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Yaras YS, Bradley LW, Yildirim DK, Lederman RJ, Kocaturk O, Oshinski J, Degertekin FL. Acousto-optic-based time domain electric field sensor for magnetic resonance imaging applications. OPTICAL ENGINEERING (REDONDO BEACH, CALIF.) 2024; 63:031008. [PMID: 39091280 PMCID: PMC11293619 DOI: 10.1117/1.oe.63.3.031008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/04/2024]
Abstract
An acousto-optic (AO)-based electric field sensor is presented for time domain measurement under magnetic resonance imaging (MRI). A fully MR-compatible sensor is designed and fabricated using a phase-shifted fiber Bragg grating mechanically coupled to a piezoelectric transducer. Mechanical resonance of the piezoelectric transducer is matched to the operating frequencies of commonly used MRI systems to increase the sensitivity of the sensor. Sensitivity of the sensor is measured as 1.27 mV/V/m, with a minimum detectable electric field of 4.4 mV/m/√/Hz. Directivity of the sensor is measured with a 18 dB orthogonal component rejection. The dynamic range of the sensor is calculated as 117 dB/Hz, which allows the measurement of electric fields up to 3.2 kV/m. In MRI studies, the AO sensor was able detect local hot spots around a reference implant accurately with high signal-to-noise ratio. AO sensor exhibited similar or better performance when compared with commercially available MRI compatible electric field sensors. Furthermore, the small size of the sensor with the flexible fiber optic link could allow in situ measurements of electric fields during critical interventional procedures such as pacemaker lead or deep brain stimulator placement as an MRI dosimeter during diagnostic scans.
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Affiliation(s)
- Yusuf S. Yaras
- Georgia Institute of Technology, G.W. Woodruff School of Mechanical Engineering, Atlanta, Georgia, United States
| | - Lee W. Bradley
- Georgia Institute of Technology, G.W. Woodruff School of Mechanical Engineering, Atlanta, Georgia, United States
| | - D. Korel Yildirim
- National Institutes of Health, National Heart Lung and Blood Institute, Bethesda, Maryland, United States
| | - Robert J. Lederman
- National Institutes of Health, National Heart Lung and Blood Institute, Bethesda, Maryland, United States
| | - Ozgur Kocaturk
- Bogazici University, Institute of Biomedical Engineering, Istanbul, Turkey
| | - John Oshinski
- Georgia Institute of Technology, Wallace H. Coulter Department of Biomedical Engineering, Atlanta, Georgia, United States
- Emory University, Department of Radiology and Imaging Sciences, Atlanta, Georgia, United States
| | - F. Levent Degertekin
- Georgia Institute of Technology, G.W. Woodruff School of Mechanical Engineering, Atlanta, Georgia, United States
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Özen AC, Russe MF, Lottner T, Reiss S, Littin S, Zaitsev M, Bock M. RF-induced heating of interventional devices at 23.66 MHz. MAGMA (NEW YORK, N.Y.) 2023:10.1007/s10334-023-01099-7. [PMID: 37195365 PMCID: PMC10386938 DOI: 10.1007/s10334-023-01099-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 04/29/2023] [Accepted: 05/04/2023] [Indexed: 05/18/2023]
Abstract
OBJECTIVE Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced heating of commonly used intravascular devices at the Larmor frequency of a 0.55 T system (23.66 MHz) with a focus on the effect of patient size, target organ, and device position on maximum temperature rise. MATERIALS AND METHODS To assess RF-induced heating, high-resolution measurements of the electric field, temperature, and transfer function were combined. Realistic device trajectories were derived from vascular models to evaluate the variation of the temperature increase as a function of the device trajectory. At a low-field RF test bench, the effects of patient size and positioning, target organ (liver and heart) and body coil type were measured for six commonly used interventional devices (two guidewires, two catheters, an applicator and a biopsy needle). RESULTS Electric field mapping shows that the hotspots are not necessarily localized at the device tip. Of all procedures, the liver catheterizations showed the lowest heating, and a modification of the transmit body coil could further reduce the temperature increase. For common commercial needles no significant heating was measured at the needle tip. Comparable local SAR values were found in the temperature measurements and the TF-based calculations. CONCLUSION At low fields, interventions with shorter insertion lengths such as hepatic catheterizations result in less RF-induced heating than coronary interventions. The maximum temperature increase depends on body coil design.
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Affiliation(s)
- Ali Caglar Özen
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
| | - Maximilian Frederik Russe
- Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Thomas Lottner
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Simon Reiss
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Sebastian Littin
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Maxim Zaitsev
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Michael Bock
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
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Lottner T, Reiss S, Rieger SB, Schuettler M, Fischer J, Bielak L, Özen AC, Bock M. Radio-frequency induced heating of intra-cranial EEG electrodes: The more the colder? Neuroimage 2022; 264:119691. [PMID: 36375783 DOI: 10.1016/j.neuroimage.2022.119691] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 09/20/2022] [Accepted: 10/16/2022] [Indexed: 11/13/2022] Open
Abstract
Many neurological disorders are analyzed and treated with implantable electrodes. Many patients with such electrodes have to undergo MRI examinations - often unrelated to their implant - at the risk of radio-frequency induced heating. The number of electrode contact sites of these implants keeps increasing due to improvements in manufacturing and computational algorithms. Electrode grids with multiple receive channels couple to the RF fields present in MRI, but, due to their proximity, a combination of leads has a coupling response which is not a superposition of the individual leads' response. To investigate the problem of RF-induced heating of coupled multi-lead implants, temperature mapping was performed on a set of intra-cranial electroencephalogram (icEEG) electrode grid prototypes with increasing number of contact sites (1-16). Additionally, electric field measurements were used to investigate the radio-frequency heating characteristics of the implants in different media combinations, simulating the device being partially immersed inside the patient. MR measurements show RF-induced heating up to 19.6 K for the single electrode, reducing monotonically with larger number of contact sites to a minimum of 0.9 K for the largest grid. The SAR calculated from temperature measurements agrees well with electric field mapping: The same trend is visible for different insertion lengths, however, the energy dissipated by the whole implant varies with the grid size and insertion length. Thus, in the tested circumstances, a larger electrode number either reduced or had a similar risk of RF induced heating, indicating, that the size of electrode grids is a design parameter, which can be used to change an implants RF response and in turn to reduce the risk of RF induced heating and improve the safety of patient with neuro-implants undergoing MRI examinations.
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Affiliation(s)
- Thomas Lottner
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Simon Reiss
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | | | | | - Johannes Fischer
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Lars Bielak
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Ali C Özen
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Michael Bock
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
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Electric Field Sensor Based on High Q Fano Resonance of Nano-Patterned Electro-Optic Materials. PHOTONICS 2022. [DOI: 10.3390/photonics9060431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
This paper presents theoretical studies of Fano resonance based electric-field (E-field) sensors. E-field sensor based on two electro-optical (EO) materials i.e., barium titanate (BaTiO3, BTO) nanoparticles and relaxor ferroelectric material Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) combined with nanostructure are studied. As for the BTO based E-field sensor, a configuration of filling the BTO nanoparticles into a nano-patterned thin film silicon is proposed. The achieved resonance quality factor (Q) is 11,855 and a resonance induced electric field enhancement factor is of around 105. As for the design of PMN-PT based E-field sensor, a configuration by combining two square lattice air holes in PMN-PT thin film but with one offsetting hole left is chosen. The achieved resonance Q is of 9,273 and an electric field enhancement factor is of around 96. The resonance wavelength shift sensitivity of PMN-PT nanostructured can reach up to 4.768 pm/(V/m), while the BTO based nanostructure has a sensitivity of 0.1213 pm/(V/m). If a spectrum analyzer with 0.1 pm resolution is considered, then the minimum detection of the electric field Emin is 20 mV/m and 0.82 V/m for PMN-PT and BTO based nanostructures, respectively. The nano-patterned E-field sensor studied here are all dielectric, it has therefore the advantage of large measurement bandwidth, high measurement fidelity, high spatial resolution and high sensitivity.
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Reiss S, Lottner T, Ozen AC, Polei S, Bitzer A, Bock M. Analysis of the RF Excitation of Endovascular Stents in Small Gap and Overlap Scenarios Using an Electro-Optical E-field Sensor. IEEE Trans Biomed Eng 2021; 68:783-792. [DOI: 10.1109/tbme.2020.3009869] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Heidt T, Reiss S, Lottner T, Özen AC, Bode C, Bock M, von Zur Mühlen C. Magnetic resonance imaging for pathobiological assessment and interventional treatment of the coronary arteries. Eur Heart J Suppl 2020; 22:C46-C56. [PMID: 32368198 PMCID: PMC7189741 DOI: 10.1093/eurheartj/suaa009] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
X-ray-based fluoroscopy is the standard tool for diagnostics and intervention in coronary artery disease. In recent years, computed tomography has emerged as a non-invasive alternative to coronary angiography offering detection of coronary calcification and imaging of the vessel lumen by the use of iodinated contrast agents. Even though currently available invasive or non-invasive techniques can show the degree of vessel stenosis, they are unable to provide information about biofunctional plaque properties, e.g. plaque inflammation. Furthermore, the use of radiation and the necessity of iodinated contrast agents remain unfavourable prerequisites. Magnetic resonance imaging (MRI) is a radiation-free alternative to X-ray which offers anatomical and functional imaging contrasts fostering the idea of non-invasive biofunctional assessment of the coronary vessel wall. In combination with molecular contrast agents that target-specific epitopes of the vessel wall, MRI might reveal unique plaque properties rendering it, for example, ‘vulnerable and prone to rupture’. Early detection of these lesions may allow for early or prophylactic treatment even before an adverse coronary event occurs. Besides diagnostic imaging, advances in real-time image acquisition and motion compensation now provide grounds for MRI-guided coronary interventions. In this article, we summarize our research on MRI-based molecular imaging in cardiovascular disease and feature our advances towards real-time MRI-based coronary interventions in a porcine model.
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Affiliation(s)
- Timo Heidt
- Department of Cardiology, Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Hugstetterstr. 55, 79106 Freiburg, Germany
| | - Simon Reiss
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany
| | - Thomas Lottner
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany
| | - Ali C Özen
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany.,German Cancer Consortium Partner Site Freiburg, German Cancer Research Center (DKFZ), Stefan-Meier-Str. 17, 79104 Freiburg, Germany
| | - Christoph Bode
- Department of Cardiology, Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Hugstetterstr. 55, 79106 Freiburg, Germany
| | - Michael Bock
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany
| | - Constantin von Zur Mühlen
- Department of Cardiology, Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Hugstetterstr. 55, 79106 Freiburg, Germany
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Özen AC, Silemek B, Lottner T, Atalar E, Bock M. MR safety watchdog for active catheters: Wireless impedance control with real-time feedback. Magn Reson Med 2020; 84:1048-1060. [PMID: 31961965 DOI: 10.1002/mrm.28153] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 11/29/2019] [Accepted: 12/09/2019] [Indexed: 12/13/2022]
Abstract
PURPOSE To dynamically minimize radiofrequency (RF)-induced heating of an active catheter through an automatic change of the termination impedance. METHODS A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔTmax . The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built-in thermistor or external data from a fiber-optical thermometer. It automatically changes the catheter input impedance until the temperature rise during MRI is minimized. If ΔTmax is exceeded, RF transmission is blocked by a feedback system. RESULTS The thermistor and fiber-optical thermometer provided consistent temperature data in a phantom experiment. During MRI, the MRsWD was able to reduce the maximum temperature rise by 25% when operated in real-time feedback mode. CONCLUSION This study demonstrates the technical feasibility of an MRsWD as an alternative or complementary approach to reduce RF-induced heating of active interventional devices. The automatic MRsWD can reduce heating using direct temperature measurements at the tip of the catheter. Given that temperature measurements are intrinsically slow, for a clinical implementation, a faster feedback parameter would be required such as the RF currents along the catheter or scattered electric fields at the tip.
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Affiliation(s)
- Ali Caglar Özen
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany.,Faculty of Medicine, University of Freiburg, Freiburg, Germany.,German Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Berk Silemek
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey.,Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Thomas Lottner
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| | - Michael Bock
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany
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Erhardt JB, Lottner T, Martinez J, Özen AC, Schuettler M, Stieglitz T, Ennis DB, Bock M. It's the little things: On the complexity of planar electrode heating in MRI. Neuroimage 2019; 195:272-284. [PMID: 30935911 DOI: 10.1016/j.neuroimage.2019.03.061] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Revised: 03/07/2019] [Accepted: 03/26/2019] [Indexed: 10/27/2022] Open
Abstract
Neurological disorders are increasingly analysed and treated with implantable electrodes, and patients with such electrodes are studied with MRI despite the risk of radio-frequency (RF) induced heating during the MRI exam. Recent clinical research suggests that electrodes with smaller diameters of the electrical interface between implant and tissue are beneficial; however, the influence of this electrode contact diameter on RF-induced heating has not been investigated. In this work, electrode contact diameters between 0.3 and 4 mm of implantable electrodes appropriate for stimulation and electrocorticography were evaluated in a 1.5 T MRI system. In situ temperature measurements adapted from the ASTM standard test method were performed and complemented by simulations of the specific absorption rate (SAR) to assess local SAR values, temperature increase and the distribution of dissipated power. Measurements showed temperature changes between 0.8 K and 53 K for different electrode contact diameters, which is well above the legal limit of 1 K. Systematic errors in the temperature measurements are to be expected, as the temperature sensors may disturb the heating pattern near small electrodes. Compared to large electrodes, simulations suggest that small electrodes are subject to less dissipated power, but more localized power density. Thus, smaller electrodes might be classified as safe in current certification procedures but may be more likely to burn adjacent tissue. To assess these local heating phenomena, smaller temperature sensors or new non-invasive temperature sensing methods are needed.
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Affiliation(s)
- Johannes B Erhardt
- Department of Microsystems Engineering-IMTEK, University of Freiburg, Freiburg, Germany; Department of Radiology, University of California, Los Angeles, CA, USA; BrainLinks-BrainTools, Freiburg, Germany
| | - Thomas Lottner
- Department of Radiology - Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Jessica Martinez
- Department of Radiology, University of California, Los Angeles, CA, USA; Department of Bioengineering, University of California, Los Angeles, CA, USA
| | - Ali C Özen
- Department of Radiology - Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany; German Cancer Consortium Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | | | - Thomas Stieglitz
- Department of Microsystems Engineering-IMTEK, University of Freiburg, Freiburg, Germany; Bernstein Center Freiburg, Freiburg, Germany; BrainLinks-BrainTools, Freiburg, Germany
| | - Daniel B Ennis
- Department of Radiology, Stanford University, Stanford, CA, USA
| | - Michael Bock
- Department of Radiology - Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
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Saniour I, Gaborit G, Perrier AL, Gillette L, Revillod G, Sablong R, Duvillaret L, Beuf O. Electro-optic probe for real-time assessments of RF electric field produced in an MRI scanner: Feasibility tests at 3 and 4.7 T. NMR IN BIOMEDICINE 2018; 31:e3849. [PMID: 29130620 DOI: 10.1002/nbm.3849] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Revised: 09/19/2017] [Accepted: 09/25/2017] [Indexed: 06/07/2023]
Abstract
During magnetic resonance imaging (MRI) examinations, the average specific absorption rate (SAR) of the whole body is calculated as an index of global energy deposition in biological tissue without taking into account the presence of metallic implants or conductive materials. However, this global SAR calculation is not sufficient to ensure patient safety and a local SAR measurement should be carried out. Several measurement techniques have already been used to evaluate the local SAR, in particular electric field (E-field) probes, but the accuracy of the measurements and the resolutions (spatial and temporal) depend strongly on the measurement method/probe. This work presents an MR-compatible, subcentimeter probe based on an electro-optic (EO) principle enabling a real-time measurement of the local E-field during MRI scans. The experiments using these probes were performed on two different MR systems (preclinical and clinical) having different static magnetic field strengths and with different volume coil geometries. The E-field was measured with unloaded (in air) and loaded volume coils in order to assess the sensing characteristics of the optical probe. The results show an excellent linearity between the measured E-field and the radiofrequency (RF) magnetic field in both experimental conditions. Moreover, the distribution of the E-field throughout the volume coil was experimentally determined and was in good agreement with numerical simulations. Finally, we demonstrate through our measurements that the E-field depends strongly on the dielectric properties of the medium.
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Affiliation(s)
- Isabelle Saniour
- Université Lyon, INSA-Lyon, Université Claude Bernard Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS UMR 5220, U1206, Lyon, France
| | - Gwenaël Gaborit
- Université Savoie-Mont-Blanc, IMEP-LAHC, UMR 5130, Le Bourget-du-Lac, France
- Kapteos, Sainte-Hélène-du-Lac, France
| | - Anne-Laure Perrier
- Université Savoie-Mont-Blanc, IMEP-LAHC, UMR 5130, Le Bourget-du-Lac, France
| | | | | | - Raphaël Sablong
- Université Lyon, INSA-Lyon, Université Claude Bernard Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS UMR 5220, U1206, Lyon, France
| | | | - Olivier Beuf
- Université Lyon, INSA-Lyon, Université Claude Bernard Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS UMR 5220, U1206, Lyon, France
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