Description:FIELD OF INVENTION:
[001] The present invention relates to the field of electromagnetic technology. The present invention, in particular, relates to a magnetic metamaterial ‘add-on’ for improving the signal-to-noise ratio of Magnetic Resonance Imaging at 1.5T.
DESCRIPTION OF THE RELATED ART:
[002] A metamaterial consisting of baseplates and split resonant ring structures for enhancing the magnetic signal has been provided. A combined arrangement of an H-shaped structure and an opening resonance ring structure micro-structure unit has been provided for strengthening the magnetic signal. An artificial microstructure, comprising an opening resonant ring formed by one filament and at least three electrode wires extending to the interior of the ring from different positions on the opening resonant ring for strengthening the electromagnetic imaging effect, has been invented. An isotropic magnetic metamaterial lens was designed to provide higher image resolution, using both inductor and capacitor-loaded ring resonators on the faces of periodic cubic unit cells. However, these reported metamaterials are bulky and involve expensive fabrication.
[003] Reference may be made to the following:
[004] Publication No. CN106877001 relates to the electromagnetic metamaterials and provides a metamaterial structure applied to a 3T magnetic resonance radio-frequency coil to improve the radiofrequency field intensity and the local signal-to-noise ratio of an image. The metamaterial structure comprises winding wires and an insulating layer that applies to the 3T magnetic resonance radiofrequency coil.
[005] The present invention is a magnetic metamaterial ‘add-on’ for improving the signal-to-noise ratio (SNR) of 1.5T MRI. Due to lower operating frequency, making a metamaterial compatible to 1.5T MRI system is much more challenging.
[006] The metamaterial comprises copper-based square-spiral elements on the top and bottom of commercial PCB substrate (FR4). RF magnetic field localization and enhancement occur due to the inductive coupling of the copper resonating spirals with RF transceiver coils.
[007] IN Publication No. 202227016887 relates to a passive MRI enhancing structure that includes an array of resonators and increases the signal-to-noise ratio of radiofrequency signals emitted by a specimen which are captured by an MRI machine. The apparatus increases the magnetic field component of radiofrequency energy during signal transmission from the MRI machine to the specimen and/ or reception of signals from the specimen to the MRI machine. The proposed structure improves the images generated by the MRI machine and/or reduces the time necessary for the MRI machine to capture the image.
[008] The invention is an “add-on” structure for radio frequency (RF) field localization without the requirement of any hardware or software modifications in the existing MRI scanners. A planar, compact, and easy-to-fabricate metamaterial.
[009] IN Publication No. 9130/DELNP/2008 relates to techniques, apparatus, and systems using one or more composite left and right-handed (CRLH) metamaterial structures to process and handle electromagnetic wave signals. Antenna, antenna arrays, and other RF devices can be formed based on CRLH metamaterial structures. The described CRLH metamaterial structures can be used in wireless communication RF front-end and antenna sub-systems. A design comprises copper-based square-spiral elements on the top and bottom of commercial PCB substrate (FR4).
[010] The magnetic metamaterial ‘add-on’ can localizes RF magnetic field localization and thus enhances SNR of 1.5T MRI.
[011] Publication No. US2012212395 relates to a metamaterial that includes at least one spiral conductor. Only a magnetic permeability is selected from among an effective dielectric constant. The magnetic permeability of the metamaterial becomes negative, so the metamaterial has a negative refractive index characteristic. The material includes unit cells arrayed in one-dimensional, two-dimensional, and three-dimensional directions. Each unit cell includes a dielectric substrate with first and second surfaces in parallel. The invented metamaterial is planar with sub-wavelength dimensions.
[012] The proposed invention has thickness = 2 cm which makes it a perfect candidate to be implemented in an MRI scanner with limited free space.
[013] Patent No. US7538946 relates to one exemplary metamaterial formed from an array of individual unit cells, at least a portion of which has a different permeability than others. These individual unit cells are arranged to provide a metamaterial having a gradient index along at least one axis. Such metamaterials can be used to form lenses, for example. The proposed invention can implemented in an MRI scanner with limited free space (= 2 cm) as compared to the lens structures where the subject undergoing scan is needed to be kept at the focal length of the lens.
[014] IN Publication No. 202141039005 relates to a digitally reconfigurable meta surface (DRM) for communication in a scatter-rich multipath channel. Specifically, the present disclosure relates to an MBM transmitter for communication in scatter-rich multipath channels. The MBM transmitter comprises a single radio frequency (RF) chain and a transmitting directional antenna.
[015] The present invention is for improving the signal-to-noise ratio (SNR) of 1.5T MRI, an application totally out of scope of the reported DRMs.
[016] IN Publication No. 8408/DELNP/2008 relates to an improved SERRS substrate for use in an improved analyte detector by depositing a Raman enhancing surface on, or within, a porous 3D support matrix made of solid support material. The support material is arranged to have a Raman dye distributed within the volume. The response to illumination of the dye is enhanced as a result of the dye being distributed within the volume and proximate to the Raman enhancing surface, which is also distributed within the volume.
[017] The present invention is for improving the signal-to-noise ratio (SNR) of 1.5T MRI, not relevant to SERS process for analyte detection.
[018] Publication No. EP2458396 relates methods to perform imaging using a metamaterial lens structure. A field source capable of generating an electromagnetic field directed to the area in an object or target. A field detector is arranged downstream from the field source. The field detector is capable of detecting a field signature associated with the area in the object or target. A metamaterial lens structure is arranged downstream from the field source. The metamaterial lens structure concentrates the electromagnetic field produced by the field source to the area in the object/target or concentrates the field signature from the area in the object/target to the field detector.
[019] The proposed invention can be implemented in an MRI scanner with limited free space (= 2 cm) as compared to the lens structures where the subject undergoing scan is needed to be kept at the focal length of the lens.
[020] Patent No. US7800368 discloses a magnetic resonance system. The system includes a transceiver having a multichannel receiver and a multichannel transmitter. Each channel of the transmitter is configured for the independent selection of frequency, phase, time, space, and magnitude, and each channel of the receiver is configured for the independent selection of space, time, frequency, phase, and gain.
[021] The proposed invention is a simple, cheap and easy to fabricate structure for boosting the performance of 1.5T MRI.
[022] The invention is a metamaterial structure can be integrated with the magnetic resonance transceiver coil as “add-on” for boosting its performance as compared to the reported state-of-the-art resonance coil.
[023] Publication No. CN105572612 provides a method of improving multichannel radio frequency coil performances, comprising the steps of: before magnetic resonance scanning, adding a magnetic meta-material into a multichannel radio frequency coil; under the condition of no radio frequency emission power, collecting the noise of each channel in the multichannel radio frequency coil; calculating the noise coupling matrix of the multichannel radio frequency coil after adding the magnetic meta-material; and in an image reconstruction process, employing the noise coupling matrix to compensate for the coupling of the multichannel radio frequency coil. The proposed invention is a simple, cheap and easy to fabricate structure for boosting the performance of 1.5T MRI.
[024] The invention is a metamaterial structure can be integrated with the magnetic resonance transceiver coil as “add-on” for boosting its performance as compared to the reported state-of-the-art resonance coil.
[025] Publication No. US2021215778 relates to a tuning system configured to tune a radiofrequency coil for use with a magnetic resonance imaging system comprising a tuning circuit including at least one tuning element configured to affect a frequency at which the radio frequency coil resonates, and a controller configured to set at least one value for the tuning element to cause the radio frequency coil to resonate at approximately a Larmor frequency of the magnetic resonance imaging system determined by the tuning system. Some aspects include a method of automatically tuning a radio frequency coil comprising determining information indicative of a Larmor frequency of the magnetic resonance imaging system, using a controller to automatically set at least one value of a tuning circuit to cause the radio frequency coil to resonate at approximately the Larmor frequency based on the determined information.
[026] The invention is a metamaterial structure can be integrated with the magnetic resonance transceiver coil as “add-on” for boosting its performance. It can be also integrated to the reported state-of-the-art tunable MRI RF coils.
[027] Publication No. US2013002253 relates to the metamaterial lenses that allow enhanced resolution imaging, for example, in MRI apparatus. An example metamaterial may be configured to have µ=-1 along three orthogonal axes. Superior performance was demonstrated using such improved designs, and in some examples, imaging resolution better than ?/500 was obtained. Using one or more lumped reactive elements in a unit cell, such as one or more lumped capacitors and/or one or more lumped inductors, allowed unit cell dimensions and hence resolution to be dramatically enhanced.
[028] The invention is an “add-on” which can be integrated in the limited free space (= 2 cm) in the MRI scanner as compared to the reported lenses for MRI where the subject undergoing scan is needed to be kept at the focal length (= 2 cm) of the lens.
[029] Publication No. CN102683880 provides a metamaterial, which comprises metamaterial units arranged in an array. The metamaterial units consist of baseplates and artificial microstructures attached on the baseplates. The artificial microstructures are two split resonant ring structures where splits of the two split resonant ring structures are against each other. Each split resonant ring structure comprises a single split resonant ring and two spiral lines spirally extending out respectively towards the interior of the ring from two tail endpoints of the single split resonant ring, wherein the two spiral lines do not intersect with each other, and further, both do not intersect with the single split resonant ring. As compared to the high negative magnetic permeability materials (lenses) which enhances the magnetic signal, the proposed invention is a design of magnetic metamaterial comprises copper-based square-spiral elements for boosting performance of 1.5T MRI.
[030] Publication No. CN103296446 provides a metamaterial. The combined arrangement of an H-shaped structure and an opening resonance ring structure is utilized for obtaining a novel manufactured micro-structure unit. The metamaterial provided with a manufactured micro-structure unit array has the advantage of being higher in negative magnetic conductivity. The major issue with the reported artificial micro-structures, for practical implementation in clinical scanners at 1.5T MRI, is their huge physical dimensions with respect to the available free space (around 2 cm) between MRI scanner coil and patient body. Therefore, integration of these bulky metamaterials is not recommended in 1.5T MRI scanners.
[031] This invention provides a solution to this problem by using a thin metamaterial as an ‘add-on’ in the 1.5T MRI receiver for SNR enhancement. The proposed structure has a thickness of less than 2 cm, making it a perfect candidate to be implemented in an MRI scanner with limited free space.
[032] Publication No. CN103187632 relates to an artificial electromagnetic material with negative magnetic permeability, which comprises at least one material sheet. Each material sheet comprises a substrate and an array of artificial microstructures attached to the surface of the substrate, which is formed by conductive filaments. Each artificial microstructure comprises an opening resonant ring formed by one filament and at least three electrode wires extending to the interior of the ring from different positions on the opening resonant ring. As compared to the high negative magnetic permeability materials (lenses) which enhances the magnetic signal, the proposed invention is a magnetic metamaterial for boosting performance of 1.5T MRI.
[033] Reference may be made to an article entitled “Development of high-efficiency metamaterial antenna structures for near-field and far-field applications” by Dave, Aditya; The University Of Minnesota; August 2022, which talks about compact, highly directional and low-loss antennas for reduced size, greater coverage, low power consumption. Partially reflective surfaces as superstrates are well known for enhancing antenna radiation. However, in the past, electrically large surfaces were used with little regard to the size and aperture efficiency of the antennas. In this dissertation, compact source antennas are used with smaller 2D metamaterial superstrates acting as partially reflective surfaces (PRS) to form metamaterial antenna (MMA) block.
[034] The invention is a metamaterial structure can be integrated with the magnetic resonance transceiver coil as “add-on” for boosting its performance of 1.5T MRI whereas the reported compact metamaterials can be used as low-loss antennas.
[035] Reference may be made to an article entitled “Development of magnetic metamaterial add-ons for improving the signal-to-noise ratio of Magnetic Resonance Imaging” by Jegyasu, Department of Electronics and Electrical Engineering, Indian Institute of Technology Guwahati, which talks about magnetic metamaterial add-ons for achieving enhancement in SNR for 1.5T MRI systems keeping the whole body SAR value of the design under safety limit i.e. 4.2 W/Kg.
[036] Reference may be made to an article entitled “A thin metallo-dielectric stacked metamaterial as “add-on” for magnetic field enhancement in clinical MRI” by Priyanka Das, Jegyasu Gupta, Debabrata Sikdar, Ratnajit Bhattacharjee; Journal of Applied Physics 132, 114901, 2022 which talks about increasing the SNR of MRI without increasing B0. An effective solution in this direction would be to boost the radiofrequency (RF) magnetic fields emitted by the body part undergoing scan, particularly by using metamaterials. The higher the received RF signal strength, the greater the signal-to-noise ratio of MRI. For a metamaterial to be used as an “add-on” in commercial scanners, its dimensions need to be designed appropriately so that it fits in the available gap between the transceiver coil and the human body. In this article, a 10-mm-thick metallo-dielectric metamaterial is designed by stacking alternate square-shaped capacitive patches and inductive apertures to enhance the RF magnetic flux density and hence, the SNR of a 1.5?T MRI system. The inter-layer electromagnetic coupling in the stacked structure is deployed for spatial localization of magnetic fields at the resonant frequency (~64?MHz), which is equal to the Larmor frequency of 1.5?T MRI. An equivalent circuit model, comprising a lumped-element third-order bandpass filter, validated the transmissivity characteristics of the metamaterial obtained using full-wave simulations. Magnetic flux density enhancement by a factor of 55 is obtained when the metamaterial add-on is placed between a surface coil and a bio-model of human head.
[037] The metamaterial comprises copper-based square-spiral elements on the top and bottom of commercial PCB substrate (FR4). RF magnetic field localization and enhancement occur due to the inductive coupling of the copper resonating spirals with RF transceiver coils. Water has been used as a dielectric sandwiched between the two copper patterned FR4 substrates to miniaturize the resonating metallic structures as compared to the BaTiO3 composite ceramics used in the reported design. The major challenge with the permittivity of the composite ceramics is to maintain its high permittivity with time. Printing of copper patterns is also costly and less feasible. This invention uses standard PCB fabrication which is very easy and cheap.
[038] Magnetic resonance imaging (MRI) is one of the popular medical diagnostic methods utilized primarily in modern healthcare. The conventional approach to enhance the performance of MRI is by stepping up the applied static magnetic field. This increases the fundamental performance parameter i.e. signal-to-noise ratio (SNR) of MRI. SNR enhancement leads to increased image resolution or decreased scan time for patients. However, the major problem of this conventional approach is tissue heating of the human body due to the absorption of high-energy electromagnetic waves. Also, implants and medical devices become unsafe at high-field MRI systems. This may pose serious safety concerns for patients undergoing the scanning process. Moreover, the application of high field comes at the expense of high expenditure on devices and settings, thus making the overall scanning process more expensive for patients. So, there is a need to find out means for making low-field MRI systems i.e., 1.5T more efficient. Improvement of radiofrequency (RF) coil technology led to the development of highly advanced multi-channel RF coils used in MRI for SNR enhancement, which leads to inhomogeneous field coverage and longer scanning time. In addition, FDA-approved gadolinium-based contrast agents have been developed and are routinely employed to improve image quality and disease conspicuity. However, these agents need to be injected inside the patient’s body to boost field emission from the tissues undergoing scan, which might have other medical side-effects.
[039] In order to overcome above listed prior art, the present invention aims to provide a magnetic metamaterial ‘add-on’ for improving the signal-to-noise ratio of magnetic resonance imaging at 1.5T. The present invention consists of a relatively compact metamaterial structure which is cheaper since it is made of readily available materials. Since fabrication is inexpensive, any commercial organization can produce the metamaterial in bulk.
OBJECTS OF THE INVENTION:
[040] The principal object of the present invention is to provide a magnetic metamaterial ‘add-on’ for improving the signal-to-noise ratio of Magnetic Resonance Imaging at 1.5T.
[041] Another object of the present invention is to provide an add-on structure for radio frequency (RF) field localization without the requirement of any hardware or software modifications in the existing MRI scanners.
[042] Yet another object of the present invention that will make MRI imaging more efficient, affordable, reliable, and accessible.
[043] Still another object of the present invention is to provide the metamaterial that helps in the improvement of clinical diagnostic scanning.
SUMMARY OF THE INVENTION:
[044] The present invention relates to the metamaterial that can be used as an accessory in all commercially available 1.5T MRI machines. The metamaterial can be integrated as an ‘add-on’ to the transceiver RF coils of 1.5T MRI for magnetic field and SNR enhancement. The proposed metamaterial can provide spatial redistribution of electromagnetic fields locally in the targets undergoing scan to minimize SAR while boosting SNR. SNR enhancement results in the improvement of image resolution and scanning efficiency. Reduction of scan time makes MRI more accessible as it reduces the wait time for the patients.
[045] The system boosts the SNR of the 1.5T MRI system by developing thin and compact magnetic metamaterial for radio frequency (RF) field localization without the requirement of any modifications in the existing MRI scanners. The proposed design is 1.76 cm thick so that it fits between the patient and receiver coil without any loss in the scanner’s sensitivity. The specific absorption rate (SAR) is under the safety limit i.e., 4.2 W/Kg for the scan using the proposed structure. This add-on structure will make the imaging more efficient, affordable, reliable, and accessible. The increment in efficiency and decrement of scanning cost will result in wider availability of MRI diagnosis, specifically for the people of lower per-capita income countries like India. The proposed metamaterial could help improve clinical diagnostic scanning of patients as it resolves the problems of other technologies involved in improving MRI.
BREIF DESCRIPTION OF THE INVENTION
[046] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments.
[047] Fig. 1 shows the geometry of the invented metamaterial (a) Top/Bottom view; (b) Side view.
[048] Fig. 2 shows (a) Integration of metamaterial with the phantom; (b) Magnetic flux density (B1-) inside the phantom; (c) Variation of magnetic flux density (B1-) with depth inside the phantom; (d) Variation of SNR enhancement factor with depth inside the phantom.
DETAILED DESCRIPTION OF THE INVENTION:
[049] This is a planar, compact, and easy-to-fabricate metamaterial, comprising subwavelength resonating metallic spirals at the Larmor frequency of 1.5T, i.e., 63.8 MHz. The proposed metamaterial comprises copper-based square-spiral elements on the top and bottom of commercial PCB substrate (FR4). RF magnetic field localization and enhancement occur due to the inductive coupling of the copper resonating spirals with RF transceiver coils. Water has been used as a dielectric sandwiched between the two copper patterned FR4 substrates to miniaturize the resonating metallic structures. The invented metamaterial, having sub-wavelength dimensions of 320 mm × 320 mm × 17.7 mm, is compact, cheap, and economical. Using commercially available materials like FR4, copper, and water for the invented design assists in its large-scale production for commercial use. Further, the dimensions of the metamaterial can be scaled up or down for applications of lower-field MRI (0.5T) and higher-field MRI (3T), respectively. The metamaterial provides SNR enhancement up to a factor of 4 for 1.5T MRI with surface and birdcage-type transceiver coil excitation.
[050] The proposed metamaterial constitutes four copper (Cu) spirals on the top of a square FR4 substrate of length a = 320 mm. Fig. 1(a) depicts a top/bottom view of the proposed metamaterial. The geometrical parameters of the spirals are: c = 34 mm, e = 5.4 mm, and f = 3 mm. These spirals have a gap of b = 4 mm and d = 4 mm in the x and z directions, respectively. These spirals are placed on the top and bottom of a water-filled plastic box, as shown in Fig. 2(b). The box has the following vertical dimensions, p = 0.5 mm and m = 15 mm along the y-axis. The metamaterial is excited by a quadrature-fed RF transceiver coil, as shown in Fig. 2(a). The proposed metamaterial resonates at the Larmor frequency of 1.5T MRI (i.e. f0= 63.8 MHz) due to the inductive coupling of resonating spirals with the RF coil. Circulating currents (i.e., magnetic dipoles) are induced on the resonating spirals of metamaterial by the magnetic flux of RF loop coil, which significantly boosts the magnetic field inside the phantom, as shown in Fig. 2(b). Full-wave electromagnetic simulations, using CST Microwave Studio Suite®, are performed using a human-properties mimicking phantom with and without metamaterial for analyzing magnetic field and SNR enhancement in the region-of-interest (ROI). Fig. 2(b) depicts high magnetic field enhancement in the ROI (white dotted rectangle) with metamaterial as compared to those without the metamaterial respectively. The received magnetic field (B1- normalized to the accepted power i.e.vPabs) gets enhanced by a factor of ~5 (as compared with the case without the metamaterial) on the surface of the phantom, which could be translated into a high signal-to-noise ratio (SNR) for 1.5T MRI. Moreover, in the presence of metamaterial, the enhanced received magnetic field shows high penetration, and the enhancement remains above unity till the depth of 100 mm inside the phantom, as shown in Fig. 2(c). The SNR enhancement factor inside the phantom is calculated by taking a ratio of magnetic fields with and without the metamaterial inside the phantom. The SNR enhancement factor is calculated as:
SNR enhancement factor = SNR2/SNR1
where, SNR2 = |sin(B1+wM?t) B1-wM|/vPabs
SNR1 = |sin(B1+woM?t) B1-woM|/vPabs
[051] Here, the transmitted RF magnetic fields are depicted by B1+wM and B1+woM along with B1-wM and B1-woM as received RF magnetic flux density with and without metamaterial, respectively. The gyromagnetic ratio (?) for the hydrogen atom is 42.577 MHz/T, and t is the pulse duration. The enhancement factor in SNR is found to be enhanced by a factor of ~4 on the surface of the bio-model (as shown in Fig.2(d). Therefore, this approach provides a cost-effective and compact metamaterial that can provide more than four times SNR enhancement in any commercial 1.5T MRI machine and ensures the usefulness of the proposed metamaterial in high-resolution organ-specific 1.5T MRI scans.
[052] Numerous modifications and adaptations of the system of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the true spirit and scope of this invention.
, Claims:WE CLAIM:
1. A magnetic metamaterial add-on for improving the signal-to-noise ratio of magnetic resonance imaging comprising four metallic (made of copper) spirals on the top of a square FR4 substrate of length 320 mm characterized in that geometrical parameters of the spirals c is 34 mm, e is 5.4 mm, and f is 3mm, wherein the spirals have a gap b is 4 mm and d is 4 mm in the x and z directions, respectively.
2. The magnetic metamaterial add-on for improving the signal-to-noise ratio of magnetic resonance imaging, as claimed in claim 1, wherein the said spirals are placed on the top and bottom of a water-filled plastic box, having p = 0.5 mm and m =15 mm along the y-axis.
3. The magnetic metamaterial add-on for improving the signal-to-noise ratio of magnetic resonance imaging, as claimed in claim 1, wherein the metamaterial is excited by a quadrature-fed RF transceiver coil, resonates at the Larmor frequency of 1.5T MRI; 63.8 MHz due to the inductive coupling of resonating spirals with the RF coil and circulating currents which are magnetic dipoles are induced on the resonating spirals of metamaterial by the magnetic flux of RF loop coil, which boosts the magnetic field inside the phantom.
4. The magnetic metamaterial add-on for improving the signal-to-noise ratio of magnetic resonance imaging, as claimed in claim 1, wherein the thickness of the water inside the plastic box ranges from 14 mm to 16 mm and the FR4 substrate thickness is in the range from 0.7 mm to 0.9 nm.
5. The magnetic metamaterial add-on for improving the signal-to-noise ratio of magnetic resonance imaging, as claimed in claim 1, wherein the thickness of the plastic sheets for making the water-filled box could range from 0.4 mm to 0.7 mm and Cu metallic layer is of thickness between 0.035 mm and 0.07 mm.
6. The magnetic metamaterial add-on for improving the signal-to-noise ratio of magnetic resonance imaging, as claimed in claim 1, wherein the metallic layer could be of copper, gold, or silver.
7. The magnetic metamaterial add-on for improving the signal-to-noise ratio of magnetic resonance imaging, as claimed in claim 1, wherein the dielectric used to fill the plastic box is water or the suspensions of Barium Titanate, Calcium Titanate, Strontium Titanate, etc.