Trivedi, Zubin ; Gehweiler, Dominic ; Wychowaniec, Jacek K. ; Ricken, Tim ; Gueorguiev, Boyko ; Wagner, Arndt ; Röhrle, Oliver: Analysing the bone cement flow in the injection apparatus during vertebroplasty. In: Proceedings in Applied Mathematics and Mechanics, Proceedings in Applied Mathematics and Mechanics. Bd. 23 (2023)
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Seyedpour, S. M. ; Henning, C. ; Kirmizakis, P. ; Herbrandt, S. ; Ickstadt, K. ; Doherty, R. ; Ricken, T.: Uncertainty with Varying Subsurface Permeabilities Reduced Using Coupled Random Field and Extended Theory of Porous Media Contaminant Transport Models. In: Water, Water. Bd. 15 (2023), Nr. 1
Zusammenfassung
To maximize the usefulness of groundwater flow models for the protection of aquifers and abstraction wells, it is necessary to identify and decrease the uncertainty associated with the major parameters such as permeability. To do this, there is a need to develop set of estimates representing subsurface heterogeneity or representative soil permeability estimates. Here, we use a coupled Random Field and extended Theory of Porous Media (eTPM) simulation to develop a robust model with a good predictive ability that reduces uncertainty. The coupled model is then validated with a physical sandbox experiment. Uncertainty is reduced by using 500 realisations of the permeability parameter using the eTPM approach. A multi-layer contaminant transport scenario with varying permeabilities, similar to what could be expected with shallow alluvial sediments, is simulated. The results show that the contaminant arrival time could be strongly affected by random field realizations of permeability compared with a modelled homogenous permeability parameter. The breakthrough time for heterogeneous permeabilities is shorter than the homogeneous condition. Using the 75% confidence interval (CI), the average contaminant concentration shows 4.4% variation from the average values of the considered area and 8.9% variation in the case of a 95% confidence interval.BibTeX
Zimmer, Manuela ; Kleiser, Benedict ; Marquetand, Justus ; Ates, Filiz: Shear wave elastography characterizes passive and active mechanical properties of biceps brachii muscle in vivo. In: Journal of the Mechanical Behavior of Biomedical Materials, Journal of the Mechanical Behavior of Biomedical Materials. Bd. 137, Elsevier BV (2023), S. 105543
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Azhdari, Mohammad ; Seyedpour, Seyed Morteza ; Lambers, Lena ; Tautenhahn, Hans-Michael ; Tautenhahn, Franziska ; Ricken, Tim ; Rezazadeh, Ghader: Non-local three phase lag bio thermal modeling of skin tissue and experimental evaluation. In: International Communications in Heat and Mass Transfer, International Communications in Heat and Mass Transfer. Bd. 149 (2023), S. 107146
Zusammenfassung
In this paper, the thermal behavior of living tissue has been modeled using a non-local three-phase lag approach. The simulation results of this model- ing have been compared with experimental results of alternating radiation with different periods on human skin, yielding satisfactory alignments. Ad- ditionally, it has been investigated that the TPL model, which is an equation with an integral term, can simulate energy accumulation within the dermal tissue. Moreover, the non-local nature of the modeling has been explored to alter the influence of phase lag terms. Furthermore, apart from numer- ically solving the equation, an analytical solution has been derived for the frequency equation, demonstrating the effects of simulation parameters on the frequency equation and simulation results. The obtained results indi cate that these parameters not only independently affect the outcomes but also interact with other parameters, leading to variations beyond their direct impacts.BibTeX
Mandl, Luis ; Mielke, André ; Seyedpour, Seyed Morteza ; Ricken, Tim: Affine transformations accelerate the training of physics-informed neural networks of a one-dimensional consolidation problem. In: Scientific Reports, Scientific Reports. Bd. 13 (2023), Nr. 1, S. 15566
Zusammenfassung
Physics-informed neural networks~(PINNs) leverage data and knowledge about a problem. They provide a nonnumerical pathway to solving partial differential equations by expressing the field solution as an artificial neural network. This approach has been applied successfully to various types of differential equations. A major area of research on PINNs is the application to coupled partial differential equations in particular, and a general breakthrough is still lacking. In coupled equations, the optimization operates in a critical conflict between boundary conditions and the underlying equations, which often requires either many iterations or complex schemes to avoid trivial solutions and to achieve convergence. We provide empirical evidence for the mitigation of bad initial conditioning in PINNs for solving one-dimensional consolidation problems of porous media through the introduction of affine transformations after the classical output layer of artificial neural network architectures, effectively accelerating the training process. These affine physics-informed neural networks~(AfPINNs) then produce nontrivial and accurate field solutions even in parameter spaces with diverging orders of magnitude. On average, AfPINNs show the ability to improve the Formula: see text relative error by Formula: see text after 25,000 epochs for a one-dimensional consolidation problem based on Biot's theory, and an average improvement by Formula: see text with a transfer approach to the theory of porous media.BibTeX
Kaya Keles, Cemre Su ; Hiller, Jennifer ; Zimmer, Manuela ; Ates, Filiz: In vivo assessment of tibialis anterior muscle in passive and active states using shear wave elastography. In: Gait & Posture, Gait & Posture. Bd. 106, 2023, S. 94
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Ates, Filiz ; Marquetand, Justus ; Zimmer, Manuela: Detecting age-related changes in skeletal muscle mechanics using ultrasound shear wave elastography. In: Scientific Reports, Scientific Reports. Bd. 13 (2023), Nr. 1, S. 20062
Zusammenfassung
Aging leads to a decline in muscle mass and force-generating capacity. Ultrasound shear wave elastography (SWE) is a non-invasive method to capture age-related muscular adaptation. This study assessed biceps brachii muscle (BB) mechanics, hypothesizing that shear elastic modulus reflects (i) passive muscle force increase imposed by length change, (ii) activation-dependent mechanical changes, and (iii) differences between older and younger individuals. Fourteen healthy volunteers aged 60--80 participated. Shear elastic modulus, surface electromyography, and elbow torque were measured at five elbow positions in passive and active states. Data collected from young adults aged 20--40 were compared. The BB passive shear elastic modulus increased from flexion to extension, with the older group exhibiting up to 52.58\% higher values. Maximum elbow flexion torque decreased in extended positions, with the older group 23.67\% weaker. Significant effects of elbow angle, activity level, and age on total and active shear elastic modulus were found during submaximal contractions. The older group had 20.25\% lower active shear elastic modulus at 25\% maximum voluntary contraction. SWE effectively quantified passive and activation-dependent BB mechanics, detecting age-related alterations at rest and during low-level activities. These findings suggest shear elastic modulus as a promising biomarker for identifying altered muscle mechanics in aging.BibTeX
Mandl, Luis ; Mielke, André ; Seyedour, Seyed Morteza ; Ricken, Tim: Affine transformations accelerate the training of physics-informed neural networks of a one-dimensional consolidation problem. In: Scientific Reports, Scientific Reports. Bd. 13 (2023), Nr. 15566
Zusammenfassung
Physics-informed neural networks (PINNs) leverage data and knowledge about a problem. They provide a nonnumerical pathway to solving partial differential equations by expressing the field solution as an artificial neural network. This approach has been applied successfully to various types of differential equations. A major area of research on PINNs is the application to coupled partial differential equations in particular, and a general breakthrough is still lacking. In coupled equations, the optimization operates in a critical conflict between boundary conditions and the underlying equations, which often requires either many iterations or complex schemes to avoid trivial solutions and to achieve convergence. We provide empirical evidence for the mitigation of bad initial conditioning in PINNs for solving one-dimensional consolidation problems of porous media through the introduction of affine transformations after the classical output layer of artificial neural network architectures, effectively accelerating the training process. These affine physics-informed neural networks (AfPINNs) then produce nontrivial and accurate field solutions even in parameter spaces with diverging orders of magnitude. On average, AfPINNs show the ability to improve the L2 relative error by 64.84% after 25,000 epochs for a one-dimensional consolidation problem based on Biot’s theory, and an average improvement by 58.80% with a transfer approach to the theory of porous media.BibTeX
Zimmer, Manuela ; Kleiser, Benedict ; Marquetand, Justus ; Ates, Filiz: Characterization of Muscle Weakness Due to Myasthenia Gravis Using Shear Wave Elastography. In: Diagnostics, Diagnostics. Bd. 13 (2023), Nr. 6
Zusammenfassung
Myasthenia gravis (MG) is often accompanied with muscle weakness; however, little is known about mechanical adaptions of the affected muscles. As the latter can be assessed using ultrasound shear wave elastography (SWE), this study characterizes the biceps brachii muscle of 11 patients with MG and compares them with that of 14 healthy volunteers. Simultaneous SWE, elbow torque and surface electromyography measurements were performed during rest, maximal voluntary contraction (MVC) and submaximal isometric contractions (up to 25%, 50% and 75% MVC) at different elbow angles from flexion to extension. We found that, with increasing elbow angle, maximum elbow torque decreased (p < 0.001), whereas muscle stiffness increased during rest (p = 0.001), MVC (p = 0.004) and submaximal contractions (p < 0.001). Muscle stiffness increased with increasing contraction intensities during submaximal contractions (p < 0.001). In comparison to the healthy cohort, muscle stiffness of MG patients was 2.1 times higher at rest (p < 0.001) but 8.93% lower in active state (75% MVC, p = 0.044). We conclude that (i) increased muscle stiffness shown by SWE during rest might be an indicator of MG, (ii) SWE reflects muscle weakness and (iii) SWE can be used to characterize MG muscle.BibTeX
Zimmer, Manuela ; Kleiser, Benedict ; Marquetand, Justus ; Ateş, Filiz: Shear wave elastography characterizes passive and active mechanical properties of biceps brachii muscle in vivo. In: Journal of the Mechanical Behavior of Biomedical Materials, Journal of the Mechanical Behavior of Biomedical Materials. Bd. 137 (2023), S. 105543
Zusammenfassung
Mechanical characterization of individual muscles in their in vivo environment is not well studied. Shear wave elastography (SWE) as a non-invasive technique was shown to be promising in quantifying the local mechanical properties of skeletal muscles. This study aimed to investigate the mechanics of the biceps brachii muscle (BB) derived from SWE in relation to elbow joint position and contraction intensity during isometric contraction. 14 healthy, young subjects participated in the study and five different joint positions (60°–180° elbow angle) were investigated. Shear elastic modulus and surface electromyography (sEMG) of the BB and elbow torque were measured simultaneously, both in passive (i.e., resting) and active states during slow, sub-maximal isometric ramp contractions up to 25%, 50%, and 75% of the maximum voluntary contraction. At passive state, the shear elastic modulus of the BB increased with increasing elbow angle (p < 0.001). Maximum elbow flexion torque was produced at 60° and it decreased with increasing elbow angle (p = 0.001). During sub-maximal contractions, both elbow angle (p < 0.001) and contraction intensity (p < 0.001) had significant effects on the shear elastic modulus but only contraction intensity (p < 0.001) affected sEMG amplitude of the BB. Although torque was decreased at extended elbow positions (150°, 180°), higher active shear elastic modulus of BB muscle was found compared to flexed positions (60°, 90°). Linear regression of the BB sEMG amplitude over elbow torque showed good agreement for all joint positions (R2 between 0.69 and 0.89) while the linear agreement between shear elastic modulus of BB and elbow torque differed between flexed (R2 = 0.70 at 60° and R2 = 0.79 at 90°) and extended positions (with the lowest R2 = 0.57 at 150°). We conclude that using SWE, we can detect length-dependent mechanical changes of BB both in passive and active states. More importantly, SWE can be used to characterize active muscle properties in vivo. The present findings have critical importance for developing muscle stiffness as a measure of individual muscle force to validate muscle models and using SWE in clinical diagnostics.BibTeX
Azhdari, Mohammad ; Seyedpour, Seyed Morteza ; Ricken, Tim ; Rezazadeh, Ghader: On the thermo-vibrational response of multi-layer viscoelastic skin tissue to laser irradiation. In: International Journal of Thermal Sciences, International Journal of Thermal Sciences. Bd. 187 (2023), S. 108160
Zusammenfassung
This paper investigates temperature and vibration responses of human multi-layer skin tissue to laser irradiation. Due to the viscoelastic property of skin, a standard linear solid model known as the Zener model with two relaxation times with dual phase-lag heat conduction model has been used to describe the temperature and displacement in a one-dimensional form. The obtained differential equations have been discretized in the weak form to balance thermal and vibrational energies. The extracted time-dependent ordinary differential equations have been solved numerically by integration over time. The investigations are based on the effect of four relaxation times of temperature, heat, strain, and stress with laser effect in the form of a single step or repeated pulses on the behavior of the skin. By examining their results, the effect of phase lags has also been discussed, showing that the heat phase lag has a complex impact on thermal response and depends on the type of laser radiation. The phase lag of temperature reduces the temperature change rate, and the strain phase lag spreads the displacement at later times, gives inertia to the system, and dampens the system's vibration.BibTeX
Trivedi, Zubin ; Gehweiler, Dominic ; Wychowaniec, Jacek K. ; Ricken, Tim ; Gueorguiev-Rüegg, Boyko ; Wagner, Arndt ; Röhrle, Oliver: Analysing the bone cement flow in the injection apparatus during vertebroplasty. In: PAMM, PAMM. Bd. 23 (2023), Nr. 1
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Suditsch, Marlon ; Ricken, Tim ; Wagner, Arndt: Patient--specific simulation of brain tumour growth and regression. In: PAMM, PAMM. Bd. 23 (2023), Nr. 1
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Seyedpour, S. M. ; Thom, A. ; Ricken, T.: Simulation of Contaminant Transport through the Vadose Zone: A Continuum Mechanical Approach within the Framework of the Extended Theory of Porous Media (eTPM). In: Water, Water. Bd. 15 (2023), Nr. 2, S. 343
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Zimmer, Manuela ; Straub, Louis ; Ates, Filiz: Towards in vivo non-invasive muscle characterization: Shear wave elastography to assess passive and active mechanics of triceps surae, Gait & Posture. Bd. 100 : Elsevier BV, 2023
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Soltani, Kamran ; Seyedpour, Seyed Morteza ; Ricken, Tim ; Rezazadeh, Ghader: Transient high-frequency spherical wave propagation in porous medium using fractional calculus technique. In: Acta Mechanica, Acta Mechanica. (2023), S. 1–19
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Kaya Keles, Cemre Su ; Ates, Filiz: How mechanics of individual muscle-tendon units define knee and ankle joint function in health and cerebral palsy—a narrative review. In: Frontiers in Bioengineering and Biotechnology, Frontiers in Bioengineering and Biotechnology. Bd. 11 (2023), S. 1287385
Zusammenfassung
This study reviews the relationship between muscle-tendon biomechanics and joint function, with a particular focus on how cerebral palsy (CP) affects this relationship. In healthy individuals, muscle size is a critical determinant of strength, with muscle volume, cross-sectional area, and moment arm correlating with knee and ankle joint torque for different isometric/isokinetic contractions. However, in CP, impaired muscle growth contributes to joint pathophysiology even though only a limited number of studies have investigated the impact of deficits in muscle size on pathological joint function. As muscles are the primary factors determining joint torque, in this review two main approaches used for muscle force quantification are discussed. The direct quantification of individual muscle forces from their relevant tendons through intraoperative approaches holds a high potential for characterizing healthy and diseased muscles but poses challenges due to the invasive nature of the technique. On the other hand, musculoskeletal models, using an inverse dynamic approach, can predict muscle forces, but rely on several assumptions and have inherent limitations. Neither technique has become established in routine clinical practice. Nevertheless, identifying the relative contribution of each muscle to the overall joint moment would be key for diagnosis and formulating efficient treatment strategies for patients with CP. This review emphasizes the necessity of implementing the intraoperative approach into general surgical practice, particularly for joint correction operations in diverse patient groups. Obtaining in vivo data directly would enhance musculoskeletal models, providing more accurate force estimations. This integrated approach can improve the clinicians’ decision-making process and advance treatment strategies by predicting changes at the muscle and joint levels before interventions, thus, holding the potential to significantly enhance clinical outcomes.BibTeX
Brendecke, Elena ; Tsitlakidis, Stefanos ; Gotze, Marco ; Hagmann, Sebastien ; Ates, Filiz: Quantifying the effects of Achilles tendon lengthening surgery: An intraoperative approach (2023)
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Arasteh-Khoshbin, O ; Seyedpour, SM ; Brodbeck, M ; Lambers, L ; Ricken, T: On effects of freezing and thawing cycles of concrete containing nano-SiO 2: experimental study of material properties and crack simulation. In: Scientific Reports, Scientific Reports. Bd. 13, Nature Publishing Group UK London (2023), Nr. 1, S. 22278
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Seyedpour, Seyed Morteza ; Lambers, Lena ; Rezazadeh, Ghader ; Ricken, Tim: Mathematical modelling of the dynamic response of an implantable enhanced capacitive glaucoma pressure sensor. In: Measurement: Sensors, Measurement: Sensors. (2023), S. 100936
Zusammenfassung
Glaucoma as an eye disease influences the optic nerve, resulting in progressive vision loss and, thus, blindness. For this disease, the most important risk factor is high intraocular pressure. Therefore, it is important to accurately measure the intraocular pressure. The present work aimes to present a mathematical description of a capacitive pressure sensor based on a Micro-Electro-Mechanical-Systems (MEMS) to measure intraocular pressure (IOP). The relatively high working bias voltage of MEMS capacitive pressure sensors restricts their potential applications as implantable sensors. Hence, Polydimethylsiloxane (PDMS) is employed as a porous elastomeric substance between the deformable and fixed electrodes of the capacitor. With a low young modulus and a higher dielectric constant, it reduces the sensor's working bias voltage. The PDMS's permittivity and young modulus are a function of the porosity volume fraction based on displacement in terms of a power law with fractional power constant. The dynamic equation of the microplate's transversal motion is used in the developed model, taking mid-plane stre-tching into account along with the generated force owing to the PDMS film squeezing. To decompose the governing nonlinear equation, a weak formulation is used with appropriate basis functions, thus integrating the attained ordinary differential equations over time. The sensor response to static pressure and step-wise alteration of the applied pressure is examined by dynamic and static analysis. The results of pull-in voltage reveal that using the PDMS as a dielectric causes a considerable reduction. Additionally, the effect of the PDMS elasticity on the capacitance and displacement was assessed along with the effects of the geometrical parameters on the sensor response.BibTeX
Trivedi, Zubin ; Gehweiler, Dominic ; Wychowaniec, Jacek K. ; Ricken, Tim ; Gueorguiev, Boyko ; Wagner, Arndt ; Röhrle, Oliver: A continuum mechanical porous media model for vertebroplasty: Numerical simulations and experimental validation. In: Biomechanics and Modeling in Mechanobiology, Biomechanics and Modeling in Mechanobiology. (2023)
Zusammenfassung
The outcome of vertebroplasty is hard to predict due to its dependence on complex factors like bone cement and marrow rheologies. Cement leakage could occur if the procedure is done incorrectly, potentially causing adverse complications. A reliable simulation could predict the patient-specific outcome preoperatively and avoid the risk of cement leakage. Therefore, the aim of this work was to introduce a computationally feasible and experimentally validated model for simulating vertebroplasty. The developed model is a multiphase continuum-mechanical macro-scale model based on the Theory of Porous Media. The related governing equations were discretized using a combined finite element–finite volume approach by the so-called Box discretization. Three different rheological upscaling methods were used to compare and determine the most suitable approach for this application. For validation, a benchmark experiment was set up and simulated using the model. The influence of bone marrow and parameters like permeability, porosity, etc., was investigated to study the effect of varying conditions on vertebroplasty. The presented model could realistically simulate the injection of bone cement in porous materials when used with the correct rheological upscaling models, of which the semi-analytical averaging of the viscosity gave the best results. The marrow viscosity is identified as the crucial reference to categorize bone cements as ‘high- ’or ‘low-’ viscosity in the context of vertebroplasty. It is confirmed that a cement with higher viscosity than the marrow ensures stable development of the injection and a proper cement interdigitation inside the vertebra.BibTeX
Lambers, Lena ; Waschinsky, Navina ; Schleicher, Jana ; König, Matthias ; Tautenhahn, Hans-Michael ; Albadry, Mohamed ; Dahmen, Uta ; Ricken, Tim: Quantifying Fat Zonation in Liver Lobules: An IntegratedMultiscale In-silico Model Combining DisturbedMicroperfusion and Fat Metabolism via aContinuum-Biomechanical Bi-scale, Tri-phasic Approach, Research Square Platform LLC (2023)
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Völter, Jan-Sören L. ; Ricken, Tim ; Röhrle, Oliver: About the applicability of the theory of porous media for the modelling of non--isothermal material injection into porous structures. In: PAMM, PAMM. Bd. 23 (2023), Nr. 1
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Trivedi, Zubin ; Gehweiler, Dominic ; Wychowaniec, Jacek K. ; Ricken, Tim ; Gueorguiev, Boyko ; Wagner, Arndt ; Röhrle, Oliver: A continuum mechanical porous media model for vertebroplasty: Numerical simulations and experimental validation. In: Biomechanics and Modeling in Mechanobiology, Biomechanics and Modeling in Mechanobiology. Bd. 22 (2023), Nr. 4, S. 1253--1266
Zusammenfassung
The outcome of vertebroplasty is hard to predict due to its dependence on complex factors like bone cement and marrow rheologies. Cement leakage could occur if the procedure is done incorrectly, potentially causing adverse complications. A reliable simulation could predict the patient-specific outcome preoperatively and avoid the risk of cement leakage. Therefore, the aim of this work was to introduce a computationally feasible and experimentally validated model for simulating vertebroplasty. The developed model is a multiphase continuum-mechanical macro-scale model based on the Theory of Porous Media. The related governing equations were discretized using a combined finite element-finite volume approach by the so-called Box discretization. Three different rheological upscaling methods were used to compare and determine the most suitable approach for this application. For validation, a benchmark experiment was set up and simulated using the model. The influence of bone marrow and parameters like permeability, porosity, etc., was investigated to study the effect of varying conditions on vertebroplasty. The presented model could realistically simulate the injection of bone cement in porous materials when used with the correct rheological upscaling models, of which the semi-analytical averaging of the viscosity gave the best results. The marrow viscosity is identified as the crucial reference to categorize bone cements as 'high- 'or 'low-' viscosity in the context of vertebroplasty. It is confirmed that a cement with higher viscosity than the marrow ensures stable development of the injection and a proper cement interdigitation inside the vertebra.BibTeX
Zimmer, Manuela ; Bunz, Elsa K. ; Ehring, Tobias ; Kaiser, Benedikt ; Kienzlen, Annika ; Schlüter, Henning ; Zürn, Manuel: In Vivo Assessment of Shear Wave Propagation in Pennate Muscles Using an Automatic Ultrasound Probe Alignment System. In: IEEE Open Journal of Engineering in Medicine and Biology, IEEE Open Journal of Engineering in Medicine and Biology. Bd. 4 (2023), S. 259–267
Zusammenfassung
Goal: Skeletal muscle mechanics can be assessed in vivo using shear wave elastography. However, the impact of pennation angle on shear wave velocity (SWV) remains unclear. This study aims to quantify the effect by automatically aligning the ultrasound probe with muscle fiber orientation. Methods: We propose an automatic ultrasound probe alignment system and compare it to manual and no alignment. SWV of the gastrocnemius medialis muscle of ten volunteers was measured during rest and isometric contractions. Results: The SWV was different between the conditions (p = 0.008). The highest SWV was obtained during the automatic alignment and differences between the conditions were most pronounced during high-level contractions. The automatic system yielded more accurate alignment compared to a manual operator (p = 0.05). Conclusions: The present study indicates that pennation angle affects SWV, hence muscle fiber orientation must be considered to reliably interpret SWV. Using automatic alignment systems allows for more accurate alignment, improving the methodology of ultrasound elastography in skeletal muscles.BibTeX
Kleiser, Benedict ; Zimmer, Manuela ; Ates, Filiz ; Marquetand, Justus: Muskelkraft und Scherwellenelastographie (SWE) bei Fazioskapulohumeraler Muskeldystrophie (FSHD). In: Ultraschall in der Medizin - European Journal of Ultrasound, Ultraschall in der Medizin - European Journal of Ultrasound. Bd. 44, Georg Thieme Verlag (2023), Nr. S 01, S. 277--
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