Patent ID: 12210076

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, the terms “ranging from . . . and . . . ” and the terms “between . . . and . . . ” used in proportion intervals have to be understood as integrating the lower and upper limit of such intervals. The terms “% in volume” have to be understood as “% in volume based on the total volume of the material”, i.e. the material composition.

The invention relates, in a first aspect, to a material for use in a pad for high field and/or very high field magnetic resonance imaging. High field magnetic resonance imaging is carried out, for example, at 3 Tesla. Very high field magnetic resonance imaging is carried out, for example, at 7 Tesla. The material according to the invention comprises at least one polar solvent having a melting point ranging from 14° C. and 50° C., a dispersant and a dielectric charge.

According to a preferred embodiment, the polar solvent is selected from the group consisting of fluoro-ethylene carbonate (FEC), diethyl-cyano-ethyl phosphonate, ethyl-1-methyl-sulfone, tetramethylene sulfone and isopropyl-methyl-sulfone, or a combination thereof. A preferred polar solvent is fluoro-ethylene carbonate. The proportion of polar solvent is comprised between 1% and 95%, preferentially between 10% and 85%, more preferentially between 14% and 53% in volume.

The dispersant, according to a specific embodiment of the invention is selected from the group consisting of gums such as xanthan or phytagel, agaroses, gelatins, glycerols, celluloses, polysaccharides, polyacrylic polymers, polyethylene glycols and polyacrylamides, or a combination thereof. The material according to the invention comprises up to 40% in volume of dispersant. Practically, the proportion of dispersant is comprised between 0.5% and 9%, preferably between 1% and 9%, more preferably comprised between 1% and 5.9% in volume.

Advantageously, the polar solvent has a high dielectric constant, i.e. superior of that of water and a melting temperature of about 20 to 25° C. The dispersant, soluble in this solvent, has a melting point of about 20 to 25° C. Together, they form a viscous matrix in which dielectric charged component of electrical permittivity, higher than the electrical permittivity of solvent, are dispersed.

The dielectric charge or dielectric charge component, which is in a particulate form, also called filler, is a material having a permittivity higher than the electrical permittivity of the solvent. For example, the filler is selected from the group consisting of SiC, BaTiO3and CaTiO3. The dielectric charge component is in particular in the form of particles, which are spherical or substantially spherical, and which have average sizes ranging from 0.1 μm to 50 μm, preferably ranging from 0.5 μm to 50 μm, more preferably ranging from 7 to 8 μm. In fact, the particles themselves have sizes ranging from 0.1 μm to 50 μm, preferably ranging from 0.5 μm to 50 μm, more preferably ranging from 7 to 8 μm. The filler, dispersed in the matrix, provides the dielectric properties of the composition. Particles properties can be adjusted to exhibit enhanced EM properties. For example, the particles may have received surface treatment in order to adjust their affinity to the matrix or have a particular shape to exhibits anisotropic EM properties. The proportion of dielectric charge is comprised between 4% and 90% preferably between 10% to 85% and more preferably between 41% to 85% in volume.

As a result, the composition of the present invention comprises a solvent, a dispersant and a dielectric filler. Wherein said solvent is a liquid having a melting temperature comprised between 14° C. and 50° C. and a permittivity ranging from 40 to 100. A non-exhaustive list of suitable solvents is presented in table 1. below with their respective permittivities at 300 MHz.

TABLE 1MeltingPermittivity atSolvent NameTemperature ( C.)300 MHzFluoro-ethylene-4099carbonateDiethyl-cyano-2350ethyl-phosphonateEthyl-methyl-3495sulfoneTetra-methylene-2560sulfoneIsopropyl-methyl-2548sulfone

Embodiments according to the invention include all combinations of a different solvent having a melting temperature between 14° C. and 50° C. or derivative of fluoroethylene carbonate or polyethylene glycol derivative having a melting temperature of between 10° C. and 50° C.

The dispersant is an additive which aims to give more viscosity to the mixture while facilitating the dispersion of the filler in the matrix. A non-exhaustive list of potential dispersants is given in the table 2 below. The function of the chosen compound will be made according to the desired properties while its length of chains will be made according to the desired viscosity and saturation level of the charge in the solvent.

TABLE 2PolyacrylamidesPolysaccharidesAgarosesGelatinsGlycerolsPolyacrylic polymersPolyethylene glycolsCelluloses

The invention relates, according to a second aspect, to a method for obtaining a material as above-defined. The method comprising the following steps.mixing the solvent manually and/or mechanically, for example with a blade or magnetic stirred rotating from 100 rpm to 500 rpm, for periods ranging from 1 to 5 minutes at temperatures ranging from 25° C. to 300° C. A mechanical stirring at 300 rpm for about 5 min at about 75° C. is preferred.adding gradually the dispersant wherein the amount of dispersant is ranging from 0.5% to 9% by volume. A volume of dispersant gradually added to the solvent stirred at 300 rpm at 75° C. is preferred.stirring mechanically and/or manually the mixture obtained in the preceding step for periods ranging from 1 minute to 300 minutes at temperatures ranging from 25° C. to 300° C. A mechanical stirring for 5 min at 75° C. is preferred.adding gradually the dielectric charge component wherein the amount of dielectric charge component is ranging from 4% to 90% by volume.stirring mechanically and/or manually the composition obtained in the preceding step for a period of time ranging from 1 minute to 300 minutes at temperatures ranging from 25° C. to 300° C. A temperature range of 25 to 200° C. is preferred.

The ordinary skill in the art is able to adapt the stirring period in function of the material amount prepared.

For an amount of dielectric charge component comprised between 40% and 50% in volume, stirring manually for 5 to 15 min. at 25° C. is preferred. For an amount of 50% in volume and above, stirring manually 30 sec. every 30 min. at 200° C. for 1 h 30 is preferred.

According to a preferred embodiment, the method comprises a step of preparing at 80° C. a matrix consisting of 14% to 81% by volume of FEC amounts from 1% to 9% by volume of PEG. The matrix is mechanically mixed for 1 to 30 minutes depending on the amount prepared. Advantageously, the dielectric charge component is in the form of particles of SiC having an average diameter of 0.5 to 7 μm. Said dielectric charge component is added into the matrix at 200° C., in an amount of 10 to 85% in volume, to obtain the composition. Said composition is homogenized with a blade or magnetic stirred as an example and/or by manual mixing for a period of time of 5 minutes or more and preferably from 5 minutes to 150 minutes at 200° C.

According to a preferred embodiment, the composition consists of 10 to 40% in volume of SiC particles, 54 to 81% of solvent and 6 to 9% of dispersant.

According to a second embodiment, the composition consists of 41 to 55% in volume of SiC particles, 41 to 53% of solvent and 4.5 to 6% of dispersant.

According to a third embodiment, the composition consists of 56 to 85% in volume of SiC particles, 14 to 40% of solvent and 1.3 to 4.4% of dispersant.

EXAMPLES

Example 1: Simulation of Permittivity at 300 MHz Related to the Volume Solvent Amount in Polyethylene Glycol (PEG)

Polyethylene glycol (PEG) has been mixed with fluoroethylene carbonate (FEC) to demonstrate the permittivity evolution of this mixture compared to the permittivity evolution of the mixture containing polyethylene glycol and water (seeFIG.1).

As it is shown inFIG.1, the permittivity of the mixtures increases with the volumetric amount of solvent. Moreover, the mixture with FEC displays better permittivity than the mixture containing water thus allowing to add more dispersant at a given permittivity level.

Example 2: Simulation of Permittivity at 300 MHz Related to the Volumetric Amount of Filler

As it is shown inFIG.2, a mixture of EEC, PEG and SiC demonstrated better permittivity at 300 MHz, compared to the mixture of water, PEG and SiC.

This association of solvent having a melting point between 14° C. and 50° C., a dispersant and a dielectric charge aims in particular to prevent the sedimentation of particles, to easily control the viscosity of the matrix, to limit the risks of heterogeneity, and to limit the evaporation of the solvent, in order to obtain a pad as efficient as those based on barium titanate but more comfortable, with a longer lifespan and lower toxicity.

Example 3: Required Quantities to Prepare 100 g of the Composite Material

The table 3 below features the quantities in g of the solvent (fluoroethylene carbonate—FEC) and dispersant (Polyethylene glycol—PEG) to be mixed for producing 100 g of solvent with dispersant:

TABLE 3% in volumeWeights (g)FEC10 to 99.513 to 99.6PEG0.5 to 900.4 to 87

The table 4 below features the quantities in g of silicon carbide powder to be mixed with the solvent with dispersant for the production of 100 g of composite:

TABLE 4% in volumeWeights (g)Solvent with10 to 95.54.5 to 87.7dispersantSiC4.5 to 9012.3 to 95.5

The table 5 below features the quantities in g of silicon carbide powder, fluoroethylene carbonate and Polyethylene glycol to mix for the realization of 169 g of composite in the ideal case:

TABLE 5% in volumeWeights (g)Solvent with5051.4dispersant (90vol. % EEC + 10vol. % PEG)SiC50117.6

The use of this matrix FEC+PEG with respect to the water makes it possible to have a real permittivity of the matrix higher than that of the water (FIG.1andFIG.2). Indeed, the addition of a gelling agent decreases the dielectric properties of the solvent. Thus, a higher permittivity of the solvent used makes it possible to reach higher levels with equal concentrations of dielectric filler. In the solvent alone, for a quantity of PEG dispersant of 10% by volume, the gain in permittivity is of the order of 18% relative to water. When the dielectric charge is added, the gain in permittivity for 40% by volume of charge is of the order of 11%. Thus, using the FEC in place of the water makes it possible to reach identical levels with a smaller amount of dielectric charge. The lifespan of the pads is increased for two main reasons. On the first hand, the melting temperature of the solvent being close to 20° C., the pad is viscous at room temperature, which limits the sedimentation of the particles and ensures good performance in the long term. Indeed, the dielectric properties of such a pad after one month of storage below the melting temperature of the FEC are identical, unlike the BaTiO3-based pads in this case. One the other hand, the evaporation temperature of the solvent being twice that of water, it is much less likely to evaporates. The pad thus retains its initial viscosity as well as its homogeneity on the timescale of 1 year.

Example 4: Permittivity Obtained for Different Materials of the Invention

The table 6 below features the obtained permittivity of different materials according to the present invention.

TABLE 6SolventDispersantChargePermittivityPermittivity(vol. %)(vol. %)(vol. %)(120 MHz)(300 MHz)FEC (87%)PEG (12%)6563Distilled—7273Water(100%)—PEG (100%)2322(theoretical)(theoretical)ChargesFEC (36%)PEG (24%)Carbon black535340(40%)FEC (36%)PEG (24%)CaTiO37470(40%)FEC (36%)PEG (24%)Cu (40%)222205FEC (36%)PEG (24%)BaTiO3(40%)14520FEC (36%)PEG (24%)SiC (40%)150118WaterPEG (20%)SiC (40%)113120(40%)FEC (25%)PEG (35%)CaTiO35447(40%)

Since its permittivity is higher than water, an 87% volume content of FEC associated to a 12% volume content of PEG has permittivity level close to distilled water alone. Permittivity levels remain while the matrix is more resilient to particles sedimentation.

This tendency is confirmed when 40% volume content of SIC are mixed with 66 wt. % of solvent and 33 wt. % of dispersant which correspond in the case of FEC and PEG (resp. water and PEG) to 36 vol. % and 24 vol. % (resp. 40 vol. % and 20 vol. %).

A few permittivity levels of different materials mixed with the same volume of solvent (36% of FEC) and dispersant (24% of PEG) are presented to display the achievable permittivity range.

A case with more dispersant (35% of PEG instead of 24%) while keeping the mass ratio of FEC and PEG to 66% is also presented. An excess of dispersant leads to a large permittivity decrease since the dispersant permittivity is as low as 23. Consequently, a trade-off should advantageously to be made between the composite viscosity and performance.