WO2025101641A1 - Device and method for optimizing magnetic resonance imaging - Google Patents

Abstract

A device and method to optimize images of a region of interest in a body acquired by an MRI system. The device includes a flexible substrate configured to be coupled to the body, the flexible substrate having a dielectric mixture of dielectric particles and a polymer, and a radio-frequency coil embedded within the dielectric mixture. The method includes (a) preparing a dielectric mixture, (b) pouring the mixture into a mold, (c) curing the mixture, (d) positioning the coil on the cured mixture, followed by pouring more of the dielectric mixture to cover the coil and (e) repeating steps (b) – (c) to cover the coil.

Description

DEVICE AND METHOD FOR OPTIMIZING MAGNETIC RESONANCE IMAGING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a non-provisional of and claims the benefit of U.S. Provisional Patent Application No. 63/596,941, filed on November 7, 2023, the contents of which are incorporated herein by reference.

BACKGROUND

[0002] Magnetic resonance imaging (MRI) is one of the most powerful non-invasive tools to see anatomical structures and diagnostic medical conditions. An MRI system resembles a general wireless communication system. Modern MRI scanners use high static magnetic fields and multi-channel radiofrequency (RF) coils to obtain better anatomical images. These RF coils, comparable to MRI antennas, are utilized to induce and acquire MR signals within the body.

[0003] The efficiency of RF coils determines the overall performance of an MRI scanner, MRI RF coils may be in the form of volume coils or surface coils. These two forms of RF coils serve two different purposes and are employed based on specific imaging requirements. Volume coils may be used for achieving images with a uniform radiofrequency field distribution throughout the entire sample of a body. Surface coils may be used for attaining enhanced signal- to-noise ratio (SNR) in localized regions of a body.

[0004] Surface array coils have been utilized to provide a larger field of view (FOV) compared to common surface coils. These surface array coils provide higher SNR across larger regions of interest (ROI), providing improved imaging capabilities. The surface array coils are commonly constructed on a conformal housing, which results in an improved filling factor when compared to common volume coils. As a result, surface array coils yield an increase in SNR, even within a central region of the body. Surface array coils are utilized in parallel transmission (pTx) techniques where each coil is independently powered and controlled to generate separate local magnetic (Bi) transmit fields with a phased receive (Rx) array coil. Surface array coils improve the homogeneity of the transmittance field, which increases the strength to receive MR signals. [0005] Current RF surface array coils comprise partially overlapping adjacent coils, implementing an uneven distribution of electrical impedances along the length of the loop, incorporating passive resonators, and utilizing interconnecting reactive impedance networks. These techniques provide increased decoupling performance, but impose limitations on the coil shape, result in irregular local magnetic fields, and introduce complexities in design due to the inclusion of additional circuitry or components. Conventional overlapping surface array coils include degrees of overlapping ranges from 10% to 30%, which varies depending on the size and shape of the surface array coil. This lack of precision in determining the optimal overlapping ratio poses challenges, especially when aiming to optimize coil performance.

[0006] Common dielectric materials in the forms of pads may be used for enhancing the signal intensity and uniformity in MR images. These dielectric pads induce a secondary magnetic field within the sample (e.g., a body), leading to improved signal intensity while reducing the specific absorption rate (SAR). These common dielectric materials are provided in the form of rigid solid blocks or slurries, which limit their flexibility and compatibility with loading RF coils and creating a body conformal coil array.

SUMMARY

[0007] The present disclosure provides a technique for fabricating a dielectric mixture medium having stretchability and flexibility. This dielectric mixture medium provides for the RF surface array coils to conform to contours and shapes of the human body.

[0008] In one embodiment, the disclosure provides a dielectric device to optimize images of a body by providing improved coil contact and signal acquisition during MRI scans. In one embodiment, the dielectric device comprises silicon carbide (SiC), titanium dioxide (TiCh), calcium titanite (CaTiCh) or barium titanate (BaTiCh), silicon polymer forming a mixture around a dielectric surface array coil.

[0009] In one embodiment, the disclosure provides a device to optimize images of a region of interest in a body acquired by an MRI system. The device comprises a flexible substrate configured to be coupled to the body, the flexible substrate comprising a dielectric mixture of dielectric particles and a polymer, and a radio-frequency coil embedded within the dielectric mixture.

[0010] In one aspect, the coil has a resonance frequency between 64 MHz (1.5 T) and 447 MHz (10.5 T).

[0011] In one embodiment, the disclosure provides a method of preparing a dielectric loaded coil comprising the steps of: (a) preparing a dielectric mixture; (b) pouring the mixture into a mold; (c) curing the mixture; (d) positioning the coil on the cured mixture, followed by pouring more of the dielectric mixture to cover the coil; and (e) repeating steps (b) - (c) to cover the coil.

[0012] In one such embodiment, the mold has the same dimensions as the coil. In one embodiment, curing the mixture comprises a vacuum. In one such embodiment, curing the mixture further comprises applying heat. In one embodiment, the dielectric material comprises dielectric powder and a biocompatible silicone elastomer. In one such embodiment, the dielectric material comprises 58 weight percent SiC relative to the weight of the mixture.

[0013] Other aspects of the present disclosure will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 illustrates an exemplary fabrication process of dielectric loaded coils.

[0015] FIG. 2 illustrates a) fabricated dielectric loaded coils (left) and conventional coils

(right) and b) stretchability and flexibility of a dielectric loaded coil.

[0016] FIG. 3 illustrates exemplary S-parameter measurements on the bench of (a) S21 measurements and comparison for three configurations shown, (b) resonance parameters for tangentially placed dielectric loaded coils, (c) resonance parameters for tangentially placed conventional coils, and (d) resonance parameters for 20% overlapped conventional coils.

[0017] FIG. 4 illustrates exemplary full wave electromagnetic simulation results of (a) simulated coil configurations (tangentially placed dielectric loaded coils (left), tangentially placed conventional coils (middle), and 20% overlapped conventional coils (right)), (b) S21 measurements and comparison for all 3 configurations, (c) resonance parameters for tangentially placed dielectric loaded coils, (d) tangentially placed conventional coils, (e) 20% overlapped conventional coils, (f) H-field distribution when only one of the coil was active for tangentially placed dielectric loaded coils, (g) H-field distribution when only one of the coils was active for tangentially placed conventional coils, and (h) H-field distribution when only one of the coils was active for 20% overlapped conventional coils.

[0018] FIG. 5 illustrates an exemplary evaluation of a dielectric loading decoupling technique in phantom imaging of (a) S21 measurements and comparison inside the scanner for three configurations, (b) MR images by using dielectric loaded coils placed tangentially near each other when the right coil is excited (left) and when the left coil is excited (right), (c) MR images by using conventional coils placed tangentially near each other when the right coil is excited (left) and when the left coil is excited (right), (d) MR images by using conventional coils 20% overlapped when the right coil is excited (left) and when the left coil is excited (right), (e) MR image by using conventional coils 20% overlapped when both coils are excited, and (f) MR image by using dielectric loaded coils placed tangentially near each other when both coils are excited.

DETAILED DESCRIPTION

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Example methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0020] The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments, “comprising,” “consisting of,” and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not.

[0021] The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about to about 4” also discloses the range “from 2 to 4.” The term “about” may refer to plus or minus 10% of the indicated number. For example, “about 10%” may indicate a rage of 9% to 11%, and “about 1” may mean from 0.9-1.1. Other meanings of “about” may be apparent from the context, such as rounding off, s, for example “about 1” may also mean from 0.5 to 1.4.

[0022] Definitions of specific functional groups and chemical terms are described in more detail below. For purposes of this disclosure, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75^th Ed., inside cover, and specific functional groups are generally defined as described therein.

[0023] For each recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the numbers 6.0, 6.1, 6.2, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

[0024] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0025] The present disclosure provides a solution for addressing challenges of decoupling and increasing the performance of the RF in multichannel RF coil arrays in MRI. The present disclosure further provides the strategic integration of a dielectric powder based elastic polymer substrate between adj cent coil elements within the array. The polymer substrate efficiently disrupts electromagnetic coupling between neighboring coils which enables independent operation of each coil element and also increases local RF magnetic field strength and reduces Specific Absorption Ratio (SAR) for improved RF safety and image quality.

[0026] In various embodiments, the multichannel RF coil arrays, as described herein, address challenges in multichannel RF coil arrays used in MRI. The multichannel RF coil arrays, as described herein, comprise a dielectric powder-based polymer substrate which provides a transformative and improved decoupling and RF performance. The dielectric powder-based polymer substrate is positioned between RF coil array elements. The dielectric powder-based polymer substrate provides a decoupling mechanism, improved RF magnetic field, and SAR reduction.

[0027] In various embodiments, the dielectric powder-based polymer substrate effectively disrupts electromagnetic coupling between adjacent coil elements. This disruption of electromagnetic coupling is provided by the properties of the dielectric powder-based substrate to alter the propagation of electromagnetic waves and induce a decoupling effect. As a result, mutual interference is minimized, enabling the simultaneous and independent operation of each individual coil element without requiring complex geometries or additional decoupling components.

[0028] In various embodiments, the dielectric-loaded coil substrate exhibits an increased local RF magnetic field. The properties of the dielectric-loaded coil substrate are configured to focus and increase the RF magnetic field in the vicinity of the coil elements. These increased properties of the dielectric-loaded coil substrate provide an increased signal.

[0029] In various embodiments, the multichannel RF coil arrays may include dielectric powders including, but not limited to, titanium dioxide, silicone carbide, barium titanite, and calcium titanite. The multichannel RF coil array may include a method of making dielectric powder-based elastic polymer. The multichannel RF coil array product may be flexible, stretchable, and may include MR invisible substrate to load coil elements. The multichannel RF coil array may also include non-overlapped or slightly overlapped RF coil arrays, where slightly overlapped RF coil arrays means equal to or less than 5% overlap of the RF coil arrays. The multichannel RF coil array may have a decoupling mechanism in which the dielectric powderbased polymer substrate effectively disrupts electromagnetic coupling between adjacent coil elements. The multichannel RF coil arrays may have increased RF magnetic field, where the dielectric loaded coil exhibits a capability to amplify the RF magnetic field. The multichannel RF coil arrays may have a reduced SAR, where the reduction of the SAR results by increasing the local RF magnetic field strength and uniformly distributing it within the region of interest (ROI).

[0030] Decoupling techniques include loop coils within a dielectric mixture. The performance evaluation of these techniques was conducted at 7 T (i.e., 300 MHz) and 9.4 T (i.e., 400 MHz) through benchtop experiments and analyses. The decoupling between the coils was measured for two different coil locations in each coil set. The results of the benchtop experiments provided that tangentially placed dielectric-loaded coils exhibited a 30% improvement in decoupling compared to tangentially placed conventional coils. Overlapped dielectric-loaded coils demonstrated a significant improvement of 47.6% in decoupling compared to overlapped conventional coils.

[0031] In some embodiments, the dielectric-loaded decoupling technique as described above and herein may be used for attaining enhanced SNR relative to a conventional coil in localized regions of a body (e.g., a near-surface region, a center region, and/or an area encompassing both a near-surface region and a center region). In some embodiments, the enhanced SNR may be at least 0.5% relative to a conventional coil. In some embodiments, the enhanced SNR may be at least 0.8% relative to a conventional coil. In some embodiments, the enhanced SNR may be at least 5% relative to a conventional coil. In some embodiments, the enhanced SNR may be at least 8% relative to a conventional coil. In some embodiments, the enhanced SNR may be at least 10% relative to a conventional coil. In some embodiments, the enhanced SNR may be at least 25% relative to a conventional coil. In some embodiments, the enhanced SNR may be at least 27% relative to a conventional coil. EXAMPLE

[0032] The present disclosure provides for fabricating flexible dielectric loaded coils, as well as an overview of the electromagnetic (EM) simulation utilized. The MR imaging parameters employed enabled the acquisition of images using different coil configurations.

[0033] Four identical loop coils in an oval shape were constructed using the center conductor of a non-magnetic coaxial cable. Each coil of the fabricated loop coils had a length of 50 mm and width of 35 mm. To achieve a resonance frequency close to 400 MHz, three capacitors were employed as distributive capacitors in each coil. These capacitors included two fixed capacitors with a value of 4.7 pF each, additionally including a trimmer capacitor that could be adjusted within a range of 2-6 pF. The coils were tuned and matched to 400 MHz using an L-Matching network. A dielectric mixture was prepared by manually dispersing silicon carbide (SiC) powder (AZTRON, EISA) with a biocompatible silicone elastomer (Ecoflex™, Smooth-On®, USA). The maximum weight to weight concentration to be achieved was 58%, indicating the weight of SiC relative to the weight of the mixture. The mixture was then poured onto two 3D printed molds with the same dimensions as the length and width of the coil with a depth of 5 mm, ensuring that it filled approximately half of the volume of the mold. Subsequently, the molds were transferred to a vacuum chamber for a duration of 5 minutes to ensure the removal of any possible air bubbles. Following the vacuum treatment, the molds were kept at room temperature (23°C) for a period of 10 minutes. To expedite the curing process, the molds were then subjected to heat using an oven for 2 minutes. Once the initial curing process is completed, two of the coils were positioned on the cured dielectric pads. Subsequently, the uncured mixture was poured into the mold to fill the remaining half of the volume of the mold and the same curing process, as described earlier, was repeated for the second half of the mold, as illustrated in FIG. 1 (a schematic representation of the process is shown in FIG. 1). The dielectric-loaded coils underwent re-tuning and re-matching using a vector network analyzer (FieldFox® N9923A, Keysight Technologies®, USA) to achieve a resonant frequency of 400 MHz. FIG. 2 (at a) depicts a visual comparison between the final dielectric-loaded coils and the conventional loop coils. By incorporating the disclosed dielectric mixture into the coils originally fabricated from the center conductor of a non-magnetic coaxial cable, the resulting product exhibited stretchability and flexibility, as illustrated in FIG. 2 (at b). [0034] A cylindrical phantom with a diameter of 50 mm was employed as the sample for conducting the decoupling test on the bench. To simulate the electrical properties of average brain tissue at 9.4 T, the phantom was filled with a solution characterized by a bulk conductivity of G = 0.59 S/m and a relative permittivity of e_r = 49.75. These specific electrical parameters were chosen to approximate the electromagnetic behavior of brain tissue at the given field strength.

[0035] To assess the performance of the dielectric loaded coils in decoupling, three separate measurements were carried out. In the first two experiments, each pair of the coils were positioned tangentially in close proximity to each other. After frequency tuning at 400 MHz and matching the coils to 50 , the scattering (S)-parameters were measured using a two-port vector network analyzer. This allowed for an evaluation of the decoupling achieved with the dielectric loaded coils in this configuration. In the third experiment, a conventional decoupling method was used, where the conventional coils were overlapped by 20%. This was performed to enhance the decoupling between the conventional coils and provide a basis for comparison with the performance of the dielectric loaded coils. Similarly, the S-parameters were measured using the two-port vector network analyzer and compared to the previous setups.

[0036] A full-wave electromagnetic (EM) simulation was conducted using HFSS Electronics Desktop (ANSYS, Inc.®, Canonsburg, PA, USA) to evaluate the decoupling performance of the dielectric loaded coils. The simulation replicated the three coil configurations employed in the bench test setup: tangentially placed dielectric loaded coils, tangentially placed conventional coils, and 20% overlapped conventional coils.

[0037] To accurately represent the experimental conditions, a cylindrical phantom with a diameter of 50 mm was modeled using electrical properties approximating brain tissue at 400 MHz. Copper loop coils with an end capacitor were designed with a diameter of 35 mm and placed around the phantom according to the desired configuration. For the dielectric loaded coils, the conventional coils were positioned inside a modeled dielectric pad with a relative permittivity of 7, ensuring similar conditions between the EM simulation and the imaging and bench tests. [0038] In each of the three configurations, the coils were tuned and matched to resonate at 400 MHz using an L-Matching network. After the tuning and matching process, only one of the ports were excited in order to emphasize and visualize the coupling between the coils more effectively.

[0039] A cryogen-free, 17 cm horizontal -bore dry magnet MRI scanner located at the Magnetic Resonance Research Center - Arizona State University® (MRRC-ASU®) was utilized to conduct high-field (9.4 T) MR imaging experiments. This advanced scanner enables small animal imaging at various field strengths, including 3 T, 7 T, or 9.4 T, and is equipped with gradient strengths of up to 2000 mT/m. The scanner console incorporates a built-in hybrid coupler that provides two outputs phased 90° apart. During the MR imaging experiments, a Fast- Low-Angle-Shot (FLASH) Sequence was employed. The imaging parameters included a repetition time (TR) of 100 ms, an echo time (TE) of 4 ms, and a flip angle (a) of 25°. The field- of-view (FOV) was set to 60 x 60 mm with a matrix size of 256 x 256, resulting in an in-plane resolution of 234 x 234 pm. Additionally, eight slices were acquired along the sample, with a slice thickness of 1 mm and a slice gap of 0.2 mm. Three sets of imaging experiments were conducted to assess the coupling between the coils: tangentially placed dielectric loaded coils, tangentially placed conventional coils and 20% overlapped conventional coils. In each set, the experimental parameters were kept constant to ensure a fair comparison of the results. To effectively visualize the level of coupling between the coils, both coils were included in the setup; however, during experiments, only one coil was actively excited while the other coil was terminated with a 50 load. Additionally, the scanner port that is supposed to be connected to the terminated coil was properly terminated in 50 Q using a high-power attenuator. S-parameters were also measured and recorded after inserting the setup into the magnetic bore of the scanner. In addition, an evaluation of signal intensity, signal uniformity, and SNR was performed on the images obtained when both coils were excited using three distinct ROIs: near the surface of the phantom, the center of the phantom, and a larger ROI encompassing both ROIs. Image uniformity was calculated using a percent image uniformity (PIU) equation defined in (1):

PIU = 100

where Smax is the average signal intensity in a small ROI chosen from the area of maximum signal intensity and Smin is the average signal intensity in a small ROI chosen from the area of minimum signal intensity.

[0040] Images were obtained from various MR studies consistently demonstrated results that aligned with the findings obtained from EM simulations and bench tests. These results serve to validate the feasibility of this novel decoupling approach, which involved loading the RF loop coils with dielectric material. The congruence between the imaging data, the simulation, and bench test results provides strong evidence for the effectiveness of the method.

[0041] FIG. 3 shows S-parameter measurements which were performed on the bench test setup to compare the decoupling performance of different coil configurations, as described above. FIG. 3 (at a) shows S21 measurements and comparison for the three configurations. FIG.

3 (at b) shows the resonance parameters for tangentially placed dielectric loaded coils. FIG. 3 (at c) shows the resonance parameters for tangentially placed conventional coils. FIG. 3 (at d) shows the resonance parameters for 20% overlapped conventional coils.

[0042] As it is shown in FIG. 3 (at a), it was observed that when dielectric loaded coils are placed tangentially near each other, a notable decoupling of 9.2 dB was achieved. Conversely, placing conventional coils in proximity results in a lower decoupling of 4.5 dB. However, introducing a 20% overlap in the placement of conventional coils improved the decoupling to 10.49 dB.

[0043] It was observed that these findings indicate that conventional coils with a 20% overlapping configuration exhibit a decoupling performance similar to that of tangentially placed dielectric loaded coils. It was observed that the potential of achieving comparable decoupling results with a simpler coil configuration.

[0044] FIGS. 3 (at b, c, and d) depict the resonance parameters (Si l and S22) for the different coil configurations. It was observed that when the dielectric loaded coils were placed tangentially near each other, the measured SI 1 at 400 MHz was -22.81 dB, while S22 was -19.06 dB. In the case of conventional coils placed tangentially near each other, the corresponding values were - 30.75 dB for SI 1 and -30.08 dB for S22. Finally, when the conventional coils were overlapped by 20%, the measured SI 1 and S22 at 400 MHz were -19.64 dB and -18.94 dB, respectively. The results obtained demonstrated that the coils were effectively resonating at 400 MHz.

[0045] Overall, the findings highlight the comparable decoupling performance of 20% overlapping conventional coils and tangentially placed dielectric loaded coils, as shown with the S-parameter measurements presented in FIG. 3.

[0046] FIG. 4 shows full-wave electromagnetic simulation results. FIG. 4 (at a) illustrates simulated coil configurations tangentially placed dielectric loaded coils (left), tangentially placed conventional coils (middle), and 20% overlapped conventional coils (right). FIG. 4 (at b) illustrates S21 measurements and comparison for three configurations. FIG. 4 (at c) illustrates resonance parameters for tangentially placed dielectric loaded coils. FIG. 4 (at d) illustrates tangentially resonance parameters for tangentially placed conventional coils. FIG. 4 (at e) illustrates resonance parameters for 20% overlapped conventional coils. FIG. 4 (at f) illustrates H-field distribution when only one of the coils was active for tangentially placed dielectric loaded coils. FIG. 4 (at g) illustrates H-field distribution when only one of the coils was active for tangentially placed conventional coils. FIG. 4 (at h) illustrates H-field distribution when only one of the coils was active for 20% overlapped conventional coils.

[0047] Three distinct coil configurations were modeled, tested, and compared in HFSS to evaluate the performance of the dielectric loading decoupling technique. FIG. 4 (at a) illustrates these configurations, which included placing dielectric loaded coils tangentially near each other, placing conventional coils tangentially near each other, and overlapping conventional coils by 20%. The coils were tuned and matched to ensure resonance at 400 MHz.

[0048] FIG. 4 (at b) illustrates the measured S21 for each simulated coil configuration. It was observed that placing dielectric loaded coils near each other resulted in a notable decoupling of 8.9 dB between the coils. Conversely, it was observed that the same placement with conventional coils exhibited a lower decoupling of only 5.88 dB. However, it was observed that introducing a 20% overlap in the placement of conventional coils improved the decoupling to 9.06 dB, which is comparable to placing dielectric loaded coils tangentially near each other. Throughout the simulations, the coils were properly tuned and matched for the target frequency, as evidenced by the resonance parameters in FIG. 4 (at c, d, and e), which resulted in values below -15 dB.

[0049] To further analyze the coupling between the coils, FIG. 4 (at f, g, and h) presents the measured H-field when only one of the coils was excited. In this figure, the excited coil demonstrated a higher H-field, while the non-excited coil exhibited a lower H-field resulting from the coupling between the two coils. Comparing FIG. 4 (at f, g, and h), it is evident that the coupling between non-overlapped conventional coils was more pronounced than that between overlapped conventional coils and non-overlapped dielectric loaded coils. Moreover, comparing the H-field plot of non-overlapped dielectric loaded coils and overlapped conventional coils revealed a similar level of decoupling between the coils.

[0050] These findings highlight the effectiveness of the dielectric loading decoupling technique and demonstrate that tangentially placed dielectric loaded coils can achieve decoupling performance similar to that of overlapping conventional coils.

[0051] FIG. 5 illustrates the evaluation of dielectric loading decoupling technique in phantom imaging. FIG. 5 (at a) illustrates S21 measurements and comparison inside the scanner for all three (3) configurations: tangentially placed dielectric loaded coils, tangentially placed conventional coils, and 20% overlapped conventional coils. FIG. 5 (at b) illustrates an MR image by using dielectric loaded coils placed tangentially near each other when the right coil is excited (left) and when the left coil is excited (right). FIG. 5 (at c) illustrates an MR image by using conventional coils placed tangentially near each other when the right coil is excited (left) and when the left coil is excited. FIG. 5 (at d) illustrates an MR image by using conventional coils 20% overlapped when the right coil is excited (left) and when the left coil is excited (right). FIG. 5 (at e) illustrates an MR image by using conventional coils 20% overlapped when both coils are excited. FIG. 5 (at f) illustrates an MR image by using dielectric loaded coils placed tangentially near each other when both coils are excited.

[0052] To evaluate and compare the performance of dielectric loaded coils in terms of decoupling, SNR, signal intensity, and signal uniformity, three sets of MR imaging experiments were conducted. The coils were tuned and matched to resonate at 400 MHz using an L-matching network inside the scanner. As shown in FIG. 5 (at a), a decoupling of 6 dB was obtained when the dielectric loaded coils were placed tangentially near each other. Tangentially placing conventional coils resulted in a decoupling of 3.5 dB, while 20% overlapping of the conventional coils yielded a comparable decoupling of 7.8 dB, which was close to the tangentially placed dielectric loaded coils.

[0053] The MR images obtained were in alignment with the measured S-parameters inside the scanner. FIG. 5 (at b) left and right demonstrate the results of using tangentially placed dielectric loaded coils when one of the coils was terminated in 50 . These figures indicate minimal coupling between the coils. Conversely, when conventional coils were placed in the same configuration (FIG. 5 (at c)), higher coupling between the coils was observed. FIG. 5 (at d) shows that overlapping the coils resulted in the similar decoupling performance as tangentially placing the dielectric loaded coils.

[0054] In FIGS. 5 (at e and f), signal intensity, signal uniformity, and SNR of the image obtained using overlapped conventional coils with both coils active were compared to that obtained using tangentially placed dielectric loaded coils with both coils active. This figure displays the ROIs that the signal intensity and SNR measurements were performed: near the surface of the phantom, the center of the phantom, and a larger ROI encompassing both ROIs. These measurements provide a comprehensive understanding of the differences between the proposed decoupling technique and the gold standard technique. In the first ROI, near the surface of the phantom, the utilization of the dielectric loading technique resulted in a 21.1% decrease in signal intensity and a 0.86% increase in SNR. Measurements at the second ROI, the center of the phantom, showed a significant improvement with a 38% increase in signal intensity and a 27.72% increase in SNR when dielectric loaded coils were used. Furthermore, in the third ROI, covering a large area of the phantom, signal intensity and SNR improved by 6.07% and 8.94%, respectively. The calculation details of these parameters are presented in Table 1. Table 1 .

Noise, Signal Intensity, and SNR measurements in each ROI

[0055] In addition to the analysis of signal intensity and SNR, a comparison of signal uniformity inside the larger ROI using equation (1), as described above, was conducted. The results revealed a significant 89.8% improvement in signal uniformity when dielectric loaded coils were employed.

[0056] These findings highlight the advantages of the proposed decoupling technique using tangentially placed dielectric loaded coils. By achieving a more homogeneous signal distribution across the larger ROI, the use of dielectric loaded coils improves signal uniformity. This is useful for producing uniform MR images with consistent image intensity throughout the region of interest, reducing potential artifacts, and enhancing diagnostic accuracy. Moreover, this decoupling technique results in improved image quality, characterized by increased signal intensity and enhanced SNR, particularly in the central region of the phantom. [0057] The conventional approach of decoupling, which involves overlapping the coils, is based on decreasing mutual inductance between adjacent coils by canceling out the magnetic flux through the non-shared area with the magnetic flux generated through the shared area. However, it has been recognized that when dielectric materials are subjected to an RF pulse, surface displacement currents are generated, leading to the conversion of electric fields to magnetic fields. Based on this understanding, it was hypothesized that the secondary magnetic field generated by these currents could potentially cancel out the magnetic field from each coil to the other coil and effectively reduce crosstalk between the coils.

[0058] The proposed decoupling technique offers new possibilities for fabricating enhanced wearable coil arrays for MRI. Current wearable coils are either not stretchable or are prone to significant performance degradation when stretched due to the direct impact on the overlapped area and the potential deterioration of decoupling between the coils. By utilizing a stretchable and flexible dielectric material, it was observed that this mitigates this risk.

[0059] SiC was employed as the dielectric material, in contrast to a previous study where TiCh was used. It was observed that the SiC-based pad exhibited a higher dielectric constant compared to the TiCh-based pad (sr = 7). It was observed that the SiC-based pad generated a stronger secondary magnetic field and demonstrated improved decoupling between the coils. Additionally, the MR images clearly indicate that the SiC-based pad offers invisibility in FLASH sequences, reducing potential sources of artifacts. The only drawback of using SiC-based dielectric loaded coils was a decrease in stretchability due to the nature of the silicon-based polymer used in the dielectric mixture. However, a reasonable stretch of 15% was observed to be achieved with this material.

[0060] The MR images were obtained using the dielectric loaded decoupling technique and demonstrated lower signal intensity in the area close to the coil compared to overlapping conventional coils. However, the penetration depth and signal uniformity increased with the use of the dielectric loaded coils, as anticipated due to the nature of dielectric materials. The decrease in signal uniformity means that physicians cannot have a clear view of both the central and close- to-coil areas simultaneously. Increasing the power to enhance the signal in the central area can result in over-flipped (too bright) regions near the coil. The improved uniformity achieved with the dielectric loaded coils addresses this issue, enabling a wider view of the sample and enhancing the overall image interpretation for physicians.

[0061] Accordingly, a novel decoupling technique for RF coils, and its performance was evaluated through bench tests, EM simulations, and MR imaging experiments. The quantitative results strongly support the feasibility and advantages of this technique. The MR imaging experiments demonstrate the improvement of penetration depth and signal uniformity. This enhanced signal uniformity enables a broader view of the sample without sacrificing image quality or introducing artifacts. Importantly, this technique paves the way for the utilization of wearable coils, ensuring that the performance of the coil array remains uncompromised even with stretching.

[0062] Accordingly, aspects of the present disclosure are set forth in the following claims.

Claims

CLAIMS What is claimed is:

1. A device to optimize images of a region of interest in a body, acquired by an MRI system, the device comprising: a flexible substrate configured to be coupled to a body, the flexible substrate including a dielectric mixture comprising dielectric particles and a polymer, and a radio-frequency coil embedded within the dielectric mixture.

2. The device of claim 1, wherein the dielectric particles comprise silicon carbide (SiC).

3. The device of claim 2, wherein the polymer is silicone.

4. The device of claim 1, wherein the flexible substrate is stretchable.

5. The device of claim 4, wherein the flexible substrate has a stretchability of about 15%.

6. The device of claim 1, wherein the coil has a resonance frequency between 64 MHz (1.5

T) and 447 MHz (10.5 T).

7. The device of claim 1, wherein the coil has a length of about 50 mm and a width of about 35 mm.

8. The device of claim 1, wherein the flexible substrate has a length of about 50 mm, a width of about 35 mm, and a depth of about 5 mm.

9. The device of claim 1, wherein the flexible substrate has a length of 50 mm, a width of 35 mm, and a depth of 5 mm.

10. The device of claim 1, wherein the flexible substrate includes a plurality of coils, and wherein each of the plurality of coils is positioned tangentially relative to an adjacent one of the plurality of coils.

11. The device of claim 10, wherein one of the plurality of coils positioned tangentially relative to the adjacent one of the plurality of coils are effectively decoupled from one another.

12. The device of claim 11, wherein each one of the plurality of coils overlaps an adjacent one of the plurality of coils by about 5%.

13. A method of preparing a dielectric loaded coil, the method comprising: a) preparing a dielectric mixture; b) pouring the mixture into a mold; c) curing the mixture; d) positioning the coil on the cured mixture, followed by pouring more of the dielectric mixture to cover the coil; e) repeating steps b) - c) to cover the coil.

14. The method of claim 13, wherein the mold has the same dimensions as the coil.

15. The method of claim 13 or 14, wherein curing the mixture further comprises applying a vacuum.

16. The method of claim 15, wherein curing the mixture further comprises applying heat.

17. The method of any one of claims 15-16, wherein the dielectric material comprises SiC powder and a biocompatible silicone elastomer.

18. The method of claim 17, wherein the dielectric material comprises 58 weight percent SiC relative to the weight of the mixture.