Cable unit for connecting a gradient coil to a power amplifier

Abstract

The invention relates to a cable unit designed for connecting a gradient coil, which is designed to generate a magnetic field gradient in one spatial direction, to a power amplifier, comprising at least one supply line, wherein the supply line comprises at least two cable elements in at least sections, wherein the at least two cable elements are electrically connected in parallel.

Description

[0001] The invention relates to a cable unit connecting a gradient coil with a power amplifier and a system comprising a gradient coil unit, a gradient control unit and three connection units including such a cable unit.

[0002] Magnetic resonance imaging (MRI) is based on alternating electromagnetic fields (RF fields) generated by a magnetic resonance imaging (MRI) scanner and their interaction with a static magnetic field, typically 1.5 Tesla, 3 Tesla, or 7 Tesla. Additionally, gradient pulses are generated using a gradient coil unit. High-frequency (HF) pulses, such as excitation pulses, are then emitted via a high-frequency antenna unit using suitable antenna elements. This causes the nuclear spins of certain atoms, resonantly excited by these RF pulses, to be tilted by a defined angle relative to the magnetic field lines of the main magnetic field. During the relaxation of the nuclear spins, high-frequency signals, known as magnetic resonance signals, are emitted. These signals are received by suitable RF antennas and then processed. The desired image data can then be reconstructed from the raw data acquired in this way.

[0003] The control of the magnetic resonance imaging (MRI) system, and in particular the control of the gradient coil unit required for spatial encoding in MRI, is typically achieved by a control unit and power amplifiers, specifically controlled by a gradient control unit. The gradient coil unit comprises three gradient coils. These three gradient coils are configured to generate a magnetic field gradient in three different, typically mutually perpendicular, spatial directions. Conventionally, a gradient coil is connected to a power amplifier via a gradient cable. The gradient cable, hereinafter also referred to as the cable unit, can include a feed line and a return line and / or be designed as a coaxial cable that integrates a feed line and a return line.The power amplifiers generate electrical currents of up to 1500 A, and in exceptional cases up to 3000 A, with frequencies in the range between 100 Hz and 10 kHz. These electrical currents are supplied to the gradient coil unit via the gradient cable.

[0004] The resulting ohmic losses can lead to heating of the gradient cable. The temperature rise increases with the current in the gradient cable during operation of the gradient coil unit. To reduce heating, conventional copper cables are used, for example, with a cross-sectional area of ​​more than 50 mm². 2 and an outer diameter of more than 40 mm. Depending on the structural conditions, the gradient cables can also be cooled by means of ventilation. Additionally, the gradient cables are typically exposed to mechanical vibrations.

[0005] The invention is based on the objective of providing a particularly powerful and robust cable unit for connecting a gradient coil to a power amplifier. This objective is achieved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0006] The cable unit according to the invention is configured to connect a gradient coil, which is designed to generate a magnetic field gradient in one spatial direction, to a power amplifier. For this purpose, the cable unit has at least one supply line, wherein the supply line comprises at least two cable elements, at least partially, and wherein the at least two cable elements are electrically connected in parallel.

[0007] A cable element typically comprises an electrical conductor and an insulating surface surrounding the conductor, in particular a protective sheath, for example made of plastic. The cable element is typically elongated. The electrical conductor can be a single conductor and / or a single- or multi-core bundle of individual conductors. In the cross-section of the cable element, the electrical conductor is typically enclosed by the insulating surface, in particular the protective sheath.

[0008] The supply line is designed to conduct an electric current from the power source, in particular the power amplifier, to the load, in particular the gradient coil. The supply line typically has a length of at least 2 m, preferably at least 4 m, and most preferably at least 5 m. The supply line can, for example, pass through a filter unit and / or an RF shield. According to the invention, the supply line is designed such that, at least in a partial section, i.e., section by section, it is divided into at least two cable elements. The at least two cable elements are electrically connected to each other in parallel, for example, by means of cable lugs. The at least two cable elements can also be arranged approximately parallel to each other.The supply line can also be designed such that it comprises a different number of electrically parallel-connected cable elements in different sections of the supply line. The supply line can be designed such that within a section of the supply line it comprises three, four, or more than four electrically parallel-connected cable elements. The supply line can comprise two, three, four, or more than four electrically parallel-connected cable elements along its entire length.

[0009] The cable unit according to the invention enables the gradient coil to be driven with particularly high currents, thus allowing for the achievement of particularly high magnetic field gradients with especially fast rise and fall rates. A multi-segment routing of cable elements also enables a redundant and therefore robust design, as well as improved ventilation of the individual cable elements and thus enhanced cooling of the cable unit. The individual cable elements connected in parallel can have a smaller cross-section than a supply line comprising only one cable element while maintaining the same maximum current, so that the required conductive material remains approximately constant.

[0010] One embodiment of the cable unit provides that at least one of the two cable elements has a cross-sectional area of ​​less than 45 mm². 2 , preferably less than 38 mm 2 , especially preferably less than 30 mm 2The parallel connection of at least two cable elements according to the invention enables a higher current flow compared to the use of a single cable element with the same cross-sectional area, thus allowing the cross-sectional area of ​​at least one cable element to be reduced. Preferably, all cable elements of the supply line and / or the cable unit have a cross-sectional area of ​​less than 45 mm². 2 , preferably less than 38 mm 2 , especially preferably less than 30 mm 2 A smaller cross-sectional area allows for greater flexibility and a smaller bending radius of the corresponding cable element, enabling flexible and customized arrangement of the cable elements. This facilitates the installation of such a cable unit, which is typically laid in confined spaces and / or in the floor.

[0011] One embodiment of the cable unit provides that the cable unit additionally includes a return line with at least one cable element, which return line is electrically connected in series with the supply line. The return line is configured to conduct an electrical current from the load, in particular the gradient coil, to the gradient control unit comprising the power amplifier. The return line can comprise one cable element. The return line can comprise at least two cable elements connected in parallel, at least partially. The supply line, the gradient coil, and the return line are typically electrically connected in series. This embodiment enables a robust power supply to the gradient coil.

[0012] One embodiment of the cable unit provides that the supply and return lines are jointly designed as at least two coaxial cables, which are at least partially electrically connected in parallel. The supply line can, for example, be the inner conductor of a coaxial cable and the return line the outer conductor of a coaxial cable, with the inner and outer conductors separated by an insulating layer. This allows the inner conductor to be considered a cable element. The outer conductor is enclosed by a protective sheath, so that it too can be considered a cable element. Such an electrical parallel connection of coaxial cables enables an integrated supply and return line with higher current ratings and / or smaller cross-sectional areas of the cable elements than when using a single coaxial cable as the supply line. This also allows the use of flexible coaxial cables.

[0013] Furthermore, the invention is based on a system comprising a gradient coil unit with three gradient coils, a gradient control unit with three power amplifiers, and three connecting units, each connecting a gradient coil with a power amplifier and each having a supply line, wherein the three gradient coils are each configured to generate a magnetic field gradient in three different spatial directions, and each supply line comprises at least one cable element. and a first connection unit of the three connection units is designed as a cable unit according to the invention.

[0014] To avoid impairing the functionality of a magnetic resonance imaging (MRI) device, it is typically located in a separate, RF-shielded compartment, preferably enclosed by an RF shield. This shield is designed to protect the generated fields from external influences and prevent the propagation of electromagnetic fields generated by the MRI device outside the RF-shielded compartment. The gradient coil unit, typically a component of an MRI device, is therefore typically located within the RF-shielded compartment. The control of the MRI device, and in particular the control of the gradient coil unit required for spatial encoding in MRI imaging, is typically achieved using a gradient control unit and power amplifiers located outside the RF-shielded compartment.The three connecting units are therefore typically guided through an RF shield, for which the RF shield may include a filter plate to maintain the shielding properties. The system according to the invention may include the magnetic resonance system.

[0015] The system according to the invention therefore comprises the components required for controlling the gradient coil unit. The use of at least two cable elements for a supply line enables the control of a gradient coil unit with particularly high magnetic field gradients and with particularly fast rise and fall rates.

[0016] Further embodiments of the system according to the invention are designed analogously to the embodiments of the cable unit according to the invention. The advantages of the system essentially correspond to the advantages of the cable unit according to the invention, which are described in detail below. Features, advantages, or alternative embodiments of the cable unit mentioned here, as well as alternative embodiments of the system, can likewise be transferred to the other claimed items and vice versa.

[0017] One embodiment of the system provides that the first connecting unit connects a first gradient coil of the three gradient coils to a first power amplifier of the three power amplifiers, and the first gradient coil is configured to generate a magnetic field gradient in the x-direction or the y-direction. A gradient coil unit is typically hollow and cylindrical around a longitudinal axis, which is horizontally oriented and designated as the z-axis, i.e., oriented in the z-direction. The x-direction is typically perpendicular to the z-axis and also horizontally oriented. The y-direction is perpendicular to both the x-axis and the y-direction.The x-direction is a spatial direction typically subjected to particularly high stress within the magnetic field gradients used in MR imaging. Consequently, the first connection unit typically conducts particularly high electrical currents frequently when driving the first gradient coil, and is therefore exposed to a particularly high temperature increase when using a conventional cable element. The use of a cable unit according to the invention for the first connection unit thus enables better temperature control by reducing the stress on individual cable elements.

[0018] One embodiment of the system provides that at least one cable element of the supply line to the first connection unit has a larger cross-sectional area than cable elements of the supply lines to a second connection unit and / or a third connection unit of the three connection units. This embodiment provides that the first connection unit, which is specifically claimed, has a larger cross-sectional area than the other cable elements, in addition to the electrical parallel connection of at least two cable elements. It has been found that electrical conductors with a larger cross-sectional area heat up less than electrical conductors with a smaller cross-sectional area. This embodiment therefore enables a particularly robust and powerful supply line and current supply to the first gradient coil.

[0019] One embodiment of the system provides that a second connection unit of the three connection units is designed as a cable unit according to the invention. According to this embodiment, at least two gradient coils can be supplied with power via a flexible and simultaneously high-performance connection unit.

[0020] One embodiment of the system provides that each of the three connection units is designed as a cable unit according to the invention. Each of the three connection units thus comprises a supply line with at least two electrically parallel cable elements, at least in sections, so that, according to this embodiment, at least six cable elements are provided as supply lines for the gradient coil unit. The at least six cable elements are typically connected in parallel at least in pairs. The at least six cable elements preferably do not differ in cross-section, construction, and / or type. The at least six cable elements are preferably interchangeable, thereby standardizing and scaling the connection units. This enables a cost-effective implementation of the system.Furthermore, existing conventional systems that connect a gradient coil unit to a gradient control unit via three supply lines, each comprising exactly one cable element, can be upgraded by adding another cable element to each of the three supply lines in parallel with the existing cable element. This enables an improved power supply to the gradient coil unit without requiring complete rewiring.

[0021] One embodiment of the system provides that the supply line to a third connection unit of the three connection units comprises a cable element and is free of electrically parallel-connected cable elements; thus, the third connection unit is free of a cable unit according to the invention. This allows for individual wiring of the third gradient coil depending on the expected use and correspondingly required power, as well as an adapted design for the asymmetrical use of the gradient coil unit.

[0022] One embodiment of the system provides that the third connection unit connects a third gradient coil of the three gradient coils to a third power amplifier of the three power amplifiers, and that the third gradient coil is configured to generate a magnetic field gradient in the z-direction. In particular, the magnetic field gradients in the z-direction require less power than the magnetic field gradients in the x-direction and / or y-direction when the image data to be generated is oriented conventionally with the magnetic resonance device. This embodiment therefore enables efficient use of the system.

[0023] One embodiment of the system provides that the number of cable elements in the supply lines of at least two of the three connection units differs from one another. This embodiment enables efficient use of the system.

[0024] One embodiment of the system provides that the cross-sections of the cable elements of the supply lines for at least two of the three connection units are different. The cable elements for supply lines of more heavily loaded gradient coils can therefore be thicker than the supply lines for less heavily loaded gradient coils. This allows for a uniform temperature change in all cable elements during operation of the gradient coil unit.

[0025] One embodiment of the system provides that each of the three connection units comprises a return line with at least one cable element electrically connected in series with the corresponding supply line. Typically, a supply line, a gradient coil, and a return line are electrically connected in series, resulting in at least three circuits. This enables an individual and robust power supply for the gradient coil unit.

[0026] One embodiment of the system provides that the system additionally includes a connection unit, which is arranged on the surface of a housing surrounding the gradient coil unit and has three connection elements, wherein all cable elements or the cable element of a supply line can be connected to each connection element. The connection unit preferably comprises three further connection elements, wherein all cable elements or the cable element of a return line can be connected to each further connection element. A connection element typically allows for the reversible connection and / or coupling of at least one cable element to a gradient coil. A connection element is typically designed as a cable lug. A connection element may also include a coaxial connector, particularly in the case of a coaxial design of the supply and return lines.The system can include a second analog connection unit, which allows for the reversible connection and / or linking of at least one cable element to a power amplifier. This embodiment enables easy replacement of cable elements and efficient installation of the system.

[0027] Further advantages, features and details of the invention will become apparent from the exemplary embodiments described below and from the drawings.

[0028] They show: Fig. 1 a schematic representation of a first embodiment of a cable unit according to the invention, Fig. 2 a schematic representation of a second embodiment of a cable unit according to the invention, Fig. 3 a schematic representation of a first embodiment of a system according to the invention, and Fig. 4 a schematic representation of a second embodiment of a system according to the invention.

[0029] Fig. Figure 1 shows a schematic representation of a first embodiment of a cable unit according to the invention. The cable unit connects a gradient coil 19a to a power amplifier 30a, wherein the gradient coil 19a and the power amplifier 30a are not encompassed by the cable unit and are in Fig. 1 is only indicated. The cable unit has a supply line 21a. The supply line 21a comprises two cable elements 23, the two cable elements 23 being electrically connected in parallel. The two cable elements 23 of the supply line 21a have a cross-sectional area of ​​less than 45 mm². 2The cable unit additionally comprises a return line 22a with a cable element 23, wherein the return line 22a is electrically connected in series with the supply line 21a and, in particular, leads from the gradient coil 19a to the power amplifier 30a, thus electrically connecting the gradient coil 19a to the power amplifier 30a. Specifically, the supply line 21a is connected in series with the return line 22a via the gradient coil 19a. Furthermore, in the illustrated embodiment, the cable unit is connected to the gradient coil 19a via a connection element 17a and a further connection element 18a. The connection element 17a is arranged on the surface of the gradient coil 19a and enables an electrical connection between the supply line 21a and the gradient coil 19a. The further connection element 18a is arranged on the surface of the gradient coil 19a and enables an electrical connection between the return line 22a and the gradient coil 19a.

[0030] Fig. Figure 2 shows a schematic representation of a second embodiment of a cable unit according to the invention. The second embodiment differs from the one shown in Figure 2. Fig. The first embodiment shown in Figure 1 differs in that the supply line 21a and the return line 22a are integrated as coaxial cables. The supply line 21a comprises two cable elements, which are configured as the inner conductors of two electrically parallel-connected coaxial cables. The return line 22a is formed by the corresponding outer conductor of the two electrically parallel-connected coaxial cables.

[0031] Fig. Figure 3 shows a schematic representation of a first embodiment of a system according to the invention. The system comprises a gradient coil unit 19 with three gradient coils 19a, 19b, 19c, a gradient control unit 28 with three power amplifiers 30a, 30b, 30c, and three connection units 20a, 20b, 20c, each connecting a gradient coil 19a, 19b, 19c to a power amplifier 30a, 30b, 30c. The three connection units 20a, 20b, 20c each have a lead wire 21a, 21b, 21c, each comprising at least one cable element 23. The three gradient coils 19a, 19b, 19c are each configured to generate a magnetic field gradient in three different spatial directions. The first connection unit 20a and the second connection unit 20b of the three connection units 20a, 20b, 20c are designed as a cable unit according to the invention.

[0032] The first connection unit 20a connects a first gradient coil 19a of the three gradient coils 19a, 19b, 19c to a first power amplifier 30a of the three power amplifiers 30a, 30b, 30c, and the first gradient coil 19a is configured to generate a magnetic field gradient in the x-direction. The first connection unit 20a additionally includes a first return line 22a with a cable element 23, which is electrically connected in series with the first supply line 21a. The first supply line 21a, the first gradient coil 19a, the first return line 22a, and the first power amplifier 30a typically form a closed circuit.

[0033] The second connection unit 20b connects a second gradient coil 19b of the three gradient coils 19a, 19b, 19c to a second power amplifier 30b of the three power amplifiers 30a, 30b, 30c, and the second gradient coil 19a is configured to generate a magnetic field gradient in the y-direction. The second connection unit 20b additionally includes a second return line 22b with a cable element 23, which is electrically connected in series with the second supply line 21b. The second supply line 21b, the second gradient coil 19b, the second return line 22b, and the second power amplifier 30b typically form a closed circuit.

[0034] The third connection unit 20c connects a third gradient coil 19c of the three gradient coils 19a, 19b, 19c to a third power amplifier 30c of the three power amplifiers 30a, 30b, 30c. The third gradient coil 19c is configured to generate a magnetic field gradient in the z-direction. The supply line 21c of the third connection unit 20c comprises exactly one cable element 23 or only electrically series-connected cable elements and is free of electrically parallel-connected cable elements. The third connection unit 20c additionally comprises a third return line 22c with a cable element 23, which is electrically connected in series with the third supply line 21c. The third supply line 21c, the third gradient coil 19c, the third return line 22c, and the third power amplifier 30c typically form a closed circuit.

[0035] The first return line 22a, the second return line 22b and / or the third return line 22c can each comprise only one cable element 23 as shown. Alternatively, the first return line 22a, the second return line 22b and / or the third return line 22c can comprise at least two cable elements 23, at least in sections, wherein the at least two cable elements 23 per return line are each electrically connected in parallel.

[0036] According to the illustrated embodiment, the system comprises a connection unit 17 with three connection elements 17a, 17b, 17c and three further connection elements 18a, 18b, 18c. The connection unit 17 is arranged on the surface of a housing surrounding the gradient coil unit 19. All cable elements 23 of the first supply line 21a can be connected to the first gradient coil 19a via a first connection element 17a of the three connection elements 17a, 17b, 17c. The first return line 22a can be connected to the first gradient coil 19a via a first further connection element 18a of the three further connection elements 18a, 18b, 18c.

[0037] All cable elements 23 of the second supply line 21b can be connected to the second gradient coil 19b via a second connection element 17b of the three connection elements 17a, 17b, 17c. The second return line 22b can be connected to the second gradient coil 19b via a second connection element 18b of the three connection elements 18a, 18b, 18c. The cable element 23 of the third supply line 21c can be connected to the third gradient coil 19c via a third connection element 17c of the three connection elements 17a, 17b, 17c. The third return line 22c can be connected to the third gradient coil 19c via a third connection element 18c of the three connection elements 18a, 18b, 18c.

[0038] Fig. Figure 4 shows a schematic representation of a second embodiment of a system according to the invention. The second embodiment of the system differs from the one shown in Figure 4. Fig.The difference in the first embodiment shown in Figure 3 is that the third connection unit 20c is also designed as a cable unit according to the invention. The cable elements 23 of the first connection unit 20a have a larger cross-sectional area than the cable elements 23 of the second connection unit 20b and / or the third connection unit 20c. For the sake of clarity, the optional connection unit 17 has been omitted from the illustration.

[0039] Although the invention has been further illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. Regardless of the grammatical gender of a particular term, persons of male, female, or other gender identities are included.

Claims

[1] Cable unit designed to connect a gradient coil, which is designed to generate a magnetic field gradient in a spatial direction, to a power amplifier, comprising at least one supply line, wherein the supply line comprises at least two cable elements at least sectionally, wherein the at least two cable elements are electrically connected in parallel. [2] Cable unit according to claim 1, wherein at least one cable element of the two cable elements has a cross-sectional area of ​​less than 45 mm² 2 exhibits. [3] Cable unit according to one of the preceding claims, further comprising a return line comprising at least one cable element, which return line is electrically connected in series with the supply line. [4] Cable unit according to claim 3, wherein the supply line and the return line are jointly formed as at least two coaxial cables which are at least partially connected electrically in parallel. [5] System comprising a gradient coil unit with three gradient coils, a gradient control unit with three power amplifiers, and three connection units, each connecting a gradient coil with a power amplifier and each comprising a supply line, wherein the three gradient coils are each configured to generate a magnetic field gradient in three different spatial directions, each supply line comprises at least one cable element, and a first connection unit of the three connection units is configured as a cable unit according to one of the preceding claims. [6] System according to claim 5, wherein the first connecting unit connects a first gradient coil of the three gradient coils to a first power amplifier of the three power amplifiers and the first gradient coil is configured to generate a magnetic field gradient in the x-direction or in the y-direction. [7] System according to one of claims 5 to 6, wherein at least one cable element of the supply line of the first connection unit has a larger cross-sectional area than cable elements of the supply lines of a second connection unit and / or a third connection unit of the three connection units. [8] System according to one of claims 5 to 7, wherein a second connecting unit of the three connecting units is designed as a cable unit according to one of claims 1 to 4. [9] System according to any one of claims 5 to 8, wherein each connection unit of the three connection units is designed as a cable unit according to any one of claims 1 to 4. [10] System according to one of claims 5 to 8, wherein the supply line of a third connection unit of the three connection units comprises a cable element and is free of electrically parallel connected cable elements. [11] System according to claim 10, wherein the third connecting unit connects a third gradient coil of the three gradient coils to a third power amplifier of the three power amplifiers and the third gradient coil is configured to generate a magnetic field gradient in the z-direction. [12] System according to one of claims 5 to 11, wherein the number of cable elements of the supply lines of at least two of the three connection units is different from each other. [13] System according to one of claims 5 to 12, wherein the cross-sections of the cable elements of the supply lines of at least two of the three connection units are different from each other. [14] System according to one of claims 5 to 13, wherein each connecting unit of the three connecting units comprises a return line with at least one cable element which is electrically connected in series with the corresponding supply line. [15] System according to one of claims 5 to 14, further comprising a connection unit arranged on the surface of a housing surrounding the gradient coil unit having three connection elements, wherein each cable element or the cable element of a supply line can be connected to each of the connection elements.

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