Evaluating Neuromuscular Function of the Biceps Brachii after Spinal Cord Injury: Assessment of Voluntary Activation and Motor Evoked Potential Input-Output Curves Using Transcranial Magnetic Stimulation

Activation of upper limb muscles is important for independent living after cervical spinal cord injury (SCI) that results in tetraplegia. An emerging, non-invasive approach to address post-SCI muscle weakness is modulation of the nervous system. A long-term goal is to develop neuromodulation techniques to reinnervate (i.e. resupply nerve to) muscle fiber and thereby increase muscle function in individuals with tetraplegia. Towards this goal, developing monitoring techniques to quantify neuromuscular function is needed to better direct neurorehabilitation. Assessment of voluntary activation (VA) is a promising approach because the location of the stimulus can be applied cortically using transcranial magnetic stimulation (TMS) or peripherally (VAPNS) to reveal what levels of the nervous system are disrupting the innervation of muscle fibers. Voluntary activation measured with TMS (VATMS) can indicate deficits in voluntary cortical drive to innervate muscle. However, measurement of VATMS is limited by technical challenges, including the difficulty in preferential stimulation of cortical neurons projecting to the target muscle and minimal stimulation of antagonists. Thus, the motor evoked potential (MEP) response to TMS in the target muscle compared to its antagonist (i.e. MEP ratio) may be an important parameter in the assessment of VATMS. Using current methodology, VATMS cannot be reliably assessed in patient populations including individuals with tetraplegia. The overall purpose of this work was to investigate novel TMS-based methods to evaluate neuromuscular function after spinal cord injury. First, we developed and evaluated new methodology to assess VATMS in individuals with tetraplegia. The objective of the first study was to optimize the biceps/triceps MEP ratio using modulation of isometric elbow flexion angle in nonimpaired participants and participants with tetraplegia following cervical SCI (C5-C6). We hypothesized that the more flexed elbow angle would increase the MEP ratio. The MEP ratio was only modulated in the nonimpaired group but not across the entire range of voluntary efforts used to estimate VATMS. However, we established that VATMS and VAPNS in individuals with tetraplegia were repeatable across days. In a second study, we aimed to optimize MEPs during the assessment of VATMS using paired pulse TMS to elicit intracortical facilitation and short-interval intracortical inhibition. We hypothesized that intracortical facilitation would lead to an increased MEP ratio compared to single pulse and that short-interval intracortical inhibition would lead to a lower MEP ratio. The MEP ratio was modulated in both groups but not across the entire range of voluntary efforts, and did not affect VATMS estimation compared to single pulse TMS. Paired pulse TMS outcomes revealed abnormal patterns of intracortical inhibition in individuals with tetraplegia. Further, VATMS was sensitive to the linearity of the voluntary moment and superimposed twitch relationship. Linearity was lower in SCI relative to nonimpaired participants. We discuss the limitations of VATMS in assessing neuromuscular impairments in tetraplegia. In a third study, we aimed to collect MEP input-output curves of the biceps in SCI and nonimpaired and evaluate curve-fitting methodology as well as their repeatability across sessions. We hypothesized that slopes would be greater in the SCI group compared to nonimpaired. Slopes obtained with linear regression were greater in tetraplegia compared to nonimpaired participants, suggesting compensatory reorganization of corticomotor pathways after SCI. Linear regression accurately represented the slope of the modeled data compared to sigmoidal function curve-fitting method. Slopes were also found to be repeatable across days in both groups. In a fourth study, we aimed to implement a low-cost navigated TMS system (\u3c $3000) that uses motion tracking, 3D printed parts and open-source software to monitor coil placement during stimulation. We hypothesized that using this system would improve coil position and orientation consistency and decrease MEP variability compared to the conventional method when targeting the biceps at rest and during voluntary contractions across two sessions in nonimpaired participants. Coil orientation error was reduced but the improvement did not translate to lower MEP variability. This low-cost approach is an alternative to expensive systems in tracking the motor hotspot between sessions and quantifying the error in coil placement when delivering TMS. Finally, we conclude and recommend future research directions to address the challenges that we identified during this work to improve our ability to monitor neuromuscular impairments and contribute to the development of more effective neurorehabilitation strategies

Long Range Automated Persistent Surveillance

This dissertation addresses long range automated persistent surveillance with focus on three topics: sensor planning, size preserving tracking, and high magnification imaging. field of view should be reserved so that camera handoff can be executed successfully before the object of interest becomes unidentifiable or untraceable. We design a sensor planning algorithm that not only maximizes coverage but also ensures uniform and sufficient overlapped camera’s field of view for an optimal handoff success rate. This algorithm works for environments with multiple dynamic targets using different types of cameras. Significantly improved handoff success rates are illustrated via experiments using floor plans of various scales. Size preserving tracking automatically adjusts the camera’s zoom for a consistent view of the object of interest. Target scale estimation is carried out based on the paraperspective projection model which compensates for the center offset and considers system latency and tracking errors. A computationally efficient foreground segmentation strategy, 3D affine shapes, is proposed. The 3D affine shapes feature direct and real-time implementation and improved flexibility in accommodating the target’s 3D motion, including off-plane rotations. The effectiveness of the scale estimation and foreground segmentation algorithms is validated via both offline and real-time tracking of pedestrians at various resolution levels. Face image quality assessment and enhancement compensate for the performance degradations in face recognition rates caused by high system magnifications and long observation distances. A class of adaptive sharpness measures is proposed to evaluate and predict this degradation. A wavelet based enhancement algorithm with automated frame selection is developed and proves efficient by a considerably elevated face recognition rate for severely blurred long range face images

Magnetized, Laser-Driven, Plasma Experiments at Astrophysically Relevant Conditions and Proton Imaging of Magnetic Fields

This thesis presents analysis relevant to two magnetized, astrophysically relevant experimental campaigns that were performed at the OMEGA laser facility. The magnetic fields of these systems were measured using proton imaging, in which high-energy protons interact with and are deflected by the electromagnetic fields, forming spatial variations in the proton fluence on the image plane. Proton images are determined by both the amplitude of the field and the orientation of the field relative to a proton's trajectory, which makes it difficult to generalize between different systems, although certain geometrical effects should always be considered. The collisionless interaction of two counter-propagating, laser-irradiated plasmas results in the formation of small-scale magnetic filaments via the Weibel instability, a process which may explain the presence of magnetic fields throughout the intergalactic medium. Proton images of experiments studying this phenomenon display repeatable features corresponding to the filaments. Through analytical approximations and statistical analysis of synthetic proton images we determined that the observed images features fundamentally correspond to the transverse extent of the constituent filaments. How the image features related to the underlying field had not previously been understood. The magnetic field produced by planets with active dynamos, like the Earth, can exert sufficient pressure to oppose inflowing, supersonic stellar wind plasmas. The effective obstacle to the flow in these systems is the pressure-balance surface between the stellar wind and the magnetic field, known as the magnetopause, and a standing bow shock forms at a standoff distance upstream from the magnetopause to redirect the flow. We performed scaled experiments to explore magnetized bow shocks, which consisted of a slow, low-density plasma flow impinging on the external azimuthal magnetic field around a current-carrying wire. We infer the presence of a shock at a significant standoff distance from the wire from the spatially resolved, optical, Thomson scattered spectra, and the inferred density jump suggests significant magnetization. We also observe the formation of a bow shock around the magnetized wire in proton images of the magnetic fields at 60, 70, and 80 ns after the initial laser drive for two different field amplitudes. Simulations of the experiment performed using the FLASH code supplement the data.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163246/1/jmlevesq_1.pd

NASA Tech Briefs, April 1995

This issue of the NASA Tech Briefs has a special focus section on video and imaging, a feature on the NASA invention of the year, and a resource report on the Dryden Flight Research Center. The issue also contains articles on electronic components and circuits, electronic systems, physical sciences, materials, computer programs, mechanics, machinery, manufacturing/fabrication, mathematics and information sciences and life sciences. In addition to the standard articles in the NASA Tech brief, this contains a supplement entitled "Laser Tech Briefs" which features an article on the National Ignition Facility, and other articles on the use of Lasers

Laser-driven ion acceleration from carbon nano-targets with Ti:Sa laser systems

Over the past few decades, the generation of high energetic ion beams by relativistic intense laser pulses has attracted great attentions. Starting from the pioneering endeavors around 2000, several groups have demonstrated muliti-MeV (up to 58 MeV for proton by then) ion beams along with low transverse emittance and ps-scale pulse duration emitted from solid targets. Owing to those superior characteristics, laser driven ion beam is ideally suitable for many applications. However, the laser driven ion beam typically exhibits a large angular spread as well as a broad energy spectrum which for many applications is disadvantageous. The utilization of nano-targets as ion source provides a number of advantages over micrometer thick foils. The presented PhD work was intended to investigate laser driven ion acceleration from carbon nano-targets and demonstrate the potential feasibility for biological studies. Two novel nano-targets are employed: nm thin diamond-like-carbon (DLC) foil and carbon nanotubes foam (CNF). Both are self-produced in the technological laboratory at Ludwig-Maximilians-Universität München. Well-collimated proton beams with extremely small divergence (half angle) of 2 degrees are observed from DLC foils, one order of magnitude lower as compared to micrometer thick targets. Two-dimensional particle-in-cellsimulations indicate a strong influence from the electron density distribution on the divergence of protons. This interpretation is supported by an analytical model. In the same studies, the highest maximum proton energy was observed with a moderate laser intensity as low as 5*10^18W/cm^2. Parallel measurements of laser transmission and reflection are used to determine laser absorption in the nano-plasma, showing a strong correlation to the maximum proton energy. This observation indicates significance of absorbed laser energy rather than incident laser intensity and is supported by an analytical model. The ion energy also depends on pulse duration, a reduced optimum pulse duration is found as compared to micrometer thick targets. This behavior is attributed to a reduction of transverse electron spread due to the reduction of thickness from micrometer to nanometer. These remarkable proton bunch characteristics enabled irradiating living cells with a single shot dose of up to 7 Gray in one nanosecond, utilizing the Advanced Titanium: sapphire LASer (ATLAS)system at Max-Planck-Institut of Quantum Optics (MPQ). The experiments represent the first feasibility demonstration of a very compact laser driven nanosecond proton source for radiobiological studies by using a table-top laser system and advanced nano-targets. For the purpose of providing better ion sources for practical application, particularly in terms of energy increase, subsequent experiments were performed with the Astra Gemini laser system in the UK. The experiments demonstrate for the first time that ion acceleration can be enhanced by exploiting relativistic nonlinearities enabled by micrometer-thick CNF targets. When the CNF is attached to a nm-thick DLC foil, a significant increase of maximum carbon energy (up to threefold) is observed with circularly polarized laser pulses. A preferable enhancement of the carbon energy is observed with non-exponential spectral shape, indicating a strong contribution of the radiation pressure to the overall acceleration. In contrast, the linear polarization give rise to a more prominent proton acceleration. Proton energies could be increased by a factor of 2.4, inline with a stronger accelerating potential due to higher electron temperatures. Three-dimensional (3D) particle-in-cell (PIC) simulations reveal that the improved performance of the double-layer targets (CNF+DLC) can be attributed to relativistic self-focusing in near-critical density plasma. Interestingly, the nature of relativistic non-linearities, that plays a major role in laserwakefield-acceleration of electrons, can also apply to the benefit of laser driven ion acceleration

Prescription of Ankle-Foot Orthoses for Children with Cerebral Palsy

Purpose: Ankle foot orthoses (AFOs) are frequently prescribed to address gait impairments for children with cerebral palsy (CP). Successful treatment with AFOs depends on optimal prescription, matching the design of the brace to the individual child’s physical impairments; however, research evidence does not exist to help health care professionals decide on the best AFO design to meet each child’s needs. Therefore, this thesis explored current AFO prescription practices, and aimed to improve evidence to assist clinicians in making prescription decisions for children with CP. Methods and Results: To examine the experiences and perspectives of clinicians on AFO prescription for children with CP, we conducted focus groups and semi-structured interviews with 32 clinicians who were involved with AFO prescription for children with CP in five Canadian rehabilitation facilities. Using Interpretive Description as a framework for analysis, we identified three categories from the data: 1) What is made, 2) How it is used, and 3) Factors that support or challenge outcomes. Throughout the interviews, the theme of prescription as a collaborative, iterative, and individualized process emerged. To explore evaluation and clinical decision-making practices of physical therapists for AFO prescription and follow-up, we invited Canadian physical therapists (PTs) working with children who have CP to complete an online survey. Sixty completed responses were received. Three researchers conducted a conventional content analysis to examine the open-ended responses, and descriptive statistics were used to summarize the closed-ended responses. Three themes were identified: 1) Focus on impairment level measures, 2) Inconsistent practices between PTs, and 3) Lack of confidence/knowledge about casting positions and AFO types. To investigate the effects of individualizing the angle of the ankle in the AFO on walking mechanics and function, gait biomechanics were studied in ten children with CP. Fifteen typically-developing children provided normative data. Using three-dimensional gait analysis, kinematics and kinetics were compared between the child’s usual AFO(s) and AFOs that were fabricated with an ankle angle that was individualized for each child. Net responses to the individualized ankle angle were positive for 60% of limbs, negative for 40%. The greatest benefits were observed at the knee, suggesting that this may be a beneficial approach to orthotic intervention for some children with CP. Conclusions: There is limited understanding of how AFOs are prescribed for children with CP in Canada. This thesis highlights the importance of multidisciplinary collaboration, objective evaluation, and individualized clinical problem-solving to facilitate the evolution of the AFO prescription from a medical directive to an orthotic device that optimally benefits the child. This is the first step toward the development of guidelines to help clinicians improve AFO prescription for children with CP

Brachial Plexus Injury

In this book, specialists from different countries and continents share their knowledge and experience in brachial plexus surgery. It discusses the different types of brachial plexus injury and advances in surgical treatments