Modeling, validation and application of a mathematical tissue-equivalent breast phantom for linear slot-scanning digital mammography.

This paper presents a mathematical tissue-equivalent breast phantom for linear slot-scanning digital mammography. A recently developed prototype linear slot-scanning digital mammography system was used for model validation; image quality metrics such as image contrast and contrast-to-noise ratio were calculated. The results were in good agreement with values measured using a physical breast-equivalent phantom designed for mammography. The estimated pixel intensity of the mathematical phantom, the analogue-to-digital conversion gain and the detector additive noise showed good agreement with measured values with correlation of nearly 1. An application of the model, to examine the feasibility of using a monochromatic filter for dose reduction and improvement of image quality in slot-scanning digital mammography, is presented.

Measuring three-dimensional knee kinematics under torsional loading.

Excessive knee joint laxity is often used as an indicator of joint disease or injury. Clinical assessment devices are currently limited to anterior-posterior drawer measurements, while tools used to measure movement in the remaining degrees of freedom are either invasive or prone to soft tissue artefact. The objective of this work was, therefore, to develop a methodology whereby in vivo knee joint kinematics could be measured in three dimensions under torsional loading while still maintaining a non-invasive procedure. A device designed to administer a subject-normalized torque in the transverse plane of the knee was securely fastened to the outer frame of an open magnetic resonance imaging (MRI) magnet. Low resolution 3D T1-weighted images (6.25 mm slice thickness) were generated by the 0.2 Tesla MRI scanner in less than 3 min while the joint was under load. The 3D image volume was then shape-matched to a high resolution image volume (1.56 mm slice thickness) scanned in a no-load position. Three-dimensional rotations and translations of the tibia with respect to the femur were calculated by comparing the transformation matrices before and after torque was applied. Results from six subjects showed that this technique was repeatable over five trials with the knee in extended and flexed positions. Differences in range of rotation were shown between subjects and between knee positions, suggesting that this methodology has sufficient utility for further application in clinical studies.

Biomechanical variables associated with Achilles tendinopathy in runners.

OBJECTIVE: The aim of this study was to investigate the kinetics, kinematics and muscle activity in runners with Achilles tendinopathy. DESIGN: Case-control study. SETTING: Biomechanics laboratory. PARTICIPANTS: 21 runners free from injury and 21 runners with Achilles tendinopathy performed 10 running trials with standardised running shoes. Injured runners were diagnosed clinically according to established diagnostic criteria. Uninjured runners had been injury-free for at least 2 years. MAIN OUTCOME MEASUREMENTS: During each trial, kinetic and lower limb kinematic data were measured using a strain gauge force plate and six infrared cameras respectively. Electromyographic (EMG) data from six muscles (tibialis anterior (TA), peroneus longus (PE), lateral gastrocnemius (LG), rectus femoris (RF), biceps femoris (BF) and gluteus medius (GM)) were measured with a telemetric EMG system. RESULTS: Knee range of motion (heel strike to midstance) was significantly lower in injured runners than in uninjured runners. Similarly, preactivation (integrated EMG (IEMG) in 100 ms before heel strike) of TA was lower for injured runners than uninjured runners. RF and GM IEMG activity 100 ms after heel strike was also lower in the injured group. However, impact forces were not different between the two groups. CONCLUSION: Altered knee kinematics and reduced muscle activity are associated with Achilles tendinopathy in runners. Rehabilitation exercises or other mechanisms (e.g. footwear) that affect kinematics and muscle activity may therefore be beneficial in the treatment of runners with Achilles tendinopathy.

Non-random fluctuations in power output during self-paced exercise.

OBJECTIVES: To analyse the power output measured during a self-paced 20-km cycling time trial, during which power output was free to vary, in order to assess the level and characteristics of the variability in power output that occurred during the exercise bout. METHODS: Eleven well-trained cyclists performed a 20-km cycling time trial, during which power output was sampled every 200 m. Power spectrum analysis was performed on the power output data, and a fractal dimension was calculated for each trial using the Higuchi method. RESULTS: In all subjects, power output was maintained throughout the trial until the final kilometre, when it increased significantly, indicating the presence of a global pacing strategy. The power spectrum revealed the presence of 1/f-like scaling of power output and multiple frequency peaks during each trial, with the values of the frequency peaks changing over the course of the trial. The fractal dimension (D-score) was similar for all subjects over the 20-km trial and ranged between 1.5 and 1.9. CONCLUSIONS: The presence of an end spurt in all subjects, 1/f-like scaling and multiple frequency peaks in the power output data indicate that the measured oscillations in power output during cycling exercise activity may not be system noise, but may rather be associated with system control mechanisms that are similar in different individuals.

Rectification and non-linear pre-processing of EMG signals for cortico-muscular analysis.

Rectification of the electromyographic (EMG) signal is a commonly used pre-processing procedure that allows detection of significant coherence between EMG and measured cortical signals. However, despite its accepted and wide-spread use, no detailed analysis has been presented to offer insight into the precise function of rectification. We begin this paper with arguments based on single motor unit action potential (AP) trains to demonstrate that rectification effectively enhances the firing rate information of the signal. Enhancement is achieved by shifting the peak of the AP spectrum toward the lower firing rate frequencies, whilst maintaining the firing rate spectra. A similar result is obtained using the analytic envelope of the signal extracted using the Hilbert transform. This argument is extended to simulated EMG signals generated using a published EMG model. Detection of firing rate frequencies is obtained using phase randomised surrogate data, where the original EMG power spectrum exceeds the averaged rectified surrogate spectra at integer multiples of firing rate frequencies. Model simulations demonstrate that this technique accurately determines grouped firing rate frequencies. Extraction of grouped firing rate frequencies prior to coherency analyses may further aid interpretation of significant cortico-muscular coherence findings.

Effect of dopamine denervation and dopamine agonist administration on serine phosphorylation of striatal NMDA receptor subunits.

Sensitization of striatal N-methyl-d-aspartate (NMDA) receptors has been implicated in the pathogenesis of the response alterations associated with dopaminomimetic treatment of parkinsonian animals and patients. To determine whether serine phosphorylation of NMDA receptor subunits by activation of Ca2+/calmodulin-dependent protein-kinase II (CaMKII) contributes to this process, we examined the effects of unilateral nigrostriatal ablation with 6-hydroxydopamine and subsequent treatment with levodopa, SKF 38393 (D1-preferring dopamine agonist), or quinpirole (D2-preferring agonist) on motor responses and phosphorylation states. Three weeks of twice-daily levodopa administration to rats shortened the duration of their rotational response to levodopa or SKF 38393 challenge, but prolonged the duration of quinpirole-induced rotation. At the same time, levodopa treatment elevated serine phosphorylation of striatal NR2A (p<0.02), but not that of NR2B subunits, without associated changes in subunit protein levels. Chronic treatment with SKF 38393 increased NR2A (p<0.0001) but decreased NR2B (p<0.004) serine phosphorylation. In contrast, chronic quinpirole treatment had no effect on NR2A but increased NR2B phosphorylation (p<0.0001). The acute intrastriatal injection of the CaMKII inhibitor KN93 (1.0 micrograms) not only normalized the levodopa-induced motor response alterations but also attenuated the D1 and D2 receptor-mediated serine phosphorylation of NR2A and NR2B subunits, respectively (p<0.02). These results suggest that a CaMKII-mediated rise in serine phosphorylation of NMDA receptor subunits induced by intermittent stimulation of D1 or D2 dopaminergic receptors contributes to the apparent enhancement in striatal NMDA receptor sensitivity and thus to the dopaminergic response plasticity in levodopa-treated parkinsonian rats.

Enhanced tyrosine phosphorylation of striatal NMDA receptor subunits: effect of dopaminergic denervation and L-DOPA administration.

Sensitization of striatal N-methyl-D-aspartate receptors (NMDAR) has been linked to events leading to the motor response changes associated with the administration of dopaminomimetics to parkinsonian animals and patients. To determine whether tyrosine phosphorylation of NMDAR subunits contributes to the apparent long-term enhancement in synaptic efficacy of these receptors, we examined the effect of unilateral nigrostriatal dopamine system ablation with 6-hydroxydopamine followed by twice-daily treatment with l-DOPA on the phosphorylation state of rat striatal NR2A and NR2B subunits. Three weeks of intermittent l-DOPA administration produced a shortening in the duration of the rotational response to dopaminergic challenge and other changes mimicking those occurring in patients with Parkinson's disease. Concurrently, tyrosine phosphorylation of NR2A and especially of NR2B subunits increased ipsilateral to the lesion (20+/-5% and 46+/-7% of intact striatum, respectively; p<0.01) without attendant changes in subunit protein levels. Selective blockade of NR2B subunits with ACEA 10-1244, but not of NR2A subunits with MDL 100,453, reversed the l-DOPA-induced response alterations. The intrastriatal injection of a tyrosine kinase inhibitor, genistein, at a dose (2.0 microg) that normalized the response shortening, attenuated the NR2A and NR2B phosphorylation increase by about 12% and 24%, respectively (p<0.01). Taken together, these results suggest that augmented tyrosine phosphorylation of NR2B subunits, alone or in combination with the smaller rise in NR2A subunit phosphorylation, contributes to the apparent enhancement in striatal NMDAR sensitivity and thus to the plastic alterations in dopaminergic responses in l-DOPA-treated parkinsonian rats.

Biomechanics of running gait.

With the recent world-wide upsurge in running, the preponderance of research has been of a physiological nature. This is understandable when the cardiovascular benefits are considered. However, the biomechanical component is also very important, especially when trying to establish the aetiology of various musculoskeletal injuries or the principles underlying successful technique. In this paper, therefore, we are concerned with various biomechanical aspects of sprinting, middle and long distance running, and jogging. The topics covered include: the class of running gait (sprinting, jogging, ascending/descending, load carrying, treadmill); electromyography; joints; kinematics (both linear and angular); kinetics (force place, joint forces and torques, work/energy/power, air resistance); mathematical techniques and models; orthopedic acids; various pathologies; different methods of recording motion; and sports footwear and surfaces. The material should be relevant to both the elite and recreational athlete.

Cerebral palsy and rhizotomy. A 3-year follow-up evaluation with gait analysis.

A recent increase in the popularity of selective rhizotomy for reduction of spasticity in cerebral palsy has led to a demand for more objective studies of outcome and long-term follow-up results. The authors present the results of gait analysis on 14 children with spastic cerebral palsy, who underwent selective posterior rhizotomy in 1985. Sagittal plane gait patterns were studied before surgery and at 1 and 3 years after surgery using a digital camera system. The parameters measured included the range of motion at the knee and thigh, stride length, speed of walking, and cadence. The range of motion at the knee was significantly increased at 1 year after surgery and further improved to a nearly normal range at 3 years after surgery. In contrast, postoperative measurements of thigh range exceeded normal values at 1 year, but decreased toward normal range at 3 years. While improvements in range of motion continued between Years 1 and 3, the children developed a more extended thigh and knee position, which indicated a more upright walking posture. Stride length and speed of walking also improved, while cadence remained essentially unchanged. This 3-year follow-up study, the first to examine rhizotomy using an objective approach, has provided some encouraging results regarding early functional outcome.

Gait before and 10 years after rhizotomy in children with cerebral palsy spasticity.

OBJECT: Selective dorsal rhizotomy is a neurosurgical procedure performed for the relief of spasticity in children with cerebral palsy, but its long-term functional efficacy is still unknown. The authors sought to address this issue by means of an objective, prospective study in which quantitative gait analysis was used. METHODS: Eleven children with spastic diplegia (mean age at initial surgery 7.8 years) were evaluated preoperatively in 1985 and then at 1, 3, and at least 10 years after surgery. For comparison, 12 age-matched healthy individuals were also studied. Retroreflective targets were placed over the hip, knee, and ankle joints, and each individual's gait was videotaped. The video data were subsequently entered into a computer for extraction and analysis of the gait parameters. An analysis of variance yielded a significant time effect (p < 0.05), and post hoc comparisons revealed differences before and after surgery and with respect to the healthy volunteers. The knee and hip ranges of motion (59 degrees and 44 degrees, respectively, for healthy volunteers) were significantly restricted in children with spastic diplegia prior to surgery (41 degrees and 41 degrees, respectively), but were within normal limits after 10 years (52 degrees and 45 degrees, respectively). The knee and hip midrange values (31 degrees and 3 degrees, respectively, for healthy volunteers), indicative of posture, were significantly elevated preoperatively (42 degrees and 15 degrees) and increased sharply at 1 year (56 degrees and 18 degrees), but by 10 years they had decreased to within normal limits (36 degrees and 9 degrees). Step length and velocity improved postoperatively but were not within the normal range after 10 years. Ten years after surgery these patients not only had increased ranges of motion, but also used that movement at approximately a normal midrange point. CONCLUSIONS: Selective dorsal rhizotomy is an effective method for alleviating spasticity. Furthermore, the authors provide evidence to show that lasting functional benefits, as measured by improved gait, can also be obtained.

Anterior cruciate ligament reconstruction and joint dynamics during stair climbing.

Athletes with anterior cruciate ligament (ACL) deficiencies exert decreased knee extension moments during level walking (quadriceps avoidance gait), and yet within a few months of ACL reconstruction they are often expected to return to competitive sport. To investigate this issue further, 10 normal subjects and seven ACL deficient patients were evaluated both pre- and post-operatively (mean follow-up of 6 months), and each performed multiple trials ascending a staircase which consisted of three steps. Bilateral joint angles, moments, powers, and work were measured and the data were ensemble averaged and statistically analyzed (repeated measures ANOVA with significance level set at 0.05). Anterior-posterior knee laxity decreased significantly (from 7.9 mm to 5.8 mm) while subjective knee function also improved following ACL reconstruction (knee score increased from 70.4 to 88.5). Pre-operatively, there were no statistically significant differences in biomechanical parameters between the patients' ACL-deficient and intact sides and the normal subjects. Post-operatively, however, statistically significant reductions were seen for the peak moment (91.9 vs 22.5 Nm), power (181 vs 84 W), and work performed (28.0 vs -5.6 J) at the injured knee, which was also the knee from which the patellar tendon graft had been harvested. These reductions were accommodated by significant increases in excursion, moment, and power at the contralateral ankle joint. The results indicate that while the ACL reconstruction were successful in restoring anterior-posterior knee stability, the decrease in knee power and work performed post-operatively by the injured (i.e., donor) knee suggests that donor site morbidity may need to be critically evaluated over a long-term period.

Effect of foot-progression angle on hip joint moments during gait.

Loosening has emerged as the most serious long-term complication of total hip replacement and torsional loading of the femoral implant has been implicated as a possible cause. In an effort to explore a strategy for minimizing this risk, the following hypothesis was tested: the foot-progression angle has a significant effect on the resultant hip moments, and particularly the internal-external rotation moment, during level walking. Twelve normal subjects performed a total of nine trials: three in which they walked normally with the right foot pointing approximately straight ahead; three in which they were told to walk with the foot internally rotated approximately 30 degrees; and three in which the foot was externally rotated about 30 degrees. The inverse dynamics approach was used to integrate the body segment parameter, kinematic and force plate data, and to solve for the resultant moment at the right hip joint. In all three conditions--foot straight, foot in, and foot out-the subjects walked at the same average speed of 1.5 (+/- 0.3) ms-1. For the flexion-extension moment (where the maximum flexion moment of 95 Nm was in good agreement with other published data), there was no significant difference between the three foot orientation conditions. For the abduction-adduction moment, the foot straight condition exhibited the classic double peak pattern with a maximum abductor moment of 57 Nm, and there was no statistically significant difference between the three curves.(ABSTRACT TRUNCATED AT 250 WORDS)

A neural network representation of electromyography and joint dynamics in human gait.

Optimization theory and other mathematical algorithms have traditionally been used to model the relationship between muscle activity and lower-limb dynamics during human gait. We introduce here an alternative approach, based on artificial neural networks with the back-propagation algorithm, to map two different transformations: (1) EMG-->joint angles; and (2) EMG-->joint moments. Normal data for 16 muscles and three joint moments and angles (hip, knee, and ankle) were adapted from the literature [Winter (1987), The Biomechanics and Motor Control of Human Gait]. Both networks were successfully trained to map the input vector onto the output vector. The models were tested by feeding in an input vector where all 16 muscles were slightly different (20%) from the training data, and the predicted output vectors suggested that the models were valid. The trained networks were then used to perform two separate simulations: 30% reduction in soleus activity; and removal of rectus femoris. Net 2, in which electromyography was mapped onto joint moments, provided the most reasonable results, suggesting that neural networks can provide a successful platform for both biomechanical modeling and simulation. We believe that this paper has demonstrated the potential of artificial neural networks, and that further efforts should be directed towards the development of larger training sets based on normal and pathological data.

Abduction-adduction moments at the knee during stair ascent and descent.

To examine the relative magnitude of the knee abduction-adduction moments during stair climbing, ten normal subjects (average weight 660 N, leg length 0.962 m, height 1.74 m) were studied during repeated trials of stair ascent and descent. Data were collected using a four-camera video system and two forces plates incorporated within a flight of three stairs. The inverse dynamics approach was used to calculate internal moments at the knee, and these moments were normalized in magnitude (to percent body weight and leg length) and time (percent stance). The primary findings were: (1) knee joint moments were similar in shape and magnitude for the first and second steps during both stair ascent and descent; (2) the abduction knee moments, although comparable in magnitude (25-45 Nm), were statistically smaller than the extension moments (60-85 Nm) for stair ascent and descent; and (3) the moment patterns were exclusively abductor throughout stance, indicating that the ground reaction vector always passed medial to the knee joint center. Although the knee abduction-adduction moment is not in the primary plane of motion, its magnitude should not be ignored when trying to understand the stability and function of the knee during stair climbing.

Closed loop problems in biomechanics. Part II--an optimization approach.

A closed loop problem in biomechanics may be defined as a problem in which there are one or more closed loops formed by the human body in contact with itself or with an external system. Under certain conditions the problem is indeterminate--the unknown forces and torques outnumber the equations. Force transducing devices, which would help solve this problem, have serious drawbacks, and existing methods are inaccurate and non-general. The purposes of the present paper are (1) to develop a general procedure for solving closed loop problems; (2) to illustrate the application of the procedure; and (3) to examine the validity of the procedure. A mathematical optimization approach is applied to the solution of three different closed loop problems--walking up stairs, vertical jumping and cartwheeling. The following conclusions are drawn: (1) the method described is reasonably successful for predicting horizontal and vertical reaction forces at the distal segments although problems exist for predicting the points of application of these forces; (2) the results provide some support for the notion that the human neuromuscular mechanism attempts to minimize the joint torques and thus, to a certain degree, the amount of muscular effort; (3) in the validation procedure it is desirable to have a force device for each of the distal segments in contact with a fixed external system; and (4) the method is sufficiently general to be applied to all classes of closed loop problems.

Closed loop problems in biomechanics. Part I--a classification system.

Biomechanics researchers have relied heavily on the inverse dynamics approach for calculating the forces and torques at human joints. However, implicit in this approach is the assumption that there are sufficient independent equations of motion to uniquely determine these unknown kinetics. There exists a class of problems, commonly referred to as closed loop problems, when there are insufficient equations and indeterminacy arises. The purposes of the present paper are (1) to develop a general classification system of closed loop problems for whole body movements; and (2) to identify the minimum number of force transducing devices necessary to uniquely determine joint kinetics for these problems. The classification system is based on the human subject's interaction with his environment and with himself. Two criteria are considered: first, the number of the subject's extremities in contact with fixed external reference systems, and second, the number of closed loops formed by those extremities not in contact with fixed external systems. Different combinations of these two criteria are examined and grouped into five cases according to the degree to which the equations of motion are over-determined, determined, or under-determined. Examples are given to illustrate the concepts. It is felt that the use of this system should aid in the understanding of joint force and torque calculations, especially with regard to the under-determined cases.

The effects of ankle guards and taping on joint motion before, during, and after a squash match.

The effects of ankle guards and taping on joint motion before, during, and after exercise were studied. Twelve league squash players played two matches, each lasting 1 hour. Two different ankle guards, and two types of tape applied by the same method, served as supports. A specially designed goniometer with electronic digital display (accuracy 1 degree) was used to determine joint range of motion: plantar-flexion and dorsiflexion, neutral inversion and eversion, plantar-flexed inversion and eversion. The results were statistically analyzed to determine the significance of the restriction provided by the supports. This revealed that the two ankle guards provided no significant support. The two tapes, however, provided significant support before exercise and after 10 minutes but not after 1 hour of exercise. Nonelastic (zinc oxide) tape proved to be the most restrictive at all times measured, especially prior to exercise, when the ankle's range of motion was decreased between 30% and 50%. However, once exercise commenced, the tape stretched, and restriction became less effective.

Phasic behavior of EMG signals during gait: Use of multivariate statistics.

The present study represents an attempt to ascertain whether there are some underlying trends that, in some combination, can explain all the variations in the linear envelopes of 16 EMG signals of selected leg muscles. Two kinds of analyses were performed: (a) a factor analysis of EMG data corresponding to 16 muscles of the lower limb and (b) a "multi-dimensional scaling" (MDS) procedure. The latter technique involved mapping the Cartesian coordinates for 16 points subject to the constraint that the distance between any two points reflected the degree of coactivity for the corresponding muscles. The results of these analyses showed that four factors could account for 91.5% of the variance in the original data set. These factors could be clearly demarcated on the "muscle map," tending to support the notion that there are motor "programs" for groups of muscles that have to perform a given function during locomotion. Further analysis of the loading matrix (i.e., correlations between each EMG vector and each of the four factors) showed groups of muscles that acted in a similar manner. The muscle groups could be divided into those that act at the times of (a) heelstrike, (b) single limb loading response, (c) propulsion phase, or else (d) acted in a biphasic manner.

Three-dimensional point localisation in low-dose X-ray images using stereo-photogrammetry.

A stereo-photogrammetric method for three-dimensional reconstruction of points in low-dose digital X-ray images obtained using a scanner with similar imaging geometry to that of computed tomography scan projection radiography, was analysed. A calibration frame containing 25 radio-opaque markers with known three-dimensional locations was scanned, and the accuracy of reconstruction of the marker positions under varying control point configurations and separation angles was assessed. Errors of less than 1 mm were obtained when nine test points were reconstructed, with 16, 11 and 7 control points at a 90 degrees separation angle, and with 16 and 11 control points at 75 degrees and 60 degrees separation angles. The optimum reconstruction, with a resultant error of 0.68 mm, was found to occur at a separation angle of 90 degrees, with the largest number of control points (16) used to calculate the parameters of the transformation. Extrapolation in the scanning direction beyond the space defined by the control points gave errors of less than 2 mm. This method should be suitable for three-dimensional point reconstruction in applications such as cephalometry, brachytherapy planning and assessment of spinal shape.

Cycling device powered by the electrically stimulated muscles of paraplegics.

The paper describes a device (Paracycle), that uses functional neuromuscular stimulation to exercise subjects, explore FNS technology and provide paraplegics with locomotion. The Paracycle is a four-wheeled cycling vehicle that may be used as a stationary exercise device or for locomotion. It incorporates a fully adjustable seat and an electric motor to assist or retard the cycling motion, as well as speed and direction controls. Furthermore, it has braces to fasten the feet to the pedals and to stabilise the ankle, as well as gearing to enable subjects with very small forces to move the vehicle forward. Results are presented for two cases studies. Good stability of the leg was achieved during the cycling motion and this would appear to be a major advantage of functional neuromuscular stimulation cycling over functional neuromuscular stimulation gait. Important areas for future research include a better understanding of the biomechanics of functional neuromuscular stimulation cycling and the development of Paracycle-like devices that can be used independently by paraplegics.