Optical Tracking Techniques Research Articles

Experimental investigation of pressure statistics in laboratory homogeneous isotropic turbulence

Pressure gradient and pressure play a key role in the evolution of structures and energy redistribution in turbulence. However, experimental investigations of pressure statistics in turbulent flows are difficult. With development in optical Lagrangian particle tracking (LPT) techniques over the past decades, it is now possible to obtain the pressure gradient fields with high accuracy from the measured acceleration fields, which gives an inspiration to study pressure statistics experimentally. In this work, we construct the instantaneous pressure and pressure gradient fields by the divergence curl correction method, using Lagrangian particle tracking data from laboratory turbulence generated in our turbulence exploration apparatus (TEA), which is newly developed with eight forcing elements arranged symmetrically in space. The measured velocity and acceleration statistics show that the laboratory turbulence in the TEA system is very close to be homogeneous and isotropic. The statistics of pressure gradient and velocity correlation conditioned on velocity confirm the interesting role of pressure gradient in the redistribution of energy in turbulence. In particular, these statistics of pressure gradient are not sensitive to spatial filtering with a filter size up to the lower end of the inertial range, indicating that these statistics capture the characteristics of the pressure gradient at scales in the inertial range or above.

Experimental investigation of particle aggregation in a humid and turbulent environment

Aggregation of wetted particles in a turbulent flow is experimentally investigated. The particles settle through nearly isotropic turbulence inside a humid air chamber. The particles are pre-chilled so that wetting occurred even at sub-saturated humidity levels. Aggregates that fall out of the turbulent flow are physically sampled and their size distributions quantified to infer bulk sticking efficiencies at various humidity levels. Optical particle tracking techniques are used to detect individual time-resolved collision events, forming an independent measure of the sticking efficiency parameterized by a collision Stokes number. The two methods are contrasted and the limitations of each are discussed. The data are used to develop a new version of the early Costa sticking model, which is utilized by various volcanic ash transport codes. The key outcome of this work is a generalized Costa sticking model which incorporates the effect of the water film thickness coating the particles.

Excess entropy and long-time diffusion in colloidal fluids with short-range interparticle attraction.

Liquid structure and dynamics are experimentally investigated in colloidal suspensions with short-range depletion attraction. The colloidal fluid samples consist of hard-sphere colloidal particles suspended along with rodlike depletants based on surfactant micelles. The spheres have a range of surface chemistries, diameters, and packing fractions, and the rodlike micelle length depends on the temperature. Thus, the combination of hard-spheres and depletants generates a sample wherein short-range interparticle attraction can be temperature-tuned in situ. Video optical microscopy and particle tracking techniques are employed to measure particle trajectories from which structural and dynamical quantities are derived, including the particle pair correlation function [g(r)], mean square displacement, long-time diffusion coefficient, and the sample two-body excess entropy (S2). The samples with stronger short-range attractions exhibit more order, as characterized by g(r) and S2. The stronger short-range attractions are also observed to lead to slower long-time diffusion and more heterogeneous dynamics at intermediate time scales. Finally, the excess entropy scaling law prediction, i.e., the exponential relationship between two-body excess entropy and long-time diffusivity, is observed across the full range of samples.

Robotic hip joint testing: Development and experimental protocols

The use of robotic systems combined with force sensing is emerging as the gold standard for in vitro biomechanical joint testing, due to the advantage of controlling all six degrees of freedom independently of one another. This paper describes a novel robotic platform and the experimental protocol used for hip joint testing. An experimental protocol implemented optical tracking and registration techniques in order to define the position of the hip joint centre of rotation (COR) in the coordinate system of the robot's end effector. The COR coordinates defined the origin of the task-related coordinate system used to control the robot, with a hybrid force/position law to simulate standard clinical tests. The axes of this frame were defined using the International Society of Biomechanics (ISB) anatomical coordinate system.Experiments were carried out on two cadaveric hip joint specimens using the robotic testing platform and a mechanical testing rig previously developed and described by our group. Simulated internal-external and adduction/abduction laxity tests were carried out with both systems and the resulting peak range of motion (ROM) was measured. Similarities and differences were observed in these experiments, which were used to highlight some of the limitations of conventional systems and the corresponding advantages of robotics, further emphasising their added value in vitro testing.

Optical Hand Tracking: A Novel Technique for the Assessment of Bradykinesia in Parkinson's Disease.

Evaluation of therapies for Parkinson's disease (PD) may benefit from objective quantification of the separate movement components of bradykinesia (i.e., velocity, amplitude, and rhythm). This study evaluated the sensitivity and reliability of parameters derived from recently available optical hand tracking techniques for patient-friendly, automated quantification of bradykinesia of the upper extremity in PD. Fifty-seven patients with PD and 57 healthy individuals (controls) performed repetitive finger tapping (RFT), alternating hand movements (AHM), and alternating forearm movements (AFM). Movement components of bradykinesia (i.e., velocity, frequency, amplitude, hesitations, and halts) were quantified using optical hand tracking. Reliability was quantified using intraclass correlation coefficients in a subgroup of 12 patients with PD and 12 controls (test-retest) and in all 57 controls (intra-trial). RFT and AHM were successfully recorded in 94% of all participants. Movement components differed between patients with PD and controls and were correlated with clinical ratings. Velocity and halt duration appeared to be most useful (i.e., the largest difference between the PD and control groups, good reliability) for the quantification of RFT, whereas frequency appeared to be most useful for the quantification of AHM. Other variables, such as frequency and amplitude of RFT, showed poor test-retest reliability, because they were susceptible to changes in movement strategy. AFM was excluded from the analysis because of problems with hand recognition. Novel optical hand tracking techniques yield promising results for patient-friendly quantification of bradykinesia of the upper extremity in PD. Future work should aim to optimize optical hand tracking and reduce susceptibility to changes in strategy.

Evaluation of Optical Flow Tracking Techniques in Cardiac Magnetic Resonance: Numerical Study

Evaluation of Optical Flow Tracking Techniques in Cardiac Magnetic Resonance: Numerical Study

Damping and non-linearity of a levitating magnet in rotation above a superconductor

We study the dissipation of moving magnets in levitation above a superconductor. The rotation motion is analyzed using optical tracking techniques. It displays a remarkable regularity together with long damping time up to several hours. The magnetic contribution to the damping is investigated in detail by comparing 14 distinct magnetic configurations and points towards amplitude-dependent dissipation mechanisms. The non-linear dynamics of the mechanical rotation motion is also revealed and described with an effective Duffing model. The magnetic mechanical damping is consistent with measured hysteretic cycles M(H) that are discussed within a modified critical state model. The obtained picture of the coupling of levitating magnets to their environment sheds light on their potential as ultra-low dissipation mechanical oscillators for high precision physics.

Quantum-Limited Mirror-Motion Estimation

We experimentally demonstrate optomechanical motion and force measurements near the quantum precision limits set by the quantum Cramér-Rao bounds. Optical beams in coherent and phase-squeezed states are used to measure the motion of a mirror under an external stochastic force. Utilizing optical phase tracking and quantum smoothing techniques, we achieve position, momentum, and force estimation accuracies close to the quantum Cramér-Rao bounds with the coherent state, while the estimation using squeezed states shows clear quantum enhancements beyond the coherent-state bounds.

Computer-Aided Dental Implant Technology

Dental Implant is a sophisticated dental surgery. Dentists must suffer fine oral surgery training so that the development of a professional dentist is quite time-consuming. We combine the medical image processing reconstruction and optical tracking techniques to provide a realistic teaching environment. The system can help dentists learning all steps during the surgery. We hope this system can increase the success ratio of surgery and lower the surgery risks. Our medical image reconstruction is reached by the toolkits named VTK. The stereo vision algorithm is introduced into this study to construct the optical tracking system. This system will provide a good study experience for dentists and to assist them during the implant surgery. After several dental medical materials show, most responses are positive. Most dentists are very interested in our system and recognize our system can greatly shorten the dental training time. During the surgery, the difficulty will also be drop down with the assistance of our system.

Magnetic tracking of eye position in freely behaving chickens

Research on the visual system of non-primates, such as birds and rodents, is increasing. Evidence that neural responses can differ dramatically between head-immobilized and freely behaving animals underlines the importance of studying visual processing in ethologically relevant contexts. In order to systematically study visual responses in freely behaving animals, an unobtrusive system for monitoring eye-in-orbit position in real time is essential. We describe a novel system for monitoring eye position that utilizes a head-mounted magnetic displacement sensor coupled with an eye-implanted magnet. This system is small, lightweight, and offers high temporal and spatial resolution in real time. We use the system to demonstrate the stability of the eye and the stereotypy of eye position during two different behavioral tasks in chickens. This approach offers a viable alternative to search coil and optical eye tracking techniques for high resolution tracking of eye-in-orbit position in behaving animals.

Computing Myocardial Motion in 4-Dimensional Echocardiography

We describe a novel method for computing dense 3D myocardial motion with high accuracy in four-dimensional (4D) echocardiography (3 dimensions spatial plus time). The method is based on a classic variational optical flow technique but exploits modern developments in optical flow research to utilize the full capabilities of 4D echocardiography. Using a variety of metrics, we present an in-depth performance evaluation of the method on synthetic, phantom, and intraoperative 4D transesophageal echocardiographic data. When compared with state-of-the-art optical flow and speckle tracking techniques currently found in 4D echocardiography, the method we present shows notable improvements in error rates. We believe the performance improvements shown can have a positive impact when the method is used as input for various applications, such as strain computation, biomechanical modeling, and automated diagnostics.

Tracking the eye non-invasively: simultaneous comparison of the scleral search coil and optical tracking techniques in the macaque monkey

From human perception to primate neurophysiology, monitoring eye position is critical to the study of vision, attention, oculomotor control, and behavior. Two principal techniques for the precise measurement of eye position—the long-standing sclera-embedded search coil and more recent optical tracking techniques—are in use in various laboratories, but no published study compares the performance of the two methods simultaneously in the same primates. Here we compare two popular systems—a sclera-embedded search coil from C-N-C Engineering and the EyeLink 1000 optical system from SR Research—by recording simultaneously from the same eye in the macaque monkey while the animal performed a simple oculomotor task. We found broad agreement between the two systems, particularly in positional accuracy during fixation, measurement of saccade amplitude, detection of fixational saccades, and sensitivity to subtle changes in eye position from trial to trial. Nonetheless, certain discrepancies persist, particularly elevated saccade peak velocities, post-saccadic ringing, influence of luminance change on reported position, and greater sample-to-sample variation in the optical system. Our study shows that optical performance now rivals that of the search coil, rendering optical systems appropriate for many if not most applications. This finding is consequential, especially for animal subjects, because the optical systems do not require invasive surgery for implantation and repair of search coils around the eye. Our data also allow laboratories using the optical system in human subjects to assess the strengths and limitations of the technique for their own applications.

An Optical-Tracking Calibration Method for MEMS-Based Digital Writing Instrument

A μIMU which consists of microelectromechanical systems (MEMS) accelerometers, gyroscopes and magnetometers has been developed for real-time estimation of human hand motions. Along with appropriate transformation and filtering algorithms, the μ IMU was implemented as a Ubiquitous Digital Writing Instrument (UDWI), which could interface with PCs in real-time via Bluetooth wireless protocol, to record the handwriting on any flat surface. However, because of the MEMS sensors' intrinsic biases and random noise such as circuit thermal noise, an effective calibration system that provides good reference measurement parameters must be developed to compare the output of the μIMU sensors to human hand motions. In this paper, we present our development of a method to calibrate three-dimensional linear accelerations and angular velocities of human writing motions measured from MEMS sensors through optical tracking techniques. In our experiments, English alphabets were written by the UDWI on a horizontal plane. The sensor output from the writing motions were transmitted wirelessly to a PC and the data were stored in the PC. Simultaneously, we recorded the pen-tip motion during the writing of each alphabet with a high-speed camera, which allowed us to exact the acceleration, velocity, and position of the UDWI's tip through appropriate optical-tracking algorithms. Then, the information is compared with the motion information obtained from the MEMS sensors in the UDWI. The motion data obtained from the high-speed camera are much more accurate, and hence could be used as reference motion data to analyze the performance of the UDWI, and eventually allows improvement of the UDWI performance.

TH-B-204B-01: Advanced Optical Imaging and Tracking Techniques for IGRT

Optical guidance (OG) such as optical distance indicator (ODI) in‐room laser alignment and live‐video camera monitoring has been routinely used in conventional radiotherapy for patient setup and monitoring. Now emerging OG using optical tracking and topologic imaging (stereovision) techniques can provide remote operators with real‐time measurements of patient body (or support apparatus) position shape and movement. The temporal and spatial OG will be an essential component in any advanced image‐guidedradiotherapy(IGRT) when patient or organ motion are considered during the dose delivery. In assisting users to become familiar with the new OG techniques this education session will start with an introduction on basic photogrammetry general camera calibration triangulation principle for 3D optical imagingsurface extraction and registration and what OG systems can and cannot do. Then the session will move to the clinical use of infrared patient positioning and tracking systems (IPT) with particular attention to the combined use with other imagingsystems detection and correction with six degrees of freedom for rigid body displacement and issues in attachment of the infrared reflection markers. That will lead up to actual use ISG integrated stereovision‐guided patient reposition and monitoring systems focusing on quantification of the body position and displacement prior to and during beam or arc irradiation. ISG adaptive radiotherapy of the brain H&N lung and breast cancer will be demonstrated using examples from early clinical trials. The effects of target motion and deformation skin tones and room light conditions are also discussed. Learning Objectives: 1. Understand the spatial and temporal characteristics of advanced OG 2. Understand the basic operation principle of 3D optical systems 3. Know how to check and calibrate the optical camerasystems 4. Understand why multiple infrared reflection markers have to be fastened to the patient 5. Know how to quantify and correct the displacements with six‐degrees of freedom 6. Know how to surrogate optical surfaceimages with CT/MR volumetric images 7. Know how to acquire reliable surfaceimages prior to and during X‐ray irradiation 8. Understand the limits and benefits in application of OG in clinical settings

A new approach to quantify the mechanical and radiation isocentres of radiotherapy treatment machine gantries

In this paper a new method is proposed to quantify and reduce the radiation beam position uncertainty due to the radiotherapy treatment machine gantry deflection. A new tool has been designed and manufactured to provide the means to measure the alignment of the collimator axis and of the beam central axis in space, using the NDI Polaris optical tracking system and Gafchromic® films. The tool can be mounted onto the accessory tray of the linacs from different manufacturers. The approach has been demonstrated with measurements of the mechanical isocentre being performed on ten linacs from three major manufacturers at four clinical sites. Measurements of the radiation isocentre were performed on a single linac. The collimator axis trajectory is modelled using a vector-end effector in order to provide more information than standard mechanical assessment methods. The method uses a mathematical optimization technique to calculate the position of the mechanical isocentre and the ‘size’ of the collimator axes intersection locus. Deviations of the collimator axes from the isocentre are expressed in terms of systematic and random error. The effects of measurement uncertainties are evaluated both via simulations and experimentally. The use of optical tracking and optimization techniques combined with an operator-induced measurement error compensation algorithm leads to a faster measurement of the mechanical isocentre (20 min for 24 angles) and eliminates operator-induced uncertainties. The uncertainty of the measurement of the mechanical isocentre was between 40 µm and 70 µm in terms of standard deviation. For some of the linacs assessed, the mechanical isocentre obtained using a standard approach with an adjustable pointer was displaced by over 1 mm from that found with the proposed method. The radii of the collimator axes intersection locus found with the proposed method were between 0.4 mm and 0.72 mm for the linacs assessed. Film measurement revealed a misalignment of the mechanical isocentre and the radiation isocentre by 0.4 mm. The proposed method potentially enables a reduction of the beam position uncertainty. This may be achieved at the planning stage by compensating for the identified systematic collimator axes deviations which were found to be reproducible. The method also creates a potential for using different setup margins independently for each axis and for each gantry angle, calculated specifically for a given linac.

Integration of Enhanced Optical Tracking Techniques and Imaging in IGRT

In external beam radiotherapy, modern technologies for dynamic dose delivery and beam conformation provide high selectivity in radiation dose administration to the pathological volume. A comparable accuracy level is needed in the 3-D localization of tumor and organs at risk (OARs), in order to accomplish the planned dose distribution in the reality of each irradiation session. In-room imaging techniques for patient setup verification and tumor targeting may benefit of the combined daily use of optical tracking technologies, supported by techniques for the detection and compensation of organ motion events. Multiple solutions to enhance the use of optical tracking for the on-line correction of target localization uncertainties are described, with specific emphasis on the compensation of setup errors, breathing movements and non-rigid deformations. The final goal is the implementation of customized protocols where appropriate external landmarks, to be tracked in real-time by means of non-invasive optical devices, are selected as a function of inner target localization. The presented methodology features high accuracy in patient setup optimization, also providing a valuable tool for on-line patient surveillance, taking into account both breathing and deformation effects. The methodic application of optical tracking is put forward to represent a reliable and low cost procedure for the reduction of safety margins, once the patient-specific correlation between external landmarks and inner structures has been established. Therefore, the integration of optical tracking with in-room imaging devices is proposed as a way to gain higher confidence in the framework of Image Guided Radiation Therapy (IGRT) treatments.

Nonintrusive rigid body tracking technique for dry particulate flows. Part I. Theoretical aspects

A unique system to nonintrusively track a particle in three dimensions is presented. It is based on the principle of magnetic induction coupling and consists of small transmitters mounted inside the particle being tracked, and a set of receiving antennae surrounding the experimental apparatus. In Part I of the sequence of two papers, the focus is on the theoretical aspects, in particular, on developing a computational technique to solve the inverse problem, i.e., find the three-dimensional position as well as orientation of the particle from the voltages induced in the antennae. The computational technique is based on the Levenberg–Marquardt algorithm, along with a scheme for providing good initializations. Through simulated experiments that include various levels of added noise in the voltage readings, the success of this algorithm is demonstrated and the feasibility of the overall technique is established. It is also shown that a system with three mutually orthogonal transmitters provides accurate results even with the noise in the voltage data. Although this system is intended for use in experimental studies of dry granular flows, it has wide applicability due to its nonintrusive nature, and is particularly useful when optical tracking techniques are not feasible.

Nonintrusive rigid body tracking technique for dry particulate flows. Part II. Practical aspects and implementation

A system, based on the principle of magnetic induction coupling, to track a particle nonintrusively in three dimensions is presented. It consists of small transmitters mounted inside the particle being tracked, and a set of receiving antennae surrounding the experimental apparatus. In Part I of the sequence of two papers, the focus is on the theoretical aspects, in particular, on developing a computational technique to solve the inverse problem of finding the three-dimensional position as well as orientation of the particle from the voltages induced in the antennae. In Part II the focus is on the actual system development, including all hardware and data acquisition aspects. The results presented here are comprehensive, as they include details of hardware/electronics, comparison of induced voltage model and actual measurements, and a set of actual tracking results. Through test experiments that include a variety of real-time trajectories, this system is tested and its success is demonstrated. Results of real trajectories of a single ball rising in a mass of other spheres in a vibrated bed are also shown. Although this system is intended for use in experimental studies of dry granular flows, it has wide applicability due to its nonintrusive nature, and is particularly useful when optical tracking techniques are not feasible.