Hip joint centre location: An ex vivo study

The human hip joint is normally represented as a spherical hinge and its centre of rotation is used to construct femoral anatomical axes and to calculate hip joint moments. The estimate of the hip joint centre (HJC) position using a functional approach is affected by stereophotogrammetric errors and soft tissue artefacts. The aims of this study were (1) to assess the accuracy with which the HJC position can be located using stereophotogrammetry and (2) to investigate the effects of hip motion amplitude on this accuracy. Experiments were conducted on four adult cadavers. Cortical pins, each equipped with a marker cluster, were implanted in the pelvis and femur, and eight skin markers were attached to the thigh. Recordings were made while an operator rotated the hip joint exploiting the widest possible range of motion. For HJC determination, a proximal and a distal thigh skin marker cluster and two recent analytical methods, the quartic sphere fit (QFS) method and the symmetrical centre of rotation estimation (SCoRE) method, were used. Results showed that, when only stereophotogrammetric errors were taken into account, the analytical methods performed equally well. In presence of soft tissue artefacts, HJC errors highly varied among subjects, methods, and skin marker clusters (between 1.4 and 38.5 mm). As expected, larger errors were found in the subject with larger soft tissue artefacts. The QFS method and the distal cluster performed generally better and showed a mean HJC location accuracy better than 10 mm over all subjects. The analysis on the effect of hip movement amplitude revealed that a reduction of the amplitude does not improve the HJC location accuracy despite a decrease of the artefact amplitude.     

Assessment of a greater trochanter-based method of locating the hip joint center

An alternative, yet unverified, predictive method that places the hip joint center (HJC) at one-quarter of the distance from the ipsolateral to the contralateral greater trochanter (GT method) is currently widely used in the biomechanics community. Therefore, the objective of this study was to confirm that this method is a viable option for estimating HJC coordinates. To accomplish this, HJC coordinates in the pelvic anatomical coordinate system were estimated via the GT method, a functional method, and the regression equations proposed by Bell et al. (1990). The HJC coordinated estimated by the functional method served as a baseline measurement. The results of this study demonstrate that all three methods evaluated offer repeatable estimates of HJC location. In comparison to the functional method, the GT method yielded a HJC estimate that was 7.6 mm medial, 12.2 mm posterior, and 4.8 mm proximal. On the other hand, the Bell regression equations estimated the HJC to be 2.6 mm medial, 7.2 mm posterior, and 21.7 mm proximal relative to the functional method. Additionally, the total 3D difference between the GT and functional methods was 23.5 mm compared to the 30.8 mm difference between the Bell and functional methods. These results suggest that the GT method is a viable option for estimating HJC coordinates.     

In vivo estimation of the glenohumeral joint centre by functional methods: Accuracy and repeatability assessment

Several algorithms have been proposed for determining the centre of rotation of ball joints. These algorithms are used rather to locate the hip joint centre. Few studies have focused on the determination of the glenohumeral joint centre. However, no studies have assessed the accuracy and repeatability of functional methods for glenohumeral joint centre.This paper aims at evaluating the accuracy and the repeatability with which the glenohumeral joint rotation centre (GHRC) can be estimated in vivo by functional methods. The reference joint centre is the glenohumeral anatomical centre obtained by medical imaging. Five functional methods were tested: the algorithm of Gamage and Lasenby (2002), bias compensated (Halvorsen, 2003), symmetrical centre of rotation estimation (Ehrig et al., 2006), normalization method (Chang and Pollard, 2007), helical axis (Woltring et al., 1985). The glenohumeral anatomical centre (GHAC) was deduced from the fitting of the humeral head.Four subjects performed three cycles of three different movements (flexion/extension, abduction/adduction and circumduction). For each test, the location of the glenohumeral joint centre was estimated by the five methods. Analyses focused on the 3D location, on the repeatability of location and on the accuracy by computing the Euclidian distance between the estimated GHRC and the GHAC. For all the methods, the error repeatability was inferior to 8.25 mm. This study showed that there are significant differences between the five functional methods. The smallest distance between the estimated joint centre and the centre of the humeral head was obtained with the method of Gamage and Lasenby (2002).     

A method to perform spinal motion analysis from functional X-ray images

Identifying spinal instability is an important aim for proper surgical treatment. Analysis of functional X-ray images delivers measurements of the range of motion (RoM) and the center of rotation (CoR). In today's practice, CoR determination is often omitted, due to the lack of accurate methods. The aim of this work was to investigate the accuracy of a new analysis software (FXA?) based on an in vitro experiment.Six bovine spinal specimens (L3-4) were mounted in a robot (KR125, Kuka). CoRs were predefined by locking the robot actuator tool center point to the estimated position of the physiologic CoR and taking a baseline X-ray. Specimens were deflected to various RoM_preset flexion/extension angles about the CoR_preset. Lateral functional radiographs were acquired and specimen movements were recorded using an optical motion tracking system (Optotrak Certus). RoM and CoR errors were calculated from presets for both methods. Prior to the experiment, the FXA? software was verified with artificially generated images.For the artificial images, FXA? yielded a mean RoM-error of 0.01±0.03° (bias±standard deviation). In the experiment, RoM-error of the FXA?-software (deviation from presets) was 0.04±0.13°, and 0.10±0.16° for the Optotrak, respectively. Both correlated with 0.998 (p<0.001). For RoM<1.0°, FXA? determined CoR positions with a bias>20 mm. This bias progressively decreased from RoM=1° (bias=6.0 mm) to RoM=9° (bias<1.5 mm).Under the assumption that CoR location variances <5 mm are clinically irrelevant on the lumbar spine, the FXA? method can accurately determine CoRs for RoMs>1°. Utilizing FXA?, polysegmental RoMs, CoRs and implant migration measurements could be performed in daily practice.     

The effect of surface area digitizations on the prediction of spherical anatomical geometries for computer-assisted applications

Intraoperative digitization of osseous structures is an integral component of computer-assisted orthopaedic surgery. This study determined the repeatability and accuracy of predicting known radii and center locations of spherical objects for different proportions of digitized surface areas and various sphere sizes. Also, we investigated these accuracies for some relevant near-spherical osseous structures where results from full area digitizations were considered to be true. Digitizations were performed using an electromagnetic tracker with a stylus on the total and fractional surfaces of 10 hemispheres, ranging from 10 to 28 mm in radius. Repeatability was quantified by digitizing five trials of the entire surface and various fractional areas of selected hemisphere sizes. Similar trials were conducted on models of a humeral and femoral head, using the full head area as baseline and digitizing 15 and 30 mm diameter areas of the full head. Mean error for the predicted radii and center positions of the hemispheres ranged from 0.39±0.29 to 0.14±0.07 mm and 0.52±0.31 to 0.22±0.12 mm, respectively. Repeatability for the predicted radii and centers produced maximum standard deviations of 0.31 and 0.42 mm, respectively. All errors decreased as fractional area (40%, 60%, 80% and 100%) increased (p<0.05). Radius of curvature and center position errors for the humeral head model were 1.51±2.11 and 2.28±1.51 mm, respectively. These errors for the femoral head model were 3.37±4.14 and 4.25±4.14 mm, respectively. Errors resulting from the prediction of radius and center indicate that non-spherical anatomical structures are more sensitive to the digitized area, and hence digitization of the largest surface possible seems warranted.     

Characterizing the effective stiffness of the pelvis during sideways falls on the hip

The force applied to the proximal femur during a fall, and thus hip fracture risk, is dependent on the effective stiffness of the body during impact. Accurate estimates of pelvis stiffness are required to predict fracture risk in a fall. However, the dynamic force–deflection properties of the human pelvis have never been measured in-vivo. Our objectives were to (1) measure the force–deflection properties of the pelvis during lateral impact to the hip, and (2) determine whether the accuracy of a mass-spring model of impact in predicting peak force depends on the characterization of non-linearities in stiffness. We used a sling and electromagnet to release the participant’s pelvis from heights up to 5 cm, simulating low-severity sideways falls. We measured applied loads with a force plate, and pelvis deformation with a motion capture system. In the 5 cm trials peak force averaged 1004 (SD 115) N and peak deflection averaged 26.3 (5.1) mm. We observed minimal non-linearities in pelvic force–deflection properties characterized by an 8% increase in the coefficient of determination for non-linear compared to linear regression equations fit to the data. Our model consistently overestimated peak force (by 49%) when using a non-linear stiffness equation, while a piece-wise non-linear fit (non-linear for low forces, linear for loads exceeding 300 N) predicted peak force to within 1% at our highest drop height. This study has important implications for mathematical and physical models of falls, including mechanical systems that assess the biomechanical effectiveness of protective devices aimed at reducing hip fracture risk.     

Determination of optimal conditions for hydrolysis of conjugated deoxynivalenol in corn and wheat with trifluoromethanesulfonic acid

Deoxynivalenol (DON) is a common mycotoxin contaminating corn and wheat and conjugated forms are also present. Recent studies have suggested that current analytical methods for DON analysis in feedstuffs do not detect conjugated forms in the absence of hydrolysis. The aim of the current study, therefore, was to determine the optimal conditions in which conjugated DON in corn and wheat can be hydrolyzed by trifluoromethanesulfonic acid (TFMSA). The optimal hydrolysis procedure was determined based on reaction duration, reaction temperature and TFMSA concentration. Total DON concentrations were determined using ELISA with free DON concentrations determined by ELISA and GC–MS. The optimal hydrolysis conditions for determination of conjugated DON in corn were found to be 0.5 M TFMSA incubated for 20 min at 22 °C. Optimal conditions for wheat samples were 0.5 M TFMSA incubated for 40 min at 40 °C. Using these optimal hydrolysis conditions, 10 corn samples and 10 wheat samples were analyzed to determine the presence of conjugated DON. All samples contained conjugated DON with an increase of 8–70% for DON in corn following hydrolysis and an increase of 7–75% for DON in wheat. This hydrolysis procedure will aid in the accurate determination of total DON and conjugated DON in feedstuffs.     

The effects of dual-channel functional electrical stimulation on stance phase sagittal kinematics in patients with hemiparesis

Sixteen subjects (aged 54.2 ± 14.1 years) with hemiparesis (7.9 ± 7.1 years since diagnosis) demonstrating a foot-drop and hamstrings muscle weakness were fitted with a dual-channel functional electrical stimulation (FES) system activating the dorsiflexors and hamstrings muscles. Measurements of gait performance were collected after a conditioning period of 6 weeks, during which the subjects used the system throughout the day. Gait was assessed with and without the dual-channel FES system, as well as with peroneal stimulation alone. Outcomes included lower limb kinematics and the step length taken with the non-paretic leg. Results with the dual-channel FES indicate that in the subgroup of subjects who demonstrated reduced hip extension but no knee hyperextension (n = 9), hamstrings FES increased hip extension during terminal stance without affecting the knee. Similarly, in the subgroup of subjects who demonstrated knee hyperextension but no limitation in hip extension (n = 7), FES restrained knee hyperextension without having an impact on hip movement. Additionally, step length was increased in all subjects. The peroneal FES had a positive effect only on the ankle. The results suggest that dual-channel FES for the dorsiflexors and hamstrings muscles may affect lower limb control beyond that which can be attributed to peroneal stimulation alone.     

Influence of muscle anatomical cross-sectional area on the moment arm length of the triceps brachii muscle at the elbow joint

The purpose of this study was to test the hypothesis that the musculotendon moment arm length is affected by the muscle anatomical cross-sectional area. The moment arm length of the triceps brachii (TB) muscle at 30°, 50°, 70°, 90°, 110° elbow flexion positions was measured in sagittal magnetic resonance images (MRI) of 18 subjects as the perpendicular distance between the center of the pulley of the humerus to the line through the center of the TB tendon. The moment arm increased as the elbow flexion angle decreased, from 1.74±0.13 cm at 110° to 2.39±0.14 cm at 30°. The maximal anatomical cross-sectional area of the TB muscle was significantly correlated with the moment arms at all joint positions (r=0.545–0.803, p<0.05). Furthermore, the circumference of the upper arm was also significantly correlated with the moment arms at all joint positions, except for 70° (r=0.504–0.702, p<0.05). These results indicate that the moment arm length of the TB muscle is affected by the muscle anatomical cross-sectional area.     

Impact of the method of exposure in total hip arthroplasty on balancing ability in response to sudden unidirectional perturbation in the first six months of the postoperative period

Introduction and objectiveTotal hip arthroplasty affects 3–5% of the elderly population. Therefore, the effectiveness of surgery and the ensuing rehabilitation is of great significance. This study investigated balancing ability in response to sudden unidirectional perturbation changes during the first 6 months of the postoperative period with respect to different methods of joint exposure during the operation (antero-lateral, direct-lateral and posterior to preserve the joint capsule). Our hypothesis is that the results may provide a tool to improve the rehabilitation procedures.Materials and methodsThe dynamic balancing ability of 25 patients with direct-lateral exposure, 22 with antero-lateral exposure and 25 with posterior exposure during a total hip arthroplasty was examined using ultrasound-based provocation tests prior to and at 6 weeks, 12 weeks and 6 months after total hip arthroplasty. The control group was represented by 45 healthy subjects of identical age. The dynamic balancing ability after unidirectional perturbation was characterised by Lehr’s damping ratio calculated from the results of tests performed with the patient standing on both limbs, standing on the affected limb and standing on the non-affected limb.ResultsIn the case of direct-lateral and antero-lateral exposure, Lehr’s damping ratio significantly decreased compared to the preoperative values at 6 weeks postoperatively, but it increased steadily afterwards. Lehr’s damping ratio while standing on the affected limb was significantly lower – even at 6 months postoperatively – than that of the control group. In the case of posterior exposure, Lehr’s damping ratio continuously increased in the postoperative period and corresponded to that of the control group at 6 months after total hip arthroplasty.Discussion and conclusionFor patients operated on using direct-lateral and antero-lateral exposure methods, the dynamic balancing ability continuously improved in the first 6 months of the postoperative period, but the dynamic balancing ability of the affected limb differed from that of the control group. In the case of posterior exposure to preserve the joint capsule the dynamic balancing ability evaluated a more rapidly compared to the other two exposure methods. There was no significant difference in the balancing ability of the control group at 6 months after total hip arthroplasty with posterior exposure. The increasing range of joint motion, muscle development, and the development of the dynamic balancing ability should be taken into account when compiling rehabilitation protocols. Differences related to the method of exposure should be considered when developing the dynamic balancing ability and abandoning therapeutic aids.     

Segmentation d’images de lésions cérébrales primitives en TEP FET : influence du volume de travail

Purpose(1) Evaluate the reproducibility of segmentation methods depending on the preselection region for tumour volume determination on ¹⁸F-fluoro-ethyl-tyrosine (FET) PET. (2) Evaluate the intra and inter-operator reproducibility of the manual delineation. (3) Compare this delineation with the segmentation methods.Materials and methodsEighteen FET PET of patients with glioblastoma were analysed. Preselection regions were determined prior to any segmentation. Two physicians delineated the tumour volume manually. The tumour volume was also delineated with a threshold method (40 and 70% of SUV_max), and a random walk based method. Pearson coefficient (r) (P < 0.05 for r > 0.468) and Jaccard indices (JI) were used to compare the volumes.ResultsManual delineation was reproducible with r = 0.97 and IJ = 0.65 for intra-operator, and r = 0.76 and IJ = 0.45 for inter-operator reproducibility. The preselection regions for a given lesion were different and the segmentation varied with the preselection region: r = 0.55 JI = 0.58; r = 0.85 JI = 0.83; r = 0.70 JI = 0.39 respectively for the threshold of 40%, 70% and the random walk. The segmentation differed form de manual delineation with r = 0.37 and JI = 0.16; r = 0.54 and JI = 0.42; r = 0.43 and JI = 0.37 respectively for the threshold of 40%, 70% and the random walk.ConclusionThe reproducibility of the segmentation methods depends extensively on the preselection region. The intra-operator reproducibility of cerebral lesion delineation on FET PET is satisfactory. The inter-operator reproducibility could be improved.     

Control of lateral weight transfer is associated with walking speed in individuals post-stroke

Restoring functional gait speed is an important goal for rehabilitation post-stroke. During walking, transferring of one’s body weight between the limbs and maintaining balance stability are necessary for independent functional gait. Although it is documented that individuals post-stroke commonly have difficulties with performing weight transfer onto their paretic limbs, it remains to be determined if these deficits contributed to slower walking speeds. The primary purpose of this study was to compare the weight transfer characteristics between slow and fast post-stroke ambulators. Participants (N = 36) with chronic post-stroke hemiparesis walked at their comfortable and maximal walking speeds on a treadmill. Participants were stratified into 2 groups based on their comfortable walking speeds (≥0.8 m/s or <0.8 m/s). Minimum body center of mass (COM) to center of pressure (COP) distance, weight transfer timing, step width, lateral foot placement relative to the COM, hip moment, peak vertical and anterior ground reaction forces, and changes in walking speed were analyzed. Results showed that slow walkers walked with a delayed and deficient weight transfer to the paretic limb, lower hip abductor moment, and more lateral paretic limb foot placement relative to the COM compared to fast walkers. In addition, propulsive force and walking speed capacity was related to lateral weight transfer ability. These findings demonstrated that deficits in lateral weight transfer and stability could potentially be one of the limiting factors underlying comfortable walking speeds and a determinant of chronic stroke survivors’ ability to increase walking speed.     

Ways to measure body temperature in the field

Body temperature (T_b) represents one of the key parameters in ecophysiological studies with focus on energy saving strategies. In this study we therefore comparatively evaluated the usefulness of two types of temperature-sensitive passive transponders (LifeChips and IPTT-300) and one data logger (iButton, DS1922L) mounted onto a collar to measure T_b in the field. First we tested the accuracy of all three devices in a water bath with water temperature ranging from 0 to 40 °C. Second, we evaluated the usefulness of the LifeChips and the modified iButtons for measuring T_b of small heterothermic mammals under field conditions. For this work we subcutaneously implanted 14 male edible dormice (Glis glis) with transponders, and equipped another 14 males with data loggers to simultaneously record T_b and oxygen consumption with a portable oxygen analyzer (Oxbox). In one individual we recorded T_b with both devices and analyzed recorded T_b patterns.LifeChips are able to measure temperature within the smallest range from 25 to 40 °C with an accuracy of 0.07±0.12 °C. IPTT-300 transponders measured temperature between 10 and 40 °C, but accuracy decreased considerably at values below 30 °C, with maximal deviations of nearly 7 °C. An individual calibration of each transponder is therefore needed, before using it at low T_bs. The accuracy of the data logger was comparatively good (0.12±0.25 °C) and stable over the whole temperature range tested (0–40 °C). In all three devices, the repeatability of measurements was high.LifeChip transponders as well as modified iButtons measured T_b reliably under field conditions. Simultaneous T_b-recordings in one edible dormouse with an implanted LifeChip and a collar-mounted iButton revealed that values of both measurements were closely correlated. Taken together, we conclude that implanted temperature-sensitive transponders represent an appropriate and largely non-invasive method to measure T_b also under field conditions.     

Lower limb joint work and joint work contribution during downhill and uphill walking at different inclinations

Work performance and individual joint contribution to total work are important information for creating training protocols, but were not assessed so far for sloped walking. Therefore, the purpose of this study was to analyze lower limb joint work and joint contribution of the hip, knee and ankle to total lower limb work during sloped walking in a healthy population. Eighteen male participants (27.0 ± 4.7 yrs, 1.80 ± 0.05 m, 74.5 ± 8.2 kg) walked on an instrumented ramp at inclination angles of 0°, ±6°, ±12° and ±18° at 1.1 m/s. Kinematic and kinetic data were captured using a motion-capture system (Vicon) and two force plates (AMTI). Joint power curves, joint work (positive, negative, absolute) and each joint’s contribution to total lower limb work were analyzed throughout the stance phase using an ANOVA with repeated measures. With increasing inclination positive joint work increased for the ankle and hip joint and in total during uphill walking. Negative joint work increased for each joint and in total work during downhill walking. Absolute work was increased during both uphill (all joints) and downhill (ankle & knee) walking. Knee joint contribution to total negative and absolute work increased during downhill walking while hip and ankle contributions decreased. This study identified, that, when switching from level to a 6° and from 6° to a 12° inclination the gain of individual joint work is more pronounced compared to switching from 12° to an 18° inclination. The results might be used for training recommendations and specific training intervention with respect to sloped walking.     

Contact forces in the tibiofemoral joint from soft tissue tensions: Implications to soft tissue balancing in total knee arthroplasty

Proper tension of the knee’s soft tissue envelope is important during total knee arthroplasty; incorrect tensioning potentially leads to joint stiffness or instability. The latter remains an important trigger for revision surgery. The use of sensors quantifying the intra-articular loads, allows surgeons to assess the ligament tension at the time of surgery. However, realistic target values are missing. In the framework of this paper, eight non-arthritic cadaveric specimens were tested and the intra-articular loads transferred by the medial and lateral compartment were measured using custom sensor modules. These modules were inserted below the articulating surfaces of the proximal tibia, with the specimens mounted on a test setup that mimics surgical conditions. For both compartments, the highest loads are observed in full extension. While creating knee flexion by lifting the femur and flexing the hip, mean values (standard deviation) of 114 N (71 N) and 63 N (28 N) are observed at 0° flexion for the medial and lateral compartment respectively. Upon flexion, both medial and lateral loads decrease with mean values at 90° flexion of 30 N (22 N) and 6 N (5 N) respectively. The majority of the load is transmitted through the medial compartment. These observations are linked to the deformation of the medial and lateral collaterals, in addition to the anatomy of the passive soft tissues surrounding the knee. In conclusion, these findings provide tangible clinical guidance in assessing the soft tissue loads when dealing with anatomically designed total knee implants.     

Fully automatic input function determination program for simple noninvasive 123I-IMP microsphere cerebral blood flow quantification method

We recently developed a simple noninvasive ¹²³I-IMP microsphere (SIMS) method using chest dynamic planar images and brain single photon emission computed tomography. The SIMS method is an automatic analysis method, except for the process of setting the region of interest (ROI) of the input function. If a fully automatic ROI setting algorithm can be developed to determine the input function for the SIMS method, repeatability and reproducibility of the analysis of regional cerebral blood flow (rCBF) of the SIMS method can be guaranteed. The purpose of this study is to develop a fully automatic input function determination program for the SIMS method and to confirm the clinical usefulness of this program.The automatic input function determination program consists of two ROI setting programs for the PA and lung regions, and it is developed using the image phase analysis of a chest RI angiogram. To confirm the clinical usefulness of this program, the rCBF in 34 patients measured using the automatic method were compared with the values obtained through the manual setting method.Input functions by the automatic and manual methods were approximately equal. A good correlation was observed between the rCBF values obtained by the automatic method and those obtained by the manual setting method (r = 0.96, p < 0.01).Further, the total time taken for the automatic SIMS analysis is 1–2 min as compared to 20–30 min for the current analysis, and therefore, this technique contributes to the improvement of the throughput of nuclear medical examinations.     

Estimating severity of sideways fall using a generic multi linear regression model based on kinematic input variables

Many research groups have studied fall impact mechanics to understand how fall severity can be reduced to prevent hip fractures. Yet, direct impact force measurements with force plates are restricted to a very limited repertoire of experimental falls. The purpose of this study was to develop a generic model for estimating hip impact forces (i.e. fall severity) in in vivo sideways falls without the use of force plates.Twelve experienced judokas performed sideways Martial Arts (MA) and Block (‘natural’) falls on a force plate, both with and without a mat on top. Data were analyzed to determine the hip impact force and to derive 11 selected (subject-specific and kinematic) variables. Falls from kneeling height were used to perform a stepwise regression procedure to assess the effects of these input variables and build the model.The final model includes four input variables, involving one subject-specific measure and three kinematic variables: maximum upper body deceleration, body mass, shoulder angle at the instant of ‘maximum impact’ and maximum hip deceleration. The results showed that estimated and measured hip impact forces were linearly related (explained variances ranging from 46 to 63%). Hip impact forces of MA falls onto the mat from a standing position (3650 ± 916 N) estimated by the final model were comparable with measured values (3698 ± 689 N), even though these data were not used for training the model. In conclusion, a generic linear regression model was developed that enables the assessment of fall severity through kinematic measures of sideways falls, without using force plates.     

A method for CP 47, 497 a synthetic non-traditional cannabinoid in human urine using liquid chromatography tandem mass spectrometry

A rapid method has been developed to analyse CP 47, 497 in human urine. Urine samples were diluted with water:acetonitrile (90:10, v/v) and sample aliquots were analysed by triple quadrupole tandem mass spectrometry with a runtime of 5 min. Multiple reaction monitoring (MRM) as survey scan was performed. The method was validated in urine, according to an in-house validation protocol based on the criteria defined in Commission Decision 2002/657/EC. Three MRM transitions were monitored. The decision limit (CCα) was 0.01 μg mL^?1 and for the detection capability a (CCβ) value of 0.02 μg mL^?1 was obtained. The measurement uncertainty of the method was 21%. Fortifying human urine samples (n = 18) in three separate assays, show the accuracy of the method to be between 95 and 96%. The precision of the method, expressed as RSD values for the within-lab reproducibility at the three levels of fortification (0.1, 0.15 and 0.2 μg mL^?1) was less than 10% respectively. The method proved to be simple, robust and time efficient. To the best of our knowledge there are no LC–MS methods for the determination of CP 47, 497 with validation data in urine.     

Assessing the accuracy and precision of musculoskeletal motion tracking using cine-PC MRI on a 3.0T platform

The rising cost of musculoskeletal pathology, disease, and injury creates a pressing need for accurate and reliable methods to quantify 3D musculoskeletal motion, fostering a renewed interest in this area over the past few years. To date, cine-phase contrast (PC) MRI remains the only technique capable of non-invasively tracking in vivo 3D musculoskeletal motion during volitional activity, but current scan times are long on the 1.5T MR platform (～2.5 min or 75 movement cycles). With the clinical availability of higher field strength magnets (3.0T) that have increased signal-to-noise ratios, it is likely that scan times can be reduced while improving accuracy. Therefore, the purpose of this study is to validate cine-PC MRI on a 3.0T platform, in terms of accuracy, precision, and subject-repeatability, and to determine if scan time could be minimized. On the 3.0T platform it is possible to limit scan time to 2 min, with sub-millimeter accuracy (<0.33 mm/0.97°), excellent technique precision (<0.18°), and strong subject-repeatability (<0.73 mm/1.10°). This represents reduction in imaging time by 25% (42 s), a 50% improvement in accuracy, and a 72% improvement in technique precision over the original 1.5T platform. Scan time can be reduced to 1 min (30 movement cycles), but the improvements in accuracy are not as large.