Self-tuning liquid metal RF coils and coil arrays for MRI.

Abstract

Self-tuning single or multi-coil elements for MR imaging systems are provided. The elements are flexible and stretchable and can conform to various body regions and patient sizes. The elements can be worn by a patient during an MR imaging session. Each coil can have one or more interdigital capacitors formed from flexible conductive traces. The capacitance of the interdigital capacitors changes under stretching to provide self-tuning. The traces can be made from a liquid metal. The liquid metal can be doped with a contrast agent such that the coils are substantially invisible on an MR image. The coils of the multi-coil element can be arranged in a single layer or a double layer.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 181,664, filed April 29, 2021, which is incorporated by reference in its entirety.

[0002] The present disclosure relates to self-tuning radio frequency (RF) coils for magnetic resonance imaging (MRI). [Background technology]

[0003] Magnetic resonance imaging (MRI) is an essential technology for non-invasively depicting anatomical structures and facilitating diagnosis. MRI systems rely on signal detection via one or more radio frequency coils. Most commercially available receiving coils are rigid, but ideally, one or more coils (coil arrays) should provide both bendability and conformal stretchability to accommodate various body regions to ensure optimal signal-to-noise ratio (SNR). However, most commercially available MRI coils are generally constructed to accommodate a general patient population (wide range of anatomical dimensions), which increases the average offset distance of the coil from the anatomical structures and therefore reduces the available SNR. Typically, their images have limited spatial imaging resolution due to suboptimal SNR.

[0004] The use of standardized sized coil designs is particularly challenging when attempting to use the same coil for adults, infants and small children. Even within the adult population, there is a wide range of sizes.

[0005] Imaging of long bones poses additional concerns because limb length and circumference vary widely within populations.

[0006] To address these challenges, certain coil arrays have been proposed that are flexible and stretchable, improving ergonomics, versatility, and patient comfort while also improving SNR and image resolution. For example, coils can be made from liquid metal. However, upon stretching, the coil dimensions change, which shifts the coil's resonant frequency, thus eliminating the SNR performance benefits gained by placing the coil closer to the anatomy (due to its flexibility). Specifically, as the coil loop element dimensions change, its resonant frequency changes accordingly. The coil inductance is proportional to the length of the coil conductor, i.e., as the coil is stretched, the coil inductance increases and the resonant frequency decreases. The frequency shift and coupling variations change the source impedance present to the preamplifier, which causes a decrease in SNR.

[0007] Several approaches have been proposed to mitigate the effect of frequency shift in flexible and extendable coils, such as broadband matching circuits and automatic tuning / matching circuitry. However, both of these mechanisms rely on additional circuitry in the system, which reduces reliability and increases power, as well as complexity and space requirements. Space is at a premium and is extremely scarce in the narrow MRI bore, especially in arrays with large channel counts and associated per-channel tuning circuitry.

[0008] One known coil construction uses AIR™ Technology, which is highly flexible but not stretchable. Additionally, other known designs for "flexible" coils are bulky and their flexibility is limited to a single direction.

[0009] The use of high impedance coaxial coils has been proposed, which offer high flexibility and form-fitting conformability while also providing good element isolation, but the diameter of the individual coils is determined by the desired resonant frequency and the properties of the coaxial cable and cannot be freely chosen, since commercially available coaxial cables have a limited and discrete set of impedances, resulting in discrete values ​​for the achievable coil diameters. Summary of the Invention [Means for solving the problem]

[0010] Thus, an RF coil for a magnetic resonance imaging (MRI) scanner is disclosed that may include a plurality of traces. The traces may be flexible. The RF coil may have a first flexible conductive trace and a second flexible conductive trace. One end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace may be shaped to form an interdigital capacitor. The other end may be connected to the MRI scanner through one or more circuits. The circuits may include tuning circuitry and a preamplifier.

[0011] In one embodiment of the present disclosure, the geometry of the interdigital capacitors and loop portions of the RF coil can be set to offset the resonant frequency shift under stretched conditions without requiring additional circuitry for retuning. For example, the number of digits, the gap between one end of the first flexible conductive trace and the corresponding end of the second flexible conductive trace, and the length of the digits can be based on at least one of the patient size, the coil size, the body part, the expected motion, or the magnetic field of the scanner.

[0012] In one aspect of the present disclosure, the flexible traces can be formed from liquid metal. The liquid metal can be encapsulated in a soft, stretchable polymer matrix that provides the material with elasticity, flexibility, and conformability to the target anatomy. The liquid metal can be formed in a microchannel. In one aspect of the present disclosure, the liquid metal can be a gallium alloy. The coil is wearable and conformable so that it is in close proximity, which provides improved high resolution imaging. In one aspect of the present disclosure, the RF coil can be conformable to a body part selected from the group consisting of the breast wall, chest wall, groin, neck, knee, and shoulder. The RF coil can stretch with the movement of the joint or body part.

[0013] In one aspect of the present disclosure, the RF coil can be stretchable by at least 30% in a first direction perpendicular to the digits of the interdigitated capacitor. Under 30% stretch, the change in resonant frequency can be less than 2% from the resonant frequency of the unstretched RF coil.

[0014] In one embodiment of the present disclosure, the RF coil (both the loop and the interdigital capacitor) can have any shape. For example, the loop can have a rectangular shape. In some embodiments, the loop can have a geometric shape other than a rectangle, such as, for example, a circle or an octagon.

[0015] In one embodiment of the present disclosure, the flexible polymer matrix can include an elastomer. In one embodiment of the present disclosure, the elastomer can be doped with a contrast agent. For example, the contrast agent can be gadolinium-based. The elastomer can be Ecoflex®. In one embodiment of the present disclosure, the ratio of Ecoflex® to contrast agent is such that the RF coil is substantially invisible on the MR image.

[0016] Also disclosed is an RF coil having a plurality of interdigital capacitors. At least two of the interdigital capacitors can be at right angles to each other. In this embodiment, the coil can include a plurality of flexible conductive traces. For example, the coil can have three or more flexible conductive traces. One end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace can be shaped to form a first interdigital capacitor. The other end of the second flexible conductive trace and a corresponding end of the third flexible conductive trace can be shaped to form a second interdigital capacitor. The first interdigital capacitor can be at right angles to the second interdigital capacitor. The other end of the third flexible conductive trace can be connectable to an MRI scanner through one or more circuits including tuning / matching circuitry and a preamplifier.

[0017] The RF coil may be stretchable by at least 30% in a first direction perpendicular to the digits of the first interdigitated capacitor and in a second direction perpendicular to the digits of the second interdigitated capacitor.

[0018] In one embodiment of the present disclosure, the RF coil further includes a fourth flexible conductive trace. One end of the fourth flexible conductive trace and the other end of the third flexible conductive trace can be shaped to form a third interdigital capacitor. The other end of the fourth flexible conductive trace can be connected to an MRI scanner through one or more circuits including tuning / matching circuitry and a preamplifier.

[0019] Also disclosed is a coil array that can include a plurality of coils. Each coil can include a plurality of flexible traces. Each coil can have a first flexible conductive trace and a second flexible conductive trace. One end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace can be shaped to form an interdigital capacitor. The other end can be connected to an MRI scanner via one or more circuits. The circuits can include tuning circuitry and preamplifiers.

[0020] In one aspect of the present disclosure, the flexible traces can be formed from a liquid metal that can be encapsulated in a soft, stretchable polymer matrix that provides the material with elasticity, flexibility, and conformability to the target anatomy. The liquid metal can be formed within a microchannel.

[0021] In one aspect of the disclosure, each coil can be positioned in the same layer of the flexible polymer matrix. In another aspect, the coils can be arranged in a bilayer, with adjacent coils positioned in different layers of the bilayer. Adjacent coils can overlap. In one aspect of the disclosure, the amount of overlap can be set such that crosstalk between adjacent coils is below a preset threshold.

[0022] In one aspect of the present disclosure, the interdigital capacitors of each coil can be aligned with the corresponding interdigital capacitors of the other coils.

[0023] In one aspect of the disclosure, the coil array is wearable and conformable. Because the coil array is wearable and conformable, it is in close proximity, which results in improved high resolution imaging. In one aspect of the disclosure, the coil array can conform to a body part selected from the group consisting of the breast wall, chest wall, groin, neck, knee, and shoulder. The coil array can stretch with movement of the joint or body part.

[0024] This patent or application document contains at least one drawing printed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. [Brief description of the drawings]

[0025] [Figure 1A] 1 illustrates a flexible, extendable coil element according to an aspect of the present disclosure. [Figure 1B] 13 illustrates another example of a flexible, expandable coil element according to an aspect of the present disclosure, where the coil loops are of different shapes. [Diagram 2] 1 illustrates an example of the change in inductance and capacitance for a coil element under a stretch condition perpendicular to the digits of an interdigitated capacitor, according to an embodiment of the present disclosure. [Diagram 3] 1 shows the theoretical relationship between trace width and change in resonant frequency under tension. [Figure 4] 1 shows the theoretical change in resonant frequency while varying the trace width w and the gap (g) between the traces of an interdigital capacitor. [Figure 5A] 1 illustrates a coil element according to an aspect of the present disclosure. [Figure 5B] 1 illustrates an example of a coil element having flexible traces. [Figure 5C] 5B shows a comparison of simulation results under various stretching conditions for the coil element shown in FIG. 5A and FIG. 5B. [Figure 5D] 5A and 5B show a comparison of simulated and measured results under various stretching conditions for the coil element shown in FIG. 5A and FIG. 5B. [Figure 5E] 5B shows the measured loaded and unloaded Q-factors and ratios of the coil elements shown in FIG. 5A. [Figure 6] 1 illustrates a coil element having multiple interdigitated capacitors according to an aspect of the present disclosure. [Figure 7A]1 illustrates different trace patterns for an interdigitated capacitor according to an aspect of the present disclosure. [Figure 7B] 1 illustrates different trace patterns for an interdigitated capacitor according to an aspect of the present disclosure. [Figure 8A] 1 illustrates an example of a multi-coil element having overlap, according to an aspect of the present disclosure. [Figure 8B] 1 shows the relationship between the overlap of coil loops of adjacent coils and crosstalk. [Figure 8C] 8A and 8B show simulation results for a two-coil element with set overlap under various tension conditions, with FIG. 8C showing the input impedance for one of the coils and FIG. 8D showing the crosstalk. [Figure 8D] 8A and 8B show simulation results for a two-coil element with set overlap under various tension conditions, with FIG. 8C showing the input impedance for one of the coils and FIG. 8D showing the crosstalk. [Figure 9] 1 illustrates a method of fabricating a single layer multi-coil element according to an aspect of the present disclosure. [Figure 10A] 1 illustrates a rendering of an exemplary mold for a single layer multi-coil element according to an aspect of the present disclosure. [Figure 10B] 10B shows an example of a mold produced based on the rendering of FIG. 10A. [Figure 10C] FIG. 10C shows an example of a single layer polymer with microchannels for two coil elements fabricated using the mold shown in FIG. 10B according to an embodiment of the present disclosure, prior to insertion of jumper wire tubes. [Figure 10D] 1 illustrates an example of two coil elements in a single layer according to an embodiment of the present disclosure. [Figure 11A] 1 shows a rendering of an example of a mold for a dual-layer multi-coil element according to an aspect of the present disclosure. [Figure 11B] 11B shows an example of a mold produced based on the rendering of FIG. 11A. [Figure 11C]1 shows two separate coil elements that are stacked to create a double-layer multi-coil element according to an embodiment of the present disclosure. [Figure 11D] 1 illustrates an example of a dual-layer, two-coil element according to an embodiment of the present disclosure. [Figure 12] 1 illustrates an example of a dual-layer, two-coil element according to an embodiment of the present disclosure fabricated using direct ink writing. [Figure 13-1] 13A-13E show simulation results for the B-field for a single coil element according to an embodiment of the present disclosure on a simulated phantom. FIGs. 13F-13J show SNR maps acquired under various stretch conditions using a single coil element according to an embodiment of the present disclosure on a real phantom. FIGs. 13K-13O show normalized SNR maps corresponding to FIGs. 13F-13J, respectively. FIG. 13P shows the normalized SNR measured through the center of a coil according to an embodiment of the present disclosure to the phantom. [Figure 13-2] Continued from Figure 13-1. [Figure 14-1] 14A-C show fast spin echo images, 14A acquired using a single unstretched coil element as described herein, 14B acquired using a single coil element stretched 15% as described herein, and 14C acquired using an 8-channel commercially available knee coil. 14D-F are corresponding SNR maps of the same sagittal slices, 14D corresponds to 14A, 14E corresponds to 14B, and 14F corresponds to 14C. [Figure 14-2] Continued from Figure 14-1. [Figure 15] 15A shows simulation results for a multi-coil element on a curved phantom according to an embodiment of the present disclosure, where FIG. 15A shows a double-layered multi-coil element on a curved phantom and FIGS. 15B-15G show the sensitivity when different coils of the double-layered multi-coil element are excited. [Figure 16]16A-16D show simulation results for a multi-coil element on a curved phantom according to an embodiment of the present disclosure, showing sensitivity at various stretch conditions, 0%, 10%, 20% and 30%, respectively, when all coils are excited. [Figure 17] 17A-17F show a comparison of measurement results of coil elements fabricated using different techniques according to embodiments of the present disclosure: in FIG. 17A / FIG. 17D, a single layer of two coil elements was used (molded) (SL); in FIG. 17B / FIG. 17E, a double layer of two coil elements was used (molded) (DL), and in FIG. 17C / FIG. 17F, a double layer of two coil elements was used (DL-DIW). [Figure 18-1] 18A-18F show a comparison of measurement results from a double-layered two-coil element fabricated using direct ink writing according to an embodiment of the present disclosure and a dedicated commercially available knee coil, where FIG. 18A / FIG. 18D are images / SNR maps acquired using the dedicated commercially available knee coil, FIG. 18B / FIG. 18E are images / SNR maps acquired using a double-layered two-coil element without stretching, and FIG. 18C / FIG. 18E are images / SNR maps acquired using a double-layered two-coil element under 15% stretching. [Figure 18-2] Continued from Figure 18-1. [Figure 19] The results of signal intensity measurements based on different dopant to polymer ratios are shown. [Figure 20-1] 20A-20I show various comparison results of pairs of single coil elements with different dopant concentrations according to an embodiment of the present disclosure, where FIGS. 20A-20C are SE images, FIGS. 20D-20F are SNR maps, and FIGS. 20G-20I are signals in a phantom. [Figure 20-2] Continued from Figure 20-1. [Figure 20-3] Continued from Figure 20-2. [Figure 21] 13 shows the results of three single coil elements with different dopant concentrations and input impedance S11 according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] FIG. 1A shows an example of a flexible, extendable coil element 10 according to an embodiment of the present disclosure for use in MRI. The coil element 10 is wearable, extendable, and can conform to a target body part, thereby minimizing the distance between the coil and the anatomical structure, thereby increasing signal sensitivity. The coil element 10 can include one or more coils. As shown in FIG. 1A, the coil element 10 includes a single coil. In one embodiment of the present disclosure, the coil element 10 includes liquid metal traces 12, 14 and a polymer matrix 20. The polymer matrix 20 includes microchannels for the liquid metal traces 12, 14. A pair of traces, for example, 12, 14, is formed on an interdigital capacitor 15. As shown in FIG. 1A, the traces 12, 14 form a rectangular loop. However, the shape of the loop is not limited to the example shown in FIG. 1A. For example, FIG. 1B shows a coil element 10' according to another embodiment of the present disclosure having a differently shaped loop. In some embodiments, traces 12' and 14' can form shapes such as circles or octagons. The shapes are not limited to the disclosed examples.

[0027] In one embodiment of the present disclosure, the polymer matrix 20 can be formed from a soft silicone elastomer. The soft silicone elastomer enables the flexibility of the coil element 10. For example, the polymer matrix 20 can be made from a material such as Ecoflex®. However, the material of the polymer matrix 20 is not limited to Ecoflex® and other materials can be used. For example, another liquid silicone can be used, such as DragonSkin™ 30 (by Smooth-On). In other embodiments, the polymer can be made from other elastomeric materials that are not silicone-based. The type of material used for the polymer matrix 20 can be selected based on the target elongation required. For example, coil elements 10 used for adults can be made with different polymer materials than coil elements 10 for infants. Additionally, coil elements 10 used for different body parts can be made with different polymer materials. Different MRI systems have different field strengths and resonant frequencies, and coil elements 100 used for different MRI systems can also have different materials.

[0028] Ecoflex® is an extremely flexible and extensible polymer, matching the elastic compliance of human skin. With a Poisson's ratio of 0.5, Ecoflex® ensures isochoric behavior, which is the favorable pressure condition for containing liquid metal in the microchannel. As described later, Ecoflex® can be doped with one or more other materials to reduce the visibility of the coil in MR images. For example, manganese (Mn) or gadolinium (Gd) can be added to Ecoflex® to increase the relaxivity and therefore reduce the signal in MR images.

[0029] Ecoflex® has a relatively low dielectric constant ε r= 2.8. In some embodiments of the present disclosure, the dielectric constant can be increased by blending the uncured polymer with a material with a high dielectric constant. For example, in some embodiments, barium titanate BaTiO3 (BTO) nanoparticles can be blended with the polymer. As shown below, other properties of the coil element 10, such as capacitance, can be modified based on the dielectric constant, since the capacitance of the interdigital capacitor is affected by the dielectric constant of the host.

[0030] In one embodiment of the present disclosure, the polymer matrix 20 and the layout of the microchannels can be formed by a mold. For example, a 3D printer can be used to create a plastic mold that includes a predetermined pattern layout for the conductive traces 12, 14 (forming the interdigital capacitor 15). The plastic mold can be a negative mold. The plastic mold can be made from polylactic acid (PLA). The mold can have a preset height to achieve a target thickness for a portion of the polymer matrix. For example, the height can be 50 μm.

[0031] Another mold of the same size (length and width) can also be prepared for the sealing part by a 3D printer. In one embodiment of the present disclosure, a high-precision 3D printer with a minimum resolution of 0.2 mm can be used.

[0032] Uncured Ecoflex® elastomer is prepared by mixing equal amounts of the two components and degassing the mixture in a vacuum chamber to remove any air bubbles, then poured into a negative mold and cured until fully solidified. The cured elastomer can be released from the negative mold and a flat sealing portion is attached that covers the patterned elastomer. In one embodiment of the present disclosure, the flat sealing portion can be between 0.5 mm and 1.5 mm thick. For example, the flat sealing portion can be 1.0 mm. The two portions can be bonded together to form a stretchable polymer matrix 20 containing patterned microchannels.

[0033] The thickness of the elastomer should be thin enough so as not to create noise or hinder flexibility or extensibility, but at the same time reduce the risk of small cracks in the matrix that could lead to spillage of the liquid metal from the polymer.

[0034] In another embodiment of the present disclosure, the polymer matrix 20 and the layout of the microchannels can be formed by direct ink writing (DIW). DIW is a 3D printing technique that uses liquid ink delivered under a controlled flow rate on a controllable path to create a target object. The materials used for DIW can be the same as those described above, such as flexible silicone resin. The DIW process can be faster than the molding process. Direct 3D printing of flexible silicone resin on various substrates is largely automated and assembly-free, making it possible to avoid the laborious manual fabrication required for the molding process. DIW reduces the turnaround time. Additionally, the DIW process can produce a thinner polymer matrix 20. A thinner polymer matrix 20 can make the coil elements 10 less visible in MR images. The liquid silicone can be spin-coated on a glass panel. The microchannels, for example, the walls of the microchannels are directly printed on the coated glass panel. For example, a 3D printer by Musashi, Japan, model SHOTmini200'ΩX, can be used. A fast-curing silicone sealant can be used as a liquid ink on the walls of the microchannels. A silicone sheet can be used to seal the channels. In one embodiment of the present disclosure, the silicone sheet can be molded or 3D printed. The two pieces can be bonded together to form a stretchable polymer matrix 20 containing patterned microchannels.

[0035] In one embodiment of the present disclosure, the liquid metal traces 12, 14 can be formed from a gallium alloy. For example, EGaIn or Galinstan® can be used. EGaIn remains in its liquid form at temperatures above 15.7°C / 60.3°F, has low vapor pressure, and is low toxic. In one embodiment of the present disclosure, particulates can be added to the gallium alloy. For example, gold particulates can be added, which can slightly increase the electrical conductivity of the liquid metal. Such improved electrical conductivity can reduce coil losses, improve the Q factor, and increase the SNR of the coil element 10.

[0036] In one embodiment of the present disclosure, a needle and syringe can be used to inject liquid metal into the microchannels to form the traces 12,14.

[0037] In another embodiment of the present disclosure, instead of liquid metal used as the material for the traces 12, 14, a conductive elastomer can be used with nanoparticles. The nanoparticles can include silver nanoparticles. Although the conductivity of the silver nanoparticles may be less than the liquid material, the conductive elastomer with silver nanoparticles can provide comparable Q-factor and SNR values.

[0038] Signal ports 30 can be formed by inserting copper wires into the ends of the microchannels to create contacts for other electrical components of the circuit. Those components can include one or more printed circuit boards with tuning electronics, matching electronics, detuning electronics and integrated preamplifier modules.

[0039] The interdigital capacitor 15 provides self-tuning, which minimizes the shift in resonant frequency under stretching conditions, allowing the coil element 10 to be used to obtain images of anatomical structures of various sizes under various bending angles. For example, the flexibility, stretchability, and self-tuning allow imaging of various complex human anatomical structures, such as the cervical spine, perineum / groin, breast / chest, neck / shoulder, or knee. However, the body parts listed herein are for illustrative purposes only, and the coil element 10 can be placed in other body parts as needed for imaging.

[0040] When the coil element 10 is stretched, for example, in the x-direction, the inductance increases. However, according to an embodiment of the present disclosure, the capacitance of the interdigital capacitor 15 decreases to offset the increase. An example of the change in inductance L and capacitance C for the coil element 10 under stretching in the x-direction is shown in FIG. 2. Thus, the change in the resonant frequency can be minimized without additional circuitry for tuning. As shown in FIG. 2, the increase in inductance is approximately linear with stretching. However, the decrease in capacitance is nonlinear, and therefore the change in capacitance cannot perfectly compensate for the linear change in inductance, and some change in resonance may occur.

[0041] An interdigital capacitor that is stretched by a factor α applied perpendicular to the fingers (digits) of the capacitor 15 (in the x direction in FIG. 1A ) exhibits a total capacitance C=C / α, where C is the initial capacitance of the interdigital capacitor 15,

number

[0042] Resonance is,

number

[0043] The characteristics of the coil element 10, including the traces 12, 14 and the interdigital capacitor 15, can be set to minimize the resonant frequency shift within a target range for a target extension range. For example, the target extension range can be 30%. The target extension range is not limited to 30% and other ranges can be used. A target extension range of 30% allows the same coil element 10 to be used to image many different body parts. The characteristics can include (a) coil circumference, (b) number of capacitor digits (fingers), (c) digit length, (d) digit width, and (e) spacing (gap) between digits.

[0044] Figure 3 shows the change in resonant frequency for ten different trace widths ranging from 0.1 mm to 1.0 mm under tension in the x-direction (Figure 1A) based on theoretical analysis. As can be seen in Figure 3, the largest change in resonant frequency occurs for the smallest trace widths. The following properties were maintained for all ten simulated trace widths: D=10 cm, w=1 mm, g=0.5 mm, b=12 mm. D is the diameter of the loop, d is the diameter of traces 12, 14, g is the spacing between digits, and b is the length of the digits.

[0045] 4 shows the change in resonant frequency while varying the trace width w and the gap (g) between the traces of the interdigital capacitor 15. When the trace gap g (the spacing between digits) is less than the trace width w, wider values ​​of trace width w result in smaller changes in frequency.

[0046] Actual coil behavior may differ from theoretical behavior because the interactions between all the members and components are more complex and are not fully considered in simplified theoretical models. In some embodiments of the present disclosure, the theoretical behavior can be used as a starting point for properties that can be determined using full wave electromagnetic field simulation. When unstretched, the resonant frequency of the coil element 10 can be set to match the operating frequency of the scanner. For example, the operating frequency of a 3T scanner is 128 MHz. It can also be matched to a resistance. For example, the resistance can be 50 ohms. The aforementioned properties can be selected to minimize shifts due to stretching, for example, for a target stretch range of 0% and 30%. For example, for a substantially rectangular loop of about 6 cm by 7 cm, the properties can include: an interdigital capacitor that can have 8 digits, each digit can have a digit length of 7 mm, and the spacing between digits can be 0.5 mm. Additionally, the width of the traces can be 0.5 mm. In some embodiments of the present disclosure, the trace width can be varied depending on the resolution of the 3D printer. To determine the properties, the model includes a polymeric material, such as Ecoflex® elastomer, and may also include a homogenous cylindrical phantom. The target stretch ranges may be different for different applications, such as elements for different body regions or body types. Different properties may be used for different target stretch ranges.

[0047] Simulation results of a coil element 10 according to an embodiment of the present disclosure were compared to a coil array of the same dimensions with a fixed value capacitor. Figures 5A and 5B show a side-by-side comparison of a coil element 10 according to an embodiment of the present disclosure (Figure 5A) with an interdigital capacitor 15 and coil element with a fixed capacitor 500 and flexible traces 505. The traces 12, 14 can be made from liquid metal as described herein.

[0048] FIG. 5C shows the simulation results with the two coil elements shown in FIG. 5A / FIG. 5B. In particular, FIG. 5C shows the input impedance S11 (on the y-axis) and the frequency (on the x-axis). The figure shows six different stretch conditions (and no stretch) with a 5% difference between the various stretch conditions. As can be seen in FIG. 5C, the reference coil element (FIG. 5B) has its input impedance S11 shifted linearly toward lower frequencies as expected. However, the input impedance of the coil element 10 according to the embodiment of the present disclosure fluctuated around the frequency (no stretch), e.g., the initial resonance frequency, by first shifting to higher frequencies (for stretches up to 15%) and then returning to lower frequencies (for stretches of 20% or more, below the target range). As can be seen in FIG. 5C, the coil element of FIG. 5B shows a shift of more than 7 MHz (7.4 MHz), which is about a 5.8% shift. However, the coil element 10 according to the embodiment of the present disclosure (FIG. 5A) shows a maximum shift of only about 2.2 MHz, which is about a 1.7% shift. Thus, according to the embodiment of the present disclosure, the frequency shift can be improved by about 70%.

[0049] Two coil designs (FIGS. 5A and 5B) with the same characteristics used in the simulations were fabricated and tested. The coil elements were connected to a 3D printed unidirectional tension test fixture. The coil elements (FIGS. 5A / 5B) were also connected to a vector network analyzer via an L-shaped tuning / matching network. FIG. 5D shows a comparison of the measured results for both coil elements as well as the simulated results. Shading has been added to highlight the total frequency shift. The simulated curves are identified by the unfilled shapes (circles / squares) and the measured curves are identified by the filled shapes (circles / squares). The squares are for the coil element 10 according to the embodiment of the present disclosure shown in FIG. 5A. The circles are for the coil element shown in FIG. 5B. As shown in FIG. 5D, the measured data matches well with the simulated results. Additionally, as shown in FIG. 5D, the frequency shift is significantly improved using the coil element 10 according to the embodiment of the present disclosure over the coil element of FIG. 5B. At a maximum measured stretch of 5 cm, corresponding to about a 27% stretch, the frequency shift for coil element 10 according to embodiments of the present disclosure is only 0.5 MHz (0.4%) compared to over 5 MHz (over 4%), which is a ten-fold reduction in frequency shift.

[0050] FIG. 5E shows the measured load Q of the coil element of FIG. 5A under various tension conditions. L and no-load Q U The quality factor and its ratio are shown. L and Phantom Q U The quality factor was measured using a pickup probe when the load was applied. The quality ratio is Q U / Q L As shown in Figure 5E, the quality ratio was about 2, which means that most of the coil loss is due to the phantom rather than the coil itself. The quality ratio is also relatively stable with respect to the stretching conditions.

[0051] 1A / 1B show one interdigital capacitor 15 in the coil. The number of interdigital capacitors 15 in the coil is not limited to one. Additional interdigital capacitors 15 can be added. The orientation of different interdigital capacitors 15 can be different. The number and orientation of the interdigital capacitors 15 can be based on the expected stretch of the coil element 10. For example, if the coil element 10 is expected to stretch in both the x-direction and the y-direction, the interdigital capacitors 15A and 15B can be perpendicular to each other.

[0052] FIG. 6 shows a coil element 10″ in which a single coil has multiple interdigital capacitors 15A-15C. Three interdigital capacitors are shown for illustrative purposes. Interdigital capacitor 15A is perpendicular to interdigital capacitors 15B / 15C. The x- and y-directions are shown in FIG. 6. The digits of interdigital capacitor 15A are perpendicular to the x-direction, and the digits of interdigital capacitors 15B / 15C are perpendicular to the y-direction. Thus, interdigital capacitor 15A can minimize frequency shift when stretched in the x-direction, and interdigital capacitors 15B / 15C can minimize frequency shift when stretched in the y-direction. Each interdigital capacitor 15 can be formed from paired traces. For example, interdigital capacitor 15B is formed from traces 612, 614, interdigital capacitor 15A is formed from traces 614, 616, and interdigital capacitor 15C is formed from traces 616, 618. Traces 612 and 618 are connected to signal port 30. In one embodiment of the present disclosure, different interdigital capacitors can have different characteristics, such as the number of digits, the length of the digits, and the spacing between the digits. These characteristics can be based on the expected stretch in one or more directions. The characteristics can also be based on the expected use, for example, the body part, the size of the patient, and the magnetic field source (such as the operating frequency).

[0053] According to aspects of the present disclosure, different coil elements 10, 10', 10'' may be used for different body parts or different sized patients. Thus, the characteristics described above, including the interdigital capacitor 15, may be customized for the body part or patient size. Additionally, the characteristics may be altered based on the strength of the magnetic field. For example, different magnetic fields may require different interdigital capacitances.

[0054] In one embodiment of the present disclosure, each digit of the interdigital capacitor 15 can have a U-shaped conductive path. In another embodiment, each digit can be formed from a single linear path.

[0055] FIG. 7A shows an example of a fluid channel configuration for an interdigital capacitor 15 according to an embodiment of the disclosure. One of the conductive traces 712 forming the interdigital capacitor is channel 1 (fluidic channel), and the other of the conductive traces 714 forming the interdigital capacitor is channel 2 (fluidic channel). FIG. 7A is a top view. The x and y directions are shown. Each fluid channel has a serpentine conductive trace encapsulated in a polymer matrix 20. As shown in FIG. 7A, each serpentine conductive trace has multiple U-shaped curves. w2 and w4 are the widths of trace 712 in different directions. w1 and w3 are the widths of trace 714 in different directions. In one embodiment of the disclosure, widths w2 and w4 can be the same. Similarly, in one embodiment of the disclosure, widths w1 and w3 can be the same. g1-g4 are various spacings between the traces (in the case of g1, it is the spacing between the sides of the U-shape). In one embodiment of the disclosure, g2, g3, and g4 can be the same. The two fluidic channels are spatially separated by the same electrically insulating polymer matrix 20 .

[0056] 7B shows another example of a two fluid channel configuration for an interdigital capacitor 15 according to an embodiment of the present disclosure. One of the conductive traces 712' forming the interdigital capacitor is channel 1 (fluidic channel), and the other of the conductive traces 714' forming the interdigital capacitor is channel 2 (fluidic channel). Each fluid channel is composed of multiple spatially separated lines located along the y-axis connected to the same signal line in the x-axis. The two fluid channels are spatially separated by the same electrically insulating polymer matrix 20.

[0057] In other aspects of the present disclosure, the coil element can include multiple coils, where one coil loop is connected to different MR imaging channels. The multiple coils form an RF coil array. The number of coils in the array can range from N=2 to N=32 or more. The number of coils may be limited only by the number of MR imaging channels of the MRI system. Adjacent coils can overlap in the z-direction. The overlap can affect the sensitivity of the individual coils. Thus, according to aspects of the present disclosure, the overlap is designed to sufficiently decouple adjacent coils, so that the sensitivity of the individual coils is distinct from each other and is only minimally affected by the presence of the neighboring element. In some aspects, the overlap can be 10% to 30% of the loop area (at rest, e.g., when not under tension).

[0058] In one aspect of the present disclosure, the overlap range can be determined using a parameter such as crosstalk S21 (or S12). Crosstalk is the effect of adjacent channels on each other. For example, S21 is a function of the transmit power of a first channel and the receive power of a second channel (physically adjacent channel). The overlap distance can be set to minimize the value of S21. In other aspects, the overlap range can be used such that the value of S21 is less than a preset value. For example, the preset value can be 10db.

[0059] The overlap value or range of values ​​can be determined using simulation. A full wave numerical simulation can be performed using the coil geometry and interdigital capacitor properties described herein. A rectangular loop of 7 x 6 cm can be used for each coil loop as the coil shape and area. 8 digits, each digit can have a digit length of 7 mm (B = 7 mm), and the spacing between digits can be 0.5 mm. Additionally, the trace width can be 0.5 mm. For the simulation, two adjacent coils (coil 1 801 and coil 2 802) as shown in Figure 8A can be used. In one embodiment of the present disclosure, the same overlap can be used for each adjacent coil. Figure 8A shows two simulated coils, coil 1 801 and coil 2 802, with overlap 810. A homogeneous phantom can also be simulated. The homogeneous phantom can be rectangular, and coil 1 801 and coil 2 802 are simulated to be located at the same location. The overlap 810 was varied from a predetermined minimum value to a predetermined maximum value. For example, the predetermined min / max can be 8mm / 17mm. For different size loops, the min and max can be different. For each modified overlap 810, S 21 The parameters were determined. Figure 8B shows the overlap and S 21 The relationship between S 21 is on the y-axis and overlap is on the x-axis. As you can see, S 21 is smallest near 12 mm. Thus, in one embodiment of the present disclosure, the overlap 810 may be approximately 12 mm. The dashed line superimposed on the curve is a predetermined threshold, e.g., -10 db. Thus, in other embodiments of the present disclosure, the overlap 810 may be between approximately 10 mm and approximately 14 mm for a coil and interdigital capacitor 15 having the characteristics described above. The overlap may be different if the coil and interdigital capacitor 15 have different characteristics, including dimensions.

[0060] To check the relative stability of the coil tuning and decoupling, coil 1 801 and coil 2 802, which are stacked by 12 mm, were linearly stretched in the x-direction from 0% to 50%. Figures 8C and 8D show the simulated S values, S, under various stretch conditions (five different stretch conditions and no stretch, here with a 10% difference between the stretch conditions). 11 and S 21 As can be seen from FIG. 8D, under stretch conditions of less than 40%, S 21 The maximum value of is less than 10 dB (approximately 128 MHz to 129 MHz). 11 is for coil 1 801. However, both coils have approximately the same S 11 , S 22 The shift in the resonant frequency of Coil 1 801 was up to about 2 MHz under simulated tension conditions.

[0061] In one aspect of the present disclosure, the coil array (multi-coil element) can have a single layer or a double layer. In a single layer, each coil is in the same layer of polymer, e.g., the coils are substantially flat. Jumper wires can be used in the overlapping areas. In a double layer element, adjacent coils are positioned in different layers, e.g., the coils are in alternating layers.

[0062] FIG. 9 illustrates a method of fabricating a single layer multi-coil element 1000 according to an embodiment of the present disclosure. The single layer multi-coil element 1000 can be molded in a similar manner as described above. For example, the layout of the polymer matrix 20′ and the microchannels 1005 can be formed by a mold at 900. For example, a 3D printer can be used to create a plastic mold that includes a predetermined pattern layout for the conductive traces (and interdigital capacitors 15) and the microchannels 1005. The plastic mold is a negative mold 1015. The plastic mold can be made from polylactic acid (PLA). The mold can have a preset height to achieve a target thickness for a portion of the polymer matrix. FIG. 10A illustrates an exemplary rendering of a mold for a two coil element (single layer). A close-up of the overlapped area is shown in the inset. As can be seen in FIG. 10A, in the overlapped area, there are gaps or interruptions 1010 in the microchannels 1005. This is because the coils are in the same layer. To avoid liquid metal from different channels touching each other, one of the coils has an interruption in the microchannel 1005. There will be an interruption at each intersection. In Figure 10A, a close-up shows a gap 1010 for one of the intersections. A similar gap 1010 exists at the other intersection.

[0063] As can be seen in FIG. 10A, the coil loops can be aligned such that the interdigital capacitors 15 of each coil are aligned when viewed in the x-direction. The large rectangle in FIG. 10A represents the dimensions of the element 1000 in the x- and y-directions, e.g., the edges of the polymer matrix. FIG. 10B shows an example of a 3D printed negative mold 1015 with the microchannels 1005 and gaps 1010 shown in FIG. 10A. While the corners have straight edges in the rendering of FIG. 10A, the polymer matrix 20 in FIG. 10B has curved corners. This is for ease of manufacturing. However, the corners may be rounded or have straight edges.

[0064] At 905, materials for the polymer matrix 1020 are provided (mixed if necessary). For example, uncured Ecoflex® elastomer can be prepared by mixing equal amounts of the two components and degassing the mixture in a vacuum chamber to remove any air bubbles. The elastomer can be poured into a negative mold 1015 and allowed to cure until sufficiently solidified. The cured elastomer can be released from the negative mold. A separate mold (not shown) can be used to create a flat sealing part. The flat sealing part that covers the patterned elastomer is attached to the bottom part with the microchannels 1005. The two parts can be bonded together to form a stretchable polymer matrix 1020 with patterned microchannels. FIG. 10C shows an example of a stretchable polymer matrix 1020 with microchannels for two coils (multiple coils).

[0065] At 910, openings are created in the polymer matrix 1020 for the tubes for the jumper wires. In one embodiment of the disclosure, the openings are in the flat sealing portion. The openings can be located at the edge of the microchannel just before the gap 1010 begins so that a continuous channel can be formed from the microchannel 1005 and the inner portion of the tube. The size of the openings can be based on the diameter of the tube. In one embodiment of the disclosure, the tube can have a diameter the same as the width of the microchannel. For example, the diameter of the tube can be 0.5 mm. In the case of two coils (such as in FIG. 10C), there are four openings. In other embodiments, the openings can be located in the bottom portion instead of the sealing portion.

[0066] At 915, a tube is inserted into each opening. In one embodiment of the present disclosure, the tube can be a thin, flexible silicone tube. The length of the tube can be based on the length of the gap 1010. The tube spans the length of the gap at the intersection (e.g., one tube for two gaps is shown in the inset of FIG. 10A / FIG. 10C). For example, the tube can have a length of about 5 mm.

[0067] At 920, the openings and tubes can be sealed 1050 using a sealant to prevent leakage. For example, a silicone epoxy can be used, such as SilPoxy by SmoothON. At 920, liquid metal can be inserted into the microchannel 1005 and tubes. The liquid metal can be injected into the microchannel 1005 and tubes using a needle and syringe. Copper wires can be connected to the liquid metal, similar to above.

[0068] Figure 10D shows an example of a single layer, two coil element 1000 with tubing and sealant fabricated as described herein. Although Figures 10A-10D show only two coils for illustrative purposes, N coils can be used in a single layer and fabricated as described herein.

[0069] In other embodiments, the coils can be configured to be bilayered. Adjacent coils can be positioned in different layers of the bilayer. For example, for a 5-coil element, coils 1, 3 and 5 can be in a first layer, and coils 2 and 4 can be in a second layer. The second layer can be on top of the first layer (or vice versa). The coils of each layer can be fabricated separately and then stacked. The distance between each coil in the same layer can be set to maintain the target overlap 810 described above. For example, each layer can have an extension region without microchannels. The extension region can face the microchannels of the other layer.

[0070] FIG. 11A shows a rendering of a mold mold for a double-layered multi-coil element 1100. As can be seen in FIG. 11A, there is an extended region 1105 where the microchannels 25 are not positioned. FIG. 11B shows an example of a mold mold for a double-layered multi-coil element 1100 corresponding to the rendering of FIG. 11A. Again, the mold mold of FIG. 11B has rounded corners for easier fabrication. However, in other embodiments, the mold mold can have straight edges as shown in the rendering of FIG. 11A. FIG. 11C shows an example of two coil elements (single coil element) fabricated separately. Coil 1 is in the first layer and coil 2 is in the second layer. The extended region 1105 of the first layer faces the microchannels 25 of the second layer and vice versa. For example, as shown in FIG. 11C, the microchannels of coil 1 face the extended region 1105 of the second layer. FIG. 11D shows an example of a double-layered multi-coil element 1100 with two coils. As can be seen, the coils are positioned such that there is a target overlap 810.

[0071] In another embodiment of the present disclosure, instead of molding the bilayer element, the bilayer element 1100' can be fabricated by DIW in a manner similar to that described above, such that the bilayer element is thinner. For example, the microchannels for each coil of the same layer can be disposed on spin-coated silicone. A thin sealing portion can be located on top of the microchannels 25 for each coil. The process can be repeated for the other layer. Again, the spacing between the microchannels can be set to achieve the target overlap 810. Each layer can include an extension region 1105 facing the microchannels 25 of the other layer to achieve the target overlap 810. FIG. 12 shows an example of a bilayer multi-coil element 1100' (two coils) fabricated using DIW. FIG. 12 also shows copper wires (also attached to the respective MR image channels) connected to the liquid metal for each coil.

[0072] As explained above, materials such as contrast agents can be added to the polymeric material to suppress the signal. This can be used to reduce the brightness at which the coil elements are seen on the MR image (or make the coil elements invisible). Although the visibility of the coil elements does not affect the quality of the image, radiologists are not accustomed to seeing the coil elements on the MR image. The intensity of the signal (such as in the case of gradient-recalled-echo (GRE) sequences) is based on the relaxation times T1 and T2. Certain contrast agents can change the timing of relaxation. For example, Gd contrast agents promote the relaxation of nearby hydrogen protons, shortening both T1 and T2. However, shortening of T1 increases the signal intensity, whereas shortening of T2 (especially when Gd is in high concentration) decreases the signal intensity. The amount of dopant used can be based on the target decrease in signal intensity. For example, the volume ratio of materials, such as Magnevist to Ecoflex®, can range from 1:10 to 2:10,000. For example, the ratio may be 5:100.

[0073] Further simulations and measurements The single coil element and the multi-coil element described herein were used in simulations and measurements to determine the SNR under certain stretch conditions. Figures 13A-13E show the simulation results for the B-field for a single coil element on a simulated phantom. The following coil characteristics were used in the simulation: a rectangular loop measuring approximately 6 cm x 7 cm, an interdigital capacitor with 8 digits, each digit 7 mm long, 0.5 mm spacing between digits, and a trace width of 0.5 mm. The polymer was Ecoflex®, the liquid metal was EGaIn, and there was no dopant. The phantom was a homogenous rectangular phantom representing average tissue properties. The sensitivity B1 field profiles of the central axial cross section are shown in Figures 13A-13E. The stretch conditions were 14%, 26%, 38% and 50% (and no stretch, Figure 13A). As can be seen in Figures 13A-13E, the coil sensitivity was relatively unaffected by stretching. However, although there was a slight decrease in sensitivity (at the center), the coil can cover a larger area when stretched and maintain a performance of, for example, 0.75±0.06 μT at the surface.

[0074] A single coil element, fabricated as described above and with the same properties as in the simulation (selected for a target stretch of 30%), was placed on the phantom and gradually stretched from 0% (FIG. 13F) to 50% (FIG. 13J). FIG. 13F-13J shows the SNR maps obtained under various stretch conditions. As can be seen in FIG. 13F-13J, the polymer and liquid metal appear on the images. The two dots of high intensity correspond to the edge of the liquid metal coil. As can be seen in FIG. 13F-13J, the SNR is maintained, for example, at the surface of the phantom, when stretched to 30%, with a SNR=516±46. This is a typical 9% variation within the target stretch range. It should be noted that even at more than 30% beyond the target stretch range, the SNR is maintained to provide a valid image, and is comparable to a commercially available rigid coil.

[0075] Figures 13K-O show normalized SNR maps. SNR varies with coil dimensions, therefore SNR is expected to decrease with coil stretch. Normalization was performed with respect to coil size. Figures 13K-O also show stable SNR (normalized) performance. Figure 13P shows normalized SNR measured through the center of the coil to the phantom. For stretches less than 30%, the normalized SNR varied by about 2% (561 ± 12).

[0076] The performance of a single coil element (rectangular loop approximately 6 cm x 7 cm, interdigital capacitor with 8 digits, each digit 7 mm long, 0.5 mm spacing between digits, 0.5 mm trace width, Ecoflex® polymer, EGaIn liquid metal, no dopants) fabricated according to embodiments of the present disclosure was compared to a commercially available knee coil. The commercially available knee coil had a dedicated 8-channel knee coil. Fast spin echo images of the sagittal plane of a healthy knee were acquired with a single coil element at no stretch and at 15% stretch. Only a portion of the knee was visible using a single coil element (single channel surface coil) and contrasted with an 8-channel commercially available knee coil, which is a volumetric multi-channel coil. Figures 14A-C show fast spin echo images, where Figure 14A was acquired using a single coil element that was not stretched as described herein, Figure 14B was acquired using a single coil element that was stretched 15% as described herein, and Figure 14C was acquired using an 8-channel commercially available knee coil. Each figure is labeled with two rectangles. The smaller rectangle is for intrinsic SNR comparison. The SNR was 282, 288, and 179 (in the smaller rectangle) in Figures 14A, 14B, and 14C, respectively. This corresponds to a 60% increase in SNR over the 8-channel commercial knee coil. The larger rectangle highlights the improved SNR. It is noted that a single coil element is shown in Figures 14A / 14B, but not in Figure 14C. Figures 14D-14F are the corresponding SNR maps for the same sagittal slices. These maps clearly show that the SNR of the single coil element described herein is improved over the 8-channel commercial knee coil (dedicated). As can be seen in Figures 14D-14F, the SNR is significantly improved (in the area corresponding to the larger rectangle). This significant improvement is due to the conformal design of the stretchable coil.

[0077] FIG. 15A shows a simulation of six coils (multi-channel coil elements or coil arrays) on a cylindrical phantom 1500. The coils were simulated to be equidistant from each other on a homogeneous cylindrical phantom. FIGS. 15B-15G show the individual sensitivity profiles for each coil. The coils were simulated as a dual-layer multi-coil element as described herein. Coils 1, 3, 5 are in one layer of the polymer matrix and coils 2, 4, 5 are in another layer. Each coil was simulated to have the same characteristics as described above. In FIGS. 15B-15G, different coils were excited to test the output of each coil and the crosstalk between the coils separately. As shown in FIGS. 15B-15G, each coil has a similar sensitivity. Additionally, FIGS. 15B-15G show the slight presence of crosstalk when one of the coils is excited. For example, in FIG. 15B, when one of the coils is energized, the adjacent coils exhibit less sensitivity (while the non-adjacent coils exhibit only minimal sensitivity), as shown by the shading.

[0078] Figures 16A-D show simulated sensitivity maps when the coils are under various stretch conditions and all of the coils are energized. Figure 16A shows no stretch (0%); Figure 16B shows 10% stretch; Figure 16C shows 20% stretch, and Figure 16D shows 30% stretch. Figures 16A-D show that the coil elements described herein assembled into a coil array can maintain good sensitivity while stretched. They also show that the coil elements (coil array) operate on a curved surface.

[0079] 17A-17F show a comparison of measurement results of multi-coil elements fabricated with different techniques according to an embodiment of the present disclosure on a phantom. Each coil element had two coils. In FIG. 17A / 17D, two coil elements in a single layer were used (molded) (SL); in FIG. 17B / 17E, two coil elements in a double layer (also called double layer) were used (molded) (DL), and in FIG. 17C / 17F, two coil elements in a double layer were used (DL-DIW). Each coil element had the same characteristics as described above. The coils were placed on a standard rectangular silicone phantom (W=22cm, L=33cm, H=16cm) for imaging at 3T (GE Healthcare, MR750). A 3D spoiled gradient echo sequence was used (TR=6.3 ms, TE=2.4 m (in-phase), FOV=20 cm, pixel size 0.8×0.8, FA=12°, BW=31.3 kHz, slice thickness=1 mm, NEX=1). The SNR maps of the coils are shown in Figures 17A-C (measured through the slice in the central axis). In the SNR maps, three lines are added, two vertical lines and one horizontal line. One of the vertical lines passes through the center of the left coil and the other through the center of the right coil. The horizontal line is 1 cm away from the surface of the phantom. Figure 17D shows the SNR along the left vertical line, Figure 17E shows the SNR along the right vertical line, and Figure 17F shows the SNR along the horizontal line, where the SNR is shown for all three coil elements (SL, DL, and DL-DIW). The elements (SL and DL) are clearly visible in Figures 17A and 17B, but are only faintly visible in Figure 17C, as would be expected given that the DL-DIW is much thinner. The DL is better visible in the image (see Figure 17B versus Figure 17A). The figures also show that the fabrication techniques result in similar sensitivity maps.

[0080] The performance of DL-DIW fabricated according to an embodiment of the present disclosure was compared with a commercially available knee coil. The commercially available knee coil had a dedicated 8-channel knee coil array. Axial and sagittal images were acquired. Images were acquired for DL-DIW without stretching and under 15% stretching. An FSE sequence with the following parameters was used: TR=4500ms, TE=8.2ms, FOV=18cm, pixel size 0.4×0.6, ETL=9, BW=83.3kHz, NEX=1, slice thickness=1mm. FIG. 18A is an image acquired using the commercially available knee coil (FIG. 18D is the corresponding SNR map). FIG. 18B is an image acquired using the unstretched DL-DIW (identified as a dual channel coil) (FIG. 18E is the corresponding SNR map). The unstretched dimension is 124mm. FIG. 18C is an image acquired using the 15% stretched DL-DIW (FIG. 18F is the corresponding SNR map). As can be seen in Figures 18A-C, signal strength is improved (images are brighter) using the DL-DIW elements over the commercial knee coil, especially near the conformal coil elements, which was expected since the DL-DIW conforms closely to the knee anatomy.

[0081] Triangles were added to each of the SNR maps (Figures 18D-F) on a comparative basis. The SNR was increased with DL-DIW over the commercial knee coil. For example, the SNR of the commercial knee coil was 40, and increased to 52 (unstretched) and 60 (15% stretched) with DL-DIW. The SNR improvement of DL-DIW is up to 50% compared to the dedicated commercial knee coil.

[0082] The effect of doping the polymer was tested by varying the concentration of the dopant in the polymer. Ecoflex® polymer was used. The dopant was Magnevist (Gd contrast agent). Samples were prepared by mixing the contrast agent with Ecoflex® in various volume ratios. Each mixture was placed in a separate test tube. In detail, all samples were degassed in a vacuum chamber to remove air bubbles, transferred to graduated plastic test tubes, and cured at room temperature. Nine doped samples and one pure sample (without dopant) were prepared with the following concentration ratios: (1) 2:10,000; (2) 5:10,000; (3) 1:1,000; (4) 2:1,000; (5) 5:1,000; (6) 1:100; (7) 2:1000; (8) 5:100; and (9) 1:10.

[0083] Samples were placed equidistantly around a standard homogeneous cylindrical phantom with an outer diameter of 9.5 cm and a length of 30 cm. Samples were also positioned within a 32-channel head coil. A 3T MRI scanner was used. Regions of interest were identified to determine mean signal intensity. A single axial slice with a spin-echo (SE) sequence was acquired (TR = 1500 ms, slice thickness 5 mm, 32TEs ranging from 8.3 to 133 ms).

[0084] Figure 19 shows the results for nine doped and one pure sample at TE = 33.2 ms. Sample concentration is on the x-axis and signal intensity is on the y-axis. Initially the signal intensity increased (24% increase) as the concentration increased from pure to 1:1,000. However, above that concentration the signal intensity decreased (at 1:10 to only 30% of the initial signal intensity without dopant). This was expected since T1 and T2 change and finally the change in T2 causes the signal intensity to decrease.

[0085] Three single coil elements were fabricated as described above using various concentrations of dopants: (1) pure Ecoflex® (no dopant); (2) 5:100; (3) 1:10. The coil geometry of the three single coil elements was the same. Each single coil element was placed on a rectangular phantom. A 3T MRI scanner was used.

[0086] 20A-C show SE images of homogeneous phantoms. In FIG. 20A, the SE image of a single coil element made from pure Ecoflex® (right side of FIG. 20A) is compared with the SE image of a single coil element made with a ratio of 5:100 to the polymer matrix (left side of FIG. 20A). In FIG. 20B, the SE image of a single coil element made from pure Ecoflex® (right side of FIG. 20B) is compared with the SE image of a single coil element made with a ratio of 1:10 to the polymer matrix (left side of FIG. 20B). In FIG. 20C, two SE images with different single coil elements made with different ratios (1:10 on the left side of FIG. 20C; 5:100 on the right side of FIG. 20C) are compared.

[0087] As can be seen from Figures 20A-20C, the image signal was reduced by up to 83% and 92% for ratios of 5:100 and 1:10, respectively, making the Magnevist-doped signal coil elements less visible on the MR images.

[0088] Figures 20D-20F show the corresponding SNR maps: Figure 20D corresponds to Figure 20A; Figure 20E corresponds to Figure 20B; Figure 20F corresponds to Figure 20C. The SNR was calculated by dividing the SE images by the standard deviation of the background noise. As can be seen in Figures 20D-20F, the SNR remained stable (426 ± 5) for all three single element coils. The SNR maps also show that the coil elements without dopant are more visible.

[0089] Figures 20G-I show the signal intensity measured in the phantom along a vertical line passing through the center of each coil. The vertical lines are shown in Figures 20A-C. Figure 20G corresponds to Figure 20A; Figure 20H corresponds to Figure 20B; Figure 20I corresponds to Figure 20C. As can be seen in Figures 20G-I, the Magnevist polymer dopant does not affect the sensitivity of the elements in the phantom. Only the sensitivity at the surface (distance = 0) is affected.

[0090] Thus, if desired, the polymer can be doped to reduce the visibility of the element on the image without sacrificing sensitivity.

[0091] In the specification and claims herein, the term "about" indicates that the recited value may be modified to some extent, provided that the modification does not result in a process or device incompatibility. For example, with respect to some elements, the term "about" may represent a variation of ±0.1%, while with respect to other elements, the term "about" may represent ±1% or ±10%, or any point therebetween. For example, the term about when used with measurements in mm may include ±0.1, 0.2, 0.3, etc., where the difference between the recited numbers may be greater the larger the recited numbers. For example, about 1.5 may include 1.2 to 1.8, where about 20 may include 19.0 to 21.0.

[0092] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the disclosure and is not exclusive. Numerous modifications and alterations will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure.

Claims

1. 1. An RF coil for a magnetic resonance imaging (MRI) scanner comprising: a first flexible conductive trace; a second flexible conductive trace; and wherein one end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace are shaped to form an interdigital capacitor; the other end of each of the first and second flexible conductive traces is connectable to an MRI scanner through one or more circuits including tuning / matching circuitry and a preamplifier; The RF coil.

2. 10. The RF coil of claim 1, wherein the first and second flexible conductive traces comprise a liquid metal formed within microchannels in a flexible polymer matrix, and optionally the liquid metal comprises a gallium alloy.

3. 3. The RF coil of claim 1, wherein the RF coil is attachable to a patient, the RF coil is stretchable by at least 30% in a first direction perpendicular to the digits of the interdigital capacitor, and the change in resonant frequency under 30% stretch is less than 2% from the resonant frequency of the unstretched RF coil.

4. 4. The RF coil of claim 3, wherein the RF coil conforms to a body part selected from the group consisting of the breast wall, chest wall, groin, neck, knee and shoulder, and the RF coil is configured to stretch with movement of the joint or body part.

5. 3. The RF coil of claim 1, wherein the number of digits, the gap between one end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace, and the length of the digits are based on at least one of the following: patient size, coil size, body part, expected movement, or scanner magnetic field.

6. The flexible polymer matrix includes an elastomer, and optionally the elastomer is 3. The RF coil of claim 2, which is doped with an agent.

7. 7. The RF coil of claim 6, wherein the contrast agent is gadolinium-based and the elastomer is Ecoflex®, and the ratio of Ecoflex® to contrast agent is such that the RF coil is substantially invisible on an MR image.

8. 1. An RF coil for a magnetic resonance imaging (MRI) scanner comprising: a plurality of flexible conductive traces including a first flexible conductive trace, a second flexible conductive trace, and a third flexible conductive trace; one end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace are shaped to form a first interdigital capacitor; the other end of the second flexible conductive trace and the corresponding end of the third flexible conductive trace are shaped to form a second interdigital capacitor, the first interdigital capacitor being perpendicular to the second interdigital capacitor; the other end of the first flexible conductive trace is connectable to an MRI scanner through one or more circuits including tuning / matching circuitry and a preamplifier; the other end of the third flexible conductive trace is connectable to an MRI scanner through one or more circuits including tuning / matching circuitry and a preamplifier; The RF coil.

9. 9. An RF coil as claimed in claim 8, which is stretchable by at least 30% in a first direction perpendicular to the digits of the first interdigitated capacitor and in a second direction perpendicular to the digits of the second interdigitated capacitor.

10. 10. The RF coil of claim 8 or 9, further comprising a fourth flexible conductive trace, one end of the fourth flexible conductive trace and the other end of the third flexible conductive trace being shaped to form a third interdigital capacitor, the other end of the fourth flexible conductive trace being connectable to an MRI scanner through one or more circuits including tuning / matching circuitry and a preamplifier.

11. A coil array including a plurality of coils, each of the plurality of coils comprising: a first flexible conductive trace; a second flexible conductive trace; and wherein one end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace are shaped to form an interdigital capacitor; the other end of each of the first and second flexible conductive traces is connectable to an MRI scanner through one or more circuits including tuning / matching circuitry and a preamplifier; The coil array.

12. 12. The coil array of claim 11, wherein each coil is positioned in the same layer of the flexible polymer matrix, or the coils are arranged in a bilayer with adjacent coils positioned in different layers of the bilayer.

13. 13. A coil array as claimed in claim 11 or 12, wherein the interdigitated capacitors of each coil are aligned with corresponding interdigitated capacitors of the other coils.

14. The coil array is wearable by a patient and is stretchable to accommodate movement of a joint or body part, the coil array being stretchable by at least 30% in a first direction perpendicular to the digits of the interdigital capacitor of each coil, and a change in resonant frequency under the 30% stretch is determined by the stretching.

13. The coil array of claim 12, which is less than 2% from the resonant frequency of the untensioned coil array.

15. 13. The coil array of claim 12, wherein adjacent coils overlap, the amount of overlap being set such that crosstalk between adjacent coils is below a preset threshold.

16. 14. The coil array of claim 13, wherein the coil array is wearable by a patient and stretchable to accommodate movement of a joint or body part, the coil array being stretchable by at least 30% in a first direction perpendicular to the digits of the interdigital capacitors of each coil, and wherein the change in resonant frequency under 30% stretch is less than 2% from the resonant frequency of the unstretched coil array.

17. 14. The coil array of claim 13, wherein adjacent coils overlap, the amount of overlap being set such that crosstalk between adjacent coils is below a preset threshold.

18. 15. The coil array of claim 14, wherein adjacent coils overlap, the amount of overlap being set such that crosstalk between adjacent coils is below a preset threshold.

19. 4. The RF coil of claim 3, wherein the number of digits, the gap between one end of the first flexible conductive trace and a corresponding end of the second flexible conductive trace, and the length of the digits are based on at least one of the following: patient size, coil size, body part, expected movement, or scanner magnetic field.

Images