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Artykuły w czasopismach na temat "Élastographie par résonance magnétique – Innovation"
Souchon, R., R. Salomir, J. Y. Chapelon, O. Beuf i O. Rouvière. "Élastographie transitoire par résonance magnétique". IRBM 30, nr 4 (wrzesień 2009): 168–70. http://dx.doi.org/10.1016/j.irbm.2009.05.003.
Pełny tekst źródłaRozprawy doktorskie na temat "Élastographie par résonance magnétique – Innovation"
Deruelle, Tristan. "Magnetic Resonance Elastography : towards prostate cancer imaging and slow compression wave imaging in softtissues". Electronic Thesis or Diss., Lyon, 2022. http://www.theses.fr/2022LYSE1068.
Pełny tekst źródłaProstate cancer is the second most prevalent cancer in men worldwide. It is suspected when the PSA density is high or/and the superficial prostate feels hard during digital rectal examination. Multiparametric MRI is now recommended prior biopsy when detecting for cancer. However, image interpretation is challenging, even for specialists, and brings many false-positive. Elastography is a technique to assess tissue stiffness by inducing small vibrations. It could provide a 3D map of the stiffness of the prostate. We believe that MR elastography could complement the current multiparametric MRI. Given prostate location and consitution, wave propagation is difficult though. The current work presents the design of a non-invasive wave generation device for the prostate. Then, a new field separation algorithm is presented. This algorithm provides a better estimation of the stiffness, and the correction of artefact generated by common vibrators. Finally, this algorithm can have applications in porous media. Indeed, in poro-elastic materials, a slow compression wave propagates. We observe such a wave in an agar gel, in a foam phantom, and in vivo in human kidney graft. In addition to the classic shear wave velocity estimation, it is now possible to estimate the compression wave velocity. This is an additional piece of information that the operator can use in its diagnostic. In the future, more porous parameters could be derived
Tardieu, Marion. "Élastographie par résonance magnétique et onde de pression guidée". Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01059105.
Pełny tekst źródłaJulea, Felicia. "Conditions de validité de l'Élastographie par Résonance Magnétique". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS053/document.
Pełny tekst źródłaMagnetic Resonance Elastography (MRE) is a imaging technique, recognized as a pertinent method for the mechanical characterization of human tissue in vivo. It offersa particular interest in clinical diagnosis because the development of a pathological process is often accompanied by modifications of the mechanical properties of diseased tissues. MRE consists of recording, along the three spatial dimensions, the displacement field induced by the propagation of a shear wave generated by excitation of the investigated tissue. Mechanical parameters such as shear wave velocity, v, and shear moduli, G' and G'', can then be mapped. The quantification of the mechanical parameters depends on the frequency of the mechanical excitation, fexc, the spatial resolution, a, the amplitude of the induced displacement field, A and the amplitude of the curl field displacement, q, with associated measurement errors, ΔA and Δq, (related to the signal-to-noise ratio, SNR) and finally the reconstruction method. All these parameters were considered to determine the precision and the accuracy of the estimated mechanical moduli and to establish the conditions of validity of MRE following the inversion of the differential equations of the displacement field. In this work, first A and A/ΔA were considered to define a validity threshold for MRE. The influence of A and A/ΔA was studied on a heterogeneous phantom acquired using a 1.5 T MRI with two different types of coils. In a first study, the displacement fields were acquired as a function of A using motion-sensitized spin-echo (REF) and gradient-echo (FFE) sequences for an isotropic spatial resolution of 1 mm. In a second study, the displacement field was acquired as a function of A using RFE for three different spatial resolutions. These studies revealed the existence of a threshold in A/ΔA beyond which the extracted parameters (G', G'') reach a plateau and the MRE is reliable. Then the number of voxels per wavelength, λ/a was considered as a parameter determining the conditions of validity of MRE. This parameter was studied according to the quality of the acquired data characterized by the ratio q//Δq. Simulations were carried in a homogeneous and isotropic elastic medium with a SNR between 5 and 30. The accuracy and the precision of the measurements were found optimal for 6 to 9 voxels per wavelength. The simulation conditions were experimentally reproduced at 2 kHz on a home-made polyvinyl alcohol phantom. The displacement fields were acquired at 11.7 T using a motion-sensitized RFE sequence with spatial resolutions ranging from 150 μm to 300 μm in order to obtain a λ/a ratio ranging from 1 to 20. The experimental results fully confirm the predictions of the simulation. The shear wave velocity decreases with λ/a. It tends towards the expected reference value when the acquisition is performed in the optimal condition, namely here when a is less than or equal to 200 μm. In addition, the standard deviation of the shear wave velocity is reduced for the optimal conditions. Therefore, accurate estimation of mechanical parameters could be deduced. This thesis first demonstrates that the precision and accuracy of MRE are optimal when the acquisitions are performed or processed for a certain wavelength sampling range determined by the SNR. We also showed that for fair comparison of the results, MRE must be carried out in a similar range of q/Δq. Taking into account the conditions of validity of MRE, determined by the ratios λ/a and q/Δq, leads to an effective quantitative measurement of the mechanical parameters making it possible to establish a relevant clinical diagnosis within the same organ, the same subject, between subjects or over time
Kurtz, Samuel. "Caractérisation et limitation des biais de mesure de l’élastographie par résonance magnétique". Electronic Thesis or Diss., Université de Montpellier (2022-....), 2023. http://www.theses.fr/2023UMONS023.
Pełny tekst źródłaMagnetic Resonance Elastography (MRE) is an adapted technique of MRI for non-invasive and in vivo characterization of mechanical properties of living tissues. MRE typically involves identifying properties associated with a displacement field induced by the propagation of shear waves in the tissue medium. The fundamental interest of MRE relies in the strong contrast of the mechanical properties of soft tissues, which are relevant biomarkers for the detection and staging of pathological processes. Since its introduction in the late 1990s, MRE has established itself as a versatile medical imaging modality providing quantitative maps of the soft tissues viscoelasticity. The field of applications of MRE is vast, and the gradual growth of this technique in a clinical setting testifies to its significant interest.However, the high degree of interdisciplinarity of MRE, and the resulting interactions between actors from different communities, represent a barrier to its development. The absence of rigorous methods for integrating measurement biases is an illustrative example of this problem. This thesis work is built around addressing this bias problem.The first axis is motivated by the need to characterize biases related to MRI measurements. To do this, an optical slicing tomography device and a digital volume correlation procedure are adapted to provide three-dimensional harmonic kinematic field measurements. The validation of the device is tested by analyzing the fields obtained on different phantom materials. The consideration of different sources of measurement errors and the diversity of measurable fields make this device a metrological tool for measuring such kinematic fields in an MRI environment.The second axis focuses on limiting the impact of measurement errors in the identification model. To achieve this, a coupled formulation of the direct adjoint problem that underlies MRE is implemented in a subzone decomposition-based identification algorithm for a nearly-incompressible, isotropic, viscoelastic model. This specific formulation relies on the presence of a complementary field to avoid the indirect influence of measurement errors through their application as Dirichlet-type boundary conditions which are particularly abundant considering the subzone decomposition of the problem. It is thus demonstrated that the non-consideration of the boundary conditions contributes significantly to the quality of identifications.The developments presented in this work are compared to several studies on reconstructions of mechanical properties of in silico data, phantoms, and in vivo human brain. These applications provide a detailed evaluation of the stability gains of the algorithm and establish new standards for driving the spatial resolution of identifications in MRE. These developments are particularly useful for validating preclinical MRE studies
Madelin, Guillaume. "Développements méthodologiques de l'IRM à bas champ : élastographie, interaction IRM-Ultasons et polarisation dynamique nucléaire". Bordeaux 2, 2005. http://www.theses.fr/2005BOR21253.
Pełny tekst źródłaThis thesis deals with low field (0. 2 T) Magnetic Resonance Imaging (MRI). Magnetic Resonance Elastography allows to assess some viscoelastic properties of tissues by imaging of acoustic strain waves. In the next part, an ultrasonic transducer was calibrated using the comparison of the balance method and laser interferometry. Then, it was tried to modify the T1 contrast of tissues by spin-phonon interaction due to the application of ultrasound at the Larmor frequency. No modification was obtained, but an acoustic streaming was observed. The visualization of this streaming makes possible to calibrate transducers and to assess some properties of liquids. The last part was dedicated to set up Dynamic Nuclear Polarization experiments, based on the polarization transfer of unpaired electrons of free radicals to the protons of water. An enhancement of the NMR signal by a factor 30 was obtained on nitroxides
Bigot, Mathilde. "Élastographie par résonance magnétique multifréquence in vitro et ex vivo pour la caractérisation d’agrégats fibrillaires cérébraux". Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1207.
Pełny tekst źródłaAmong several biological processes involved in dementia, fibrillar aggregation of endogenous proteins with altered conformation is an early characteristic of neurodegenerative diseases. Magnetic resonance elastography (MRE), an imaging technique that maps the mechanical properties of tissues, has recently been applied in neurodegenerative diseases. Although mechanical changes associated with these diseases have been detected, the mechanical effect of fibril has not yet been isolated in clinical or preclinical studies. This thesis work aims to exploit the fractal properties of fibrils to differentiate them from non-aggregated proteins. The exponent of the power law, obtained by adjusting multi-frequency MRE data acquired on phantom and rat brain ex vivo, could reveal at the macroscopic scale the presence of these fibrillar aggregates at the microscopic scale. During this thesis, an MRI elastography bench for imaging in vitro and ex vivo samples was developed. This device made it possible to implement a series of multi-frequency MRE measurements (400 to 1200Hz) on agarose samples containing two types of fibrils, α-Syn and Aβ, and a non-aggregated protein used as a control. The same device has made it possible to characterize with multi-frequency MRE (800 to 1200Hz) rat brains ex vivo previously injected with α-Syn in the striatum. For each rat, the contralateral striatum was injected with saline solution and used as a control. All MRE data were acquired on a 4.7T preclinical system using a modified RARE sequence. After a direct 3D inversion, the storage modulus, phase angle and wave velocity were extracted from the elastograms. The power law exponent is obtained by adjusting to the multi-frequency data. In inclusions containing fibrils, y was significantly higher than in those containing nonaggregated protein. This result is all the more interesting because the mono-frequency parameters were not affected much by the presence of fibrils: multi-frequency MRE provides information on the microstructure of tissues and makes it possible to characterize fibrillar proteins, however small they may be (a few μm). In rats, storage and loss modules decrease significantly over all frequencies studied compared to contralateral striatum. The parameters y and ϕ on the other hand do not allow discriminating between fibril injection and control injection. Further experiments would be needed to understand the absence of ex vivo detection. This thesis constitutes an original methodological contribution in the field of MRE, by isolating for the first time the biomechanical effect of fibrillar structures involved in neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease
Testu, Julien. "Mise en œuvre de l'élastographie par résonance magnétique multifréquentielle au Centre hospitalier universitaire de Sherbrooke". Mémoire, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/11090.
Pełny tekst źródłaDebernard, Laëtitia. "Caractérisation des propriétés mécaniques des muscles avec la technique d'Élastographie par Résonance Magnétique (ERM)". Compiègne, 2011. http://www.theses.fr/2011COMP1974.
Pełny tekst źródłaThe objective of my thesis was to characterize the mechanical properties of the muscles of the thigh with magnetic resonance elastography (MRE) during physiological changes (growing muscle and age-related changes) and pathological process (Duchenne muscular dystrophy). This thesis depicted that shear modulus was a mechanical parameter more sensitive to the aged-related neuromuscular changes, while the attenuation coefficient was more related to the muscle quality, thus to the age and gender-related structural changes. Study of viscoelastic parameters of muscle tissue (vastus medialis and sartorius) and subcutaneous adipose tissue, with multi-frequency tests ERMs and rheological models (Voigt, Zener and Springpot) showed that the model Springpot was the best adapted for simulation of the viscoelastic properties. In addition, mapping of the shear modulus was correlated with the cartography of the muscle hardness, obtained by ultrasound elastography, thus validating the feasibility of the MRE to detect physiological changes in muscle. Finally, these data were used for the development of phantoms, reflecting muscle mechanical properties. All data, set up with that thesis, will be of use for the clinician to better determine the pathophysiology of neuromuscular disorder, to help in the choice of treatment (therapeutic or surgical) and in the evaluation of future treatments with a gain of function and tissue for the simulation the musculoskeletal system
Leclerc, Gwladys. "Identification expérimentale et numérique des propriétés mécanique des tissus biologiques avec la technique d'Elastographie par Résonance Magnétique (ERM) : application au tissu hépatique". Compiègne, 2012. http://www.theses.fr/2012COMP2038.
Pełny tekst źródłaMy research work was to identify experimentally and numerically the mechanical properties of the liver with Magnetic Resonance Elastography (MRE) technique. The first in vitro part of this project was to develop a phantom mimicking the mechanical properties of the liver. Hyper-viscoelastic properties of the phantom were identified with compression tests, and MRE tests performed with a multifrequency protocol using a hepatic driver generating waves within the liver. In parallel to this experimental identification, a finite element analysis of the propagation of the wave was made through a simplified 2D model, composed of the phantom, with the boundary conditions of MRE test (amplitude of displacement of the membrane, frequency), subsequently with a 3D model. An inverse method was also developed to numerically characterize the elastic properties of the phantom. The results obtained experimentally and numerically were similar (μ = 4 kPa), the identification process was validated and the phantom reveals the elastic properties of fibrotic liver tissue. The second in vivo part was focused on the study of the viscoelastic properties of healthy and fibrotic livers with multifrequency MRE tests. The elasticity increases with the stage of fibrosis. An analysis of the post-treatment (inversion algorithm, rheological models) showed different results of the viscosity with the stage of fibrosis. In addition, a 3D finite element model of the liver was reconstructed, with anatomical MRI slices, to simulate a MRE test and to analyze the behavior of the shear waves. These simulations enabled to adapt MRE protocols before the clinical phase
Hagot, Pascal. "Evaluation de l’interaction fluide-structure dans les Voies Aériennes Supérieures par Imagerie par Résonance Magnétique". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112059/document.
Pełny tekst źródłaObstructive Sleep Apnea (OSA) is a common disorder occurring in almost 3 million French people. However, current diagnosis methods are not sufficient to precisely define obstructing sites and doesn't take into account the fluid structure coupling which plays an important role during upper airway closing. During this thesis, we developed a series of tools exploring upper airway closing process. On the one hand, a screening tool of the structure and the mechanical properties of the upper airway, and on the other hand, a screening tool exploring with dynamic images of inert gases flow into the upper airway, were obtained using conventional hydrogen MRI coupled to magnetic resonance elastography (MRE) and helium-3 or fluor-19 gases MRI, respectively. Geometric and biomechanical data obtained using MRI/MRE are injected into a numerical model given the compliance and the state law of upper airway. Contributions of anatomical restriction on airway collapse are also investigated using a multi-compartmental two-dimensional fluid structure interaction model during a breath inspiration to predicted airway mechanical changes and collapse pressures. Furthermore, helium 3 and sulfur hexafluoride flow was modeled at steady state using commercial finite volume software to evaluate potential feasibility to image upper airway collapsibility during OSA. First dynamic MR imaging using sulfur hexafluoride (SF6) was obtained showing the feasibility of this technique. Using SF6, 6 times denser than air, shows a higher sensibility to upper airway obstruction. This thesis opens a new imaging modality to probe and to diagnose upper airway obstruction
Części książek na temat "Élastographie par résonance magnétique – Innovation"
BEUF, Olivier, Philippe GARTEISER, Kevin TSE VE KOON i Jonathan VAPPOU. "Imagerie quantitative biomécanique par élastographie par résonance magnétique". W Les enjeux de l’IRM, 177–207. ISTE Group, 2023. http://dx.doi.org/10.51926/iste.9113.ch7.
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