Magnetic resonance imaging device with a curved field generating unit

Abstract

The present invention discloses a magnetic resonance imaging apparatus having a curved field generating unit. The invention relates to a magnetic resonance imaging apparatus comprising a field generating unit, the field generating unit being configured to provide a magnetic field in an imaging volume of the magnetic resonance imaging apparatus, wherein the field generating unit comprises at least one magnet, wherein the at least one magnet delimits the imaging volume in at least one spatial direction, and wherein the at least one magnet is curved in such a way that a perpendicular distance between a line oriented in an approach direction to the imaging volume and a surface of the at least one magnet oriented toward the imaging volume varies in the approach direction to the imaging volume.

Description

Technical Field

[0001] The invention relates to a magnetic resonance imaging apparatus comprising a field generating unit comprising at least one magnet, wherein the field generating unit is configured to provide a magnetic field in an imaging volume of the magnetic resonance imaging apparatus. Background Art

[0002] Magnetic resonance tomography represents a well-known imaging method for acquiring images of the interior of an object under examination. For magnetic resonance measurements, the object under examination is usually positioned in a strong and uniform static magnetic field (B0 field) of a magnetic resonance imaging device. The static magnetic field can comprise a magnetic field strength of 0.2 Tesla to 7 Tesla, so that the nuclear spins within the object under examination are aligned along the static magnetic field. In order to trigger so-called nuclear spin resonance, radio frequency excitation pulses are emitted into the object under examination. Each radio frequency excitation pulse causes the magnetization of the nuclear spins within the object under examination to deviate from the static magnetic field by a certain amount, which is called the flip angle. The radio frequency excitation pulse can comprise an alternating (electric) magnetic field, the frequency of which corresponds to the Larmor frequency at the corresponding static magnetic field strength. The excited nuclear spins may exhibit a rotating and decaying magnetization (nuclear magnetic resonance), which can be detected using a dedicated radio frequency antenna. For spatial encoding of the measurement data, rapidly switched magnetic gradient fields are superimposed on the static magnetic field.

[0003] The received nuclear magnetic resonance images are usually digitized and stored as complex values ​​in a k-space matrix. This k-space matrix can be used as the basis for reconstructing magnetic resonance images and determining spectral data. Magnetic resonance images are usually reconstructed by a multidimensional Fourier transform of the k-space matrix.

[0004] During an imaging examination, a patient is typically enclosed in the bore of an MRI device (e.g., in a solenoid scanner) or between a pair of magnets (e.g., in a C-scanner). Due to the spatial limitations within the bore or between the pair of magnets, MRI offers limited utility for surgical procedures or biopsies. Since the patient typically needs to be positioned within the MRI device, the size of the bore, as well as other dimensions of the MRI device, is determined by the size of the human body. This can be unsatisfactory from a cost and / or space utilization perspective, particularly if the examination is limited to an area of ​​the patient's body that is significantly smaller than the imaging volume provided by the MRI device. Furthermore, claustrophobic patients or children may not be able to tolerate the long examination times typically associated with MRI measurements.

[0005] Furthermore, the field generation of the magnetic resonance imaging apparatus must be set up to ensure a fixed relative position of the magnets contained therein, for example to counteract the magnetic forces that arise. Since patients of different sizes must fit within the magnetic resonance imaging apparatus without physical interference with any hardware components, the magnets are usually positioned at a considerable distance from the imaging volume of the magnetic resonance imaging apparatus. This can reduce the efficiency of the field generation unit (characterized, for example, by the ratio of the volume of magnetic material required to the available magnetic field strength in the imaging volume) as well as the efficiency of the power and / or cooling infrastructure of the magnetic resonance imaging apparatus. Even specialized scanners adapted for a specific body region of the patient can encounter this problem when using conventional solenoid or C-type scanners. Summary of the Invention

[0006] It is therefore an object of the present invention to increase the efficiency of a field generating unit of a magnetic resonance imaging apparatus.

[0007] This object is achieved by a magnetic resonance imaging device according to the invention. Further advantageous embodiments are specified in the technical solution of the invention.

[0008] The magnetic resonance imaging apparatus of the present invention comprises a field generating unit configured to provide a magnetic field in an imaging volume of the magnetic resonance imaging apparatus, wherein the field generating unit comprises at least one magnet, wherein the at least one magnet confines the imaging volume in at least one spatial direction.

[0009] The field generating unit may include a plurality of magnets required for performing magnetic resonance measurements. For example, the field generating unit may include at least one magnet configured to generate a static magnetic field in an imaging volume of the magnetic resonance imaging device. The static magnetic field may be the B0 field of the magnetic resonance imaging device, including a substantially uniform magnetic field or a predetermined magnetic gradient field. In another example, the field generating unit includes at least one gradient coil for generating a temporary magnetic gradient field in the imaging volume. It is also conceivable that the field generating unit includes at least one radio frequency antenna for transmitting radio frequency excitation pulses within the power and frequency range of the magnetic resonance measurement into an image acquisition region of the magnetic resonance imaging device. The at least one radio frequency antenna may also be configured to receive magnetic resonance signals (nuclear magnetic resonance) from the image acquisition region.

[0010] The imaging volume can be characterized by a predefined magnetic field direction and / or magnetic field strength. For example, the imaging volume can include a volume having a substantially uniform magnetic field direction and / or uniform magnetic field strength. Such a volume can be the isocenter of the magnetic resonance imaging device. It is also contemplated that the imaging volume includes a predefined magnetic gradient field. Such a magnetic gradient field can be used to spatially encode magnetic resonance signals acquired from an examination subject positioned within the imaging volume.

[0011] The at least one magnet can restrict the imaging volume in at least one spatial direction in such a manner that approaching or entering the imaging volume from a direction substantially corresponding to the at least one spatial direction is impractical or impossible. For example, the at least one magnet can prevent or block approaching the imaging volume in any direction substantially consistent with the at least one direction.

[0012] The at least one magnet is bent in such a way that a perpendicular distance between a line oriented in the approach direction to the imaging body and a surface of the at least one magnet oriented toward the imaging body varies in the approach direction to the imaging body.

[0013] At least one magnet can be configured as a main magnet for generating a static magnetic field in an imaging volume. However, at least one magnet can also correspond to a gradient coil, a gradient coil assembly and / or a radio frequency antenna of a magnetic resonance imaging device. In one example, at least one magnet is curved in such a manner that a surface of at least one magnet directed toward the imaging volume comprises a non-planar shape. In a preferred embodiment, the surface of at least one magnet directed toward the imaging volume comprises the shape of a cone or a truncated cone. However, other shapes, such as a hemisphere, or any complex three-dimensional shape that tapers in the direction toward the imaging volume are also conceivable. When providing at least one magnet having a curved surface directed toward the imaging volume or tapering in the direction toward the imaging volume, a gap can be advantageously provided for adapting to a patient's body region. For example, when the patient's eye region, jaw region, or heart is positioned in the imaging volume, the tapered surface of at least one magnet directed toward the imaging volume can advantageously adapt to the patient's shoulder or abdominal region.

[0014] The approach direction to the imaging volume can be characterized by a substantially straight line leading from any point in the environment or examination room to the imaging volume. The line is oriented along the approach direction to the imaging volume. Preferably, the trajectory defined by the line is unobstructed by components of the magnetic resonance imaging apparatus. The approach direction relates to a trajectory along which the patient can enter the imaging volume.

[0015] The perpendicular distance between the line and the surface of the at least one magnet oriented toward the imaging body can vary along the approach direction to the imaging body in such a manner that the perpendicular distance decreases in the direction toward the imaging body. For example, the perpendicular distance between the line and the surface of the at least one magnet oriented toward the imaging body can decrease in the direction toward the imaging body in a linear, nonlinear, hyperbolic, parabolic, exponential, or similar manner. The perpendicular distance can be understood as the distance between an arbitrarily selected point on the line and the closest point on the surface of the at least one magnet oriented toward the imaging body. In particular, the perpendicular distance can be characterized by the length of the normal vector of the line connecting the arbitrarily selected point on the line and the closest point on the surface of the at least one magnet oriented toward the imaging body.

[0016] When the at least one magnet is provided with a curved surface oriented toward the imaging volume, the average distance between the center of the imaging volume and the at least one magnet can be reduced while still providing sufficient clearance to accommodate the patient's body and / or body region within the image acquisition area of ​​the magnetic resonance imaging device. Consequently, the efficiency of the field generating unit can be advantageously increased compared to conventional solenoid and / or C-type magnetic resonance imaging devices having comparable magnetic field strengths.

[0017] According to a further embodiment of the magnetic resonance imaging apparatus according to the invention, the field generating unit comprises a second magnet, wherein the at least one magnet and the second magnet are arranged in such a way that access to the imaging volume is provided in at least two perpendicular spatial directions.

[0018] For example, at least one magnet can confine the imaging volume in a first spatial direction, and a second magnet can confine the imaging volume in a second spatial direction different from the first spatial direction. The first spatial direction and the second spatial direction can be oriented in parallel. In particular, the first spatial direction and the second spatial direction can be oriented in opposite directions at an angle of 180°. However, the two spatial directions can also be oriented at an angle of less than 180° or greater than 180°. The at least one magnet and the second magnet can be carried and / or kept separate by a support structure of the magnetic resonance imaging device, and the imaging volume can be positioned in a free body or in a gap between the at least one magnet and the second magnet. It is conceivable that access to the imaging volume can be provided along any unobstructed line connecting any selected position in the examination room with the center of the imaging volume. The examination room can be a room in which the magnetic resonance imaging device is positioned and / or in which magnetic resonance measurements can be performed.

[0019] At least one magnet and / or the second magnet may include an axis of rotational symmetry. In one embodiment, the first approach direction to the imaging volume may be oriented substantially perpendicular to the axis of rotational symmetry of the at least one magnet and / or the second magnet. The second approach direction may be oriented substantially perpendicular to the first approach direction and the axis of rotational symmetry of the at least one magnet and / or the second magnet. However, the first approach direction and / or the second approach direction may also include an angle relative to the axis of rotational symmetry of the at least one magnet and / or the second magnet. The axis of rotational symmetry may be characterized in that after rotating the at least one magnet and / or the second magnet through at least a portion of a revolution about the axis of rotational symmetry, the at least one magnet and / or the second magnet appears the same. It is also contemplated that the at least one magnet and / or the second magnet includes a higher order discrete rotational symmetry with n>1. This may mean that rotating the at least one magnet and / or the second magnet through an angle of 360° / n about the axis of rotational symmetry does not change the at least one magnet and / or the second magnet.

[0020] Preferably, the imaging volume can be approached via multiple approach directions. In one embodiment, the imaging volume can be approached via at least two substantially perpendicular spatial directions. However, the imaging volume can also be approached via three substantially perpendicular spatial directions. The three perpendicular spatial directions can correspond to the axes of a Cartesian coordinate system, with the origin of the Cartesian coordinate system being at the center of the imaging volume.

[0021] The approach direction to the imaging volume in each of the at least two perpendicular spatial directions is angled relative to a main direction of the magnetic field lines in the imaging volume.

[0022] Preferably, the angle between each of the at least two perpendicular spatial directions and the main direction of the magnetic field lines in the imaging volume is a non-zero angle. For example, the angle between each of the at least two perpendicular spatial directions and the main direction of the magnetic field lines in the imaging volume can include values ​​in the range of 1° to 180°, 10° to 170°, or 30° to 150°. However, any angle that deviates from a substantially parallel orientation with respect to the main direction of the magnetic field lines in the imaging volume is conceivable.

[0023] In one embodiment, at least one magnet and the second magnet can be separated by a shielding coil. The shielding coil can be configured to shield the at least one magnet and / or the second magnet from electromagnetic interference and / or magnetic fields provided by other magnets (e.g., the at least one magnet can be shielded from the second magnet and / or electromagnetic interference in the environment). For example, the shielding coil can be positioned adjacent to a surface of the at least one magnet that is oriented away from the imaging body. However, the shielding coil can also be positioned adjacent to a surface of the at least one magnet that is oriented toward the imaging body. In a preferred embodiment, the at least one magnet includes a first shielding coil positioned adjacent to the at least one magnet. Similarly, the second magnet can include a second shielding coil positioned adjacent to the second magnet.

[0024] When the at least one magnet and the second magnet are arranged in such a manner as to provide access to the imaging subject in at least two perpendicular spatial directions, accessibility to the imaging subject can be advantageously enhanced while maintaining or reducing the distance between the at least one magnet and / or the second magnet and the imaging subject. Thus, a better compromise between the efficiency of the field generating unit and accessibility to the imaging subject can be advantageously provided compared to conventional magnetic resonance imaging apparatuses.

[0025] According to another embodiment of the magnetic resonance imaging apparatus of the present invention, the surface of the second magnet oriented toward the imaging body is curved in such a manner that a perpendicular distance between a line oriented along an approach direction to the imaging body and the surface of the second magnet oriented toward the imaging body varies in the approach direction to the imaging body.

[0026] The curvature of the surface of the second magnet oriented toward the imaging body can correspond to the curvature of the surface of the at least one magnet oriented toward the imaging body. For example, the at least one magnet and the second magnet can be arranged symmetrically relative to the imaging body. In this case, the first distance between the center of the imaging body and the nearest point on the surface of the at least one magnet can correspond to the second distance between the center of the imaging body and the nearest point on the surface of the second magnet. It is also conceivable that the at least one magnet and the second magnet are arranged symmetrically relative to a symmetry plane passing through the center of the imaging body. In this embodiment, the shape of the at least one magnet can substantially correspond to the shape of the second magnet. However, the at least one magnet and the second magnet can also include different shapes. For example, the curvature of the surface of the at least one magnet oriented toward the imaging body can include a different shape, slope, and / or surface area than the surface of the second magnet oriented toward the imaging body. In particular, the at least one magnet and the second magnet can be arranged asymmetrically relative to the imaging body. In one embodiment, the first distance can be different from the second distance. It is also conceivable that the at least one magnet and the second magnet constrain the imaging body from two opposing sides.

[0027] When a second magnet is provided having a curved surface oriented toward the imaging volume, the image acquisition region of the magnetic resonance imaging apparatus can advantageously be adapted to better accommodate the patient from more than one side and / or to match the contours of a patient's body region (e.g., the patient's abdomen, shoulders, and / or neck). Thus, a specialized scanner can be provided with high efficiency of the field generating unit and increased patient comfort.

[0028] In another embodiment of the magnetic resonance imaging device, the surface of the second magnet directed toward the imaging body is shaped in such a way that the perpendicular distance between a line oriented along the approach direction to the imaging body and the surface of the second magnet directed toward the imaging body is constant in the approach direction to the imaging body.

[0029] For example, the surface of the second magnet that is oriented toward the imaging body can be substantially flat or planar. In this case, the approach direction to the imaging body can be oriented parallel to the flat or planar surface of the second magnet. It is conceivable that the second surface area of ​​the surface of the second magnet that is oriented toward the imaging body is different from the first surface area of ​​the surface of at least one magnet that is oriented toward the imaging body. The second surface area can exceed the first surface area or be less than the first surface area. However, it is also conceivable that the first surface area and the second surface area substantially match.

[0030] Providing a second magnet with a substantially planar or flat surface oriented toward the imaging volume can advantageously reduce the manufacturing cost of the field generating unit, while still providing at least one magnet with a curved surface oriented toward the imaging volume to improve the efficiency of the field generating unit. In one example, the flat or planar surface of the second magnet oriented toward the imaging volume can advantageously be used to accommodate the patient's back, which typically has a flatter or more uniform topology than the patient's front.

[0031] In another embodiment of the magnetic resonance imaging apparatus of the present invention, the at least one magnet and / or the second magnet is configured to generate a static magnetic field in the imaging volume, wherein the static magnetic field is uniform throughout the imaging volume, or wherein the static magnetic field comprises a predefined magnetic field gradient across the imaging volume.

[0032] The at least one magnet and / or the second magnet may represent a main magnet of a field generating unit configured to provide a BO magnetic field. It is contemplated that the BO magnetic field provided by the at least one magnet and / or the second magnet is a static magnetic field having particularly high magnetic homogeneity. However, the BO magnetic field provided by the at least one magnet may also include a predefined magnetic field gradient. This predefined magnetic field gradient may be used to spatially encode magnetic resonance signals acquired from the image acquisition region.

[0033] In one embodiment, at least one magnet and a second magnet are arranged on opposite sides of the imaging volume and represent two poles or magnet segments of a combined magnet to provide a uniform BO magnetic field. To this end, the magnetic field strengths of the at least one magnet and the second magnet can be substantially identical. However, the magnetic field strengths of the at least one magnet and the second magnet can also differ, thereby providing a predefined magnetic field gradient across the imaging volume. It is also contemplated that the at least one magnet is configured as a solenoid circumferentially surrounding the imaging volume. In this case, the second magnet can be omitted.

[0034] When at least one magnet having a curved surface oriented toward the imaging volume is provided for generating the BO magnetic field, the main components of the field generating unit can be shaped in a manner that allows for better adaptation to specific body regions of the patient and / or improves the efficiency of the magnetic resonance imaging apparatus. Furthermore, the curved surface of the at least one magnet oriented toward the imaging volume can enhance the convergence of magnetic field lines within the imaging volume, thereby providing a stronger magnetic gradient field.

[0035] In a preferred embodiment, at least one magnet comprises a gradient coil set, wherein the gradient coil set is configured to generate a magnetic gradient field in the imaging volume.

[0036] At least one magnet is configured as a gradient magnet including a gradient coil assembly. The gradient coil assembly may include one or more gradient coils. For example, the gradient coil assembly may include one, two, three, or more gradient coils. The gradient coil may be composed of wire wound in a manner that provides a substantially planar, curved, or tubular shape. The axial cross-section of the tubular gradient coil may be circular, oval, or polygonal. In one embodiment, the gradient coil assembly of at least one magnet may include a gradient coil that circumferentially surrounds the imaging volume along the approach direction to the imaging volume. The gradient coil may be configured as a tubular solenoid, and the diameter of the tubular solenoid may vary along the approach direction to the imaging volume.

[0037] However, the gradient coil assembly may also include at least two gradient coils positioned on opposite sides of the imaging volume. The gradient coil assembly may be positioned such that the direction of approach to the imaging volume is oriented substantially perpendicular to the gradient coil assembly's axis of rotational symmetry. It is also conceivable that the gradient coil assembly be positioned on one side of the imaging volume. For example, the first gradient coil and the second gradient coil of the gradient coil assembly may be positioned adjacent to each other and bound the imaging volume in substantially one spatial direction.

[0038] In another embodiment of the magnetic resonance imaging apparatus of the present invention, the field generating unit comprises a second magnet, wherein the second magnet comprises a second gradient coil set.

[0039] The second gradient coil assembly may include one or more gradient coils. The second gradient coil assembly may be arranged along the rotational symmetry axis of the at least one magnet and / or the second magnet. In particular, the rotational symmetry axis of the second gradient coil assembly may coincide with the rotational symmetry axis of the at least one magnet. In one embodiment, the rotational symmetry axis of the at least one magnet coincides with the direction of approach to the imaging object. However, according to another embodiment, the rotational symmetry axis of the at least one magnet is oriented substantially orthogonal to the direction of approach to the imaging object. In the latter case, the gradient coil assembly and the second gradient coil assembly may be positioned on opposite sides of the imaging object. However, it is also conceivable that the first gradient coil and the second gradient coil of the at least one magnet are positioned on opposite sides of the imaging object, and the first gradient coil and the second gradient coil of the second magnet are positioned on opposite sides of the imaging object. The first gradient coil of the at least one magnet may be positioned adjacent to the first gradient coil of the second magnet and / or the second gradient coil of the second magnet.

[0040] The second gradient coil set is configured to generate a second magnetic gradient field in the imaging volume, wherein the second magnetic gradient field is oriented perpendicular to the magnetic gradient field provided by the at least one magnet.

[0041] In another embodiment, the field generating unit of the magnetic resonance imaging apparatus of the present invention includes a third magnet, wherein the third magnet includes a third gradient coil assembly, and wherein the third gradient coil assembly is configured to generate a third magnetic gradient field in the imaging volume, wherein the third magnetic gradient field is oriented perpendicular to the magnetic gradient field provided by at least one magnet. It is also contemplated that the gradient fields of the first magnet, the second magnet, and the third magnet are oriented substantially perpendicular to one another. Preferably, the third magnet includes a curved surface that is similar to or different from the curved surfaces of the first magnet and / or the second magnet.

[0042] When a gradient coil assembly with a curved surface is provided according to the present invention, the efficiency of the gradient system can be advantageously increased compared to conventional magnetic resonance imaging devices. A possible advantage of the increased efficiency of the gradient system can be an increased switching rate of the gradient coils or gradient coil assemblies compared to conventional magnetic resonance imaging devices.

[0043] In another embodiment of the magnetic resonance imaging device, the second magnet is curved in such a way that the perpendicular distance between a line oriented in the approach direction to the imaging volume and a surface of the second magnet oriented toward the imaging volume varies in the approach direction to the imaging volume, wherein the curvature of the second magnet differs from the curvature of at least one magnet.

[0044] As described above, at least one magnet and / or the second magnet can represent the main magnet or gradient magnet of the magnetic resonance imaging device. The curvature of the surface of the second magnet directed toward the imaging body is different from the curvature of the surface of the at least one magnet directed toward the imaging body. For example, the curvature of the surface of the at least one magnet directed toward the imaging body may include a shape, slope and / or surface area that is different from the surface of the second magnet directed toward the imaging body. At least one magnet and the second magnet can be positioned adjacent to each other. In this case, at least one magnet and the second magnet can advantageously be arranged in a manner that facilitates the proximity of a specific body region of the patient to the imaging body and / or accommodates a specific body region of the patient positioned within the imaging body. In an alternative embodiment, at least one magnet and the second magnet limit the imaging body in essentially two opposite spatial directions.

[0045] The different curvatures of the surfaces of at least one magnet and the second magnet directed toward the imaging body can advantageously make it possible to reduce the distance between at least a portion of the at least one magnet and the imaging body and / or at least a portion of the second magnet and the imaging body, thereby improving the efficiency of the field generating unit.

[0046] In an alternative embodiment, the surface of the second magnet directed toward the imaging body is shaped in such a way that the perpendicular distance between a line oriented along the approach direction to the imaging body and the surface of the second magnet directed toward the imaging body is constant in the approach direction to the imaging body.

[0047] For example, the surface of the second magnet that is oriented toward the imaging body can be substantially planar or flat. It is also conceivable that the surface of the second magnet that is oriented toward the imaging body is oriented parallel to the approach direction to the imaging body. In addition, at least one magnet and the second magnet can be positioned adjacent to each other. Therefore, a particularly compact or space-saving arrangement of the at least one magnet and the second magnet can be advantageously provided. In this case, the at least one magnet is preferably positioned closer to the imaging body than the second magnet. However, the at least one magnet and the second magnet can also be arranged in such a way that the imaging body is limited by the at least one magnet and the second magnet in substantially two opposite spatial directions.

[0048] Providing a second magnet having a substantially flat or planar surface oriented toward the imaging volume can advantageously reduce manufacturing costs and / or the effort required to assemble the field generating unit, while still enabling at least one magnet to be positioned close to the imaging volume. Thus, the cost-effectiveness of the magnetic resonance imaging apparatus can be advantageously tailored to the needs of a specific body region of the patient.

[0049] In one embodiment of the magnetic resonance imaging apparatus of the present invention, at least one magnet is configured to surround at least a portion of the imaging volume along at least a portion of a line oriented along an approach direction to the imaging volume, wherein the approach direction to the imaging volume is oriented parallel to a main direction of the magnetic field lines within the imaging volume.

[0050] The at least one magnet can represent a main magnet or a gradient magnet including a gradient coil assembly. The at least one magnet can encompass at least a portion of the surface of an imaginary cylinder, the axis of rotational symmetry of the imaginary cylinder coinciding with a line oriented along the approach direction to the imaging volume. Specifically, the at least one magnet can encompass an arc of the imaginary cylinder along the direction of the imaging volume. For example, the angle defining the arc can exceed 60°, 90°, 120°, 150°, or 180°.

[0051] Preferably, the at least one magnet is shaped such that the minimum perpendicular distance between a line oriented in the direction of approach to the imaging volume and a surface of the at least one magnet oriented toward the imaging volume is located at the center of the imaging volume. For example, a first perpendicular distance between the line oriented in the direction of approach to the imaging volume and the surface of the at least one magnet oriented toward the imaging volume is located at a first distance from the imaging volume, and a second perpendicular distance between the line oriented in the direction of approach to the imaging volume and the surface of the at least one magnet oriented toward the imaging volume is located at a second distance from the imaging volume. The at least one magnet may be curved such that the first perpendicular distance exceeds the second perpendicular distance, and the first distance exceeds the second distance. It is also conceivable that the perpendicular distance between the line oriented in the direction of approach to the imaging volume and the surface of the at least one magnet oriented toward the imaging volume increases in a direction away from the center of the imaging volume along the line oriented in the direction of approach to the imaging volume. The overall shape of the at least one magnet may substantially correspond to an hourglass, a double cone, a double truncated cone, or the like.

[0052] According to one embodiment of the magnetic resonance imaging apparatus according to the present invention, the field generating unit comprises a second magnet, wherein the second magnet is configured to surround at least a portion of the imaging body along at least a portion of a line oriented in an approach direction to the imaging body, wherein the second magnet is bent in such a way that a perpendicular distance between the line oriented in the approach direction to the imaging body and a surface of the second magnet oriented toward the imaging body varies in the approach direction to the imaging body.

[0053] The slope of the curvature of the surface of the second magnet oriented toward the imaging body may correspond to the slope of the curvature of the surface of the at least one magnet oriented toward the imaging body at one or more cross sections of the field generating unit along the approach direction to the imaging body. However, the slope of the curvature of the at least one magnet and the second magnet may also be different at one or more cross sections of the field generating unit along the approach direction to the imaging body. In a preferred embodiment, the at least one magnet and the second magnet include the same shape but different sizes. For example, the diameter and / or length of the at least one magnet may be different from the diameter and / or length of the second magnet. However, the shape of the second magnet may also be different from that of the second magnet.

[0054] Similar to the at least one magnet, the second magnet can represent a main magnet or a gradient magnet including a second gradient coil assembly. The second magnet can encompass at least a portion of the surface area of ​​an imaginary cylinder, the axis of rotational symmetry of the imaginary cylinder coinciding with a line oriented along the approach direction to the imaging volume. In particular, the second magnet can encompass at least one arc of the imaginary cylinder along the direction of the imaging volume. For example, the angle defining the arc can exceed 60°, 90°, 120°, 150°, or 180°.

[0055] When a magnet is arranged to surround at least a portion of the imaging volume along at least a portion of a line oriented in an approach direction to the imaging volume, the surrounding of the imaging volume with the magnetic material can be advantageously enhanced. Thus, the uniformity and / or magnetic field strength within the imaging volume can be increased compared to conventional C-type or dipole magnetic resonance imaging devices.

[0056] In a preferred embodiment, the at least one magnet and / or the second magnet circumferentially surrounds the imaging volume along a line oriented in the approach direction to the imaging volume.

[0057] Preferably, at least one magnet is configured as a solenoid magnet comprising a tube shape. At least one magnet may comprise any cross-section, such as a circular, oval, elliptical, or polygonal cross-section. The center of the imaging volume may be located along the axis of rotational symmetry of the tube, in particular the geometric center of the tube. In one example, at least one magnet may be a main magnet providing a static magnetic field within the imaging volume. In another example, at least one magnet may be a gradient magnet comprising a gradient coil assembly circumferentially surrounding the imaging volume along a line oriented along an approach direction to the imaging volume.

[0058] Similarly, the second magnet can be configured as a solenoid magnet that circumferentially surrounds the imaging body along a line oriented in the direction of approach to the imaging body. Similar to the at least one magnet, the second magnet can include a tubular shape with an arbitrarily shaped cross-section. The second magnet can surround at least a section of the at least one magnet along at least a portion of the line oriented in the direction of approach to the imaging body. However, in an alternative embodiment, the second magnet can also be at least partially surrounded by the at least one magnet along at least a portion of the line oriented in the direction of approach to the imaging body.

[0059] The diameter of at least one magnet and / or the second magnet may vary in the direction of approach to the imaging body. In one embodiment, the cross-section of the at least one magnet and / or the second magnet having the smallest diameter substantially coincides with the position of the center of the imaging body along a line oriented in the direction of approach to the imaging body. In another example, the first diameter of the at least one magnet and / or the second magnet located at a first distance from the imaging body exceeds the second diameter of the at least one magnet and / or the second magnet located at a second distance from the imaging body, wherein the first distance exceeds the second distance. In a preferred embodiment, the diameter of the at least one magnet and / or the second magnet increases in a direction away from the center of the imaging body along the line oriented in the direction of approach to the imaging body.

[0060] When a solenoid magnet is provided having a varying diameter along a line oriented in an approach direction to an imaging volume, the efficiency of the field generating unit can be advantageously improved compared to conventional solenoid magnetic resonance imaging apparatuses. Furthermore, the increased magnet diameter at the opening or end of the magnet can advantageously facilitate approaching a patient or a region of the patient's body to the imaging volume compared to existing solenoid magnetic resonance imaging apparatuses.

[0061] According to one embodiment of the magnetic resonance imaging apparatus of the present invention, the at least one magnet and / or the second magnet comprises at least one of the following:

[0062] ·Permanent magnets,

[0063] Electromagnets,

[0064] High-temperature superconducting magnets,

[0065] Low-temperature superconducting magnets.

[0066] At least one magnet and / or the second magnet may be composed of coils and / or tubular magnet segments. The coils and / or tubular magnet segments may include wires made of a material exhibiting superconducting properties. The wires may be connected to a cryostat to maintain the wire temperature below a predetermined value (e.g., the superconducting temperature). In the case of low-temperature superconducting magnets, liquid helium may be used as a coolant to ensure the wire temperature remains below 4K. Low-temperature superconducting magnets may include materials such as niobium titanium, niobium tin, niobium germanium, and their alloys. In contrast, high-temperature superconducting magnets exhibit superconducting properties within a temperature range of 30K to 90K. High-temperature superconducting magnets may include materials such as barium copper oxide, copper calcium oxide, and magnesium diboride, but also include fullerenes and the like. The wires may be wound and / or arranged into various shapes, such as solenoids, as substantially planar rings, or as tubular magnet segments. Preferably, the wires of the high-temperature superconducting magnets and / or low-temperature superconducting magnets are embedded in a matrix made of an electrical conductor such as copper, aluminum, or gold.

[0067] By using high temperature superconducting magnets and / or low temperature superconducting magnets, the magnetic field strength provided by the at least one magnet and / or the second magnet may advantageously be increased compared to comparably sized permanent magnets or electromagnets.

[0068] The permanent magnets can be composed of any suitable magnetic material, such as aluminum-nickel-cobalt, neodymium-iron-boron, or samarium-cobalt alloys. Furthermore, the surface of the permanent magnets directed toward the imaging volume can have a conical or truncated pyramidal shape. In one embodiment, the permanent magnets can be composed of smaller, stacked permanent magnets. Permanent magnets advantageously provide a low-cost solution for generating a magnetic field within the imaging volume. The use of permanent magnets can advantageously avoid the cost and space required for cooling equipment typically associated with superconducting magnets and electromagnets.

[0069] The electromagnet can be a non-superconducting magnet. Specifically, the electromagnet can include an electrical conductor wound in a predetermined pattern. The electrical conductor can be wound around a magnetic core made of, for example, a ferromagnetic or ferrimagnetic material. The magnetic core of the electromagnet can have a cylindrical, rectangular, prismatic, or any other desired shape. The use of an electromagnet can advantageously increase the magnetic field strength compared to a permanent magnet of comparable size. This higher magnetic field strength can advantageously improve the quality and / or signal-to-noise ratio of magnetic resonance images acquired by an MRI device.

[0070] According to one embodiment, at least one magnet and a second magnet limit the imaging volume in two spatial directions oriented at an angle of 180° to each other, wherein the minimum distance between the at least one magnet and the center of the imaging volume is equal to or different from the minimum distance between the second magnet and the center of the imaging volume.

[0071] The at least one magnet and the second magnet can be arranged symmetrically relative to the imaging body, provided that the minimum distance between the center of the imaging body and the at least one magnet is equal to the minimum distance between the center of the imaging body and the second magnet. In the symmetrical arrangement of the at least one magnet and the second magnet relative to the imaging body, the volume, size, shape, and / or curvature of the surfaces of the at least one magnet and the second magnet oriented toward the imaging body can be substantially identical. By providing a symmetrical arrangement of the at least one magnet and the second magnet relative to the imaging body, the design and / or manufacturing effort of providing different magnets for the field generating unit can be advantageously avoided.

[0072] In the case where the minimum distance between the center of the imaging volume and the at least one magnet is not equal to the minimum distance between the center of the imaging volume and the second magnet, the at least one magnet and the second magnet are arranged asymmetrically relative to the imaging volume. The asymmetrical arrangement of the at least one magnet and the second magnet relative to the imaging volume can be characterized by different volumes, sizes, shapes, and / or curvatures of the surfaces of the at least one magnet and the second magnet that are oriented toward the imaging volume. It is also conceivable that the at least one magnet and the second magnet include different magnetic field strengths and / or different magnetic materials. In this case, different volumes of magnetic material and / or different shapes may be required to match the at least one magnet and the second magnet. Therefore, the minimum distance between the center of the imaging volume and the at least one magnet can be equal to the minimum distance between the center of the imaging volume and the second magnet. However, due to the difference in volume, size, shape, and / or curvature of the surfaces of the at least one magnet and the second magnet that are oriented toward the imaging volume, the at least one magnet and the second magnet can be arranged asymmetrically relative to the imaging volume.

[0073] When providing an asymmetric arrangement of the at least one magnet and the second magnet relative to the imaging volume, the curvature of the surfaces of the at least one magnet and the second magnet directed toward the imaging volume can be matched to the geometry of a specific body region of the patient. Thus, the gap size between the at least one magnet and the second magnet and / or the approach direction to the imaging volume can be optimized for imaging of the specific body region. Furthermore, by taking the geometry of the specific body region into consideration, both the at least one magnet and the second magnet can be advantageously positioned closer to the imaging volume, thereby improving the efficiency of the field generating unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Further advantages and details of the present invention can be seen from the following description of the embodiments and the accompanying drawings.

[0075] Figure 1 is a schematic diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0076] Figure 2 is a schematic diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0077] Figure 3 is a schematic diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0078] Figure 4 is a schematic diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0079] Figure 5 is a schematic diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0080] Figure 6 is a schematic diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0081] Figure 7 is a schematic diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention, and

[0082] Figure 8 The relationship between the switching rate of the field generating unit of the present invention and the gap of the aperture of the magnetic resonance imaging device of the present invention is shown. DETAILED DESCRIPTION

[0083] Figure 1 A schematic diagram of a magnetic resonance imaging apparatus 10 of the present invention is depicted, which is configured to perform magnetic resonance measurements on the jaw region and / or eye region of a patient 15. The use of the magnetic resonance imaging apparatus 10 for imaging the jaw region and / or eye region of the patient 15 should be understood as an example. The magnetic resonance imaging apparatus 10 of the present invention can also be configured to perform cardiac imaging, mammographic imaging, neurological imaging, urological imaging, orthopedic imaging, prostate imaging, or imaging of other body regions of the patient 15.

[0084] In the depicted embodiment, the magnetic resonance imaging apparatus 10 includes a field generating unit 12 having a first magnet 13 and a second magnet 14. The first magnet 13 and the second magnet 14 are supported by a support structure 11, which maintains a predetermined distance between the first magnet 13 and the second magnet 14. The support structure 11 can be implemented as an iron yoke 18. The free body between the first magnet 13 and the second magnet 14 represents an image acquisition region 17 configured to accommodate an examination object 15 (e.g., a body region of a patient 15). The image acquisition region 17 is defined by the first magnet 13 and the second magnet 14 in two opposite spatial directions.

[0085] The patient 15 can be positioned in the image acquisition region 17 in an upright or standing position. However, the patient 15 can also be positioned in the image acquisition region 17 in a sitting or lying position. In the latter case, the patient 15 can be positioned by a dedicated patient positioning device (not shown). However, the magnetic resonance imaging device 10 can also include a positioning unit 29 for adjusting the position and / or orientation of the field generating unit 12 relative to the patient 15. For example, the positioning unit 29 can include a rotary joint configured to rotate the field generating unit 12 along the rotation direction WX and / or the rotation direction WY. The position of the field generating unit 12 along the Y direction and / or the Z direction can be adjusted by a suitable telescope system and / or rail system mechanically connected to the support structure 11. Of course, other embodiments of the support structure 11 and / or the positioning unit 29 can be envisaged. In particular, the positioning unit 29 can also be configured to position the field generating unit 12 along at least one spatial direction and / or to rotate the field generating unit 12 in at least one rotational direction (not shown).

[0086] The surfaces of the first and second magnets 13, 14 that face the imaging volume 30 are curved in such a manner that the perpendicular distance between a line oriented along the approach direction 16 to the imaging volume 30 and the surface of the first magnet 14 that faces the imaging volume 30 varies along the approach direction 16 to the imaging volume 30. In the depicted embodiment, the first and second magnets 13, 14 are arranged symmetrically relative to the imaging volume 30. The surfaces of the first and second magnets 13, 14 that face the imaging volume 30 have a cone or dome shape. Due to the curvature of the first and second magnets 13, 14, clearance is provided for the shoulders of the patient 15. Consequently, the minimum distance between the first magnet 13 and the imaging volume 30 and the minimum distance between the second magnet 14 and the imaging volume 30 can be reduced compared to conventional C-type magnetic resonance imaging equipment while still providing sufficient clearance for the shoulders of the patient 15.

[0087] In the example shown, the first magnet 13 and the second magnet 14 are main magnets configured to generate a static magnetic field in the image acquisition region 17. The field generating unit 12 may further comprise a gradient field system 27 having at least one gradient coil 28 (see Figure 4 and Figure 5 ), the gradient coils 28 are used to generate magnetic gradient fields, which are used to spatially encode magnetic resonance signals acquired during magnetic resonance measurement. Preferably, the field generating unit 12 also includes a radio frequency system having at least one radio frequency antenna (not shown), which is configured to transmit radio frequency excitation pulses into the image acquisition region 17. The at least one radio frequency antenna can also be configured to receive magnetic resonance signals from the image acquisition region 17, in particular, from the imaging volume 30. In one embodiment, the at least one radio frequency antenna can be configured as a local coil.

[0088] To control the field generating unit 12 and at least one radio frequency antenna, the magnetic resonance imaging apparatus 10 includes a control unit 20. The control unit 20 is configured to control the magnetic resonance imaging apparatus 10 to perform magnetic resonance measurements of a body region of the patient 15 positioned within an imaging volume 30. To this end, the control unit 20 may include signal connections to a gradient control unit 21 and a radio frequency antenna control unit 22. It is also contemplated that the gradient control unit 21 and the radio frequency antenna control unit 22 are integrated within the control unit 20. Furthermore, the control unit 20 may include a processing unit 24 configured to coordinate the acquisition of magnetic resonance image data and / or the reconstruction of magnetic resonance image data acquired from the imaging volume 30. It is also contemplated that the processing unit 24 is also configured to evaluate and / or process data, such as magnetic resonance signals and / or magnetic resonance image data. The control unit 20 may include a controller, a microcontroller, analog circuits, a logic unit, or the like. The processing unit 24 may include a processor, such as a CPU, a GPU, or the like. It is also contemplated that the control unit 20 and / or the processing unit 24 include memory and / or internal storage devices, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, HDD, SSD, or the like.

[0089] Control information (e.g., imaging parameters and / or magnetic resonance image data) may be displayed on the output unit 25. The output unit 25 may include at least one monitor configured to display control information and / or images acquired by the magnetic resonance imaging apparatus 10 to an operator of the magnetic resonance imaging apparatus 10. The magnetic resonance imaging apparatus 10 may further include an input unit 26 configured to receive information and / or parameters input by the operator during an imaging examination.

[0090] The magnetic resonance imaging apparatus 10 shown may of course include other components commonly included in magnetic resonance imaging apparatuses 10. The general mode of operation of a magnetic resonance imaging apparatus 10 is well known to those skilled in the art. Therefore, further description of the general components or the sequence of magnetic resonance measurements is not considered necessary.

[0091] Figure 2 An embodiment of a magnetic resonance imaging apparatus 10 of the present invention is depicted in which a first magnet 13 and a second magnet 14 are arranged asymmetrically relative to an imaging volume 30. In the illustrated example, the volume and height of the first magnet 14 exceed those of the second magnet 14. The first magnet 13 may also have a higher magnetic field strength than the second magnet 14. Consequently, the imaging volume 30 provided by the first magnet 13 and the second magnet 14 may be offset toward the surface of the first magnet 13 that is oriented toward the imaging volume 30. Furthermore, the minimum distance between the center 31 of the imaging volume and the first magnet 13 and the minimum distance between the center 31 of the imaging volume and the second magnet 14 are not equal.

[0092] In the example depicted, the surface of the second magnet 14 that is oriented toward the imaging volume 30 is curved in such a way that it accommodates the neck region and the upper back region of the patient 15. In contrast, the surface of the first magnet 13 that is oriented toward the imaging volume 30 is curved in such a way that it provides clearance for the breast region of the patient 15. Figure 2 As can be seen in FIG, sufficient clearance is provided to facilitate access of the patient 15 to the imaging volume 30 along at least two perpendicular spatial directions. For example, the patient 15 can access the imaging volume 30 along the Y direction as well as the X direction. The two perpendicular directions of access to the imaging volume 30 are oriented perpendicular to the main direction of the magnetic field lines in the imaging volume 30, which is substantially coincident with the Z direction.

[0093] Figure 3Another embodiment of the magnetic resonance imaging apparatus 10 of the present invention is shown, in which the surface of the second magnet 14 oriented toward the imaging volume 30 is curved in such a manner that the perpendicular distances 37 (e.g., 37a, 37b, and 37c) between a line oriented along the approach direction 16 to the imaging volume 30 and the surface of the second magnet 14 oriented toward the imaging volume 30 are constant along the approach direction 16 to the imaging volume 30. In contrast, the surface of the first magnet 13 oriented toward the imaging volume 30 is curved in such a manner that the perpendicular distances 37 (e.g., 37d, 37e, and 37f) between a line oriented along the approach direction 16 to the imaging volume 30 and the surface of the first magnet 13 oriented toward the imaging volume 30 vary along the approach direction 16 to the imaging volume 30. In the example shown, the first magnet 13 and the second magnet 14 represent the main magnets of the field generating unit 12, which are arranged asymmetrically with respect to the imaging volume 30. However, it is also conceivable that the first magnet 13 and the second magnet 14 are gradient magnets of a gradient system. In this case, the first magnet 13 and the second magnet 14 may each include a gradient coil assembly configured to generate a magnetic gradient field in the imaging volume 30 .

[0094] It is envisaged that the first magnet 13 and the second magnet 14 comprise an axis of rotational symmetry which passes through the centre 31 of the imaging volume and is oriented substantially parallel to the Z direction.

[0095] Figure 4 Another embodiment of the magnetic resonance imaging apparatus 10 of the present invention is shown, which comprises a gradient system 27 comprising gradient coil sets 28a and 28b. In the depicted example, the first magnet 13 comprises a first gradient coil set 28a on one side of an imaging volume 30 and a first gradient coil set 28b positioned in a substantially opposite direction on the other side of the imaging volume 30. The first gradient coil set 28a and the first gradient coil set 28b can be configured as (mirror image) transverse gradient coils having a fingerprint winding pattern. However, other winding patterns are also conceivable. For example, the winding pattern of the first gradient coil set 28a and the first gradient coil set 28b can comprise a winding pattern according to Figure 4 In particular, according to the arrangement of the lines of the substantially circular or annular shape of the lines depicted in Figure 4 The first magnet 13 of the illustrated embodiment may be configured to generate a magnetic gradient field oriented in the Z direction. In alternative embodiments, the element 28a may be interpreted as the first magnet 13 and the element 28b may be interpreted as the second magnet 14 .

[0096] exist Figure 4In the illustrated embodiment, the first gradient coil assembly 28a and the shielding coil 34a are positioned adjacent to each other. In a similar manner, the first gradient coil assembly 28a and the second gradient coil assembly (not shown) can be positioned adjacent to each other. In an alternative embodiment, the first gradient coil assembly 28a can be positioned adjacent to the first gradient coil assembly 28b. In a preferred embodiment, the first gradient coil assembly 28a is positioned adjacent to the shielding coil 34a, and the first gradient coil assembly 28b is positioned adjacent to the shielding coil 34b. The shielding coils 34a and 34b can be configured to shield the first gradient coil assembly 28a and the first gradient coil assembly 28b from electromagnetic interference and / or magnetic fields provided by additional magnets (e.g., magnets positioned adjacent to the first gradient coil assembly 28a and / or the first gradient coil assembly 28b). As Figure 4 , the shield coil 34a can be positioned adjacent to a surface of the first gradient coil assembly 28a that is oriented away from the imaging volume 30. Likewise, the shield coil 34b can be positioned adjacent to a surface of the first gradient coil assembly 28b that is oriented away from the imaging volume 30. However, the shield coils 34a and 34b can also be positioned adjacent to surfaces of the first gradient coil assembly 28a and the first gradient coil assembly 28b that are oriented toward the imaging volume 30.

[0097] According to an alternative embodiment, Figure 4 The magnetic resonance imaging apparatus 10 depicted in FIG may include a second magnet 14 positioned adjacent to the first magnet 13. For example, the second magnet 14 may include a second gradient coil assembly 28c positioned adjacent to the first gradient coil assembly 28a (see FIG. Figure 5 ) and a second gradient coil assembly 28d positioned adjacent to the first gradient coil assembly 28b. The second gradient coil assemblies 28c and 28d can be positioned adjacent to the shield coils 34a and 34b and include similar shapes. Preferably, the shield coil 34a is positioned between the first gradient coil assemblies 28a and 28b and the second gradient coil assemblies 28c and 28d. However, the shield coil 34a can also be positioned adjacent to the surface of the second gradient coil assemblies 28c and 28d that is oriented away from the imaging volume to shield the first magnet 13 and the second magnet 14 from the main magnet (not shown) that generates a static magnetic field within the imaging volume 30.

[0098] Figure 5Another embodiment of the magnetic resonance imaging apparatus 10 of the present invention is shown, which includes a gradient system 27 in which the first magnet 13 is configured as a gradient magnet. The first magnet 13 includes a first gradient coil set 28a and a first gradient coil set 28b. The first gradient coil set 28a and the first gradient coil set 28b are arranged in such a manner that they constrain the imaging volume 30 in two substantially opposite spatial directions. In the depicted embodiment, the wiring pattern of the first gradient coil set 28a and the first gradient coil set 28b of the first magnet 13 can be configured to provide a magnetic gradient field oriented in the Y direction.

[0099] According to one embodiment, the magnetic resonance imaging apparatus 10 of the present invention may further include a second magnet 14 including second gradient coil assemblies 28 c and 28 d arranged on two opposite sides of the imaging volume 30. The second gradient coil assemblies 28 c and 28 d may be configured to provide a magnetic gradient field along the X direction. To this end, the winding patterns of the second gradient coil assemblies 28 c and 28 d may substantially correspond to the winding patterns of the first gradient coil assemblies 28 a and 28 b, but may be rotated by an angle of 90° or 270°.

[0100] The magnetic resonance imaging apparatus 10 of the present invention may further include a third magnet (not shown). The third magnet may include a third gradient coil assembly (not shown) having a winding pattern, the winding pattern being composed of Figure 4 The first magnet 13 is composed of a substantially circular or annular line (e.g., the first gradient coil set 28a). In particular, the third magnet can represent a gradient magnet configured to provide a magnetic gradient field oriented along the Z direction. The magnetic resonance imaging device 10 of the present invention can also include shielding coils 34a and 34b positioned adjacent to the first magnet 13, the second magnet 14, and / or the third magnet. For example, the shielding coils 34a and 34b can be positioned adjacent to the surfaces of the gradient coil sets of the first gradient coil sets 28a and 28b, the second gradient coil sets 28c and 28d, and / or the third magnet that are oriented away from the imaging volume 30. In a preferred embodiment, the shielding coils 34a and 34b can be configured to shield the first magnet 13, the second magnet 14, and / or the third magnet from the main magnet used to generate a static magnetic field within the imaging volume 30.

[0101] It is contemplated that the curvature of the surfaces of the first gradient coil assemblies 28a and 28b of the first magnet 13 that are oriented toward the imaging body 30 may differ from the curvature of the surfaces of the second gradient coil assemblies 28c and 28d of the second magnet 14 that are oriented toward the imaging body. For example, the curvature of the first gradient coil assembly 28a may differ from the curvature of the second gradient coil assembly 28c. However, the curvatures of the surfaces of the first gradient coil assemblies 28a and 28b and the second gradient coil assemblies 28c and 28d that are oriented toward the imaging body 30 may be substantially the same.

[0102] Figure 6 1 shows an embodiment of a magnetic resonance imaging apparatus 10 of the present invention, in which the first magnet 13 and the second magnet 14 are arranged symmetrically with respect to an imaging volume 30. Therefore, the minimum distance between the center 31 of the imaging volume and the surface of the first magnet 13 oriented toward the imaging volume 30 can coincide with the minimum distance between the center 31 of the imaging volume and the surface of the second magnet 14 oriented toward the imaging volume 30. The first magnet 13 and the second magnet 14 can represent the main magnet (or portions of the main magnet) of the field generating unit 12, which is configured to provide a static magnetic field in the imaging volume 30. However, the first magnet 13 and the second magnet 14 can also represent gradient magnets, each of which includes a gradient coil assembly configured to provide a magnetic gradient field within the imaging volume 30.

[0103] Figure 7 An embodiment of a magnetic resonance imaging apparatus 10 of the present invention is depicted in which a first magnet 13 is configured to surround at least a portion of an imaging volume 30 along at least a portion of an approach direction 16 to the imaging volume 30, and wherein the approach direction 16 to the imaging volume 30 is oriented parallel to a main direction of magnetic field lines within the imaging volume 30. The first magnet 13 may be a gradient magnet including a gradient coil set 28a that surrounds an arc of an imaginary cylinder (not shown) whose cylinder axis corresponds to a line oriented along the approach direction 16 to the imaging volume 30. Similarly, the second magnet 14 may be a gradient magnet including a gradient coil set 28b that surrounds an arc of an imaginary cylinder along the approach direction 16 to the imaging volume 30. For example, the angles defining the arc of the imaginary cylinder surrounded by the first magnet 13 and / or the second magnet 14 may include angles such as: Figure 7 180°. However, the angle defining the arc of the imaginary cylinder may also include values ​​below 180° or above 180°. In a preferred embodiment, the first gradient magnet 13 and the second gradient magnet 14 circumferentially surround the imaging volume 30 in such a manner that the angle defining the arc of the imaginary cylinder includes a value of substantially 360°. The gradient coil assembly 28a of the first magnet 13 and the gradient coil assembly 28b of the second magnet 14 may be configured to provide a substantially vertical magnetic gradient field within the imaging volume 30. The first gradient magnet 13 and / or the second gradient magnet 14 may include a fingerprint-like winding pattern oriented in the transverse direction.

[0104] In a preferred embodiment, the first magnet 13 and the second magnet 14 are configured as tubular solenoidal magnets that circumferentially surround the imaging volume 30 along at least a portion of the approach direction 16 to the imaging volume 30. For example, the gradient coil assembly 28a and the gradient coil assembly 28b can circumferentially surround the imaging volume 30 and / or the patient 15 along a line oriented along the approach direction 16 to the imaging volume 30. The diameter 33 of the gradient coil assembly 28a and / or the gradient coil assembly 28b can vary along the approach direction 16 to the imaging volume 30. In particular, the minimum diameter 33 of the gradient coil assembly 28a and / or the gradient coil assembly 28b can be located at the center 31 of the imaging volume.

[0105] In an alternative embodiment, the second magnet 14 can be configured as a conventional solenoid having a cylindrical shape that circumferentially surrounds the first magnet 13 along the approach direction 16 to the imaging volume 30. The magnetic resonance imaging apparatus 10 of the present invention may further include a main magnet (not shown) for generating a static magnetic field within the imaging volume 30. The main magnet may include a conventional cylindrical shape or a tubular shape depending on the first magnet 13. As described above, the magnetic resonance imaging apparatus 10 of the present invention may further include a shielding coil 34 positioned adjacent to the first magnet 13 and / or the second magnet 14.

[0106] In other embodiments, elements 13 and 14 represent segments of a main magnet configured to provide a static magnetic field within imaging volume 30. For example, elements 13 and 14 may represent outer surface 14 and inner surface 13 of the main magnet. It is also contemplated that first magnet 13 includes shield coil 34 positioned adjacent to a surface of first magnet 13 that is oriented away from or toward imaging volume 30.

[0107] Figure 8 The graph in FIG depicts the dependence of the switching rate of a gradient magnet having a curved surface oriented toward the imaging volume 30 on the gap of the patient bore according to an embodiment of the magnetic imaging apparatus 10 of the present invention. Figures 1 to 6 As shown, the clearance of the patient bore can be related to the minimum distance between the surfaces of the first magnet 13 and the second magnet 14 that are oriented toward the imaging volume 30. Figure 8 , when the distance between the first magnet 13 and the second magnet 14 at the imaging volume 30 decreases, the switching rate of the gradient system increases. Therefore, according to the above embodiment, when a curved surface oriented toward the imaging volume 30 is used, the efficiency of the field generating unit 12 (as represented by the switching rate) increases. In one example, the gap of the patient bore of a conventional magnetic resonance imaging device may be approximately 44 cm, while the gap of the patient bore of an embodiment of the magnetic resonance imaging device 10 according to the present invention may be approximately 26 cm, thereby increasing the switching rate from approximately 100 mT / m / ms to over 750 mT / m / ms.

[0108] The above embodiments are to be regarded as examples, and individual embodiments may be expanded by features of other embodiments.

Claims

1. A magnetic resonance imaging apparatus (10), comprising a field generating unit (12), the field generating unit (12) being configured to provide a magnetic field in an imaging volume (30) of the magnetic resonance imaging apparatus (10), wherein: The field generating unit (12) comprises at least one magnet (13) and a second magnet (14), wherein the at least one magnet (13) delimits the imaging volume (30) in at least one spatial direction, wherein the at least one magnet (13) and the second magnet (14) are arranged in such a way that access to the imaging volume (30) is provided in at least two perpendicular spatial directions, and wherein the approach direction (16) to the imaging volume (30) in each of the at least two perpendicular spatial directions is angled relative to a main direction of magnetic field lines within the imaging volume (30), wherein the at least one magnet (13) is bent in such a way that a perpendicular distance between a line oriented along the approach direction (16) to the imaging volume (30) and a surface of the at least one magnet (13) oriented towards the imaging volume (30) varies in the approach direction (16) to the imaging volume (30), wherein The second magnet (14) is curved in such a way that the perpendicular distance between a line oriented in the approach direction (16) to the imaging body (30) and a surface of the second magnet (14) oriented toward the imaging body (30) varies in the approach direction (16) to the imaging body (30), wherein the curvature of the second magnet (14) is different from the curvature of the at least one magnet (13), or The surface of the second magnet (14) oriented toward the imaging body (30) is shaped in such a way that a vertical distance between a line oriented in the approach direction (16) to the imaging body (30) and the surface of the second magnet (14) oriented toward the imaging body (30) is constant in the approach direction (16) to the imaging body (30).

2. The magnetic resonance imaging apparatus (10) according to claim 1, wherein The surface of the at least one magnet (13) oriented toward the imaging volume (30) comprises the shape of a cone or a frustum of a cone.

3. The magnetic resonance imaging apparatus (10) according to claim 1 or 2, wherein: The at least one magnet (13) and / or the second magnet (14) are configured to generate a static magnetic field in the imaging volume (30), wherein the static magnetic field is uniform throughout the imaging volume (30), or wherein the static magnetic field comprises a predefined magnetic field gradient across the imaging volume (30).

4. The magnetic resonance imaging apparatus (10) according to claim 1 or 2, wherein: The at least one magnet (13) includes a gradient coil set (28), and wherein the gradient coil set (28) is configured to generate a magnetic gradient field in the imaging volume (30).

5. The magnetic resonance imaging apparatus (10) according to claim 4, wherein The second magnet (14) includes a second gradient coil set (28), and wherein the second gradient coil set (28) is configured to generate a second magnetic gradient field in the imaging volume (30), wherein the second magnetic gradient field is oriented perpendicular to the magnetic gradient field provided by the at least one magnet (13).

6. The magnetic resonance imaging apparatus (10) according to claim 1 or 2, wherein: The at least one magnet (13) and the second magnet (14) are positioned adjacent to each other.

7. The magnetic resonance imaging apparatus (10) according to claim 1 or 2, wherein: The at least one magnet (13) and / or the second magnet (14) comprises at least one of the following: permanent magnet, electromagnet, High-temperature superconducting magnets, Low-temperature superconducting magnets.

8. The magnetic resonance imaging apparatus (10) according to claim 1 or 5, wherein: The at least one magnet (13) and the second magnet (14) limit the imaging volume (30) in two spatial directions, which are oriented at an angle of 180° to each other, wherein the minimum distance between the at least one magnet (13) and the center (31) of the imaging volume is not equal to the minimum distance between the second magnet (14) and the center (31) of the imaging volume.

9. A magnetic resonance imaging apparatus (10), comprising a field generating unit (12), the field generating unit (12) being configured to provide a magnetic field in an imaging volume (30) of the magnetic resonance imaging apparatus (10), wherein: The field generating unit (12) comprises at least one magnet (13), wherein the at least one magnet (13) limits the imaging volume (30) in at least one spatial direction, wherein the at least one magnet (13) is bent in such a way that a perpendicular distance between a line oriented along an approach direction (16) to the imaging volume (30) and a surface of the at least one magnet (13) oriented toward the imaging volume (30) varies in the approach direction (16) to the imaging volume (30), wherein the at least one magnet is configured as a solenoid circumferentially surrounding the imaging volume, wherein the approach direction (16) to the imaging volume (30) is oriented parallel to a main direction of magnetic field lines within the imaging volume (30), and Therein, the at least one magnet is shaped in such a way that the smallest perpendicular distance between a line oriented in the approach direction to the imaging volume and a surface of the at least one magnet oriented toward the imaging volume is located in the center of the imaging volume.

10. The magnetic resonance imaging apparatus (10) according to claim 9, wherein The field generating unit (12) includes a second magnet (14), wherein the second magnet (14) is configured to surround at least a portion of the imaging body (30) along at least a portion of a line oriented along an approach direction (16) to the imaging body (30), and wherein the second magnet (14) is bent in such a way that a vertical distance between the line oriented along the approach direction (16) to the imaging body (30) and a surface of the second magnet (14) oriented toward the imaging body (30) varies in the approach direction (16) to the imaging body (30).

11. The magnetic resonance imaging apparatus (10) according to claim 9 or 10, wherein: The at least one magnet (13) circumferentially surrounds the imaging volume (30) along a line oriented in an approach direction (16) to the imaging volume (30).

12. The magnetic resonance imaging apparatus (10) according to claim 9 or 10, wherein: The at least one magnet (13) comprises at least one of the following: permanent magnet, electromagnet, High-temperature superconducting magnets, Low-temperature superconducting magnets.

13. The magnetic resonance imaging apparatus (10) according to claim 10, wherein: The second magnet (14) circumferentially surrounds the imaging body (30) along a line oriented in an approach direction (16) to the imaging body (30).

14. The magnetic resonance imaging apparatus (10) according to claim 10, wherein: The second magnet (14) includes at least one of the following: permanent magnet, electromagnet, High-temperature superconducting magnets, Low-temperature superconducting magnets.

Images