It has been recognized that the amplitude of a magnetic field gradient (G) is proportional to the current density, to which current density the sensitivity (S) of the gradient coil unit is proportional. Increasing the number of conductors, particularly the number of turns, typically increases the current density. If the number of turns is doubled using an electrical conductor of half the thickness, the sensitivity (S) is typically doubled and the electrical resistance (R) quadruples. The inductance (L) typically quadruples, which means that, without additional action, the slew rate (SR) is halved according to U=L dI/dt+RI and SR=U/L·S, where the resistive component is negligible compared to the inductive component. The slew rate can be kept constant by doubling the voltage e.g. by using two separately drivable primary conductor pattern pairs according to the disclosure. According to this example, the power loss P=I²·R=(G/S)². R dissipated as heat remains unchanged unless a higher amplitude of the magnetic field gradient (G) is generated.

Since the higher sensitivity (S) typically enables a higher amplitude of the magnetic field gradient (G), the power loss dissipated as heat also increases with it, and there is an increased cooling requirement. For example, the generation of high gradient moments combined with the possibility of fast switching of the gradient coil unit, i.e. a high slew rate, requires new cooling options.

The use of hollow conductors in conjunction with a plurality of cooling circuits according to this embodiment provides efficient cooling and dissipation of power loss over an extended period of time. This embodiment enables a maximum magnetic field gradient amplitude of any suitable value, such as e.g. at least 180 mT/m, at least 200 mT/m, and to be generated at any suitable slew rate such as e.g. at least 180 mT/m/ms, at least 200 mT/m/ms, such as when the two gradient amplifier units are each driven with a voltage of between 2200 V and 2300 V and/or with a current of between 1100 and 1300 A. The ohmic resistance of the primary coil and/or the gradient coil unit can be e.g. between 400 mΩ and 500 mΩ, and the inductance between e.g. 1350 μH and 3500 μH, between 2000 μH and 3000 μH, etc.

One embodiment of the gradient coil unit provides that the portion of the electrical conductor is disposed in such a way that the two adjacent turns each run in pairs and/or one turn in each case has a smaller distance from a first adjacent turn than from a second adjacent turn. This embodiment provides particularly uniform cooling of the primary coil. In addition, such a gradient coil unit is particularly durable to manufacture.

One embodiment of the gradient coil unit provides that the electrical conductor is disposed spirally in turns such that each of the two spiral conductor patterns has at least 35 turns.

According to this embodiment, the electrical conductor is configured such that it surrounds at least one fixed point within a quadrant in any suitable number of turns, such as e.g. at least 35 turns, at least 39 turns, at least 45 turns, etc., at least partially in a spiral manner. The turns can be assigned to the first section or the second section. The electrical conductor typically has less than 65, less than 55, less than 50 turns, etc., within a quadrant.

Such a high number of turns per unit area provides a particularly high current density and thus a particularly high maximum gradient amplitude.

One embodiment of the gradient coil unit provides that the electrical conductor has a cross-sectional area of any suitable size, such as e.g. less than 35 mm², less than 32 mm², less than 30 mm², etc. The cross-sectional area of the electrical conductor typically includes the cross-sectional area of the conductive material of the electrical conductor, e.g. the hollow conductor. The cross-sectional area of the hollow region of the electrical conductor, e.g. of the hollow conductor, which hollow region can be configured to hold a coolant, is typically between any suitable range of dimensions such as e.g. 9 mm²and 16 mm², between 11 mm²and 14 mm², between 12 mm²and 13 mm², etc. A hollow conductor configured in this way can conduct an electric current with a strength of between 800 A and 1500 A, between 800 A and 1200 A, etc., particularly well with the lowest possible power loss while at the same time providing direct cooling by means of the coolant.

One embodiment of the gradient coil unit provides that each of the spiral conductor patterns is configured such that it spirally surrounds two fixed points, e.g. within a quadrant. The two fixed points may be at different positions in the longitudinal direction. A first fixed point of the two fixed points is typically closer to a center of the gradient coil unit in the longitudinal direction than a second fixed point of the two fixed points. The first fixed point and the second fixed point may be at the same position in the circumferential direction. The number of turns of the electrical conductor surrounding the first fixed point is typically at least three times, at least five times, etc., the number of turns of the electrical conductor surrounding the second fixed point. The spiral conductor pattern may be configured such that the turns surrounding the second fixed point run counter to the turns surrounding the first fixed point and/or an electric current in turns surrounding the first fixed point flows counter to an electric current in turns surrounding the second fixed point. This embodiment enables the force acting on the gradient coil unit to be reduced. In addition, any leakage field generated by the primary coil and/or gradient coil unit is reduced.

According to one embodiment of the gradient coil unit, the two primary conductor pattern pairs are separated from each other by a plane perpendicular to the cylinder axis. The two primary conductor pattern pairs may be symmetrical with respect to a plane perpendicular to the cylinder axis, e.g. the center plane of the gradient coil unit in the longitudinal direction. According to this embodiment, a primary conductor pattern pair spans half the length of the gradient coil unit in a fully circumferential manner. This embodiment can be durably manufactured and effectively enables the two primary conductor pattern pairs to be driven separately.

One embodiment of the gradient coil unit comprises an additional primary coil configured to generate a magnetic field gradient in a second spatial direction corresponding to the longitudinal direction, wherein the additional primary coil comprises two helical conductor patterns surrounding the cylinder axis, which two helical conductor patterns are spatially separated from each other by a plane perpendicular to the cylinder axis and are separately drivable, and each of the two helical conductor patterns comprises an additional electrical conductor implemented as a hollow conductor.

Each of the two helical conductor patterns may comprise one additional electrical conductor and/or is disposed within two quadrants having a common edge. A first helical conductor pattern of the two helical conductor patterns may be disposed within the same quadrants as the first primary conductor pattern pair. A second helical conductor pattern of the two helical conductor patterns may be disposed within the same quadrants as the second primary conductor pattern pair.

The helical conductor patterns are each disposed on a lateral surface of a cylinder and/or helically surround said cylinder. The two helical conductor patterns typically have the same diameter and/or are disposed coaxially with the primary coil and/or the cylinder axis.

This embodiment, the additional primary coil allows a magnetic field gradient to be generated in the longitudinal direction with the same specifications, e.g. the same amplitude and slew rate as the primary coil in the first spatial direction. Accordingly, this embodiment of the gradient coil unit is universally usable.

One embodiment of the gradient coil unit provides that the additional electrical conductor of a helical conductor pattern of the two helical conductor patterns can be divided into at least two serially interconnected additional sections, and the additional electrical conductor is disposed helically in additional turns in such a way that two adjacent additional turns of the additional electrical conductor are assignable to the at least two mutually different additional sections.

The two additional sections may merge continuously into one another at exactly one position, and are accordingly contiguous at this position. The length of the two additional sections may differ by less than 5%, less than 1%, etc. The additional turns may be disposed in such a way that, when the additional primary coil is driven, e.g. when the helical conductor pattern is driven, an electric current in two adjacent additional turns is aligned identically and/or in parallel. The two additional sections may be at the same radial distance from the cylinder axis and/or are longitudinally adjacent and/or disposed in parallel. The two additional sections can also be disposed adjacent to each other in the radial direction.

By virtue of its arrangement, the gradient coil unit according to this embodiment can have a higher conductor density compared to a conventional gradient coil unit and can therefore generate a higher magnetic field gradient amplitude in the longitudinal direction while maintaining a high slew rate. The improved cooling due to the arrangement of the additional windings and the use of the hollow conductor can remove heat generated due to power loss particularly effectively.

One embodiment of the gradient coil unit comprises a fourth cooling circuit having a fourth coolant and a fifth cooling circuit having a fifth coolant, wherein the electrical conductor in a first additional section of the two serially interconnected additional sections encloses the fourth coolant as a hollow conductor, and the electrical conductor in a second additional section of the two serially interconnected additional sections encloses the fifth coolant as a hollow conductor.

Due to the improved cooling, this embodiment, similarly to the embodiment of the gradient coil unit comprising the first cooling circuit and the second cooling circuit for the primary coil, allows a high-amplitude magnetic field gradient to be used in the second spatial direction, e.g. at least 35 mT/m, over a period of at least 30 minutes.

It is also conceivable for the electrical conductor of a helical conductor pattern to be subdivided into at least four serially interconnected additional sections, and for the additional electrical conductor to be disposed helically in additional turns such that four adjacent additional turns of the additional electrical conductor are assignable to the at least four mutually different additional sections. In this case, the gradient coil unit may comprise two additional cooling circuits in addition to the fourth cooling circuit and fifth cooling circuit, so that each section of the hollow conductor is cooled by a different one of the four cooling circuits, e.g. has the corresponding coolants flowing through it. This enables eight cooling circuits to be connected to the additional primary coil, thereby ensuring that it can be cooled with an effectiveness comparable to that of the primary coil.

One embodiment of the gradient coil unit comprises a secondary coil configured to shield the magnetic field gradient generated by the primary coil in a periphery of the gradient coil unit comprising two secondary conductor pattern pairs, wherein one of each of the two secondary conductor pattern pairs is disposed in the same half as one of the two primary conductor pattern pairs and is connected in series with said primary conductor pattern pair, and comprises a spirally arranged electrical conductor.

The spirally arranged electrical conductor of a secondary conductor pattern pair typically corresponds to the electrical conductor of the corresponding primary conductor pattern pair. The half typically comprises two quadrants. The spirally arranged electrical conductor of a secondary conductor pattern pair typically spirally surrounds at least partially a fixed point within each quadrant of the two quadrants. Each secondary conductor pattern pair of the two secondary conductor pattern pairs may comprise two secondary spiral conductor patterns, wherein one secondary spiral conductor pattern is disposed within each quadrant. The spirally arranged electrical conductor of a secondary conductor pattern pair can be a hollow conductor or a solid conductor. The secondary coil is typically farther from the cylinder axis than the primary coil.

In one embodiment of the gradient coil unit, the secondary conductor pattern pair has less than 60% of the turns of the primary conductor pattern pair. The secondary coil is typically more loosely wound and/or turns of the secondary conductor pattern pair are spaced farther apart than turns of a spiral conductor pattern of a primary conductor pattern pair. This provides efficient shielding while minimizing material usage.

One embodiment of the gradient coil unit comprises a third cooling circuit having a third coolant, wherein the electrical conductor comprised by a secondary conductor pattern pair is implemented as a hollow conductor enclosing the third coolant. According to this embodiment, the secondary coil may be cooled by at least two different cooling circuits. The gradient coil unit may comprise an eighth cooling circuit having an eighth coolant. The third cooling circuit and the eighth cooling circuit may be jointly configured to cool a secondary conductor pattern pair. For instance, the third cooling circuit can be configured to cool a portion of the secondary conductor pattern pair disposed in a first quadrant of the half. The eighth cooling circuit can be configured to cool a portion of the secondary conductor pattern pair disposed in a second quadrant of the half. In addition, the cooling is provided directly by causing the third coolant and the eighth coolant to flow through the hollow conductor. This ensures efficient cooling of the secondary conductor pattern pair and thus of the secondary coil.

In addition, the disclosure proceeds from a gradient system comprising a gradient coil unit according to the disclosure and at least two gradient amplifier units, wherein one of the two gradient amplifier units is connected to one of the two primary conductor pattern pairs in each case.

A gradient amplifier unit connected to a primary conductor pattern pair is configured to generate a defined electrical voltage and/or a defined electrical current in the primary conductor pattern pair, typically as specified by a gradient control unit and/or an MR control sequence. The two gradient amplifier units connected to two primary conductor pattern pairs which are to be assigned to a primary coil, e.g. are incorporated in a primary coil, are typically controlled synchronously and/or simultaneously and/or with the same amplitude. The electrical currents and/or electrical voltages generated by these two gradient amplifier units typically differ by less than any suitable value, e.g. less than 1%, by less than 0.5%, etc., e.g. at any point in time when an MR control sequence is played out.

The gradient system may comprise four gradient amplifier units and two additional gradient amplifier units, e.g. a total of six gradient amplifier units. The gradient coil unit may comprise two primary coils and one additional primary coil, e.g. four primary conductor pattern pairs and two helical conductor patterns. One primary conductor pattern pair of each of the four primary conductor pattern pairs can typically be driven by one of the four gradient amplifier units in each case. One helical conductor pattern of the two helical conductor patterns is typically drivable by one of the two additional gradient amplifier units in each case.

Each of the two primary coils and the additional primary coil are configured to generate a magnetic field gradient in one spatial direction in each case, wherein the three spatial directions are different from one another, e.g. orthogonal to one another.

Due to the large number of gradient amplifier units and the special circuitry, a gradient system of this type is configured to generate particularly high electrical voltages in the individual primary conductor pattern pairs and/or helical conductor patterns. This provides particularly high magnetic field gradient amplitudes, especially in the first direction, while ensuring high rise and fall rates despite a high primary coil inductance.

The disclosure also proceeds from a magnetic resonance apparatus comprising a main magnet, a radiofrequency antenna unit, a gradient system according to the disclosure, and a gradient control unit connected to the gradient system and configured to cause the gradient system to generate a magnetic field gradient in the first spatial direction. The gradient control unit is configured to forward information according to an MR control sequence, e.g. gradient pulses, to the gradient amplifier units comprised by the gradient system.

Embodiments of the magnetic resonance device according to the disclosure and of the gradient system according to the disclosure are analogous to embodiments of the gradient coil unit according to the disclosure. The advantages of the magnetic resonance apparatus according to the disclosure and of the gradient system according to the disclosure essentially correspond to the advantages of the gradient coil unit according to the disclosure which are set out in detail above. Features, advantages, or alternative embodiments mentioned herein can likewise be applied to the other claimed subject matters, and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features, and details of the disclosure will emerge from the exemplary embodiments described below and from the associated drawings in which:

FIG. 1 illustrates a first embodiment of an example primary coil of a gradient coil unit according to the disclosure,

FIG. 2 illustrates a second embodiment of an example primary coil of a gradient coil unit according to the disclosure,

FIG. 3 illustrates a third embodiment of an example primary coil of a gradient coil unit according to the disclosure,

FIG. 4 illustrates an embodiment of an example additional primary coil of a gradient coil unit according to the disclosure,

FIG. 5 illustrates a first embodiment of an example secondary coil of a gradient coil unit according to the disclosure,

FIG. 6 illustrates a second embodiment of an example secondary coil of a gradient coil unit according to the disclosure,

FIG. 7 illustrates a first embodiment of an example electrical conductor of a primary conductor pattern pair, said conductor being implemented as a hollow conductor,

FIG. 8 illustrates a first embodiment of an example arrangement of an electrical conductor of a primary conductor pattern pair, said conductor being implemented as a hollow conductor,

FIG. 9 illustrates a second embodiment of an example arrangement of an electrical conductor of a primary conductor pattern pair, said conductor being implemented as a hollow conductor or a helical conductor pattern,

FIG. 10 illustrates a first embodiment of an example electrical conductor of a secondary conductor pattern pair, said conductor bring implemented as a hollow conductor,

FIG. 11 illustrates an example gradient system according to the disclosure, and

FIG. 12 illustrates an example magnetic resonance device according to the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIG. 1 illustrates a first embodiment of a primary coil 30 of a gradient coil unit 19 according to the disclosure. The primary coil 30 which surrounds a cylinder axis in a hollow cylindrical manner in the longitudinal direction z is shown here in unrolled form in the circumferential direction dφ.

The primary coil 30 comprises two primary conductor pattern pairs 31, 32. Each primary conductor pattern pair 31, 32 can be driven separately. For this purpose, each primary conductor pattern pair 31, 32 is connected to a respective gradient amplifier unit 85, 87. Said gradient amplifier unit 85, 87 is incorporated in the gradient system comprising the gradient coil unit 19 and/or may not be implemented as part of the gradient coil unit 19. Each primary conductor pattern pair 31, 32 spans two quadrants of the primary coil 30 in each case. A quadrant of the primary coil 30 is typically defined by z=[0; +/−zmax] and dφ=[0; +/−180°]. +/−zmax typically defines a respective longitudinal end of the gradient coil unit 19 in the longitudinal direction z. In addition, each primary conductor pattern pair 31, 32 comprises two spiral conductor patterns 41, 42, 43, 44, wherein one of the two spiral conductor patterns 41, 42, 43, 44 is disposed in one of the two quadrants in each case. Each spiral conductor pattern 41, 42, 43, 44 is thus limited to one quadrant.

For example, the first primary conductor pattern pair 31 of the two primary conductor pattern pairs 31, 32 can comprise the two spiral conductor patterns 41, 42, wherein a first conductor pattern 41 of the two spiral conductor patterns 41, 42 can be disposed in the quadrant defined by z=[0; +zmax] and dφ=[0; +180°] and a second conductor pattern 42 of the two spiral conductor patterns 41, 42 can be disposed in the quadrant defined by z=[0; +zmax] and dφ=[+180°; 360°]. Each primary conductor pattern pair 31, 32 comprises an electrical conductor 86, 88 implemented as a hollow conductor 80 and/or is a defined geometrical arrangement of the corresponding electrical conductor 86, 88. A spiral conductor pattern 41, 42, 43, 44 typically surrounds at least one first fixed point 38 at least partially in a spiral shaped manner in each case, which is shown only for the first conductor pattern 41 of the spiral conductor patterns 41, 42, 43, 44 in FIG. 1.

The primary coil 30 is configured to generate a magnetic field gradient in a first spatial direction, e.g. in the x-direction or in the y-direction. For example, the two primary conductor pattern pairs 31, 32 may be jointly configured to generate the magnetic field gradient in the first spatial direction. The arrows marked on the conductor patterns 41, 42, 43, 44 indicate a direction of current flow for generating a magnetic field gradient in the first spatial direction. In the embodiment shown, the two pairs of primary conductor patterns are separated from each other by a plane perpendicular to the cylinder axis, i.e. by a plane perpendicular to the longitudinal direction z at z=0.

FIG. 2 illustrates a second embodiment of an example primary coil of a gradient coil unit according to the disclosure. The second embodiment differs from the first embodiment shown in FIG. 1 in that a portion of the electrical conductor 86, 88 of a primary conductor pattern pair 31, 32, which is to be assigned to a spiral conductor pattern of the two spiral conductor patterns 41, 42, 43, 44, can be divided into two serially interconnected sections 41a, 41b, 42a, 42b, 43a, 43b, 44a, 44b. Here, the portion of the electrical conductor 86, 88 is disposed spirally in turns in such a way that two adjacent turns of the electrical conductor 86, 88 can be assigned to the two mutually different sections 41a, 41b, 42a, 42b, 43a, 43b, 44a, 44b.

A first primary conductor pattern pair 31 of the two primary conductor pattern pairs 31, 32 comprises the two conductor patterns 41, 42. Each of the two conductor patterns 41, 42 comprises two serially connected sections 41a, 41b, 42a, 42b of the electrical conductor 86, wherein a first conductor pattern 41 of the two conductor patterns 41, 42 comprises the two connected sections 41a, 41b of the electrical conductor 86. The two sections 41a, 41b of the electrical conductor 86 are disposed spirally in turns surrounding the first fixed point 38 in such a way that two adjacent turns can be associated with the different sections 41a, 41b in each case.

The turns and/or the two sections 41a, 41b of the portion of the electrical conductor 86 may be arranged such that the two adjacent turns run in pairs and one turn of a first section 41a is at a lesser distance from a first adjacent turn 41b than from a second adjacent turn 41b in each case. The electrical conductor 86, 88 may be disposed spirally in turns such that each spiral conductor pattern 41, 42, 43, 44 has at least 35 turns.

FIG. 3 illustrates a third embodiment of an example primary coil of a gradient coil unit according to the disclosure. The third embodiment differs from the second embodiment shown in FIG. 2 in that each of the spiral conductor patterns 41, 42, 43, 44 is configured such that it spirally surrounds two eyes 38, 39. The two eyes 38, 39 may differ in the longitudinal direction z and/or are disposed within a quadrant.

FIG. 4 illustrates an embodiment of an additional primary coil 50. The additional primary coil 50 is configured to generate a magnetic field gradient in a second spatial direction corresponding to the longitudinal direction z. The additional primary coil 50 comprises two helical conductor patterns 51, 52 surrounding the cylinder axis. The two helical conductor patterns 51, 52 are spatially separated from each other by a plane perpendicular to the cylinder axis, e.g. perpendicular to the longitudinal direction z at z=0.

Each of the two helical conductor patterns 51, 52 comprises an additional electrical conductor 91, 92 implemented as a hollow conductor 80. Each of the two helical conductor patterns 51, 52 can be driven separately. For this purpose, a helical conductor pattern 51, 52 is connected to a respective additional gradient amplifier unit 89, 90, typically by the additional electrical conductor 91, 92. Said additional gradient amplifier unit 89, 90 is incorporated in the gradient system comprising the gradient coil unit 19 and/or may not be implemented as part of the gradient coil unit 19.

Each additional electrical conductor 91, 92 of a helical conductor pattern 51, 52 can be subdivided into at least two serially interconnected additional sections 51a, 51b, 52a, 52b. The additional electrical conductor 91, 92 is arranged helically in additional turns such that two adjacent additional turns of the additional electrical conductor 91, 92 are to be assigned to the at least two mutually different additional sections 51a, 51b, 52a, 52b.

FIG. 5 illustrates a first embodiment of a secondary coil 60 of a gradient coil unit according to the disclosure. The secondary coil 60 is configured to shield the magnetic field gradient generated by the primary coil 30 at a periphery of the gradient coil unit 19. The secondary coil 60 comprises two secondary conductor pattern pairs 61, 62, wherein one of the two secondary conductor pattern pairs 61, 62 is disposed in the two same quadrants in each case, e.g. in the same half of the gradient coil unit as one of the two primary conductor pattern pairs 31, 32, and is connected in series therewith. This can mean that a secondary conductor pattern pair 61, 62 is formed by the same electrical conductor 86, 88 as a primary conductor pattern pair 31, 32 connected in series with the corresponding secondary conductor pattern pair 61, 62. Each secondary conductor pattern pair 61, 62 may comprise two secondary spiral conductor patterns 61a, 61b, 62a, 62b which are disposed in mutually different quadrants in each case. The primary conductor pattern pairs 31, 32 and the gradient amplifier units 85, 87 are typically not part of the secondary coil 60 and are shown schematically in FIG. 5 to visualize the interconnection.

In addition, each of the two secondary conductor pattern pairs 61, 62 comprises an at least partially spirally arranged electrical conductor 86, 88. The electrical conductor 86, 88 of a secondary conductor pattern pair 61, 62 is in each case may be configured such that it at least partially spirally surrounds at least one fixed point 38 within a quadrant. A secondary conductor pattern pair 61, 62 has less than 60% of the turns of the corresponding primary conductor pattern pair 31, 32.

FIG. 6 illustrates a second embodiment of a secondary coil 60 of a gradient coil unit according to the disclosure. This second embodiment differs from the first embodiment shown in FIG. 5 in that the electrical conductor 86, 88 of a secondary conductor pattern pair 61, 62 surrounds at least two fixed points 38, 39 at least partially in a spiral manner within a quadrant. The number of fixed points 38, 39 surrounded by a secondary conductor pattern pair 61, 62 within a quadrant may correspond to the number of fixed points 38, 39 surrounded by a spiral conductor pattern 41, 42, 43, 44 within a quadrant. The number of fixed points 38, 39 surrounded at least partially in a spiral manner by a primary conductor pattern pair 31, 32 may correspond to the number of fixed points 38, 39 surrounded at least partially in a spiral manner by a secondary conductor pattern pair 61, 62.

FIG. 7 illustrates a first embodiment of an electrical conductor 86, 88, implemented as a hollow conductor 80, of a primary conductor pattern pair 31, 32, which hollow conductor 80 encloses a coolant 81, in a view representing a cross-section, e.g. the cross-sectional area, of the electrical conductor 86, 88. The additional electrical conductor 91, 92 can be implemented analogously to the electrical conductor 86, 88 shown in FIG. 7.

FIG. 8 illustrates a first embodiment of an arrangement of an electrical conductor 86, 88, implemented as a hollow conductor 80, of a primary conductor pattern pair 31, 32, e.g. the first electrical conductor 86 of the first primary conductor pattern pair 31. The view shown in FIG. 8 can represent a cross-section in a radial direction r perpendicular to the longitudinal axis z of four adjacent turns. The four adjacent turns can be associated with two serially interconnected sections 41a, 41b, wherein the electrical conductor 86 is disposed such that the two adjacent turns run pairwise in each case, and a turn is spaced farther apart from a first adjacent turn than from a second adjacent turn in each case. The two sections 41a, 41b are cooled by means of different cooling circuits 71a, 71b: the first section 41a encloses a first coolant 81a of a first cooling circuit 71a. The second section 41b encloses a second coolant 81b of a second cooling circuit 71b.

FIG. 9 illustrates a second embodiment of an arrangement of an additional electrical conductor 91, 92 of a helical conductor pattern 51, 52 implemented as a hollow conductor 80, e.g. the first additional electrical conductor 91 of the first helical conductor pattern 51. The view shown in FIG. 9 can represent a cross-section in radial direction r parallel to the longitudinal axis z of four adjacent turns. In the embodiment shown, the additional electrical conductor 91 of the helical conductor pattern 51 can be subdivided into four serially interconnected additional sections 51a, 51b, 51c, 51d. The additional electrical conductor 91 is arranged helically in additional turns such that four adjacent additional turns of the additional electrical conductor 91 can be assigned to the four mutually different additional sections 51a, 51b, 51c, 51d. As in the case shown, two of the four additional sections 51a, 51b, 51c, 51d can be adjacent in the radial direction r and two of the four additional sections 51a, 51b, 51c, 51d can be adjacent in the longitudinal direction z in each case. The four additional sections 51a, 51b, 51c, 51d may be cooled by means of different additional cooling circuits: the first additional section 51a encloses a fourth coolant 81d of a fourth cooling circuit 71d. The second additional section 51b encloses a fifth coolant 81e of a fifth cooling circuit 71e. The third additional section 51c encloses a sixth coolant 81f of a sixth cooling circuit 71f. The fourth additional section 51d encloses a seventh coolant 81g of a seventh cooling circuit 71g.

The electrical conductor 86, 88 can be implemented analogously to the additional electrical conductor 91 shown in FIG. 8, e.g. also in the representation of a cross-section of four adjacent turns in a radial direction r perpendicular to the longitudinal axis z.

FIG. 10 illustrates a first embodiment of an electrical conductor 86, implemented as a hollow conductor 80, of a secondary conductor pattern pair 61, which hollow conductor 80 encloses a third coolant 81c of a third cooling circuit 71c, in a view representing a cross-section, e.g. the cross-sectional area of the electrical conductor 86.

FIG. 11 illustrates a gradient system according to the disclosure. The gradient system comprises a gradient coil unit 19 according to the disclosure and at least two gradient amplifier units 85, 87, wherein one of the two gradient amplifier units 85, 87 is connected to one of the two primary conductor pattern pairs 31, 32 in each case. The gradient coil unit 19 comprises two primary conductor pattern pairs 31, 32 implemented as part of a primary coil 30 for generating a magnetic field gradient in a first spatial direction. The illustrated embodiment of the gradient coil unit 19 comprises two secondary conductor pattern pairs 61, 62 implemented as part of a secondary coil 60 for shielding the magnetic field gradient generated by the primary coil 30 in a periphery of the gradient coil unit 19. A first primary conductor pattern pair 31 of the two primary conductor pattern pairs 31, 32, a first secondary conductor pattern pair 61 of the two secondary conductor pattern pairs 61, 62 comprising two secondary spiral conductor patterns 61a, 61b, and a first gradient amplifier unit 85 of the two gradient amplifier units 85, 87 are connected in series with a first electrical conductor 86 of the at least two electrical conductors 86, 88. A second primary conductor pattern pair 32 of the two primary conductor pattern pairs 31, 32, a second secondary conductor pattern pair 62 of the two secondary conductor pattern pairs 61, 62 comprising two secondary spiral conductor patterns 62a, 62b, and a second gradient amplifier unit 87 of the two gradient amplifier units 85, 87 are connected in series with a second electrical conductor 86 of the at least two electrical conductors 86, 88.

The primary conductor pattern pairs 31, 32 comprise serially interconnected sections 41a, 41b, 42a, 42b, 43a, 43b, 44a,