Medical Engineering & Physics

Published by Elsevier
Print ISSN: 1350-4533
The Wigner-Ville spectral analysis was utilized to demonstrate a high-resolution time-frequency distribution of heart rate variability below 0.05 Hz. There are different time-frequency characteristics between the normal subject and the patient with severe congestive heart failure. The former consists of multiple and broad-band spectral peaks, while the latter presents unique spectral peaks. Based on Bayes theory, a classifier for the unique spectral peaks was developed. After the beneficial improvement with low-dose beta-blockers, the unique spectral peaks had disappeared or the time of occurrence was reduced in most patients.
Synchronized oscillation of smooth muscle cells tension in arterioles is the main control system of microvascular skin blood flow. An important autogenic vasomotion activity is recognized in 0.1Hz oscillations through power spectrum analysis of laser Doppler flowmetry. Severe dysautonomia in diabetic neuropathy is correlated with loss of 0.1Hz vasomotor activity, hence with impaired blood microcirculation. FREMS is a novel transcutaneous electrotherapy characterized by sequences of electrical stimuli of high voltage and low pulse duration which vary both in frequency and duration. We have evaluated the changes in laser Doppler flow in the volar part of the forearm before, during and after FREMS. Normal controls (n=10, 6 females, age range 21-39 years) demonstrated significant 0.1Hz vasomotion power spectra at baseline conditions associated with large oscillations of adrenergic cutaneous sweat activity sampled from the hand; people with diabetes type 2 and severe dysautonomia (n=10, 5 females, age range 63-75 years) displayed a significant decrease of 0.1Hz vasomotion power spectra. During FREMS application we observed an increase (p<0.05) of 0.1Hz vasomotion power spectra only in the diabetic group, despite persistence of adrenergic cutaneous sweat activity suppression in this group. However, after the application of the stimuli, the relative energy values around the 0.1Hz peak remained significantly higher than preapplication values in the diabetic group (p<0.05). From these findings, we suggest that FREMS is able to synchronize smooth cell activity, inducing and increasing 0.1Hz vasomotion, independently from the autonomic nervous system.
The addition of cryopreservative agents (CPAs) to chondrocytes and natural and engineered cartilage is critical to protect the cells and tissues from freezing damage during cryopreservation, but this may cause cell damage, e.g. by osmotic shock. The damage could be minimized by the control of the cell volume excursion with the knowledge of cell membrane permeability. In this study, the cell volume responses of chondrocytes to three commonly used CPAs were evaluated using a perfusion microscope stage. The osmotic response of chondrocytes was measured to the perfusion with 1.4 M dimethyl sulfoxide (Me2SO), 1,2-propanediol and glycerol at 21 degrees C. Cell volumes and their transients were determined with image analysis. The cell membrane permeability parameters, including the hydraulic conductivity (Lp), the CPA permeability (omega) and the reflection coefficients (sigma) in the Kedem-Katchalsky (K-K) model, and the Lp and omega in the two-parameter model were determined. The correlated K-K parameters at 21 degrees C were Lp=0.166 +/- 0.035, 0.149 +/- 0.061, 0.212 +/- 0.041 microm/min atm, omega=(7.630 +/- 0.174) x 10(-2), (1.428 +/- 0.627) x 10(-2), (2.744 +/- 0.775) x 10(-2) microm/s and sigma=0.91 +/- 0.09, 0.82 +/- 0.11, 0.88 +/- 0.10 for Me(2)SO, glycerol and 1,2-propanediol, respectively. For the two-parameter model, the parameter values were Lp=0.163 +/- 0.040, 0.128 +/- 0.031, 0.169 +/- 0.025 microm/min atm, omega=(7.881 +/- 0.178) x 10(-2), (1.529 +/- 0.525) x 10(-2), (3.716 +/- 0.493) x 10(-2) microm/s for Me2SO, glycerol and 1,2-propanediol, respectively. No significant difference in the predictions of cell volume excursion during CPA addition was observed when using either the K-K model or the two-parameter model and it was hence advised to adopt the simple two-parameter model in the evaluation. The measured parameters can be used to optimise the CPA addition and removal protocols to maximize the cell survival during cryopreservation.
This paper contains the details of a new technique for measuring the mechanical phase constants of transverse waves in human tibia, in vivo. The measurements are made in the frequency range from 100 to 1000 Hz. The importance of these measurements is that healthy tibia has quite small phase delays along the bone at these frequencies. On the other hand, a fractured tibia has a large phase delay at the fracture site. This paper establishes a set of typical phase delays for a range of tibia so that subsequent measurements on fractured patients can be interpreted. It contains a description of the method of measuring the phase delay and a detailed analysis of errors. In particular, it includes an account of the phase delay through the soft tissues as well as the bone and how the former can be eliminated. It is not an exhaustive account of this topic but contains sufficient results to show that the measurements can be made relatively easily. Finally, there is a theoretical model which can be used to predict the phase shift. However, in order to use the model various other measurements are necessary and a direct measurement of phase is easier than using a model.
The repeatability and reproducibility (precision within and between laboratories, respectively) of an international standard method (ISO 11948-1, the Rothwell method) for measuring the absorption capacity of incontinence pads was investigated. The 74 shaped disposable bodyworn insert pads for heavy incontinence on the UK market in spring 1997 were tested in three laboratories experienced in using the method, one in each of England, Spain and Sweden. Coefficients of variation (standard deviation as a proportion of the mean) for five repeats rarely exceeded 5% within any laboratory. However, there were systematic differences between laboratories: results from the Swedish and Spanish laboratories typically exceeded those from the English laboratory by 13% and 8%, respectively. The good repeatability suggests that the method is capable of adequate precision but the poor reproducibility implies that the instructions in the standard for building and/or using the test apparatus are inadequate, leaving too much room for interpretation. Having studied the data presented here and viewed videos of the apparatus in use in five laboratories (including the three contributing to this note) the ISO working group which wrote the original standard has identified several likely sources of imprecision and is now working to revise the standard to improve its reproducibility.
The ability of ISO 11948-1 (the Rothwell method) to predict the leakage performance of disposable bodyworn pads for heavy urinary incontinence was investigated by measuring correlations between models based on clinical evaluations of 138 diapers and inserts (the two major design categories), and technical models based on their Rothwell absorption capacities and design features. Correlations were poorer than in the original 1993 study for the standard (r < or =0.87 compared with r < or =0.95), but still strong enough to help with purchasing choices. For a given Rothwell capacity, the leakage performance of diapers was far superior to inserts; for example, diapers containing 450 and 300 g of urine performed, as well as inserts containing 300 and 100 g, respectively. No evidence was found for any other design feature having a significant impact on leakage performance. The coefficient of variation for Rothwell capacity (a measure of product consistency) had significant impact on the leakage performance of diapers, but not inserts. The probability of diapers with the poorest consistency leaking exceeded that for the best by about 10 percentage points. Similarly, diapers were about 10 percentage points more likely to leak when used at night than during the day. Differences between day-time and night-time use of inserts were not studied.
ISO 11948-2--an international standard laboratory method developed to predict the leakage performance of small disposable pads for lightly incontinent women--was investigated. The repeatability and reproducibility (precision within and between laboratories, respectively) of two variants on the method were found to be poor. The coefficient of variation for each method variant in each laboratory (two laboratories ran each variant) was higher than 40% for about half the 12 products evaluated. Results differed by up to 94% between laboratories for a given product. The ability of the method to predict the leakage performance of pads was investigated by measuring correlations between the clinical evaluations of the 12 products, and technical evaluations using ISO 11948-2. Correlations were very weak (r < or= 0.487). Accordingly, it is recommended that 11948-2 is withdrawn. A second international standard method (ISO 11948-1)--developed for evaluating large pads, but sometimes used on small ones--was also investigated. Correlations between the clinical evaluations of the 12 products and technical evaluations using ISO 11948-1 were weak (r < or = 0.560). Accordingly, it is recommended that ISO 11948-1 is not used for evaluating small disposable bodyworn pads for women.
A new protocol for cryopreservation of arteries frozen at -80 degrees C was compared to the reference protocol for cryopreservation at -150 degrees C and to freshly harvested arteries. The aim of the study is to evaluate both protocols as global procedures to freeze and thaw arteries commonly used in tissue banks. Changes in mechanical properties of rabbit common carotid arteries were studied. Vascular segments were tested in vitro under dynamics loading conditions. Pressure and diameter were recorded simultaneously by a high fidelity transducer and an echotracking device, respectively. The pressure-diameter relationship was fitted by the arctangent Langewouters' model and the arterial thickness was derived from histological measurements. Histological sections showed that the fresh and -80 degrees C groups were less damaged by hemodynamic load and histological preparation than the -150 degrees C group (p<0.05). No differences between fresh and cryopreserved arteries regarding the structural (diameter, intimal-media thickness) and mechanical parameters (distensibility, circumferential stress, elastic modulus) were found. The isobaric circumferential stress was reduced in frozen arteries. These results demonstrate that the cryopreservation at -80 degrees C preserves the histological structure and mechanical properties better than the cryopreservation at -150 degrees C, suggesting that the new cryopreservation protocol at -80 degrees C is a method of choice for treating vessel replacement in vascular surgery.
Load deflection and hysteresis measurements were made on 37 wheelchair seating cushions according to ISO 16840-2:2007. Load deflection plots for all 37 cushions are reported and fundamental aspects of graph interpretation discussed. ISO hysteresis data are also reported and interpretation discussed.
This paper comments on the paper by C.N. Bellini et al. 'Loss in mechanical contact of cementless acetabular prostheses due to postoperative weight bearing: A biomechanical model' [Med. Eng. Phys. 29(2) (2007) 175-181].
Children with disabilities are transported on a daily basis to schools and developmental facilities. When they travel, they often remain seated in their wheelchairs in vehicles. To study injury risk of pediatric wheelchair users in motor vehicle crashes, three of the same pediatric manual wheelchairs were sled impact tested with a seated Hybrid III 6-year-old ATD using a 20 g/48 km/h frontal crash pulse. The sled test results were compared to kinematic limitations and injury criteria specified in the ANSI/RESNA WC-19, FMVSS 213 and FMVSS 208. All sled test results were below the limits specified in the ANSI/RESNA WC-19 standard and FMVSS 213. All tests exceeded the N(ij) limit of 1 specified in FMVSS 208, and one test exceeded the limit of peak neck tension force. Chest deflection resulting from one of three tests was at the limit specified in FMVSS 208. Our results suggest that children with disabilities who remain seated in their wheelchairs in vehicles may be at risk of neck injury in a frontal impact motor vehicle crash. However, limitations in the biofidelity of the Hybrid III ATD neck raise concern as to the translatability of these findings to the real world. Additional studies are needed to investigate the influence of neck properties and ATD neck biofidelity on injury risk of children who travel seated in their wheelchairs.
Dynamic models of the human trunk have been extensively used to investigate the biomechanics of lower back pain and postural instability in different populations. Despite their diverse applications, previous models rely on intrinsic upper body segment parameters (UBSP), e.g., each segment's mass-inertia characteristics. However, a comprehensive UBSP set allowing state-of-the-art, three-dimensional (3D) dynamic modeling does not exist to date. Therefore, our objective was to establish a UBSP set of all vertebral trunk segments that is accurate and complete. Based on high-resolution, transverse color images, anatomical structures of the Male Visible Human (MVH) were digitally reconstructed via commercial software. Subsequently, we identified the 3D spinal joint and 3D center of mass coordinates, the mass, and the moment of inertia tensor for 24 vertebral trunk segments and 4 upper limb segments (two segments per arm). Since the MVH images are public domain, the parameters are uniquely verifiable and expandable to also include lower limb parameters. To demonstrate the UBSP set's practicality, the parameters were finally implemented in a previously proposed inverse dynamics model of the upper body. Our findings reveal that an accurate and complete UBSP set has been obtained that will be beneficial to (1) systemize thinking in postural control studies; (2) quantify the effect of impact forces on the head and trunk (e.g., during whiplash); (3) suggest population-specific experiments based on theoretical insights into trunk dynamics (e.g., regarding lower back pain); or (4) assess the feasibility of new surgical techniques (e.g., spinal fusion) and neuroprostheses (e.g., after spinal cord injury).
The validation of a coupled 1D-0D model of the lower-limb arterial hemodynamics is presented. This study focuses on pathological subjects (6 patients, 72.7±11.1years) suffering from atherosclerosis who underwent a femoro-popliteal bypass surgery. The 1D model comprises four vessels from the upper-leg, peripheral networks are modeled with three-element windkessels and in vivo velocity is prescribed at the inlet. The model is patient-specific: its parameters reflect the physiological condition of the subjects. In vivo data are acquired invasively during bypass surgery using B-mode ultrasonography and catheter. Simulations from the model compare well with measured velocity (u) and pressure (p) waveforms: average relative root-mean-square error between numerical and experimental waveforms are limited to ϵp=9.6%, ϵu=16.0%. The model is able to reproduce the intensity and shape of waveforms observed in different clinical cases. This work also details the introduction of blood leakages along the pathological arterial network, and the sensitivity of the model to its parameters. This study constitutes a first validation of a patient-specific numerical model of a pathological arterial network. It presents an efficient tool for engineers and clinicians to help them improve their understanding of the hemodynamics in diseased arteries.
This paper reports on radio path attenuation measurements made in a hospital complex at a spot frequency of 2.340 GHz. Power loss figures for fixed path propagation in a variety of building types have been determined for proposed telemetry use in operational ward situations. Throughout the hospital, the radio paths assessed all exhibited a loss in excess of that calculated for free-space communications. Modern buildings had external wall losses of 10-25 dB, with dividing walls in wards contributing an additional 5 dB. Received signal strength levels indicated a Rayleigh distribution for obstructed paths. Temporal testing was used to find the rate and depth of signal fades caused by the movement of personnel and equipment during normal ward usage; signal level reductions of greater than 35 dB were common during busy periods.
This paper discusses the design and operational assessment of a minimum-power, 2.45 GHz portable pulse receiver and associated base transmitter comprising the interrogation link in a duplex, cross-band RF transponder designed for short-range, remote patient monitoring. A tangential receiver sensitivity of - 53 dBm was achieved using a 50 ohms microstrip stub-matched zero-bias diode detector and a CMOS baseband amplifier consuming 20 microA from + 3 V. The base transmitter generated an on-off keyed peak output of 0.5 W into 50 ohms. Both linear and right-hand circularly-polarised antennas were employed in system evaluations carried out within an operational Coronary Care Unit ward. For transmitting antenna heights of between 0.3 and 2.2 m above floor level. transponder interrogations were 95% reliable within the 82 m2 area of the ward, falling to an average of 46% in the surrounding rooms and corridors. Separating the polarisation modes, using the circular antenna set gave the higher overall reliability.
Investigative research efforts using a cardiovascular model required the determination of central circulatory haemodynamic and arterial system parameters for the evaluation of cardiovascular performance. These calculations required continuous beat-to-beat measurement of pressure within the four chambers of the heart and great vessels. Sensitivity and offset drift, longevity, and sources of error for eight 3F dual-tipped micromanometers were determined during 21 days of implantation in goats. Subjects were instrumented with pairs of chronically implanted fluid-filled access catheters in the left and right ventricles, through which dual-tipped (test) micromanometers were chronically inserted and single-tip (standard) micromanometers were acutely inserted. Acutely inserted sensors were calibrated daily and measured pressures were compared in vivo to the chronically inserted sensors. Comparison of the pre- and post-gain calibration of the chronically inserted sensors showed a mean sensitivity drift of 1.0 +/- 0.4% (99% confidence, n = 9 sensors) and mean offset drift of 5.0 +/- 1.5 mmHg (99% confidence, n = 9 sensors). Potential sources of error for these drifts were identified, and included measurement system inaccuracies, temperature drift, hydrostatic column gradients, and dynamic pressure changes. Based upon these findings, we determined that these micromanometers may be chronically inserted in high-pressure chambers for up to 17 days with an acceptable error, but should be limited to acute (hours) insertions in low-pressure applications.
The last few decades have produced significant improvements in the design of upper limb prostheses through the increasing use of technology. However the limited function exhibited by these devices remains rooted in their single degree of freedom format. Commercial myoelectric hand prostheses warrant high grip forces to ensure stable prehension due to a planar pincer movement. Hence precise and conscious effort is required on the part of the user to ensure optimum grip. Consumers have shown dissatisfaction with the status quo due to the excessive weight and poor function of existing artificial hands. Increasing the number of grasping patterns and improving the visual feedback from an object in the hand are cited as key objectives. This paper outlines the development of the six-axis Southampton-Remedi hand prosthesis that addresses these design issues by maintaining stable prehension with minimal grip force. Constraints such as modularity, anthropomorphism, and low weight and power consumption are factors that have been adhered to throughout the design process.
Bi-2223 tape is a low-cost, long-length high temperature superconducting material. The new application of Bi-2223 tape for gradient coils for magnetic resonance imaging (MRI) is studied in this paper. Because Bi-2223 tape has a much higher critical current density and a much lower power loss than copper, a Bi-2223 high temperature superconductor (HTS) gradient coil shows great advantages in high gradient strengths, long continuous gradient rating, and free of cooling system over a copper gradient coil. The power losses of Bi-2223 tapes at working frequencies of gradient coils are compared to copper. The critical current degradation of tapes is also discussed. A prototype of HTS tape gradient coil is fabricated and its gradient field distributions are measured. Technical issues of resistance, gradient strength, continuous gradient rating, and cryostat are also discussed.
A field-usable sleepiness tester could reduce sleepiness related accidents. 15 subjects' postural steadiness was measured with a Nintendo(®) Wii Fit balance board every hour for 24h. Body sway was quantified with complexity index, CI, and the correlation between CI and alertness predicted by a three-process model of sleepiness was calculated. The CI group average was 8.9±1.3 for alert and 7.9±1.4 for sleep deprived subjects (p<0.001, ρ=0.94). The Wii Fit board detects the impairment of postural steadiness. This may allow large scale sleepiness testing outside the laboratory setting.
The objective of this study is to determine the three-dimensional dynamic response of the human knee joint. A three-dimensional anatomical dynamic model was thus developed and consists of two body segments in contact (the femur and tibia) executing a general three-dimensional dynamic motion within the constraints of the different ligamentous structures. Each of the articular surfaces at the tibio–femoral joint was represented mathematically by a separate mathematical function. The joint ligaments were modelled as nonlinear elastic springs. The six-degrees-of-freedom joint motions were characterized by using six kinematic parameters, and ligamentous forces were expressed in terms of these six parameters. Knee response was studied by considering sudden external forcing pulse loads applied to the tibia.
The recent development in Oxford lateral unicompartmental knee arthroplasty (UKA) design requires a valid method of assessing its kinematics. In particular, the use of single plane fluoroscopy to reconstruct the 3D kinematics of the implanted knee. The method has been used previously to investigate the kinematics of UKA, but mostly it has been used in conjunction with total knee arthroplasty (TKA). However, no accuracy assessment of the method when used for UKA has previously been reported. In this study we performed computer simulation tests to investigate the effect of the different geometry of the unicompartmental implant has on the accuracy of the method in comparison to the total knee implants. A phantom was built to perform in vitro tests to determine the accuracy of the method for UKA. The computer simulations suggested that the use of the method for UKA would prove less accurate than for TKA's. The rotational degrees of freedom for the femur showed greatest disparity between the UKA and TKA. The phantom tests showed that the in-plane translations were accurate to <0.5mm RMS and the out-of-plane translations were less accurate with 4.1mm RMS. The rotational accuracies were between 0.6 degrees and 2.3 degrees which are less accurate than those reported in the literature for TKA, however, the method is sufficient for studying overall knee kinematics.
A decrease in bone density at the hip or spine has been shown to increase the risk of fracture. A limitation of the bone mineral density (BMD) measurement is that it provides only a measure of a bone sample's average density when projected onto a 2D surface. Effectively, what determines bone fracture is whether an applied load exceeds ultimate strength, with both bone tissue material properties (can be approximated through bone density), and geometry playing a role. The goal of this project was to use bone geometry and BMD obtained from radiographs and DXA measurements respectively to estimate fracture risk, using a two-dimensional finite element model (FEM) of the sagittal plane of lumbar vertebrae. The Canadian Multicentre Osteoporosis Study (CaMos) data was used for this study. There were 4194 men and women over the age of 50 years, with 786 having fractures. Each subject had BMD testing and radiographs of their lumbar vertebrae. A single two dimensional FEM of the first to fourth lumbar vertebra was automatically generated for each subject. Bone tissue stiffness was assigned based on the BMD of the individual vertebrae, and adjusted for patient age. Axial compression boundary conditions were applied with a force proportional to body mass. The resulting overall strain from the applied force was found. Men and women were analyzed separately. At baseline, the sensitivity of BMD to predict fragility fractures in women and men was 3.77% and 0.86%, while the sensitivity of FEM to predict fragility fractures for women and men was 10.8% and 11.3%. The FEM ROC curve demonstrated better performance compared to BMD. The relative risk of being considered at high fracture risk using FEM at baseline, was a better predictor of 5 year incident fragility fracture risk compared to BMD.
High gradient magnetic separation (HGMS) of magnetic materials from fluids or waste products has many established industrial applications. However, there is currently no technology employing HGMS for ex-vivo biomedical applications, such as for the removal of magnetic drug- or toxin-loaded spheres from the human blood stream. Importantly, human HGMS applications require special design modifications as, in contrast to conventional use where magnetic elements are permanently imbedded within the separation chambers, medical separators need to avoid direct contact between the magnetic materials and blood to reduce the risk of blood clotting and to facilitate convenient and safe treatment access for many individuals. We describe and investigate the performance of a magnetic separator prototype designed for biomedical applications. First, the capture efficiency of a prototype HGMS separator unit consisting of a short tubing segment and two opposing magnetizable fine wires along the outside of the tubing was investigated using 2D mathematical modeling. Second, the first-pass effectiveness to remove commercially available, magnetic polystyrene spheres from human blood using a single separator unit was experimentally verified. The theoretical and experimental data correlated well at low flow velocities (<5.0 cm/s) and high external magnetic fields (>0.05 T). This prototype separator unit removed >90% in a single pass of the magnetic spheres from water at mean flow velocity < or =8.0 cm/s and from blood mimic fluids (ethylene glycol-water solutions) at mean flow velocity < or =2.0 cm/s. In summary, we describe and prove the feasibility of a HGMS separator for biomedical applications.
(a) An illustration of the five poses chosen for idealized outline construction to measure the performance of the automatic registration algorithm in vivo and a diagram of a dual fluoroscopic imaging system (DFIS) for capturing the dynamic motion of the shoulder joint; (b) An illustration of the virtual DFIS in computer space used to reproduce the measured joint kinematics, shown with a projection of the titanium spheres for RSA registration. 
A stepwise overview of the automated registrations algorithm to select the outermost points of the point cloud model for position optimization. (1) Compartmentalize projected points from the model; (2–3) determine boundary grids with left-looking outlining technique; (4–5) select points in each grid that are closest to the outer edge; and (6) finalized outline on the point cloud model. 
An illustration of the minimization optimization that the automatic 2D–3D image-model registration algorithm performs between the 3D model projection in blue and the bony outline on the fluoroscopic image plane in red. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.) 
Projections from the virtual source to the virtual intensifier are captured by the outer most points on the 3D model and projected onto the intensifier plane to create ideal bony outlines shown in blue. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.) 
Fluoroscopic imaging, using single plane or dual plane images, has grown in popularity to measure dynamic in vivo human shoulder joint kinematics. However, no study has quantified the difference in spatial positional accuracy between single and dual plane image-model registration applied to the shoulder joint. In this paper, an automatic 2D-3D image-model registration technique was validated for accuracy and repeatability with single and dual plane fluoroscopic images. Accuracy was assessed in a cadaver model, kinematics found using the automatic registration technique were compared to those found using radiostereometric analysis. The in vivo repeatability of the automatic registration technique was assessed during the dynamic abduction motion of four human subjects. The in vitro data indicated that the error in spatial positional accuracy of the humerus and the scapula was less than 0.30mm in translation and less than 0.58° in rotation using dual plane images. Single plane accuracy was satisfactory for in-plane motion variables, but out-of-plane motion variables on average were approximately 8 times less accurate. The in vivo test indicated that the repeatability of the automatic 2D-3D image-model registration was 0.50mm in translation and 1.04° in rotation using dual images. For a single plane technique, the repeatability was 3.31mm in translation and 2.46° in rotation for measuring shoulder joint kinematics. The data demonstrate that accurate and repeatable shoulder joint kinematics can be obtained using dual plane fluoroscopic images with an automatic 2D-3D image-model registration technique; and that out-of-plane motion variables are less accurate than in-plane motion variables using a single plane technique.
An exercise ergometer, for isometric or dynamic contraction of both dorsiflexion and/or plantarflexion exercise, was designed and constructed for a 3.0 T head-only MR scanner. The principal features of this MR-compatible ergometer include electronic devices for quantification of force (during isometric exercise) and angular displacement (during dynamic exercise), without any significant losses to external motions or frictions. The ergometer was also made to be adjustable for subject leg length and was designed for suspension within the bore of the magnet to eliminate transmission of force and vibration to the MR scanner. A description of the design and construction, as well as the important technical features, is presented herein.
Coarctation of the aorta is a congenital heart disease defined as an obstruction of the aorta distal to the left subclavian artery (between the aortic arch and descending aorta). It is usually associated with other diseases such as bicuspid and tricuspid aortic stenosis. If the coarctation remains uncorrected it can lead to hypertension, left ventricular failure and aortic dissection. Numerous investigations pointed out that there is a relationship between the genesis and the progression of cardiovascular disease and the locally irregular flow occurring at the diseased zone. Therefore, to examine the relationship between arterial disease and hemodynamics conditions, detailed quantitative studies on flow dynamics in arterial models are clearly inquired. In this study we numerically investigate pulsatile blood flow in a simplified model of the aorta (curved pipe) with coexisting coarctation of the aorta and aortic stenosis. Three severities of aortic stenoses (0.61 cm(2), 1.0 cm(2) and 1.5 cm(2)) coexisting with aortic coarctations (50%, 75% and 90% by area) are investigated. An experimentally validated numerical model from literature is used and baseline results are validated against it. To ensure having a physiologically relevant model using this geometry, flow properties are set so that the Dean number falls in the physiological range for the aorta. The results show that the coexistence of these pathologies significantly modifies the flow in a curved pipe. The maximal velocity is shifted towards the outer wall and can reach values as high as 5m/s just downstream of the coarctation. The wall shear stress distribution is significantly modified compared to the normal, unobstructed case. Finally, a clinically significant pressure gradient is induced by the curvature of the tube (up to 36 mmHg). This can lead to an overestimation of the severity of the coarctation using catheterization.
An elastohydrodynamic lubrication (EHL) simulation of a metal-on-metal (MOM) total hip implant was presented, considering both steady state and transient physiological loading and motion gait cycle in all three directions. The governing equations were solved numerically by the multi-grid method and fast Fourier transform in spherical coordinates, and full numerical solutions were presented included the pressure and film thickness distribution. Despite small variations in the magnitude of 3D resultant load, the horizontal anterior-posterior (AP) and medial-lateral (ML) load components were found to translate the contact area substantially in the corresponding direction and consequently to result in significant squeeze-film actions. For a cup positioned anatomically at 45 degrees , the variation of the resultant load was shown unlikely to cause the edge contact. The contact area was found within the cup dimensions of 70-130 degrees and 90-150 degrees in the AP and ML direction respectively even under the largest translations. Under walking conditions, the horizontal load components had a significant impact on the lubrication film due to the squeeze-film effect. The time-dependent film thickness was increased by the horizontal translation and decreased during the reverse of this translation caused by the multi-direction of the AP load during walking. The minimum film thickness of 12-20 nm was found at 0.4s and around the location at (95, 125) degrees. During the whole walking cycle both the average and centre film thickness were found obviously increased to a range of 40-65 nm, compared with the range of 25-55 nm under one load (vertical) and one motion (flexion-extension) condition, which suggested the lubrication in the current MOM hip implant was improved under 3D physiological loading and motion. This study suggested the lubrication performance especially the film thickness distribution should vary greatly under different operating conditions and the time and location that potential wear may occur was very sensitive to specific loading and motion conditions. This may provide some explanation to the large variations in wear from hip simulators and clinical studies, and also stress the importance of using more realistic loading and motion conditions in the tribological study of MOM hip prostheses.
Walking aids have been associated with falls and it is believed that incorrect use limits their usefulness. Measures are therefore needed that characterize their stable use and the classification of key events in walking aid movement is the first step in their development. This study presents an automated algorithm for detection of lift-off (LO) and touch-down (TD) events of a pick-up walker. For algorithm design and initial testing, a single user performed trials for which the four individual walker feet lifted off the ground and touched down again in various sequences, and for different amounts of frame loading (Dataset_1). For further validation, ten healthy young subjects walked with the pick-up walker on flat ground (Dataset_2a) and on a narrow beam (Dataset_2b), to challenge balance. One 88-year-old walking frame user was also assessed. Kinematic data were collected with a 3D optoelectronic camera system. The algorithm detected over 93% of events (Dataset_1), and 95% and 92% in Dataset_2a and b, respectively. Of the various LO/TD sequences, those associated with natural progression resulted in up to 100% correctly identified events. For the 88-year-old walking frame user, 96% of LO events and 93% of TD events were detected, demonstrating the potential of the approach.
Different models have been used in the literature for the simulation of surface contact in biomechanical knee models. However, there is a lack of systematic comparisons of these models applied to the simulation of a common case, which will provide relevant information about their accuracy and suitability for application in models of the implanted knee. In this work a comparison of the Hertz model (HM), the elastic foundation model (EFM) and the finite element model (FEM) for the simulation of the elastic contact in a 3D model of the prosthetic knee is presented. From the results of this comparison it is found that although the nature of the EFM offers advantages when compared with that of the HM for its application to realistic prosthetic surfaces, and when compared with the FEM in CPU time, its predictions can differ from FEM in some circumstances. These differences are considerable if the comparison is performed for prescribed displacements, although they are less important for prescribed loads. To solve these problems a new modified elastic foundation model (mEFM) is proposed that maintains basically the simplicity of the original model while producing much more accurate results. In this paper it is shown that this new mEFM calculates pressure distribution and contact area with accuracy and short computation times for toroidal contacting surfaces. Although further work is needed to confirm its validity for more complex geometries the mEFM is envisaged as a good option for application in 3D knee models to predict prosthetic knee performance.
A model of the lumbar spine capable of taking into account realistic loads derived from human activity would be of great benefit in studying its normal biomechanical functioning as well as its in vivo behavior in injured and surgically altered states. This paper proposes a method to analyze the mechanical response of the lumbar spine subjected to loads derived from human activity, combining a non-linear finite element model (FEM) and an optimization-based force predicting algorithm. Loads borne by the lumbar spine at the T12-L1 level (joint loads) are first predicted with the optimization algorithm and then applied to the FEM, while a boundary condition prescribing the relative L1-sacrum rotation is imposed onto the FEM to account for three-dimensional physiological thorax-pelvis orientation. The prescribed rotation is achieved through the application of moments on L1. To account for the effect of these moments on lumbar joint loads, an iteration between the optimization technique and the FEM computation has been carried out. This method provides two main benefits over previous studies: first, it allows for the application of any 3D loading condition while considering the real 3D rotation measured between the thorax and the pelvis, and second, it makes it possible to estimate the moments that must be applied on L1 in order to maintain this rotation, taking them into account when predicting joint loads. As an example application of the method, results are presented for the lumbar spine mechanical response at the time of peak T12-L1 joint force during walking.
Graphical user interface (GUI) designed for identifying the splines: this figure illustrates how the GUI may provide epipolar lines; in this case, an epipolar line is drawn on the PA that corresponds to the control point identified on L5 vertebra on the lateral radiograph. 
Effect of varying the weight ( i ) of each of the first three principal deformation modes of the statistical shape model in turn for − 3, 0 (mean model), and 3 times the standard deviation ( i ) of the deformation mode. The statistical shape model describes the variability of 6 landmarks per vertebrae (endplates – red strong points medially located; pedicles – green small points laterally located) by modeling their relative location, orientation and shape on an articulated fashion. For illustration purposes, 3D models of complete vertebrae were rendered. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.) 
Fitting error of the deformable AM, calculated as the distance between the endplates of the AM (red dots) and their estimated positions on the user-defined splines. The AM is first projected to the PA and LAT radiographs where the operator identified the splines and then the error (white thick line-segments) is calculated for each endplate on each radiograph. (AM represented by 6 points per vertebra connected using black thin line-segments, and user-defined splines represented by thick black curves with control points as white circles.) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.) 
This paper proposes a novel method for fast 3D reconstructions of the scoliotic spine from two planar radiographs. The method uses a statistical model of the shape of the spine for computing the 3D reconstruction that best matches the user input (about 7 control points per radiograph). In addition, the spine was modelled as an articulated structure to take advantage of the dependencies between adjacent vertebrae in terms of location, orientation and shape. The accuracy of the method was assessed for a total of 30 patients with mild to severe scoliosis (Cobb angle [22°, 70°]) by comparison with a previous validated method. Reconstruction time was 90 s for mild patients, and 110 s for severe. Results show an accuracy of ∼0.5mm locating vertebrae, while orientation accuracy was up to 1.5° for all except axial rotation (3.3° on moderate and 4.4° on severe cases). Clinical indices presented no significant differences to the reference method (Wilcoxon test, p ≤ 0.05) on patients with moderate scoliosis. Significant differences were found for two of the five indices (p=0.03) on the severe cases, while errors remain within the inter-observer variability of the reference method. Comparison with state-of-the-art methods shows that the method proposed here generally achieves superior accuracy while requiring less reconstruction time, making it especially appealing for clinical routine use.
Top-cited authors
Peter Zioupos
  • Cranfield University
Liisa Kuhn
  • UConn Health Center
Gearóid ÓLaighin
  • University of Galway
Marco Viceconti
  • University of Bologna
Ming Zhang
  • The Hong Kong Polytechnic University