Description:FIELD OF INVENTION:
[001] The present invention relates to the field of MRI imaging. The present invention, in particular, relates to a metasurface-inspired flexible wraps for enhancing the signal-to-noise ratio of clinical 1.5T MRI.
DESCRIPTION OF THE RELATED ART:
[002] In spite of the advances in the various state-of-the-art clinical imaging techniques, scanning human body parts using non-invasive methodology is still challenging. One of the major non-invasive diagnostic modalities is Magnetic resonance imaging (MRI) which uses quantum precessions of nuclei inside body tissues for their scanning. MRI scanners with applied static magnetic field (B0) of 1.5T is the most commonly used among the MRI systems with different magnitudes of B0 such as 0.5T, 1.5T, 3T, 7T, etc. Under the field strength of 1.5T, the tissue nuclei (protons i.e., 1H) align with the B0 which creates a net magnetization. In addition, the body protons are excited by transverse radiofrequency (RF) pulses which are generated by MRI transceiver coils at the Larmor frequency (f0). These protons start to process at this resonance frequency about the axis of B0 under RF excitation. The Larmor frequency is directly proportional to B0 as: f0 = (?/2p) B0 where '?' is the gyromagnetic ratio of tissue protons. When the RF excitation stops, each processing nuclei relaxes and emits an RF magnetic signal at the Larmor frequency of 1.5T MRI i.e., f0 = 63.8 MHz. These RF signals are detected as an induced voltage by MRI transceiver arrays which are further spatially encoded to construct images of body parts undergoing scan. The scanned image quality is defined by the key performance parameter of the MRI i.e., signal-to-noise ratio (SNR). Higher field-driven MRI scanners are developed to increase the SNR, which can be translated to better image resolution and/or lower image acquisition time. However, this high magnetization increases the Larmor frequencies of the processing nuclei which could lead to tissue heating (measured as specific absorption rate or SAR), low magnetic field penetration inside the body organs due to high attenuation, and potential safety concerns for patients carrying metallic implants. Therefore, there is a need to find alternative methods for boosting the SNR without increasing the magnetization inside the scanners.
[003] In recent decades, numerous standard hardware approaches have been executed for boosting the SNR of 1.5T MRI, such as parallel imaging and improved transceiver designs. However, these hardware optimization techniques lead to inhomogeneity in the magnetic field coverage and a longer scanning time. Thus, the advances for SNR improvement should be focused on implementing novel materials such as high dielectric constant materials, metallic resonators, and metamaterials inside the MRI receiver arrays. High permittivity pads can aid in the magnetic field distribution in the subject undergoing scan by focusing it in the region-of-interest (ROI). However, there could be a potential chemical leakage of the pad’s composites during an MRI scan. Volume coil resonators can provide uniformity in the magnetic field distribution throughout the subject but need to be redesigned according to the subject’s body shapes.
[004] Recently, metasurfaces which are artificially-made 2D structures with a sub-wavelength periodicity have demonstrated unusual electromagnetic properties in various frequency ranges such as microwave, terahertz, and optical. Although metasurfaces are primarily used for far-field applications, these structures can also enhance and redistribute electromagnetic fields in the near-field region. This opens new doors for metasurface applications in medical diagnostic techniques such as MRI.
[005] In the literature, metasurfaces have been discussed to boost SNR and transmit/receive efficiency improvement for 1.5T MRI. However, the translation of the reported metasurfaces in clinical 1.5T MRI applications is promising but still impractical as they are not flexible or conformal enough to cover different body parts such as head, legs etc. Further, the same body parts of different subjects will also have different anatomies, which need to be imaged efficiently. So, for better imaging of the subjects undergoing the scan, there is a need to wrap the metasurface around the body parts so that the RF transceiver coil can be placed as close as possible to the subject’s body. Implementing rigid metasurfaces on the subject effectively pushes the curved anatomies of the body parts away from the transceiver coils. Thus, there is a reduction in the received RF signal inside the 1.5T MRI scanner, which could degrade the SNR enhancement throughout the volume of interest despite using the reported metasurfaces. In addition, the complicated structures of these metasurfaces potentially require high-cost materials and manufacturing modalities.
[006] Reference may be made to the following:
[007] Publication No. CA2991583 relates to aspects of the subject disclosure may include, for example, a connector that includes a first port configured to receive electromagnetic waves guided by a first dielectric core of a first transmission medium. A waveguide is configured to guide the electromagnetic waves from the first port to the second port. The second port is configured to transmit the electromagnetic waves to a second dielectric core of a second transmission medium. Other embodiments are disclosed.
[008] Publication No. WO2009079718 relates to a polymeric plastics film; a plurality of magnetic regions in spaced relationship about the film, each being provided by a respective layer of magnetic film formed with opposed magnetic poles on opposite faces of the polymeric plastics film.
[009] Patent No. US3557354 relates to a selected interval of a recurring input signal that is repetitively sampled in amplitude at the same time-positions during successive signal averaging cycles. During the first signal-averaging cycle, the amplitude sample obtained at each of these time positions is processed as an average of one recurrence of the portion of the selected input interval occurring at that time position. It is stored in a memory channel associated with that time position. During each succeeding signal-averaging cycle, the difference in amplitude between each amplitude sample and the average stored in the associated memory channel during the preceding signal-averaging cycle is divided by a selected factor. The quotient is algebraically added as a correction factor to the average stored in the associated memory channel during the preceding signal-averaging cycle to update that average. This may be accomplished for each time position of each sweep by shifting a number indicative of the average stored during the preceding sweep in the associated memory channel x places in an accumulator, adding by signed counting a number indicative of the difference in amplitude between the amplitude sample obtained at that time position and the average stored during the preceding sweep in the associated memory channel to the shifted number in the accumulator, shifting the resultant number back x places in the accumulator to provide a corrected average for that time position, and storing the corrected average in the associated memory channel.
[010] Patent No. US10267957 relates to structures for scattering light at multiple wavelengths are disclosed. Scattering elements are fabricated with different geometric dimensions and arrangements to scatter or focus light at the same focal distance for each wavelength or at different focal distances according to the desired application. The scattering elements fabricated on a substrate can be peeled off with a polymer matrix and attached to a lens to modify the optical properties of the lens.
[011] Publication No. US2014210466 relates to a Magnetic Resonance Imaging (MRI) receiver that includes a receiver coil on a substrate. The receiver coil includes one or more capacitors. The construction of the capacitors allows for the use of very flexible substrates and allows the capacitors themselves to be highly flexible. The increased flexibility permits the MRI receiver to be conformed to the patient's body and improves the MRI process accordingly.
[012] Publication No. CN218811787 relates to a flexible magnetic separation device, which comprises a flexible substrate and a magnetic separation device, wherein the flexible substrate is of a soft body structure, and the strong magnet is fixedly connected to the flexible substrate. The device can be flexibly matched with containers of any shape or specifications by utilizing the flexibility of the shape of the flexible substrate. The strong magnets can synchronously change along with the change of the shape of the flexible substrate so that magnetic beads in liquid in the containers are effectively adsorbed, the functional flexibility and practicability of the structure are improved, and the device is suitable for popularization and application. And a plurality of strong magnets is used so that the strong magnets wrap the periphery of the container, the magnetic attraction distance is shortened, and the magnetic attraction separation effect is more efficient and quicker.
[013] Publication No. CN110164678 relates to communication electronic components, particularly a magnetic flexible wireless energy transmitting and receiving module and a preparation method. The magnetic flexible wireless energy transmitting and receiving module comprises a magnetic film and a flexible layer configured to wrap the periphery of the magnetic film. The magnetic film comprises a nickel-zinc magnetic layer, a polyimide layer, and a silver coil layer sequentially connected from bottom to top. The flexible layer is a polydimethylsiloxane layer. The polydimethylsiloxane layer wraps the nickel-zinc magnetic layer, the polyimide layer, and the silver coil layer to form a protective layer. According to the invention, the receiving module provided by the invention has a flexible characteristic and can wirelessly transmit energy after being bent. The flexible magnetic film is fused into the flexible wireless energy receiving module, enhancing the magnetic coupling between the transmitting and receiving coil. The wireless energy transmission efficiency is improved, and a magnetic field for wireless energy transmission is effectively prevented from interfering with a nearby conductive object or electronic equipment.
[014] Publication No. US2013200897 relates to a liner for a bore of a waveguide. The liner is an aperture passing through it and is formed of a metamaterial with a negative electrical permittivity and near zero. When the liner is installed in the waveguide, it lowers the cutoff frequency of the waveguide while allowing the waveguide to remain hollow. This liner can be used in the bore of an MRI machine to lower the cutoff frequency of the MRI machine to allow the MRI machine to operate using waves having a lower frequency than if the liner was not used. The invention is a flexible metamaterial structure that can be integrated as an “add-on” inside the reported next-generation MRI machine with a metamaterial liner.
[015] Publication No. CN102683880 relates to a metamaterial, which comprises a plurality of metamaterial units arranged in an array way. The metamaterial units consist of baseplates and artificial microstructures attached on the baseplates; the artificial microstructures are two split resonant ring structures; splits of the two split resonant ring structures are over 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. The reported metamaterial design is not flexible/conformal enough to cover different body parts such as head, legs, etc., undergoing clinical MRI scan.
[016] Publication No. CN103296446 relates to a metamaterial. The combined arrangement of an H-shaped structure and an opening resonance ring structure is utilized for obtaining a novel man-made micro-structure unit. The metamaterial, provided with an artificial micro-structure unit array, has the advantage of being higher in negative magnetic conductivity. In addition, based on the metamaterial provided with the high negative magnetic conductivity, the invention further provides a magnetic signal-strengthening device. Because the man-made micro-structure unit in the metamaterial is a magnetism micro-structure, when the frequency of the magnetism micro-structure under the condition of the negative magnetic conductivity is designed to be the same as an MRI working frequency, a magnetic signal received by a receiving coil can be strengthened, and an imaging effect is strengthened. In addition, convenience can be brought to the design of the receiving coil since the magnetic signal is strengthened, the receiving coil does not need to be tightly abutted against a portion to be tested, and therefore design cost and manufacturing costs are reduced. The reported metamaterial, magnetic signal strengthening device, are not flexible enough to cover different body parts such as head, legs, etc., undergoing scan.
[017] Publication No. CN103187632 relates to an artificial electromagnetic material with negative magnetic permeability, which comprises at least one material sheet, wherein each material sheet comprises a substrate and a plurality of artificial microstructures attached to the surface of the substrate and formed by conductive filaments, and 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. With the adoption of the artificial microstructure having the structure, an absolute value of the negative magnetic permeability of the artificial electromagnetic material can be increased obviously, so that a negative magnetic permeability effect is strengthened, and the requirement for a negative magnetic permeability value under specific conditions is met. The reported metamaterial, artificial electromagnetic material with negative magnetic permeability, could find in MRI scanning using metamaterial. However, these artificial electromagnetic materials are not flexible enough to cover different body parts such as head, legs, etc., undergoing scan.
[018] Publication No. US2013002253 relates to 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 reduced unit cell dimensions and hence resolution to be dramatically enhanced. In some examples, a cubic unit cell was used with an essentially isotropic magnetic permeability of µ=-1 obtained at an operating electromagnetic frequency and wavelength (?).
[019] The article entitled “Boosting magnetic resonance imaging signal-to-noise ratio using magnetic metamaterials” by Duan G, Zhao X, Anderson SW, Zhang X, Europepmc, 2019 talks about the development of a magnetic metamaterial enabling a marked boost in radio frequency field strength, ultimately yielding a dramatic increase in the SNR (~ 4.2X) of MRI. Applying the reported magnetic metamaterials in MRI has the potential for rapid clinical translation, offering marked enhancements in SNR, image resolution, and scan efficiency, thereby leading to an evolution of this diagnostic tool. In the aforementioned manuscript, helical magnetic metamaterials have been discussed to boost SNR and transmit/receive efficiency improvement for 1.5T MRI. However, the translation of the reported metasurfaces in clinical 1.5T MRI applications is promising but still impractical as they are not flexible or conformal enough to cover different body parts such as head, legs etc.
[020] The article entitled “Flexible and compact hybrid metasurfaces for enhanced ultra-high field in vivo magnetic resonance imaging” Rita Schmidt, Alexey Slobozhanyuk, Pavel Belov, and Andrew Webb, Scientific Reports, 2017 May 10 talks about a new hybrid metasurface structure comprising a two-dimensional metamaterial surface and a very high permittivity dielectric substrate that has been designed to enhance the local performance of an ultra-high field MRI scanner. This new flexible and compact resonant structure is the first metasurface that can be integrated with multi-element close-fitting receive coil arrays used for all clinical MRI scans. We demonstrate the utility of the metasurface acquiring in-vivo human brain images and proton MR spectra with enhanced local sensitivity on a commercial 7 Tesla system. However, designing a compact resonating wire-array metamaterial-based pad to provide uniform enhanced magnetic field distribution at 1.5T still remains challenging. This is mainly due to the comparatively longer free-space wavelength (??0 ~ 4.7m) at 1.5T MRI as compared to higher static field MRIs.
[021] The article entitled “Research of transparent ris technology toward 5G evolution & 6G” Daisuke Kitayama, Yuto Hama, Kensuke Miyachi, and Yoshihisa Kishiyama, NTT DOCOMO Technical Journal (Vol. 23, No. 2), Oct. 2021 talks about the intelligent radio environment (IRE), an important concept in “New Radio Network Topology” now under discussion on the road to 5G evolution & 6G. We also describe NTT DOCOMO’s initiatives toward the reconfigurable intelligent surface (RIS), an important component of IRE, and metamaterial/metasurface technologies as elemental technologies of RIS.
[022] In order to overcome above listed prior art, the present invention aims to provide a compact, flexible, and easy-to-fabricate metasurface to achieve non-invasive diagnostic of human body parts inside 1.5T MRI scanners. It is a flexible metasurface that can be implemented in an MRI scanner with limited free space (= 2 cm) and also wrapped around body parts (with different anatomies) and give significant ??1- enhancement inside 1.5T MRI scanners.
[023] It is a wearable add-on for achieving SNR enhancement of clinical 1.5T MRI transceiver arrays. The metasurface-based ‘add-on’ can be wrapped around different body parts (with different curvatures) going inside the clinical MRI scanners. This will enable enhancement in the received magnetic field in the region undergoing scan, enhancing the quality of MR images.
OBJECTS OF THE INVENTION:
[024] The principal object of the present invention is to provide a metasurface-inspired flexible structure that can be wrapped on patients’ body parts with different curvatures for boosting the signal-to-noise ratio (SNR) while undergoing commercial 1.5T MRI scans.
[025] Another object of the present invention is to provide a compact, flexible, and easy-to-fabricate metasurface to achieve non-invasive diagnostic of human body parts inside 1.5T MRI scanners.
[026] Yet another object of the present invention is to provide a wearable add-on for achieving SNR enhancement of clinical 1.5T MRI transceiver arrays.
SUMMARY OF THE INVENTION:
[027] The present invention relates to the metasurface-inspired flexible structure that can be wrapped on patients’ body parts with different curvatures for boosting the signal-to-noise ratio (SNR) while undergoing commercial 1.5T MRI scans. The metasurface is a wearable add-on inside 1.5T MRI transceiver arrays for significant SNR enhancement in scans of different body parts such as head, legs, etc. It is a flexible metasurface that comprises a polyimide substrate of thickness 0.18mm sandwiched between rectangular windings and square patches of copper of thickness 0.035 mm. The subwavelength-sized design is optimized for functioning inside the 1.5T MRI scanner, which has a resonance frequency (??0) of 63.8 MHz.
[028] A flexible rectangular windings-based magnetic metasurface has been developed that is capable of boosting SNR by a magnitude of 11 and compatible for use in the clinical 1.5T MRI machines. The flexible magnetic metasurface will act as an add-on to the existing MRI scanners. It can be wrapped around various body parts such as head, legs, etc., for a uniform and substantial boost of SNR, resulting in enhanced body imaging.
[029] In an embodiment, the dimensions of the metamaterial can be scaled up or down for applications of lower-field MRI (0.5T) and higher-field MRI (0.3T), respectively.
BRIEF DESCRIPTION OF THE INVENTION
[030] 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 its scope, for the invention may admit to other equally effective embodiments.
[031] Figure 1 shows the geometry of invented metasurface.
[032] Figure 2 shows (a) Simulation view of phantom wrapped by the metasurface inside a birdcage coil. (b) Frequency response of the reflection coefficient. (c) Comparison of received magnetic field distribution |B1-/vPabs| inside the phantom with and without the magnetic metasurface. (d) B1-(T) along the depth of the phantom with and without the metasurface. (e) SNR enhancement factor along the depth of the phantom.
DETAILED DESCRIPTION OF THE INVENTION:
[033] The present invention provides a metasurface-inspired flexible structure that can be wrapped on patients’ body parts with different curvatures to boost the signal-to-noise ratio (SNR) while undergoing commercial 1.5T MRI scans. The system provides a boost of ~11 times in ??1- as well, as the SNR enhancement factor is observed on the surface of metasurface-wrapped bio-model under excitation of the transceiver birdcage coil while maintaining specific absorption rate well under the safety limit. The metasurface is used as a wearable add-on inside 1.5T MRI transceiver arrays for significant SNR enhancement in scans of different body parts such as head, legs, etc.
[034] The metasurface-inspired flexible structure is wrapped on patients’ body parts with different curvatures for boosting the signal-to-noise ratio (SNR) while undergoing commercial 1.5T MRI scans. Fig.1. demonstrates the top and bottom views of the metasurface, an array of 8×8 unit cells, which constitutes polyimide substrate of thickness of 0.18mm sandwiched between rectangular windings and square patches of copper of thickness of 0.035 mm. The rectangular windings have strip thickness b = 0.5 mm with a gap of g = 0.5 mm between these strips. The inner radius of the windings is r = 6 mm with a square patch of length d = 5 mm attached to the center of the windings. The bottom side of the unit cell constitutes a square patch of length Du= 29 mm. The overall dimension of the unit cell is Lu× Lu=30 mm×30 mm.
[035] Figure 1 shows geometry of the invented metamaterial.
[036] Top and bottom view of the metasurface (with an array of unit cells) constituting polyimide substrate sandwiched between rectangular windings and square patches of copper. A zoomed-in view of the unit cells is also demonstrated for both the top and bottom views of the metasurface.
[037] The metasurface is wrapped around a phantom (of radius 100 mm) which mimics human-properties (er = 65, s = 0.4 S/m). The metasurface-wrapped phantom is kept under a 16-rung high pass quadrature birdcage coil with an inner diameter of 300 mm and a rung length of 180 mm (designed in CST Microwave Studio Suite®). Spiral resonators can act as resonant magnetic unit cells as they generate circulating currents (i.e., magnetic dipoles) when excited by an RF source. The designed metasurface resonates at the operating frequency of 1.5T MRI (f0 = 63.8 MHz and significantly boosts the received magnetic field inside the phantom with higher field penetration compared to the scanning setup without the metasurface, as shown in Fig. 2(b, c & d). The received magnetic field (B1- normalized to the accepted power i.e., vPabs) gets enhanced by a factor of ~11 (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.
[038] Moreover, in the presence of metamaterial, the enhanced received magnetic field shows high penetration, and the enhancement remains above unity till the depth of 90 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(B+1wM?t) B-1wM |/vPabs
SNR1 = |sin(B+1woM?t) B-1woM |/vPabs
[039] Here, the transmitted RF magnetic fields are depicted by B+1wM and B+1woM along with B-1wM and B-1woM 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. Numerical simulations demonstrate a ~11 times boost in the SNR on the surface of the phantom, which remains above unity till the depth of 100 mm inside the phantom, as shown in Fig. 2(e). Thus, the designed magnetic metasurface, used as a “flexible add-on,” should be able to boost imaging of human body parts with different curvatures from commercial 1.5T MRI scanners.
[040] 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 metasurface-inspired flexible wrap for enhancing the signal-to-noise ratio of clinical 1.5T MRI comprises an array of 8×8 of unit cells characterized in that polyimide substrate of thickness 0.11 mm to 0.24 mm sandwiched between rectangular windings and square patches of copper of thickness 0.035 mm to 0.07 mm wherein the rectangular windings have strip thickness (b) 0.5 mm with a gap (g) 0.5 mm between these strips with the inner radius (r) of the windings with a square patch of length 5 mm attached on the center of the windings, and the bottom side of the unit cell constitutes a square patch of length Du = 29 mm.
2. The metasurface-inspired flexible wraps, as claimed in claim 1, wherein the overall dimension of the unit cell is Lu× Lu = 30 mm×30 mm.
3. The metasurface-inspired flexible wraps, as claimed in claim 1, wherein the copper-coated polyimide substrate could be in the form of a flexible sheet that is applied as a ‘wrappable add-on’ to transceiver coils of commercial 1.5T MRI scanners for boosting SNR of scanned images of different body parts.
4. The metasurface-inspired flexible wraps, as claimed in claim 1, wherein the dielectric substrates such as Polyethylene Terephthalate (PET), Rogers RT5880, or Rogers RT5870 can also be used.
5. The metasurface-inspired flexible wraps, as claimed in claim 1, wherein the material for metallic layer is gold (Au) or silver (Ag).
6. A method for increasing the RF magnetic field localization of 1.5T MRI in the body part with different anatomies undergoing scan includes wrapping the metasurface around different body parts, going inside the clinical MRI scanners, with radii ranging from 100 mm to 150 mm for high magnetic field enhancement in the ROI and scanning the body part undergoing which is represented by a water-filled cylindrical PTFE box whose height could be of any value between 250 mm to 350 mm.
7. The method for increasing the RF magnetic field localization of 1.5T MRI, as claimed in claim 6, wherein the magnetic field enhancement is by a factor of 11 and the SNR enhancement is by a factor of 11.