Radio frequency coil unit with pressure reservoir for magnetic resonance imaging

Various methods and systems are provided for radio frequency coil units for magnetic resonance imaging. In one example, a radio frequency (RF) coil unit for magnetic resonance imaging (MM) includes an outer layer forming an exterior of the RF coil unit, a pressure reservoir enclosed by the outer layer, wherein the pressure reservoir forms a sealed chamber, and an array of RF coil elements enclosed by the outer layer, wherein the array of RF coil elements is disposed outside of the sealed chamber of the pressure reservoir.

FIELD

Embodiments of the subject matter disclosed herein relate to radio frequency (RF) coil for magnetic resonance imaging (MRI), and more particularly, to surface coils with pressure reservoir for MRI.

BACKGROUND

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 B0. When an imaging subject is placed in the magnetic field B0, the nuclear spins associated with the hydrogen nuclei in the imaging subject become polarized such that the magnetic moments associated with these spins become preferentially aligned along the direction of the magnetic field B0, resulting in a small net magnetization along that axis. The hydrogen nuclei are excited by a radio frequency signal 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 a radio frequency (RF) signal. This RF signal (or MR signal) is detected by one or more RF coil units and is transformed into the image using reconstruction algorithms.

In order to detect the RF signals emitted by the body of the subject, an RF coil unit is often positioned proximate anatomical features to be imaged by the MM system. Quality of images produced by the MRI system is greatly influenced by how closely the RF coil unit conforms to the contours of the body of the subject during the image acquisition.

BRIEF DESCRIPTION

In one embodiment, a radio frequency (RF) coil unit for magnetic resonance imaging (MM) includes an outer layer forming an exterior of the RF coil unit, a pressure reservoir enclosed by the outer layer, wherein the pressure reservoir forms a sealed chamber, and an array of RF coil elements enclosed by the outer layer, wherein the array of RF coil elements is disposed outside of the sealed chamber of the pressure reservoir.

The drawings illustrate specific aspects of the described an RF coil unit with a pressure reservoir for MM. Together with the following description, the drawings demonstrate and explain the principles of the structures, methods, and principles described herein. In the drawings, the size of components may be exaggerated or otherwise modified for clarity. Well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the described components, systems and methods.

DETAILED DESCRIPTION

The following description relates to various embodiments for an RF coil unit. A magnetic resonance imaging (MM) system, such as the MRI system shown byFIG.1, may include an RF coil unit, such as the RF coil unit shown byFIG.2. The RF coil unit includes a plurality of flexible RF coil elements (which may be referred to herein as RF coils) and an adjustable pressure reservoir. The pressure reservoir is positioned within an interior formed by an outer layer of the RF coil unit and includes a plurality of openings shaped to receive coupling electronics of the flexible RF coil elements, as shown byFIG.3. An interior of the pressure reservoir is a sealed chamber that is fluidly isolated from the interior of the RF coil unit as shown byFIG.4, and a pressure within the interior of the pressure reservoir is adjustable via a fluid passage arranged to extend through the outer layer of the RF coil unit. The coupling electronics seat within the openings of the pressure reservoir, as shown byFIG.5. A pressure within the pressure reservoir may be adjusted via the fluid passage, in order to form the RF coil unit to a body of a subject to be imaged by the MRI system, as shown byFIGS.6-13. A loop portion of each RF coil element, as shown byFIG.14, may bend or flex with the pressure reservoir as the RF coil unit is formed to the body of the patient. As such, the loop portion of each RF coil element may be positioned closer to the body of the patient as the RF coil unit is formed to the body, and an imaging signal-to-noise ratio (SNR) of the RF coil unit may be increased.

The RF coil unit may be used to image a variety of different anatomical structures of a subject (e.g., a foot, shoulder, Cervical-spine, etc. of the subject) without the use of straps or other fixtures. Imaging anatomical structures via conventional RF coil units may be more difficult due to variance in the shape and size of the anatomical structures for different subjects (e.g., patients). However, by configuring the RF coil unit as described herein, the RF coil unit may be adapted to image a large variety of anatomical structures for patients of different shape and/or size. The pressure reservoir may maintain its shape while formed to the body by adjusting the pressure within the interior of the pressure reservoir. The flexibility of the RF coil elements maintains the RF coil elements close to the anatomy to be imaged. Further, because the RF coil unit may form to the body without the use of straps or other fasteners, cost of the RF coil unit may be reduced relative to conventional RF coil units that couple via straps or other fasteners and fixtures, and time to setup the RF coil unit for imaging may be reduced.

In some embodiments, the RF coil unit may be used as a stabilizer for pediatric scans by adjusting the pressure within the pressure reservoir to form the RF coil unit to the body. Motion of the subject during a scan (e.g., during imaging via the MRI system) may result in imaging artifacts. Improved rigidity of the RF coil unit during the scan may reduce imaging artifacts by reducing the likelihood of movement of the subject. As one example, adjusting the pressure (e.g., gas pressure) within the pressure reservoir may increase the rigidity of the RF coil unit by compressing plastic pellets (e.g., polystyrene pellets) disposed within the pressure reservoir. The increased rigidity of the RF coil unit may sufficiently reduce movement of the subject to be imaged during a pediatric scan (e.g., imaging of an infant). Because the pressure reservoir is positioned within the RF coil unit, the RF coil unit may maintain the position of the subject to be imaged without additional straps and/or other fasteners. Additionally, the outer layers of the RF coil unit may be formed of a soft, fabric material in order to increase patient comfort.

In this configuration, the RF coil unit is positioned against the body of the subject such that the RF coil elements are arranged between the body and the pressure reservoir. This arrangement may increase patient comfort and positions the RF coils elements close to the body. As a result, the SNR of images of the subject obtained by the MRI system via the RF coil unit may be increased.

In some embodiments, the RF coil unit may include eight (8) RF coil elements. The RF coil elements may be arranged along a layer of flexible cloth material, such as a fabric, with the pressure reservoir positioned against the loop portion of each RF coil element (e.g., such that the loop portions are positioned between the layer of cloth and the pressure reservoir). The RF coil elements each include a loop portion and a coupling electronics portion. The loop portion of each RF coil element may be fixed (e.g., stitched) to the cloth material. In other embodiments, the cloth material may be positioned between the loop portions and the pressure reservoir, with the loop portions fixed to the cloth material. The coupling electronics of the RF coil elements (e.g., feed boards) are placed through the openings extending through a thickness of the pressure reservoir to enable cables (e.g., electrical wires) coupled to the RF coil elements to be positioned at an opposing side of the pressure reservoir (e.g., a side opposite to the side at which the loop portions are positioned). Additional layer(s) made of, for example, fabric may be positioned at each side of the pressure reservoir. In some embodiments, the RF coil unit may include additional layers positioned at opposing sides of the coupling electronics and configured to cool the coupling electronics.

The coupling electronics of each RF coil element may be enclosed inside a respective plastic housing (e.g., each feed board of each RF coil element may be enclosed within a separate housing relative to each other feed board). In some embodiments, the housings of the coupling electronics may be shaped to seat within the openings of the pressure reservoir (e.g., each housing may have approximately a same shape as each opening of the pressure reservoir). For each RF coil element, MRI signals may be received (e.g., measured) by the loop portion and processed by the corresponding coupling electronics of the RF coil element. The coupling electronics may then transmit electronic signals to the MRI system via an output cable.

Turning now toFIG.1, a magnetic resonance imaging (MRI) apparatus10is illustrated. MRI apparatus10includes a magnetostatic field magnet unit12, a gradient coil unit13, an RF coil unit14, an RF body or volume coil unit15, a transmit/receive (T/R) switch20, an RF driver unit22, a gradient coil driver unit23, a data acquisition unit24, a controller unit25, a patient table or bed26, a data processing unit31, an operating console unit32, and a display unit33. In some embodiments, the RF coil unit14is a surface coil, which is a local coil typically placed proximate to the anatomy of interest of a subject16. Herein, the RF body coil unit15is a transmit coil that transmits RF signals, and the local surface RF coil unit14receives the MR signals. As such, the transmit body coil (e.g., RF body coil unit15) and the surface receive coil (e.g., RF coil unit14) are separate but electromagnetically coupled components. The MRI apparatus10transmits electromagnetic pulse signals to the subject16placed in an imaging space18with a static magnetic field formed to perform a scan for obtaining magnetic resonance signals from the subject16. One or more images of the subject16can be reconstructed based on the magnetic resonance signals thus obtained by the scan.

The magnetostatic field magnet unit12includes, for example, an annular superconducting magnet, which is mounted within a toroidal vacuum vessel. The magnet defines a cylindrical space surrounding the subject16and generates a constant primary magnetostatic field B0.

The MRI apparatus10also includes a gradient coil unit13that forms a gradient magnetic field in the imaging space18so as to provide the magnetic resonance signals received by the RF coil arrays with three-dimensional positional information. The gradient coil unit13includes three gradient coil systems, each of which generates a gradient magnetic field along one of three spatial axes perpendicular to each other, and generates a gradient field in each of a frequency encoding direction, a phase encoding direction, and a slice selection direction in accordance with the imaging condition. More specifically, the gradient coil unit13applies a gradient field in the slice selection direction (or scan direction) of the subject16, to select the slice; and the RF body coil unit15or the local RF coil arrays may transmit an RF pulse to a selected slice of the subject16. The gradient coil unit13also applies a gradient field in the phase encoding direction of the subject16to phase encode the magnetic resonance signals from the slice excited by the RF pulse. The gradient coil unit13then applies a gradient field in the frequency encoding direction of the subject16to frequency encode the magnetic resonance signals from the slice excited by the RF pulse.

The RF coil unit14is disposed, for example, to enclose the region to be imaged of the subject16. In some examples, the RF coil unit14may be referred to as the surface coil or the receive coil. In the static magnetic field space or imaging space18where a static magnetic field B0is formed by the magnetostatic field magnet unit12, the RF coil unit15transmits, based on a control signal from the controller unit25, an RF pulse that is an electromagnet wave to the subject16and thereby generates a high-frequency magnetic field B1. This excites a spin of protons in the slice to be imaged of the subject16. The RF coil unit14receives, as a magnetic resonance signal, the electromagnetic wave generated when the proton spin thus excited in the slice to be imaged of the subject16returns into alignment with the initial magnetization vector. In some embodiments, the RF coil unit14may transmit the RF pulse and receive the MR signal. In other embodiments, the RF coil unit14may only be used for receiving the MR signals, but not transmitting the RF pulse.

The RF body coil unit15is disposed, for example, to enclose the imaging space18, and produces RF magnetic field pulses orthogonal to the main magnetic field B0produced by the magnetostatic field magnet unit12within the imaging space18to excite the nuclei. In contrast to the RF coil unit14, which may be disconnected from the MRI apparatus10and replaced with another RF coil unit, the RF body coil unit15is fixedly attached and connected to the MRI apparatus10. Furthermore, whereas local coils such as the RF coil unit14can transmit to or receive signals from only a localized region of the subject16, the RF body coil unit15generally has a larger coverage area. The RF body coil unit15may be used to transmit or receive signals to the whole body of the subject16, for example. It should be appreciated that the particular use of the RF coil unit14and/or the RF body coil unit15depends on the imaging application.

The T/R switch20can selectively electrically connect the RF body coil unit15to the data acquisition unit24when operating in receive mode, and to the RF driver unit22when operating in transmit mode. Similarly, the T/R switch20can selectively electrically connect the RF coil unit14to the data acquisition unit24when the RF coil unit14operates in receive mode, and to the RF driver unit22when operating in transmit mode. When the RF coil unit14and the RF body coil unit15are both used in a single scan, for example if the RF coil unit14is configured to receive MR signals and the RF body coil unit15is configured to transmit RF signals, then the T/R switch20may direct control signals from the RF driver unit22to the RF body coil unit15while directing received MR signals from the RF coil unit14to the data acquisition unit24. The coils of the RF body coil unit15may be configured to operate in a transmit-only mode or a transmit-receive mode. The coils of the local RF coil unit14may be configured to operate in a transmit-receive mode or a receive-only mode.

The RF driver unit22includes 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 (e.g., RF coil unit15) and form a high-frequency magnetic field in the imaging space18. The RF driver unit22modulates, based on a control signal from the controller unit25and 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 unit15.

The gradient coil driver unit23drives the gradient coil unit13based on a control signal from the controller unit25and thereby generates a gradient magnetic field in the imaging space18. The gradient coil driver unit23includes three systems of driver circuits (not shown) corresponding to the three gradient coil systems included in the gradient coil unit13.

The data acquisition unit24includes 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 unit14. In the data acquisition unit24, the phase detector phase detects, using the output from the RF oscillator of the RF driver unit22as a reference signal, the magnetic resonance signals received from the RF coil unit14and 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 unit31.

The MRI apparatus10includes a table26for placing the subject16thereon. The subject16may be moved inside and outside the imaging space18by moving the table26based on control signals from the controller unit25.

The controller unit25includes 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 pre-determined 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 card. The controller unit25is connected to the operating console unit32and processes the operation signals input to the operating console unit32and furthermore controls the table26, RF driver unit22, gradient coil driver unit23, and data acquisition unit24by outputting control signals to them. The controller unit25also controls, to obtain a desired image, the data processing unit31and the display unit33based on operation signals received from the operating console unit32.

The operating console unit32includes user input devices such as a touchscreen, keyboard and a mouse. The operating console unit32is 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 unit25.

The data processing unit31includes 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 unit31is connected to the controller unit25and performs data processing based on control signals received from the controller unit25. The data processing unit31is also connected to the data acquisition unit24and generates spectrum data by applying various image processing operations to the magnetic resonance signals output from the data acquisition unit24.

The display unit33includes a display device and displays an image on the display screen of the display device based on control signals received from the controller unit25. The display unit33displays, for example, an image regarding an input item about which the operator inputs operation data from the operating console unit32. The display unit33also displays a two-dimensional (2D) slice image or three-dimensional (3D) image of the subject16generated by the data processing unit31.

Now referring toFIG.2, an RF coil unit200in an assembled configuration is shown, according to an exemplary embodiment. The RF coil unit200may be used as the RF coil unit14described above with reference toFIG.1. RF coil unit200includes an outer layer202forming an exterior of the RF coil unit200. In some embodiments, the outer layer202may be formed of a relatively soft and flexible material (e.g., fabric). An interior of the RF coil unit200includes a plurality of flexible RF coil elements and an adjustable pressure reservoir, as described further below. Each of the RF coil elements may include a loop portion electronically coupled to respective coupling electronics (e.g., feed board). The RF coil elements may receive MR signals, process, and transmit to an output connector210of the RF coil unit200via a coil-interfacing cable212electronically coupled to the coupling electronics of each RF coil element. The output connector210may interface with an input of an MRI system (e.g., controller unit25of MRI apparatus10shown byFIG.1and described above) in order to image a subject (e.g., a patient) via the RF coil unit200and MRI system.

The pressure reservoir disposed within the interior of the RF coil unit200includes a sealed chamber formed by, for example, plastic, leather, or any other appropriate material. The sealed chamber fluidly coupled to a fluid passage204extending through the outer layer202via an opening216of the outer layer202. The fluid passage204may include one or more valves (e.g., check valves) configured to maintain a pressure (e.g., gas pressure) within the pressure reservoir. For example, a care provider (e.g., clinician) may couple the fluid passage204to a vacuum pump in order to remove gases from the interior of the pressure reservoir and decrease the pressure within the pressure reservoir relative to ambient air pressure (e.g., atmospheric pressure). In some embodiments, the fluid passage204may include a first valve (e.g., check valve) enabling gases to flow out of the pressure reservoir but not into the pressure reservoir. The fluid passage204may additionally include a second valve (e.g., pressure relief valve) configured to enable gases to flow into the pressure reservoir during conditions in which the second valve is in an opened position (e.g., to expand the pressure reservoir from a compressed condition to an uncompressed condition) and to prevent gases from flowing into the pressure reservoir during conditions in which the second valve is in a fully closed position. The first valve and/or second valve may be normally closed valves that do not enable gases to flow into and/or out of the pressure reservoir during conditions in which the valves are in a fully closed position. However, the first valve and/or second valve may be actuated (e.g., electrically actuated via the processing system of the MRI system, physically actuated by an operator of the MRI system, etc.) from the fully closed position to an opened position in order to adjust the pressure within the pressure reservoir (e.g., increase or decrease the gas pressure within the pressure reservoir).

As one example, the care provider may couple the fluid passage204to the vacuum pump, which may open the first valve in order to flow gases out of the pressure reservoir without flowing gases into the pressure reservoir (e.g., while maintaining the second valve in the fully closed position). As a result, the pressure of the pressure reservoir is decreased, pellets disposed within the pressure reservoir may be compressed together, and the RF coil unit200is formed against a body of a subject to be imaged. The first valve may then automatically close when the vacuum pump is decoupled from the fluid passage to maintain the lowered pressure of the pressure reservoir. Maintaining the pressure of the pressure reservoir in this way may maintain a shape of the RF coil unit relative to the body of the subject. When a scan is over, the care provider may actuate the second valve to an opened position to flow ambient air into the pressure reservoir. As a result, the pressure within the pressure reservoir may adjust to be approximately equal to ambient air pressure (e.g., atmospheric air pressure external to the interior of the pressure reservoir), and the pellets disposed within the interior of the pressure reservoir may no longer be compressed together. Flowing ambient air into the pressure reservoir in this way (e.g., relieving the pressure within the pressure reservoir) may restore the shape of the RF coil unit200to its normal, uncompressed shape (e.g., the shape shown byFIG.2).

In some embodiments, at least one of the valves described above may be formed together with the fluid passage204as a single piece (e.g., integrated together with the fluid passage as a single unit). InFIG.2, the RF coil unit200is substantially rectangular. It should be understood that the RF coil unit can be any appropriate shape, such as square, circle, oval, and so on, for various applications. The RF coil unit can also be any appropriate size, according to applications.

Now referring toFIG.3, an interior portion of the RF coil unit200ofFIG.2is shown.FIG.3shows the RF coil unit200in partial cross-section in order to illustrate a relative arrangement of the RF coil loop portions, coupling electronics, pressure reservoir, and other components of the RF coil unit200. Various different views of the RF coil unit200are shown byFIGS.2-5, and reference axes299are included for comparison of the different views.

The RF coil unit200includes eight (8) RF coil elements arranged to form an RF coil array. Each coil element includes a loop portion and a coupling electronics portion electrically connected to the loop portion. Specifically, RF coil unit200includes a first row of RF coil elements including a first loop portion334and first coupling electronics portion318, a second loop portion336and second coupling electronics portion320, a third loop portion338and third coupling electronics portion322, and a fourth loop portion340and fourth coupling electronics portion324(e.g., with first loop portion334and first coupling electronics portion318corresponding to the first RF coil element, second loop portion336and second coupling electronics portion320corresponding to the second RF coil element, and so forth). The RF coil unit200additionally includes a second row of RF coil elements including a fifth loop portion342and fifth coupling electronics portion326, a sixth loop portion344and sixth coupling electronics portion328, a seventh loop portion346and seventh coupling electronics portion330, and an eighth loop portion348and eighth coupling electronics portion332. The RF coil elements of the first row may partially overlap the RF coil elements of the second row. For example, first loop portion334partially overlaps fifth loop portion342, second loop portion336partially overlaps sixth loop portion344, etc. Further, within each row, adjacent RF coil elements may partially overlap each other. For example, first loop portion334partially overlaps adjacent second loop portion336, fifth loop portion342partially overlaps adjacent sixth loop portion344, etc. Each RF coil element may be electronically isolated from each other RF coil element, such that the overlapping of the RF coil elements does not interfere with MR signals acquired by the RF coil elements to image a body of a subject. In some embodiments, the RF coil unit200may include a different number of RF coil elements (e.g., 12 RF coil elements, 16 RF coil elements, etc.).

In some embodiments, the loop portions may be arranged along a layer of flexible cloth material such that the loop portions are positioned between the layer of cloth material and the pressure reservoir300. The loop portion of each RF coil element may be fixed (e.g., stitched) to the cloth material. In other embodiments, the cloth material may be positioned between the loop portions and the pressure reservoir300, with the loop portions fixed to the cloth material.

Each RF coil element is coupled (e.g., electronically coupled) to respective coupling electronics (e.g., feed board). In some embodiments, each feed board is packaged within a respective housing. In some embodiments, the housings may be formed from a plastic material.

In some embodiments, each of the coupling electronics portion is seated within a respective opening of the pressure reservoir300. Specifically, first coupling electronics portion318is seated within first opening302, second coupling electronics portion320is seated within second opening304, third coupling electronics portion322is seated within third opening306, fourth coupling electronics portion324is seated within fourth opening308, fifth coupling electronics portion326is seated within fifth opening310, sixth coupling electronics portion328is seated within sixth opening312, seventh coupling electronics portion330is seated within seventh opening314, and eighth coupling electronics portion332is seated within eighth opening316. Each of the openings of the pressure reservoir300extends through the pressure reservoir300(e.g., extends entirely through the pressure reservoir300from a first side301of the pressure reservoir300, as shown byFIG.4, to an opposing, second side303of the pressure reservoir300). Each of the openings is not fluidly coupled to an interior of the pressure reservoir300(e.g., gases such as air maintained within the interior of the pressure reservoir300do not flow into or out of the interior of the pressure reservoir300at any of the first opening302, second opening304, third opening306, fourth opening308, fifth opening310, sixth opening312, seventh opening314, or eighth opening316). The sidewalls (e.g., inner sidewalls, such as inner sidewall337, which are offset or spaced apart from outer sidewalls forming an outer perimeter of the pressure reservoir300, such as outer sidewall339) of the pressure reservoir300are sealed at each of the openings configured to receive the housings of the coupling electronics, such that each of the openings forms a respective through-hole between the first side301and second side303of the pressure reservoir300. Each of the openings (which may be referred to herein as through-holes) is sealed such that the openings fluidly isolate an interior of the pressure reservoir300from ambient atmosphere (e.g., gas does not flow between the interior of the pressure reservoir300and ambient atmosphere via the openings).

The coupling electronics may be coupled to an output board354via respective electrical wires, as shown byFIGS.3-4, and the output board354may output electrical signals from each of the coupling electronics to the coil-interfacing cable212. The RF coil unit200may additionally include one or more baluns350and352electrically coupled between the output board354and the coupling electronics of each RF coil element. The coil-interfacing cable212may be coupled to an MRI system as described above in order to transmit the signals from the RF coil elements to the MM system for imaging of a subject via the RF coil unit200.

In some embodiments, each of the openings of the pressure reservoir300(e.g., first opening302, second opening304, third opening306, fourth opening308, fifth opening310, sixth opening312, seventh opening314, and eighth opening316) may be covered (e.g., closed or capped) with respective thermal patches358and thermal patches400, as shown by the exploded view ofFIG.4. Specifically, as described above, when the RF coil unit200is fully assembled, the coupling electronics are seated within the respective openings of the pressure reservoir300. The openings may be covered at the first side301of the pressure reservoir300by thermal patches358, and the openings may be covered at the second side303of the pressure reservoir by thermal patches400, with the housings positioned between the thermal patches358and thermal patches400within the openings. In this configuration, the thermal patches358and thermal patches400may aid in retaining the coupling electronics within the corresponding openings. Further, in some embodiments, thermal patches358and/or thermal patches400may be formed from materials having high thermal conductivity. As a result, the thermal patches358at the first side301and thermal patches400at the second side303may increase a transfer of heat away from the housings when the RF coil unit200is utilized to image a subject (e.g., a patient). An operating temperature of the coupling electronics may be reduced by the thermal patches, resulting in increased patient comfort.

In order to further increase patient comfort, in some embodiments, the RF coil unit200may include a first plurality of flexible spacers356positioned between the first side301of the pressure reservoir300and a first outer layer360of the RF coil unit200, and/or a second plurality of flexible spacers402positioned between the second side303of the pressure reservoir300and an opposing, second outer layer364of the RF coil unit200. The first outer layer360and the second outer layer364may correspond to the outer layer202inFIG.2. In some embodiments, the first and second outer layers360and364are made of one piece of material being folded. In some embodiments, the first and second outer layers360and364are made of two pieces of material that are stitched together to form the exterior of the RF coil unit200. The flexible spacers356and flexible spacers402may be formed from a foam material in some embodiments. In other embodiments, the flexible spacers356and flexible spacers402may be formed from fire-retardant material. In some embodiments, each of the flexible spacers356at the first side301may be positioned in contact with a respective thermal patch of thermal patches358(e.g., positioned directly against the respective thermal patch without other components between), and each of the flexible spacers402at the second side303may be positioned in contact with a respective thermal patch of thermal patches400. The flexible spacers356and flexible spacers402may increase an amount of air within the RF coil unit200surrounding the openings of the pressure reservoir300which may reduce a temperature of the coupling electronics during operation.

After the RF coil unit200is fully assembled along assembly axis499, the coupling electronics within each housing are coupled to both of the RF coil elements at the second side303and the electrical wires at the first side301. In this configuration, each RF coil element positioned at the second side303is electrically coupled to a corresponding electrical wire positioned at the first side301by coupling electronics within a corresponding housing, with each electrical wire joined to the output board354at the first side301.

The relative arrangement of the RF coil elements, pressure reservoir300, and housings is further illustrated by the cross-sectional view of the RF coil unit200shown byFIG.5(taken along axis214shown byFIGS.2-3). As appreciated inFIG.5, the pressure reservoir300may include loose fill that includes a plurality of particles within the pressure reservoir, such as pellets510, in the interior volume of the pressure reservoir. The pellets may be comprised of polystyrene or other suitable material.

In some embodiments, the outer layers of the RF coil unit200(e.g., first outer layer360and second outer layer364) may include multiple sub-layers and/or different types of material. In the embodiment shown byFIG.5, the second outer layer364includes three sub-layers, with each sub-layer formed from a different material. Specifically, the second outer layer364includes outermost sub-layer502, innermost sub-layer506, and mid sub-layer504. In some embodiments, the innermost sub-layer506may be formed of fire-retardant fabric material, the mid sub-layer504may be formed of fire-retardant material, and the outermost sub-layer502may be formed of polyurethane-coated fabric material. However, in other embodiments, the outer layers may include a different number of sub-layers and/or different types of materials.

Referring now toFIGS.6-13, various coupled configurations of an RF coil units are shown. Specifically,FIG.6shows RF coil unit600formed to subject602,FIG.7shows RF coil700formed to subject702,FIG.8shows RF coil800formed to subject802,FIG.9shows RF coil900formed to subject902,FIG.10shows RF coil1000formed to subject1002,FIG.11shows RF coil1100formed to subject1102,FIG.12shows RF coil1200formed to subject1202, andFIG.13shows RF coil1300formed to subject1302. Each of the RF coil units600,700,800,900,1000,1100,1200, and1300may be the same as the RF coil unit200described above with reference toFIGS.2-5, in some embodiments. Each of the RF coil units includes a pressure reservoir, which may be the same as the pressure reservoir300described above. In each ofFIGS.6-13, the pressure (e.g., gas pressure) within the interior of the pressure reservoir is reduced below atmospheric pressure in order to form the RF coil unit to the body of the subject, similar to the examples described above (e.g., such that pellets disposed within the interior of the pressure reservoir are compressed to increase a rigidity of the pressure reservoir and RF coil unit).

FIG.6shows RF coil unit600formed to the neck and chest of subject602,FIG.7shows RF coil unit700formed to a shoulder of subject702,FIG.8shows RF coil unit800formed to the head and neck of subject802,FIG.9shows RF coil unit900formed to the head of subject902,FIG.10shows RF coil unit1002formed to the torso of subject1002(e.g., an infant),FIG.11shows RF coil unit1100formed to the lower back of subject1102,FIG.12shows RF coil unit1200formed to a foot of subject1202, andFIG.13shows RF coil unit1300formed to a knee of subject1302. As described above, in some embodiments, each of the RF coil units shown byFIGS.6-13may be the same as the RF coil unit200shown byFIGS.2-5and described above. The RF coil unit200may thus be formed to the multiple different anatomical structures of a subject to be imaged shown byFIGS.6-13. The examples shown byFIGS.6-13are not limiting and in some embodiments, the RF coil unit200may be formed to other anatomical features of a subject (e.g., a thigh, arm, upper back, etc. of the subject).

Turning now toFIG.14, a schematic view of an RF coil element1402including a loop portion1401coupled to a controller unit1410via coupling electronics portion1403and a coil-interfacing cable1412is shown. The RF coil element1402is one non-limiting example of an RF coil element of RF coil unit200.

In some embodiments, the loop portion1401may be a distributed capacitance loop portion (also known as “Air Coil”), as disclosed in Patent Application PCT/US2017/062971, which is incorporated herein by reference for all purposes. In other embodiments, the loop portion1401may be any appropriate flexible coil (e.g., a coil including copper wires and discrete capacitors).

The coupling electronics portion1403may be coupled to the loop portion of the RF coil element1402. In some embodiments, the coupling electronics portion1403may include a decoupling circuit1404, impedance inverter circuit1406, and a pre-amplifier1408. The decoupling circuit1404may effectively decouple the RF coil element1402during a transmit operation. Typically, the RF coil element1402in its receive mode may be coupled to a body of a subject being imaged by the MR apparatus in order to receive electromagnetic radiation from the body. The RF coil element1402may be decoupled 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 element1402.

The impedance inverter circuit1406may form an impedance matching network between the RF coil element1402and the pre-amplifier1408. The impedance inverter circuit1406is configured to transform a coil impedance of the RF coil element1402into an optimal source impedance for the pre-amplifier1408. The impedance inverter circuit1406may include an impedance matching network and an input balun. The pre-amplifier1408receives MR signals from the corresponding RF coil element1402and amplifies the received MR signals. In one example, the pre-amplifier may have a low input impedance that is configured to generate a relatively high impedance in the coil to reduce the coupling between coil elements in receive mode.

The coil-interfacing cable1412, such as an RF coil array interfacing cable, may be used to transmit signals between the RF coil elements of the RF coil unit and other aspects of the processing system, for example to control the RF coil elements and/or to receive information from the RF coil elements.

The technical effect of configuring the RF coil unit to form to the body of the patient by adjusting the gas pressure within the pressure reservoir is to position the RF coil elements closer to the body of the patient to increase SNR, with the coupling electronics of the RF coil elements positioned within the openings of the pressure reservoir to increase thermal performance of the RF coil unit and increase patient comfort.