Patent Description:
Magnetic resonance imaging (MRI) is a medical imaging modality that can create images of the inside of a human body without using x-rays or other ionizing radiation. MRI systems include a superconducting magnet to create a strong, uniform, static magnetic field. When a human body, or part of a human body, is placed in the magnetic field, the nuclear spins associated with the hydrogen nuclei in tissue water become polarized, wherein the magnetic moments associated with these spins become preferentially aligned along the direction of the magnetic field, resulting in a small net tissue magnetization along that axis. MRI systems also include gradient coils that produce smaller amplitude, spatially-varying magnetic fields with orthogonal axes to spatially encode the magnetic resonance (MR) signal by creating a signature resonance frequency at each location in the body. Radio frequency (RF) coils are then used to create pulses of RF energy at or near the resonance frequency of the hydrogen nuclei, which add energy to the nuclear spin system. As the nuclear spins relax back to their rest energy state, they release the absorbed energy in the form of an MR signal. This signal is detected by the MRI system and is transformed into an image using a computer and known reconstruction algorithms.

As mentioned, RF coils are used in MRI systems to transmit RF excitation signals ("transmit coil"), and to receive the MR signals emitted by an imaging subject ("receive coil"). Coil-interfacing cables may be used to transmit signals between the RF coils and other aspects of the processing system, for example to control the RF coils and/or to receive information from the RF coils. However, conventional RF coils tend to be bulky, rigid and are configured to be maintained at a fixed position relative to other RF coils in an array. This bulkiness and lack of flexibility often prevents the RF coil loops from coupling most efficiently with the desired anatomy and make them very uncomfortable to the imaging subject.

Further, coil-to-coil interactions dictate that the coils be sized and/or positioned non-ideally from a coverage or imaging acceleration perspective.

According to the invention, a posterior radio frequency (RF) coil assembly for a magnetic resonance imaging (MRI) system is provided as defined in claim <NUM>. In this way, a flexible RF coil assembly may be provided that allows for RF coils in an array to be positioned more arbitrarily, allowing placement and/or size of the coils to be based on desired anatomy coverage, without having to account for fixed coil overlaps or electronics positioning. The coils may conform to the subject anatomy with relative ease. Additionally, the cost and weight of the coils may be significantly lowered due to minimized materials and production process, and environmentally-friendlier processes may be used in the manufacture and miniaturization of the RF coils of the present disclosure versus conventional coils.

It should be understood that the brief description above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

<CIT> discloses a magnetic resonance imaging system to be used over a target area of a subject and includes first and second RF coils for receiving an RF signal from the subject. The first RF coil is fixed to a position device and movable over the target area of subject. The second RF coil is larger than the first RF coil and has a larger field of view than the first RF coil. The system further includes an image processing device programmed to process RF signals coupled from the first RF coil and the second RF coil to form an MRI image.

<CIT> discloses a nuclear magnetic resonance coil comprising electrically conductive coil loop segments wherein the coil loop segments are alternately arranged on opposed sides of a dielectric material layer, wherein consecutively arranged coil loop segments partially overlapping each other.

<CIT> discloses an MRI antenna array which includes a housing and a substrate, antenna elements and circuitry encapsulated by the housing. The housing, antenna elements, and substrate are flexible to allow the housing to distort in three dimensions to conform to contours of a patient. The antenna elements are mounted to the substrate in a manner that permits each element to maintain a desired resonance when the housing is distorted in three dimensions. The circuitry is electrically coupled with the antenna elements to maintain tuning and isolation of the elements when the housing is distorted in three dimensions.

<CIT> discloses an antenna which has a conductor loop oscillating a high frequency current in a current flow direction during an operation of the antenna. The loop is divided into loop sections in the current flow direction, where the loop sections are coupled to each other by a capacitor. The loop is arranged on a conductor board, so that the loop sections are designed as conducting paths that run on the conductor board. The board includes an electrically isolating carrier layer with two boundary layers that lie opposite to each other with respect to the carrier layer.

VESTER "A Low Input Impedance MRI Preamplifier Using a Purely Capacitive Feed-back Network" discloses the advantages and potential of a distributed capacitance method in RF coils, including E-field improvement, reliability improvement and costs reduction.

<CIT> describes a radiofrequency transducer, for nuclear magnetic resonance spectroscopy, comprising a radiofrequency transmission line formed into a loop, having terminals for the connection of a radiofrequency source or receiver thereto in such a manner that the transmission properties of the loop counteract the impedance due to its loop geometry. The transducer may comprise first and second elongate conductors spaced by a dielectric material, for example polytetrafluoroethylene, and shaped to form the said loop, terminals for the two conductors being provided at opposite ends of the loop.

The present disclosure will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:.

The following description relates to various embodiments of a radio frequency (RF) coil in MRI systems. In particular, systems and methods are provided for a low-cost, flexible, and lightweight RF coil that is effectively transparent in multiple respects. The RF coil is effectively transparent to subjects, given the low weight of the coil and flexible packaging that is enabled by the RF coil. The RF coil is also effectively transparent to other RF coils in an array of RF coils, due to minimization of magnetic and electric coupling mechanisms. Further, the RF coil is effectively transparent to other structures through capacitance minimization and is transparent to positrons through mass reduction, enabling use of the RF coil in hybrid positron emission tomography (PET)/MR imaging systems. The RF coil of the present disclosure may be used in MRI systems of various magnetic field strengths.

The MRI system may include a posterior RF coil array, as shown by <FIG>. The posterior RF coil array is shaped to support a body of a subject imaged by the MRI system. The posterior RF coil array may include a plurality of flexible RF coils, with each RF coil including a loop portion and coupling electronics portion configured to interface with a processor or controller unit of the MRI system. The RF coils are embedded within the posterior RF coil array and positioned to be proximate to outer surfaces of each RF coil array configured to be positioned against the body of a subject undergoing imaging.

The RF coil of the present disclosure includes a significantly smaller amount of copper, printed circuit board (PCB) material and electronic components than used in a conventional RF coil and includes parallel elongated wire conductors, encapsulated and separated by a dielectric material, forming the coil element. The parallel wires form a low reactance structure without need for discrete capacitors. The minimal conductor, sized to keep losses tolerable, eliminates much of the capacitance between coil loops, and reduces electric field coupling. By interfacing with a large sampling impedance, currents are reduced and magnetic field coupling is minimized. The electronics are minimized in size and content to keep mass and weight low and prevent excessive interaction with the desired fields. Packaging can now be extremely flexible which allows conforming to anatomy, optimizing signal to noise ratio (SNR) and imaging acceleration.

A traditional receive coil for MR is comprised of several conductive intervals joined between themselves by capacitors. By adjusting the capacitors' values, the impedance of the RF coil may be brought to its minimal value, usually characterized by low resistance. At resonant frequency, stored magnetic and electric energy alternate periodically. Each conductive interval, due to its length and width, possesses a certain self-capacitance, where electric energy is periodically stored as static electricity. The distribution of this electricity takes place over the entire conductive interval length of the order of <NUM>-<NUM>, causing similar range electric dipole field. In a proximity of a large dielectric load, self-capacitance of the intervals change - hence detuning of the coil. In case of a lossy dielectric, dipole electric field causes Joule dissipation characterized by an increase overall resistance observed by the coil.

In contrast, the RF coil of the present disclosure represents almost an ideal magnetic dipole antenna as its common mode current is uniform in phase and amplitude along its perimeter. The capacitance of the RF coil is built between the two wire conductors along the perimeter of the loop. The conservative electric field is strictly confined within the small cross-section of the two parallel wires and dielectric filler material. In the case of two RF coils overlapping, the parasitic capacitance at the cross-overs or overlaps is greatly reduced in comparison to two overlapped copper traces. RF coil thin cross-sections allows better magnetic decoupling and reduces or eliminates critical overlap between two loops in comparison to two traditional trace-based loops.

<FIG> illustrates a magnetic resonance imaging (MRI) apparatus <NUM> that includes a superconducting magnet unit <NUM>, a gradient coil unit <NUM>, an RF coil unit <NUM>, an RF body or volume coil unit <NUM>, a transmit/receive (T/R) switch <NUM>, an RF driver unit <NUM>, a gradient coil driver unit <NUM>, a data acquisition unit <NUM>, a controller unit <NUM>, a table <NUM>, a data processing unit <NUM>, an operating console unit <NUM>, and a display unit <NUM>. In one example, the RF coil unit <NUM> is a surface coil, which is a local coil that is typically placed proximate to the anatomy of interest of a subject <NUM>. Herein, the RF body coil unit <NUM> is a transmit coil that transmits RF signals, and the local surface RF coil unit <NUM> receives MR signals. As such, the transmit body coil (e.g., RF body coil unit <NUM>) and the surface receive coil (e.g., RF coil unit <NUM>) are independent but electromagnetically coupled structures. The MRI apparatus <NUM> transmits electromagnetic pulse signals to the subject <NUM> placed in an imaging space <NUM> with a static magnetic field formed to perform a scan for obtaining MR signals from the subject <NUM> to reconstruct an image of the subject <NUM> based on the MR signals obtained by the scan.

The superconducting magnet unit <NUM> includes, for example, an annular superconducting magnet, which is mounted within a toroidal vacuum vessel. The magnet defines a cylindrical space surrounding the subject <NUM>, and generates a constant, strong, uniform, static magnetic field along the Z direction of the cylindrical space.

The MRI apparatus <NUM> also includes the gradient coil unit <NUM> that generates a gradient magnetic field in the imaging space <NUM> so as to provide the MR signals received by the RF coil unit <NUM> with three-dimensional positional information. The gradient coil unit <NUM> includes three gradient coil systems, each of which generates a gradient magnetic field, which inclines into one of three spatial axes perpendicular to each other, and generates a gradient magnetic field in each of frequency encoding direction, phase encoding direction, and slice selection direction in accordance with the imaging condition. More specifically, the gradient coil unit <NUM> applies a gradient magnetic field in the slice selection direction of the subject <NUM>, to select the slice; and the RF body coil unit <NUM> transmits an RF signal to a selected region of interest (ROI) of the subject <NUM> and excites it. The gradient coil unit <NUM> also applies a gradient magnetic field in the phase encoding direction of the subject <NUM> to phase encode the MR signals from the ROI excited by the RF signal. The gradient coil unit <NUM> then applies a gradient magnetic field in the frequency encoding direction of the subject <NUM> to frequency encode the MR signals from the ROI excited by the RF signal.

The RF coil unit <NUM> is disposed, for example, to enclose the region to be imaged of the subject <NUM>. In some examples, the RF coil unit <NUM> may be referred to as the surface coil or the receive coil. In the static magnetic field space or imaging space <NUM> where a static magnetic field is formed by the superconducting magnet unit <NUM>, the RF coil unit <NUM> transmits, based on a control signal from the controller unit <NUM>, an RF signal that is an electromagnet wave to the subject <NUM> and thereby generates a high-frequency magnetic field. This excites a spin of protons in the slice to be imaged of the subject <NUM>. The RF coil unit <NUM> receives, as a magnetic resonance signal, the electromagnetic wave generated when the proton spin thus excited in the slice to be imaged of the subject <NUM> returns into alignment with the initial magnetization vector. The RF coil unit <NUM> may transmit and receive an RF signal using the same RF coil.

The RF body coil unit <NUM> is disposed, for example, to enclose the imaging space <NUM>, and produces RF magnetic field pulses orthogonal to the main magnetic field produced by the superconducting magnet unit <NUM> within the imaging space <NUM> to excite the nuclei. In contrast to the RF coil unit <NUM>, which may be disconnected from the MRI apparatus <NUM> and replaced with another RF coil unit, the RF body coil unit <NUM> is fixedly attached and connected to the MRI apparatus <NUM>. Furthermore, whereas local coils such as those comprising the RF coil unit <NUM> can transmit to or receive signals from only a localized region of the subject <NUM>, the RF body coil unit <NUM> generally have a larger coverage area. The RF body coil unit <NUM> may be used to transmit or receive signals to the whole body of the subject <NUM>, for example. Using receive-only local coils and transmit body coils provides a uniform RF excitation and good image uniformity at the expense of high RF power deposited in the subject. For a transmit-receive local coil, the local coil provides the RF excitation to the region of interest and receives the MR signal, thereby decreasing the RF power deposited in the subject. It should be appreciated that the particular use of the RF coil unit <NUM> and/or the RF body coil unit <NUM> depends on the imaging application.

The T/R switch <NUM> can selectively electrically connect the RF body coil unit <NUM> to the data acquisition unit <NUM> when operating in receive mode, and to the RF driver unit <NUM> when operating in transmit mode. Similarly, the T/R switch <NUM> can selectively electrically connect the RF coil unit <NUM> to the data acquisition unit <NUM> when the RF coil unit <NUM> operates in receive mode, and to the RF driver unit <NUM> when operating in transmit mode. When the RF coil unit <NUM> and the RF body coil unit <NUM> are both used in a single scan, for example if the RF coil unit <NUM> is configured to receive MR signals and the RF body coil unit <NUM> is configured to transmit RF signals, then the T/R switch <NUM> may direct control signals from the RF driver unit <NUM> to the RF body coil unit <NUM> while directing received MR signals from the RF coil unit <NUM> to the data acquisition unit <NUM>. The coils of the RF body coil unit <NUM> may be configured to operate in a transmit-only mode, a receive-only mode, or a transmit-receive mode. The coils of the local RF coil unit <NUM> may be configured to operate in a transmit-receive mode or a receive-only mode.

The RF driver unit <NUM> includes a gate modulator (not shown), an RF power amplifier (not shown), and an RF oscillator (not shown) that are used to drive the RF coil unit <NUM> and form a high-frequency magnetic field in the imaging space <NUM>. The RF driver unit <NUM> modulates, based on a control signal from the controller unit <NUM> and using the gate modulator, the RF signal received from the RF oscillator into a signal of predetermined timing having a predetermined envelope. The RF signal modulated by the gate modulator is amplified by the RF power amplifier and then output to the RF coil unit <NUM>.

The gradient coil driver unit <NUM> drives the gradient coil unit <NUM> based on a control signal from the controller unit <NUM> and thereby generates a gradient magnetic field in the imaging space <NUM>. The gradient coil driver unit <NUM> includes three systems of driver circuits (not shown) corresponding to the three gradient coil systems included in the gradient coil unit <NUM>.

The data acquisition unit <NUM> includes a pre-amplifier (not shown), a phase detector (not shown), and an analog/digital converter (not shown) used to acquire the magnetic resonance signals received by the RF coil unit <NUM>. In the data acquisition unit <NUM>, the phase detector phase detects, using the output from the RF oscillator of the RF driver unit <NUM> as a reference signal, the magnetic resonance signals received from the RF coil unit <NUM> and amplified by the pre-amplifier, and outputs the phase-detected analog magnetic resonance signals to the analog/digital converter for conversion into digital signals. The digital signals thus obtained are output to the data processing unit <NUM>.

The MRI apparatus <NUM> includes a table <NUM> for placing the subject <NUM> thereon. The subject <NUM> may be moved inside and outside the imaging space <NUM> by moving the table <NUM> based on control signals from the controller unit <NUM>.

The controller unit <NUM> includes a computer and a recording medium on which a program to be executed by the computer is recorded. The program when executed by the computer causes various parts of the apparatus to carry out operations corresponding to predetermined scanning. The recording medium may comprise, for example, a ROM, flexible disk, hard disk, optical disk, magneto-optical disk, CD-ROM, or non-volatile memory. The controller unit <NUM> is connected to the operating console unit <NUM> and processes the operation signals input to the operating console unit <NUM> and furthermore controls the table <NUM>, RF driver unit <NUM>, gradient coil driver unit <NUM>, and data acquisition unit <NUM> by outputting control signals to them. The controller unit <NUM> also controls, to obtain a desired image, the data processing unit <NUM> and the display unit <NUM> based on operation signals received from the operating console unit <NUM>.

The operating console unit <NUM> includes user input devices such as a touchscreen, keyboard and a mouse. The operating console unit <NUM> is used by an operator, for example, to input such data as an imaging protocol and to set a region where an imaging sequence is to be executed. The data about the imaging protocol and the imaging sequence execution region are output to the controller unit <NUM>.

The data processing unit <NUM> includes a computer and a recording medium on which a program to be executed by the computer to perform predetermined data processing is recorded. The data processing unit <NUM> is connected to the controller unit <NUM> and performs data processing based on control signals received from the controller unit <NUM>. The data processing unit <NUM> is also connected to the data acquisition unit <NUM> and generates spectrum data by applying various image processing operations to the magnetic resonance signals output from the data acquisition unit <NUM>.

The display unit <NUM> includes a display device and displays an image on the display screen of the display device based on control signals received from the controller unit <NUM>. The display unit <NUM> displays, for example, an image regarding an input item about which the operator inputs operation data from the operating console unit <NUM>. The display unit <NUM> also displays a two-dimensional (2D) slice image or three-dimensional (3D) image of the subject <NUM> generated by the data processing unit <NUM>.

During a scan, RF coil array interfacing cables (not shown) may be used to transmit signals between the RF coils (e.g., RF coil unit <NUM> and RF body coil unit <NUM>) and other aspects of the processing system (e.g., data acquisition unit <NUM>, controller unit <NUM>, and so on), for example to control the RF coils and/or to receive information from the RF coils. As explained previously, the RF body coil unit <NUM> is a transmit coil that transmits RF signals, and the local surface RF coil unit <NUM> receives the MR signals. More generally, RF coils are used to transmit RF excitation signals ("transmit coil"), and to receive the MR signals emitted by an imaging subject ("receive coil"). In an example, the transmit and receive coils are a single mechanical and electrical structure or array of structures, with transmit/receive mode switchable by auxiliary circuitry. In other examples, the transmit body coil (e.g., RF body coil unit <NUM>) and the surface receive coil (e.g., RF coil unit <NUM>) may be independent structures that are physically coupled to each other via a data acquisition unit or other processing unit. For enhanced image quality, however, it may be desirable to provide a receive coil that is mechanically and electrically isolated from the transmit coil. In such case it is desirable that the receive coil, in its receive mode, be electromagnetically coupled to and resonant with an RF "echo" that is stimulated by the transmit coil. However, during transmit mode, it may be desirable that the receive coil is electromagnetically decoupled from and therefore not resonant with the transmit coil, during actual transmission of the RF signal. Such decoupling averts a potential problem of noise produced within the auxiliary circuitry when the receive coil couples to the full power of the RF signal. Additional details regarding the uncoupling of the receive RF coil will be described below.

As mentioned previously, traditional RF coils may include acid etched copper traces (loops) on PCBs with lumped electronic components (e.g., capacitors, inductors, baluns, resisters, etc.), matching circuitry, decoupling circuitry, and pre-amplifiers. Such a configuration is typically very bulky, heavy and rigid, and requires relatively strict placement of the coils relative to each other in an array to prevent coupling interactions among coil elements that may degrade image quality. As such, traditional RF coils and RF coil arrays lack flexibility and hence may not conform to subject anatomy, degrading imaging quality and patient comfort.

Thus, according to examples disclosed herein, an RF coil array, such as RF coil unit <NUM>, may include distributed capacitance wires rather than copper traces on PCBs with lumped electronic components. As a result, the RF coil array may be lightweight and flexible, allowing placement in low-cost, lightweight, waterproof, and/or flame-retardant fabrics or materials. The coupling electronics portion coupling the loop portion of the RF coil (e.g., the distributed capacitance wire) may be miniaturized and utilize a low input impedance pre-amplifier, which is optimized for high source impedance (e.g., due to impedance matching circuitry) and allows flexible overlaps among coil elements in an RF coil array. Further, the RF coil array interfacing cable between the RF coil array and system processing components may be flexible and include integrated transparency functionality in the form of distributed baluns, which allows rigid electronic components to be avoided and aids in spreading of the heat load.

Turning now to <FIG>, a schematic view of an RF coil <NUM> including a loop portion <NUM> coupled to a controller unit <NUM> via a coupling electronics portion <NUM> and a coil-interfacing cable <NUM> is shown. In one example, the RF coil may be a surface receive coil, which may be single- or multi-channel. The RF coil <NUM> is one non-limiting example of RF coil unit <NUM> of <FIG> and as such may operate at one or more frequencies in the MRI apparatus <NUM>. The coil-interfacing cable <NUM> may be a coil-interfacing cable extending between the electronics portion <NUM> and an interfacing connector of an RF coil array or a RF coil array interfacing cable extending between the interfacing connector of the RF coil array and the MRI system controller unit <NUM>. The controller unit <NUM> may be associated with and/or may be a non-limiting example of the data processing unit <NUM> or controller unit <NUM> in <FIG>.

The coupling electronics portion <NUM> is coupled to the loop portion of the RF coil <NUM>. Herein, the coupling electronics portion <NUM> may include a decoupling circuit <NUM>, impedance inverter circuit <NUM>, and a pre-amplifier <NUM>. The decoupling circuit <NUM> may effectively decouple the RF coil during a transmit operation. Typically, the RF coil <NUM> in its receive mode may be coupled to a body of a subject being imaged by the MR apparatus in order to receive echoes of the RF signal transmitted during the transmit mode. If the RF coil <NUM> is not used for transmission, then it may be necessary to decouple the RF coil <NUM> from the RF body coil while the RF body coil is transmitting the RF signal. The decoupling of the receive coil from the transmit coil may be achieved using resonance circuits and PIN diodes, microelectromechanical systems (MEMS) switches, or another type of switching circuitry. Herein, the switching circuitry may activate detuning circuits operatively connected to the RF coil <NUM>.

The impedance inverter circuit <NUM> may form an impedance matching network between the RF coil <NUM> and the pre-amplifier <NUM>. The impedance inverter circuit <NUM> is configured to transform a coil impedance of the RF coil <NUM> into an optimal source impedance for the pre-amplifier <NUM>. The impedance inverter circuit <NUM> may include an impedance matching network and an input balun. The pre-amplifier <NUM> receives MR signals from the corresponding RF coil <NUM> and amplifies the received MR signals. In one example, the pre-amplifier may have a low input impedance that is configured to accommodate a relatively high blocking or source impedance. Additional details regarding the RF coil and associated coupling electronics portion will be explained in more detail below with respect to <FIG> and <FIG>. The coupling electronics portion <NUM> may be packaged in a very small PCB approximately <NUM><NUM> in size or smaller. The PCB may be protected with a conformal coating or an encapsulating resin.

The coil-interfacing cable <NUM>, such as a RF coil array interfacing cable, may be used to transmit signals between the RF coils and other aspects of the processing system, for example to control the RF coils and/or to receive information from the RF coils. The RF coil array interfacing cables may be disposed within the bore or imaging space of the MRI apparatus (such as MRI apparatus <NUM> of <FIG>) and subjected to electro-magnetic fields produced and used by the MRI apparatus. In MRI systems, coil-interfacing cables, such as coil-interfacing cable <NUM>, may support transmitter-driven common-mode currents, which may in turn create field distortions and/or unpredictable heating of components. Typically, common-mode currents are blocked by using baluns. Baluns or common-mode traps provide high common-mode impedances, which in turn reduces the effect of transmitter-driven currents.

Thus, coil-interfacing cable <NUM> may include one or more baluns. In traditional coil-interfacing cables, baluns are positioned with a relatively high density, as high dissipation/voltages may develop if the balun density is too low or if baluns are positioned at an inappropriate location. However, this dense placement may adversely affect flexibility, cost, and performance. As such, the one or more baluns in the coil-interfacing cable may be continuous baluns to ensure no high currents or standing waves, independent of positioning. The continuous baluns may be distributed, flutter, and/or butterfly baluns. Additional details regarding the coil-interfacing cable and baluns will be presented below with respect to <FIG> and <FIG>.

<FIG> is a schematic of an RF coil <NUM> having segmented conductors formed in accordance with an embodiment. RF coil <NUM> is a non-limiting example of RF coil <NUM> of <FIG> and as such includes loop portion <NUM> and coupling electronics portion <NUM> of RF coil <NUM>. The coupling electronics portion allows the RF coil to transmit and/or receive RF signals when driven by the data acquisition unit <NUM> (shown in <FIG>). In the illustrated embodiment, the RF coil <NUM> includes a first conductor <NUM> and a second conductor <NUM>. The first and second conductors <NUM>, <NUM> may be segmented such that the conductors form an open circuit (e.g., form a monopole). The segments of the conductors <NUM>, <NUM> may have different lengths, as is discussed below. The length of the first and second conductors <NUM>, <NUM> may be varied to achieve a select distributed capacitance, and accordingly, a select resonance frequency.

The first conductor <NUM> includes a first segment <NUM> and a second segment <NUM>. The first segment <NUM> includes a driven end <NUM> at an interface terminating to coupling electronics portion <NUM>, which will be described in more detail below. The first segment <NUM> also includes a floating end <NUM> that is detached from a reference ground, thereby maintaining a floating state. The second segment <NUM> includes a driven end <NUM> at the interface terminating to the coupling electronics portion and a floating end <NUM> that is detached from a reference ground.

The second conductor <NUM> includes a first segment <NUM> and a second segment <NUM>. The first segment <NUM> includes a driven end <NUM> at the interface. The first segment <NUM> also includes a floating end <NUM> that is detached from a reference ground, thereby maintaining a floating state. The second segment <NUM> includes a driven end <NUM> at the interface, and a floating end <NUM> that is detached from a reference ground. The driven end <NUM> may terminate at the interface such that end <NUM> is only coupled to the first conductor through the distributed capacitance. The capacitors shown around the loop between the conductors represent the capacitance between the wire conductors.

The first conductor <NUM> exhibits a distributed capacitance that grows based on the length of the first and second segments <NUM>, <NUM>. The second conductor <NUM> exhibits a distributed capacitance that grows based on the length of the first and second segments <NUM>, <NUM>. The first segments <NUM>, <NUM> may have a different length than the second segments <NUM>, <NUM>. The relative difference in length between the first segments <NUM>, <NUM> and the second segments <NUM>, <NUM> may be used to produce an effective LC circuit have a resonance frequency at the desired center frequency. For example, by varying the length of the first segments <NUM>, <NUM> relative to the lengths of the second segments <NUM>, <NUM>, an integrated distributed capacitance may be varied.

In the illustrated embodiment, the first and second wire conductors <NUM>, <NUM> are shaped into a loop portion that terminates to an interface. But in other embodiments, other shapes are possible. For example, the loop portion may be a polygon, shaped to conform the contours of a surface (e.g., housing), and/or the like. The loop portion defines a conductive pathway along the first and second conductors. The first and second conductors are void of any discrete or lumped capacitive or inductive elements along an entire length of the conductive pathway. The loop portion may also include loops of varying gauge of stranded or solid conductor wire, loops of varying diameters with varying lengths of the first and second conductors <NUM>, <NUM>, and/or loops of varying spacing between the first and second conductors. For example, each of the first and second conductors may have no cuts or gaps (no segmented conductors) or one or more cuts or gaps (segmented conductors) at various locations along the conductive pathway.

Distributed capacitance (DCAP), as used herein, represents a capacitance exhibited between conductors that grows evenly and uniformly along the length of the conductors and is void of discrete or lumped capacitive components and discrete or lumped inductive components. In the examples herein, the capacitance may grow in a uniform manner along the length of the first and second conductors <NUM>, <NUM>.

A dielectric material <NUM> encapsulates and separates the first and second conductors <NUM>, <NUM>. The dielectric material <NUM> may be selectively chosen to achieve a select distributive capacitance. The dielectric material <NUM> may be based on a desired permittivity ε to vary the effective capacitance of the loop portion. For example, the dielectric material <NUM> may be air, rubber, plastic, or any other dielectric material. In one example, the dielectric material may be polytetrafluoroethylene (pTFE). For example, the dielectric material <NUM> may be an insulating material surrounding the parallel conductive elements of the first and second conductors <NUM>, <NUM>. In an example useful for understanding the invention, the first and second conductors <NUM>, <NUM> may be twisted upon one another to form a twisted pair cable. As another example, the dielectric material <NUM> may be plastic material. In an example useful for understanding the invention, the first and second conductors <NUM>, <NUM> may form a coaxial structure in which the plastic dielectric material <NUM> separates the first and second conductors.

As another example, the first and second conductors may be configured as planar strips.

The coupling electronics portion <NUM> is operably and communicatively coupled to the RF driver unit <NUM>, the data acquisition unit <NUM>, controller unit <NUM>, and/or data processing unit <NUM> to allow the RF coil <NUM> to transmit and/or receive RF signals. In the illustrated embodiment, the coupling electronics portion <NUM> includes a signal interface <NUM> configured to transmit and receive the RF signals. The signal interface <NUM> may transmit and receive the RF signals via a cable. The cable may be a <NUM>-conductor triaxial cable having a center conductor, an inner shield, and an outer shield. The center conductor is connected to the RF signal and pre-amp control (RF), the inner shield is connected to ground (GND), and the outer shield is connected to the multi-control bias (diode decoupling control) (MC_BIAS). A 10V power connection may be carried on the same conductor as the RF signal.

As explained above with respect to <FIG>, the coupling electronics portion <NUM> includes a decoupling circuit, impedance inverter circuit, and pre-amplifier. As illustrated in <FIG>, the decoupling circuit includes a decoupling diode <NUM>. The decoupling diode <NUM> may be provided with voltage from MC_BIAS, for example, in order to turn decoupling diode <NUM> on. When on, decoupling diode <NUM> causes conductor <NUM> to short with conductor <NUM>, thus causing the coil be off-resonance and hence decouple the coil during a transmit operation, for example.

The impedance inverter circuit includes a plurality of inductors, including first inductor 370a, second inductor 370b, and third inductor 370c; a plurality of capacitors, including first capacitor 372a, a second capacitor 372b, a third capacitor 372c, and a fourth capacitor 372d; and a diode <NUM>. The impedance inverter circuit includes matching circuitry and an input balun. As shown, the input balun is a lattice balun that comprises first inductor 370a, second inductor 370b, first capacitor 372a, and second capacitor 372b. In one example, diode <NUM> limits the direction of current flow to block RF receive signals from proceeding into decoupling bias branch (MC_BIAS).

The pre-amplifier <NUM> may be a low input impedance pre-amplifier that is optimized for high source impedance by the impedance matching circuitry. The pre-amplifier may have a low noise reflection coefficient, γ, and a low noise resistance, Rn. In one example, the pre-amplifier may have a source reflection coefficient of γ substantially equal to <NUM> and a normalized noise resistance of Rn substantially equal to <NUM> in addition to the low noise figure. However, γ values substantially equal to or less than <NUM> and Rn values substantially equal to or less than <NUM> are also contemplated. With the pre-amplifier having the appropriate γ and Rn values, the pre-amplifier provides a blocking impedance for RF coil <NUM> while also providing a large noise circle in the context of a Smith Chart. As such, current in RF coil <NUM> is minimized, the pre-amplifier is effectively noise matched with RF coil <NUM> output impedance. Having a large noise circle, the pre-amplifier yields an effective SNR over a variety of RF coil impedances while producing a high blocking impedance to RF coil <NUM>.

In some examples, the pre-amplifier <NUM> may include an impedance transformer that includes a capacitor and an inductor. The impedance transformer may be configured to alter the impedance of the pre-amplifier to effectively cancel out a reactance of the pre-amplifier, such as capacitance caused by a parasitic capacitance effect. Parasitic capacitance effects can be caused by, for example, a PCB layout of the pre-amplifier or by a gate of the pre-amplifier. Further, such reactance can often increase as the frequency increases. Advantageously, however, configuring the impedance transformer of the pre-amplifier to cancel, or at least minimize, reactance maintains a high impedance (i.e. a blocking impedance) to RF coil <NUM> and an effective SNR without having a substantial impact on the noise figure of the pre-amplifier. The lattice balun described above may be a non-limiting example of an impedance transformer.

In examples, the pre-amplifier described herein may a low input pre-amplifier. For example, in some embodiments, a "relatively low" input impedance of the preamplifier is less than approximately <NUM> ohms at resonance frequency. The coil impedance of the RF coil <NUM> may have any value, which may be dependent on coil loading, coil size, field strength, and/or the like. Examples of the coil impedance of the RF coil <NUM> include, but are not limited to, between approximately <NUM> ohms and approximately <NUM> ohms at <NUM>. 5T magnetic field strength, and/or the like. The impedance inverter circuitry is configured to transform the coil impedance of the RF coil <NUM> into a relatively high source impedance. For example, in some embodiments, a "relatively high" source impedance is at least approximately <NUM> ohms and may be greater than <NUM> ohms.

The impedance transformer may also provide a blocking impedance to the RF coil <NUM>. Transformation of the coil impedance of the RF coil <NUM> to a relative high source impedance may enable the impedance transformer to provide a higher blocking impedance to the RF coil <NUM>. Exemplary values for such higher blocking impedances include, for example, a blocking impedance of at least <NUM> ohms, and at least <NUM> ohms.

<FIG> is a schematic of an RF coil <NUM> and coupling electronics portion <NUM> according to another embodiment. The RF coil of <FIG> is a non-limiting example of the RF coil and coupling electronics of <FIG>, and as such includes a loop portion <NUM> and coupling electronics portion <NUM>. The coupling electronics allows the RF coil to transmit and/or receive RF signals when driven by the data acquisition unit <NUM> (shown in <FIG>). The RF coil <NUM> includes a first conductor <NUM> in parallel with a second conductor <NUM>. At least one of the first and second conductors <NUM>, <NUM> are elongated and continuous.

In the illustrated embodiment, the first and second conductors <NUM>, <NUM> are shaped into a loop portion that terminates to an interface. But in other embodiments, other shapes are possible. For example, the loop portion may be a polygon, shaped to conform the contours of a surface (e.g., housing), and/or the like. The loop portion defines a conductive pathway along the first and second conductors <NUM>, <NUM>. The first and second conductors <NUM>, <NUM> are void of any discrete or lumped capacitive or inductive components along an entire length of the conductive pathway. The first and second conductors <NUM>, <NUM> are uninterrupted and continuous along an entire length of the loop portion. The loop portion may also include loops of varying gauge of stranded or solid conductor wire, loops of varying diameters with varying lengths of the first and second conductors <NUM>, <NUM>, and/or loops of varying spacing between the first and second conductors. For example, each of the first and second conductors may have no cuts or gaps (no segmented conductors) or one or more cuts or gaps (segmented conductors) at various locations along the conductive pathway.

The first and second conductors <NUM>, <NUM> have a distributed capacitance along the length of the loop portion (e.g., along the length of the first and second conductors <NUM>, <NUM>). The first and second conductors <NUM>, <NUM> exhibit a substantially equal and uniform capacitance along the entire length of the loop portion. Distributed capacitance (DCAP), as used herein, represents a capacitance exhibited between conductors that grows evenly and uniformly along the length of the conductors and is void of discrete or lumped capacitive components and discrete or lumped inductive components. In the examples herein, the capacitance may grow in a uniform manner along the length of the first and second conductors <NUM>, <NUM>. At least one of the first and second conductors <NUM>, <NUM> are elongated and continuous. In the illustrated embodiment, both the first and second conductors <NUM>, <NUM> are elongated and continuous. But in other embodiments, only one of the first or second conductors <NUM>, <NUM> may be elongated and continuous. The first and second conductors <NUM>, <NUM> form continuous distributed capacitors. The capacitance grows at a substantially constant rate along the length of the conductors <NUM>, <NUM>. In the illustrated embodiment, the first and second conductors <NUM>, <NUM> form elongated continuous conductors that exhibits DCAP along the length of the first and second conductors <NUM>, <NUM>. The first and second conductors <NUM>, <NUM> are void of any discrete capacitive and inductive components along the entire length of the continuous conductors between terminating ends of the first and second conductors <NUM>, <NUM>. For example, the first and second conductors <NUM>, <NUM> do not include any discrete capacitors, nor any inductors along the length of the loop portion.

A dielectric material <NUM> separates the first and second conductors <NUM>, <NUM>. The dielectric material <NUM> may be selectively chosen to achieve a select distributive capacitance. The dielectric material <NUM> may be based on a desired permittivity ε to vary the effective capacitance of the loop portion. For example, the dielectric material <NUM> may be air, rubber, plastic, or any other dielectric material. In one example, the dielectric material may be polytetrafluoroethylene (pTFE). For example, the dielectric material <NUM> may be an insulating material surrounding the parallel conductive elements of the first and second conductors <NUM>, <NUM>. In an example useful for understanding the invention, the first and second conductors <NUM>, <NUM> may be twisted upon one another to form a twisted pair cable. As another example, the dielectric material <NUM> may be a plastic material. In an example useful for understanding the invention, the first and second conductors <NUM>, <NUM> may form a coaxial structure in which the plastic dielectric material <NUM> separates the first and second conductors <NUM>, <NUM>. As another example, the first and second conductors <NUM>, <NUM> may be configured as planar strips.

The first conductor <NUM> includes a first terminating end <NUM> and a second terminating end <NUM> that terminates at the interface. The first terminating end <NUM> is coupled to the coupling electronics portion <NUM>. The first terminating end <NUM> may also be referred to herein as a "drive end. " The second terminating end <NUM> is also referred to herein as a "second drive end.

The second conductor <NUM> includes a first terminating end <NUM> and a second terminating end <NUM> that terminates at the interface. The first terminating end <NUM> is coupled to the coupling electronics portion <NUM>. The first terminating end <NUM> may also be referred to herein as a "drive end. " The second terminating end <NUM> is also referred to herein as a "second drive end.

The loop portion <NUM> of the RF coil <NUM> is coupled to coupling electronics portion <NUM>. The coupling electronics portion <NUM> may be the same coupling electronics described above with respect to <FIG> and <FIG>, and hence like reference numbers are given to like components and further description is dispensed with.

As appreciated by <FIG> and <FIG>, the two parallel conductors comprising the loop portion of an RF coil may each be continuous conductors, as illustrated in <FIG>, or one or both of the conductors may be non-continuous, as illustrated in <FIG>. For example, both conductors shown in <FIG> may include cuts, resulting in each conductor being comprised of two segments. The resulting space between conductor segments may be filled with the dielectric material that encapsulates and surrounds the conductors. The two cuts may be positioned at different locations, e.g., one cut at <NUM>° and the other cut at <NUM>° (relative to where the loop portion interfaces with the coupling electronics). By including discontinuous conductors, the resonance frequency of the coil may be adjusted relative to a coil that includes continuous conductors. In an example, an RF coil that includes two continuous parallel conductors encapsulated and separated by a dielectric, the resonance frequency may be a smaller, first resonance frequency. If that RF coil instead includes one discontinuous conductor (e.g., where one of the conductors is cut and filled with the dielectric material) and one continuous conductor, with all other parameters (e.g., conductor wire gauge, loop diameter, spacing between conductors, dielectric material) being the same, the resonance frequency of the RF coil may be a larger, second resonance frequency. In this way, parameters of the loop portion, including conductor wire gauge, loop diameter, spacing between conductors, dielectric material selection and/or thickness, and conductor segment number and lengths, may be adjusted to tune the RF coil to a desired resonance frequency.

<FIG> shows a cross-sectional view of a distributed capacitance loop portion <NUM> of an example RF coil. As appreciated by <FIG>, loop portion <NUM> includes first wire conductor <NUM> and second wire conductor <NUM> surrounded by and encapsulated in dielectric material <NUM>. Each wire conductor may have a suitable cross-sectional shape, herein a circular cross-sectional shape. However, other cross-sectional shapes for the wire conductors are possible, such as elliptical, cylindrical, rectangular, triangular, hexagonal, etc. The wire conductors may be separated by a suitable distance, and the distance separating the conductors as well as the diameters of the wire conductors may be selected to achieve a desired capacitance. Further, each of the first wire conductor <NUM> and second wire conductor <NUM> may be a seven conductor stranded wire (e.g., comprised of seven stranded wires), but solid conductors may also be used instead of stranded wire. Stranded wire may provide more flexibility relative to solid conductors, at least in some examples.

The RF coils presented above with respect to <FIG> may be utilized in order to receive MR signals during an MR imaging session. As such, the RF coils of <FIG> may be non-limiting examples of RF coil unit <NUM> of <FIG> and may be configured to be coupled to a downstream component of the MRI system, such as a processing system. The RF coils of <FIG> may be present in an array of RF coils having various configurations. <FIG>, described in more detail below, illustrate various embodiments for an anterior RF coil array that may include one or more of the RF coils described above with respect to <FIG>. The anterior RF coil array may be a high density (referring to the number of coil elements) anterior array or a high definition (referring to image resolution) anterior array (HDAA).

<FIG> illustrates a posterior RF coil array according to embodiments of the disclosure. <FIG> includes a first schematic drawing <NUM> of the posterior RF coil array while a normal patient is being imaged. First schematic drawing <NUM> includes the posterior RF coil array <NUM> housed within a deformable material enclosure <NUM>. The RF coil array <NUM> comprises two layers: a top soft layer (the RF coil array <NUM>) and a bottom hard layer (the MRI system table interface <NUM>). The top soft layer includes the RF coil array housed in a soft block of deformable material sized for coverage of the entire upper body on the surface, with the flexible RF coil array inside, arranged as close to the top surface as possible. The deformable material of deformable material enclosure <NUM> may comprise foam, memory foam, expanded foam, polyurethane foam, gels such as hydrogel, cells of water (similar to a waterbed), or other suitable deformable material. When the patient lies on the RF coil array/deformable material enclosure, the patient will sink into the deformable material, such as a memory foam mattress, and the RF coil array may conform to the patient's unique shape, and thus be right up against the patient's body.

The RF coil array and MRI system table interface through wired (connector) or wireless (inductive coupling) methods, ensuring connectivity between the RF coil array and the MRI system. The RF coil loops of the RF coil array include coupling electronics for each RF coil loop of the RF coil array, e.g., decoupling circuitry, impedance matching, and a pre-amplifier, as well as baluns or other common mode traps. The coupling electronics may be in the form of miniaturized PCBs that are coupled to the RF coil loops. A coil-interfacing cable extends from each coupling electronics PCB and may include baluns or common mode traps similar to those described with respect to <FIG> to an interfacing connector and a MRI system table interface.

The advantages of the design include improved image quality by the improved proximity of the coil array to the body, accommodating varying as well as pathological anatomy, imaging the cervical spine, improvement in patient comfort, ease of use for technologists.

Thus, as explained above, when the patient lies on the RF coil array, the deformable material (which may be in the form of a mattress in one example) deforms due to the patient's weight, and conforms to the patient's anatomy, regardless of the anatomy's unique topology or sizing. The flexible RF coil loops inside the deformable material deforms along with the deformable material, keeping the RF coil loops relatively proximate and normal to the patient's body, which aids in obtaining superior image quality.

<FIG> also includes a second schematic drawing <NUM> of the posterior RF coil array while a patient with kyphosis is being imaged. Second schematic drawing <NUM> includes the posterior RF coil array <NUM> housed within a deformable material enclosure <NUM>. The RF coil array <NUM> comprises two layers: a top soft layer (the RF coil array <NUM>) and a bottom hard layer (the MRI system table interface <NUM>). The posterior RF coil array of the present disclosure conforms to pathological anatomy, such as kyphosis, lordosis, and scoliosis, improving the imaging quality in these cases, as illustrated by schematic drawing <NUM> of <FIG>, which shows the regions of high curvature of the patient's anatomy still maintaining close contact with the RF coil array. The posterior RF coil array of the present disclosure also conforms to the cervical spine, a region that existing systems do not typically accommodate well, but is of high importance in trauma cases. The posterior RF coil array may provide improved image quality due to the RF coils being proximate to the patient's body, along the entire length of the RF coil array, unlike in rigid coil designs. Furthermore, dampening of vibration and movement provided by the deformable material may help improve image quality. Further still, the deformable mattress-like RF coil array may improve patient comfort and allow for a wide array of patient body types and shapes to be accommodated for maximum versatility. The conforming mattress of deformable material as shown in <FIG> lessens the effect of the patient's body tissue spreading out over the MR table, giving a better image of the anatomy at rest in its natural state. The simplicity of the RF coil array configuration makes the array modular to accommodate new and existing technologies, such as going cable-less, as well as co-residing with system coils and other body coils. The posterior RF coil array of the present disclosure may also improve ease of use for technologists - the technologist may place the coil on the table and simply instruct the patient to lie on it.

<FIG> illustrates an example RF coil array <NUM> that may be implemented as a conforming posterior RF coil array. The illustrated RF coil array <NUM> includes twelve rows of RF coils with each row comprising five RF coils for a <NUM>-channel posterior RF coil array. Each RF coil including a RF coil loop <NUM> with a coupling electronics PCB <NUM> coupled to each RF coil loop <NUM>. The RF coil loops <NUM> are arranged such that the coupling electronics PCBs <NUM> are all oriented towards the center of the RF coil array, so that the coil-interfacing cables <NUM> extending from each coupling electronics PCB <NUM> extend down toward the center of the array. There is a coil-interfacing cable <NUM> extending from each coupling electronics PCB. Each of these coil-interfacing cables are bundled together to form at least two cable assemblies <NUM>. <NUM> including baluns <NUM>, <NUM> on the coil interfacing cables and at least two cable assemblies. The cable assemblies connect to two interfacing connectors730, <NUM> at one end of the posterior RF coil array to interface with at least two RF coil array interfacing cables (not shown).

<FIG> shows an example conforming posterior RF coil array <NUM> including <NUM> RF coils <NUM> embedded within grooves of a deformable material <NUM>, such as a foam, memory foam, expanded foam, polyurethane foam, gels such as hydrogel, cells of water (similar to a waterbed), or other suitable deformable material. Each RF coil of the array is a non-limiting example of the RF coil loops described above with respect to <FIG> and as such includes an integrated capacitor coil loop <NUM> and a coupling electronics unit <NUM> directly coupled to the coil loop. In some examples, coil interfacing cables <NUM> and/or cable assemblies <NUM>, <NUM> of the array may include continuous/contiguous baluns throughout their length to eliminate the cylinder-shaped lumpy baluns. Thus, even when embedded within grooves of a deformable material, each RF coil maintains flexibility in multiple dimensions.

Thus, RF coil array <NUM> includes twelve rows of five RF coils, including a first row, a second row, a third row, a fourth row, a fifth row, a sixth row, a seventh row, an eighth row, a ninth row, a tenth row, an eleventh row, and a twelfth row. Each row includes five RF coils and associated coupling electronics PCBs. The RF coil and coupling electronics arrangement of first row will be described in more detail below, but it is to be understood that each other row includes a similar configuration and hence additional description of each row is dispensed with.

First row includes five RF coils, and each RF coil includes a loop portion comprised of distributed capacitance parallel wire conductors and a coupling electronics unit in the form of a miniaturized PCB supporting decoupling circuitry, impedance matching circuitry, and a pre-amplifier. Each RF coil loop and coupling electronics unit may be a non-limiting example of the loop portion and coupling electronics portion described above with respect to <FIG> and <FIG>.

Accordingly, a loop portion of a first RF coil <NUM> is coupled to a first coupling electronics unit <NUM>, a loop portion of a second RF coil is coupled to a second coupling electronics unit, a loop portion of a third RF coil is coupled to a third coupling electronics unit, a loop portion of a fourth RF coil is coupled to a fourth coupling electronics unit, and a loop portion of a fifth RF coil is coupled to a fifth coupling electronics unit.

Each coupling electronics unit may be coupled to its respective RF coil loop in such a manner that each coupling electronics unit is orientated toward the center of the RF coil array <NUM>. For example, first coupling electronics unit and second coupling electronics unit may each be coupled to a right side of a respective RF coil loop, fourth coupling electronics unit and fifth coupling electronics unit may each be coupled to a left side of a respective RF coil loop, and third coupling electronics unit may be coupled to a bottom side of its RF coil loop.

By orientating each coupling electronics unit toward the center of the array, the coil-interfacing cable from each coupling electronics unit to the cable assemblies <NUM>, <NUM> and ultimately to RF coil array interfacing cables (not shown) may be simplified. As shown in <FIG>, each coupling electronics unit <NUM> includes a coil-interfacing cable <NUM> extending therefrom to the cable assembly <NUM> or <NUM>, and to at least two interfacing connectors <NUM>, <NUM>. Each coil-interfacing cable form the first row through the sixth row joins into cable assembly <NUM> and interfacing connector <NUM>. Each coil-interfacing cable from the seventh row through the twelfth row joins into cable assembly <NUM> and interfacing connector <NUM>.

A plurality of baluns <NUM>, <NUM> may be distributed along the coil-interfacing cables <NUM> and the cable assemblies <NUM>, <NUM>. For example, rather than including lumped baluns, each coil-interfacing cable (or cable assembly) may be encased in a continguous/continuous distributed or flutter balun, such as those described with respect to <FIG>.

The coil-interfacing cables may include one or more baluns. In traditional coil-interfacing cables, baluns are positioned with a relatively high density, as high dissipation/voltages may develop if the balun density is too low or if baluns are positioned at an inappropriate location. However, this dense placement may adversely affect flexibility, cost, and performance. As such, the one or more baluns in the coil-interfacing cable may be continuous baluns to ensure no high currents or standing waves, independent of positioning. The continuous baluns may be distributed, flutter, and/or butterfly baluns. Additional details regarding the coil-interfacing cable and baluns will be presented below with respect to <FIG>.

<FIG> shows an exploded view of an example posterior RF coil array <NUM> that includes both the loop portions of the RF coils and the coupling electronics units together in the same deformable housing. The posterior RF coil array includes a coil array <NUM>, herein including <NUM> RF coils each having a miniaturized electronics PCB, as described above with respect to <FIG>. Each coil of the RF coil array is coupled to a section of flexible fabric material <NUM>, via stitching or other attachment mechanism, or embedded into grooves formed in a foam material. Sandwiching the coil array and attached material is an inner enclosure comprising a first section <NUM> and second section <NUM> of material. The material of the inner enclosure may be NOMEX® or other suitable material that provides padding, spacing, and/or flame-retardant properties. An outer enclosure comprising a first section <NUM> and a second section <NUM> of material sandwiches the coil array, attached material, and inner enclosure. The material of the first section <NUM> of the outer enclosure may be comprised of a biocompatible material that is cleanable, thus enabling use of the RF coil array in clinical contexts. The second section <NUM> of material of the outer enclosure may be comprised of the deformable material, such as memory foam. In this way, the RF coils may be positioned on a top surface of a deformable, mattress-like support. The RF coils may flex and deform as needed to accommodate patient anatomy. In another embodiment, the first section <NUM> and second section <NUM> of material may be eliminated from the posterior RF coil array, such that the section of flexible fabric material <NUM> is sandwiched between a first section <NUM> and second section <NUM> of padded or deformable material. In yet another embodiment, the coil array <NUM> may be embedded within a padded or deformable material, such as memory foam. The coil array illustrated in <FIG> may be placed on an MR table, integrated within the MR table, as described above in order to perform MR imaging.

<FIG> shows a cross-sectional view of another embodiment of a posterior RF coil array <NUM>. Posterior RF coil array <NUM> includes a first, outer layer <NUM>. Outer layer <NUM> may be comprised of one or more sheets of a flexible fabric material, such as DARTEX® material. Outer layer <NUM> may have a first thickness <NUM>. In one example, first thickness <NUM> may be <NUM> or less. Posterior RF coil array <NUM> includes a second, inner layer <NUM>. Inner layer <NUM> may be comprised of a compressible material such as memory foam and may have a second thickness <NUM>. Second thickness <NUM> may be greater than first thickness <NUM> and may be <NUM>, in one example.

Inner layer <NUM> may have a plurality of annular grooves each configured to accommodate an RF coil. As shown in <FIG>, inner layer <NUM> includes a first annular groove <NUM>. First annular groove <NUM> accommodates first RF coil <NUM>. For example, first annular groove <NUM> may be a cut, indentation or groove formed in inner layer <NUM> that is sized to fit first RF coil <NUM>. When first RF coil <NUM> is positioned in first annular groove <NUM>, the material comprising inner layer <NUM> may surround the loop portion of first RF coil <NUM>, therein embedding the loop portion of first RF coil <NUM> in the second inner layer. Similar configurations are present for each RF coil of posterior RF coil array <NUM>. Thus, inner layer <NUM> includes a second annular groove <NUM> (accommodating second RF coil <NUM>), a third annular groove <NUM> (accommodating third RF coil <NUM>), a fourth annular groove <NUM> (accommodating fourth RF coil <NUM>), and a fifth annular groove <NUM> (accommodating fifth RF coil <NUM>). While not shown in <FIG>, a plurality of rectangular grooves may be present in inner layer <NUM>, each adjacent a respective annular groove. The rectangular grooves may accommodate the coupling electronics portion of each RF coil.

Each annular groove (and hence each RF coil) may be present at a top portion of inner layer <NUM>, and thus a top surface of each RF coil may not be covered by the material comprising inner layer <NUM>. However, outer layer <NUM> may cover the top surface of each RF coil. Each of outer layer <NUM> and inner layer <NUM> may be compressible, allowing the RF coils embedded therein to conform to a shape of the subject positioned on the posterior RF coil array.

While <FIG> was described with respect to a posterior RF coil array, other RF coil arrays described herein may have a similar configuration. As such, each RF coil array described herein may include a plurality of RF coils embedded in an inner layer of deformable material and covered with an outer layer of compressible material. However, in some examples, the RF coils described above may not be embedded in a compressible material as described with respect to <FIG>, but may instead be stitched or otherwise coupled to or between one or more layers of flexible material, such as DARTEX®.

One example clinical context in which the disclosed RF coil arrays may be utilized is a posterior RF coil array. Traditional posterior arrays may be rigid, as the arrays are positioned under the surface of the rigid MR table, meaning that they may be far away from relevant regions of a patient's unique anatomy.

For patients with spinal deformities, such as kyphosis, hyperlordosis, scoliosis, et cetera, the problems are exaggerated as the spine curves further away from the surface of the table and RF coil array, and the hard surface may cause the patient discomfort during long imaging sessions.

Thus, the RF coils described herein may be incorporated into a posterior RF coil array that is housed in a deformable and flexible material, thus bringing the RF coil loop closer to the subject anatomy. In doing so, the issues of widely varying patient anatomy, as well as extending coverage to cervical spine, may be addressed while improving patient comfort.

The conductor wires and coil loops used in the RF coil or RF coil array may be manufactured in any suitable manner to get the desired resonance frequency for a desired RF coil application. The desired conductor wire gauge, such as <NUM> or <NUM> American Wire Gauge (AWG) or any other desired wired gauge may be paired with a parallel conductor wire of the same gauge and encapsulated with a dielectric material using an extrusion process or a three-dimensional (3D) printing or additive manufacturing process. This manufacturing process may be environmentally friendly with low waste and low-cost.

Thus, the RF coil described herein includes a twin lead conductor wire loop encapsulated in a pTFE dielectric that may have no cuts or at least one cut in at least one of the two parallel conductor wires and a miniaturized coupling electronics PCB coupled to each coil loop (e.g., very small coupling electronics PCB approximately the size of <NUM><NUM> or smaller). The PCBs may be protected with a conformal coating or an encapsulation resin. In doing so, traditional components are eliminated and capacitance is "built in" the integrated capacitor (INCA) coil loops. Interactions between coil elements are reduced or eliminated. The coil loops are adaptable to a broad range of MR operating frequencies by changing the gauge of conductor wire used, spacing between conductor wires, loop diameters, loop shapes, and the number and placement of cuts in the conductor wires.

The RF coil loops described and illustrated herein are transparent in PET/MR applications, aiding dose management and signal-to-noise ratios (SNR). The miniaturized electronic PCB includes decoupling circuitry, impedance inverter circuitry with impedance matching circuitry and an input balun, and a pre-amplifier. The pre-amplifier sets new standards in coil array applications for lowest noise, robustness, and transparency. The pre-amplifier provides active noise cancelling to reduce current noise, boost linearity, and improve tolerance to varying coil loading conditions. Additionally, as explained in more detail below, a cable harness with baluns for coupling each of the miniaturized electronic feedthrough PCBs to the RF coil array connector that interfaces with the MRI system may be provided.

The RF coil described herein is exceptionally lightweight, and may weigh less than <NUM> grams per coil element versus <NUM> grams per coil element with General Electric Company's Geometry Embracing Method (GEM) suite of flexible RF coil arrays. For example, a <NUM>-channel RF coil array according to the disclosure may weigh less than <NUM>. The RF coil described herein is exceptionally flexible and durable as the coil is extremely simple with very few rigid components and allowing floating overlaps. The RF coil described herein is exceptionally low-cost, e.g., greater than a ten times reduction from current technology. For example, a <NUM>-channel RF coil array could be comprised of components and materials of less than $<NUM>. The RF coil described herein does not preclude current packaging or emerging technologies and could be implemented in RF coil arrays that do not need to be packaged or attached to a former, or implemented in RF coil arrays that are attached to flexible formers as flexible RF coil arrays or attached to rigid formers as rigid RF coil arrays.

The RF coil array may be supported by fabric and housed in another flexible material enclosure, but the RF coil array remains flexible in multiple dimensions and the RF coils may not be fixedly connected to one another. In some examples, the RF coils may be slidably movable relative to each other, such that varying amounts of overlap among RF coils is acceptable.

As mentioned previously, the RF coil array of the present disclosure may be coupled to a RF coil array interfacing cable that includes contiguous, distributed baluns or common-mode traps in order to minimize high currents or standing waves, independent of positioning. High stress areas of the RF coil array interfacing cable may be served by several baluns. Additionally, the thermal load maybe shared through a common conductor. The inductance of the central path and return path of the RF coil array interfacing cables are not substantially enhanced by mutual inductance, and therefore are stable with geometry changes. Capacitance is distributed and not substantially varied by geometry changes. Resonator dimensions are ideally very small, but in practice may be limited by blocking requirements, electric and magnetic field intensities, local distortions, thermal and voltage stresses, etc..

<FIG> illustrates a block schematic diagram of a continuous common mode trap assembly <NUM> formed in accordance with various embodiments. The common mode trap assembly <NUM> may be configured as a transmission cable <NUM> configured for transmission of signals between a processing system <NUM> and a RF coil array <NUM> of an MRI system. Transmission cable <NUM> is a non-limiting example of a RF coil array interfacing cable <NUM> of <FIG>, processing system <NUM> is a non-limiting example of controller unit <NUM> of <FIG>, and RF coil array <NUM> is a non-limiting example of a plurality of RF coils <NUM> and coupling electronics <NUM> of <FIG>.

In the illustrated embodiment, the transmission cable <NUM> (or RF coil array interfacing cable) includes a central conductor <NUM> and plural common mode traps <NUM>, <NUM>, <NUM>. It may be noted that, while the common mode traps <NUM>, <NUM>, and <NUM> are depicted as distinct from the central conductor <NUM>, in some embodiments, the common mode traps <NUM>, <NUM>, <NUM> may be integrally formed with or as a part of the central conductor <NUM>.

The central conductor <NUM> in the illustrated embodiment has a length <NUM>, and is configured to transmit a signal between the RF coil array <NUM> and at least one processor of an MRI system (e.g., processing system <NUM>). The central conductor <NUM> may include one or more of a ribbon conductor, a wire conductor, a planar strip conductor, or a coaxial cable conductor, for example. The length <NUM> of the depicted central conductor <NUM> extends from a first end of the central conductor <NUM> (which is coupled to the processing system <NUM>) to a second end of the central conductor <NUM> (which is coupled to the RF coil array <NUM>). In some embodiments, the central conductor may pass through a central opening of the common mode traps <NUM>, <NUM>, <NUM>.

The depicted common mode traps <NUM>, <NUM>, <NUM> (which may be understood as cooperating to form a common mode trap unit <NUM>), as seen in <FIG>, extend along at least a portion of the length <NUM> of the central conductor <NUM>. In the illustrated embodiment, common mode traps <NUM>, <NUM>, <NUM> do not extend along the entire length <NUM>. However, in other embodiments, the common mode traps <NUM>, <NUM>, <NUM> may extend along the entire length <NUM>, or substantially along the entire length <NUM> (e.g., along the entire length <NUM> except for portions at the end configured to couple, for example, to a processor or RF coil array). The common mode traps <NUM>, <NUM>, <NUM> are disposed contiguously. As seen in <FIG>, each of the common mode traps <NUM>, <NUM>, <NUM> is disposed contiguously to at least one other of the common mode traps <NUM>, <NUM>, <NUM>. As used herein, contiguous may be understood as including components or aspects that are immediately next to or in contact with each other. For example, contiguous components may be abutting one another. It may be noted that in practice, small or insubstantial gaps may be between contiguous components in some embodiments. In some embodiments, an insubstantial gap (or conductor length) may be understood as being less than <NUM>/<NUM>th of a wavelength of a transmit frequency in free space. In some embodiments, an insubstantial gap (or conductor length) may be understood as being two centimeters or less. Contiguous common mode traps, for example, have no (or insubstantial) intervening gaps or conductors therebetween that may be susceptible to induction of current from a magnetic field without mitigation provided by a common mode trap.

For example, as depicted in <FIG>, the common mode trap <NUM> is contiguous to the common mode trap <NUM>, the common mode trap <NUM> is contiguous to the common mode trap <NUM> and the common mode trap <NUM> (and is interposed between the common mode trap <NUM> and the common mode trap <NUM>), and the common mode trap <NUM> is contiguous to the common mode trap <NUM>. Each of the common mode traps <NUM>, <NUM>, <NUM> are configured to provide an impedance to the receive transmitter driven currents of an MRI system. The common mode traps <NUM>, <NUM>, <NUM> in various embodiments provide high common mode impedances. Each common mode trap <NUM>, <NUM>, <NUM>, for example, may include a resonant circuit and/or one or more resonant components to provide a desired impedance at or near a desired frequency or within a target frequency range. It may be noted that the common mode traps <NUM>, <NUM>, <NUM> and/or common mode trap unit <NUM> may also be referred to as chokes or baluns by those skilled in the art.

In contrast to systems having separated discrete common mode traps with spaces therebetween, various embodiments (e.g., the common mode trap assembly <NUM>) have a portion over which common mode traps extend continuously and/or contiguously, so that there are no locations along the portion for which a common mode trap is not provided. Accordingly, difficulties in selecting or achieving particular placement locations of common mode traps may be reduced or eliminated, as all locations of interest may be included within the continuous and/or contiguous common mode trap. In various embodiments, a continuous trap portion (e.g., common mode trap unit <NUM>) may extend along a length or portion thereof of a transmission cable. The continuous mode trap portion may be formed of contiguously-joined individual common mode traps or trap sections (e.g., common mode traps <NUM>, <NUM>, <NUM>). Further, contiguous common mode traps may be employed in various embodiments to at least one of lower the interaction with coil elements, distribute heat over a larger area (e.g., to prevent hot spots), or help ensure that blocking is located at desired or required positions. Further, contiguous common mode traps may be employed in various embodiments to help distribute voltage over a larger area. Additionally, continuous and/or contiguous common mode traps in various embodiments provide flexibility. For example, in some embodiments, common mode traps may be formed using a continuous length of conductor(s) (e.g., outer conductors wrapped about a central conductor) or otherwise organized as integrally formed contiguous sections. In various embodiments, the use of contiguous and/or continuous common mode traps (e.g., formed in a cylinder) provide for a range of flexibility over which flexing of the assembly does not substantially change the resonant frequency of the structure, or over which the assembly remains on frequency as it is flexed.

It may be noted that the individual common mode traps or sections (e.g., common mode traps <NUM>, <NUM>, <NUM>) in various embodiments may be constructed or formed generally similarly to each other (e.g., each trap may be a section of a length of tapered wound coils), but each individual trap or section may be configured slightly differently than other traps or sections. For example, in some embodiments, each common mode trap <NUM>, <NUM>, <NUM> is tuned independently. Accordingly, each common mode trap <NUM>, <NUM>, <NUM> may have a resonant frequency that differs from other common mode traps of the same common mode trap assembly <NUM>.

Alternatively or additionally, each common mode trap may be tuned to have a resonant frequency near an operating frequency of the MRI system. As used herein, a common mode trap may be understood as having a resonant frequency near an operating frequency when the resonant frequency defines or corresponds to a band that includes the operating frequency, or when the resonant frequency is close enough to the operating frequency to provide on-frequency blocking, or to provide a blocking impedance at the operating frequency.

Further additionally or alternatively, each common mode trap may be tuned to have a resonant frequency below an operating frequency of the MRI system (or each common mode trap may be tuned to have resonant frequency above an operating frequency of the MRI system). With each trap having a frequency below (or alternatively, with each trap having a frequency above) the operating frequency, the risk of any of the traps canceling each other out (e.g., due to one trap having a frequency above the operating frequency and a different trap having a frequency below the operating frequency) may be eliminated or reduced. As another example, each common mode trap may be tuned to a particular band to provide a broadband common mode trap assembly.

In various embodiments, the common mode traps may have a two-dimensional (2D) or three-dimensional (3D) butterfly configuration to counteract magnetic field coupling and/or local distortions.

<FIG> is a perspective view of a RF coil array interfacing cable <NUM> including a plurality of continuous and/or contiguous common mode traps according to an embodiment of the disclosure. The RF coil array interfacing cable <NUM> includes an outer sleeve or shield <NUM>, a dielectric spacer <NUM>, an inner sleeve <NUM>, a first common mode trap conductor <NUM>, and a second common mode trap conductor <NUM>.

The first common mode trap conductor <NUM> is wrapped in a spiral about the dielectric spacer <NUM>, or wrapped in a spiral at a tapering distance from a central conductor (not shown) disposed within the bore <NUM> of the RF coil array interfacing cable <NUM>, in a first direction <NUM>. Further, the second common mode trap conductor <NUM> is wrapped in a spiral about the dielectric spacer <NUM>, or wrapped in a spiral at a tapering distance from the central conductor disposed within the bore <NUM>, in a second direction <NUM> that is opposite to the first direction <NUM>. In the illustrated embodiment, the first direction <NUM> is clockwise and the second direction <NUM> is counter-clockwise.

The conductors <NUM> and <NUM> of the RF coil array interfacing cable <NUM> may comprise electrically-conductive material (e.g., metal) and may be shaped as ribbons, wires, and/or cables, for example. In some embodiments, the counterwound or outer conductors <NUM> and <NUM> may serve as a return path for a current passing through the central conductor. Further, in various embodiments, the counterwound conductors <NUM> and <NUM> may cross each other orthogonally (e.g., a center line or path defined by the first common mode trap conductor <NUM> is perpendicular to a center line or path defined by the second common mode trap conductor <NUM> as the common mode trap conductors cross paths) to eliminate, minimize, or reduce coupling between the common mode trap conductors.

It may be further noted that in various embodiments the first common mode trap conductor <NUM> and the second common mode trap conductor <NUM> are loosely wrapped about the dielectric spacer <NUM> to provide flexibility and/or to reduce any binding, coupling, or variation in inductance when the RF coil array interfacing cable <NUM> is bent or flexed. It may be noted that the looseness or tightness of the counterwound outer conductors may vary by application (e.g., based on the relative sizes of the conductors and dielectric spacer, the amount of bending or flexing that is desired for the common mode trap, or the like). Generally, the outer or counterwound conductors should be tight enough so that they remain in the same general orientation about the dielectric spacer <NUM>, but loose enough to allow a sufficient amount of slack or movement during bending or flexing of the RF coil array interfacing cable <NUM> to avoid, minimize, or reduce coupling or binding of the counterwound outer conductors.

In the illustrated embodiment, the outer shielding <NUM> is discontinuous in the middle of the RF coil array interfacing cable <NUM> to expose a portion of the dielectric spacer <NUM> which in some embodiments is provided along the entire length of the RF coil array interfacing cable <NUM>. The dielectric spacer <NUM>, may be comprised, as a non-limiting example, of TEFLON® or another dielectric material. The dielectric spacer <NUM> functions as a capacitor and thus may be tuned or configured to provide a desired resonance. It should be appreciated that other configurations for providing capacitance to the RF coil array interfacing cable <NUM> are possible, and that the illustrated configurations are exemplary and non-limiting. For example, discrete capacitors may alternatively be provided to the RF coil array interfacing cable <NUM>.

Further, the RF coil array interfacing cable <NUM> includes a first post <NUM> and a second post (not shown) to which the first common mode trap conductor <NUM> and the second common mode trap conductor <NUM> are fixed. To that end, the first post <NUM> and the second post are positioned at the opposite ends of the common mode trap, and are fixed to the outer shielding <NUM>. The first post <NUM> and the second post ensure that the first and second common mode trap conductors <NUM> and <NUM> are positioned close to the outer shielding <NUM> at the ends of the RF coil array interfacing cable <NUM>, thereby providing a tapered butterfly configuration of the counterwound conductors as described further herein.

The tapered butterfly configuration includes a first loop formed by the first common mode trap conductor <NUM> and a second loop formed by the second common mode trap conductor <NUM>, arranged so that an induced current (a current induced due to a magnetic field) in the first loop and an induced current in the second loop cancel each other out. For example, if the field is uniform and the first loop and the second loop have equal areas, the resulting net current will be zero. The tapered cylindrical arrangement of the loops provide improved flexibility and consistency of resonant frequency during flexing relative to two-dimensional arrangements conventionally used in common mode traps.

Generally, a tapered butterfly configuration as used herein may be used to refer to a conductor configuration that is flux cancelling, for example including at least two similarly sized opposed loops that are symmetrically disposed about at least one axis and are arranged such that currents induced in each loop (or group of loops) by a magnetic field tends to cancel out currents induced in at least one other loop (or group of loops). For example, with reference to <FIG>, in some embodiments, counterwound conductors (e.g., conductors wound about a central member and/or axis in opposing spiral directions) may be spaced a distance radially from the central conductor <NUM> to form the common mode traps <NUM>, <NUM>, <NUM>. As depicted in <FIG>, the radial distance may be tapered towards the end of the common mode traps to reduce or altogether eliminate fringe effects. In this way, the common mode traps <NUM>, <NUM>, <NUM> may be continuously or contiguously positioned without substantial gaps therebetween.

The tapered spiral configuration of the common mode trap conductors described herein above is particularly advantageous when multiple common mode trap conductors are contiguously disposed in a common mode trap assembly. As an illustrative example, <FIG> is a perspective view of a RF coil array interfacing cable <NUM> including a plurality of continuous and/or contiguous common mode traps coupling an RF coil array <NUM> to a processing system <NUM>. RF coil array interfacing cable <NUM> includes a first common mode trap <NUM> and a second common mode trap <NUM> positioned adjacent to each other on a central conductor <NUM>.

The first common mode trap <NUM> includes a first common mode trap conductor <NUM> and a second common mode trap conductor <NUM> counterwound in a tapered spiral configuration. To that end, the first and second conductors <NUM> and <NUM> are fixed to posts <NUM> and <NUM>. It should be noted that the posts <NUM> and <NUM> are aligned on a same side of the common mode trap <NUM>.

Similarly, the second common mode trap <NUM> includes a third common mode trap conductor <NUM> and a fourth common mode trap conductor <NUM> counterwound in a tapered spiral configuration and fixed to posts <NUM> and <NUM>. It should be noted that the posts <NUM> and <NUM> are aligned on a same side of the common mode trap <NUM>.

As depicted, the common mode traps <NUM> and <NUM> are separated by a distance, thereby exposing the central conductor <NUM> in the gap <NUM> between the common mode traps. Due to the tapering spiral configuration of the common mode trap conductors of the common mode traps, the gap <NUM> can be minimized or altogether eliminated in order to increase the density of common mode traps in a common mode trap assembly without loss of impedance functions of the common mode traps. That is, the distance can be made arbitrarily small such that the common mode traps are in face-sharing contact, given the tapered spiral configuration.

It should be appreciated that while the RF coil array interfacing cable <NUM> includes two common mode traps <NUM> and <NUM>, in practice a RF coil array interfacing cable may include more than two common mode traps.

Further, the common mode traps <NUM> and <NUM> of the RF coil array interfacing cable <NUM> are aligned such that the posts <NUM>, <NUM>, <NUM>, and <NUM> are aligned on a same side of the RF coil array interfacing cable. However, in examples where cross-talk between the common mode traps may be possible, for example if the tapering of the counterwound conductors is more severe or steep, the common mode traps may be rotated with respect to one another to further reduce fringe effects and/or cross-talk between the traps.

Additionally, other common mode trap or balun configurations are possible. For example, the exterior shielding of each common mode trap may be trimmed such that the common mode traps can be overlapped or interleaved, thus increasing the density of the common mode traps.

Claim 1:
A posterior radio frequency (RF) coil assembly for a magnetic resonance imaging (MRI) system, comprising:
an RF coil array including a plurality of RF coils and a deformable material (<NUM>) housing the plurality of RF coils, each RF coil comprising a loop portion of distributed capacitance wire conductors and
a coupling electronics portion (<NUM>) coupled to the loop portion of the RF coil, wherein terminating ends of the loop portion terminate at an interface to the coupling electronics portion of the RF coil,
wherein each loop portion of distributed capacitance wire conductors comprises two parallel wire conductors (<NUM>, <NUM>) encapsulated and separated by a dielectric material (<NUM>) along an entire length of the loop portion between the terminating ends thereof such that a capacitance exhibited between the two wire conductors grows in an even and uniform manner along the length of the conductors,
wherein each loop portion is void of any capacitive and inductive lumped components along an entire length of the loop portion between the terminating ends thereof, and
wherein a capacitance of each loop portion is a function of a spacing between the respective two parallel wire conductors, a position and/or number of cuts on the two parallel wire conductors, and the dielectric material.