Gradient coil unit for a magnetic resonance device

Abstract

Gradient coil unit comprising a first conductor structure arranged on a surface of a first cylinder with first radius, a second conductor structure arranged on a surface of a second cylinder with second radius, and a third conductor structure arranged on a surface of a third cylinder with third radius. where the first radius is smaller than the second radius and the second radius is smaller than the third radius, the first ladder structure is shorter in the longitudinal direction than the second ladder structure and the third ladder structure and the gradient coil unit is asymmetric.

Description

[0001] The invention relates to a gradient coil unit comprising a first conductor structure, a second conductor structure, a third conductor structure, and a magnetic resonance device.

[0002] In a magnetic resonance imaging (MRI) scanner, the body being examined, particularly a patient, is typically exposed to a relatively strong main magnetic field, for example, 1.5, 3, or 7 Tesla, in a patient acquisition area using a main magnet. Additionally, gradient pulses are generated using a gradient coil unit. High-frequency (HF) pulses, especially 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 HF 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 high-frequency antennas and then further processed.The desired image data can then be reconstructed from the raw data acquired in this way.

[0003] A gradient coil unit is typically designed to generate a magnetic field gradient in at least one spatial direction. The gradient coil unit is controlled by electrical currents with amplitudes reaching several hundred amperes and subject to frequent and rapid changes in current direction with rise and fall rates of several hundred kilovolts. Due to the positioning of the gradient coil unit within the main magnet of the magnetic resonance instrument, a large force acts upon it. This force is associated with a torque, which can cause movement and / or bending of the gradient coil unit. This can lead to vibrations during operation.

[0004] Stronger magnetic field gradients and / or rise and fall rates typically allow for faster raw data acquisition and / or higher image resolution. Particularly when examining the head of a subject, especially in diffusion-weighted imaging and / or when using a magnetic resonance imaging (MRI) system with a primary magnetic field exceeding 3 Tesla, very strong magnetic field gradients of up to 250 mT / m with rise and fall rates of up to 1000 T / s / m, and in special cases up to 2000 T / s / m, are desirable. Besides increased vibrations of the gradient coil unit, such specifications are limited by interaction with the subject.For example, when using a main gradient coil unit integrated into the magnetic resonance imaging (MRI) machine, peripheral nerve stimulation of the subject occurs at a magnetic field gradient of 20 mT / m and above, with a rise rate of 100 T / s / m. It is known that higher magnetic field gradients and / or rise and fall rates can be achieved more efficiently the smaller the area of ​​investigation encompassed by the gradient coil unit and / or the radial diameter of the gradient coil unit.

[0005] Gradient coil units are known, particularly for head examinations, which can be positioned within the patient's imaging area as needed. Examples of these are disclosed in DE 198 29 298 C2, DE 101 51 668 B4 and DE 10 2005 033 955 A1.

[0006] US 8,766,635 B2 discloses a gradient coil unit comprising a force compensation coil. US 7,141,974 B2 discloses a noise reduction device in a magnetic resonance imaging (MRI) machine.

[0007] The invention is based on the objective of providing a gradient coil unit for generating magnetic field gradients for improved imaging. This objective is achieved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0008] The invention relates to a gradient coil unit comprising a first conductor structure arranged on a surface of a first cylinder with a first radius, a second conductor structure arranged on a surface of a second cylinder with a second radius, and a third conductor structure arranged on a surface of a third cylinder with a third radius, wherein the first radius is smaller than the second radius and the second radius is smaller than the third radius.

[0009] A conductor structure typically comprises an electrical conductor. The geometric arrangement of an electrical conductor can be referred to as a conductor structure. A conductor structure arranged on a cylinder is typically saddle-shaped. The radius of the cylinder typically determines the curvature of the conductor structure in the radial direction. The gradient coil unit according to the invention is therefore designed with three layers, wherein the first, second, and third conductor structures are each arranged in a saddle shape on different layers. The gradient coil unit can also comprise a fourth conductor structure arranged on the surface of a fourth cylinder with a fourth radius, wherein the fourth radius is smaller than the first radius or larger than the third radius. The first and second conductor structures are typically electrically connected to each other.The second conductor structure and the third conductor structure are typically electrically connected to each other.

[0010] The first radius is typically less than 27 cm, preferably less than 25 cm, and particularly preferably less than 23 cm. The first radius is typically greater than 16 cm, preferably greater than 19 cm, and particularly preferably greater than 22 cm. The second radius is typically less than 34 cm, preferably less than 32 cm, and particularly preferably less than 30 cm. The second radius is typically greater than 25 cm, preferably greater than 27 cm, and particularly preferably greater than 29 cm. The third radius is typically less than 45 cm, preferably less than 40 cm, and particularly preferably less than 35 cm. The third radius is typically greater than 28 cm, preferably greater than 30 cm, and particularly preferably greater than 32 cm. The third radius is typically at least 3 cm, preferably at least 5 cm, and particularly preferably at least 7 cm larger than the second radius.

[0011] The advantage of the gradient coil unit according to the invention is that the three-layer design simultaneously enables good compensation of a torque acting when generating a magnetic field gradient and of a resulting stray magnetic field.

[0012] The first, second, and third conductor structures comprised of the gradient coil unit according to the invention are typically configured to generate a magnetic field gradient in one spatial direction. The gradient coil unit can include additional conductor structures for generating magnetic field gradients in additional spatial directions. Preferably, the gradient coil unit comprises three additional conductor structures for generating a magnetic field gradient in an additional spatial direction. The gradient coil unit can include at least two further additional conductor structures for generating a magnetic field gradient in a further spatial direction.

[0013] One embodiment of the gradient coil unit provides that the third conductor structure at least partially surrounds the second conductor structure radially, and the second conductor structure at least partially surrounds the first conductor structure radially. At least one sub-region of the gradient coil unit is typically designed in a hollow cylindrical shape. In this sub-region, the first, second, and third conductor structures are preferably arranged in a saddle-like configuration on different layers. The first radius, second radius, and third radius typically define the distance of the first, second, and third conductor structures from a central axis of the hollow cylinder described by the sub-region. The portions of the first, second, and third conductor structures arranged in this sub-region of the gradient coil unit are typically arranged concentrically.

[0014] The advantage of this embodiment is that the gradient coil unit can be manufactured to be particularly compact and with a small radial dimension. This allows for space-saving integration of the gradient coil unit within the housing of a magnetic resonance imaging (MRI) device and / or a flexible gradient coil unit with a large inner radius and / or a small outer radius. A large inner radius allows for convenient positioning of the object under investigation within the investigation area and / or the additional integration and / or positioning of a high-frequency antenna unit within the investigation area surrounded by the gradient coil unit. This enables the generation of particularly high magnetic field gradients of up to 200 mT / m, preferably up to 250 mT / m, in a very short time, for example, within 0.2 ms.On the other hand, positioning the high-frequency antenna unit within the gradient coil unit allows for the generation of high-frequency pulses with a particularly homogeneous spatial distribution within the scan area. Both of these factors positively influence the resulting image data quality and / or reduce the raw data acquisition time. A high-frequency antenna unit positioned within the scan area surrounded by the gradient coil unit typically comprises at least two high-frequency antennas with at least two channels for preferably individual control of at least two high-frequency antennas.

[0015] A first embodiment of the gradient coil unit according to the invention provides that the first conductor structure is shorter in the longitudinal direction than the second conductor structure and the third conductor structure.

[0016] The gradient coil unit is typically designed in a hollow cylindrical shape, and the longitudinal end of the gradient coil unit can be defined as the cross-section of the gradient coil unit at a plane perpendicular to the longitudinal axis at a position of maximum or minimum longitudinal extent. According to this embodiment, the inner first conductor structure has a shorter length than the second and third conductor structures, with the third conductor structure typically at least partially radially surrounding the second conductor structure, and the second conductor structure at least partially radially surrounding the first conductor structure. The first, second, and third conductor structures are preferably arranged flush at a first longitudinal end of the gradient coil unit; in particular, they terminate at the first longitudinal end.The first ladder structure preferably terminates at a second longitudinal end opposite the first longitudinal end, whereas the second ladder structure and / or the third ladder structure are designed in such a way that they extend to a third longitudinal end.

[0017] The gradient coil unit according to the first embodiment of the invention is asymmetrical. The examination area is typically the area enclosed by the gradient coil unit, within which raw data from a test object can be acquired, provided the test object is positioned at least partially within the examination area. The gradient coil unit described in this embodiment enables particularly precise positioning of a patient's head as the test object within the examination area. Typically, the neck and shoulder area adjoin the head caudally, with the shoulder area having a larger radial circumference than the head and neck.The gradient coil unit is preferably dimensioned such that the first radius is larger than the radius of an average head, but less than half the lateral extent of an average shoulder region. The second and / or third radius, on the other hand, is preferably larger than half the lateral extent of an average shoulder region.

[0018] The area enclosed by the first conductor structure is preferably referred to as the test area. The gradient coil unit is preferably designed such that the head of a test object can be positioned centrally within the test area, while the shoulder area of ​​the test object can be positioned outside the test area and simultaneously enclosed by the second conductor structure and / or the third conductor structure. The first radius is preferably selected such that a high-frequency antenna unit can be positioned between the inner surface of the first conductor structure and the head of the test object.

[0019] The advantage of this embodiment is that the head of the object under investigation can be conveniently positioned within the center of the investigation area, and the radius of the first conductor structure is small, typically less than 26 cm. This allows the gradient coil unit to be operated particularly efficiently with especially large magnetic field gradients and rise and fall rates, such as 200 mT / m and 2000 T / s / m. The maximum magnetic field gradient that can be generated by the gradient coil unit is typically at least 150 mT / m, preferably at least 200 mT / m. A maximum rise and / or fall rate achievable by the gradient coil unit is typically at least 800 T / s / m, preferably at least 1000 T / s / m, and particularly preferably at least 1500 T / m / s.Furthermore, the influence of the magnetic field gradients on the trunk of the subject can be reduced, so that the limit value for peripheral nerve stimulation can still be met.

[0020] One embodiment of the gradient coil unit provides that the first conductor structure and the second conductor structure are jointly configured to generate a magnetic field gradient in one direction within a test area enclosed by the first conductor structure.

[0021] A magnetic field gradient is typically a magnetic field that increases linearly in a spatial direction. A magnetic field gradient is typically generated temporarily by electric currents in a conductor structure. These electric currents are typically generated according to a specified MR control sequence by a gradient control unit in the gradient coil unit, particularly when controlling the gradient coil unit and / or the magnetic resonance imaging (MRI) system. A magnetic field gradient is typically described as homogeneous if it increases linearly in a spatial direction. A magnetic field gradient is also typically described as homogeneous if the gradient of the resulting magnetic field, and in particular its spatial derivative, is constant, especially spatially constant.

[0022] Depending on their arrangement and / or configuration, the first and second conductor structures preferably determine the shape of the magnetic field gradient when an electric current is applied to them. Due to the preferably small radius of the first conductor structure, a magnetic field gradient can be generated particularly efficiently. The first and second conductor structures preferably replace a conventional primary coil, which normally comprises a conductor structure.

[0023] Typically, the first and second conductor structures are each enclosed twice by the gradient coil unit in a symmetrical arrangement. Depending on their spatial positioning, these conductor structures work together to generate a magnetic field gradient in either the x-direction or the y-direction.

[0024] One embodiment of the gradient coil unit provides that the first conductor structure and / or the second conductor structure are designed to compensate for a torque on the gradient coil unit that arises when a magnetic field gradient is generated.

[0025] During operation of the gradient coil unit, a first electric current typically flows in the first conductor structure, and / or a second electric current flows in the second conductor structure, and / or a third electric current flows in the third conductor structure. The interaction of the first electric current in the first conductor structure, and / or the second electric current in the second conductor structure, and / or the third electric current in the third conductor structure, with the main magnetic field acting in the region of the first conductor structure, and / or the second conductor structure, and / or the third conductor structure, causes a Lorentz force, which in turn causes a torque on the gradient coil unit. This can lead to vibrations during operation of the gradient coil unit.

[0026] In conventional symmetrical conductor structures and / or symmetrical gradient coil units, which can be divided into four mutually symmetrical quadrants, forces acting at different positions within the conductor structure can at least partially cancel each other out. This typically results in a negligible torque. However, a symmetrically designed gradient coil unit optimized for acquiring raw data from the head of a test object has numerous disadvantages. For example, to acquire high-quality raw data, the area under investigation, particularly the head, must be positioned at the center of the gradient coil unit.Due to the required dimensions of a conductor structure in the longitudinal direction of a conventional symmetrical gradient coil unit, the head of a test object can typically only be positioned in the center of the gradient coil unit if the symmetrical gradient coil unit is designed to accommodate the head, neck, and shoulder area of ​​the test object. This necessitates a large radius of the test area, which reduces the efficiency of the gradient coil unit.

[0027] Preferably, the first conductor structure is shorter in the longitudinal direction than the second and third conductor structures. Spatial regions of the gradient coil unit can be identified on which a particularly large torque acts due to the Lorentz force. These regions are positioned, in particular, at the longitudinal end of the first conductor structure facing the torso. If the first conductor structure were inherently designed to compensate for a torque, a longer extension along the longitudinal axis would be required. This would only allow positioning of the head in the center of the gradient coil unit with a simultaneously larger radius, which would be associated with a reduction in efficiency.

[0028] Forces and / or torques resulting from a first electric current in the first conductor structure are preferably reduced and / or compensated by a second electric current in the second conductor structure. This allows the first conductor structure to be free of an additional conductor loop for torque compensation, for example, at a longitudinal end of the first conductor structure facing away from the body. Conversely, the second conductor structure can be arranged predominantly at the longitudinal end of the second conductor structure facing the body. This allows for a short extension of the gradient coil unit in the direction facing away from the body. The first electric current, the second electric current, and / or the third electric current can be different from each other.The first electric current, the second electric current, and / or the third electric current can be staggered in time and / or of different magnitudes. The first electric current, the second electric current, and / or the third electric current can also be of the same magnitude and / or occur simultaneously.

[0029] This embodiment of the gradient coil unit enables the efficient generation of a magnetic field gradient using the first and second conductor structures, wherein the first and second conductor structures are designed to compensate for a torque. In particular, such a gradient coil unit can have a particularly small first radius and simultaneously allow the head of a test object to be positioned at the center of the test area of ​​the gradient coil unit, thereby making the efficiency of the gradient coil unit particularly high.

[0030] A second embodiment of the gradient coil unit according to the invention provides that the third conductor structure is designed to compensate for a stray magnetic field generated when a magnetic field gradient is created by means of the first and / or second conductor structure. Preferably, the third conductor structure is symmetrical. The third conductor structure can also be configured such that a maximum of 40%, preferably a maximum of 30%, and particularly preferably a maximum of 20% of the third conductor structure is arranged in the half of the gradient coil unit facing away from the torso.

[0031] A stray magnetic field is typically a magnetic field that arises outside the patient acquisition and / or examination area when the first conductor structure and / or the second conductor structure is activated, i.e., when an electric current is applied to the first conductor structure and / or the second conductor structure. The stray magnetic field typically does not contribute to imaging but can negatively affect it. The stray magnetic field can interact with components surrounding the gradient coil unit. For example, it can induce an electric current and / or heat up an electrically conductive environment adjacent to the gradient coil unit, such as a wall enclosing the main magnet's cryostat, a thermal shield, and / or a high-frequency antenna unit.It was recognized that, particularly in the radial outer area of ​​the gradient coil unit, preferably in the region of a wall enclosing the cryostat of a main magnet on the inside and / or a temperature shield, a stray magnetic field and / or eddy currents caused by a stray magnetic field can negatively affect the efficiency of cooling the main magnet and / or the homogeneity of a magnetic field gradient generated by the gradient coil unit. In particular, the third conductor structure of the gradient coil unit according to the invention can be designed such that an electric current in the third conductor structure reduces the stray magnetic field and, in particular, results in reduced electromagnetic interaction.

[0032] This embodiment of the gradient coil unit provides that the first and second conductor structures are designed to generate a magnetic field gradient and compensate for the resulting torque. The third conductor structure is preferably optimized primarily to compensate for a stray magnetic field, particularly one generated by the first and second conductor structures. The compensation of a stray magnetic field has previously been neglected, especially in gradient coil units that can be flexibly positioned within the patient acquisition area of ​​a magnetic resonance imaging (MRI) scanner, due to their distance from the cryostat of the main magnet. This embodiment allows for reduced heating of the main magnet's cryostat, resulting in lower energy input and / or reduced coolant requirements.This is particularly advantageous for superconducting main magnets with superconductors without immersion in a superconducting medium.

[0033] One embodiment of the gradient coil unit provides that in a protrusion area of ​​the second conductor structure, in which protrusion area the first conductor structure is shorter in the longitudinal direction than the second conductor structure, the second conductor structure is designed to reduce a torque on the gradient coil unit that arises when a magnetic field gradient is generated.

[0034] When the head of a test subject is positioned in the gradient coil unit, the overhanging section is characterized by its location at the longitudinal end of the gradient coil unit facing the torso. The second conductor structure is preferably arranged predominantly within this overhanging section. Preferably, a maximum of 30%, more preferably a maximum of 20%, and particularly preferably a maximum of 10% of the second conductor structure is arranged in the half of the gradient coil unit facing away from the torso. This embodiment of the gradient coil unit allows for particularly convenient positioning of the test subject's head within the examination area enclosed by the first conductor structure, as the shoulder area of ​​the test subject can be positioned within the overhanging section. The overhanging section typically has a larger radius than the radius of the first conductor structure.

[0035] A third embodiment of the gradient coil unit according to the invention provides that the gradient coil unit can be flexibly positioned within a patient acquisition area of ​​a magnetic resonance imaging (MRI) device. The gradient coil unit can, for example, be arranged and / or fixed to a patient positioning device of the MRI device. Such a gradient coil unit is typically designed to accommodate at least a portion of the object being examined. The gradient coil unit can be positioned before the examination is performed.

[0036] The magnetic resonance imaging (MRI) scanner may also include a main gradient coil unit. When the gradient coil unit is positioned within the patient acquisition area of ​​the MRI scanner, it can be used instead of the main gradient coil unit. This allows for particularly high magnetic field gradients and / or rise and fall rates to be achieved very efficiently in a specific area, typically the head, of the patient, while areas of the patient outside this area are less affected by the magnetic field gradients and / or by peripheral nerve stimulation. This is particularly advantageous with an MRI scanner that has a main magnetic field greater than 3 Tesla and / or for dedicated head examinations.

[0037] A fourth embodiment of the gradient coil unit according to the invention provides that the first conductor structure and / or the second conductor structure and / or the third conductor structure is asymmetrically designed. Such a gradient coil unit allows for convenient positioning of a head in the center of the investigation area of ​​the gradient coil unit while simultaneously providing good torque compensation and reduction of stray magnetic fields.

[0038] A fifth embodiment of the gradient coil unit according to the invention provides that the second conductor structure is arranged spirally around a central point. The second conductor structure can also be at least partially helical and / or ring-shaped and / or circular. Such a second conductor structure enables particularly good torque compensation.

[0039] One embodiment of the gradient coil unit provides that the third conductor structure spirally surrounds at least two centers. The third conductor structure can also be at least partially helical and / or ring-shaped and / or circular. Such a third conductor structure enables particularly effective reduction of stray magnetic fields.

[0040] One embodiment of the gradient coil unit provides that the gradient coil unit comprises two of each of the first, second, and third conductor structures, with each of the first, second, and third conductor structures arranged within one half of the gradient coil unit, and that the gradient coil unit is symmetrical. Typically, two mutually symmetrical saddle coils are required to generate a magnetic field gradient. Two mutually symmetrical first conductor structures preferably enable the generation of a magnetic field gradient in one direction. Two mutually symmetrical second conductor structures preferably enable the compensation of a torque generated during the generation of the magnetic field gradient.Two third conductor structures arranged symmetrically to each other preferably enable compensation of a stray magnetic field that arises when the first and second conductor structures are controlled.

[0041] Furthermore, the invention relates to a magnetic resonance device comprising a gradient coil unit according to the invention, a gradient control unit, and a main magnet. The magnetic resonance device preferably comprises a Fig. Figure 3 shows a gradient coil unit comprising at least two first conductor structures, two second conductor structures, and two third conductor structures. The magnetic resonance device can also include a gradient coil unit according to at least one of the embodiments described above. The gradient coil unit according to the invention can be integrated into the magnetic resonance device. The gradient coil unit according to the invention can also be installed separately from the magnetic resonance device. The gradient coil unit according to the invention can be connected to the magnetic resonance device. Embodiments of the magnetic resonance device according to the invention are designed analogously to the embodiments of the gradient coil unit according to the invention. The magnetic resonance device can have further control components, which are necessary and / or advantageous.The magnetic resonance device can also be configured to send, receive, and / or process control signals. The advantages of the magnetic resonance device according to the invention essentially correspond to the advantages of the gradient coil unit according to the invention, which have been described in detail above. Features, advantages, or alternative embodiments mentioned herein can also be applied to the other claimed items and vice versa.

[0042] Further advantages, features and details of the invention will become apparent from the exemplary embodiments described below and from the drawings.

[0043] They show: Fig. 1 a schematic representation of a magnetic resonance device according to the invention, Fig. 2. A schematic representation of a gradient coil unit to illustrate parameters, Fig. 3 a schematic representation of a first embodiment of a gradient coil unit according to the invention, Fig. 4 a schematic representation of a second embodiment of a gradient coil unit according to the invention, Fig. 5 a schematic representation of an embodiment of a first conductor structure, Fig. 6 a schematic representation of an embodiment of a second conductor structure, Fig. 7 a schematic representation of an embodiment of a third conductor structure.

[0044] Fig. Figure 1 shows a schematic representation of a magnetic resonance imaging (MRI) device 11 according to the invention. The MRI device 11 comprises a detector unit formed by a magnetic unit 13 with a main magnet 17 for generating a strong and, in particular, constant main magnetic field 18. The MRI device 11 also has a cylindrical patient acquisition area 14 for receiving a patient 15, wherein the patient acquisition area 14 is enclosed in a cylindrical shape in a circumferential direction by the magnetic unit 13. The patient 15 can be moved into the patient acquisition area 14 by means of a patient positioning device 16 of the MRI device 11. For this purpose, the patient positioning device 16 has a patient table that is movably arranged within the MRI device 11.

[0045] The magnetic unit 13 can optionally include a main gradient coil unit 19, which is used for spatial coding during imaging. The main gradient coil unit 19 is controlled by a main gradient control unit 28. The main gradient coil unit 19 is typically used in the absence of a gradient coil unit 21 according to the invention. The gradient coil unit 21 according to the invention can be flexibly positioned within a patient acquisition area 14. Preferably, the gradient coil unit 21 is arranged on the patient positioning device 16 such that a body part, preferably the head, of the patient 15 can be positioned within the gradient coil unit 21. The space encompassed by the gradient coil unit 21 is referred to as the examination area 22. The gradient coil unit 21 is controlled by a gradient control unit 33.Furthermore, the magnet unit 13 includes a high-frequency antenna unit 20, which in the illustrated case is designed as a body coil permanently integrated into the magnetic resonance device 11, and a high-frequency antenna control unit 29 for exciting a polarization that arises in the main magnetic field 18 generated by the main magnet 17. The high-frequency antenna unit 20 is controlled by the high-frequency antenna control unit 29 and emits high-frequency pulses into an examination space, which is essentially formed by the patient reception area 14. Alternatively and / or additionally, the high-frequency antenna unit 29 can be designed such that it can be positioned in the examination area 22 surrounded by the gradient coil unit 21 and / or arranged on and / or integrated into the gradient coil unit 21.

[0046] The magnetic resonance imaging (MRI) device 11 includes a control unit 24 for controlling the main magnet 17, the gradient control unit 28, and the high-frequency antenna control unit 29. The control unit 24 centrally controls the MRI device 11, for example, by performing MR control sequences. The control unit 24 also includes a reconstruction unit (not shown) for reconstructing medical image data acquired during the MRI scan. The MRI device 11 includes a display unit 25. Control information, such as control parameters, as well as reconstructed image data, can be displayed on the display unit 25, for example, on at least one monitor, for a user. The MRI device 11 also includes an input unit 26, by means of which information and / or control parameters can be entered by a user during a measurement procedure.The control unit 24 can include the gradient control unit 28 and / or the high-frequency antenna control unit 29 and / or the display unit 25 and / or the input unit 26.

[0047] The depicted magnetic resonance device 11 can, of course, include further components that magnetic resonance devices 11 typically possess. Furthermore, the general operating principle of a magnetic resonance device 11 is known to those skilled in the art, so a detailed description of the further components is omitted.

[0048] Fig. Figure 2 shows a schematic representation of a gradient coil unit 21 to illustrate parameters. The gradient coil unit 21 typically has a cylindrical outer surface. The gradient coil unit 21 is typically subdivided into two halves. One half of the gradient coil unit 21 typically comprises at least a first conductor structure 41, a second conductor structure 42, and a third conductor structure 43. The gradient coil unit 21 typically has at least one first conductor structure 41, one second conductor structure 42, and one third conductor structure 43 in each of the two halves. The two halves of the gradient coil unit 21 are typically symmetrical, preferably axially symmetrical, to each other.

[0049] One half of the gradient coil unit 21 is preferably connected along the z-axis through the two longitudinal ends of the gradient coil unit 21 at z min and z maxThe first half of the gradient coil unit 21 is defined in a first direction by its maximum extent in that direction. The second half of the gradient coil unit 21 is defined in a second direction by the distance of an outer surface of the gradient coil unit 21 from the origin along the second direction. The first and second directions are typically perpendicular to each other. If the first conductor structure 41 and the second conductor structure 42 are configured to generate a magnetic field gradient in the x-direction, then the first direction corresponds to the x-direction. If the first conductor structure 41 and the second conductor structure 42 are configured to generate a magnetic field gradient in the y-direction, then the first direction corresponds to the y-direction.

[0050] Fig. Figure 3 shows a schematic representation of a first embodiment of a gradient coil unit 21 according to the invention. Fig. Figure 3 shows an axial cross-section, preferably through the axial center, of a first embodiment of the gradient coil unit 21 according to the invention. The gradient coil unit 21 is divided into a primary coil 31 and a secondary coil 32. The primary coil 31 comprises a first conductor structure 41, 41' and a second conductor structure 42, 42'. The gradient coil unit 21, in particular the primary coil 31, preferably comprises two of the first conductor structures 41, 41'. The two first conductor structures 41, 41' are preferably arranged point-symmetrically with respect to the center point 0 of the area under investigation 22. The gradient coil unit 21, in particular the primary coil 31, preferably comprises two of the second conductor structures 42, 42'. The two second conductor structures 42, 42' are preferably arranged point-symmetrically with respect to the center point 0 of the gradient coil unit 21.The second conductor structure 42, 42' has a larger radius to the center point 0 of the gradient coil unit 21 compared to the first conductor structure 41, 41'. The two first conductor structures 41, 41' and the two second conductor structures 42, 42' are configured together to generate a magnetic field gradient in a test area 22. In the illustrated case, the two first conductor structures 41, 41' and the two second conductor structures 42, 42' are configured together to generate a magnetic field gradient in the x-direction. One first conductor structure 41 and one second conductor structure 42 are typically arranged within one half of the gradient coil unit 21. The other first conductor structure 41' and the other second conductor structure 42' are typically arranged within the other half of the gradient coil unit 21.

[0051] Furthermore, the primary coil 31 shown comprises two additional first conductor structures 45, 45' and two additional second conductor structures 46, 46'. The two additional first conductor structures 45, 45' and the two additional second conductor structures 46, 46' are typically constructed analogously to the two first conductor structures 41, 41' and the two second conductor structures 42, 42', but differ by an angle dφ of 90°. Consequently, in the illustrated case, the two additional first conductor structures 45, 45' and the two additional second conductor structures 46, 46' are jointly configured to generate a magnetic field gradient in the y-direction. The primary coil 31 shown is therefore configured to generate magnetic field gradients in both the x-direction and the y-direction.

[0052] The secondary coil 32 preferably comprises a third conductor structure 43, 43'. The gradient coil unit 21, in particular the secondary coil 32, preferably comprises the third conductor structure 43, 43' twice. The two third conductor structures 43, 43' are preferably arranged point-symmetrically with respect to the center point 0 of the gradient coil unit 21. The secondary coil 32, in particular the third conductor structure 43, 43', is designed to compensate for a stray magnetic field generated when a magnetic field gradient is created by means of the two first conductor structures 41, 41' and the two second conductor structures 42, 42'. The secondary coil 32 preferably has a larger radius, in particular with respect to the center point 0 of the gradient coil unit 21, than the primary coil 31.

[0053] Furthermore, the depicted secondary coil 32 includes two additional third conductor structures 47, 47'. These two additional third conductor structures 47, 47' are typically constructed analogously to the two third conductor structures 43, 43', but differ by an angle dφ of 90°. Consequently, in the depicted case, the two additional third conductor structures 47, 47' together compensate for a stray magnetic field generated when a magnetic field gradient is created by means of the two additional first conductor structures 45, 45' and the two additional second conductor structures 46, 46'. The additional third conductor structure 47, 47' is therefore designed to compensate for a stray magnetic field generated when a magnetic field gradient is created in the y-direction.The secondary coil 31 shown is therefore designed to compensate for stray magnetic fields that arise during the generation of magnetic field gradients in the x-direction and in the y-direction.

[0054] The gradient coil unit 21 preferably comprises a further conductor structure, not shown in detail, encompassed by the primary coil 31, which is configured to generate a magnetic field gradient in the z-direction. Likewise, the gradient coil unit 21 preferably comprises a further conductor structure, not shown in detail, encompassed by the secondary coil 32, which is configured to compensate for a stray magnetic field arising when a magnetic field gradient is generated in the z-direction.

[0055] The conductor structures 41, 42, 43, 45, 46, 47, 41', 42', 43', 45', 46', 47' mentioned above are typically arranged at least partially concentrically and / or nested within one another. Their order, in particular their distance from the center point 0 of the gradient coil unit 21, is shown in Fig. Figure 3 is shown as an example and can also be configured differently. In particular, the third conductor structure 43, 43' surrounds the second conductor structure 42, 42' at least partially radially, and the second conductor structure 42, 42' surrounds the first conductor structure 41, 41' at least partially radially. The third conductor structure 43, 43' and the second conductor structure 42, 42' are typically arranged concentrically. The first conductor structure 41, 41' and the second conductor structure 42, 42' are typically arranged at least partially concentrically.

[0056] Fig. Figure 4 shows a schematic representation of a second embodiment of a gradient coil unit 21 according to the invention. Fig. Figure 4 shows a cross-section at y = 0 of a second embodiment of the gradient coil unit 21 according to the invention. The gradient coil unit 21 comprises the first conductor structure 41, 41', the second conductor structure 42, 42', and the third conductor structure 43, 43', wherein the first conductor structure 41, 41' is shorter in the longitudinal direction, i.e., parallel to the z-axis, than the second conductor structure 42, 42' and the third conductor structure 43, 43'. The area within the gradient coil unit 21, which is radially surrounded only by the second conductor structure 42, 42' and / or the third conductor structure 43, 43', but not by the first conductor structure 41, 41', can be referred to as the overhang area 23. The overhang area 23 is preferably not part of the investigation area 22. Within the investigation area 22, the magnetic field gradient is typically particularly homogeneous.The investigation area 22 is typically only a sub-area of ​​the area surrounded by the first conductor structure 41, 41' and / or the area enclosed by the gradient coil unit 21, minus the overhang area 23. The investigation area 22 typically adjoins the overhang area 23.

[0057] During a magnetic resonance examination, magnetic resonance signals are typically acquired and / or encoded within the examination area 22. In the illustrated example, image data of the patient's head can therefore be generated. The patient's shoulders 15 are positioned outside the examination area 22, specifically within the overhang area 23. A portion of the second conductor structure 42, 42' enclosing the overhang area 23 is therefore preferably configured primarily to reduce a torque on the gradient coil unit 21 that arises during the generation of a magnetic field gradient. Nevertheless, according to this embodiment, the first conductor structure 41, 41' and the second conductor structure 42, 42' can jointly be configured to generate a magnetic field gradient in the examination area 22 enclosed by the first conductor structure 41, 41'.The longitudinal end of the gradient coil unit 21 adjoining the overhang area 23 is referred to below as z. min designated.

[0058] Fig. Figure 5 shows a schematic representation of an embodiment of a first conductor structure 41. The first conductor structure 41 is shown planar, in particular unrolled. The ordinate describes dφ. Within the gradient coil unit 21, the first conductor structure 41 is preferably saddle-shaped with a first radius to the center 0 of the gradient coil unit 21. In particular, it can be seen that the first conductor structure 41 is at a distance of at least one-fifth, for example about one-quarter, of the length of the gradient coil unit 21 from the longitudinal end at z. minexhibits a characteristic that typically corresponds to the overhang area 23. The first conductor structure 41 is preferably at least partially spiral and / or circular and / or helical in shape. In the simplified embodiment shown, the first conductor structure 41 circularly surrounds a first center point 51. Typically, the first conductor structure 41 is similar to the one shown, but spiral in shape. The first conductor structure 41 can also spirally surround another center point. The position of the first center point 51 on the z-axis typically defines the center point of the gradient coil unit 21 and / or the center point of the investigation area 22.

[0059] Fig. Figure 6 shows a schematic representation of an embodiment of a second conductor structure 42. The second conductor structure 42 is shown planar, in particular unrolled. Within the gradient coil unit 21, the second conductor structure 42 is preferably saddle-shaped with a second radius around the center point 0 of the gradient coil unit 21. The second conductor structure 42 typically extends over the entire extent of the gradient coil unit 21 in the z-direction. The first conductor structure 41 and / or the second conductor structure 42 can be configured to compensate for a torque on the gradient coil unit 21 that arises during the generation of a magnetic field gradient.Typically, the second conductor structure 42, in particular the portion of the second conductor structure 42 located in the overhang region 23, is designed to compensate for a torque on the gradient coil unit 21 that arises during the generation of a magnetic field gradient. Additionally, the second conductor structure 42 is typically designed to generate a magnetic field gradient together with the first conductor structure 41. For both functionalities, the second conductor structure 42 is typically arranged spirally around a second center point 52. In the simplified embodiment, the wider conductor structure 42 encloses a second center point 52 in a circular fashion. Typically, the second conductor structure 42 is similar to the one shown, but spirally arranged.The second center point 52 is preferably positioned closer to the longitudinal end of the gradient coil unit 21 that closes off the overhang region 23 than to the longitudinal end of the gradient coil unit 21 that faces away from the overhang region 23. The second center point 52 is preferably positioned closer to the longitudinal end of the gradient coil unit 21 that closes off the overhang region 23 than the first center point 51. The second conductor structure is preferably designed such that the spatial density of the second conductor structure in the area between the second center point 52 and the longitudinal end that closes off the overhang region 23 is at least 30%, preferably at least 50%, and particularly preferably at least 70% greater than in the area between the second center point 52 and the longitudinal end opposite the overhang region 23.

[0060] Fig.Figure 7 shows a schematic representation of an embodiment of a third conductor structure 43. The third conductor structure 43 is shown planar, in particular unrolled. Within the gradient coil unit 21, the third conductor structure 43 is preferably saddle-shaped with a third radius to the center point 0 of the gradient coil unit 21. The third conductor structure 43 typically extends over at least 80%, preferably over at least 90%, of the extent of the gradient coil unit 21 in the z-direction. The third conductor structure 43 is typically designed to compensate for a stray magnetic field generated when a magnetic field gradient is created by means of a first conductor structure 41 and / or a second conductor structure 42. In the simplified embodiment shown, the third conductor structure 43 encloses the centers 53, 54 in a circular fashion. Typically, the third conductor structure 43 runs similarly to the one shown, but in a spiral shape.When considering the projection onto the z-axis, the first center point 51 is preferably arranged between the two centers 53, 54.

[0061] 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 by the person skilled in the art without leaving the scope of protection of the invention.

Claims

[1] Gradient coil unit comprising a first conductor structure arranged on a surface of a first cylinder with a first radius, a second conductor structure arranged on a surface of a second cylinder with a second radius and a third conductor structure arranged on a surface of a third cylinder with a third radius, where the first radius is smaller than the second radius and the second radius is smaller than the third radius, the first ladder structure is shorter in the longitudinal direction than the second ladder structure and the third ladder structure and the gradient coil unit is asymmetric. [2] Gradient coil unit comprising a first conductor structure arranged on a surface of a first cylinder with a first radius, a second conductor structure arranged on a surface of a second cylinder with a second radius and a third conductor structure arranged on a surface of a third cylinder with a third radius, where the first radius is smaller than the second radius and the second radius is smaller than the third radius, and the third conductor structure is designed to compensate for a stray magnetic field that arises when a magnetic field gradient is generated by means of the first conductor structure and / or the second conductor structure [3] Gradient coil unit comprising a first conductor structure arranged on a surface of a first cylinder with first radius, a second conductor structure arranged on a surface of a second cylinder with second radius and a third conductor structure arranged on a surface of a third cylinder with third radius, where the first radius is smaller than the second radius and the second radius is smaller than the third radius, and the gradient coil unit can be flexibly positioned within a patient acquisition area of ​​a magnetic resonance imaging device. [4] Gradient coil unit comprising a first conductor structure arranged on a surface of a first cylinder with first radius, a second conductor structure arranged on a surface of a second cylinder with second radius and a third conductor structure arranged on a surface of a third cylinder with third radius, where the first radius is smaller than the second radius and the second radius is smaller than the third radius, and the first ladder structure and / or the second ladder structure and / or the third ladder structure is asymmetrically designed. [5] Gradient coil unit comprising a first conductor structure arranged on a surface of a first cylinder with a first radius, a second conductor structure arranged on a surface of a second cylinder with a second radius and a third conductor structure arranged on a surface of a third cylinder with a third radius, where the first radius is smaller than the second radius and the second radius is smaller than the third radius, and the second ladder structure is arranged spirally around a central point. [6] Gradient coil unit according to one of the preceding claims, wherein the third conductor structure at least partially surrounds the second conductor structure radially and the second conductor structure at least partially surrounds the first conductor structure radially. [7] Gradient coil unit according to any one of the preceding claims, wherein the first conductor structure and the second conductor structure are jointly configured to generate a magnetic field gradient in one direction within a test area enclosed by the first conductor structure. [8] Gradient coil unit according to one of the preceding claims, wherein the first conductor structure and / or the second conductor structure are designed to compensate for a torque on the gradient coil unit that arises when generating a magnetic field gradient. [9] Gradient coil unit according to one of the preceding claims, wherein in a protrusion area of ​​the second conductor structure, in which protrusion area the first conductor structure is shorter in the longitudinal direction than the second conductor structure, the second conductor structure is designed to reduce a torque arising on the gradient coil unit when generating a magnetic field gradient. [10] Gradient coil unit according to one of the preceding claims, wherein the third conductor structure surrounds at least two centers in a spiral manner. [11] Gradient coil unit according to one of the preceding claims, wherein the gradient coil unit comprises the first conductor structure, the second conductor structure and the third conductor structure twice each, a first conductor structure, a second conductor structure and a third conductor structure are arranged within one half of the gradient coil unit and the gradient coil unit is symmetrical. [12] Magnetic resonance device comprising a gradient coil unit according to one of the preceding claims, a gradient control unit and a main magnet.

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