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The role of surface tension in the lubrication of metal-on-metal (CoCrMo alloy) hip resurfacings has been investigated to try to explain why all metal joints fail to be lubricated with simple water-based lubricants (sodium carboxymethyl cellulose), which have similar rheology to synovial fluid, but are lubricated with the same fluid with the addition of a proportion of bovine serum. As part of this study, surfactants, in the form of detergents, when added to carboxymethyl cellulose, have been shown to produce a predominantly fluid-film lubrication mechanism with friction even lower than the biological lubricant containing serum. Friction factors were reduced by 80% when a detergent was added to the lubricant. It is considered that the failure of the water-based fluids to generate fluid-film lubrication is due to the fact that 'boundary slip' takes place where the fluid does not fully attach to the bounding solid surfaces as assumed in Reynolds' equation, thereby drawing in less lubricant than predicted from hydrodynamic theory. The addition of surfactants either in the form of natural materials such as serum or in the form of detergent reduces surface tension and helps the water-based lubricant to attach more fully to the bounding surfaces resulting in more fluid entrainment and thicker fluid-film formation. This was confirmed by up to 70% lower wear being found when these joints were lubricated in a detergent solution rather than 25% bovine serum.

The objectives of our in vitro study were to evaluate a knee wear simulation based on patient daily activities in combination with artificial ageing of polyethylene inserts to create an optimised simulation of in vivo wear modes. A wear simulation was performed on fixed bearing unicompartmental knee arthroplasty (UKA) devices in a direct comparison of level walking (as given by the ISO 14243-1:2002(E) profiles) and in a customised test configuration based on activities for level walking (10%), stairs ascending (40%), stairs descending (40%), chair rising (8%) and deep squatting (2%). The cumulative gravimetric wear was estimated to be 15.3mg for level walking (ISO) and 69.6 mg for high demanding activities (HDA). The gravimetric wear rate of the ISO group was 3.0mg/million cycles, compared to 11.7 mg/million cycles for the HDA protocol. Level walking wear testing conditions (ISO) and artificial ageing alone is not sufficient to reproduce in vivo failure modes. After 3 million cycles all gliding surfaces of the HDA group developed in the tibio-femoral articulation markable areas of structural material fatigue and delamination. In conclusion a combination of artificial ageing to clinical relevant oxidation grades and a sequence of various high demanding daily patient activities is necessary to represent a revised in vitro behaviour of abrasive-adhesive wear and delamination in artificial knee replacements., (Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.)

With the aging but still active population, research on total joint replacements relies increasingly on numerical methods, such as finite element analysis, to improve wear resistance of components. However, the validity of finite element models largely depends on the accuracy of their material behavior and geometrical representation. In particular, material properties are often based on manufacturer data or literature reports, but can alternatively be estimated by matching experimental measurements and structural predictions through modal analyses and identification of eigenfrequencies. The aim of the present study was to compare the accuracy of common setups used for estimating the eigenfrequencies of typical components often used in prosthetized joints. Eigenfrequencies of cobalt-chrome and ultra-high-molecular weight polyethylene components were therefore measured with four different setups, and used in modal analyses of corresponding finite element models for an iterative adjustment of their material properties. Results show that for the low-damped cobalt chromium endoprosthesis components, all common measuring setups provided accurate measurements. In the case of high-damped structures, measurements were only possible with setups including a continuously excitation system such as electrodynamic shakers. This study demonstrates that the iterative back-calculation of eigenfrequencies can be a reliable method to estimate the elastic properties for finite element models.

Ceramic-on-metal (COM) hip replacements, where the head is BIOLOX® Delta ceramic and the liner is CoCrMo alloy, have demonstrated reduced wear under standard simulator conditions compared to metal-on-metal (MOM) bearings. COM hips are now being used clinically around the world. MOM hip resurfacings have raised concerns regarding poor clinical performance and increased in vivo wear was associated with steeply inclined acetabular components and translationally malpositioned components. The aim of this study was to compare the wear rates of MOM and COM total hip prostheses under adverse edge-loading conditions in a hip simulator test. COM and MOM 36 mm hip prostheses were tested in a hip simulator, with liners mounted to provide a clinical inclination angle of 55°. A simplified gait cycle and microseparation conditions were applied for two million cycles in 25% new born calf serum. The overall mean volumetric wear rate of COM bearings under adverse conditions was 0.36 ± 0.55 mm³/million cycles; this was significantly less than MOM wear (1.32 ± 0.91 mm³/million cycles). Under these adverse conditions; the contact zone on the head intersects the rim of the cup causing substantially elevated contact stresses, disrupting the protective boundary and mixed lubrication regime causing changes in types and severity of wear mechanisms. In COM bearings, the harder head does not become damaged when there is lubricant starvation and wear does not accelerate. In conclusion, COM bearings showed reduced wear compared to MOM bearings under standard and adverse clinically relevant simulator conditions and COM bearings may provide an advantage over MOM bearings under edge-loading conditions clinically., (Copyright © 2013 Wiley Periodicals, Inc.)

In this study, five commercially available poly(methyl methacrylate) PMMA bone cements were tested to investigate the effects of antibiotics on the severity of crevice corrosion. Bone cements with varying chemistry were also tested. A test method was developed in part reference to ASTM F746-04. Cylindrical specimens were fitted with a bone cement tapered collar, creating consistent crevice conditions. Crevice corrosion was then studied using potentiodynamic polarization techniques in 0.9% NaCl solution (pH7.4) at 37°C. Surface analyses using a light microscope and scanning electron microscopy were also conducted to investigate the surface morphology after accelerated electrochemical testing. Initial testing of commercially available bone cements indicated that different PMMA bone cements can affect the initiation and propagation mechanism of crevice corrosion. Further studies, utilising electrochemical and mass spectroscopy techniques, have identified that the addition of radiopaque agent and antibiotics affect the initiation mechanisms of 316L stainless steel, whilst significantly increasing the extent of propagation in CoCrMo alloys., (Copyright © 2013 Wiley Periodicals, Inc.)

The paper focuses on presenting data obtained from spin test experiments of a turbine engine like rotor disk and assessing their correlation to the development of a structural health monitoring and fault detection system. The data were obtained under various operating conditions such as the rotor disk being artificially induced with and without a notch and rotated at a rotational speed of up to 10,000 rpm under balanced and imbalanced state. The data collected included blade tip clearance, blade tip timing measurements, and shaft displacements. Two different sensor technologies were employed in the testing: microwave and capacitive sensors, respectively. The experimental tests were conducted at the NASA Glenn Research Center's Rotordynamics Laboratory using a high precision spin system. Disk flaw observations and related assessments from the collected data for both sensors are reported and discussed.

Doses for panoramic dental radiography are assessed in terms of the dose-width product (DWP) or dose-area product, which gives a measure of the radiation through a whole exposure. The DWP can be measured using a pencil ionisation chamber (IC) similar to that used for computed tomography dose assessment. However, ICs are sensitive to radiation incident from all directions and so backscatter from the image receptor may increase the recorded dose. This study compares measurements performed using four options: a pencil IC mounted straight on the image receptor, the IC mounted with a steel plate to the rear to standardise scatter conditions, the IC mounted with a steel plate and lead collimators in front to minimise the effect of extra-focal radiation, and a Quart Dido employing a one square centimetre semiconductor detector (SD) designed for panoramic measurements. The results indicate that modification of the current method by incorporating a steel plate reduced the measurement dose by 7% on average, but the reduction was greater for units with semiconductor imaging plates. The measurements with the SD agree more closely with the IC with the steel plate to the rear. An IC with a backing plate to standardise scatter or a suitable SD is recommended for measurement on panoramic dental units.

Objective: To evaluate the effect of screw insertion torque on the mechanical properties of four 3.5 mm locking systems: New Generation Devices (NGD), Securos (PAX), Synthes (SYN), and Veterinary Orthopedic Implants (VOI)., Study Design: In vitro mechanical study., Methods: Screws were inserted at 1.5 Nm, 2.5 Nm, and 3.5 Nm torques, using dedicated drill guides and a calibrated torque screwdriver. Locking mechanisms were tested under shear loading conditions using a custom-design probe. Tests were conducted under displacement control until failure. Load to failure and interface stiffness were compared between and within groups using a two-factor ANOVA (P < .05). Failure modes were described., Results: The SYN group had significantly greater mechanical properties compared to all other groups at any given insertion torque. Insertion torque had a significant effect on the PAX group, increasing the load to failure by 126% when increasing the insertion torque from 1.5 Nm to 3.5 Nm. Insertion torque had no significant effect on the mechanical properties of the VOI group and limited effect on the NGD and SYN groups. Single failure mode, by screw head decoupling or screw shaft fracture, occurred in the SYN and VOI groups, respectively. In contrast, NGD and PAX systems failed through a combination of screw decoupling and/or bending., Conclusions: Regardless of insertion torque, the SYN locking mechanism showed the highest failure loads, interfacial stiffness as well as consistent failure mode. These findings highlight the dependability of this system. When using the PAX system an insertion torque of at least 2.5 Nm should be recommended., (© Copyright 2013 by The American College of Veterinary Surgeons.)

During a helical tomotherapy a binary MLC is used for fluence modulation. The 64 pneumatically driven leaves of the MLC are either completely open or closed. The fast and frequent leaf movements result in a high demand of accuracy and stability of the MLC. This article is based on the analytical investigation of the accuracy and the stability of the MLC. Different patterns of MLC movements were generated to investigate the characteristics of the MLC. One of the considered aspects contains the friction between the leaves. The influence of variations of the compressed air on the MLC was also explored. The integrated MVCT detector of the tomotherapy system deposits the treatment data in a matrix. The detector is triggered with the linear accelerator, which is pulsed by 300Hz. The data matrix is available after the treatment. An IDL (Interactive Data Language) routine was programmed in order to analyse the matrix. The points of time, at which the leaves open (POT), and the period, in which the leaves stay open (LOT), were measured and compared with the desired values. That procedure has been repeated several times a week for approximately 6 months to investigate the stability of the MLC. Relative deviations of the LOT from -0.4% to -5.4% were measured. The friction between the leaves had no significant influence on the LOT. The available compressed air, that is used to move the leaves, depends on the number of moving leaves and also on the previous movements of the MLC. Variations of the compressed air resulted in deviations of the LOT from -1.8% to -3.7%. The measured POT deviates from the programmed POT up to -18.4ms±0.7ms. This maximal deviation correlates with a shift of the gantry angle of 0.52̊ which is negligible. The MLC has shown a stable behaviour over the 6 months. A separate consideration of the leaves showed no higher standard deviation of the LOT than ±0.7ms during the investigated time. The variation between the different leaves is much higher than the deviations of LOT caused by friction and changes of compressed air. The deviations of the LOT vary between -2.6ms and -11.0ms. The developed method is feasible in order to recognize a deterioration of the MLC performance., (Copyright © 2012. Published by Elsevier GmbH.)

The reduced intraoperative visibility of minimally invasive implanted unicondylar knee arthroplasty makes it difficult to remove bone and cement debris, which have been reported on the surface of damaged and retrieved bearings. Therefore, the aim of this study was to analyze the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro. Fixed bearing unicompartmental knee prostheses were tested using a knee-wear-simulator according to the ISO standard 14243-1:2002(E) for 5.0 million cycles. Afterwards bone debris (particle size 671 ± 262 μm) were added to the test fluid in a concentration of 5 g/l for 1.5 million cycles, followed by 1.5 million cycles blended with cement debris (particle size 644 ± 186 μm) in the same concentration. Wear rate, knee-kinematics and wear-pattern were analyzed. The wear rate reached 12.5 ± 1.0 mm³/million cycles in the running-in and decreased during the steady state phase to 4.4 ± 0.91 mm³/million cycles. Bone particles resulted in a wear rate of 3.0 ± 1.27 mm³/million cycles with no influence on the wear rate compared to the steady state phase. Cement particles, however, lead to a significantly higher wear rate (25.0 ± 16.93 mm³/million cycles) compared to the steady state phase. The careful removal of extruded cement debris during implantation may help in reducing wear rate. Bone debris are suggested to have less critical influence on the prostheses wear rate.

Purpose: To determine quantitative quality control procedures to evaluate technical variability in multi-center measurements of the diffusion coefficient of water as a prerequisite to use of the biomarker apparent diffusion coefficient (ADC) in multi-center clinical trials., Materials and Methods: A uniform data acquisition protocol was developed and shared with 18 participating test sites along with a temperature-controlled diffusion phantom delivered to each site. Usable diffusion weighted imaging data of ice water at five b-values were collected on 35 clinical MRI systems from three vendors at two field strengths (1.5 and 3 Tesla [T]) and analyzed at a central processing site., Results: Standard deviation of bore-center ADCs measured across 35 scanners was <2%; error range: -2% to +5% from literature value. Day-to-day repeatability of the measurements was within 4.5%. Intra-exam repeatability at the phantom center was within 1%. Excluding one outlier, inter-site reproducibility of ADC at magnet isocenter was within 3%, although variability increased for off-center measurements. Significant (>10%) vendor-specific and system-specific spatial nonuniformity ADC bias was detected for the off-center measurement that was consistent with gradient nonlinearity., Conclusion: Standardization of DWI protocol has improved reproducibility of ADC measurements and allowed identifying spatial ADC nonuniformity as a source of error in multi-site clinical studies., (Copyright © 2012 Wiley Periodicals, Inc.)

In this letter, we describe a novel gain measurement approach for semiconductor edge-emitting lasers, with which TE and TM gain spectra can be easily obtained by collecting the amplified spontaneous emissions at dual facets of the device. An unstrained and continuously-operated GaAs/AlGaAs single quantum well laser strip is used to illustrate this method. The measured gain spectra are compared with theoretical gain curves to analyze the gain polarization characteristics and the relevant subband structure in the valence band of the well using the measured gain spectra.

Objective: CAD/CAM ceramic restorative material is routinely bonded to tooth substrates using adhesive cement. This study investigates micro-crack growth and damage in the ceramic/dentin adhesive interface under fatigue shear testing monitored using the acoustic emission (AE) technique with optical coherence tomography (OCT)., Methods: Ceramic/dentin adhesive samples were prepared to measure the shear bond strength (SBS) under static load. Fatigue shear testing was performed using a modified ISO14801 method. Loads in the fatigue tests were applied at 80%, 70%, and 60% of the SBS to monitor interface debonding. The AE technique was used to detect micro-crack signals in static and fatigue shear bond tests., Results: The results showed that the average SBS value in the static tests was 10.61±2.23MPa (mean±standard deviation). The average number of fatigue cycles in which ceramic/dentin interface damage was detected in 80%, 70% and 60% of the SBS were 152, 1962 and 9646, respectively. The acoustic behavior varied according to the applied load level. Events were emitted during 60% and 70% fatigue tests. A good correlation was observed between crack location in OCT images and the number of AE signal hits., Significance: The AE technique and OCT images employed in this study could potentially be used as a pre-clinical assessment tool to determine the integrity of cemented load bearing restored ceramic material. Sustainable cyclic load stresses in ceramic/dentin-bonded specimens were substantially lower than the measured SBS. Predicted S-N curve showed that the maximum endured load was 4.18MPa passing 10(6) fatigue cyclic., (Copyright © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

A new technique to investigate the spatial distribution of the reflection spectrum along fabricated long weak fiber Bragg gratings (FBG) is experimentally demonstrated, together with its potential applications for distributed fiber sensing and broadband signal processing. A short pulsed coherent light signal is launched into a FBG and the signal frequency is scanned through the FBG reflection spectrum. When the pulse duration is set much shorter than the transit time through the grating a time-resolved reflected signal can be obtained for each signal frequency. It informs about the distribution of the refractive index periodic perturbation along the entire FBG length, hence the uniformity or frequency chirp information of the fabricated FBG. This technique has been implemented to demonstrate a distributed temperature sensing system with high spatial resolution and to also realize a robust all-fiber tunable delay line for broadband signals.

We developed a method for group delay and group delay dispersion measurements, based on location of interference resonance peaks. Such resonance peaks can be observed in transmittance or in reflectance when two mirrors are placed parallel to each other and separated by a thin air spacer. By using a novel approach, based on simultaneous processing of the data acquired for different spacer distances we obtained reliable results with high resolution. Measurements were performed both in transmittance and reflectance layouts depending on the reflectivity of the mirror to be measured. The developed method allows dispersion measurements of ultraviolet mirrors and ultra-broadband mirrors spanning more than one optical octave to be performed.

We present a novel measurement scheme using a double-clad fiber coupler (DCFC) and a fiber Bragg grating (FBG) to resolve cladding modes. Direct measurement of the optical spectra and power in the cladding modes is obtained through the use of a specially designed DCFC spliced to a highly reflective FBG written into slightly etched standard photosensitive single mode fiber to match the inner cladding diameter of the DCFC. The DCFC is made by tapering and fusing two double-clad fibers (DCF) together. The device is capable of capturing backward propagating low and high order cladding modes simply and efficiently. Also, we demonstrate the capability of such a device to measure the surrounding refractive index (SRI) with an extremely high sensitivity of 69.769 ± 0.035 μW/RIU and a resolution of 1.433 × 10(-5) ± 8 × 10(-9) RIU between 1.37 and 1.45 RIU. The device provides a large SRI operating range from 1.30 to 1.45 RIU with sufficient discrimination for all individual captured cladding modes. The proposed scheme can be adapted to many different types of bend, temperature, refractive index and other evanescent wave based sensors.

When implanted inside the body, bioprosthetic heart valve leaflets experience a variety of cyclic mechanical stresses such as shear stress due to blood flow when the valve is open, flexural stress due to cyclic opening and closure of the valve, and tensile stress when the valve is closed. These types of stress lead to a variety of failure modes. In either a natural valve leaflet or a processed pericardial tissue leaflet, collagen fibers reinforce the tissue and provide structural integrity such that the very thin leaflet can stand enormous loads related to cyclic pressure changes. The mechanical response of the leaflet tissue greatly depends on collagen fiber concentration, characteristics, and orientation. Thus, understating the microstructure of pericardial tissue and its response to dynamic loading is crucial for the development of more durable heart valve, and computational models to predict heart valves' behavior. In this work, we have characterized the 3D collagen fiber arrangement of bovine pericardial tissue leaflets in response to a variety of different loading conditions under Second-Harmonic Generation Microscopy. This real-time visualization method assists in better understanding of the effect of cyclic load on collagen fiber orientation in time and space.

Background: Many of the physiological changes that lead to diabetic foot ulceration, such as muscle atrophy and skin hardening, are manifested at the foot-ground interface via pressure and shear points. Novel shear-reducing insoles have been developed, but their magnitude of shear stiffness has not yet been compared with regular insoles. The aim of this study was to develop an apparatus that would apply shear force and displacement to an insole's forefoot region, reliably measure deformation, and calculate insole shear stiffness., Methods: An apparatus consisting of suspended weights was designed to test the forefoot region of insoles. Three separate regions representing the hallux; the first and second metatarsals; and the third, fourth, and fifth metatarsals were sheared at 20 mm/min for displacements from 0.1 to 1.0 mm in both the anteroposterior and mediolateral directions for two types of insoles (regular and shear reducing)., Results: Shear reduction was found to be significant for the intervention insoles under all testing conditions. The ratio of a regular insole's effective stiffness and the experimental insole's effective stiffness across forefoot position versus shear direction, gait instance versus shear direction, and forefoot position versus gait instance was 270% ± 79%, 270% ± 96%, and 270% ± 86%, respectively. The apparatus was reliable with an average measured coefficient of variation of 0.034 and 0.069 for the regular and shear-reducing insole, respectively., Conclusion: An apparatus consisting of suspended weights resting atop three locations of interest sheared across an insole was demonstrated to be capable of measuring the insole shear stiffness accurately, thus quantifying shear-reducing effects of a new type of insole., (© 2013 Diabetes Technology Society.)

Condition monitoring of rotating machines is important in the prevention of failures. As most machine malfunctions are related to bearing failures, several bearing diagnosis techniques have been developed. Some of them feature the bearing vibration signal with statistical measures and others extract the bearing fault characteristic frequency from the AM component of the vibration signal. In this paper, we propose to transform the vibration signal to the Teager-Kaiser domain and feature it with statistical and energy-based measures. A bearing database with normal and faulty bearings is used. The diagnosis is performed with two classifiers: a neural network classifier and a LS-SVM classifier. Experiments show that the Teager domain features outperform those based on the temporal or AM signal., (Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.)

We propose a measurement protocol and parameter estimation algorithm to recover the powers and relative phases of each of the vector modes present at the output of an optical fiber that supports the HE₁₁, TE₀₁, HE₂₁, and TM₀₁ modes. The measurements consist of polarization filtered near-field intensity images that are easily implemented with standard off-shelf components. We demonstrate the accuracy of the method on both simulated and measured data from a recently demonstrated fiber that supports stable orbital angular momentum states.

We focused partially coherent laser light onto an optical fiber end-face and captured a high-quality reflective cross-sectional image of the fiber. By analyzing the reflected light intensity distribution of the captured fiber image, we can achieve refractive-index profiling of a step-index multimode optical fiber. The measurement error caused by the reflected light from the other fiber end-face positioned in air can be greatly improved by inserting that end of the fiber into water. This simple and easy technique for fiber index profiling by employing reduced-coherence laser light is very useful in determining the refractive index profiles of various multimode optical fibers.

Based on a distributed method of bit-error-rate (BER) monitoring, a novel multi-link faults restoration algorithm is proposed for dynamic optical networks. The concept of fuzzy fault set (FFS) is first introduced for multi-link faults localization, which includes all possible optical equipment or fiber links with a membership describing the possibility of faults. Such a set is characterized by a membership function which assigns each object a grade of membership ranging from zero to one. OSPF protocol extension is designed for the BER information flooding in the network. The BER information can be correlated to link faults through FFS. Based on the BER information and FFS, multi-link faults localization mechanism and restoration algorithm are implemented and experimentally demonstrated on a GMPLS enabled optical network testbed with 40 wavelengths in each fiber link. Experimental results show that the novel localization mechanism has better performance compared with the extended limited perimeter vector matching (LVM) protocol and the restoration algorithm can improve the restoration success rate under multi-link faults scenario.

Aim: To find out whether it is possible to anaesthetize patients safely without analgesia and sedation, using burst pacing prolonged until the patient becomes unconscious., Methods: One hundred and four patients undergoing implantation or reimplantation of a cardioverter-defibrillator were included. Patients randomized into Group B underwent prolonged burst pacing without analgesia and sedation. Patients in Group T underwent a T-wave shock under analgesia and sedation. Blood samples for measurement of serum neuron-specific enolase were taken before surgery and 6, 24, and 48 h after the procedure., Results: From the 104 patients, 51 were randomly assigned to Group B and 53 to Group T. Four patients from Group B were switched to Group T (ventricular fibrillation not induced by burst pacing). The clinical characteristics of both groups were similar. The mean total time of cardiac arrest was significantly longer in Group B (23.0 ± 4.4 s, median 22.7) vs. Group T (10.3 ± 3.0 s, median 10.0), P < 0.0001 (Mann-Whitney U-test). The effectiveness of both induction methods was similar (92.1% in Group B and 100% in Group T). The mean neuron-specific enolase levels after 6, 24, and 48 h were similar in Groups B and T (13.1 ± 6.3 and 11.6 ± 5.8 mg/L, 14.5 ± 7.5 and 13.4 ± 6.0 mg/L, and 14.9 ± 5.9 and 12.2 ± 6.0 mg/L, respectively) as were these levels compared with baseline neuron-specificenolase levels (14.0 ± 5.9 and 13.4 ± 4.0 mg/L, respectively), P = NS for all., Conclusion: Despite a longer time of total cardiac arrest, prolonged burst pacing appears to be a safe and effective method for induction of ventricular fibrillation during cardioverter-defibrillator testing, which enables omission of analgesia and sedation or general anaesthesia.

In two patients treated with cardiac resynchronization therapy (CRT), left ventricular (LV) pacing failure occurred due to ring conductor fractures of the bipolar LV lead (co-radial model). CRT was resumed by pacing between the tip conductor of the LV lead and the coil conductor of the right ventricular lead. However, shortly thereafter, subsequent fracture of the tip conductor developed, and implantation of a new LV lead was required. When one of the bipolar conductors of a co-radial designed LV lead fractures, reimplantation of a new LV lead is a better therapeutic option (than changing the LV pacing mode) in order to reliably continue CRT treatment.

A new testing technique based on the use of a liquid crystal spatial light modulator (SLM) is proposed to analyze the optical quality of multifocal intraocular lenses (MIOLs). Different vergences and decentrations of the incident beam can be programmed onto the SLM in order to record the point spread function (PSF) for different object positions. From these axial PSFs, the through-focus modulation transfer function is computed. Because there are no moving parts in the experimental setup, this method is fast and versatile to assess MIOLs. Experimental results confirm the potential of the proposed method.

Currently, imaging methods are used to diagnose loosening of endoprosthetic implants, but fail to achieve 100% accuracy. In this study, a passive sensor array which is based on the interaction between magnetic oscillators inside the implant and an excitation coil outside the patient was investigated. The excited oscillators produce sound in the audible range, which varies according to the extent of loosening. By performing several experimental tests, the sensor array was optimized to guarantee reproducible and selective excitation of the sound emission. Variation in the distance between the oscillators demonstrated a definite influence on the quality of the generated sound signal. Furthermore, a numerical design analysis using the boundary element method was generated for consideration of the magnetic field and the selectivity of the oscillators during excitation. The numerical simulation of the coil showed the higher selectivity of a coil with a C-shape compared to a cylindrical coil. Based on these investigations, the passive sensor system reveals the potential for detection of implant loosening. Future aims include the further miniaturization of the oscillators and measurements to determine the sensitivity of the proposed sensor system.

We demonstrate the use of the classical Ronchi test to characterize aberrations in focusing optics at a hard x-ray free-electron laser. A grating is placed close to the focus and the interference between the different orders after the grating is observed in the far field. Any aberrations in the beam or the optics will distort the interference fringes. The method is simple to implement and can provide single-shot information about the focusing quality. We used the Ronchi test to measure the aberrations in a nanofocusing Fresnel zone plate at the Linac Coherent Light Source at 8.194 keV.

Total internal reflection fluorescence (TIRF) microscopy has the exciting laser beam incident beyond critical angle from the glass side of a glass/aqueous interface formed by the coverslip and aqueous sample. The aqueous side evanescent field decays exponentially with distance from the interface with penetration depth depending on incidence angle. Through-the-objective TIRF has the exciting laser focused at the back focal plane (BFP) creating a refracted parallel beam approaching the interface in the small gap between objective and coverslip, making incidence angle challenging to measure. Objective axial scanning does not affect incidence angle but translates beam and interface intersection detected by the fluorescence center of mass from fluorescent spheres attached to the aqueous side of the interface. Center of mass translation divided by the axial translation is the tangent of the incidence angle that is sampled repeatedly over objective trajectory to obtain a best estimate. Incidence angle is measured for progressively larger radial positions of the focused beam on the BFP. A through-the-objective TIRF microscope, utilizing a micrometer and relay lenses to position the focused beam at the BFP, is calibrated for incidence angle. Calibration depends on microscope characteristics and TIRF objective and is applicable to any interface or sample.

Determining the MR compatibility of medical implants and devices is becoming increasingly relevant. In most cases, the heating of conductive implants due to radiefrequency (RF) excitation pulses is measured by fluoroptic temperature sensors in relevant tests for approval. Another common method to determine these heating effects is MR thermometry using the proton resonance frequency. This method gives good results in homogeneous phantoms. However in many cases, technical shortcomings such as susceptibility artifacts prohibit exact proton resonance frequency thermometry near medical implants. Therefore, this work aimed at developing a fast T₁-based method which allows controlled MR-related heating of a medical implant while simultaneously quantifying the spatial and temporal temperature distribution. To this end, an inversion recovery snapshot Fast Low-Angle Shot (FLASH) sequence was modified with additional off-resonant heating pulses. With an accelerated imaging method and a sliding-window technique, every 7.6 s a new temperature map could be generated with a spatial in-plane resolution of 2 mm. The temperature deviation from calculated temperature values to reference fluoroptic probe was found to be smaller than 1 K., (Copyright © 2012 Wiley Periodicals, Inc.)

This study investigates the characteristics of contemporary pacemaker pulses as recorded from the body surface. Twelve-lead paced ECGs from 140 patients (68 ± 12 years, 71% males) were collected at 32,000 samples per second. Pacer pulses were manually annotated based on the high-sampling rate data stream. The results show that durations of the various pulses are stable, while amplitudes exhibit large variations. Also, more than 50% of pulses have either durations <0.5 ms or amplitudes <2 mV, which are the AAMI/IEC thresholds for detection and marking of pacemaker pulses on an ECG report. Therefore the current standards for pacemaker pulse detection are not fit for purpose and require to be updated. Further, this study suggests that a high-sampling rate database should be used as a standard test for pacemaker annotation and detection from body surface ECGs., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The temporal dynamics of ultrashort laser pulses undergoing filamentary propagation are investigated with a real-time stereographic above-threshold ionization (ATI) phasemeter. The experimental setup is capable of measuring the pulse duration as well as the carrier-envelope phase distribution of pulses originating from a femtosecond filament, which is either truncated in length or fully propagated. Truncation, by means of a semi-infinite gas cell, allows to elucidate the nonlinear evolution and temporal dynamics of ultrashort laser pulses as a function of the propagation length. We observe the formation of few-cycle pulses as well as temporal pulse splitting dynamics during the propagation of the pulse inside the filament. For the first time, we demonstrate the compression of 35 fs pulses down to a duration of sub-4 fs in a single femtosecond filament. This corresponds to sub-1.5 cycles of the electric field.

At the ionising radiation department of the D.I. Mendeleyev Institute for Metrology, a semiconductor detector was calibrated in the energy range 200-8500 keV using (n,2γ) and (n,γ) reactions. Separate cylindrical targets (77 mm diameter and 10mm height) were made from mercuric sulphate, sodium chloride and metallic titanium. A (252)Cf spontaneous fission neutron source, placed in 150 mm diameter polyethylene ball, was used to generate thermal neutrons. The optimal target dimensions were determined taking into account the thermal neutron cross-sections and gamma-radiation attenuations in the target materials. The influence of the background radiation induced by neutrons from the walls, floors and ceilings was also taken into account. The shapes of the efficiency curves for point and volume sources in the 200-8500 keV range have been investigated. The experimental results are in good agreement with Monte-Carlo calculations. The emission rate of the 6.13 MeV photons from a (238)Pu-(13)C source was determined with an expanded uncertainty, U(c), of 10% (k=2)., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In this work we suggest an original fault signature based on an improved combination of Hilbert and Park transforms. Starting from this combination we can create two fault signatures: Hilbert modulus current space vector (HMCSV) and Hilbert phase current space vector (HPCSV). These two fault signatures are subsequently analysed using the classical fast Fourier transform (FFT). The effects of mechanical faults on the HMCSV and HPCSV spectrums are described, and the related frequencies are determined. The magnitudes of spectral components, relative to the studied faults (air-gap eccentricity and outer raceway ball bearing defect), are extracted in order to develop the input vector necessary for learning and testing the support vector machine with an aim of classifying automatically the various states of the induction motor., (Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.)

Background: An insulin pump shutoff system can prevent nocturnal hypoglycemia and is a first step on the pathway toward a closed-loop artificial pancreas. In previous pump shutoff studies using a voting algorithm and a 1 min continuous glucose monitor (CGM), 80% of induced hypoglycemic events were prevented., Methods: The pump shutoff algorithm used in previous studies was revised to a single Kalman filter to reduce complexity, incorporate CGMs with different sample times, handle sensor signal dropouts, and enforce safety constraints on the allowable pump shutoff time., Results: Retrospective testing of the new algorithm on previous clinical data sets indicated that, for the four cases where the previous algorithm failed (minimum reference glucose less than 60 mg/dl), the mean suspension start time was 30 min earlier than the previous algorithm. Inpatient studies of the new algorithm have been conducted on 16 subjects. The algorithm prevented hypoglycemia in 73% of subjects. Suspension-induced hyperglycemia is not assessed, because this study forced excessive basal insulin infusion rates., Conclusions: The new algorithm functioned well and is flexible enough to handle variable sensor sample times and sensor dropouts. It also provides a framework for handling sensor signal attenuations, which can be challenging, particularly when they occur overnight., (© 2012 Diabetes Technology Society.)

The two-dimensional (2D) ionization chamber array MatriXX Evolution is one of the 2D ionization chamber arrays developed by IBA Dosimetry (IBA Dosimetry, Germany) for megavoltage real-time absolute 2D dosimetry and verification of intensity-modulated radiation therapy (IMRT). The purpose of this study was to (1) evaluate the performance of ion chamber array for submegavoltage range brachytherapy beam dose verification and quality assurance (QA) and (2) use the end-to-end dosimetric evaluation that mimics a patient treatment procedure and confirm the primary source strength calibration agrees in both the treatment planning system (TPS) and treatment delivery console computers. The dose linearity and energy dependence of the 2D ion chamber array was studied using kilovoltage X-ray beams (100, 180 and 300 kVp). The detector calibration factor was determined using 300 kVp X-ray beams so that we can use the same calibration factor for dosimetric verification of high-dose-rate (HDR) brachytherapy. The phantom used for this measurement consists of multiple catheters, the IBA MatriXX detector, and water-equivalent slab of RW3 to provide full scattering conditions. The treatment planning system (TPS) (Oncentra brachy version 3.3, Nucletron BV, Veenendaal, the Netherlands) dose distribution was calculated on the computed tomography (CT) scan of this phantom. The measured and TPS calculated distributions were compared in IBA Dosimetry OmniPro-I'mRT software. The quality of agreement was quantified by the gamma (γ) index (with 3% delta dose and distance criterion of 2 mm) for 9 sets of plans. Using a dedicated phantom capable of receiving 5 brachytherapy intralumenal catheters a QA procedure was developed for end-to-end dosimetric evaluation for routine QA checks. The 2D ion chamber array dose dependence was found to be linear for 100-300 kVp and the detector response (k(user)) showed strong energy dependence for 100-300 kVp energy range. For the Ir-192 brachytherapy HDR source, dosimetric evaluation k(user) factor determined by photon beam of energy of 300 kVp was used. The maximum mean difference between ion chamber array measured and TPS calculated was 3.7%. Comparisons of dose distribution for different test plans have shown agreement with >94.5% for γ ≤1. Dosimetric QA can be performed with the 2D ion chamber array to confirm primary source strength calibration is properly updated in both the TPS and treatment delivery console computers. The MatriXX Evolution ionization chamber array has been found to be reliable for measurement of both absolute dose and relative dose distributions for the Ir-192 brachytherapy HDR source., (Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.)

Purpose: No commercially available device for measuring individual IOL surface topographies exists on the market. The purpose of this paper is to show the applicability of clinically available corneal topographers for measuring individual IOLs consisting of a spherical surface on one side and a freeform surface on the other side., Methods: Three measurement principles (Placido rings: Tomey TMS-2N, Scheimpflug: Oculus Pentacam, optical coherence tomography: Tomey CASIA) are applied in determining the IOLs' surface and compared against the design data used for producing the surfaces. Spherical and freeform IOLs are measured and analysed in both radius of curvature (ROC) and higher-order residual parameters by analysing the residuals., Results: Repeatability and reproducibility measurements show a sub-μm precision for the TMS-2N system, while the Pentacam's values are located around 10μm and the CASIA system's values gather around 20μm. The TMS-2N system works best at detecting a sample's ROC and residual properties within the range of 8mm to 13.5mm mean ROC. In this range, the deviations from the theoretical ROC are about 45μm. The Pentacam doesn't have this limitation, but faces problems with exporting measurements of freeform surfaces. In some circumstances the program crashes and prevents the export. If being able to export the Pentacam measurements show an average deviation of 100μm from the theoretical ROC value. The CASIA system shows high amounts of noise which makes it not applicable in this field, having deviations of several 100μm from the theoretical ROC value. Residual comparison for the higher-order samples shows sub-μm precision for the TMS-2N, about 1μm precision for the Pentacam and several μm for the CASIA system. The values for the customized samples are slightly increased, several μm for the TMS-2N, up to 30μm for the Pentacam system and around 75μm for the CASIA system., Conclusion: The TMS-2N system is an appropriate device for measuring individual IOL surface topographies for ROCs between 8mm to 13.5mm. The Pentacam and CASIA induced relatively high level of variation and noise. Future application of the TMS-2N in this field will reveal its long-term statistics., (Copyright © 2012. Published by Elsevier GmbH.)

We report a fiber optic photoluminescence (PL) measurement system using a novel hybrid probe composed of a series of single mode fiber (SMF) and double-clad fiber (DCF) terminated with a coreless silica fiber (CSF) segment and glass micro-lens formed on its cleaved-facet. The fiber probe provided a good guidance and focusing capability for the excitation photon with a focal length of 125 μm and a beam diameter of 13.6 μm. Utilizing a special DCF-to-DCF coupling scheme, the photoluminescence signals were efficiently collected and delivered to a photodetector with a low loss. Utilizing the proposed system, PL morphology was investigated over a 200 × 200 μm(2) area for two types of InGaN/GaN blue light emitting diode (LED) epi-wafers grown on 1) an un-patterned sapphire substrate (UPSS), and 2) a patterned sapphire substrate (PSS). The uniformity in the relative PL intensity and the spectral uniformity in terms of the peak PL wavelength were experimentally compared and analyzed.

A method for measuring the effective refractive-index differences in a few-mode fiber by applying axial fiber stretching is described. This method represents a straightforward technique for characterization of few-mode fibers. Interference between LP01 and LP11 and in some cases also between LP11 and LP21 are observed in a fiber designed for support of LP01 and LP11. The relative strength of the coupled modes depends on specific splicing characteristics, and in some cases only two modes are seen. The results agree well with theoretical predictions for the fiber under investigation.

In this work we tackled the problem of accurate measurement of internal-external (IE) rotations in the prosthetic knee. We presented a magnetic measurement system to be implanted in the knee prostheses in order to measure IE without soft tissue artifacts. The measurement system consisted of a permanent magnet attached under the tibial plate of the prosthesis and a combination of magnetic sensors in the polyethylene insert. Two different sensor configurations were designed, and five different angle estimators for measurement of IE angles were defined and tested based on several static and dynamic measurements toward a stereophotogrammetry motion capture system. Also a noise analysis was done to see which estimators are less sensitive to measurement noise. One-sensor configuration provided lower power budget with dynamic RMS error of 0.49° and a noise range of ±0.53°. Two-sensor configuration doubles the power consumption but provided slightly lower dynamic RMS error (0.37°) and a noise range of ±0.42°, and offers the possibility of having redundancy in case of damaged sensor., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Pre-clinical wear testing of intervertebral disc prostheses is commonly carried out according to ISO 18192-1. Ten million multiaxial loading cycles are applied at a frequency of 1 Hz. At this frequency, testing takes about 4 months. Testing at higher frequencies would therefore be desirable. ISO 18192-1 also offers testing at 2 Hz; however, it says the impact on the implant material behaviour as well as on the accuracy of the test machine shall be investigated by the user. Since such data are not available so far, the aim of this study was to carry out comparative wear tests at 1 and 2 Hz. Seven Prodisc-L lumbar disc prostheses were tested. After a pre-soak period, the implants were placed in specimen cups filled with calf serum, mounted to a Spine Wear Simulator and loaded according to ISO 18192-1. Testing was carried out at a temperature of 37 ± 2 °C. Four million loading cycles were applied at 1 Hz and eight million at 2 Hz in an alternating sequence. Each time after 12 days of testing the implants were removed to measure the weight and the height of the polyethylene cores. Then, the test serum was exchanged and the implants were remounted to the testing machine. The mean wear rate was 5.6 ± 2.3 mg per million cycles at 1 Hz and 7.7 ± 1.6 mg per million cycles at 2 Hz during the first six million loading cycles (p < 0.05) and 2.0 ± 0.6 and 4.1 ± 0.7 mg per million cycles during the second six million cycles (p < 0.05). Similarly, the mean heightloss was also smaller at 1 Hz than at 2 Hz (p < 0.05) with -0.02 ± 0.02 mm versus -0.04 ± 0.02 mm per million cycles during the first half of testing and -0.01 ± 0.01 versus -0.02 ± 0.01 mm per million cycles during the second half. The accuracy of the test machine was within the limits described by ISO 18192-1 at both frequencies. The results showed that the wear rate was higher at the beginning than at the end of testing. Also, the results indicated that testing at 2 Hz increases the wear rate compared with 1 Hz in case of a polyethylene-on-metal implant design. In the absence of retrieval studies it is difficult to decide which rate results in a more physiological wear pattern. However, a loading frequency of 1 Hz is probably closer to physiology than 2 Hz since the loading amplitudes prescribed by ISO 18192-1 are high. They rather represent movements like tying shoes or standing up from a chair than walking or sitting. The authors therefore suggest testing at 1 Hz.

(6)LiF:Mg,Cu,P and (7)LiF:Mg,Cu,P glass-rod thermoluminescent dosemeters (TLDs) were used for measurements of out-of-field photon and neutron doses produced by Varian iX linear accelerator. Both TLDs were calibrated using 18-MV X-ray beam to investigate their dose-response sensitivity and linearity. CR-39 etch-track detectors (Luxel+, Landauer) were employed to provide neutron dose data to calibrate (6)LiF:Mg,Cu,P TLDs at various distances from the isocentre. With cadmium filters employed, slow neutrons (<0.5 eV) were distinguished from fast neutrons. The average in-air photon dose equivalents per monitor unit (MU) ranged from 1.5±0.4 to 215.5±94.6 μSv at 100 and 15 cm from the isocentre, respectively. Based on the cross-calibration factors obtained with CR-39 etch-track detectors, the average in-air fast neutron dose equivalents per MU range from 10.6±3.8 to 59.1±49.9 μSv at 100 and 15 cm from the isocentre, respectively. Contribution of thermal neutrons to total neutron dose equivalent was small: 3.1±7.2 μSv per MU at 15 cm from the isocentre.

Laboratory wear simulations of the dual-bearing surface Charité total disc replacement (TDR) are complicated by the non-specificity of the device's center of rotation (CoR). Previous studies have suggested that articulation of the Charité preferentially occurs at the superior-bearing surface, although it is not clear how sensitive this phenomenon is to lubrication conditions or CoR location. In this study, a computational wear model is used to study the articulation kinematics and wear of the Charité TDR. Implant wear was found to be insensitive to the CoR location, although seemingly non-physiologic endplate motion can result. Articulation and wear were biased significantly to the superior-bearing surface, even in the presence of significant perturbations of loading and friction. The computational wear model provides novel insight into the mechanics and wear of the Charité TDR, allowing for better interpretation of in vivo results, and giving useful insight for designing future laboratory physical tests.

Purpose: In vivo range verification is one of the most important parts of proton therapy to fully utilize its benefits delivering high radiation dose to tumor, while sparing the normal tissue with the so-called Bragg peak. Currently, however, range verification method is not used in clinics. The purpose of the present study is to optimize and evaluate the configuration of an array-type prompt gamma measurement system on determining distal dose edge for in vivo range verification of proton therapy., Methods: To effectively measure the prompt gammas against the background gammas, the Monte Carlo simulations with the MCNPX code were employed in optimizing the configuration of the measurement system, and the Monte Carlo method was also used to understand the effect of the background gammas, mainly neutron capture gammas, in the measured gamma distribution. To reduce the effect of the background gammas, the optimized energy window of 4-10 MeV in measuring the prompt gammas was employed. A parameterized source was used to maximize computation speed in the optimization study. A simplified test measurement system, using only one detector moving from one measurement location to the next, was constructed and applied to therapeutic proton beams of 80-220 MeV. For accurate determination of the distal dose edge, the sigmoidal curve-fitting method was applied to the measured distributions of the prompt gammas, and then, the location of the half-value between the maximum and minimum value in the curve-fitting was determined as the distal dose edge and compared with the beam range assessed by the proton dose distribution., Results: The parameterized source term employed in optimization process improved the calculation speed by up to ∼300 times. The optimization study indicates that an array-type measurement system with 3, 2, 2, and 150 mm for scintillator thickness, slit width, septal thickness, and slit length, respectively, can effectively measure the prompt gamma distributions minimizing the contribution of background gammas. The present results show that a few hundred counts of prompt gammas can be easily obtained by measuring 10 s at each measurement location for proton beams of ∼4 nA. The distal dose edges determined by the prompt gamma distribution are 5.45, 14.73, and 27.74 cm for proton beams of 5.17 (80 MeV), 14.99 (150 MeV), and 27.38 (220 MeV) cm, respectively., Conclusions: The results show that the array-type measurement system can measure prompt gamma distributions from a therapeutic proton beam within a short measurement time, and that the distal dose edge can be determined within a few millimeters of error without using any sophisticated analysis.

The mechanical complications of osteosyntheses after hip fractures are previously investigated by mostly static or dynamic uniaxial loading test systems. However, the physiologic loading of the hip joint during a normal gait is a multiplanar, dynamic movement. Therefore, we constructed a system to test osteosyntheses for hip fractures under physiologic multiplanar loading representative of normal gait. To evaluate the testing system, 12 femora pairs were tested under 25,000 cycles with two standard osteosyntheses (Proximal Femoral Nail Antirotation/Gamma3 Nail). For angular movement, the varus collapse to cut out (∝CO) (∝CO=4.8°±2.1° for blade and ∝CO=7.8°±3.8° for screw) was the dominant failure mode, and only slight rotational angle shifts (∝Rot) (∝Rot=1.7°±0.4° for blade and ∝Rot=2.4°±0.3° for screw) of the femoral head around the implant axis were observed. Angular displacements in varus direction and rotation were higher in specimens reinforced with screws. Hence, the cut out model and the migration directions showed a distinction between helical blade and hip screw. However, there were no significant differences between the different implants. The new setup is able to create clinical failures and allows to give evidence about the anchorage stability of different implant types under dynamic gait motion pattern.

Passive detectors, as albedo or track-etch, still dominate the field of neutron personal dosimetry, mainly due to their low-cost, high-reliability and elevated throughput. However, the recent appearance in the market of electronic personal dosemeters for neutrons presents a new option for personal dosimetry. In addition to passive detectors, electronic personal dosemeters necessitate correction factors, concerning their energy and angular response dependencies. This paper reports on the results of a method to evaluate personal dosemeters for workplace where neutrons are present. The approach here uses few instruments and does not necessitate a large mathematical workload. Qualitative information on the neutron energy spectrum is acquired using a simple spectrometer (Nprobe), reference values for H*(10) are derived from measurements with ambient detectors (Studsvik, Berthold and Harwell) and angular information is measured using personal dosemeters (electronic and bubbles dosemeters) disposed in different orientations on a slab phantom.

An otological drill is a fundamental apparatus used for bone-milling in ear surgery. A common problem in bone-milling is that the drill bit slips on the bone surface. To improve the operational safety of such a surgery, this article presents a new apparatus combined with an intelligent method for identifying drill slippage. A two-axis force sensor is installed on a modified drill, and it detects the force of the bone's reaction to the drill bit. By integrating the unit reaction forces of the bone and the drill bit on the contact area, the functions of the force signals are deduced, which can reflect changes in the milling parameters. Based upon these functions, the slippage force, which is an important factor in drill slippage, is then extracted. An adaptive filter is specially designed to suppress interference in the slippage force. Drill slippage can be identified by calculating the variations in the filtering results. Five surgeons were invited to carry out an experiment in which they used this method on calvarian bones. Their average recognition rate of drill slippage was 86%, and only 1% of normal millings were identified as milling faults.

A high resolution optical vector network analyzer (OVNA) implemented based on a wideband and wavelength-tunable optical single-sideband (OSSB) modulator is proposed and experimentally demonstrated. The OSSB modulation is achieved using a phase modulator and a tunable optical filter with a passband having two steep edges and a flat top. Wideband and wavelength-tunable OSSB modulation is achieved. The incorporation of the OSSB modulator into the OVNA is experimentally evaluated. The measurement of the magnitude and phase response of an ultra-narrow-band fiber Bragg grating (FBG) and that of the stimulated Brillouin scattering (SBS) in a single-mode fiber is performed. A measurement resolution as high as 78 kHz is achieved.