Local coil with segmented antenna device

Description

[0001] The invention relates to a local coil for a magnetic resonance imaging device with an antenna device, wherein the antenna device has a conductor loop and a plurality of electronic functional groups.

[0002] Magnetic resonance imaging scanners are imaging devices that, to create an image of a subject, align the nuclear spins of the subject with a strong external magnetic field and then excite them to precess around this alignment using an alternating magnetic field. The precession, or return, of the spins from this excited state to a lower-energy state, in turn generates a response alternating magnetic field, which is received via antennas.

[0003] Using magnetic gradient fields, a spatial coding is imprinted on the signals, which subsequently allows the received signal to be assigned to a volume element. The received signal is then evaluated, and a three-dimensional image of the object under examination is provided.

[0004] To achieve the best possible signal-to-noise ratio (SNR), the antenna coils for reception are positioned as close as possible to the patient. This is achieved using so-called local coils, which are typically connected to the magnetic resonance imaging scanner via cables. To simplify use and reduce the number of different variants, local coil arrays or matrices are available that can be used for different purposes. However, rigid cable connections and bulky electronic components in the local coil array are a hindrance.

[0005] Document WO 2005 / 052621 A1 discloses a magnetic resonance imaging scanner with a local coil. The local coil has a radio-frequency antenna with electronic components arranged on a substrate. The electronic components are electrically connected to the radio-frequency antenna, arranged in a central region of the radio-frequency antenna, and surrounded by the radio-frequency antenna.

[0006] Document US 2013 / 0137969 A1 describes a magnetic resonance antenna array comprising a substrate and a housing, with electronic circuits enclosed within the housing. The circuits are electrically coupled to antenna elements.

[0007] From document US 2007 / 0262777 A1, a low-cross-section local coil is designed to resonate at a magnetic resonance frequency of the magnetic resonance system. A flat induction coil is coupled to the antenna. The induction coil provides selective frequency filtering for high-frequency signals received or transmitted by the antenna.

[0008] Document US 5168230 A describes an MR coil pair for two different Larmor frequencies or nuclei. It features two individual coils tuned to two different resonant frequencies. The coils have the same contour and are stacked closely together.

[0009] A radio-frequency antenna for a magnetic resonance system is known from document WO 2018 / 069247 A1. The antenna comprises a printed circuit, a plurality of conductor elements on the circuit, a plurality of feed points for exciting the conductor elements, a connection port, and a plurality of feed lines connecting the connection port to the feed points.

[0010] Document DE 102006055136 A1 describes a high-frequency coil arrangement comprising a plurality of conductor tracks forming basic coils with capacitors interconnected therein, wherein conductor tracks of different basic coils intersect at nodes. At least one switching means for selectively and reversibly connecting the conductor tracks to form different coil geometries is provided at least at some of the nodes.

[0011] A local coil for a magnetic resonance imaging device is known from DE 102011079564 A1. The local coil comprises a flexible antenna support section with several antennas and an electronics section with electronic components connected to the antennas via supply lines. At least part of the electronics section is located outside the antenna support section.

[0012] The task therefore arises to improve local coils for a versatile application.

[0013] The object is achieved by a local coil according to the invention according to claim 1.

[0014] The local coil according to the invention for a magnetic resonance imaging scanner comprises an antenna device with a conductor loop and a plurality of electronic functional groups. An antenna device is considered to be an electrical device designed to receive alternating electrical and / or magnetic fields in a predetermined frequency range from a spatial volume adjacent to the local coil and to transmit them as electrical or optical signals via a signal connection or a wireless connection to the magnetic resonance imaging scanner for imaging. The alternating fields are preferably magnetic resonance signals from excited nuclear spins from a patient at a frequency referred to as the Larmor frequency, which are determined by the type of nuclear spins and a static magnetic field B0 of the magnetic resonance imaging scanner. The conductor loop is designed as an induction loop.

[0015] The electronic functional groups of the local coil according to the invention are arranged at a distance from one another. The functional groups are arranged along the extension of the conductor loop. The electronic functional groups are arranged alternatively on or between flexible conductor segments that connect individual conductor loops to form an antenna matrix or an antenna array. Preamplifiers (LNA, low noise amplifier), baluns (BALUN, balancer / unbalancer), mixers, diplexers, impedance matching networks, and safety circuits for protecting the antenna and / or the patient are considered electronic functional groups. All components that must interact to fulfill one of these functions and are therefore arranged spatially adjacent to one another as a group are considered electronic functional groups.

[0016] The electronic functional groups are electrically connected to each other by flexible conductor segments. Flexible conductor segments are electrical conductors that form sections of the conductor loop and adapt to the shape of the patient through the application of minimal force, such as the weight of the electronic functional groups. It is also conceivable that the local coil can be manually shaped into the desired shape by an operator. For this purpose, the local coil can, for example, have a sheath made of a flexible material or be divided into several segments that are pivotably connected to one another.

[0017] In principle, it is also conceivable that the conductor loop is formed by a single flexible conductor segment.

[0018] The combination of electronic functional groups distributed across the local coil and their flexible connection advantageously provides a local coil that provides a more uniform thickness and flexibility while avoiding concentrated heat sources caused by central electronics.

[0019] In the local coil according to the invention, components of an electronic functional group are arranged directly on a flexible conductor segment. This is considered to be directly arranged if the components are not first arranged on a circuit board and then connected to the flexible conductor segment. The electronic components can, for example, be soldered to the flexible conductor segment. The flexible conductor segment can also provide conductor tracks and / or conductive through-connectors for connecting or distributing components of the electronic functional group, particularly in an embodiment with more than two conductor levels.

[0020] Especially for simple electronic functional assemblies with small, robust components, arranging the components directly on the flexible conductor segment enables a space-saving design. For example, detune circuits with a few components must be distributed at specific positions across the conductor loop to achieve optimal performance. This type of arrangement is particularly suitable for areas where the flexible conductor segment is subject to low mechanical stress and / or deformation. It is also conceivable for individual sensitive components to be protected from mechanical stress by their own frames or housings.

[0021] For mechanically sensitive components and more heavily loaded or moving sections of the flexible conductor segments, however, it may be advantageous to arrange an electronic functional group at the required location in this section and to relocate the component to the electronic functional group.

[0022] According to the invention, the flexible conductor segment is stiffened in the region of the electronic functional group. The stiffening is achieved according to the invention by providing a stiffer carrier material in the flexible conductor segment at the location of the functional group, by providing additional layers of the carrier material, and / or by making one layer of the carrier material thicker than in the adjacent flexible region.

[0023] This is conceivable, for example, for extension capacitors or detuning diodes. The circuitry required to control the detuning diode can then be arranged on the electronic functional group to achieve a sensible distribution of the rigid, heavy, and / or heat-generating components. However, more complex functions can also be implemented by directly mounting them on a stiffened section of a flexible conductor segment.

[0024] Further advantageous embodiments are specified in the dependent claims.

[0025] In one conceivable embodiment of the local coil according to the invention, the flexible conductor segments comprise a flexible printed circuit board with at least three layers. Conventional flexible printed circuit boards consist of an insulating carrier material with conductor surfaces, also referred to as layers, arranged on opposite surfaces of the carrier material. The flexible conductor segments according to the invention, in contrast, comprise at least one further layer of a conductor and an insulating intermediate layer, so that additional control and signal connections can be provided between the electronic functional groups. It is also conceivable that capacitances, for example for capacitive coil enlargement, can be provided by means of the additional conductor and insulator surfaces.The flexible conductor segments can be designed to be mechanically separated, so that they are only mechanically connected to one another by the electronic functional groups, or they can be only electrically separated, so that only one or more electrical connections between the flexible conductor segments are established by the electronic functional group.

[0026] A flexible printed circuit board with at least three layers advantageously enables the implementation of control and signal lines without separate, freely wired lines. Capacitances provided by the conductor surfaces in multilayer technology advantageously avoid discrete capacitances, whose mechanical properties are particularly susceptible to interference when processed on flexible carrier materials.

[0027] In one possible embodiment of the local coil according to the invention, a flexible conductor segment has a shielded electrical signal line and / or a control line for the electronic functional groups. A shielded signal line is considered to be a signal line in a multilayer flexible printed circuit board, in which the shielding effect is achieved by conductor surfaces in the multilayer flexible printed circuit board that are adjacent to a signal line in a flexible printed circuit board, comparable to a coaxial shield around a core of a conventional coaxial cable. Preferably, the adjacent conductor surfaces are in signal connection with a signal ground reference. The signal line can be provided in a similar way to a coaxial line with an asymmetrical conductor or differentially by two symmetrical signal conductors.A control line is a signal line designed to transmit a signal for the function of an electrical functional group that is not a magnetic resonance signal. These are preferably auxiliary or control signals transmitted from the magnetic resonance imaging system to the local coil, such as detune, clock, or auxiliary frequency signals and supply voltages.

[0028] Due to higher signal levels or other radiation resistance, shielding by adjacent conductor surfaces may also be unnecessary.

[0029] Advantageously, the mechanical structure of the antenna device can be simplified by additional signal lines in the flexible conductor segment.

[0030] In one conceivable embodiment of the local coil according to the invention, a flexible conductor segment has a sheath wave barrier. Sheath wave barriers may be necessary, particularly in flexible conductor segments between individual conductor loops of an antenna matrix with larger dimensions, to prevent overloading the circuit or endangering patients from induced currents and voltages. A sheath wave barrier is considered to be, in particular, a filter that prevents the propagation of an electrical signal at the Larmor frequency via one or more conductors of the flexible conductor segment. Such a signal is induced, for example, when the magnetic resonance imaging scanner emits a radio-frequency signal at the Larmor frequency to excite the nuclear spins to be examined. In a preferred embodiment, the flexible conductor segment is wound into a drum or coil as part of the sheath wave barrier.

[0031] Advantageously, an inductance for a standing wave barrier can be provided by rolling the flexible conductor segment into a drum or coil without additional conductors or connection points.

[0032] In one possible embodiment of the local coil according to the invention, the local coil has a plurality of antenna devices with a plurality of antenna loops. The antenna devices can all be of the same type or belong to different, previously described embodiments. The antenna devices preferably form a matrix in which the areas enclosed by the conductor loops only partially overlap and each individually overlaps at least partially disjoint areas in order to record magnetic resonance signals from different regions of the examination subject. The plurality of antenna devices has plug connections on the conductor loops, with which the antenna devices are electrically and mechanically connected to one another. It is conceivable that an antenna matrix of the local coil is formed in this way from identical antenna devices.The connector can, for example, exchange induced magnetic resonance signals between the conductor loops to provide decoupling of the conductor loops. However, it is also conceivable that control signals, clocks, oscillator signals, or even supply voltages and currents can be distributed via the antenna devices of the local coil through flexible conductor segments without additional free wiring.

[0033] Advantageously, the plug connections between the conductor loops allow for a cost-effective provision of an antenna matrix of the local coil.

[0034] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0035] They show: Fig. 1 shows a schematic overview of a magnetic resonance imaging system with a local coil according to the invention; Fig. 2 shows a schematic representation of a local coil from the prior art; Fig. 3 shows a schematic representation of a local coil according to the invention with an exemplary distribution of functional groups; Fig. 4 shows a schematic representation of a flexible conductor segment according to the invention.

[0036] Fig. 1 shows a schematic representation of an embodiment of a magnetic resonance imaging device 1 with a local coil 50 according to the invention.

[0037] The magnet unit 10 has a field magnet 11 that generates a static magnetic field B0 for aligning nuclear spins of samples or the patient 100 in a recording area. The recording area is characterized by an extremely homogeneous static magnetic field B0, whereby the homogeneity particularly affects the magnetic field strength or magnitude. The recording area is almost spherical and arranged in a patient tunnel 16 that extends in a longitudinal direction 2 through the magnet unit 10. A patient bed 30 is movable in the patient tunnel 16 by the traversing unit 36. The field magnet 11 is typically a superconducting magnet that can generate magnetic fields with a magnetic flux density of up to 3T, and even higher in the latest devices. However, permanent magnets or electromagnets with normally conducting coils can also be used for lower field strengths.

[0038] Furthermore, the magnet unit 10 has gradient coils 12, which are designed to superimpose variable magnetic fields in three spatial directions on the magnetic field B0 for spatial differentiation of the acquired imaging regions in the examination volume. The gradient coils 12 are typically coils made of normally conducting wires that can generate mutually orthogonal fields in the examination volume.

[0039] The magnet unit 10 also has a body coil 14, which is designed to radiate a radio-frequency signal supplied via a signal line into the examination volume and to receive resonance signals emitted by the patient 100 and transmit them via a signal line. However, the magnetic resonance signal from the patient is preferably recorded by the local coil 50, which is described in more detail below and is arranged closer to the patient 100.

[0040] A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals.

[0041] Thus, the control unit 20 has a gradient control 21 which is designed to supply the gradient coils 12 with variable currents via supply lines, which provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0042] Furthermore, the control unit 20 has a radio-frequency unit 22, which is designed to generate a radio-frequency pulse with a predetermined temporal profile, a predetermined amplitude, and spectral power distribution for exciting a magnetic resonance of the nuclear spins in the patient 100. Pulse powers in the kilowatt range can be achieved. The excitation pulses can be transmitted into the patient 100 via the body coil 14 or via a local transmitting antenna.

[0043] A controller 23 communicates with the gradient controller 21 and the radiofrequency unit 22 via a signal bus 25. The local coil 50 according to the invention is arranged on the patient 100 and is in wired or wireless signal connection with the radiofrequency unit 22.

[0044] Fig. 2 shows a schematic representation of a conventional local coil 150 from the prior art. The conventional local coil 150 has a plurality of conductor loops 51 that form an antenna matrix or array. The conductor loops 51 partially overlap to achieve decoupling between adjacent conductor loops 51 through the opposite flow direction of the magnetic field in overlapping and non-overlapping areas.

[0045] In the conventional local coil 150, a central electronic assembly 152 is arranged between each two conductor loops 51, combining various functional groups. These include, for example, a balun 60 and a matching network 65, which match the impedance and symmetry of the conductor loop 51 to the first preamplifier stage 61. Furthermore, second preamplifier stages 62 for further amplification, a mixer 63 for converting the amplified magnetic resonance signals to an intermediate frequency, and a diplexer for combining or separating signals of different frequencies, such as the oscillator signal, intermediate frequencies, and detuning signals, are located on the central electronic assembly 152.

[0046] The signals of the central electronic assembly 152 are combined via separate signal lines to a central connection unit 70, to which a cable is directly attached or can be connected via a plug to a corresponding multi-pin socket on the connection unit 70.

[0047] The Fig. 3 , in contrast, shows a local coil 50 according to the invention with an exemplary distribution of functional groups. The functional groups are connected to conductor loops 51 by flexible conductor segments 52. For example, functional groups such as the balun 60, the first preamplifier 61, and the matching network 65 are connected to one another by flexible conductor segments 52, but at the same time are arranged at a distance from one another along the conductor loop 51. Since the balun 60 and the matching network 65 ensure electrical adaptation of the signals from the conductor loop 51 to the first preamplifier stage 61, it is advantageous to arrange them adjacent to one another along the extent of the conductor loop 51. The same applies to the second amplifier stage 62, which transmits its output signal via the mixer 63 and the diplexer 64. These are therefore also preferably arranged adjacent to one another along the conductor loop 51.

[0048] The functional units such as fuse 67, detuning circuit 66, matching network 65 or first preamplifier stage 61, which directly process or influence the MR signal received by the conductor loop 51 as an antenna coil, are an immediate part of the closed conductor loop in the sense that they are also electrically integrated into the conductor loop 51.

[0049] Furthermore, since the mixer 63 and the diplexer 64 combine and forward the signals of two conductor loops 51, the mixer 63 and the diplexer 64 are preferably arranged in an area in which two conductor loops 51 overlap, the signals of which are then combined.

[0050] The conductor loops 51 are arranged on or on a flexible carrier material 81, as will be described below. Fig.4 will be explained in more detail. Along the conductor loop 51, but not directly electrically integrated into it and arranged on the common flexible carrier material 81, are further functional units, such as the previously mentioned mixers 63, diplexers 64 or second amplifier stages 62 and balun 60. These are connected to the other units and / or the connection unit 70 by separate conductors on the flexible carrier material 81 as supply, signal or control lines.

[0051] One or more electronic functional groups are formed directly on the flexible conductor segment 52, in that the flexible conductor segment provides the connecting and supply lines and the components are mounted directly on the flexible conductor segment 52. To reduce the mechanical load on the components of the electronic functional assembly, additional layers of the flexible carrier material 81 are provided in the region where the components are mounted, the flexible carrier material 81 is made thicker in one or more layers in this region and / or layers are made with a stiffer carrier material, so that the flexible conductor segment 52 is stiffened in the region of the electronic functional group and significantly reduces mechanical forces on the components and the solder connections.In this way, the functional assembly can be designed in one piece with the flexible conductor segment and error-prone connections can be avoided.

[0052] In unclaimed embodiments, the functional groups can also be designed as single- or multi-layer separate printed circuit boards. The printed circuit boards can be rigid in order to protect sensitive components such as ceramic capacitors that are attached or soldered thereto against mechanical stress. Preferably, the individual printed circuit boards are then designed to be small in their extension parallel to the conductor loop 51, for example, smaller than half, a third, or a quarter of the extension of a connecting flexible conductor segment 52. Thus, the entire conductor loop 51, as a combination of flexible and rigid elements, nevertheless exhibits sufficient flexibility. In principle, however, it is also conceivable to design the printed circuit board of a functional group to be flexible for less sensitive components.

[0053] A connection between the functional group and the flexible conductor segment 52 is preferably established on separate circuit boards by a positive and / or non-positive, electrically conductive connection. For example, the circuit boards of the functional group can be connected to each other by a complementary plug-socket system. A clamping device is also conceivable, by means of which the flexible conductor segment 52 is electrically and mechanically connected.

[0054] Fig. 4 1 schematically illustrates a flexible conductor segment 52 according to the invention. The flexible conductor segment 52 has several layers of a flexible insulator as a flexible carrier material 81. This flexible carrier material 81 is preferably a dielectric with high quality and low dielectric losses. Layers of a conductor material are arranged between or on these flexible carrier materials 81. The conductor material is in the form, for example, of foils or wires made of a highly conductive material or metal such as copper, silver, or aluminum. These can be designed as flat shielding surfaces 83 or as conductor tracks 82, 84. Conductor tracks 82 that are not surrounded by shielding surfaces 83 can, for example, be designed as a conductor loop 51 for receiving magnetic resonance signals. In contrast, conductor tracks 84 that are arranged between two shielding surfaces 83 can be provided for forwarding magnetic resonance signals and / or control signals.With predetermined distances between them and between the shielding surfaces, electrical properties in terms of characteristic impedance and interference can be achieved that are comparable to coaxial cables, or, in the case of two parallel conductor tracks, comparable to shielded symmetrical cables. Symmetrical cables are advantageous here because, for example, the antenna loops themselves provide symmetrical signals. It is also conceivable that between two layers of the flexible carrier material 81, in the space between the two conductor tracks in the plane, there may be no carrier material, but rather another dielectric, including air.

[0055] By means of the Fig. 4Various combinations and functions can be realized using the basic options for designing a flexible conductor segment 52 shown. For example, it would be conceivable for the conductor tracks 82 on the surface to form part of a conductor loop 51 of an antenna. It can also be provided that electrically interconnected conductor tracks 82 are provided on opposite surfaces of the conductor segment, which can replace a separate, thick conductor due to the skin effect. Shielded control and signal lines can be formed inside, which also interconnect conductor loops 51 to form a matrix or connect them to a connection unit 70 for connection to the magnetic resonance imaging scanner 1. Supply voltages or currents can also be conducted to the functional groups in this way.

[0056] The flexible conductor segment 52 can also provide additional electrical functions. Opposing conductor surfaces similar to the shielding surfaces 83, but without the conductor track 81 in between, separated only by a dielectric and electrically insulated from each other, can provide capacitances that, for example, replace soldered extension capacitances.

[0057] In areas in which a flexible conductor segment 52 is simultaneously designed as an electronic functional assembly by means of assembly, one or more of the layers of the flexible carrier material 81 can be designed as a stiffener by means of a greater thickness and / or additional layers of the same carrier material or even stiffer material can fulfil this purpose in order to protect the applied components against mechanical stresses due to bending and twisting.

[0058] By rolling a flexible conductor segment 52 into a drum or coil, the inductance of the conductor tracks 81 in the flexible conductor segment 52 can also be increased or controlled. Furthermore, it is conceivable to guide the flexible conductor segment through a barrier pot or to wind it around a core. This, and in conjunction with the capacitors, can also provide sheath wave barriers that prevent standing waves, particularly on connections between the conductor loops.

[0059] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention as defined by the claims.

Claims

1. Local coil for a magnetic resonance tomography scanner (1) having an antenna device, wherein the antenna device has a conductor loop (51) and a plurality of electronic function groups, wherein a function group is one of preamplifiers, baluns, mixers, diplexers, impedance matching networks, and safety circuits for protection of the antenna and / or patient, wherein the electronic function groups are arranged in a distributed manner spaced apart from one another and are electrically connected to one another by flexible conductor segments (52), wherein the electronic function groups are arranged along the extension of the conductor loop and / or the antenna device has a plurality of conductor loops and the electronic function groups are arranged on or between flexible conductor segments, the individual conductor loops connect to form an antenna matrix, characterised in that components of an electronic function group are arranged directly on a flexible conductor segment (52), wherein the components are not arranged on a circuit board and are connected by the circuit board to the flexible conductor segment, wherein the flexible conductor segment (52) has a bracing in the region of the electronic function group, wherein the bracing has a stiffer carrier material in the flexible conductor segment and / or additional layers of a carrier material and / or a layer of the carrier material thicker in comparison to the adjacent flexible region.

2. Local coil according to claim 1, wherein the flexible conductor segments (52) have a flexible circuit board with at least three layers.

3. Local coil according to claim 1, wherein a flexible conductor segment (52) has a shielded electrical signal line and / or a control line for the electronic function groups.

4. Local coil according to claim 1, wherein a flexible conductor segment (52) has a standing wave trap, wherein the flexible conductor segment (52) is rolled up to form a drum in the standing wave trap.

5. Local coil according to one of the preceding claims, wherein the local coil (50) has a plurality of antenna devices with a plurality of conductor loops (51) and the plurality of conductor devices has electrically conductive connections on the conductor loops (51), with which the antenna devices are electrically connected to one another.