Estimation of the finite center of rotation in planar movements.

The finite center of rotation (FCR) is often used to assess joint function. It was the purpose of this study to compare the accuracy of the procedure of Crisco et al. [4] for estimating the FCR with a procedure which uses least-squares principles. The procedures were evaluated using noisy data rotated about a known FCR. Both procedures demonstrated increasing accuracy of FCR estimation with increasing rotation angle. As the centroid of a pair of markers was moved further from the FCR, accuracy of its location decreased. Noise levels had a strong influence on FCR estimation accuracy, with the least-squares procedure being better able to cope with noise. Increasing the number of landmarks increased FCR estimation accuracy. The accuracy of the procedure of Crisco et al. [4] increased when multiple estimates of the FCR were averaged. On all of the evaluations performed, the least-squares procedure gave small improvements in the accuracy of estimating the FCR, but was not able to circumvent the inaccuracies which arise when landmarks are not appropriately positioned, numerous, or if the rotation angle is small.     

Accuracy and repeatability of quantitative fluoroscopy for the measurement of sagittal plane translation and finite centre of rotation in the lumbar spine

Quantitative fluoroscopy (QF) was developed to measure intervertebral mechanics in vivo and has been found to have high repeatability and accuracy for the measurement of intervertebral rotations. However, sagittal plane translation and finite centre of rotation (FCR) are potential measures of stability but have not yet been fully validated for current QF. This study investigated the repeatability and accuracy of QF for measuring these variables. Repeatability was assessed from L2-S1 in 20 human volunteers. Accuracy was investigated using 10 consecutive measurements from each of two pairs of linked and instrumented dry human vertebrae as reference; one which tilted without translation and one which translated without tilt. The results found intra- and inter-observer repeatability for translation to be 1.1 mm or less (SEM) with fair to substantial reliability (ICC 0.533–0.998). Intra-observer repeatability of FCR location for inter-vertebral rotations of 5° and above ranged from 1.5 mm to 1.8 mm (SEM) with moderate to substantial reliability (ICC 0.626–0.988). Inter-observer repeatability for FCR ranged from 1.2 mm to 5.7 mm, also with moderate to substantial reliability (ICC 0.621–0.878). Reliability was substantial (ICC > 0.81) for 10/16 measures for translation and 5/8 for FCR location. Accuracy for translation was 0.1 mm (fixed centre) and 2.2 mm (moveable centre), with an FCR error of 0.3 mm(x) and 0.4 mm(y) (fixed centre). This technology was found to have a high level of accuracy and with a few exceptions, moderate to substantial repeatability for the measurement of translation and FCR from fluoroscopic motion sequences.     

An automatic method for determining the centre of rotation of a mechanically scanned reflection UCT system

A method will be described for determining the centre of rotation of a mechanically scanned reflection ultrasound computed tomography system. It is based on the principle of obtaining opposing images of a test object containing many point targets. The method is automatic in the sense that the centre of rotation is calculated by a computer without the need for an operator to make direct measurements on the mechanical system. For the particular reflection UCT system described here, the centre of rotation is obtained in 3-5 min with a repeatability (+/-2 SD) of +/-0.3 mm. Ways in which even higher accuracy can be obtained are discussed. The basic principle of the method is applicable to any concentric imaging system for which a good approximation to an ideal point target can be produced.     

Three-dimensional analysis of cervical spine segmental motion in rotation

Introduction

The movements of the cervical spine during head rotation are too complicated to measure using conventional radiography or computed tomography (CT) techniques. In this study, we measure three-dimensional segmental motion of cervical spine rotation in vivo using a non-invasive measurement technique.

Material and methods

Sixteen healthy volunteers underwent three-dimensional CT of the cervical spine during head rotation. Occiput (Oc) – T1 reconstructions were created of volunteers in each of 3 positions: supine and maximum left and right rotations of the head with respect to the bosom. Segmental motions were calculated using Euler angles and volume merge methods in three major planes.

Results

Mean maximum axial rotation of the cervical spine to one side was 1.6° to 38.5° at each level. Coupled lateral bending opposite to lateral bending was observed in the upper cervical levels, while in the subaxial cervical levels, it was observed in the same direction as axial rotation. Coupled extension was observed in the cervical levels of C5-T1, while coupled flexion was observed in the cervical levels of Oc-C5.

Conclusions

The three-dimensional cervical segmental motions in rotation were accurately measured with the non-invasive measure. These findings will be helpful as the basis for understanding cervical spine movement in rotation and abnormal conditions. The presented data also provide baseline segmental motions for the design of prostheses for the cervical spine.     

Contact mechanics of a thin-walled capsule adhered onto a rigid planar substrate

A thin-walled capsule, modelled as an incompressible liquid droplet contained in a thin flexible membrane, was allowed to adhere onto a rigid substrate. The contact mechanics were formulated, based on linear elasticity, to portray quantitatively the relationships between osmotic inflation, contact area and angle, membrane stretching and adhesion strength. The predicted results shed light on fundamental adhesive contact mechanics in a cell-substrate system.     

A fast method for calibrating video-based motion analysers using only a rigid bar

Video-camera systems are widely used in biomechanics and clinical fields to measure the 3D kinematic measurements of human motion. To be used, they need to be calibrated, that is the parameters which geometrically define the cameras have to be determined. It is shown here how this can be achieved by surveying a rigid bar in motion inside the working volume, and in a very short time: less than 15 s on a Pentium III. The exterior parameters are estimated through the coplanarity constraint, the camera focal lengths through the properties of epipolar geometry and the principal points with a fast evolutionary optimisation which guarantees convergence when the initial principal points cannot be adequately estimated. The method has been widely tested on simulated and real data. Results show that its accuracy is comparable with that obtained using methods based on points of known 3D coordinates (DLT): 0.37 mm RMS error over a volume with a diagonal ≈1.5m. A preferential absolute reference system is obtained from the same bar motion data and is used to guide an intelligent decimation of the data. Finally, the role that the principal points play in achieving a high accuracy, which is questioned in the computer vision domain, is assessed through simulations.     

Compensation of in-plane rigid motion for in vivo intracoronary ultrasound image sequence

Intracoronary ultrasound (ICUS) is an interventional imaging modality that is used to acquire a series of tomographic images from the vascular lumen, for diagnosis and treatment of coronary artery diseases in clinical settings. Motion artifacts caused by cardiac dynamics and the pulsatile blood flow within the vascular lumen, during continuous pullback (non-gated) ICUS image acquisition, hinder visualization of longitudinal cuts, assessment of arterial morphology and hemodynamics, and three-dimensional (3-D) vessel reconstruction. The aim of this study is to develop a method to compensate for in-plane rigid motion in non-gated in vivo ICUS sequences. The signals associated with cardiac motion are first detected from the gray-scale image sequence. They are represented with rigid motion parameters between luminal contours extracted from successive slices. Subsequently, the signals were filtered to separate the dynamic components caused by cardiac motion from those caused by the irregular morphology of the vascular lumen. Dynamic components were then compensated by performing a back transformation of related pixels within the vessel region in each frame. The method is validated by computer-simulation and using real ICUS image data. Possible sources of error are discussed based on the experimental results.     

A planar finite element model of bolus containment in the oral cavity

As individuals age, one of the objective changes that occurs in the oropharyngeal swallow is the development of a delay between bolus entry into the pharynx and the initiation of airway protection mechanisms. For longer delays, this phenomenon is sometimes referred to as "premature spillage," and it has been suggested that such spillage, which is a risk factor for dysphagia, may be associated with pre-swallow lingual gestures, or "tongue pumping." The goal of the current study was to develop a simplified two-dimensional computational model of the oropharynx to simulate the containment of a Newtonian fluid bolus within the oral cavity in response to a given pattern of lingual gestures for different viscosities. An arbitrary Lagrangian-Eulerian simulation was performed using the commercial finite element software package, LS-Dyna. It was found that for a given lingual motion, higher viscosity Newtonian boluses, consistent with those offered therapeutically, were able to be contained within the simulated oral cavity while a lower viscosity bolus would be "spilled," suggesting a potential mechanisim by which thickened liquids may reduce aspiration. Although the current data must be validated with more realistic, three-dimensional geometric information and for a wider range of bolus rheologies, they represent an exciting first step towards realistic modeling of oropharyngeal bolus flow.     

A method of calculating a lung clinical target volume DVH for IMRT with intrafractional motion

The motion of lung tumors from respiration has been reported in the literature to be as large as 1-2 cm. This motion requires an additional margin between the Clinical Target Volume (CTV) and the Planning Target Volume (PTV). In Intensity Modulated Radiotherapy (IMRT), while such a margin is necessary, the margin may not be sufficient to avoid unintended high and low dose regions to the interior on moving CTV. Gated treatment has been proposed to improve normal tissues sparing as well as to ensure accurate dose coverage of the tumor volume. The following questions have not been addressed in the literature: (a) what is the dose error to a target volume without a gated IMRT treatment? (b) What is an acceptable gating window for such a treatment. In this study, we address these questions by proposing a novel technique for calculating the three-dimensional (3-D) dose error that would result if a lung IMRT plan were delivered without a gated linac beam. The method is also generalized for gated treatment with an arbitrary triggering window. IMRT plans for three patients with lung tumors were studied. The treatment plans were generated with HELIOS for delivery with 6 MV on a CL2100 Varian linear accelerator with a 26 pair MLC. A CTV to PTV margin of 1 cm was used. An IMRT planning system searches for an optimized fluence map phi(x,y) for each port, which is then converted into a dynamic MLC file (DMLC). The DMLC file contains information about MLC subfield shapes and the fractional Monitor Units (MUs) to be delivered for each subfield. With a lung tumor, a CTV that executes a quasiperiodic motion z(t) does not receive phi(x,y), but rather an Effective Incident Fluence EIF(x,y). We numerically evaluate the EIF(x,y) from a given DMLC file by a coordinate transformation to the Target's Eye View (TEV). In the TEV coordinate system, the CTV itself is stationary, and the MLC is seen to execute a motion -z(t) that is superimposed on the DMLC motion. The resulting EIF(x,y) is input back into the dose calculation engine to estimate the 3-D dose to a moving CTV. In this study, we model respiratory motion as a sinusoidal function with an amplitude of 10 mm in the superior-inferior direction, a period of 5 s, and an initial phase of zero.     

A profile of glenohumeral internal and external rotation motion in the uninjured high school baseball pitcher, part I: motion

Context:

The magnitude of motion that is normal for the throwing shoulder in uninjured baseball pitchers has not been established. Chronologic factors contributing to adaptations in motion present in the thrower''s shoulder also have not been established.

Objectives:

To develop a normative profile of glenohumeral rotation motion in uninjured high school baseball pitchers and to evaluate the effect of chronologic characteristics on the development of adaptations in shoulder rotation motion.

Design:

Cohort study.

Setting:

Baseball playing field.

Patients or Other Participants:

A total of 210 uninjured male high school baseball pitchers (age = 16±1.1 years, height = 1.8 + 0.1 m, mass = 77.5±11.2 kg, pitching experience = 6±2.3 years).

Intervention(s):

Using standard goniometric techniques, we measured passive rotational glenohumeral range of motion bilaterally with participants in the supine position.

Main Outcome Measure(s):

Paired t tests were performed to identify differences in motion between limbs for the group. Analysis of variance and post hoc Tukey tests were conducted to identify differences in motion by age. Linear regressions were performed to determine the influence of chronologic factors on limb motion.

Results:

Rotation motion characteristics for the population were established. We found no difference between sides for external rotation (ER) at 0° of abduction (t₂₀₉ = 0.658, P = .51), but we found side-to-side differences in ER (t₂₀₉ = −13.012, P<.001) and internal rotation (t₂₀₉ = 15.304, P<.001) at 90° of abduction. Age at the time of testing was a significant negative predictor of ER motion for the dominant shoulder (R² = 0.019, P = .049) because less ER motion occurred at the dominant shoulder with advancing age. We found no differences in rotation motion in the dominant shoulder across ages (F_4,205 range, 0.451–1.730, P>.05).

Conclusions:

This range-of-motion profile might be used to assist with the interpretation of normal and atypical shoulder rotation motion in this population. Chronologic characteristics of athletes had no influence on range-of-motion adaptations in the thrower''s shoulder.     

A finite state model for respiratory motion analysis in image guided radiation therapy

Effective image guided radiation treatment of a moving tumour requires adequate information on respiratory motion characteristics. For margin expansion, beam tracking and respiratory gating, the tumour motion must be quantified for pretreatment planning and monitored on-line. We propose a finite state model for respiratory motion analysis that captures our natural understanding of breathing stages. In this model, a regular breathing cycle is represented by three line segments, exhale, end-of-exhale and inhale, while abnormal breathing is represented by an irregular breathing state. In addition, we describe an on-line implementation of this model in one dimension. We found this model can accurately characterize a wide variety of patient breathing patterns. This model was used to describe the respiratory motion for 23 patients with peak-to-peak motion greater than 7 mm. The average root mean square error over all patients was less than 1 mm and no patient has an error worse than 1.5 mm. Our model provides a convenient tool to quantify respiratory motion characteristics, such as patterns of frequency changes and amplitude changes, and can be applied to internal or external motion, including internal tumour position, abdominal surface, diaphragm, spirometry and other surrogates.     

On the impact of longitudinal breathing motion randomness for tomotherapy delivery

The purpose of this study is to explain the unplanned longitudinal dose modulations that appear in helical tomotherapy (HT) dose distributions in the presence of irregular patient breathing. This explanation is developed by the use of longitudinal (1D) simulations of mock and surrogate data and tested with a fully 4D HT delivered plan. The 1D simulations use a typical mock breathing function which allows more flexibility to adjust various parameters. These simplified simulations are then made more realistic by using 100 surrogate waveforms all similarly scaled to produce longitudinal breathing displacements. The results include the observation that, with many waveforms used simultaneously, a voxel-by-voxel probability of a dose error from breathing is found to be proportional to the realistically random breathing amplitude relative to the beam width if the PTV is larger than the beam width and the breathing displacement amplitude. The 4D experimental test confirms that regular breathing will not result in these modulations because of the insensitivity to leaf motion for low-frequency dynamics such as breathing. These modulations mostly result from a varying average of the breathing displacements along the beam edge gradients. Regular breathing has no displacement variation over many breathing cycles. Some low-frequency interference is also possible in real situations. In the absence of more sophisticated motion management, methods that reduce the breathing amplitude or make the breathing very regular are indicated. However, for typical breathing patterns and magnitudes, motion management techniques may not be required with HT because typical breathing occurs mostly between fundamental HT treatment temporal and spatial scales. A movement beyond only discussing margins is encouraged for intensity modulated radiotherapy such that patient and machine motion interference will be minimized and beneficial averaging maximized. These results are found for homogeneous and longitudinal on-axis delivery for unplanned longitudinal dose modulations.     

Validity of the total body centre of gravity during gait using a markerless motion capture system

Purpose: The purpose of this study was to examine the validity of total body centre of gravity (COG) measurement during gait with markerless motion capture system (MLS) on the basis of values acquired with a marker-based motion capture system (MBS).

Materials and methods: Thirty young healthy subjects walked on a flat surface as coordinate data from their bodies were acquired using the Kinect v2 (as a MLS) and Vicon systems (as a MBS). COG was calculated using coordinate data of the total body. Comparisons of COG ensemble curves in the mediolateral and vertical directions were performed between MLS and MBS throughout the gait cycle. The relative consistency between these systems was assessed using Pearson correlation coefficients.

Results: The COG trajectory made by using MLS data followed the trend of the COG trajectory with MBS in the mediolateral direction. In the vertical direction, however, the COG trajectories did not match between two systems. High correlation coefficients (r >?0.79) were observed from 30% to 80% of the gait cycle. The greatest difference of COG between MLS and MBS in the mediolateral direction was 1.1?mm. Differences in the vertical direction appeared to be proportional to the distance between the participant and the Kinect v2 sensor.

Conclusion: In the mediolateral direction, COG calculated with MLS data during gait was validated with COG calculated on the basis of a MBS. Further correction of systematic error is necessary to improve the validity of COG calculations in the vertical direction.     

Organization of arm movements in three-dimensional space. Wrist motion is piecewise planar

It is shown that human subjects are incapable of producing with the arm, in free space, planned or extemporaneously drawn trajectories in which the plane of wrist motion changes smoothly or continuously. The three-dimensional nature of these movements results from the fact that the plane of motion changes abruptly from one segment of the trajectory to the next, being confined to one plane during each segment (i.e. piecewise planar).     

The phenyl group motion in polystyrene and a model of restricted internal rotation

The ¹³C NMR relaxation functions are calculated for the case of restricted rotational diffusion of a C? H dipole pair about an internal rotational axis. The model is applied to the interpretation of recent ¹³C experiments of polystyrene in a region where the relaxation of all C atoms of the phenyl ring exhibits the same temperature coefficient. It is concluded that the velocity of the phenyl group motion may be overestimated if complete rotation is assumed. By means of the model of restricted internal rotation one finds D/D₀<0,1 for the ratio of internal and mean segmental rotational diffusion constants.