to plan the desired shape of reconstructured bone structures, but also to generate prototypes for soft tissue implants. The paper describes a system which allows to calculate a symmetry plane in the facial area automatically and computes proposals for implants or transplants. This is done by using a Simulated Annealing algorithm to determine the best reflection and morphologig operators to calculate the implant. The system presented has been used to calculate soft tissue implants in the facial area and a replacement for parts of the lower jaw.

Comparison of tracking techniques for intraoperative presentation of medical data using a see-through head-mounted display.

Tracking of a see-through head-mounted display is a necessary precondition for proper overlay of virtual data and real scenes within the display. In our contribution, the intention and technique for Intraoperative Presentation will be presented. Focus will be the tracking of the display device. We will illustrate and compare three different optical tracking approaches and the results achieved by using them.

Interactive simulation of tooth cleaning with an interdental brush.

Proper cleaning of tooth interspaces is significant to sufficient caries prophylaxis. In this article we present a system for the simulation of this cleaning procedure using an interdental brush. Various application areas for the simulation are presented and the purpose of our work is explained. Simulation methods are shown, including data acquisition and preprocessing, an editor for the design of simulated interdental brushes and the mathematical methods on which the simulation of flexible parts of the brush is based. The presentation of the haptic user interface and a glance on the overall simulation system complete the chapter on methods. Afterwards we show first results of our work, and the article ends with a conclusion and a view on further work to be done in future.

Improvement of intestinal peptide absorption by a synthetic bile acid derivative, cholylsarcosine.

The potential of the nontoxic bile salt derivative, cholylsarcosine, to enhance the intestinal absorption of peptides was investigated in vitro and in situ. The permeation of the two model peptides octreotide and vasopressin-[arg(8)CT>/=CS, whereas ursodeoxycholic acid exhibited no absorption enhancement. Determination of the cytotoxic potential of the bile salts revealed the same rank order. In rats, octreotide and desmopressin were absorbed from the gastrointestinal-tract with moderate absorption efficiency. Coadministration of bile salts resulted in an increased absorption efficiency. The effect of CS was similar to that of CT. In conclusion, CS shows absorption enhancement properties and a relatively low cytotoxicity. It offers an alternative as absorption enhancer as compared to conventional bile acids which may have a potential cocarcinogenic risk.

3D norm data: the first step towards semiautomatic virtual craniofacial surgery.

When planning craniofacial surgical interventions, the ideal appearance of the patient is very important. The final appearance should be as close as possible to that which the patient would have if he/she were without defects. Our first step towards achieving this is to build a database containing sets of three-dimensional CT images that allows for comparison of the shape of a patient with defects to the typical shape of an age- and sex-matched "average" person without defects. We started to collect CT data from patients without pathologies and, in co-operation with two radiology institutes (in Mannheim and Heidelberg), over 100 CT data sets have now been collected and classified according to age and sex. It is necessary to choose an appropriate statistical method to calculate the norm data from the different data sets. Based on the statistical method, an age- and sex-matched "average" model of the anatomy will be created.

The effect of triiodothyronine on myocardial contractile performance after epinephrine exposure: implications for donor heart management.

BACKGROUND: This study analyzes in the experimental model of isolated human atrial myocardium whether the myocardial contractile depression occurring after high-dose/long-term catecholamine exposure (as typically occurring in brain-dead organ donors) can be reversed by thyroid hormone administration. METHODS: Isolated trabeculae were prepared from atrial myocardium from patients undergoing coronary artery bypass (n = 15). Initial measurements of isometric force were carried out (measurement conditions of 37 degrees C, Krebs Henseleit solution, supramaximal electrical stimulation, 1 Hz, at optimal length). Then the trabeculae were incubated for 6 hours at 26 degrees C in a Krebs Henseleit solution containing epinephrine 10(-7) mol/L and the fluorescent dye FURA-2/AM for calcium measurements. At the end of the incubation period, isometric force, isotonic shortening, and intracellular calcium transient (FURA-2 "ratio method") were measured. After 30 minutes administration of triiodothyronine (5 x 10(-9) mol/L), the measurements were repeated. Control groups included 6 hours incubation in 4 degrees C Krebs Henseleit solution (n = 5); 6 hours incubation in 26 degrees C FURA-2/AM (n = 5); and 6 hours incubation in epinephrine 10(-7) mol/L (n = 5). RESULTS: After 6 hours catecholamine exposure isometric force declined significantly to 56.8% (p < .0001) and isotonic shortening to 54% of its initial value (p < .01). Administration of triiodothyronine was associated with a significant recovery of the isotonic shortening amplitude (p < .005), of isometric force development (p < .01), an increased velocity of force development (p < .0001), and of diastolic force decay (p < .005). At the same time the shape of the intracellular calcium transient became smaller as a result of an accelerated diastolic decay. The amplitude of the calcium transient remained unaltered, whereas the calcium time integral was reduced (p < .05). CONCLUSION: In the model of isolated human myocardium, experimental depression of the contractile performance resulting from long-term catecholamine exposure could be reversed by a 30-minute triiodothyronine incubation. The experimental data showing increased force amplitudes at unaltered amplitudes of the intracellular calcium transient and an even-reduced calcium time integral provide strong evidence for a sensitization of the contractile apparatus for calcium by triiodothyronine. The data provide additional knowledge to explain the successful administration of triiodothyronine in donor heart management.

Virtual jaw: a 3D simulation for computer assisted surgery and education.

The jaw is one of the most complex joints in the human body. Its sliding and gliding movements are difficult to understand. Therefore, up to now there exist only mechanical simulations. But there is a strong need for a computer model of the jaw--the virtual jaw--to support physicians and surgeons in diagnoses and preoperative planning. During the preoperative planning of craniofacial operations for example, individual patient data has to be examined and the operation has to be simulated. In the education of physicians such a simulation system gives a much better understanding of the anatomy and functionality of the jaw than static images in text books do. The paper presents a 3D simulation of the human mastication apparatus which can be used for the preoperative planning of craniofacial surgeries as well as the education of dentists and surgeons. It consists of three interacting components: A kinematic model which defines the constraints of the articulation, a model for the mastication muscles and a 3D graphical interface.

Myocardial length-force relationship in end stage dilated cardiomyopathy and normal human myocardium: analysis of intact and skinned left ventricular trabeculae obtained during 11 heart transplantations.

UNLABELLED: The Frank-Starling-mechanism (FSM) was analyzed in isolated intact and skinned human left ventricular myocardium obtained from 11 heart transplantations (normal donor hearts (NDH), n = 8; dilated cardiomyopathy (DCM), n = 11). The new technique to utilize muscle strips from normal donor hearts which were actually implanted is described in detail. METHODS: I) In electrically stimulated left ventricular trabeculae (37 degrees C, oxygenated Krebs-Henseleit solution, supramaximal electrical stimulation, frequency 1 Hz) force development was analyzed as a function of muscle length (NDH = 8; DCM = 11). II) In an additional series left ventricular myocardium was demembranized ("skinned") by Triton-X-100. At different sarcomere lengths and calcium concentrations corresponding to pCa values of 4.3, 5.5, and 8.0 force development was measured (DCM = 11; NDH = 9). RESULTS: I) Developed force increased up to an optimum as a function of muscle length in intact NDH- and DCM-myocardium. However, the relative increment of developed force after any length step was smaller in DCM than in NDH. Near "Lmax" (muscle length associated with maximum developed force) passive resting tension was considerably elevated in DCM, indicating significantly increased diastolic stiffness. II) In skinned left ventricular DCM- and NDH-myocardium developed force depended on sarcomere length with an optimum near 2.2 microns. However, a reduction of activator calcium concentration from pCa 4.3 to pCa 5.5 produces a smaller percent decline in force at short sarcomere lengths in DCM than it does in NDH. CONCLUSION: The present study shows that except for diastolic stiffness and a smaller relative force increment after any length step in DCM the Frank Starling mechanism is still present in isolated human left ventricular DCM- as in NDH-myocardium. The current study does not allow to decide whether in skinned myocardium the smaller percent decline in force after reduction of activator calcium concentrations in DCM is caused by an increased calcium sensitivity at short sarcomere lengths or decreased sensitivity at long sarcomere lengths.

Simulation of jaw-movements for the musculoskeletal diagnoses.

Simulations of static and dynamic aspects of the functionality of the human body are getting more important as the complexity of operations increases. The preoperative planning of maxillofacial operations like the repositioning of the jaw is an example for such operation. Here, but also in other medical fields, simulation can help to estimate the results of a procedure or can facilitate the diagnosis through a better view of the anatomy and pathology of the patient. A virtual view on the pathology and the possibility of simulating the postoperative results simplifies and improves the preoperative planning. The goal of our research is the development of a graphical simulation of the human mastication system to give the surgeon an impression on the inner anatomy of his patient. This simulation allows him to predict the aesthetic and functional outcome of his operation. The main focus of this paper is the introduction of a kinematic model of the temporomandibular joint. This kinematic model describes the geometrical and analytical movement of the jaw by specially defined axes. It is the basis for an animated simulation of the mandible movement. Through integration of the muscles and muscle forces, we come to a realistic dynamic simulation of the whole mastication system.

Biochemical constraints for survival under Martian conditions.

A wide variety of terrestrial organisms, the so-called "anhydrobiotes," has learned to survive in a state of extreme dehydration in dry environments. Strategies for survival include the accumulation of certain polyols and nonreducing saccharides, which help to prevent damage to membranes and proteins, but at low water partial pressure DNA is also progressively damaged by various lesions, including strand breaks and cross-linking to proteins. These lesions, if they are not too numerous, can be repaired before the first replication step after rehydration, but long-term exposure to dry conditions finally diminishes the chances of survival as these lesions accumulate. If an organism has no chance to repair the accumulated DNA damage during intermittent periods of active life, survival will not exceed a few decades. The restriction of survival by dryness-induced DNA lesions is corroborated by new data on conidia of Aspergillus and the free plasmid pBR 322. Our results will be discussed with respect to the chance of finding dormant life or biochemical fossils on the surface of Mars.

ERA-experiment "Space Biochemistry".

The general goal of the experiment was to study the response of anhydrobiotic (metabolically dormant) microorganisms (spores of Bacillus subtilis, cells of Deinococcus radiodurans, conidia of Aspergillus species) and cellular constituents (plasmid DNA, proteins, purple membranes, amino acids, urea) to the extremely dehydrating conditions of open space, in some cases in combination with irradiation by solar UV-light. Methods of investigation included viability tests, analysis of DNA damages (strand breaks, DNA-protein cross-links) and analysis of chemical effects by spectroscopic, electrophoretic and chromatographic methods. The decrease in viability of the microorganisms was as expected from simulation experiments in the laboratory. Accordingly, it could be correlated with the increase in DNA damages. The purple membranes, amino acids and urea were not measurably effected by the dehydrating condition of open space (in the dark). Plasmid DNA, however, suffered a significant amount of strand breaks under these conditions. The response of these biomolecules to high fluences of short wavelength solar UV-light is very complex. Only a brief survey can be given in this paper. The data on the relatively good survival of some of the microorganisms call for strict observance of COSPAR Planetary Protection Regulations during interplanetary space missions.