Computer-controlled Motion Research Articles

Use of a computer-controlled kinematic-electromyographic motion analysis system to investigate gait patterns of healthy subjects on the level walkway and the treadmill (author's transl)

In an attempt to clarify the question if the level walkway and the treadmill present comparable conditions for analytic examinations of the human gait we investigated in either situation with a computer-controlled motion analysis system some kinematic and electromyographic aspects of the gait pattern of 20 healthy subjects. The results show that on the treadmill certain kinematic events in the time pattern of the gait cycle are shifted towards the beginning of the full stride. Moreover, in the treadmill walk the amplitude of the angular motion of the thigh is diminished in the forward and enhanced in the backward direction, while the angular amplitude of the shank is diminished in either direction. As to the electromyographic results, we found in the treadmill walk a prolonged activity of the gluteus maximus, and adductor magnus, the semitendinosus, and the gastrocnemius muscle. These results show that there may exist significant kinematic and electromyographic differences between the treadmill and the normal level walk. This fact has to be considered whenever a treadmill is considered for gait analytical investigations.

Evaluation of lumbar segmental instability in degenerative diseases by using a new intraoperative measurement system

In vivo quantitative measurement of lumbar segmental stability has not been established. The authors developed a new measurement system to determine intraoperative lumbar stability. The objective of this study was to clarify the biomechanical properties of degenerative lumbar segments by using the new method. Twenty-two patients with a degenerative symptomatic segment were studied and their measurements compared with those obtained in normal or asymptomatic degenerative segments (Normal group). The measurement system produces cyclic flexion-extension through spinous process holders by using a computer-controlled motion generator with all ligamentous structures intact. The following biomechanical parameters were determined: stiffness, absorption energy (AE), and neutral zone (NZ). Discs with degeneration were divided into 2 groups based on magnetic resonance imaging grading: degeneration without collapse (Collapse[-]) and degeneration with collapse (Collapse[+]). Biomechanical parameters were compared among the groups. Relationships among the biomechanical parameters and age, diagnosis, or radiographic parameters were analyzed. The mean stiffness value in the Normal group was significantly greater than that in Collapse(-) or Collapse(+) group. There was no significant difference in the average AE value among the Normal, Collapse(-), and Collapse(+) groups. The NZ in the Collapse(-) was significantly higher than in the Normal or Collapse(+) groups. Stiffness was negatively and NZ was positively correlated with age. Stiffness demonstrated a significant negative and NZ a significant positive relationship with disc height, however. There were no significant differences in stiffness between spines in the Collapse(-) and Collapse(+) groups. The values of a more sensitive parameter, NZ, were higher in Collapse(-) than in Collapse(+) groups, demonstrating that degenerative segments with preserved disc height have a latent instability compared to segments with collapsed discs.

SU-FF-T-224: Experimental Evaluation of a Robust Optimization Method for IMRT of Moving Targets

Purpose: Tumor motion during irradiation reduces target coverage and increases dose to healthy tissues. The standard clinical approaches using margins are overly conservative because they only take into account the maximum amplitude of the movement. Comparable coverage and reduced dose to healthy organs appears achievable with robust motion-adaptive treatment planning, based on the nominal expected probability distribution of target position, and considering the uncertainty of its realization during treatment. We test a robust approach to IMRT [Chan et al. Phys Med Biol 51:2567–2583 (2006)] using patient data, to evaluate the effect of target motion variability and the MLC motion interplay on the outcome. Method and Materials: We built our robust framework using external marker motion data (traces), acquired during patient treatments. These included 251 traces from two lung, one cardiac and one liver patient. Long-term shifts (such as exhale baseline drift) were removed from the data by band pass filtering. IMRT plans with varying grades of robustness were tested on 52 traces of two patients. A computer-controlled motion phantom reproduced traces during plan delivery on a linac. The dose was measured with a two dimensional detector array consisting of 1020 chambers with a resolution of 7.6 mm. Results: Although tumor coverage differed for each delivery fraction due to MLC interplay and motion variability, it converged to the expected level after multiple fractions. For equivalent target coverage, 17mm peak-to-peak motion, the integral dose was reduced by 15% compared to the margin solution. Conclusions: Dosimetric tests largely confirmed that the robust motion-adaptive approach to IMRT planning allows one to better manage the effect of motion, and can be extended to any uncertainty described by probability density functions. With target monitoring during the treatments, motion-adaptive plans and the underlying robust framework could be verified and re-adjusted if necessary.

F2-laser microfabrication of multilevel diffractive optical elements

The 157nm F2-laser drives strong and precisely controllable interactions with fused silica, the most widely used material for bulk optics, optical fibers, and planar optical circuits. A diffractive optical element (DOE) breaks apart wavefronts and redirects segmented beamlets through phase control for novel beam steering and shaping applications. This paper shows that precise excisions of 10-30 nm depth are available from the F2 laser for the generation of efficient DOEs for the visible and ultraviolet spectrum. F2-laser radiation was applied with beam homogenization optics and high-precision computer-controlled motion stages to shape up to 16-level, 256 × 256 pixel DOE devices on bulk glasses, with distinguishable level-tolevel spacing of ∼100 nm and surface roughness of ∼13 nm. The 1st order diffraction efficiency was ∼35%. The farfield pattern when illuminated with a HeNe laser was found to agree with simulations based on an iterative Fourier transform algorithm. Future improvements in the laser micromachining process and possible directions are also offered.

Parallel Synthesis and High Throughput Dissolution Testing of Biodegradable Polyanhydride Copolymers

We have demonstrated that polycondensation reactions can be carried out in a combinatorial fashion and that the polymer library can be screened at high throughput using a rapid prototyping technique to fabricate multiwell substrates. A linearly varying compositional library of 100 different biodegradable polyanhydride random copolymers that are promising carriers for controlled drug delivery was designed, fabricated, and characterized by IR microscopy within a few hours. The polyanhydride copolymer library was based on 1,6-bis(p-carboxyphenoxy)hexane (CPH) and sebacic anhydride (SA) and was characterized with infrared microspectroscopy to determine the composition within each well. Since degradation and release rates depend on copolymer composition, we also developed new high-throughput methods to investigate drug release from this library of copolymers by designing specific wells for each task. A subset of this library was chosen, and a substrate was designed and fabricated to enable the synthesis and monitoring of dye dissolution from a range of polyanhydride copolymers in a parallel fashion using a CCD camera. Multisample substrates were fabricated with a novel rapid prototyping method that consists of an organic solvent-resistant array of 10 x 10 microwells of 2-muL volume each. The libraries were deposited with a custom-built liquid dispensing system consisting of a series of computer-controlled volume-dispensing pumps and XYZ motion stages. The parallel dye dissolution study displayed a decreasing rate of release with increasing CPH content. This result agrees with previously published data for dye release from poly(CPH-co-SA) copolymers. The methodology described in this work is amenable to numerous applications in the arenas of high-throughput polymer synthesis and characterization.

Remote edge detection of subcutaneous stiffeners

Construction of narrow-gap double skin components requires, at some stage, blind welding from one side. During construction, due to thermal distortion, the hidden stiffeners (spacers or stringers) may move sufficiently far from their designated locations that assembly welds, made from one side, could miss the stringers completely. Thus, a real-time sensor capable of identifying and accurately locating spacer edges beneath the outer skin is required. Outer skin magnetic properties and plate/spacer separation seriously influence the capabilities of the best candidate detecting methods. Initial trials were undertaken using a non-destructive testing (NDT) eddy current method to detect beneath aluminium plate. Probe design and construction concentrated on air-cored absolute coils, on which finite element analysis (FEA) was used to predict electrical response. When the refined detector system was tested on magnetic material (mild steel), it was found to be preferable if a static magnetic field was applied to the plate component. Applied magnetism had a profound effect on coil field penetration and hence detectability (maximum plate thickness rose swiftly from 3mm, unmagnetized, to over 12mm, magnetized). As a sensor, the eddy current detector was shown to be capable of finding subcutaneous edges in both aluminium and mild steel fabrications. What has been developed is a sensor simply requiring computer-controlled movement to allow completely automatic hidden edge finding.

SU-FF-J-40: Independent Measurement of CyberKnife Synchrony Accuracy Using Optical Tracking

Purpose: Synchrony provides respiratory motion compensation for CyberKnife by monitoring skin motion and dynamically steering the beam to follow the moving tumor. This study is designed to measure the accuracy and precision of the beam steering by recording the motions of both the linac and a ball-cube target using an independent optical tracker. Method and Materials: The target is a ball-cube phantom, which was CT scanned and planned for a 3000 cGy at 100% isodose line treatment using dynamic SRS (Synchrony). Respiratory motion was generated using a computer-controlled 3D motion simulator. We simulated regular respiratory motion as three sinusoids with the following extents: 10 mm SI, 10 mm AP, and 5 mm LR. The respiratory period was 5 seconds. All three axes were in phase. We used the Optotrak Certus (Northern Digital, Waterloo, Canada) optical tracking system for measurements in this study. Active LEDs were attached to the linac and the motion simulator to provide constant measurement of their position. Measurements were recorded at 30 Hz. We measured the tracking accuracy by computing the distance between the linac and the target. When Synchrony is active, the linac should follow the motion of the target exactly, so this distance should remain constant. We used the standard deviation of the linac-to-target distance during each beam as a measure of the beam steering accuracy. Results: We were able to track 61 of the 98 beams used during treatment. Other beams were not trackable because the linac or robot blocked the view of the Optotrak. Based on these beams, the standard deviation of the linac-to-target distance was 0.82 ±/− 0.27 mm. Conclusion: These measurements provide independent, high-precision measurement of the tracking accuracy of CyberKnife with Synchrony. They demonstrate the system's capabilities for respiratory motion compensation.

Computer-Controlled Microcirculatory Support System for Endothelial Cell Culture and Shearing

Endothelial cells (ECs) lining the inner lumen of blood vessels are continuously subjected to hemodynamic shear stress, which is known to modify EC morphology and biological activity. This paper describes a self-contained microcirculatory EC culture system that efficiently studies such effects of shear stress on EC alignment and elongation in vitro. The culture system is composed of elastomeric microfluidic cell shearing chambers interfaced with computer-controlled movement of piezoelectric pins on a refreshable Braille display. The flow rate is varied by design of channels that allow for movement of different volumes of fluid per variable-speed pump stroke. The integrated microfluidic valving and pumping system allowed primary EC seeding and differential shearing in multiple compartments to be performed on a single chip. The microfluidic flows caused ECs to align and elongate significantly in the direction of flow according to their exposed levels of shear stress. This microfluidic system overcomes the small flow rates and the inefficiencies of previously described microfluidic and macroscopic systems respectively to conveniently perform parallel studies of EC response to shear stress.

The accuracy of dynamic wedge dose computation in the ADAC Pinnacle RTP system

The nonphysical wedge is a modality that uses computer-controlled jaw motion to generate wedge-shaped dose distributions. There are Varian enhanced dynamic wedges (EDWs) and Siemens virtual wedges (VWs). We recently commissioned dynamic wedges on both Varian and Siemens LINACs. The beam data, acquired with a Wellhöfer chamber array and a Sun Nuclear profiler, are used for modeling in the ADAC Pinnacle system. As recommended by ADAC, only a limited number of beam data is measured and used for beam modeling. Therefore, the dose distributions of dynamic wedges generated by Pinnacle must be examined. Following the commissioning of the dynamic wedges, we used Pinnacle to generate a number of dose distributions with different energies, wedge angles, field sizes, and depths. The computed data from Pinnacle are then compared with the measured data. The deviations of the output factor in all square and rectangular fields are mostly within 2.0% for both EDW and VW. For asymmetric fields, the deviations are within 3%. However, exceptions of differences more than 3% have been found in a larger field and large wedge combinations. The precision of the beam profiles generated by Pinnacle is also evaluated. As a result of this investigation, we present a scope of quality assurance tests that are necessary to ensure acceptable consistency between the delivered dose and the associated treatment plan when dynamic wedges are applied. PACS numbers: 8753 Dq, 87.53.Xd

The accuracy of dynamic wedge dose computation in the ADAC Pinnacle RTP system

The nonphysical wedge is a modality that uses computer‐controlled jaw motion to generate wedge‐shaped dose distributions. There are Varian enhanced dynamic wedges (EDWs) and Siemens virtual wedges (VWs). We recently commissioned dynamic wedges on both Varian and Siemens LINACs. The beam data, acquired with a Wellhöfer chamber array and a Sun Nuclear profiler, are used for modeling in the ADAC Pinnacle system. As recommended by ADAC, only a limited number of beam data is measured and used for beam modeling. Therefore, the dose distributions of dynamic wedges generated by Pinnacle must be examined. Following the commissioning of the dynamic wedges, we used Pinnacle to generate a number of dose distributions with different energies, wedge angles, field sizes, and depths. The computed data from Pinnacle are then compared with the measured data.The deviations of the output factor in all square and rectangular fields are mostly within 2.0% for both EDW and VW. For asymmetric fields, the deviations are within 3%. However, exceptions of differences more than 3% have been found in a larger field and large wedge combinations. The precision of the beam profiles generated by Pinnacle is also evaluated. As a result of this investigation, we present a scope of quality assurance tests that are necessary to ensure acceptable consistency between the delivered dose and the associated treatment plan when dynamic wedges are applied.PACS numbers: 8753 Dq, 87.53.Xd

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Focus on Software

Flexible tooling for localized electrochemical deposition with wire-electrodischarge grinding

This paper describes the application of electrodes with varying diameters made by wire-electrodischarge grinding (WEDG) in the localized electrochemical deposition (LECD) of nickel micro-columns. WEDG has been widely used in the fabrication of extremely fine cylindrical pins mainly used as tool electrodes for micro-electrodischarge machining of fine holes or as contoured cores in the electroforming of micropipes. Similar to electrolysis, LECD is a new deposition technique which uses conductive tips as anode electrodes to focus the electric field that drives the process such that deposition is largely localized on the smooth cathode surface beneath the anode tip. The degree of localization depends mainly on the anode diameter, the anode-to-cathode separation, the insulation or non-insulation of the anode, and the computer-controlled motion of the anode tip during the deposition process. Considering the parameter of anode tip diameter alone, the ability to fabricate tips of differing diameters will allow a wide range in resolution of structures deposited via LECD. WEDG provides this flexible tooling for LECD at the micro to meso-scale. Experiments were carried out on a custom-built LECD rig on which nickel columns were deposited from a nickel sulphamate plating solution, using stationary and rotating WEDG-ed tips with diameters ranging from 25 to 120 μm. Aspect ratios of up to 9:1 were achieved and deposited column diameters were found to display a linear relationship with the WEDG-ed anode tip diameters. Electrode rotation was also found to improve column cross-sectional roundness and overall dimensional control for fabrication with LECD.

The application of electron beam delivery using dose rate variation and dynamic couch motion in conformal treatment of the cranial-spinal axis

Radiation therapy to the cranial-spinal axis is typically targeted to the spinal cord and to the cerebrospinal fluid (CSF) in the subarachnoid space adjacent to the spinal cord and brain. Standard techniques employed in the treatment of the whole central nervous system do little to compensate for the varying depths of spinal cord along the length of the spinal field. Lateral simulation films, sagittal magnetic resonance imaging (MRI), or computerized tomography (CT) are used to estimate an average prescription depth for treatment along the spine field. However, due to the varying depth of the target along the spinal axis, even with the use of physical compensators, there can be considerable dose inhomogeneity along the spine field. With the advent of treatment machines that have full dynamic capabilities, a technique has been devised that will allow for more conformal dose distribution along the full length of the spinal field. This project simulates this technique utilizing computer-controlled couch motion to deliver multiple small electron beams of differing energies and intensities. CT planning determines target depth along the entire spine volume. The ability to conform dose along the complete length of the treatment field is investigated through the application of superpositioning of the fields as energies and intensities change. The positioning of each beam is registered with the treatment couch dynamic motion. This allows for 1 setup in the treatment room rather than multiple setups for each treatment position, which would have been previously required. Dose-volume histograms are utilized to evaluate the dose delivered to structures in the beam exit region. This technique will allow for precise localization and delivery of a homogeneous dose to the entire CSF space.

Spherical navigator echoes for full 3D rigid body motion measurement in MRI.

We developed a 3D spherical navigator (SNAV) echo technique that can measure rigid body motion in all six degrees of freedom simultaneously by sampling a spherical shell in k-space. 3D rotations of an imaged object simply rotate the data on this shell and can be detected by registration of k-space magnitude values. 3D translations add phase shifts to the data on the shell and can be detected with a weighted least-squares fit to the phase differences at corresponding points. MRI pulse sequences were developed to study k-space sampling strategies on such a shell. Data collected with a computer-controlled motion phantom with known rotational and translational motions were used to evaluate the technique. The accuracy and precision of the technique depend on the sampling density. Roughly 2000 sample points were necessary for accurate detection to within the error limits of the motion phantom when using a prototype time-intensive sampling method. This number of samples can be captured in an approximately 27-ms double excitation SNAV pulse sequence with a 3D helical spiral trajectory. Preliminary results with the helical SNAV are encouraging and indicate that accurate motion measurement suitable for retrospective or prospective correction should be feasible with SNAV echoes.

Inverse kinematics model of parallel macro-micro manipulator system

An improved design, which employs the integration of optic, mechanical and electronic technologies for the next generation large radio telescope, is presented in this note. The authors propose the concept of parallel macro-micro manipulator system from the feed support structure with a rough tuning subsystem based on a cable structure and a fine tuning subsystem based on the Stewart platform. According to the requirement of astronomical observation, the inverse kinematics model of this parallel macro-micro manipulator system is deduced. This inverse kinematics model is necessary for the computer-controlled motion of feed.

Experimental observation of dip-coating phenomena and the prospect of using motion control to minimize fluid retention

A computer controlled dip-coating apparatus was constructed to investigate physical aspects of transient coating processes and the feasibility of minimizing fluid retention during such operations. Electrobalance measurement of mass retention and drainage has elucidated a number of features which have not received prior notice. Relaxation processes were observed when the substrate motion was halted: the long-time behavior agreed with a combination of Landau–Levich and Jeffreys theories. However, short-time meniscus relaxation produced significant departures which are not fully understood. Comparisons of fluid retention were made for variable draw lengths: good agreement between Landau–Levich theory and experiment was observed even for very short withdrawal lengths, indicating the rapid transition to the steady-state regime. Computer-controlled substrate motion was performed to acquire preliminary information of its effect on mass retention. We investigated constant acceleration and constant speed withdrawal segments over a fixed process time. Experiments involving constant speed withdrawal periods interrupted by drainage periods revealed that more interruptions produced less fluid retention overall; in the limit of an infinite number of interruptions, the retention reached a minimum — equivalent to withdrawing the plate at the time-averaged speed. In addition, ramped speed experiments indicated very little difference over the accessible motion range. As a whole, the study revealed no procedures which could reduce mass retention below that which would be obtained with the slowest allowable constant speed withdrawal.

Design and Validation of a Motion Stage for In Vitro MR Experiments

A computer-controlled motion stage was designed to facilitate motion studies and simulations of cardiac magnetic resonance (MR) experiments. The stage was constructed to move a phantom of up to 6 kg at velocities up to 15 cm/sec along a two-dimensional trajectory within an MR scanner. The operation of the motion stage was validated and found to be accurate to within 0.08 cm in displacement and 1.5 cm/sec in velocity (root-mean-square error). No image degradation was observed.J. Magn. Reson. Imaging 1999;10:972–977. © 1999 Wiley-Liss, Inc.

Design and validation of a motion stage for in vitro MR experiments.

A computer-controlled motion stage was designed to facilitate motion studies and simulations of cardiac magnetic resonance (MR) experiments. The stage was constructed to move a phantom of up to 6 kg at velocities up to 15 cm/sec along a two-dimensional trajectory within an MR scanner. The operation of the motion stage was validated and found to be accurate to within 0.08 cm in displacement and 1.5 cm/sec in velocity (root-mean-square error). No image degradation was observed.J. Magn. Reson. Imaging 1999;10:972-977.

Proposal of A New Space Atomic Frequency Standard

A new prototype atomic fountain clock working in the micro-gravity environment is proposed. The successive Ramsey interactions of cold atoms and oscillatory field are realized by means of computer-controlled periodic motion of oscillatory field while the cold atoms stay still relatively in the prototype. Preliminary analyses in comparison with the atomic fountain clock working on the ground show that higher stability is obtainable in the prototype.

The Torus Treadmill: realizing locomotion in VEs

Locomotion in virtual environments (VEs) remains one of the major problems in current virtual reality research. The most intuitive way to move about the real world is to travel on foot. People often feel a better sense of distance or direction while walking than while riding in a vehicle. This article discusses the development of a locomotion device that provides a sense of walking. In terms of natural interaction, the physical exertion of walking proves essential to locomotion. The research of my colleagues and I aims to give users a sense of walking while their position remains localized in the physical world. We've developed several prototypes of interface devices for walking. From the results of our research, we concluded that an infinite surface would offer an ideal means for giving people a sense of walking. Our device, called the Torus Treadmill, uses a torus-shaped surface to realize the locomotion interface. The surface employs 12 sets of treadmills connected side-by-side and driven in a perpendicular direction. These treadmills generate an infinite surface. We measured the motion of the users' feet with magnetic sensors. The floor moves in the opposite direction of the walker, canceling the motion of each step. The walker's position remains localized in the real world by this computer-controlled motion of the floor. The walker can freely change direction. An image of the virtual space appears in a head-mounted display corresponding to the walker's virtual position.