Biomedical subjects

Thilo Pfau

Publications and source records attributed to Thilo Pfau.

5 recordsLinked to original sources

PubMed2007

The determination of muscle volume with a freehand 3D ultrasonography system.

Muscle morphology determines muscle function. An objective method to determine muscle volume in vivo will facilitate understanding of basic muscle function and will also provide a valuable tool for the clinician to assess the effectiveness of treatment. In this method-validation study, it is hypothesised that a freehand 3-D ultrasonography system provides a noninvasive method that allows the determination of muscle volume with high accuracy and precision. To test the hypotheses, repeated measurements were performed (1) on cadaver muscles in situ, (2) isolated muscles and (3) live animals. Volume measurements performed with 3-D ultrasonography were compared with measurements based on computed tomography and the water displacement method. The results of this study showed that 3-D ultrasound provided excellent precision and accuracy in the measurements on the isolated muscles and good precision in vivo. It is concluded that 3-D ultrasonography is an innovative technique that allows objective determination of muscle volume in vivo.

Animals↗

PubMed2007

Gait characterisation and classification in horses.

Although a large number of foot-fall sequences are possible in quadrupeds, few sequences are routinely used. The aim of this paper is to characterise, by foot-fall pattern, the gaits used by horses and develop a novel technique to classify symmetric and asymmetric gaits using one common criterion. To achieve this speed and relative foot-fall, timings of all four limbs of eight Icelandic horses were measured using accelerometers. Linear discriminant analysis (LDA) was performed to find criteria that are optimal for discriminating between the different gaits. This also allowed us to evaluate whether gaits should be considered a continuum or as discrete entities. Foot-fall timings (stance times, swing times, duty factors and stride frequencies) for walk, tolt, trot, pace, left canter, right canter, left gallop and right gallop during over-ground locomotion at a range of speeds are presented. In the gaits of walk, tolt, trot and pace, foot-fall timings were equal between left and right hindlimbs and forelimbs so these gaits can be considered as symmetrical. Differences in stance times and duty factors were observed between gaits but are unlikely to be of biological significance due to their similar magnitude and inconsistent relative trends. This implies that metabolics or peak limb forces derived from contact times are unlikely to be the principal driving factors in gait transition between walk, trot, pace, canters and gallops, although these factors may influence the use of tolt at the lower and higher speeds. Gaits did cluster in the LDA space and the running gaits (tolt, trot, pace, left and right canters and gallops) could be considered a kinematic continuum but the relative relationship with walk may be more complex. Thus, LDA analysis has enabled common criteria to be discovered to accurately classify equine gaits on the basis of foot-fall timings on a stride-by-stride basis.

Animals↗

PubMed2006

A comparison of three-dimensional ultrasound, two-dimensional ultrasound and dissections for determination of lesion volume in tendons.

The purpose of this work was to evaluate the accuracy and precision of a freehand three-dimensional (3-D) ultrasonography system in the determination of lesion volume in tendons. The accuracy and precision of a 3-D ultrasonography system was assessed by performing repeated measurements on a phantom of known volume. Volume measurements of tendon lesions performed with 3-D ultrasonography were compared with measurements based on a series of two-dimensional (2-D) ultrasound (US) scans and to direct measurements from dissections. A novel method for the creation of tendon lesions in vitro was developed. 3-D US showed excellent precision and accuracy in measurements of the phantom (mean measured volume = 3.76 mL, calculated volume = 3.77 mL, coefficient of variation (CoV) = 0.54%) and good repeatability in the determination of tendon lesions (repeatability coefficient = 0.00047). All three methods examined were repeatable (repeatability coefficient for 2-D US = 0.00032, repeatability coefficient for dissections = 0.00076). However, each of the methods produced different results and no constant relationship could be found between any of the measurement methods. Both 3-D and 2-D US proved to be repeatable techniques for the measurement of the volume of a tendon lesion. Even if they produced different results, each of them can be repeatedly used individually. It was not possible to define which one provided the most accurate value as a result of difficulties encountered in lesion identification on histology, and therefore the lack of a gold standard.

Animals↗

PubMed2006

Centre of mass movement and mechanical energy fluctuation during gallop locomotion in the Thoroughbred racehorse.

During locomotion cyclical interchange between different forms of mechanical energy enhances economy; however, 100% efficiency cannot be achieved and ultimately some mechanical work must be performed de novo. There is a metabolic cost associated with fluctuations in mechanical energy, even in the most efficient animals. In this study we investigate the exchanges between different forms of mechanical energy involved in high-speed gallop locomotion in Thoroughbred race horses during over-ground locomotion using innovative, mobile data collection techniques. We use hoof-mounted accelerometers to capture foot contact times, a GPS data logger to monitor speed and an inertial sensor mounted over the dorsal spinous processes of the fourth to sixth thoracic vertebrae (the withers) of the horse to capture trunk movement with six degrees of freedom. Trunk movement data were used to estimate the movement of the centre of mass (CoM). Linear (craniocaudal, mediolateral and dorsoventral) and rotational (roll, pitch and heading) kinematic parameters (displacement, velocity and acceleration) were calculated for seven horses at gallop speeds ranging from 7 to 17 m s(-1) during their regular training sessions. These were used to estimate external mechanical energy (potential energy and linear kinetic energy of the CoM) as well as selected components of internal energy (angular kinetic energy). Elastic energy storage in the limbs was estimated from duty factor, sine wave assumptions and published leg stiffness values. External mechanical energy changes were dominated by changes in craniocaudal velocity. Potential energy change, which was in phase with craniocaudal energy during the front limb stances, was small. Elastic energy storage in the limbs was small compared to the overall amplitude of fluctuation of external mechanical energy. Galloping at high speeds does not therefore fit classical spring mass mechanics.

Acceleration↗

PubMed2005

A method for deriving displacement data during cyclical movement using an inertial sensor.

Biomechanical studies often employ optical motion capture systems for the determination of the position of an object in a room-based coordinate system. This is not ideal for many types of study in locomotion since only a few strides may be collected per ;trial', and outdoor experiments are difficult with some systems. Here, we report and evaluate a novel approach that enables the user to determine linear displacements of a proprietary orientation sensor during cyclical movement. This makes experiments outside the constraints of the laboratory possible, for example to measure mechanical energy fluctuations of the centre of mass during over-ground locomotion. Commercial orientation sensors based on inertial sensing are small and lightweight and provide a theoretical framework for determining position from acceleration. In practice, the integration process is difficult to implement because of integration errors, integration constants and the necessity to determine the orientation of the measured accelerations. Here, by working within the constraints of cyclical movements, we report and evaluate a method for determining orientation and relative position using a modified version of a commercial inertial orientation sensor that combines accelerometers, gyroscopes and magnetometers, thus giving a full set of movement parameters (displacement, velocity and acceleration in three dimensions). The 35 g sensor was attached over the spine of a horse exercising on a treadmill. During canter locomotion (9.0 m s-1), the amplitudes of trunk movement in the x (craniocaudal), y (mediolateral) and z (dorsoventral) directions were 99.6, 57.9 and 140.2 mm, respectively. Comparing sensor displacement values with optical motion capture values for individual strides, the sensor had a median error (25th, 75th percentile) in the x, y and z directions of 0.1 (-9.7, +10.8), -3.8 (-15.5, +13.7) and -0.1 (-6.3, +7.1) mm, respectively. High-pass filtering of the displacement data effectively separated non-cyclical from cyclical components of the movement and reduced the interquartile ranges of the errors considerably to (-3.6, 6.2), (-4.0, 3.8) and (-4.5, 5.1) for x, y and z displacement, respectively, during canter locomotion. This corresponds to (-3.2, 5.5)%, (-6.7, 6.3)% and (-3.3, 3.7)% of the range of motion.

Acceleration↗