Single fluoroscopic image based 2D/3D reconstruction of a scaled, patient-specific vertebral model

Purpose Accurate three-dimensional (3D) models of lumbar vertebrae can enable image-based 3D kinematic analysis. The common approach to derive 3D models is by direct segmentation of CT or MRI datasets. However, these have the disadvantages that they are expensive, timeconsuming and/or induce high-radiation doses to the patient. In this study, we present a technique to automatically reconstruct a scaled 3D lumbar vertebral model from a single two-dimensional (2D) lateral fluoroscopic image. Methods Our technique is based on a hybrid 2D/3D deformable registration strategy combining a landmark-to-ray registration with a statistical shape model-based 2D/3D reconstruction scheme. Fig. 1 shows different stages of the reconstruction process. Four cadaveric lumbar spine segments (total twelve lumbar vertebrae) were used to validate the technique. To evaluate the reconstruction accuracy, the surface models reconstructed from the lateral fluoroscopic images were compared to the associated ground truth data derived from a 3D CT-scan reconstruction technique. For each case, a surface-based matching was first used to recover the scale and the rigid transformation between the reconstructed surface model Results Our technique could successfully reconstruct 3D surface models of all twelve vertebrae. After recovering the scale and the rigid transformation between the reconstructed surface models and the ground truth models, the average error of the 2D/3D surface model reconstruction over the twelve lumbar vertebrae was found to be 1.0 mm. The errors of reconstructing surface models of all twelve vertebrae are shown in Fig. 2. It was found that the mean errors of the reconstructed surface models in comparison to their associated ground truths after iterative scaled rigid registrations ranged from 0.7 mm to 1.3 mm and the rootmean squared (RMS) errors ranged from 1.0 mm to 1.7 mm. The average mean reconstruction error was found to be 1.0 mm. Conclusion An accurate, scaled 3D reconstruction of the lumbar vertebra can be obtained from a single lateral fluoroscopic image using a statistical shape model based 2D/3D reconstruction technique. Future work will focus on applying the reconstructed model for 3D kinematic analysis of lumbar vertebrae, an extension of our previously-reported imagebased kinematic analysis. The developed method also has potential applications in surgical planning and navigation.

Combining 3D tracking and surgical instrumentation to determine the stiffness of spinal motion segments: a validation study

The spine is a complex structure that provides motion in three directions: flexion and extension, lateral bending and axial rotation. So far, the investigation of the mechanical and kinematic behavior of the basic unit of the spine, a motion segment, is predominantly a domain of in vitro experiments on spinal loading simulators. Most existing approaches to measure spinal stiffness intraoperatively in an in vivo environment use a distractor. However, these concepts usually assume a planar loading and motion. The objective of our study was to develop and validate an apparatus, that allows to perform intraoperative in vivo measurements to determine both the applied force and the resulting motion in three dimensional space. The proposed setup combines force measurement with an instrumented distractor and motion tracking with an optoelectronic system. As the orientation of the applied force and the three dimensional motion is known, not only force-displacement, but also moment-angle relations could be determined. The validation was performed using three cadaveric lumbar ovine spines. The lateral bending stiffness of two motion segments per specimen was determined with the proposed concept and compared with the stiffness acquired on a spinal loading simulator which was considered to be gold standard. The mean values of the stiffness computed with the proposed concept were within a range of ±15% compared to data obtained with the spinal loading simulator under applied loads of less than 5 Nm.

Retraining of interjoint arm coordination after stroke using robot-assisted time-independent functional training

We have developed a haptic-based approach for retraining of interjoint coordination following stroke called time-independent functional training (TIFT) and implemented this mode in the ARMin III robotic exoskeleton. The ARMin III robot was developed by Drs. Robert Riener and Tobias Nef at the Swiss Federal Institute of Technology Zurich (Eidgenossische Technische Hochschule Zurich, or ETH Zurich), in Zurich, Switzerland. In the TIFT mode, the robot maintains arm movements within the proper kinematic trajectory via haptic walls at each joint. These arm movements focus training of interjoint coordination with highly intuitive real-time feedback of performance; arm movements advance within the trajectory only if their movement coordination is correct. In initial testing, 37 nondisabled subjects received a single session of learning of a complex pattern. Subjects were randomized to TIFT or visual demonstration or moved along with the robot as it moved though the pattern (time-dependent [TD] training). We examined visual demonstration to separate the effects of action observation on motor learning from the effects of the two haptic guidance methods. During these training trials, TIFT subjects reduced error and interaction forces between the robot and arm, while TD subject performance did not change. All groups showed significant learning of the trajectory during unassisted recall trials, but we observed no difference in learning between groups, possibly because this learning task is dominated by vision. Further testing in stroke populations is warranted.

A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs

We present a near-infrared (0.9-2.4 mu m) spectroscopic study of 73 field ultracool dwarfs having spectroscopic and/or kinematic evidence of youth (approximate to 10-300 Myr). Our sample is composed of 48 low-resolution (R approximate to 100) spectra and 41 moderate-resolution spectra (R greater than or similar to 750-2000). First, we establish a method for spectral typing M5-L7 dwarfs at near-IR wavelengths that is independent of gravity. We find that both visual and index-based classification in the near-IR provides consistent spectral types with optical spectral types, though with a small systematic offset in the case of visual classification at J and K band. Second, we examine features in the spectra of similar to 10 Myr ultracool dwarfs to define a set of gravity-sensitive indices based on FeH, VO, Ki, Nai, and H-band continuum shape. We then create an index-based method for classifying the gravities of M6-L5 dwarfs that provides consistent results with gravity classifications from optical spectroscopy. Our index-based classification can distinguish between young and dusty objects. Guided by the resulting classifications, we propose a set of low-gravity spectral standards for the near-IR. Finally, we estimate the ages corresponding to our gravity classifications.

Jet energy measurement with the ATLAS detector in proton-proton collisions at sqrt(s) = 7 TeV

The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of sqrt(s) = 7 TeV corresponding to an integrated luminosity of 38 inverse pb. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0.4 or R=0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pt > 20 GeV and pseudorapidities eta<4.5. The JES systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams. The JES uncertainty is less than 2.5% in the central calorimeter region (eta<0.8) for jets with 60 < pt < 800 GeV, and is maximally 14% for pt < 30 GeV in the most forward region 3.2 50 GeV after a dedicated correction for this effect. The JES is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pt, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pt jets recoiling against a high-pt jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, providing an improved jet energy resolution and a reduced flavour dependence of the jet response. The JES systematic uncertainty determined from a combination of in situ techniques are consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pt jets.

Intraoperative determination of the load-displacement behavior of scoliotic spinal motion segments: preliminary clinical results

Introduction: Spinal fusion is a widely and successfully performed strategy for the treatment of spinal deformities and degenerative diseases. The general approach has been to stabilize the spine with implants so that a solid bony fusion between the vertebrae can develop. However, new implant designs have emerged that aim at preservation or restoration of the motion of the spinal segment. In addition to static, load sharing principles, these designs also require a profound knowledge of kinematic and dynamic properties to properly characterise the in vivo performance of the implants. Methods: To address this, an apparatus was developed that enables the intraoperative determination of the load–displacement behavior of spinal motion segments. The apparatus consists of a sensor-equipped distractor to measure the applied force between the transverse processes, and an optoelectronic camera to track the motion of vertebrae and the distractor. In this intraoperative trial, measurements from two patients with adolescent idiopathic scoliosis with right thoracic curves were made at four motion segments each. Results: At a lateral bending moment of 5 N m, the mean flexibility of all eight motion segments was 0.18 ± 0.08°/N m on the convex side and 0.24 ± 0.11°/N m on the concave side. Discussion: The results agree with published data obtained from cadaver studies with and without axial preload. Intraoperatively acquired data with this method may serve as an input for mathematical models and contribute to the development of new implants and treatment strategies.

A Stellar Census of the Tucana-Horologium Moving Group

We report the selection and spectroscopic confirmation of 129 new late-type (SpT = K3-M6) members of the Tucana-Horologium moving group, a nearby (d similar to 40 pc), young (tau similar to 40 Myr) population of comoving stars. We also report observations for 13 of the 17 known Tuc-Hor members in this spectral type range, and that 62 additional candidates are likely to be unassociated field stars; the confirmation frequency for new candidates is therefore 129/191 = 67%. We have used radial velocities, Ha emission, and Li-6708 absorption to distinguish between contaminants and bona fide members. Our expanded census of Tuc-Hor increases the known population by a factor of similar to 3 in total and by a factor of similar to 8 for members with SpT >= K3, but even so, the K-M dwarf population of Tuc-Hor is still markedly incomplete. Our expanded census allows for a much more detailed study of Tuc-Hor than was previously feasible. The spatial distribution of members appears to trace a two-dimensional sheet, with a broad distribution in X and Y, but a very narrow distribution (+/- 5 pc) in Z. The corresponding velocity distribution is very small, with a scatter of +/- 1.1 km s(-1) about the mean UVW velocity for stars spanning the entire 50 pc extent of Tuc-Hor. We also show that the isochronal age (tau similar to 20-30 Myr) and the lithium depletion boundary age (tau similar to 40 Myr) disagree, following the trend in other pre-main-sequence populations for isochrones to yield systematically younger ages. The H alpha emission line strength follows a trend of increasing equivalent width with later spectral type, as is seen for young clusters. We find that moving group members have been depleted of measurable lithium for spectral types of K7.0-M4.5. None of our targets have significant infrared excesses in the WISE W3 band, yielding an upper limit on warm debris disks of F < 0.7%. Finally, our purely kinematic and color-magnitude selection procedure allows us to test the efficiency and completeness for activity-based selection of young stars. We find that 60% of K-M dwarfs in Tuc-Hor do not have ROSAT counterparts and would have been omitted in X-ray-selected samples. In contrast, GALEX UV-selected samples using a previously suggested criterion for youth achieve completeness of 77% and purity of 78%, and we suggest new SpT-dependent selection criteria that will yield > 95% completeness for tau similar to 40 Myr populations with GALEX data available.

Range of motion in anterior femoroacetabular impingement

The range of motion of normal hips and hips with femoroacetabular impingement relative to some specific anatomic reference landmarks is unknown. We therefore described: (1) the range of motion pattern relative to landmarks; (2) the location of the impingement zones in normal and impinging hips; and (3) the influence of surgical débridement on the range of motion. We used a previously developed and validated noninvasive 3-D CT-based method for kinematic hip analysis to compare the range of motion pattern, the location of impingement, and the effect of virtual surgical reconstruction in 28 hips with anterior femoroacetabular impingement and a control group of 33 normal hips. Hips with femoroacetabular impingement had decreased flexion, internal rotation, and abduction. Internal rotation decreased with increasing flexion and adduction. The calculated impingement zones were localized in the anterosuperior quadrant of the acetabulum and were similar in the two groups and in impingement subgroups. The average improvement of internal rotation was 5.4 degrees for pincer hips, 8.5 degrees for cam hips, and 15.7 degrees for mixed impingement. This method helps the surgeon quantify the severity of impingement and choose the appropriate treatment option; it provides a basis for future image-guided surgical reconstruction in femoroacetabular impingement with less invasive techniques.

Algorithms for autonomous tandem operation of a dual M113 system

In mid-July 2003, the U.S. Army Tank-Automotive & Armaments Command (TACOM) performed a series of experiments at Keweenaw Research Center (KRC), with a remote operated mine roller system. This system, named Panther Lite, consists of two M113 Armored Personnel Carriers (APC’s) connected by a Tandem Vehicle Linkage Assembly (TVLA). The system has three sets of mine rollers, two of which are connected to the front of the lead vehicle with one set trailing from the trail vehicle. Currently, the system requires two joystick controllers. One regulates the braking of the tracks, throttle, and transmission of the lead vehicle and the other controls the braking and throttle of the rear vehicle. One operator controls both joysticks, attempting to maneuver the lead vehicle along a desired path. At the same time, this operator makes compensation maneuvers to reduce lateral loads in the TVLA and to guide the rear mine rollers along the desired path. The purpose of this project is to create algorithms that would allow the slave (trail) vehicle to operate using inputs that maneuver the control (lead) vehicle. The project will be completed by first reconstructing the experimental data. Kinematic models will be generated and simulations created. The models will then be correlated with the reconstructions of the experimental data. The successful completion of this project will be a first step to eliminating the need for the second joystick.

Effect of mesh distortion on the accuracy of high order vorticity-velocity CFD approaches

The numerical solution of the incompressible Navier-Stokes equations offers an alternative to experimental analysis of fluid-structure interaction (FSI). We would save a lot of time and effort and help cut back on costs, if we are able to accurately model systems by these numerical solutions. These advantages are even more obvious when considering huge structures like bridges, high rise buildings or even wind turbine blades with diameters as large as 200 meters. The modeling of such processes, however, involves complex multiphysics problems along with complex geometries. This thesis focuses on a novel vorticity-velocity formulation called the Kinematic Laplacian Equation (KLE) to solve the incompressible Navier-stokes equations for such FSI problems. This scheme allows for the implementation of robust adaptive ordinary differential equations (ODE) time integration schemes, allowing us to tackle each problem as a separate module. The current algortihm for the KLE uses an unstructured quadrilateral mesh, formed by dividing each triangle of an unstructured triangular mesh into three quadrilaterals for spatial discretization. This research deals with determining a suitable measure of mesh quality based on the physics of the problems being tackled. This is followed by exploring methods to improve the quality of quadrilateral elements obtained from the triangles and thereby improving the overall mesh quality. A series of numerical experiments were designed and conducted for this purpose and the results obtained were tested on different geometries with varying degrees of mesh density.

Evaluating stress patterns for Plio-Quaternary brittle deformation along the Calama-Olacapato-El Toro fault zone, Central Andes

Understanding the geometry and kinematics of the major structures of an orogen is important to elucidate its style of deformation, as well as its tectonic evolution. We describe the temporal and spatial changes in the state of stress of the trans-orogen area of the Calama-Olacapato-El Toro (COT) Fault Zone in the Central Andes, at about 24°S within the northern portion of the Puna Plateau between the Argentina-Chile border. The importance of the COT derives principally from the Quaternary-Holocene activity recognized on some segments, which may shed new light on its possible control on Quaternary volcanism and on the seismic hazard evaluation of the area. Field geological surveys along with kinematic analysis and numerical inversion of ∼140 new fault-slip measurements have revealed that this portion of the COT zone, previously considered a continuous, long-lived lineament, in reality has been subjected to three different kinematic regimes: 1) a Miocene transpressional phase with the maximum principal stress (σ1) chiefly trending NNE-SSW; 2) an extensional phase that started by 9 Ma, with a horizontal NW-SE-striking minimum principal stress (σ3) – permutations between σ2 and σ3 axes have been recognized at two sites – and 3) a left-lateral strike-slip phase with a horizontal ∼E-W &sigma1 and ∼N-S σ3 dating to the Late Pliocene-Quaternary. Spatially, in the Quaternary, the left-lateral component decreases toward the westernmost tip of the COT, where it transitions to extension; this produced to a N-S horst and graben structure. Hence, even if transcurrence is still active in the eastern portion of the COT, as focal mechanisms of crustal earthquakes indicate, our study demonstrates that extension is becoming the predominant structural style of deformation, at least in the western region. These major temporal and spatial changes in the tectonic regimes are attributed in part to changes in the magnitude of the boundary forces due to subduction processes. The overall orogen-perpendicular extension might be the result of vertical stress larger than both the horizontal stresses induced by gravitational effect of a thickened crust.

Swimming as a model of task-specific locomotor retraining after spinal cord injury in the rat

BACKGROUND: The authors have shown that rats can be retrained to swim after a moderately severe thoracic spinal cord contusion. They also found that improvements in body position and hindlimb activity occurred rapidly over the first 2 weeks of training, reaching a plateau by week 4. Overground walking was not influenced by swim training, suggesting that swimming may be a task-specific model of locomotor retraining. OBJECTIVE: To provide a quantitative description of hindlimb movements of uninjured adult rats during swimming, and then after injury and retraining. METHODS: The authors used a novel and streamlined kinematic assessment of swimming in which each limb is described in 2 dimensions, as 3 segments and 2 angles. RESULTS: The kinematics of uninjured rats do not change over 4 weeks of daily swimming, suggesting that acclimatization does not involve refinements in hindlimb movement. After spinal cord injury, retraining involved increases in hindlimb excursion and improved limb position, but the velocity of the movements remained slow. CONCLUSION: These data suggest that the activity pattern of swimming is hardwired in the rat spinal cord. After spinal cord injury, repetition is sufficient to bring about significant improvements in the pattern of hindlimb movement but does not improve the forces generated, leaving the animals with persistent deficits. These data support the concept that force (load) and pattern generation (recruitment) are independent and may have to be managed together with respect to postinjury rehabilitation.

Der Einfluss kinematischer Parameter auf den Energiebedarf eines Regalbediengerätes

Bisher wurde noch nicht erforscht wie sich die Variation kinematischer Parameter konkret auf den Energiebedarf von Regalbediengeräten auswirkt. Dieser Beitrag untersucht daher die energetischen Folgen bei unterschiedlichen Geschwindigkeiten und Beschleunigungen der Antriebe eines Regalbediengerätes. Veränderte Geschwindigkeiten und Beschleunigungen beeinflussen jedoch auch die Fahr- und Hubzeiten des Regalbediengerätes. Daher wird ebenfalls eine Berechnungsmethode vorgestellt, mit der der optimale Startpunkt des Hubwerkes und die optimale Fahrgeschwindigkeit auf Basis der eingestellten kinematischen Parameter berechnet werden können.

Simulationsgestützte Untersuchung der Spurtreue von Routenzügen

Für den innerbetrieblichen Transport und besonders für die Materialversorgung in der Produktion werden zunehmend Routenzüge eingesetzt, die aus einem Schleppfahrzeug und bis zu fünf Anhängern bestehen. Um gute Manövrierbarkeit und einen geringen Platzbedarf zu gewährleisten, sollten Routenzuganhänger möglichst spurtreu sein. In diesem Beitrag wird die Spurtreue exemplarisch für zwei am Markt verfügbare Anhänger für Routenzüge mit zwei ungelenkten und vier gelenkten Rädern untersucht. Hierfür wird zunächst ein Gütekriterium definiert, das die maximale Abweichung von der Spurtreue quantitativ erfasst. Außerdem werden Testszenarien vorgeschlagen, um die verschiedenen Fahrwerks- und Lenkkonzepte vergleichen zu können. Mit Hilfe eines entwickelten analytischen Modells werden die Abweichungen in der Spurtreue bei stationärer Kreisfahrt für die zwei gewählten Konzepte berechnet und dargestellt. Zusätzlich wird eine Mehrkörper-Simulation, die eine tiefere physikalische Modellierung und die Untersuchung komplexerer Fahrmanöver erlaubt, durchgeführt und mit den analytischen Ergebnissen verglichen. Es kann gezeigt werden, dass neben der Lenkkinematik weitere Parameter wie das Schräglaufverhalten der Reifen Einfluss auf die Spurtreue haben.

GPS-only gravity field determination from GOCE data

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) is now in orbit for more than four years. This is longer than the originally planned lifetime of the satellite and after three years on the same altitude the satellite has been lowered to 235 km in several steps. In the frame of the GOCE High-level Processing Facility the Astronomical Institute of the University of Bern (AIUB) is responsible for the determination of the official Precise Science Orbit (PSO) product. Kinematic GOCE orbits are part of this product and are used by several institutions in- and outside the HPF for determining the low degrees of the Earth’s gravity field. AIUB GOCE GPS-only gravity field solutions using the Celestial Mechanics Approach and covering the Release 4 period as well as a more recent time interval at the lower orbit altitude are shown and discussed. Special attention is paid to the impact of systematic deficiencies in the kinematic orbits on the resulting gravity fields, e.g., related to the geomagnetic equator, and on possibilities to get rid of them.