Anne-Laure Perrier

New trends in MRI of cartilage: Advances and limitations in small animal studies

Due to the actual interest for bioengineering in the osteoarthritis (OA) healing context, researchers need accurate qualitative and quantitative methodologies to evaluate in vivo the integration and functionality of their cartilage-like biomaterials. As in clinical diagnostic strategies, advances in Magnetic Resonance Imaging (MRI) seem promising for non-vulnerant assessments of articular cartilage bio-architecture and morphology in small animal models. These experimental models are commonly used to monitor the physiopathology of OA and to evaluate therapeutic responses mediated by chondroprotective drugs or tissue engineering. Nowadays, the application of MR protocols to in vivo small animal cartilage imaging is achievable with the development of high magnetic fields and the adaptation of methodologies to reach the required spatial resolution and contrast. The purpose of this article is to summarize these current MRI strategies used for in vivo small animal articular cartilage assessments.

Unbiased Electro-Optic Waveguide as a Sensitive Nuclear Magnetic Resonance Sensor

A pigtailed Ti:LiNbO3 waveguide is here associated to a specific nuclear magnetic resonant coil to perform a low invasive magnetic field measurement. The developed device exploits a passive electro-optic transduction between the measured magnetic field and polarization state modulation of a laser probe beam. Because of the use of integrated optics, the coil electromotive force induces a dramatically enhanced electric field, thus leading to sensitivity improvement. A minimum detectable magnetic field lower than 60 fT. Hz-1/2 is achieved at the resonant frequency of 128 MHz. A dynamic range exceeding 100 dB is experimentally demonstrated.

Potentialities of an Electro-Optic Crystal Fed by Nuclear Magnetic Resonant Coil for Remote and Low-Invasive Magnetic Field Characterization

In this paper, we demonstrate the use of a LiTaO3 crystal associated with a typical nuclear magnetic resonant loop coil to perform an optically remote radio frequency magnetic-field characterization. The whole transduction scheme is theoretically and experimentally studied. The measurement dynamics reaches 60 dB. The minimum detectable magnetic field is lower than 1 nT, which corresponds to an induced inner crystal electric field as low as 30 mV/m. To evaluate the spatial potentialities of the sensor, a 1-D mapping of the field along an asymmetric butterfly-shaped loop coil is performed. The result is in good agreement with finite-difference time-domain simulations and demonstrates the vectorial behavior of the sensor device.

Design of a Two-Channel NMR Coil Using an Impedance Transformation Approach

In the field of small-animal magnetic resonance imaging, multi-channel coils are increasingly being used. Two-channel coils based on a common conductor between the two elements are not considerably used and theoretical equations are not explicitly given. In this paper, the design of a two-channel nuclear magnetic resonance coil based on common conductor for imaging applications has been carried out using an impedance transformation approach. The equations and simulations result at an operating frequency of 300 MHz are confirmed by the characterization of the two-channel receiver coil prototype.

Linear electro-optic effect for nuclear magnetic resonance coil

An electrooptic transduction is here used to perform a low invasive characterization of the magnetic field in the context of magnetic resonance imaging. A resonant coil is coupled to a passive electrooptic crystal and the electromotive force of the magnetic field sensor is converted into a polarization state modulation of a laser probe beam. The optical conversion is demonstrated and lead to a fiber remote measurement of the magnetic field. The setup sensitivity and dynamics are finally dramatically enhanced using a LiNbO3 integrated waveguide. The minimum detectable field is as low as 60 fT.Hz-1/2 and the dynamics exceeds 100 dB.

Design of a Four-Channel Surface Receiver Coil Array Without Preamplifiers for the Decoupling Between Elements: Validation for High-Resolution Rat Knee MR Imaging

In magnetic resonance imaging, multichannel coil arrays are increasingly being used to improve signal-to-noise ratio in order to increase spatial and/or temporal image resolution. A recent decoupling technique allows conception of two-channel surface transceiver coil arrays. This technique, based on a common conductor, does not require an additional preamplifier for the decoupling between elements. In this case, the coil array loops are directly connected to the independent transmit/receive switches and preamplifiers of the MR system. Using this common conductor decoupling technique, a topology of a four-channel coil array is developed and described in this paper. A four-channel surface receiver coil array is designed to perform the simultaneous acquisition of both rat knee joints at 7 T. Without the use of additional preamplifiers, a good decoupling between channels is obtained and very high spatial resolution 3-D images with a voxel size of

SONDE ELECTRO-OPTIQUE POUR LA MESURE QUANTITATIVE DU CHAMP ELECTRIQUE RADIOFREQUENCE DURANT UN EXAMEN IRM

49\times 49\times 98~\mu{\rm m}^{3}

Experimental and simulated distribution of the RF electrical field inside a birdcage coil

is achieved in 1 h 22 min scan time. Acquisitions allow the quantification of cartilage morphological parameters such as thickness and volume.