Lorentz Force Electrical Impedance Tomography

This article describes a method called Lorentz Force Electrical Impedance Tomography. The electrical conductivity of biological tissues can be measured through their sonication in a magnetic field: the vibration of the tissues inside the field induces an electrical current by Lorentz force. This current, detected by electrodes placed around the sample, is proportional to the ultrasonic pressure, to the strength of the magnetic field and to the electrical conductivity gradient along the acoustic axis. By focusing at different places inside the sample, a map of the electrical conductivity gradient can be established. In this study experiments were conducted on a gelatin phantom and on a beef sample, successively placed in a 300 mT magnetic field and sonicated with an ultrasonic transducer focused at 21 cm emitting 500 kHz bursts. Although all interfaces are not visible, in this exploratory study a good correlation is observed between the electrical conductivity image and the ultrasonic image. This method offers an alternative to detecting pathologies invisible to standard ultrasonography

Imaging of Shear Waves Induced by Lorentz Force in Soft Tissues

This study presents the first observation of elastic shear waves generated in soft solids using a dynamic electromagnetic field. The first and second experiments of this 5 study showed that Lorentz force can induce a displacement in a soft phantom and that this displacement was detectable by an ultrasound scanner using speckle-tracking algorithms. For a 100 mT magnetic field and a 10 ms, 100 mA peak-to-peak electrical burst, the displacement reached a magnitude of 1 um. In the third experiment, we showed that Lorentz force can induce shear waves in a phantom. A physical model 10 using electromagnetic and elasticity equations was proposed. Computer simulations were in good agreement with experimental results. The shear waves induced by Lorentz force were used in the last experiment to estimate the elasticity of a swine liver sample

Acousto-electrical speckle pattern in Lorentz force electrical impedance tomography

Ultrasound speckle is a granular texture pattern appearing in ultrasound imaging. It can be used to distinguish tissues and identify pathologies. Lorentz force electrical impedance tomography is an ultrasound-based medical imaging technique of the tissue electrical conductivity. It is based on the application of an ultrasound wave in a medium placed in a magnetic field and on the measurement of the induced electric current due to Lorentz force. Similarly to ultrasound imaging, we hypothesized that a speckle could be observed with Lorentz force electrical impedance tomography imaging. In this study, we first assessed the theoretical similarity between the measured signals in Lorentz force electrical impedance tomography and in ultrasound imaging modalities. We then compared experimentally the signal measured in both methods using an acoustic and electrical impedance interface. Finally, a bovine muscle sample was imaged using the two methods. Similar speckle patterns were observed. This indicates the existence of an "acousto-electrical speckle" in the Lorentz force electrical impedance tomography with spatial characteristics driven by the acoustic parameters but due to electrical impedance inhomogeneities instead of acoustic ones as is the case of ultrasound imaging

Electromagnetic Hydrophone with Tomographic System for Absolute Velocity Field Mapping

The velocity and pressure of an ultrasonic wave can be measured by an electromagnetic hydrophone made of a thin wire and a magnet. The ultrasonic wave vibrates the wire inside a magnetic field, inducing an electrical current. Previous articles reported poor spatial resolution of comparable hydrophones along the axis of the wire. In this study, submillimetric spatial resolution has been achieved by using a tomographic method. Moreover, a physical model is presented for obtaining absolute measurements. A pressure differential of 8% has been found between piezoelectric and electromagnetic hydrophone measurements. These characteristics show this technique as an alternative to standard hydrophones

Propagation ultrasonore dans des gels modélisant les tissus biologiques

Dans le cadre de l'application à la destruction des tumeurs cancéreuses par ultrasons de forte intensité (projet ANR cavitherapus), nos travaux portent sur l'étude de la propagation des ondes ultrasonores dans des gels qui se comportent comme des tissus biologiques. Afin de valider un modèle\ud de propagation acoustique, une étude expérimentale des propriétés acoustiques et thermiques de différents gels est menée

Spatially broad opening of the blood-brain barrier with an unfocused ultrasound transducer in rabbits

International audienceThe aim of this work was to study the opening of the blood-brain barrier (BBB) over a large volume using an unfocused ultrasound device in the presence of ultrasound contrast agents in rabbits. A mono-element planar 1MHz ultrasound transducer was used to perform burst sonications in 24 healthy New-Zealand white rabbits after craniectomy and during intravenous injection of Sonovue®. The transducer was operated with a pulse repetition frequency of 1Hz, and a range of pulses lengths and in situ acoustic pressures (10-35ms and 0.3-1MPa respectively). Opening of the BBB was observed in contrast-enhanced images in a 4.7T MRI, through blue dye extravasation and with confocal microscopy. Adverse effects were analyzed on histology. A significant BBB opening limited spatially to the extent of the ultrasound field was observed. BBB opening appeared during the sonication and lasted for several hours. Monitoring was possible on MRI sequences as a significant gadolinium contrast enhancement (p<0.0001). BBB opening was associated with perivascular blood red cell extravasation and transient vascular spasm. In conclusion, the BBB can be opened in large areas of the brain with low power unfocused ultrasound, with limited tissue damage, and could permit safe drug delivery in the brain. Work supported by CarThera and Région Ile-de-France

La manufacture de la rue Delbos, dernière faïencerie de Bordeaux

Lafon de Ribeyrolles Cyril. La manufacture de la rue Delbos, dernière faïencerie de Bordeaux. In: Sèvres. Revue de la Société des Amis du musée national de Céramique, n°20, 2011. pp. 138-142

Les frères Fenal. Potiers et faïenciers à Pexonne

Lafon de Ribeyrolles Cyril. Les frères Fenal. Potiers et faïenciers à Pexonne. In: Sèvres. Revue de la Société des Amis du musée national de Céramique, n°21, 2012. pp. 109-118

A 10.5 cm Ultrasound Link for Deep Implanted Medical Devices

A study on ultrasound link for wireless energy transmission dedicated to deeply implanted medical devices is presented. The selection of the frequency to avoid biological side effects (e. g., cavitations), the choice of the power amplifier to drive the external transducers and the design of the rectifier to maximize the energy extraction fromthe implanted transducer are described in details. The link efficiency is characterized in water using a phantom material for a transmitter-receiver distance of 105 mm, transducers active area of 30 mm x 96 mm and 5 mm x 10 mm, respectively, and a system efficiency of 1.6% is measured

Benchmarking CIVA Healthcare platform for transcranial ultrasound simulation

International audienceObjectives:Recent work presented benchmarking and intercomparison of several transcranial acoustic modelling tools. We expand on that work with benchmarking of the CIVA Healthcare Simulation platform.Methods:The 18 unique numerical benchmarks provided in [1] were reproduced in the CIVA Healthcare simulation platform, which uses a ray-tracing model to provide rapid calculation of acoustic fields.All simulations were performed using a desktop PC. Benchmark values and intercomparisons were generated using the MATLAB code provided in supplemental material, with the CIVA results beingappended to the existing comparisons.[1] Aubry et al (2022). JASA, 152(2)Results:Very good agreement was found between the results obtained by CIVA and those obtained through other methods, with the most significant differences being observed in large 3D calculations througha real skull. These large 3D simulations used a lower number of rays and internal reflections to decrease computation time in order to accommodate the atypically large simulated domain, withoutsignificant deterioration of the results. In contrast with full-wave methods, the ray-tracing model provides fast calculation of the acoustic field only at specified points, typically near the focal target, without simulation of the field in theintervening or surrounding space.Conclusions:The CIVA Healthcare Simulation platform shows strong agreement with other models of transcranial ultrasound modelling. These results serve to validate the CIVA ray-tracing method, andfurther build confidence in the use of computational modelling to support transcranial ultrasound therapies.Acknowledgements:This work was financially supported by the Focused Ultrasound Foundation, and conducted incooperation with the CEA-LIST (French Alternative Energies and Atomic Energy Commission)