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Systematic Analysis of the Improvements in Magnetic Resonance Microscopy with Ferroelectric Composite Ceramics

Magnetic Resonance Microscopy enables imaging of samples in the millimetre domain with sub-micrometric resolution. We developed a new type of probe made of ceramic material allowing to produce images with resolution twice higher than with conventional metal probes.

In magnetic resonance microscopy (MRM), an imaging modality that focuses on imaging of samples of a few millimetres size, the commonly used probe is a solenoid coil made of copper wire. When fed by an electrical current, it produces a magnetic field which is essential to obtain an image. Doing so, an electric field is also generated within the biological sample. The latter usually being conductive, it induces dielectric losses and represents a source of noise. At fixed acquisition time, this phenomenon intrinsically limits the achievable signal-to-noise ratio (SNR) and, therefore, the resolution.
In this framework, several research works have evoked and demonstrated the potential of ceramic probes to overcome this limitation at several static magnetic field intensities B0. These probes exploit the first transverse electric mode of an annular-ring dielectric resonator which is simply excited by a small current loop. Among the special features of this resonator are its axial magnetic field, similar to that of the reference probe, together with an insignificant electric field. The resonator properties are chosen so that the mode of interest resonates at a frequency close to the Larmor frequency of protons at the given B0 field intensity. At 17 T, the studied resonator had to be made of a ceramic with relative permittivity 530 while ensuring a low intrinsic loss level within the dielectric material to avoid additional noise during the MRI acquisition. These constraints – high permittivity and low losses – could be relieved with a customised new ferroelectric ceramic material containing magnesium additives.
A semi-analytical model was set up to propose an estimation of the achievable SNR. This allowed to compare the performances of the ceramic probe with the solenoid coil as a parametric estimation problem depending on the electromagnetic properties of both the ferroelectric material and the sample. Numerical simulations validated this approach in the studied configuration that was also experimentally tested for imaging of vegetal sample (ilex aquifolium) at 17 T.
Experimental investigations in MRI confirmed predictions of the theoretical and numerical studies, that is an SNR gain of around 2 in favour of the ceramic probe over the solenoid coil. This was explained by the very limited electric field – sample interaction in the case of ceramic probe, thanks to the electric field distribution presenting remarkably low values in the sample region.
This research paves the way for a novel approach of microscopy probes development. Optimized designs of ceramic probes are enabled by the opportunity to elaborate customized ferroelectric materials. For a sample with given dimensions and properties, it has become possible to make an informed decision about choosing a solenoid coil or a ceramic probe in order to reach the best image resolution.
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Partner :
- CEA NEUROSPIN - Read the article of CEA Joliot Curie
- ITMO University

Reference : M. A.C. Moussu, L. Ciobanu, S. Kurdjumov, E. Nenasheva, B. Djemai, M. Dubois, A. Webb, S. Enoch, P. Belov, R. Abdeddaim, S. Glybovski, “Systematic Analysis of the Improvements in Magnetic Resonance Microscopy with Ferroelectric Composite Ceramics”, accepted for publication in Advanced Materials
Version of Record online : 17 May 2019

https://doi.org/10.1002/adma.201900912

Contacts :
Marine Moussu, Institut Fresnel - UMR7249, Marseille -
Luisa Ciobanu, CEA Neurospin, Gif-sur-Ivette
Stanislav Glybovski, ITMO University, Saint-Pétersbourg

http://www.mcube-project.eu
TWITTER : @MCUBE19

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement n°736937