Graded coil unit for interventional MR imaging
Patent Information
- Application Number
- AT2022192179T
- Authority / Receiving Office
- AT · AT
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-08-25
- Publication Date
- 2026-06-15
- Estimated Expiration
- 2042-08-25
AI Technical Summary
Conventional gradient coil units in magnetic resonance devices pose challenges for interventional MR imaging due to limited accessibility of the examination area, making it difficult for medical professionals to perform minimally invasive procedures effectively.
A gradient coil unit design featuring a hollow cylindrical primary coil and secondary coil, where the primary coil is shorter than the secondary coil, allowing for a larger inner diameter and a funnel-shaped opening at one end, enhancing accessibility and enabling better interventional MR imaging.
The design improves accessibility to the examination area, facilitating easier and more controlled use of surgical needles during minimally invasive procedures while maintaining a compact and efficient magnetic field gradient generation.
Abstract
Description
[0001] The invention relates to a gradient coil unit for interventional MR imaging and a magnetic resonance apparatus.
[0002] In a magnetic resonance scanner, the body to be examined, particularly a patient, is typically exposed to a relatively high main magnetic field, for example, 1.5 or 3 Tesla, using a main magnet. During magnetic resonance imaging (MR imaging), gradient pulses are generated using a gradient coil unit. In addition, high-frequency radio-frequency pulses (RF pulses), particularly excitation pulses, are then emitted via a radio-frequency antenna unit using suitable antenna devices. This causes the nuclear spins of certain atoms resonantly excited by these RF pulses to be tilted by a defined flip angle relative to the magnetic field lines of the main magnetic field. During the relaxation of the nuclear spins, radio-frequency signals, so-called magnetic resonance signals, are emitted, which are received by suitable radio-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 conventionally comprises three primary coils and three corresponding secondary coils. The three primary coils are typically comprised by a primary coil unit. The three secondary coils are typically comprised by a secondary coil unit. A primary coil is typically designed to generate a magnetic field gradient in one spatial direction, particularly within a patient receiving area. A magnetic field gradient is typically a first-order and / or linear-order magnetic field, particularly a magnetic field whose amplitude increases linearly along one spatial direction. Outside the patient receiving area, the effect of a primary coil is largely suppressed by a secondary coil associated with the primary coil. The secondary coil typically surrounds the corresponding primary coil and is electrically connected in series with it.The magnetic field gradient and the main magnetic field typically exhibit the homogeneity required for MR imaging only within a portion of the patient receiving area, also called the examination area. The examination area is typically located centrally, i.e., centrally within the cylindrical patient receiving area. Due to the length of so-called closed magnetic resonance scanners, it is difficult to reach from one end of the scanner, for example, by medical personnel. The size of the examination area can be, for example, 40 cm x 40 cm x 40 cm.
[0004] In minimally invasive medical procedures, medical instruments, such as catheters and / or surgical needles, are inserted into a patient, typically under image monitoring. Image monitoring allows images to be captured that visualize the medical instrument in relation to its anatomical surroundings. While X-ray imaging, particularly fluoroscopy, has traditionally been used for image monitoring of minimally invasive medical procedures, it has recently been proposed to use magnetic resonance imaging (MRI) devices for image monitoring. This is typically referred to as interventional MRI.
[0005] A special type of medical instrument frequently used for minimally invasive medical procedures is the surgical needle, which is used for biopsy, ablation, or brachytherapy, for example. It has also been proposed that surgical needles be used under real-time magnetic resonance imaging. Traditionally, such minimally invasive medical procedures are performed step by step, with the surgical needle being placed on the subject outside the examination area of the magnetic resonance scanner. The subject is then positioned within the patient receiving area using a patient positioning device such that the surgical needle is positioned within the examination area, and the position and / or orientation of the surgical needle can be monitored using MR imaging.The physician performs the actual invasive procedure in the initial position outside the examination area. Further checks with repeated positioning of the examination subject within the examination area are typically required.
[0006] The invention is based on the object of providing a gradient coil unit that is particularly well suited for interventional MR imaging. This object is achieved by the features of the independent claims. Advantageous embodiments are described in the subclaims.
[0007] The gradient coil unit according to the invention surrounds a cylindrical patient receiving area and comprises a hollow-cylindrical primary coil and a hollow-cylindrical secondary coil, which coaxially and / or concentrically surrounds the primary coil and the patient receiving area. The gradient coil unit has a first longitudinal end in a longitudinal direction, which first longitudinal end is designed to receive an examination subject. The gradient coil unit has a second longitudinal end opposite the first longitudinal end in the longitudinal direction. The primary coil has a first length in the longitudinal direction, which first length is limited by a first longitudinal position facing the first longitudinal end and a second longitudinal position facing the second longitudinal end.The secondary coil has a second length in the longitudinal direction, which second length is delimited by a third longitudinal position facing the first longitudinal end and a fourth longitudinal position facing the second longitudinal end. The first longitudinal position is at a greater distance from the first longitudinal end than the third longitudinal position. The first length is preferably shorter than the second length.
[0008] The gradient coil unit is therefore designed as a hollow cylinder and at least partially surrounds the patient receiving area. The gradient coil unit is preferably designed as a whole-body coil, so that the patient receiving area can, for example, completely accommodate and / or enclose an abdomen and / or a shoulder region of the examination subject in the circumferential direction. The cylinder axis of the gradient coil unit can be referred to as the longitudinal axis and / or z-axis and is typically aligned horizontally and / or is parallel to the longitudinal direction. The primary coil is preferably designed to generate a magnetic field gradient in one spatial direction. The secondary coil is preferably designed to shield the magnetic field gradient generated by the primary coil in the area of the gradient coil unit facing away from the patient receiving area.The first longitudinal end of the gradient coil unit is typically arranged on the side of the examination zone on which an examination subject can be introduced into the examination zone using a patient support device. The second longitudinal end of the gradient coil unit typically corresponds to the side of the gradient coil unit on which the connecting cables of the gradient coil unit are provided. The second longitudinal end is typically facing away from the first longitudinal end in the longitudinal direction. The first length and the second length typically refer to parallel straight lines, in particular in the longitudinal direction, between the first longitudinal end and the second longitudinal end. The second longitudinal position can correspond to the fourth longitudinal position. The second longitudinal position and / or the fourth longitudinal position is typically facing away from the first longitudinal end. The primary coil and the secondary coil can therefore be designed flush at the second longitudinal end.A longitudinal position is typically a coordinate of the longitudinal axis, in particular a coordinate of the z-axis.
[0009] The gradient coil unit according to the invention is therefore designed such that the primary coil arranged on the side of the gradient coil unit facing the patient receiving area is shorter than the secondary coil. The shorter first length of the primary coil, in particular, allows a larger inner diameter of the patient receiving area to be realized at the first longitudinal end. This facilitates access to the examination area for medical personnel from outside the gradient coil unit and thus enables particularly effective interventional MR imaging.
[0010] One embodiment of the gradient coil unit comprises a casing that at least partially encloses the gradient coil unit and is funnel-shaped at the first longitudinal end. Such a casing can be designed as a housing and / or sleeve and / or enclosure for the primary coil and the secondary coil. Accordingly, the gradient coil unit preferably has a funnel-shaped opening at the first longitudinal end, which allows medical personnel particularly good access to the examination area, even from outside the gradient coil unit. In particular, medical personnel can turn their upper body and / or shoulder area toward the opening, which particularly facilitates interventional MR imaging within the patient acquisition area.
[0011] One embodiment of the gradient coil unit provides that the first longitudinal position and the third longitudinal position differ by at least 3 cm, preferably by at least 4 cm, particularly preferably by at least 6 cm. The first longitudinal position is therefore at least 3 cm shorter from an isocenter of the gradient coil unit than the third longitudinal position. The distance of the first longitudinal position from the isocenter of the gradient coil unit is typically shorter than the distance of the second longitudinal position from the isocenter of the gradient coil unit.
[0012] The distance of the first longitudinal position to the isocenter of the gradient coil unit is typically between 500 mm and 700 mm, preferably between 580 mm and 620 mm, particularly preferably between 590 mm and 610 mm. The distance of the second longitudinal position to the isocenter of the gradient coil unit is typically between 620 mm and 750 mm, preferably between 650 mm and 710 mm, particularly preferably between 670 mm and 690 mm. The distance of the third longitudinal position to the isocenter of the gradient coil unit typically differs by less than 2 cm, preferably by less than 1 cm, particularly preferably by less than 0.5 cm from the distance of the second longitudinal position to the isocenter of the gradient coil unit. The first length is typically between 1100 mm and 1400 mm, preferably between 1200 mm and 1300 mm, particularly preferably between 1235 mm and 1265 mm.The second length is typically between 1200 mm and 1400 mm, preferably between 1250 mm and 1350 mm, particularly preferably between 1285 mm and 1315 mm. The distance of the second longitudinal position from the isocenter of the gradient coil unit is typically between 600 mm and 700 mm, preferably between 620 mm and 680 mm, particularly preferably between 640 mm and 660 mm.
[0013] This design allows for a funnel-shaped opening at the first longitudinal end and better accessibility of the examination area while maintaining a compact design.
[0014] One embodiment of the gradient coil unit provides that the second longitudinal position and the fourth longitudinal position differ by a maximum of 4 cm, preferably by a maximum of 2 cm, particularly preferably by a maximum of 1 cm. The secondary coil and the primary coil can also be flush at the second longitudinal end. This enables a particularly compact design of the gradient coil unit.
[0015] One embodiment of the gradient coil unit provides that the gradient coil unit has an inner diameter of at least 840 mm and a spatial extension in the longitudinal direction of at most 1350 mm. The inner diameter typically refers to the diameter of the cylinder surrounded by the primary coil and / or the casing. According to this embodiment, the inner diameter of the gradient coil unit is at least 840 mm, preferably at least 855 mm, particularly preferably at least 865 mm. The spatial extension of the gradient coil unit in the longitudinal direction can correspond to the second length and / or be greater than this. According to this embodiment, the length of the gradient coil unit in the longitudinal direction is less than 1350 mm, preferably less than 1340 mm, particularly preferably less than 1328 mm.
[0016] This design allows for an examination area with a diameter of 800 mm and a distance of less than 600 mm between the funnel entrance and the isocenter and / or the examination area. This geometry allows for particularly simple yet controlled use of interventional needles within the patient receiving area.
[0017] An embodiment of the gradient coil unit provides that the gradient coil unit can be divided and / or articulated into four quadrants, the primary coil comprises four spiral-shaped primary conductor structures, each of which is arranged within a quadrant surrounding a primary fixed point, and the secondary coil comprises four spiral-shaped secondary conductor structures, each of which is arranged within a quadrant surrounding a secondary fixed point.In addition, this embodiment of the gradient coil unit provides a first section of the primary coil, which is delimited in the longitudinal direction by the first longitudinal position and by a further primary longitudinal position at a distance of at most 25% of the first length from the first longitudinal position, preferably at a distance between 10% and 25% of the first length from the first longitudinal position, and is free of a connecting conductor, which connecting conductor connects two primary conductor structures to one another and / or a primary conductor structure to a secondary conductor structure.
[0018] The gradient coil unit is typically divisible into four quadrants and / or the gradient coil unit comprises four quadrants, wherein these four quadrants typically define only four disjoint geometric regions of the gradient coil unit. The four quadrants typically denote regions of the gradient coil unit, wherein a transition between two quadrants is in each case free of any physical and / or visible separation. The primary conductor structure is preferably part of the primary coil, which typically comprises the primary conductor structure four times, each arranged in a quadrant of the four quadrants, and the primary coil is configured to generate a magnetic field gradient in one spatial direction. A conductor structure, as described below, can be configured as a primary conductor structure or a secondary conductor structure. The conductor structure typically comprises a geometric arrangement of an electrical conductor.The conductor structure is typically arranged on a cylinder and has a saddle-shaped configuration. The conductor structure is typically spatially delimited by a quadrant of the gradient coil unit. The conductor structure is preferably at least partially spiral-shaped, comprising windings of varying radii relative to a fixed point. A primary conductor structure typically surrounds a primary fixed point at least partially spirally, and / or a secondary conductor structure typically surrounds a secondary fixed point at least partially spirally.
[0019] The four primary conductor structures and the four secondary conductor structures are typically electrically connected in series. Electrical conductors connecting two primary conductor structures from different quadrants or connecting two secondary conductor structures from different quadrants or connecting a primary conductor structure and a secondary conductor structure can be referred to as connecting conductors. Connecting conductors can be configured as primary connecting conductors or as secondary connecting conductors. Primary connecting conductors typically connect two primary conductor structures from two different quadrants or a primary conductor structure with a secondary conductor structure. Secondary connecting conductors typically connect two secondary conductor structures from two different quadrants. A connecting conductor typically represents an electrical connection between two quadrants and / or between a primary coil and a secondary coil.A connecting conductor is typically predominantly straight and in particular not spiral-shaped.
[0020] According to this embodiment, the first section of the gradient coil unit is free of a connecting conductor and consequently preferably comprises exclusively electrical conductors that are part of a primary conductor structure and thus actively contribute to generating a magnetic field gradient. The first section can therefore be used spatially particularly efficiently to generate the magnetic field gradient, since all terminals and technically required connections are typically arranged outside the first section. According to this embodiment, connecting conductors are arranged outside the first section and / or in particular near the second longitudinal end, whereby they have a less pronounced influence on the homogeneity of the examination region and the magnetic field gradient at the first longitudinal end.In addition, the density of the electrical conductor encompassed by the conductor structures, in particular the primary conductor structures, is typically lower in the region outside the first section and / or in particular near the second longitudinal end than in the first section, whereby the primary coil has sufficient space in this region to accommodate the connecting conductors. The electrical conductors within the first section can therefore be optimized with regard to ideal homogeneity of the magnetic field gradient near the first longitudinal end without taking connecting conductors into account. The first section typically borders on the first longitudinal end, whereby the examination region, in particular the region of high homogeneity of the magnetic field gradients, can be generated particularly close to the first longitudinal end. This enables particularly good access to the examination region for medical personnel and thus particularly easy-to-perform interventional MR imaging.
[0021] One embodiment of the gradient coil unit provides that the primary conductor structures, in particular the primary conductor structures arranged within a quadrant overlapping with the first section, each have the highest density of electrical conductors within the first section. The corresponding primary conductor structures are therefore designed such that the maximum density of the electrical conductor of the corresponding primary conductor structure is present within at least a partial region of the first section. The partial region typically comprises at least 10%, preferably at least 15%, particularly preferably at least 20% of the first section. In particular, a primary conductor structure arranged within a quadrant adjacent to the first longitudinal end is designed such that the highest current density of the primary coil can be generated in the first section.According to this embodiment, the primary conductor structures facing the first longitudinal end in the first section provide a particularly small spacing between adjacent turns of the electrical conductor of the primary conductor structures. This enables a particularly high current density at the first longitudinal end, averaged longitudinally across the first section, at at least one position in the circumferential direction. The density of an electrical conductor can be determined by the number of electrical conductors per cross-sectional area of the primary coil perpendicular to the electrical conductor and / or the sum of the area of the conductor cross-sections per cross-sectional area of the primary coil perpendicular to the electrical conductor.The higher the density of spirally arranged electrical conductors with unidirectional current flow, and in particular the smaller the distance between adjacent windings, such as in a primary conductor structure within a quadrant, the higher the electrical current density in this region. This enables a particularly high current density within the first section, which in particular leads to the region within the patient receiving area with the highest homogeneity of the magnetic field gradients, i.e. the examination region, being closer to the first longitudinal end than to the second longitudinal end. This makes the examination region particularly accessible from the first longitudinal end for interventional examinations. In addition, the gradient coil unit can be designed to be particularly short in the longitudinal direction compared to conventional gradient coil units.
[0022] One embodiment of the gradient coil unit comprises a primary connecting conductor, which connects two primary conductor structures to each other and / or a primary conductor structure to a secondary conductor structure, and which connects to a turn of the primary conductor structure closest to the at least one primary fixed point. According to this embodiment, the primary connecting conductor connects an eye of a primary conductor structure to another primary conductor structure or secondary conductor structure. This makes it possible, in particular, to design the first section free of a connecting conductor, in particular a primary connecting conductor, since the connecting conductor can lead from the primary fixed point to the second longitudinal end.
[0023] One embodiment of the gradient coil unit provides that a second section of the secondary coil, which is delimited in the longitudinal direction by the third longitudinal position and by a further secondary longitudinal position at a distance of at most 25% of the second length from the third longitudinal position, preferably at a distance of between 10% and 25% of the second length from the third longitudinal position, is free of a secondary connecting conductor that connects two secondary conductor structures to one another and / or a primary conductor structure to a secondary conductor structure. The first section and the second section overlap at least partially in the longitudinal direction and in the circumferential direction. This embodiment provides a structure of the secondary coil analogous to the primary coil. This enables efficient shielding of the primary coil, which provides a first section free of a connecting conductor. The advantages of such a primary coil are transferable to this embodiment.
[0024] One embodiment of the gradient coil unit provides that the secondary conductor structures, in particular the secondary conductor structures arranged within a quadrant overlapping with the second section, each have the highest density of electrical conductors within the second section. The corresponding secondary conductor structures are therefore designed such that the maximum density of the electrical conductor of the corresponding secondary conductor structure is present within at least a partial region of the second section. The partial region typically comprises at least 10%, preferably at least 15%, particularly preferably at least 20% of the second section. In particular, a secondary conductor structure arranged within a quadrant adjacent to the first longitudinal end is designed such that the highest current density of the secondary coil can be generated in the second section.
[0025] According to this embodiment, the secondary conductor structures facing the first longitudinal end in the longitudinal direction provide a particularly small distance between adjacent turns of the electrical conductor of the secondary conductor structures in the first section. This enables a particularly high current density at the first longitudinal end, averaged longitudinally over the second section at at least one position in the circumferential direction. The density of an electrical conductor can be determined by the number of electrical conductors per cross-sectional area of the secondary coil perpendicular to the electrical conductor and / or the sum of the area of the conductor cross-sections per cross-sectional area of the secondary coil perpendicular to the electrical conductor. This enables a particularly high current density within the second section, which in particular leads to a particularly good shielding of a magnetic field gradient generated by the primary coil.In addition, the gradient coil unit can be designed to be particularly short in the longitudinal direction compared to conventional gradient coil units.
[0026] One embodiment of the gradient coil unit comprises a secondary connecting conductor connecting two secondary conductor structures to each other and / or connecting a primary conductor structure to a secondary conductor structure at a turn of the secondary conductor structure closest to the at least one secondary fixed point. According to this embodiment, the secondary connecting conductor connects an eye of a secondary conductor structure to another secondary conductor structure or primary conductor structure. This makes it possible, in particular, to design the second section free of a connecting conductor, in particular a secondary connecting conductor, since the connecting conductor can lead from the secondary fixed point to the second longitudinal end.
[0027] Furthermore, the invention is based on a magnetic resonance apparatus comprising a detector unit with a main magnet, a radio-frequency antenna unit, and a gradient coil unit according to the invention, wherein the gradient coil unit coaxially and / or concentrically surrounds the radio-frequency antenna unit. The magnetic resonance apparatus further comprises a control unit configured to control the detector unit. The spatial extent of the radio-frequency antenna unit in the longitudinal direction is shorter than the second length. The detector unit therefore comprises the main magnet, the gradient coil unit according to the invention, and the radio-frequency antenna unit. The secondary coil has a longer spatial extent than the radio-frequency antenna unit. The radio-frequency antenna unit is typically arranged within the gradient coil unit. The length of the radio-frequency antenna unit in the longitudinal direction can also be shorter than the first length.
[0028] The length of the radio-frequency antenna unit in the longitudinal direction is typically limited by a seventh longitudinal position facing the first longitudinal end and an eighth longitudinal position. The seventh longitudinal position can have a smaller distance from an isocenter of the gradient coil unit than the first longitudinal position and / or the third longitudinal position. The eighth longitudinal position can have a smaller distance from an isocenter of the gradient coil unit than the second longitudinal position and / or the fourth longitudinal position. This prevents the radio-frequency antenna unit from spatially restricting the opening of the gradient coil unit according to the invention at the first longitudinal end and thus enables good access to the examination region. Embodiments of the magnetic resonance apparatus according to the invention are designed analogously to the embodiments of the gradient coil unit according to the invention.The advantages of the magnetic resonance apparatus 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 subject matter, and vice versa.
[0029] Further advantages, features and details of the invention will become apparent from the exemplary embodiments described below and from the drawings.
[0030] They show: Fig. 1 shows a magnetic resonance apparatus according to the invention in a schematic representation, Fig. 2 shows an embodiment of a gradient coil unit according to the invention in a first view in a schematic representation, Fig. 3 shows an embodiment of a gradient coil unit according to the invention in a second view, Fig. 4 shows a schematic representation of a cylinder for explaining parameters.
[0031] Figure 1shows a magnetic resonance device 11 according to the invention. The magnetic resonance device 11 comprises a detector unit 13 with a main magnet 17 for generating a strong and, in particular, constant main magnetic field 18. In addition, the magnetic resonance device 11 has a cylindrical patient receiving area 14 for receiving a patient 15, wherein the patient receiving area 14 is cylindrically enclosed in a circumferential direction by the detector unit 13. The patient 15 can be pushed into the patient receiving area 14 by means of a patient support device 16 of the magnetic resonance device 11. For this purpose, the patient support device 16 has a patient table that is movably arranged within the magnetic resonance device 11.The detector unit 13 further comprises a radio-frequency antenna unit 20, which in the illustrated case is designed as a body coil permanently integrated into the magnetic resonance scanner 11, and a radio-frequency antenna control unit 29 for exciting a polarization that arises in the main magnetic field 18 generated by the main magnet 17. The radio-frequency antenna unit 20 is controlled by the radio-frequency antenna control unit 29 and radiates radio-frequency pulses into an examination room, which is essentially formed by the patient receiving area 14.
[0032] Furthermore, the detector unit 13 has a gradient coil unit 19 according to the invention, which is used for spatial coding during imaging. The gradient coil unit 19 is controlled by a gradient control unit 28. The gradient coil unit 19 comprises a hollow cylindrical secondary coil 40 coaxially surrounding a primary coil 30, wherein the secondary coil 40 has a second length parallel to the main magnetic field 18, which second length is longer than the first length of the primary coil 30 parallel to the main magnetic field 18. The main magnetic field 18 is preferably oriented in the longitudinal direction. The radio-frequency antenna unit 20 has a length in the longitudinal direction that is shorter than the second length.
[0033] The magnetic resonance scanner 11 has a control unit 24 for controlling the main magnet 17, the gradient control unit 28, and the radio-frequency antenna control unit 29. The control unit 24 centrally controls the magnetic resonance scanner 11, for example, by performing MR control sequences. The magnetic resonance scanner 11 has a display unit 25. Furthermore, the magnetic resonance scanner 11 has an input unit 26, by means of which information and / or control parameters can be entered by a user during a measurement process. The control unit 24 can comprise the gradient control unit 28 and / or the radio-frequency antenna control unit 29 and / or the display unit 25 and / or the input unit 26.
[0034] The illustrated magnetic resonance device 11 may, of course, include additional components that magnetic resonance devices 11 typically have. The general functioning of a magnetic resonance device 11 is also known to those skilled in the art, so a detailed description of the additional components is omitted.
[0035] Figure 2shows an embodiment of a gradient coil unit 19 according to the invention in a first schematic view. The gradient coil unit 19 comprises a hollow cylindrical primary coil 30 and a hollow cylindrical secondary coil 40, which coaxially surrounds the primary coil 30 and the patient receiving area 14. The secondary coil 40 typically has a larger radius, in particular a greater distance from the z-axis, than the primary coil 30. The gradient coil unit 19 is delimited in the longitudinal direction z by a first longitudinal end l1 and a second longitudinal end l2 opposite the first longitudinal end l1 in the longitudinal direction z. The first longitudinal end l1 of the gradient coil unit 19 is designed to receive an examination subject, in particular a patient 15.The primary coil 30 has a first length in the longitudinal direction z, which is delimited by a first longitudinal position z1 facing the first longitudinal end l1 and a second longitudinal position z2 facing away from it in the longitudinal direction z. The secondary coil 40 has a second length delimited by a third longitudinal position z3 facing the first longitudinal end l1 and a fourth longitudinal position z4. The first length is shorter than the second length, and the first longitudinal position z1 is at a greater distance from the first longitudinal end l1 than the third longitudinal position z3 is from the first longitudinal end l1. The gradient coil unit 19 additionally comprises a casing 12 which at least partially encloses the gradient coil unit 19 and is funnel-shaped at the first longitudinal end l1. In particular, the casing 12 has a taper starting from the first longitudinal position z1 to the first longitudinal end l1 perpendicular to the longitudinal direction z.The isocenter 0 of the gradient coil unit 19 is typically the spatial center of the outer cylinder and / or the inner cylinder and / or the examination area 10. The examination area 10 is a subarea of the patient receiving area 14.
[0036] Figure 3 shows an embodiment of a gradient coil unit 19 according to the invention in a second view. Here, the primary coil 30 and the secondary coil 40 are each shown in unrolled form. The coordinates of the circumferential direction dϕ apply to the primary coil 30 and the secondary coil 40. Separate axes in the longitudinal direction z are indicated for the primary coil 30 and the secondary coil 40, which, however, at least partially overlap. As in Figure 2As shown, the second longitudinal position z2 can correspond to the fourth longitudinal position z4. The primary coil 30 and the secondary coil 40 differ in their radial distance r from the longitudinal direction z. The primary coil 30 has a first radius r1 from the longitudinal direction z, and the secondary coil 40 has a second radius r2 from the longitudinal direction z, wherein the second radius r2 is greater than the first radius r1.
[0037] The Figure 3The primary coil 30 shown is preferably designed to generate a magnetic field gradient in the x-direction. The gradient coil unit 19 can be divided into four quadrants, which differ in pairs by their position in the longitudinal direction z or by their position in the circumferential direction dϕ. One quadrant is defined, for example, by z = [0; l1] and dϕ = [90°; 270°], and an opposite quadrant by z = [l2; 0] and dϕ = [270°; 90°]. The primary coil 30 comprises four spiral-shaped primary conductor structures 31a, 31b, 31c, 31d, each of which is arranged within a quadrant. One of the four spiral-shaped primary conductor structures 31a, 31b, 31c, 31d surrounds at least partially a primary fixed point 32a, 32b, 32c, 32d in a spiral shape, wherein one of the four primary fixed points 32a, 32b, 32c, 32d is arranged in a respective quadrant.The secondary coil 40 comprises four spiral-shaped secondary conductor structures 41a, 41b, 41c, 41d, each arranged within a quadrant. Each of the four spiral-shaped secondary conductor structures 41a, 41b, 41c, 41d at least partially spirally surrounds a secondary fixed point 42a, 42b, 42c, 42d, with each of the four secondary fixed points 42a, 42b, 42c, 42d being arranged in a respective quadrant.
[0038] A first section 38 of the primary coil 30 is delimited in the longitudinal direction z by the first longitudinal position z1 and by a further primary longitudinal position z5, wherein the distance of the further primary longitudinal position z5 to the first longitudinal position z1 is at most 25%, preferably between 10% and 25% of the first length. The first section 38 is free of a connecting conductor 33, 43, which connects two primary conductor structures 31a, 31b, 31c, 31d to one another and / or a primary conductor structure 31a, 31b, 31c, 31d to a secondary conductor structure 41a, 41b, 41c, 41d. Connecting conductors 33, 43 are in Figure 3 schematically represented by straight lines.
[0039] In addition, the primary conductor structures 31a, 31b arranged within the quadrants adjacent to the first longitudinal end are configured such that the highest current density of the primary coil 30 can be generated in the first section 38 and / or the primary conductor structures 31a, 31b have the highest density of electrical conductors within the first section 38. The primary coil 30 and in particular the primary conductor structures 31a, 31b, 31c, 31d encompassed by the primary coil 30 are accordingly configured such that the highest current density of the primary coil 30 can be generated within the first section 38, in particular within a partial region of the first section 38, and / or the highest density of electrical conductors of the primary coil 30 is present.
[0040] The gradient coil unit 19 comprises primary connecting conductors 33a, 33b, 33c, 33d, which each connect two primary conductor structures 31a, 31b, 31c, 31d to each other and / or connect a primary conductor structure 31a, 31b, 31c, 31d to a secondary conductor structure 41a, 41b, 41c, 41d. A primary connecting conductor 33a, 33b, 33c, 33d connects to a turn of the primary conductor structure 31a, 31b, 31c, 31d that is closest to the corresponding primary fixed point 32a, 32b, 32c, 32d.
[0041] A second section 48 of the secondary coil 40 is delimited in the longitudinal direction z by the third longitudinal position z3 and by a further secondary longitudinal position z6, wherein the distance between the further secondary longitudinal position z6 and the third longitudinal position z3 is at most 25%, preferably between 10% and 25% of the second length. The second section 48 is free of a connecting conductor 33, 43, and in particular free of a secondary connecting conductor 43a, which connects two secondary conductor structures 41a, 41b, 41c, 41d to one another. A connecting conductor 33, 43 can be designed as a primary connecting conductor 33a, 33b, 33c, 33d and / or a secondary connecting conductor 43a.
[0042] In addition, the secondary conductor structures 41a, 41b arranged within the quadrants adjacent to the first longitudinal end l1 are designed such that the highest current density of the secondary coil 40 can be generated in the second section 48 and / or the secondary conductor structures 41a, 41b have the highest density of electrical conductors within the second section 48. The secondary coil 40 and in particular the secondary conductor structures 41a, 41b, 41c, 41d encompassed by the secondary coil 40 are accordingly designed such that the highest current density of the secondary coil 40 can be generated within the second section 48, in particular within a partial region of the second section 48, and / or the highest density of electrical conductors of the secondary coil 40 is present.
[0043] The gradient coil unit 19, and in particular the secondary coil 40, comprise a secondary connecting conductor 43a, which interconnects two secondary conductor structures 41a, 41b and connects each of the secondary conductor structures 41a, 41b to a respective turn of the secondary conductor structures 41a, 41b closest to the secondary fixed points 42a, 42b. Further secondary conductor structures 41c, 41d can each be serially connected to a respective primary conductor structure 31c, 31d by a primary connecting conductor 33c, 33d. Preferably, all primary conductor structures 31a, 31b, 31c, 31d and secondary conductor structures 41a, 41b, 41c, 41d are connected in series, with an electrical voltage being generated by a gradient amplifier unit 39. The gradient amplifier unit 39 is preferably formed as part of the gradient control unit 28.
[0044] The gradient coil unit 19 preferably comprises the Figure 3illustrated primary conductor structures 31a, 31b, 31c, 31d and secondary conductor structures 41a, 41b, 41c, 41d once again, but rotated by 90° in the circumferential direction dϕ, which are designed to generate a magnetic field gradient in the y-direction, in particular by control by a further gradient amplifier unit.
[0045] Figure 4 shows a schematic representation of a cylinder to explain parameters. The cylinder axis corresponds to the longitudinal direction z, in particular the longitudinal direction z of the gradient coil unit 19. The circumferential direction can be characterized by dϕ. The direction perpendicular to the circumferential direction dϕ is referred to as the radial direction r. The direction denoted by x is typically perpendicular to the longitudinal direction z and oriented horizontally.
[0046] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.
Claims
1. A gradient coil unit surrounding a cylindrical patient receiving area and comprising a hollow-cylindrical primary coil and a hollow-cylindrical secondary coil coaxially surrounding the primary coil and the patient receiving area, wherein the gradient coil unit has a first longitudinal end in a longitudinal direction, which first longitudinal end is designed to receive an examination subject, and the gradient coil unit has a second longitudinal end opposite the first longitudinal end in the longitudinal direction, wherein the primary coil has a first length in the longitudinal direction, which first length is delimited by a first longitudinal position facing the first longitudinal end and a second longitudinal position facing the second longitudinal end, wherein the secondary coil has a second length in the longitudinal direction, which second length is delimited by a third longitudinal position facing the first longitudinal end and a fourth longitudinal position facing the second longitudinal end,wherein the first longitudinal position has a greater distance from the first longitudinal end than the third longitudinal position., 2. Gradient coil unit according to claim 1, comprising a casing which at least partially encloses the gradient coil unit and is funnel-shaped at the first longitudinal end.
3. Gradient coil unit according to one of the preceding claims, wherein the first longitudinal position and the third longitudinal position differ by at least 3 cm.
4. Gradient coil unit according to one of the preceding claims, wherein the second longitudinal position and the fourth longitudinal position differ by at most 4 cm.
5. Gradient coil unit according to one of the preceding claims, wherein the gradient coil unit has an inner diameter of at least 840 mm and a spatial extension in the longitudinal direction of at most 1350 mm.
6. Gradient coil unit according to one of the preceding claims, wherein the gradient coil unit is divisible into four quadrants, the primary coil comprises four spiral primary conductor structures, each of which is arranged within a quadrant surrounding a primary fixed point, the secondary coil comprises four spiral secondary conductor structures, each of which is arranged within a quadrant surrounding a secondary fixed point, a first section of the primary coil, which is delimited in the longitudinal direction by the first longitudinal position and by a further primary longitudinal position at a distance of at most 25% of the first length from the first longitudinal position, is free of a connecting conductor, which connecting conductor connects two primary conductor structures to one another and / or a primary conductor structure to a secondary conductor structure.
7. The gradient coil unit of claim 6, wherein the primary conductor structures arranged within a quadrant overlapping the first section each have the highest density of electrical conductors within the first section.
8. Gradient coil unit according to one of claims 6 to 7, comprising a primary connecting conductor connecting two primary conductor structures to one another and / or a primary conductor structure to a secondary conductor structure, and which connects to a turn of the primary conductor structure closest to the at least one primary fixed point.
9. Gradient coil unit according to one of claims 6 to 8, wherein a second section of the secondary coil, which is delimited in the longitudinal direction by the third longitudinal position and by a further secondary longitudinal position at a distance of at most 25% of the second length from the third longitudinal position, is free of a secondary connecting conductor which connects two secondary conductor structures to one another and / or a primary conductor structure to a secondary conductor structure.
10. The gradient coil unit of claim 9, wherein the secondary conductor structures arranged within a quadrant overlapping with the second section each have the highest density of electrical conductors within the second section.
11. Gradient coil unit according to one of claims 6 to 10, comprising a secondary connecting conductor connecting two secondary conductor structures to one another and / or a primary conductor structure to a secondary conductor structure, and which connects to a turn of the secondary conductor structure closest to the at least one secondary fixed point.
12. A magnetic resonance apparatus comprising a detector unit with a main magnet, a radio-frequency antenna unit and a gradient coil unit according to one of the preceding claims, wherein the gradient coil unit coaxially surrounds the radio-frequency antenna unit, and a control unit configured to control the detector unit, wherein a spatial extension of the radio-frequency antenna unit in the longitudinal direction is shorter than the second length.