Guillaume Dubois

Intervertebral disc characterization by shear wave elastography: An in vitro preliminary study

Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. While geometrical personalization of the spine is no more an issue, thanks to recent technological advances, non-invasive personalization of soft tissue’s mechanical properties remains a challenge. Ultrasound elastography is a relatively recent measurement technique allowing the evaluation of soft tissue’s elastic modulus through the measurement of shear wave speed. The aim of this study was to determine the feasibility of elastographic measurements in intervertebral disc. An in vitro approach was chosen to test the hypothesis that shear wave speed can be used to evaluate intervertebral disc mechanical properties and to assess measurement repeatability. In total, 11 oxtail intervertebral discs were tested in compression to determine their stiffness and apparent elastic modulus at rest and at 400 N. Elastographic measurements were performed in these two conditions and compared to these mechanical parameters. The protocol was repeated six times to determine elastographic measurement repeatability. Average shear wave speed over all samples was 5.3 ± 1.0 m/s, with a repeatability of 7% at rest and 4.6% at 400 N; stiffness and apparent elastic modulus were 266.3 ± 70.5 N/mm and 5.4 ± 1.1 MPa at rest, respectively, while at 400 N they were 781.0 ± 153.8 N/mm and 13.2 ± 2.4 MPa, respectively. Correlations were found between elastographic measurements and intervertebral disc mechanical properties; these preliminary results are promising for further in vivo application.

DETERMINATION OF TIME-DEPENDENT FORCES IN HUMAN MANDIBLE DISTRACTION OSTEOGENESIS

Distraction Osteogenesis (DO) is often used for the treatment of traumas with important bone defects as ballistic wounds. External bone transport devices are thus preferred, mainly in reason of the forces encountered [Labbe, 2005]. Bone callus participates in these resisting forces and its mechanical response strongly depends on time [Richards, 1999]. Mandibular DO forces have already been studied but without considerations about immediate timedependency [Robinson, 2001]. In this context, the aim of this study was to determine the time-dependent forces supported by a distraction device (DEOS, OBL, France), see figure 1. From these measurements, the time-dependent force-displacement behaviour of bone regenerate during the early phases of human mandible DO has been evaluated.

Local Texture Anisotropy as an Estimate of Muscle Quality in Ultrasound Imaging

This study introduces local pattern texture anisotropy as a novel parameter to differentiate healthy and disordered muscle and to gauge the severity of muscle impairments based on B-mode ultrasound images. Preliminary human results are also presented. A local pattern texture anisotropy index (TAI) was computed in one region of interest in the short head of the biceps brachii. The effects of gain settings and box sizes required for TAI computation were investigated. Between-day reliability was studied in patients with sporadic inclusion body myositis (n = 26). The ability of the TAI to discriminate dystrophic from healthy muscle was evaluated in patients with Duchenne muscular dystrophy and healthy controls (n = 16). TAI values were compared with a gray-scale index (GSI). TAI values were less influenced by gain settings than were GSI values. TAI had lower between-day variability (typical error = 2.3%) compared with GSI (typical error = 2.3% vs. 8.3%, respectively). Patients with Duchenne muscular dystrophy had lower TAIs than controls (0.76 ± 0.06 vs. 0.87 ± 0.03, respectively, p <0.05). At 40% gain, TAI values correlated with percentage predicted elbow flexor strength in inclusion body myositis (R = 0.63, p <0.001). The TAI may be a promising addition to other texture-based approaches for quantitative muscle ultrasound imaging.

Muscle parameters estimation based on biplanar radiography

The evaluation of muscle and joint forces in vivo is still a challenge. Musculo-Skeletal (musculo-skeletal) models are used to compute forces based on movement analysis. Most of them are built from a scaled-generic model based on cadaver measurements, which provides a low level of personalization, or from Magnetic Resonance Images, which provide a personalized model in lying position. This study proposed an original two steps method to access a subject-specific musculo-skeletal model in 30 min, which is based solely on biplanar X-Rays. First, the subject-specific 3D geometry of bones and skin envelopes were reconstructed from biplanar X-Rays radiography. Then, 2200 corresponding control points were identified between a reference model and the subject-specific X-Rays model. Finally, the shape of 21 lower limb muscles was estimated using a non-linear transformation between the control points in order to fit the muscle shape of the reference model to the X-Rays model. Twelfth musculo-skeletal models were reconstructed and compared to their reference. The muscle volume was not accurately estimated with a standard deviation (SD) ranging from 10 to 68%. However, this method provided an accurate estimation the muscle line of action with a SD of the length difference lower than 2% and a positioning error lower than 20 mm. The moment arm was also well estimated with SD lower than 15% for most muscle, which was significantly better than scaled-generic model for most muscle. This method open the way to a quick modeling method for gait analysis based on biplanar radiography.

Fracture characterization in cancellous bone specimens via surface difference evaluation of 3D registered pre- and post-compression micro-CT scans.

To cite this article: M. Prot, G. Dubois, T. J. Cloete, D. Saletti & S. Laporte (2015) Fracture characterization in cancellous bone specimens via surface difference evaluation of 3D registered preand post-compression micro-CT scans, Computer Methods in Biomechanics and Biomedical Engineering, 18:sup1, 2030-2031, DOI: 10.1080/10255842.2015.1069608 To link to this article: http://dx.doi.org/10.1080/10255842.2015.1069608

What is the recommended size of a Volume of Interest for cancellous bone? A skeleton-based study

The study of the bone fracture is an important issue for osteoporosis and car safety. The behavior of cancellous bone is strongly linked to the micro-architecture, the strain rate (Prot et al. 2015...

Comparison of two MRI sequences for subject-specific 3D thigh muscle reconstruction

1. IntroductionFatatrophyofskeletalmuscleistheoutcomeoftheageingprocessorvariousneuromuscularpathologies.Toquantifymuscle volume and fat infiltration (FI), magneticresonance imaging (MRI) is used in clinical diagnosticsand research concerning the high image quality andabsence of irradiation. Although T1-weighted turbo spin-echo (TSE) sequence MRIs are used clinically, however,the acquisition duration is long, which raises acquisitioncosts and hardly avoids breathing artefacts in abdomenimages. T1-weighted, ultrafast gradient-echo, volumetricinterpolated breath-hold examination (VIBE) MRI canacquire datasets within a breath-hold (,25s), therebyreducing breathing artefacts. Therefore, VIBE MRI hasgreat potential for clinical research and applications,although image quality is limited by the reducedacquisition duration. To quantify FI in skeletal muscles,Dixon method is preferably considered for T1-weightedsequences. On the basis of differences of signal phase infat and water, this method is found to be insensitive to theinhomogeneity of the magnetic field (Dixon 1984);therefore, it allows whole body fat quantification.Three-dimensional (3D) subject-specific musclereconstruction allows quantitative analyses of musclemorphology. Semi-automated deformation of parametricspecific objects (DPSO) method (Jolivet etal. 2007)uses areduced datasets for muscle reconstruction, reducing timerequired by manual reconstruction.This study aims to compare the feasibility andaccuracy of VIBE and TSE MRI in 3D subject-specificthigh muscle geometry reconstruction and skeletal muscleFI quantification.2. MethodsTen female patients (average age 58.5

Intervertebral disc characterisation by elastography: a preliminary study

Simulation of the human spine mechanical behavior allows insights on several subjects of study, both in research and clinical application. For instance, it can be used to study growth (Villemure et al., 2002), surgical procedures (Lafage et al., 2004) or scoliosis progression (Drevelle et al., 2010). Reliable simulations require information on the subject-dependent geometry and on the tissues mechanical properties. Thanks to recent technological and technical advances, geometry of the spine can be easily and precisely personalized (Humbert et al., 2009). In vivo personalization of the tissues mechanical properties, however, remains a challenge. Ultrasound elastography has been a subject of research since the early 90s (Ophir et al., 1991), but only recently new quantitative techniques started being introduced in the clinical setting (Tanter et al., 2008). This technique allows the evaluation of the tissue’s elastic modulus through the measurement of shear waves’ speed of propagation in the tissue; it has been successfully applied to asses several tissues, such as muscles, prostate, liver and breasts. The hypothesis that was explored in this preliminary study was that intervertebral disc stiffness could be evaluated by elastographic measurements.

Muscle Shear Wave Elastography in Inclusion Body Myositis: Feasibility, Reliability and Relationships with Muscle Impairments

Degenerative muscle changes may be associated with changes in muscle mechanical properties. Shear wave elastography (SWE) allows direct quantification of muscle shear modulus (MSM). The aim of this study was to evaluate the feasibility and reliability of SWE in the severely disordered muscle as observed in inclusion body myositis. To explore the clinical relevance of SWE, potential relationships between MSM values and level muscle impairments (weakness and ultrasound-derived muscle thickness and echo intensity) were investigated. SWE was performed in the biceps brachii at 100°, 90°, 70° and 10° elbow flexion in 34 patients with inclusion body myositis. MSM was assessed before and after five passive stretch-shortening cycles at 4°/s from 70° to 10° elbow angle and after three maximal voluntary contractions to evaluate potential effects of muscle pre-conditioning. Intra-class correlation coefficients and standard errors of measurements were >0.83 and <1.74 kPa and >0.64 and <1.89 kPa for within- and between-day values, respectively. No significant effect of passive loading-unloading and maximal voluntary contractions was found (all p values  >0.18). MSM correlated to predicted muscle strength (all Spearman correlation coefficients (ρ) > 0.36; all p values < 0.05). A significant correlation was found between muscle echo intensity and muscle shear modulus at 70° only (ρ = 0.38, p <0.05). No correlation was found between muscle thickness and MSM (all ρ values > 0.23 and all p values > 0.25, respectively). Within- and between-day reliability of muscle SWE was satisfactory and moderate, respectively. SWE shows promise for assessing changes in mechanical properties of the severely disordered muscle. Further investigations are required to clarify these findings and to refine their clinical value.

Comparative finite element analysis of skull mechanical properties following parietal bone graft harvesting in adults

INTRODUCTION Parietal bone grafts are commonly used in cranio-maxillo-facial surgery. Both the outer and the internal layer of the calvarium can be harvested. The bone defect created by this harvesting may induce significant weakening of the skull that has not been extensively evaluated. Our aim was to evaluate the consequences of parietal bone graft harvesting on mechanical properties of the skull using a finite element analysis. METHODS Finite elements models of the skull of 3 adult patients were created from CT scans. Parietal external and internal layer harvest models were created. Frontal, lateral, and parietal loading were modeled and von Mises stress distributions were compared. RESULTS The maximal von Mises stress was higher for models of bone harvesting, both on the whole skull and at the harvested site. Maximal von Mises stress was even higher for models with internal layer defect. CONCLUSIONS Harvesting parietal bone modifies the skulls mechanical strength and can increase the risk of skull fracture, mainly on the harvested site. Outer layer parietal graft harvesting is indicated. Graft harvesting located in the upper part of the parietal bone, close to the sagittal suture and with smooth internal edges and corners should limit the risk of fracture.