Magnetic resonance imaging device with asymmetric field generating unit

Abstract

The present invention relates to a magnetic resonance imaging apparatus with an asymmetric field generation unit, the magnetic resonance imaging apparatus comprising a field generation unit for generating at least one magnetic gradient field, wherein the field generation unit comprises a first magnet and a second magnet, which delimit an imaging volume of the magnetic resonance imaging apparatus in two spatial directions, and wherein the first magnet and the second magnet are arranged asymmetrically with respect to the imaging volume. The present invention also relates to a method for acquiring images of a diagnostically relevant body region of a patient using a magnetic resonance imaging apparatus according to the present invention.

Description

Technical Field

[0001] The present invention relates to a magnetic resonance imaging apparatus comprising a field generation unit for generating at least one magnetic gradient field, wherein the field generation unit comprises a first magnet and a second magnet, which delimit an imaging volume of the magnetic resonance imaging apparatus in two spatial directions, and wherein the first magnet and the second magnet are arranged asymmetrically with respect to the imaging volume. The present invention also relates to a method for acquiring images of a diagnostically relevant body region of a patient using a magnetic resonance imaging apparatus according to the invention. Background Art

[0002] Magnetic resonance tomography represents an important imaging method for acquiring images of the interior of an object under examination. In order to perform magnetic resonance measurements, the object under examination is usually located in a strong and uniform static magnetic field (B0 field) of a magnetic resonance imaging device. The static magnetic field can include a magnetic field strength of 0.2 Tesla to 7 Tesla, so that the nuclear spins inside the object under examination are aligned along the static magnetic field. In order to trigger the 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 in 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 include 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 rotated 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 a basis for magnetic resonance image reconstruction and for determining spectral data. Magnetic resonance images are usually reconstructed using a multidimensional Fourier transform of the k-space matrix.

[0004] During an imaging examination, the patient is typically confined within the bore of an MRI device or between a pair of magnets. Due to spatial limitations within the bore or the space between the magnets, MRI is of limited use for surgical procedures or biopsies. Because the patient needs to be positioned within the MRI device, the size of the bore and other dimensions of the MRI device are 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, patients with claustrophobic conditions or children may not be able to tolerate the extended examination times typically associated with MRI measurements. Summary of the Invention

[0005] It is therefore an object of the present invention to provide a magnetic resonance imaging apparatus for imaging a dedicated body region of a patient with enhanced patency and / or accessibility.

[0006] This object is achieved by the magnetic resonance imaging device according to the invention. Further advantageous embodiments are specified in the dependent claims.

[0007] The magnetic resonance imaging device of the present invention comprises a field generating unit, wherein the field generating unit comprises a first magnet and a second magnet, the first magnet and the second magnet limiting an imaging volume of the magnetic resonance imaging device from two spatial directions, and wherein the field generating unit is configured to provide a static magnetic field within the imaging volume.

[0008] The first magnet may represent a main magnet that provides a magnetic field within the imaging volume. The static magnetic field may be the B0 field of the magnetic resonance imaging device, which B0 field includes a substantially uniform magnetic field or a predetermined magnetic gradient field within the imaging volume. The second magnet may be smaller than the first magnet. It is conceivable that the second magnet is primarily configured to improve the characteristics of the magnetic field provided by the first magnet within the imaging volume, such as magnetic field strength, magnetic field direction and / or magnetic field uniformity. It is also conceivable that the second magnet improves the efficiency of the field generating unit compared to a single-sided magnet design. The first magnet and the second magnet may be supported by a support structure. The support structure may be mechanically connected to the first magnet and the second magnet to maintain a predetermined relative position of the first magnet and the second magnet.

[0009] In a preferred embodiment, the first magnet and the second magnet are positioned along a common axis. The first magnet and / or the second magnet may be rotationally symmetric, and the common axis may be the rotational symmetry axis of the first magnet and the second magnet. The imaging volume of the field generating unit may be positioned along the common axis between the first magnet and the second magnet. However, the first magnet and the second magnet may also be positioned such that the rotational symmetry axis of the first magnet is angled relative to the rotational symmetry axis of the second magnet. It is conceivable that the trajectory defined by the center of mass of the projection of the first magnet in the direction of the imaging volume corresponds to the rotational symmetry axis of the first magnet. Similarly, the trajectory defined by the center of mass of the projection of the second magnet in the direction of the imaging volume may correspond to the rotational symmetry axis of the second magnet. However, the first magnet and / or the second magnet need not include rotational symmetry. It is also conceivable that the magnetic field axis of the first magnet corresponds to the magnetic field axis of the second magnet or is angled relative to the magnetic field axis of the second magnet.

[0010] It is conceivable that the axis passing through the first magnet and / or the second magnet and the center of the imaging volume is characterized by the trajectory of the center of mass of the projection of the first magnet and / or the second magnet in the direction of the center of the imaging volume. The first magnet and the second magnet limit the imaging volume in two spatial directions. In one example, the first magnet can limit the imaging volume in a first spatial direction and the second magnet can limit 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°.

[0011] The imaging volume can be characterized by a predetermined 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 predetermined 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.

[0012] The first magnet and the second magnet are arranged asymmetrically with respect to the imaging volume. For example, the first magnet and the second magnet can be arranged asymmetrically with respect to any plane oriented orthogonally along the trajectory of the projection of the first magnet and / or the second magnet in the direction of the imaging volume. The term "projection" can be interpreted as an imaginary image of the first magnet and / or the second magnet on a two-dimensional plane. The asymmetrical arrangement of the first magnet and the second magnet can also mean that the size, shape, amount of magnetic material, magnetic field strength and / or any other properties of the first magnet are different from those of the second magnet. It is also conceivable that the absolute distance between the first magnet and the imaging volume is different from the absolute distance between the second magnet and the imaging volume. In particular, the first magnet and the second magnet can comprise different shapes and / or geometric structures.

[0013] The first and second magnets are arranged such that access to the imaging volume is provided along at least two perpendicular spatial directions, wherein the directions of the access to the imaging volume are angled relative to a main magnetic field direction of the magnetic field in the imaging volume.

[0014] As described above, the first magnet and the second magnet can be supported by a support structure, and the imaging volume can be positioned in the free volume or gap between the first magnet and the second magnet. It is contemplated that access to the imaging volume can be provided along any unobstructed line connecting any selected location in the examination room with the center of the imaging volume. The examination room can be a room in which a magnetic resonance imaging device is positioned and / or in which magnetic resonance measurements are performed. In one example, a first access direction to the imaging volume can be oriented substantially perpendicular to the rotational symmetry axis of the first magnet and / or the second magnet. A second access direction can be oriented substantially perpendicular to the first access direction and the rotational symmetry axis of the first magnet and / or the second magnet. However, the first access direction and / or the second access direction can also be at any angle relative to the rotational symmetry axis of the first magnet and / or the second magnet. Preferably, the imaging volume can be accessed via multiple access directions. In one embodiment, the imaging volume can be accessed via at least two substantially perpendicular spatial directions. However, the imaging volume can also be accessed 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.

[0015] In one embodiment, a magnetic resonance imaging device includes a radio frequency system comprising at least one radio frequency antenna for transmitting and / or receiving radio frequency radiation. The at least one radio frequency antenna can be carried by the first magnet, the second magnet, and / or the support structure. For example, the radio frequency antenna can be positioned on a pole face of the first magnet and / or the second magnet or recessed into a pole face of the first magnet and / or the second magnet. However, the at least one radio frequency antenna can also be configured as a local coil. Such a local coil can be attached to an examination subject, such as a human or an animal. In particular, the radio frequency antenna can be positioned at different locations relative to the magnetic resonance imaging device.

[0016] Compared to conventional MRI systems, providing an MRI system with an asymmetrical arrangement of the first and second magnets can enhance accessibility and / or openness of the MRI system. For example, the range of motion of a patient's limbs and / or medical devices can be advantageously increased. Consequently, the suitability of the MRI system for surgical and / or therapeutic interventions can be increased.

[0017] As a further advantage, the obstruction of the patient's field of view by the bore or field generating unit of the magnetic resonance imaging apparatus can be significantly reduced compared to conventional magnetic resonance imaging apparatuses. Consequently, interruptions of magnetic resonance measurements in claustrophobic patients can be reduced, and eye contact between parents and children can be maintained during imaging examinations.

[0018] Due to the enhanced accessibility and / or openness, the MRI apparatus of the present invention can be easily integrated with other imaging modalities, such as flatbed or C-arm X-ray scanners, ultrasound scanners, and optical imaging devices. In particular, the other imaging modalities can advantageously provide high-resolution navigation data that can be used to improve the efficiency of MRI examinations and the quality of the acquired MRI images.

[0019] Compared to known C-type magnet arrangements, which can be susceptible to oscillations caused by vibrations in the environment and / or by a cold head, the asymmetric arrangement of the field generating units of the present invention is also less sensitive to dynamic field variations. Consequently, a lighter construction of the support structure can be used, thereby reducing costs and further enhancing the accessibility and / or openness of the magnetic resonance imaging apparatus.

[0020] According to an embodiment of the magnetic resonance imaging apparatus of the present invention, the first magnet comprises a superconducting magnet, and the second magnet comprises a permanent magnet or an electromagnet.

[0021] The permanent magnets can be made of any suitable magnetic material such as Alnico (aluminum-nickel-cobalt), NeFeB (neodymium-iron-boron), or SmCo (samarium-cobalt). In addition, the permanent magnets can include any desired shape. In one embodiment, the permanent magnets include a rod-like shape. The rod-like shape can include a rectangular rod-like shape, a cylindrical rod-like shape, or a rod-like shape with a polygonal cross-section, such as a prism. Rod-like permanent magnets provide a low-cost solution for generating a magnetic field within the imaging volume. In another embodiment, the permanent magnets can be made of smaller stacked permanent magnets. The use of permanent magnets can advantageously avoid the cost and space required for cooling devices typically associated with superconducting magnets and electromagnets.

[0022] The electromagnet can be a non-superconducting magnet. Specifically, the electromagnet can include an electrical conductor 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 equivalent size. This higher magnetic field strength can advantageously enhance the quality and / or signal-to-noise ratio of magnetic resonance images acquired via a magnetic resonance imaging device.

[0023] Superconducting magnets can include coils of superconducting wire and / or tubular magnet sections. The superconducting wire can be connected to a cryostat to maintain the temperature of the superconducting wire below a predetermined value. In one example, liquid helium can be used as a coolant to ensure that the temperature of the superconducting wire is below 4K. The coils of superconducting wire can be arranged in a variety of shapes, such as solenoids, substantially planar annular or tubular magnet sections. The use of superconducting magnets can advantageously increase the magnetic field strength compared to comparably sized permanent magnets or electromagnets.

[0024] In a preferred embodiment, the first magnet is larger than the second magnet, and the first magnet comprises a superconducting magnet.The second magnet may comprise a permanent magnet as a low-cost solution for better controlling the magnetic field characteristics provided by the first magnet.

[0025] According to a further embodiment of the magnetic resonance imaging apparatus, the first magnet comprises a plurality of magnet segments, wherein each magnet segment comprises a magnetic field axis, and wherein the magnetic field axes of the plurality of magnet segments are oriented parallel to the magnetic field axis of the first magnet.

[0026] The magnet segments can be positioned separately from each other or adjacent to each other. The magnetic field axis can correspond to an axis passing through the south pole and the north pole of the first magnet. In particular, the north pole can be associated with a point on the surface of the first magnet where the direction of the magnetic field is oriented away from the first magnet in a substantially linear manner. Similarly, the south pole can be associated with a point on the surface of the first magnet where the direction of the magnetic field is oriented towards the first magnet in a substantially linear manner. It is conceivable that the magnetic field axis of the first magnet corresponds to the rotational symmetry axis of the first magnet. This surface of the first magnet can be a pole face of the first magnet. In a preferred embodiment, the magnetic field axis of the plurality of magnet segments substantially corresponds to the magnetic field axis of the first magnet.

[0027] In one example, the first magnet comprises a superconducting magnet having multiple tubular magnet segments, each comprising a wire coiled to provide a tubular shape. Preferably, the multiple tubular magnet segments comprise a circular axial cross-section. However, the cross-sections of the multiple tubular magnet segments may also be elliptical, oval, or polygonal. In this case, the first magnet may comprise higher-order discrete rotational symmetry, with n > 1. This may mean that rotating the first magnet by an angle of 360° / n about the rotational symmetry axis does not alter the first magnet. The tubular magnet segment may represent a substantially planar or flat loop or coil of superconducting wire. In particular, the tubular magnet segment may comprise one or more windings formed of superconducting wire. The substantially planar or flat loop or coil formed of wire is characterized in that the diameter or circumference of the tubular magnet segment significantly exceeds the width of the tubular magnet segment along the rotational symmetry axis of the first magnet. However, it is also conceivable that the tubular magnet segment comprises multiple windings, thereby comprising a more three-dimensional shape extending along the rotational symmetry axis of the first magnet.

[0028] The rotational symmetry axis of each tubular magnet segment can be positioned along the magnetic field axis and / or the rotational symmetry axis of the first magnet. Multiple tubular magnet segments can be positioned along the rotational symmetry axis of the first magnet at uniform intervals or at arbitrary intervals. It is also conceivable that two or more tubular magnet segments with different diameters are concentrically arranged at substantially the same position on the rotational symmetry axis of the first magnet. Preferably, the multiple tubular magnet segments are electrically connected via a dedicated bridge or wire. Such a bridge or wire can include a highly conductive metal, such as gold, copper or aluminum, and can also include a superconducting material.

[0029] In a further embodiment of the magnetic resonance imaging apparatus, the second magnet comprises a plurality of magnet segments, wherein each magnet segment comprises a magnetic field axis, and wherein the magnetic field axes of the plurality of magnet segments are oriented parallel to the magnetic field axis of the second magnet.

[0030] When multiple magnet segments are provided that are arranged along the magnetic field axis of the first magnet, the characteristics of the magnetic field within the imaging volume can be advantageously tailored to a particular imaging application. For example, the multiple magnet segments can be arranged such that the position, magnetic field strength, and / or magnetic field uniformity of the magnetic field between the first magnet and the second magnet are optimized for imaging an eye region or a dental region of a patient.

[0031] According to one embodiment of the magnetic resonance imaging apparatus of the present invention, each magnet segment comprises a tubular shape, wherein the diameter of at least a first magnet segment among the plurality of magnet segments is different from the diameter of at least a second magnet segment among the plurality of magnet segments. It is also conceivable that the diameter of at least a third magnet segment, at least a fourth magnet segment, or at least a fifth magnet segment is different from the diameter of the first magnet segment, the second magnet segment, and / or the other magnet segments. In one embodiment, each magnet segment among the plurality of magnet segments has a different diameter. However, it is also conceivable that two, three, four, or more magnet segments among the plurality of magnet segments have the same diameter.

[0032] The magnetic field axis of each of the plurality of magnet segments is positioned along the magnetic field axis of the first magnet such that the overall shape of the first magnet corresponds to a cone, a frustum, a disk, a cylinder, or a sequence thereof. The magnetic field axis of each magnet segment can correspond to an axis of rotational symmetry of each magnet segment. However, because the magnet segments comprise coiled wire, the magnet segments, and therefore the first magnet, may not be completely rotationally symmetric. The overall shape of the first magnet can be characterized by the shape of a virtual envelope surface or a virtual envelope curve that circumferentially surrounds the plurality of magnet segments of the first magnet.

[0033] In one example, the first magnet may include a superconducting magnet having a plurality of tubular magnet segments. Each tubular magnet segment may include a wire coiled in a manner to provide a tubular shape. Several of the plurality of tubular magnet segments may be arranged along the rotational symmetry axis of the first magnet such that the diameters of the plurality of tubular magnet segments increase or decrease in one direction, thereby providing an overall shape that is conical or frustoconical. In another example, a plurality of tubular magnet segments arranged in a manner that decreases in diameter in one direction may be followed by a plurality of tubular magnet segments that increase in diameter in the direction, thereby providing an overall shape that is disk-shaped or hourglass-shaped. Of course, any shape of the first magnet can be provided by an appropriate arrangement of tubular magnet segments having different diameters or a uniform diameter.

[0034] By appropriately arranging the plurality of magnet segments along the magnetic field axis of the first magnet, the position and / or shape of the imaging volume can be advantageously tailored to match the target anatomical structure, such as the prostate or heart of a patient. Thus, a dedicated MRI apparatus can be provided that enables customized coverage of the target anatomical structure while simultaneously enhancing accessibility and / or patency, compared to conventional MRI apparatuses. Furthermore, the size and / or system cost of such a dedicated MRI apparatus can be reduced compared to conventional apparatuses.

[0035] According to another embodiment of the magnetic resonance imaging apparatus, the first magnet and / or the second magnet comprises a combination of at least two of the following:

[0036] ·Permanent magnets,

[0037] Electromagnets,

[0038] High-temperature superconducting wires,

[0039] Low-temperature superconducting wire and / or

[0040] Inductive magnets.

[0041] In a preferred embodiment, the first magnet or the second magnet comprises a combination of at least two of the magnets described above. It is also conceivable that the first magnet and the second magnet each comprise a combination of at least two of the magnets described above. Low temperature superconducting wires can have superconducting properties at a temperature of about 4K, whereas high temperature superconducting materials can have superconducting properties in the temperature range of 30K to 90K. Examples of high temperature superconductors or materials having high temperature superconducting properties are barium copper oxides (e.g., YBCO, ReBCO), calcium copper oxides (e.g., BSCCO), and doped fullerene compounds (e.g., Cs2RbC 60), magnesium diboride, etc. In one embodiment, one or more tubular magnet segments of the superconducting magnet can be arranged along the rotational symmetry axis of the second magnet so that the one or more tubular magnet segments at least partially surround the permanent magnet, electromagnet or induction magnet along at least a portion of the rotational symmetry axis. In another example, the first magnet includes a solenoid electromagnet or a superconducting magnet, which circumferentially surrounds the permanent magnet along at least a portion of the rotational symmetry axis of the first magnet. It is conceivable that the permanent magnet, electromagnet, induction magnet or superconducting magnet acts as a stray field accommodation unit, which is configured to align or modify the magnetic stray field of the field generating unit in a predetermined manner. The induction magnet can be a ferromagnetic pole that is magnetized in the presence of another magnet. Of course, other combinations and / or arrangements of the above-mentioned magnet types are also conceivable.

[0042] When using a combination and / or arrangement of different types of magnets, the characteristics of the magnetic field can be advantageously optimized for a specific imaging application. The optimized magnetic field can reduce the cost of magnetic resonance imaging equipment and can also improve image quality, image acquisition duration, and / or patient experience.

[0043] According to another embodiment of the magnetic resonance imaging apparatus, the first magnet comprises a superconducting magnet and the second magnet comprises a superconducting magnet, wherein the magnetic resonance imaging apparatus comprises one of the following:

[0044] a cryostat connected to the combination of the first magnet and the second magnet, or

[0045] • A first cryostat connected to the first magnet and a second cryostat connected to the second magnet.

[0046] The cryostat may include a coolant thermally coupled to the first and / or second magnets. The first and second magnets may include high-temperature superconducting materials and / or low-temperature superconducting materials, which may be cooled to corresponding temperatures via the cryostat. The cryostat may be any type of container configured to store or preserve the coolant at the superconducting temperature of the first and / or second magnets. The cryostat may include thermal insulation configured to reduce the input of thermal energy from components of the magnetic resonance imaging apparatus and / or the environment surrounding the magnetic resonance imaging apparatus. In a preferred embodiment, the cryostat contains a fluid with a low boiling point, such as argon, nitrogen, neon, helium, etc. It is contemplated that the cryostat may also include a pulse tube refrigerator, a Gifford-McMahon refrigerator, a Stirling cryocooler, a Joule-Thomson cooler, etc., configured to maintain a predetermined temperature of the coolant in the cryostat.

[0047] It is contemplated that the first and second magnets are connected to a combined cryostat. To this end, the portion of the combined cryostat may include at least a portion of the first magnet and at least a portion of the second magnet. However, the support structure supporting the first and second magnets may also include fluid channels configured to conduct a coolant and enable heat exchange between the coolant and the superconducting wires of the first and / or second magnets. The coolant may be conveyed through the fluid channels via a compressor or similar device.

[0048] In one embodiment, the first magnet can be connected to a first cryostat, and the second magnet can be connected to a second cryostat. It is conceivable that the first magnet comprises a low-temperature superconducting magnet, while the second magnet comprises a high-temperature superconducting magnet, thereby requiring different temperature levels and corresponding separation of coolants through the first and second cryostat. However, the coolant can also pass through the fluid channels of the first magnet and then through the fluid channels of the second magnet. Thus, the temperature level of the coolant can be increased from the superconducting temperature of the low-temperature superconducting magnet before passing through the high-temperature superconducting magnet, which has a higher superconducting temperature. In this case, the combined cryostat may be sufficient to adequately cool both the first and second magnets.

[0049] When suitable concepts are provided for cooling the first and second magnet using a combined cryostat or a first and second cryostat, the space requirement for the cooling device and / or the energy costs associated with cooling the magnetic resonance imaging device can be advantageously reduced compared to conventional magnetic resonance imaging devices.

[0050] According to another embodiment, the magnetic resonance imaging device of the present invention includes a support structure, which is configured to provide structural support to the field generating unit, wherein the support structure includes a positioning unit, which is configured to adjust the position and / or orientation of the field generating unit in at least one spatial direction.

[0051] The positioning unit can be configured to position the magnetic resonance imaging device along one axis or two perpendicular axes of a Cartesian coordinate system. Preferably, the positioning unit is configured to position the magnetic resonance imaging device along three perpendicular axes of the Cartesian coordinate system. For example, the positioning unit can include a track system and / or a telescopic system configured to transport the magnetic resonance imaging device along a predetermined trajectory. The positioning unit can also include hinges and / or movable joints configured to adjust the orientation of the magnetic resonance imaging device. For example, the magnetic resonance imaging device can be positioned and / or oriented relative to a patient's diagnostically relevant body region via the positioning unit. While the magnetic resonance imaging device is positioned and / or oriented relative to the patient, the patient can rest in a predetermined posture (e.g., lying, sitting, or standing). Adjusting the position and / or orientation of the magnetic resonance imaging device can include adjusting the position of the imaging volume to cover at least a portion of the diagnostically relevant body region. The patient can also be placed on a patient positioning device configured to position the patient in a desired orientation relative to the magnetic resonance imaging device.

[0052] In one embodiment, the magnetic resonance imaging device is configured as a mobile unit, wherein the support structure and / or the positioning unit are configured such that the position and / or orientation of the magnetic resonance imaging device can be adjusted, and wherein the support structure and / or the positioning unit are separate from an examination room in which the magnetic resonance imaging device is positioned. The mobile unit may comprise wheels and / or other means for enabling adjustment of the position and / or orientation of the magnetic resonance imaging device. It is conceivable that the wheels are mechanically connected to the support structure and / or represent at least a part of the positioning unit, which is configured to adjust the position and / or orientation of the field generating unit in at least one spatial direction. The examination room may be a dedicated space in a hospital or any kind of hall or room configured for performing magnetic resonance measurements.

[0053] When a positioning unit is provided, the imaging volume of the magnetic resonance imaging system can advantageously be adapted to the position of a body region of a patient who is immobile or whose mobility is restricted. The asymmetrical arrangement of the field generating units provides more space for maneuvering the patient and / or the magnetic resonance imaging system, thereby advantageously facilitating the adaptation of the imaging volume to the diagnostically relevant body region of the patient.

[0054] In another embodiment of the magnetic resonance imaging apparatus of the invention, the first magnet and / or the second magnet comprises a pole face pointing towards the imaging volume, wherein the pole face of the first magnet and / or the second magnet pointing towards the imaging volume comprises a non-planar surface.

[0055] The pole faces can be characterized by the terminating surfaces of the first and / or second magnets. It is contemplated that the magnetic field strength at the pole faces of the first and / or second magnets is particularly high. The pole faces can also refer to the sides of the first and / or second magnets that point toward or away from the imaging volume. In the case of permanent magnets, the pole faces can be the terminating surfaces of the north and / or south poles. In the case of magnets comprising coiled wire, the pole faces can refer to the surfaces of an imaginary membrane, an imaginary envelope, or an imaginary curved envelope that circumferentially surrounds the magnets. For example, a tubular magnet segment of a superconducting magnet can include planar, circular pole faces at each end of its tubular shape. However, when multiple tubular magnet segments having different diameters are stacked or strung together along a common axis of rotational symmetry, the imaginary curved envelope that circumferentially surrounds the multiple tubular magnet segments can include pole faces with curved surfaces. The curvature or shape of the pole faces can be related to the sequence of the tubular magnet segments and the diameters of the individual tubular magnet segments. The non-planar surface of the polar face may be characterized by a curved, arched, concave, and / or convex surface of the polar face.

[0056] In one embodiment, the polar surface of the first magnet and / or the second magnet pointing towards the imaging volume comprises a cone, a frustoconical shape or a hemispherical shape.

[0057] In another embodiment, the polar face of the first magnet pointing toward the imaging volume and / or the polar face of the second magnet pointing toward the imaging volume include projections and / or depressions having an irregular or complex three-dimensional shape. It is contemplated that the non-planar surface of the polar face is shaped to enhance accessibility to the imaging volume compared to a planar polar face.

[0058] In a preferred embodiment, the non-planar surface of the first magnet and / or the second magnet, which is directed toward the imaging volume, comprises a cutout and / or a recess configured to accommodate a body part of the patient located in the gap between the first magnet and the second magnet.

[0059] When the first magnet and / or the second magnet are provided with non-planar surfaces, accessibility to the imaging volume between the first magnet and the second magnet is advantageously enhanced. This facilitates positioning of a patient's body region within the imaging volume. For example, the magnetic resonance imaging device may be a dedicated dental scanner. Thus, when the patient's head region is positioned between the first magnet and the second magnet, the non-planar surfaces may be shaped into a tapered shape that advantageously accommodates the patient's shoulders. Furthermore, when the pole faces are provided with cutouts and / or recesses configured to accommodate a patient's body portion, the distance between the first magnet and the second magnet may advantageously be reduced, resulting in less damage to the patient. Consequently, the magnetic field strength and / or magnetic field uniformity in the imaging volume may advantageously be increased.

[0060] In a preferred embodiment, the magnetic resonance imaging apparatus of the present invention further comprises a stray field accommodation unit, wherein the stray field accommodation unit is configured to align the magnetic stray field of the field generating unit so that the magnetic field strength and / or magnetic field uniformity in the center of the imaging volume is increased, wherein the stray field accommodation unit comprises at least one of the following:

[0061] a backing plate attached to the first magnet and / or to the second magnet, wherein the backing plate comprises a ferromagnetic material, and wherein the backing plate is attached to a pole face of the first magnet and / or the second magnet facing away from the imaging volume,

[0062] a yoke attached to the first magnet and the second magnet, wherein the yoke comprises a ferromagnetic material,

[0063] a shielding coil attached to the first magnet and / or the second magnet, wherein the shielding coil comprises a circular shape, and wherein a center of the shielding coil is positioned along a locus defined by a center of mass of a projection of the first magnet and / or the second magnet in the direction of the center of the imaging volume.

[0064] Examples of ferromagnetic materials include iron, cobalt, nickel, lanthanides, gadolinium, etc. Ferromagnetic materials can be used as solid materials or fluids. For example, the back plate and / or the yoke can be made of iron or an iron alloy.

[0065] The yoke may represent a support structure or at least a part of a support structure. Thus, the yoke may provide structural support to the field generating unit and maintain a predetermined distance between the first magnet and the second magnet. In particular, the yoke may be configured to counteract the magnetic attraction between the first magnet and the second magnet. It is conceivable that the yoke is attached to the pole faces of the first magnet and the second magnet facing away from the imaging volume. The yoke may comprise an arm or column that is substantially C-shaped or U-shaped to avoid crossing or restricting the free volume near the imaging volume. The arm or column of the yoke may comprise one or more individual elements evenly distributed around the first magnet and the second magnet. However, one or more individual elements of the arm or column may also be distributed on one side of the field generating unit.

[0066] The back plate is attached to the side or pole face of the first magnet and / or the second magnet facing away from the imaging volume. Preferably, the back plate is centered along the rotational symmetry axis of the first magnet and / or the second magnet. The back plate can also be centered along the magnetic field axis of the first magnet and / or the second magnet. It is conceivable that the axial cross-section of the back plate matches the axial cross-section of the first magnet and / or the second magnet. The back plate and / or the yoke can also include a ferromagnetic fluid, such as ferromagnetic nanoparticles in a solution, suspension or emulsion. In this case, the ferromagnetic fluid can be encapsulated in a dedicated container or channel within the back plate and / or the yoke.

[0067] The shielding coil may comprise a resistive wire comprising a highly conductive metal, such as gold, copper or aluminium. However, the shielding coil may also comprise a superconducting material, such as a high temperature superconductor or a low temperature superconductor. The shielding coil may be carried by the first magnet and / or the second magnet. For example, the shielding coil may be mechanically attached to the first magnet and / or the second magnet. Preferably, the centre of the substantially circular shielding coil is positioned along an axis of rotational symmetry of the first magnet and / or the second magnet.

[0068] In one embodiment, the first magnet includes a first shielding coil, and the second magnet includes a second shielding coil. In another example, the first magnet includes an iron backing plate, and the second magnet includes a shielding coil. In yet another example, the first magnet and the second magnet are supported by an iron yoke. However, the first magnet and / or the second magnet may still include a shielding coil for better alignment of magnetic stray fields. Of course, other combinations and / or arrangements of the first magnet, the second magnet, and the stray field containment unit are contemplated.

[0069] When providing a stray field containment unit according to the above-described embodiments, alignment of magnetic stray fields can be advantageously achieved without restricting or compromising accessibility to the imaging volume. As a further advantage, the characteristics of the magnetic field within the imaging volume can be advantageously improved. Furthermore, the yoke connecting the first and second magnets can advantageously be used to optimize magnetic field flux and provide mechanical support, vibration damping, a thermal bridge, and / or connection to the cryostat.

[0070] According to another embodiment of the magnetic resonance imaging apparatus according to the invention, the field generating unit comprises a gradient field system having at least one gradient coil for generating at least one magnetic gradient field, wherein the first magnet and / or the second magnet comprises a pole face pointing towards the imaging volume, and wherein the at least one gradient coil of the gradient system is as follows:

[0071] Positioned near the polar face of the first and / or second magnet pointing towards the imaging volume, and / or

[0072] • At least partially recessed into the pole face of the first magnet and / or the second magnet pointing towards the imaging volume.

[0073] Preferably, the at least one gradient coil is positioned on the pole face of the first magnet pointing toward the imaging volume, thereby covering at least a portion of the pole face. In particular, the surface of the at least one gradient coil can substantially match the non-planar surface of the pole face pointing toward the imaging volume. However, it is also conceivable that the pole face of the first magnet pointing toward the imaging volume includes a recess or cutout, in which the at least one gradient coil is positioned. Thus, the at least one gradient coil can be at least partially recessed into the pole face of the first magnet.

[0074] In one embodiment, the second magnet may include a second gradient coil. Similar to the at least one gradient coil, the second gradient coil may cover a pole face of the second magnet that points toward the imaging volume. It is also contemplated that the second gradient coil may be at least partially recessed into the pole face of the second magnet and / or conform to a non-planar surface of the pole face of the second magnet.

[0075] The magnetic resonance imaging apparatus may further include a third gradient coil. The third gradient coil may be supported by the first magnet and / or the second magnet. However, the third gradient coil may also be supported by the support structure. In one embodiment, the third gradient coil may be a TRASE (Transmit Array Spatial Encoding) coil of the radio frequency system. Such a TRASE coil may provide radio frequency excitation pulsed phase gradients, rather than the static gradient fields provided by the first and second magnets. The TRASE coil may, for example, be supported by the first magnet, the second magnet, and / or the support structure.

[0076] In yet another embodiment of the magnetic resonance imaging apparatus, the third gradient coil is omitted. In this case, spatial encoding in one spatial direction can be provided via predetermined magnetic field gradients generated by the first magnet and the second magnet.

[0077] If the at least one gradient coil is positioned on a pole face of the first magnet and / or the second magnet pointing toward the imaging volume, a space-efficient arrangement of the gradient system can advantageously be provided.

[0078] According to another embodiment of the magnetic resonance imaging apparatus according to the invention, the first magnet and the second magnet are arranged such that an angle defining a path to the imaging volume exceeds 60°, 75°, 90° or 105°, wherein the angle is enclosed by the center of the imaging volume, the first magnet and the second magnet.

[0079] The angle defining the path to the imaging volume can be formed by a first tangent line to the first magnet passing through the center of the imaging volume and a second tangent line to the second magnet passing through the center of the imaging volume, excluding the rotational symmetry axis of the first magnet and the second magnet. The first tangent line and the second tangent line can lie in a common plane oriented parallel to the rotational symmetry axis of the first magnet and / or the second magnet.

[0080] In preferred embodiments, the angle defining the path to the imaging volume exceeds 75°, 90°, or 105°. This angle can be increased by reducing the size of the first magnet and / or the second magnet. It is also contemplated that increasing this angle can be achieved by providing the first magnet and / or the second magnet with non-planar pole faces as described above.

[0081] Due to the asymmetric arrangement of the field generating units, the MRI apparatus of the present invention can include an increased angle enclosed by the center of the imaging volume, the first magnet, and the second magnet, compared to conventional C-type MRI apparatuses, thereby improving accessibility to the imaging volume. For example, an MRI examination of a patient's limbs may require positioning the patient's body outside the imaging volume. Increasing the angle enclosed by the center of the imaging volume, the first magnet, and the second magnet can facilitate comfortable posture during the MRI examination. Furthermore, access to the space between the first magnet and the second magnet can be advantageously facilitated, particularly for patients with motor impairments or pain.

[0082] According to one embodiment of the magnetic resonance imaging apparatus of the present invention, a second distance between the center of the imaging volume and the closest point on the polar surface of the second magnet pointing toward the imaging volume exceeds a first distance between the center of the imaging volume and the closest point on the polar surface of the first magnet pointing toward the imaging volume, and wherein a ratio of the second distance to the first distance ranges between 1.5 and 8.

[0083] The closest point on the polar face of the first magnet that points to the imaging volume can be positioned on the rotational symmetry axis and / or magnetic field axis of the first magnet. Similarly, the closest point on the polar face of the second magnet that points to the imaging volume can be positioned along the rotational symmetry axis and / or magnetic field axis of the second magnet. It is conceivable that the rotational symmetry axis and / or magnetic field axis of the second magnet are oriented parallel to the rotational symmetry axis and / or magnetic field axis of the first magnet. In a preferred embodiment, the rotational symmetry axis of the second magnet is consistent with the rotational symmetry axis of the first magnet. Because the first magnet and the second magnet are arranged asymmetrically with respect to the imaging volume, the second distance exceeds the first distance. Preferably, the second distance exceeds the first distance by at least 1.5 times, at least 2 times, at least 3 times, at least 4 times or more.

[0084] When selecting a level of asymmetry, an appropriate balance between the size of the imaging volume and the position of the first and second magnets can be considered. A larger imaging volume is typically positioned closer to the first magnet, while a smaller volume can typically be positioned at a greater distance from the first magnet. Thus, the size of the imaging volume and / or the distance between the imaging volume and the first magnet can be adjusted via the size of the first magnet and the size of the second magnet.

[0085] The size of the imaging volume and / or the distance between the imaging volume and the first magnet may be limited by the location of the diagnostically relevant body region within the patient. For example, the first distance may need to exceed the depth of the diagnostically relevant body region within the patient's body. Furthermore, the distance between the first and second magnets may need to exceed the size of the body part that needs to be positioned between the first and second magnets.

[0086] When providing an asymmetric arrangement of the first and second magnets, the distance between the imaging volume and the first magnet can be reduced compared to conventional C-type magnetic resonance imaging devices. Consequently, body regions that are eccentrically positioned relative to the principal axis of the patient's body, such as eyes and / or teeth, can be advantageously imaged using a more compact asymmetric field generating unit. This can advantageously reduce system costs compared to conventional magnetic resonance imaging devices by reducing the overall size of the magnetic resonance imaging device.

[0087] According to an embodiment of the magnetic resonance imaging apparatus of the present invention, the imaging volume comprises a shape of an ellipsoid, a disk, a star, a polyhedron, a torus or a combination thereof.

[0088] The shape of the imaging volume can be adjusted by modifying the size and / or shape of the first and / or second magnets, as well as the relative position of the first and second magnets. In one example, the first magnet comprises a superconducting magnet having a conical pole face pointing toward the imaging volume. The length and / or inclination of the conical pole face can be adjusted by adjusting the arrangement and / or diameter of the multiple tubular magnet segments of the superconducting magnet. However, the shape of the imaging volume can also be adjusted by adjusting the shape and / or position of the second magnet and the magnetic field containment unit.

[0089] In one embodiment, the imaging volume comprises a U-shape, a C-shape, or a semi-circular ring shape. An imaging volume having such a shape can advantageously match a patient's dental region, such as the jawbone or dental arch. In another embodiment, the imaging volume comprises an ellipsoidal or oval shape to encompass both eyes of the patient. In a preferred embodiment, the shape of the imaging volume matches the shape of the target anatomical structure of a dedicated magnetic resonance imaging device.

[0090] When providing an imaging volume that matches the shape of a target anatomical structure, the acquisition of magnetic resonance image data can be advantageously limited to the target anatomical structure, thereby improving the efficiency of the imaging examination. In addition, when providing a dedicated magnetic resonance imaging device with a matching imaging volume, the size of the magnetic resonance imaging device can be advantageously reduced compared to a conventional magnetic resonance imaging device.

[0091] According to an embodiment of the magnetic resonance imaging apparatus of the invention, the first magnet comprises a bore which is directed along its axis of rotational symmetry thereby providing an unobstructed view through the first magnet from the free volume between the first and second magnets.

[0092] According to an alternative embodiment of the magnetic resonance imaging apparatus according to the invention, the first magnet comprises an output unit, wherein the output unit is positioned on a pole face of the first magnet pointing towards the imaging volume, and wherein the output unit comprises a display, which is oriented in the direction of the imaging volume such that: when the patient is suitably positioned for an imaging examination within the free volume between the first magnet and the second magnet, at least one eye of the patient is aligned with the display of the output unit.

[0093] Preferably, the display is configured to provide visual content to the patient during the imaging examination. The visual content can include video and / or image materials and associated audio that can be output via a dedicated speaker of an output unit or an examination room. In one example, a free field of view through the first magnet is simulated via an output unit and a camera positioned on the back side of the first magnet away from the imaging volume. For this purpose, the output of the display of the output unit can include a video signal captured by a camera positioned on the back side of the first magnet. Therefore, the patient can be given the impression that they can view through the first magnet. However, other suitable visual content can be provided to entertain the patient, inform the patient and / or relax the patient. The output unit and / or the first magnet can include a mechanical frame that is configured to stop the patient's head in a predetermined position and / or orientation. It is also conceivable that the output unit is at least partially recessed into the polar surface of the first magnet that points to the imaging volume.

[0094] When the first magnet or the output unit is provided with an aperture along an axis of rotational symmetry, a patient positioned between the first and second magnets can advantageously maintain visual contact with family members and / or medical personnel positioned behind the first magnet. Furthermore, particularly in the case of claustrophobic patients and / or children, the risk of interrupting the imaging examination can be reduced by providing entertaining or informative content via the output unit to distract the patient from the imaging examination.

[0095] The method according to the invention for acquiring an image of a diagnostically relevant body region of a patient using a magnetic resonance imaging apparatus according to an embodiment of the magnetic resonance imaging apparatus described above comprises the following steps:

[0096] aligning at least a portion of a diagnostically relevant body region of the patient with the imaging volume,

[0097] performing a first magnetic resonance measurement to acquire first magnetic resonance image data from a diagnostically relevant body region,

[0098] adjusting the relative position and / or orientation of the magnetic resonance imaging device and the patient via rotation of the magnetic resonance imaging device and / or the patient positioning device,

[0099] performing a second magnetic resonance measurement to acquire second magnetic resonance image data from the diagnostically relevant body region,

[0100] reconstructing an image of a diagnostically relevant body region of the patient from the first magnetic resonance image data and the second magnetic resonance image data,

[0101] Outputting images of the patient's diagnostically relevant body area.

[0102] Aligning at least a portion of the patient's diagnosis-related body area with the imaging volume can include adjusting the position and / or orientation of the magnetic resonance imaging device and / or the patient positioning device so that at least a portion of the diagnosis-related body area is positioned within the imaging volume between the first magnet and the second magnet (or covered by the imaging volume). Since the first magnet and the second magnet are arranged asymmetrically, a portion of the diagnosis-related body area can be positioned closer to the first magnet than to the second magnet. The patient's diagnosis-related body area can be a jaw area, an eye area, a prostate, a heart, etc. However, other body areas are also conceivable.

[0103] Performing a first magnetic resonance measurement comprises acquiring first magnetic resonance image data from a portion of the diagnostically relevant body region covered by the imaging volume.

[0104] Adjusting the relative position and / or orientation of the magnetic resonance imaging device and the patient may comprise rotating the magnetic resonance imaging device around the patient via the positioning unit. It is also conceivable that the patient is rotated via the patient positioning unit. In a preferred embodiment, the patient positioning device comprises a chair for the patient to sit on or a standing aid for the patient to lean on in a substantially upright posture. The patient positioning device may comprise an adjustment device for adjusting the orientation and / or spatial position of the patient relative to the magnetic resonance imaging device. Rotating the magnetic resonance imaging device and / or the patient positioning device may cause the imaging volume to move along a substantially circular or curved trajectory relative to the diagnostically relevant body region, thereby covering at least another part of the diagnostically relevant body region. The rotation of the magnetic resonance imaging device and / or the patient may involve discontinuous or quasi-continuous motion.

[0105] Performing the second magnetic resonance measurement includes acquiring second magnetic resonance image data from another portion of the diagnostically relevant body region. When performing the second magnetic resonance measurement, the imaging volume of the magnetic resonance imaging device may have already covered the other portion of the diagnostically relevant body region or moved along a substantially circular or curved trajectory. It is contemplated that at least a third magnetic resonance measurement, at least a fourth magnetic resonance measurement, at least a fifth magnetic resonance measurement, or even more magnetic resonance measurements may be performed in a similar manner to acquire magnetic resonance image data from multiple portions of the diagnostically relevant body region of the patient.

[0106] An image of a diagnosis-related body area is reconstructed based on the first magnetic resonance image data and the second magnetic resonance image data. In a preferred embodiment, the image of the diagnosis-related body area is reconstructed based on the magnetic resonance image data acquired from multiple parts of the diagnosis-related body area of ​​the patient. In one example, reconstructing the image of the diagnosis-related body area may include reconstructing a first image based on the first magnetic resonance image data, and reconstructing a second image based on the second magnetic resonance image data. The image of the diagnosis-related body area can be created by stitching the first image and the second image together. However, it is also conceivable that the first magnetic resonance image data and the second magnetic resonance image data are merged in the image space (k-space) before reconstructing the image of the diagnosis-related body area from the image space. Of course, other methods for reconstructing the image of the diagnosis-related body area based on the first magnetic resonance imaging data and the second magnetic resonance image data can be used.

[0107] Outputting the image of the patient's diagnostically relevant body region may include saving the image of the diagnostically relevant body region to a storage unit of the magnetic resonance imaging device, a medical information system and / or the cloud. However, it is also conceivable that the image of the diagnostically relevant body region is output via an output unit of the magnetic resonance imaging device.

[0108] When using the method according to the invention, magnetic resonance image data can advantageously be acquired from a volume that exceeds the imaging volume of the magnetic resonance imaging apparatus according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] Other advantages and details of the present invention can be understood from the following description of the embodiments and the accompanying drawings. The accompanying drawings show:

[0110] Figure 1 is a schematic illustration of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0111] Figure 2 is a schematic illustration of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0112] Figure 3 is a schematic illustration of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0113] Figure 4 is a diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0114] Figure 5 is a diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0115] Figure 6 is a diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0116] Figure 7 is a schematic illustration of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0117] Figure 8 is a diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention,

[0118] Figure 9 is a flow chart of an embodiment of the method of the present invention. DETAILED DESCRIPTION

[0119] Figure 1 A schematic illustration of a magnetic resonance imaging device 10 according to the present invention is depicted, which is configured to perform a magnetic resonance imaging examination of the jaw region and / or the eye region of a patient 15. The use of the magnetic resonance imaging device 10 for imaging the jaw region and / or the eye region of a patient 15 is to be understood as an example. The magnetic resonance imaging device 10 according to 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. For these imaging applications, the field generation unit 12 of the magnetic resonance imaging device 10 can be positioned and / or oriented relative to the diagnostically relevant body region of the patient 15 via a positioning unit 29.

[0120] The magnetic resonance imaging apparatus 10 includes a field generation unit 12 having a first magnet 13 and a second magnet 14. In this example, 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 also be implemented as an iron yoke 18. The free volume between the first magnet 13 and the second magnet 14 represents an image acquisition region 17, which is configured to accommodate a body region of an examination subject 15, such as a patient 15. The image acquisition region 17 is bounded in two spatial directions by the field generation unit 12. The patient 15 can be positioned within the image acquisition region 17 using a patient positioning device 16. However, the magnetic resonance imaging apparatus 10 may further include a positioning unit 29 for adjusting the position and / or orientation of the field generation unit 12 relative to the patient 15. For example, the positioning unit 29 may include a rotary joint configured to rotate the field generation unit 12 along a rotational direction WX and / or a rotational direction WY. The position of the field generating unit 12 along the Y direction and / or the Z direction can be adjusted via a suitable telescopic system and / or rail system mechanically connected to the support structure 11. Of course, other embodiments of the support structure 11 and the positioning unit 29 are conceivable. In particular, the positioning unit 29 can also be configured to position the field generating unit 12 along the X direction and / or to rotate the field generating unit 12 along the WZ direction (not shown).

[0121] The first magnet 13 is configured to generate a magnetic field in the image acquisition region 17, while the second magnet 14 can be primarily configured to enhance the properties of the magnetic field provided by the first magnet 13. The field generation unit 12 further comprises a gradient field system 27 having at least one gradient coil 28 for generating a magnetic gradient field for spatially encoding magnetic resonance signals acquired during a magnetic resonance imaging examination. Preferably, the field generation unit 12 comprises a radio frequency system having at least one radio frequency antenna (not shown), which is configured to transmit radio frequency excitation pulses in 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. The at least one radio frequency antenna can also be configured as a local coil.

[0122] 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 an imaging examination. 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 contemplated that the processing unit 24 is further configured to evaluate and 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.

[0123] Control information such as 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 via 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.

[0124] The illustrated magnetic resonance imaging apparatus 10 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 the imaging examination is deemed unnecessary.

[0125] Figure 2 A cross-sectional view of an embodiment of a magnetic resonance imaging device 10 of the present invention is shown. In this example, an angle 33 defining the path to the imaging volume 30 is enclosed by the center 31 of the imaging volume, the first magnet 13 and the second magnet 14. The angle 33 is formed by a first tangent 41 of the first magnet 13 passing through the center 31 of the imaging volume and a second tangent 42 of the second magnet 14 passing through the center 31 of the imaging volume. The angle 33 does not include an axis 32 defined by the locus of the center of mass of the projection of the first magnet 13 in the direction of the imaging volume 30. The axis 32 may correspond to an axis of rotational symmetry of the magnetic resonance imaging device 10. In a preferred embodiment, the angle 33 exceeds 60°, 75°, 90° or 105°. The angle 33 may be increased by reducing the size of the first magnet 13 and / or the second magnet 14. However, it is also conceivable that the angle 33 may be increased by providing a device having a configuration such as Figure 7 This is achieved by the first magnet 13 and / or the second magnet 14 having the non-planar pole faces shown in FIG.

[0126] In the depicted embodiment, the gradient coils 28b of the second magnet 14 are positioned on the pole face of the second magnet 14 pointing toward the imaging volume 30 such that the gradient coils 28b protrude from the pole face. Conversely, the gradient coils 28a of the first magnet 13 are recessed into the pole face of the first magnet 13 pointing toward the imaging volume 30. The magnetic resonance imaging apparatus may include a plurality of magnetic resonance imaging devices that are not located in the imaging volume 30. Figure 2 At least a third gradient coil 28 is depicted in FIG.

[0127] exist Figure 3 In the embodiment of the present invention, the magnetic resonance imaging apparatus 10 is configured to perform an imaging examination of the prostate of a patient 15. The patient positioning apparatus 16 may be a patient bed configured to accommodate the patient 15 in a side-lying position. The asymmetric arrangement of the first magnet 13 and the second magnet 14 relative to the imaging volume 30 may facilitate positioning the patient 15 in the image acquisition region 17, particularly for disabled and / or overweight patients 15. Due to the enhanced accessibility to the imaging volume 30 provided by the magnetic resonance imaging apparatus 10, adjustment of the relative position of the imaging volume 30 and the prostate of the patient 15 is facilitated. It is also contemplated that placement of a local coil (such as an endorectal coil or a surface coil) is facilitated compared to conventional magnetic resonance imaging apparatuses or C-type magnetic resonance imaging apparatuses.

[0128] Figure 4Another embodiment of a magnetic resonance imaging apparatus 10 is shown. In this example, the first magnet 13 comprises a superconducting magnet having a plurality of tubular magnet segments 34. In contrast, the second magnet 14 comprises a permanent magnet. The pole face of the second magnet 14 pointing toward the imaging volume 30 is truncated conically in shape. The pole face of the first magnet 13 pointing toward the imaging volume 30 is conical in shape because the diameter of the tubular magnet segments 34 decreases in the direction of the imaging volume 30. The magnetic field axis of the tubular magnet segments 34 is oriented along the magnetic field axis of the first magnet 13. In the example shown, the first magnet 13 includes an axis of rotational symmetry 32. The tubular magnet segments 34 are oriented in parallel, and the rotational symmetry axis of each tubular magnet segment 34 is aligned with the rotational symmetry axis 32 of the first magnet 13.

[0129] In this example, the magnetic resonance imaging apparatus 10 further includes an iron yoke 18. The iron yoke 18 is connected to the pole faces of the first magnet 13 and the second magnet 14 that are oriented away from the imaging volume 30. In order to improve visibility, the iron yoke 18 is connected to the first magnet 13 at Figure 4 Not shown in the figure.

[0130] The magnetic resonance imaging apparatus 10 further includes at least one gradient coil 28 recessed into a pole face of the second magnet 14 that faces the imaging volume 30. The at least one gradient coil 28 is embedded in a frustum-shaped section of the pole face, providing a substantially flat surface. However, the at least one gradient coil may also include a non-planar surface and / or protrude from the pole face of the second magnet 14 that faces the imaging volume 30. The shaped pole faces of the first and second magnets 13, 14 increase accessibility to the imaging volume 30 for the patient 15. For example, the patient 15 can easily enter the imaging volume 30 from two perpendicular spatial directions, such as the X and Y directions. Simultaneously, the imaging volume 30 is confined by the field generating unit 12 in a first direction oriented toward the first magnet 13 along the Z direction and in a second direction oriented toward the second magnet 14 along the Z direction. Furthermore, when the jaw region of the patient 15 is positioned within the imaging volume 30, the shaped pole faces of the first and second magnets 13, 14 prevent collision with the patient's 15 shoulder (not shown).

[0131] The frustoconical section of the second magnet 14 may be a tapered end piece of a permanent magnet constituting the second magnet 14. However, it is also conceivable that the frustoconical section consists of an inductive magnet, preferably iron, connected or mounted to the second magnet 14.

[0132] Figure 5Another embodiment of the magnetic resonance imaging apparatus 10 of the present invention is shown. In this example, the second magnet 14 is a ferromagnetic pole connected to an iron yoke 18. Due to its positioning relative to the magnetic field of the first magnet 13, the ferromagnetic pole acts as an induction magnet. The iron yoke 18 is connected to a back plate 36, which covers the pole face of the first magnet 14 facing away from the imaging volume 30. It is conceivable that the ferromagnetic pole increases the magnetic field strength and / or magnetic field uniformity in the center 31 of the imaging volume compared to a permanent magnet of similar size. Using small ferromagnetic poles can also increase accessibility to the imaging volume 30.

[0133] Figure 6 FIG. 1 shows an embodiment of the magnetic resonance imaging apparatus 10 of the present invention, wherein the second magnet 14 comprises a shielding coil 35. Figure 5 In the embodiment shown in FIG, the first magnet 13 includes a back plate 36 as a magnetic stray field containment unit. However, the second magnet 14, which is also composed of ferromagnetic poles, includes a shielding coil 35 as a stray field containment unit. The shielding coil 35 can be attached to the second magnet 14 (not shown) so that the center of the substantially circular wire of the shielding coil 35 is positioned along the axis of rotational symmetry of the second magnet 14 or the trajectory of the center of mass of the projection of the second magnet 14 in the direction of the imaging volume 30. Figure 6 As depicted in FIG, the use of the shielding coil 35 and the backing plate 36 can improve the characteristics of the magnetic field provided by the first magnet 13, such as the magnetic field uniformity. It is conceivable that Figure 6 The magnetic resonance imaging apparatus 10 shown in FIG. 1 further includes a support structure 11 to provide structural support to the first magnet 13 and the second magnet 14 .

[0134] Figure 7 An embodiment of a magnetic resonance imaging apparatus 10 of the present invention is depicted in which both the first magnet 13 and the second magnet 14 comprise superconducting magnets. The magnetic resonance imaging apparatus 10 further comprises an axis of rotational symmetry 32 which coincides with the locus of the center of mass of the projection of the first magnet 13 in the direction of the imaging volume 30.

[0135] In the depicted example, the imaging volume 30 comprises a substantially spherical shape. However, the imaging volume 30 may also comprise a different shape, such as an oval shape, an ellipsoidal shape, a disk shape, a star shape, or a polyhedron shape.

[0136] The upper body of the patient 15 is positioned between the first magnet 13 and the second magnet 14 so that the position of the jaw region of the patient 15 coincides with the position of the imaging volume 30. The polar surface of the second magnet 14 pointing toward the imaging volume 30 can accommodate the back or shoulders of the patient 15 during the imaging examination, thereby increasing the comfort of the patient and the accessibility of the imaging volume 30. In this embodiment, by tapering the polar surface of the second magnet 14 pointing toward the imaging volume 30, an angle 33 (see FIG. 3 ) of accessibility to the imaging volume 30 is defined. Figure 2 ) increases.

[0137] The superconducting magnets of both the first magnet 13 and the second magnet 14 include a plurality of tubular magnet segments 34a and 34b oriented parallel to each other along an axis of rotational symmetry 32. The diameter of the tubular magnet segments 34b of the second magnet 14 decreases in the direction of the imaging volume 30, thereby providing conical pole faces. The tubular magnet segments 34a of the first magnet 13 are arranged such that the diameter of a first set of tubular magnet segments decreases in a direction away from the imaging volume 30. The first set of tubular magnet segments is followed by a second set of tubular magnet segments with larger diameters at a greater distance from the imaging volume 30. The overall shape of the superconducting magnets can thus correspond to a truncated cone formed by short cylindrical segments. The pole faces of the first magnet 13 pointing toward the imaging volume 30 include planar surfaces. This arrangement of the first and second magnets 13, 14 may be particularly suitable for accommodating patients 15 in a standing or upright position.

[0138] The first magnet 13 may further comprise an aperture 37 along the axis of rotational symmetry 32 to enable the patient 15 to observe the area behind the first magnet 13. However, it is also conceivable that an output unit (not shown) having a display is recessed into the polar face of the first magnet 13 pointing toward the imaging volume 30. The display of the output unit may provide the patient 15 with entertaining or informative visual content and / or a video stream from a camera (not shown) positioned on the back side of the first magnet 13.

[0139] Figure 8 Another embodiment of a magnetic resonance imaging device 10 of the present invention is shown, which comprises a permanent magnet as the second magnet 14 and a superconducting magnet as the first magnet 13. In this example, the first magnet 13 comprises a coil of superconducting wire, wherein the lighter colored sections of the first magnet 13 may correspond to opposite coils compared to the darker colored sections. An imaging volume 30 may be positioned near the first magnet 13. In the case of a dedicated magnetic resonance imaging device 10 for ophthalmic imaging, the distance between the pole face pointing towards the imaging volume 30 and the center 31 of the imaging volume may substantially correspond to the distance between the tip of the nose of the patient 15 and the center of the eye. The imaging volume 30 may be as shown. Figure 8It is also contemplated that the imaging volume 30 comprises the shape of an ellipsoid, a disk, a star, a polyhedron, a torus, or a combination thereof.

[0140] The rotational symmetry axis of the second magnet 14 can coincide with the rotational symmetry axis 32 of the first magnet 13. However, it is also conceivable that the rotational symmetry axis of the second magnet 14 is displaced in a parallel manner relative to the rotational symmetry axis of the first magnet 13. In another embodiment, the rotational symmetry axis of the second magnet 14 is angled relative to the rotational symmetry axis 32 of the first magnet 13.

[0141] Figure 9 A flow chart of the method according to the invention is shown for acquiring images of a diagnostically relevant body region of a patient 15 using the magnetic resonance imaging device 10 according to the above-described embodiment.

[0142] In step S1, at least a portion of a diagnostically relevant body region of the patient 15 is aligned with the imaging volume 30. Aligning the diagnostically relevant body region of the patient 15 with the imaging volume 30 may include aligning the patient 15 with the imaging volume 30 via Figure 1 or Figure 3 The patient positioning device 16 shown in the figure adjusts the position and / or orientation of the patient 15. The positioning and / or orientation of the patient 15 can be performed automatically, semi-automatically or manually. In a preferred embodiment, aligning the diagnosis-related body region of the patient 15 with the imaging volume 30 includes adjusting the position and / or orientation of the magnetic resonance imaging device 10 via the positioning unit 29 and / or the support structure 11. It is also conceivable that a first alignment (e.g., a rough alignment) of the diagnosis-related body region of the patient 15 with the imaging volume 30 is achieved via the patient positioning device 16, and a second alignment (e.g., a fine adjustment) of the diagnosis-related body region of the patient 15 with the imaging volume 30 is achieved via the positioning unit of the magnetic resonance imaging device 10, or vice versa. Aligning the imaging volume 30 with the diagnosis-related body region can include adjusting the position of the imaging volume 30 to match the position of at least a portion of the diagnosis-related body region of the patient 15.

[0143] It is conceivable that the diagnosis-relevant body region of the patient 15 is larger than the imaging volume 30 of the magnetic resonance imaging device 10. Therefore, after aligning the diagnosis-relevant body region of the patient 15 with the imaging volume 30, only a portion of the diagnosis-relevant body region of the patient 15 may be covered by the imaging volume 30.

[0144] Due to the asymmetrical arrangement of the field generating unit 12 , certain diagnostically relevant body regions of the patient 15 can be evaluated by placing the patient in the gap between the first magnet 13 and the second magnet 14 , facing the first magnet 13 or the second magnet 14 .

[0145] In step S2, a first magnetic resonance measurement is performed to acquire first magnetic resonance image data from the diagnostically relevant body region. The magnetic resonance measurement may include any imaging sequence, such as a UTE (ultra-short echo time), a ZTE (zero echo time), a TSE (turbo spin echo), a GRE (gradient echo) sequence, or any other known imaging sequence suitable for performing an imaging examination of the diagnostically relevant body region of the patient 15. The first magnetic resonance image data may be limited to the portion of the diagnostically relevant body region of the patient 15 that is covered by the imaging volume 30 of the magnetic resonance imaging device 10.

[0146] Step S3 includes adjusting the relative position and / or orientation of the magnetic resonance imaging device 10 and the patient 15 via rotation of the magnetic resonance imaging device 10 and / or the patient positioning device 16. As described above, the position and / or orientation of the magnetic resonance imaging device 10 and / or the patient positioning device 16 can be adjusted to align another part of the diagnosis-related body area with the imaging volume 30. In a preferred embodiment, the first magnet 13 and the second magnet 14 rotate around the patient 15 so that the imaging volume 30 covers different parts of the diagnosis-related body area of ​​the patient 15. The another part of the diagnosis-related body area may not include the following part of the diagnosis-related body area: the first magnetic resonance image data has been acquired from this part. However, the another part of the diagnosis-related body area may also include the following at least a part of the diagnosis-related body area: the first magnetic resonance image data has been acquired from said at least a part.

[0147] In step S4, a second magnetic resonance measurement is performed to acquire second magnetic resonance image data from the diagnostically relevant body region. Preferably, the second magnetic resonance measurement includes the same type of imaging sequence as used for the first magnetic resonance measurement. According to step S3, the second magnetic resonance image data can be restricted to a further portion of the diagnostically relevant body region covered by the adjusted imaging volume 30. However, the second magnetic resonance image data can also include portions of the diagnostically relevant body region that are already included in the first magnetic resonance image data.

[0148] In one embodiment, steps S3 and S4 are repeated a plurality of times, each time aligning another portion of the diagnostically relevant body region with the imaging volume 30 by adjusting the position and / or orientation of the magnetic resonance imaging device 10 and / or the patient positioning device 16. Preferably, the magnetic resonance imaging device 10 is rotated relative to the patient 15 such that the center 31 of the imaging volume is positioned along a substantially circular or curved trajectory.

[0149] In step S5, an image of the diagnosis-relevant body region of the patient 15 is reconstructed based on the first magnetic resonance image data and the second magnetic resonance image data. For example, reconstructing the image of the diagnosis-relevant body region may comprise reconstructing a first image from the first magnetic resonance image data and reconstructing a second image from the second magnetic resonance image data by means of the processing unit 24. The image of the diagnosis-relevant body region may then be created by stitching the first image and the second image together. It is also conceivable that the first image and the second image include parts of the same anatomical structure within the diagnosis-relevant body region. Thus, the anatomical structure can be used to align the first image with the second image. However, it is also conceivable that the first magnetic resonance image data and the second magnetic resonance image data are merged in image space (k-space) before reconstructing the image of the diagnosis-relevant body region.

[0150] It is conceivable that the relative positions of the imaging volume 30 and the diagnostically relevant body region are selected so as to obtain a continuous imaging region covering the diagnostically relevant body region. For example, in the case of the jawbone and / or dental arch, the imaging region may follow a U-shaped or C-shaped shape and include multiple imaging volumes positioned along the contours of the U-shaped or C-shaped. By subsequently acquiring magnetic resonance image data of portions of the diagnostically relevant body region at different orientations of the magnetic resonance imaging device 10 relative to the patient 15, a larger volume of the patient 15 can be covered than in a single position or in a symmetrical imaging volume configuration (e.g., the patient 15 faces the first magnet 13 during the first magnetic resonance measurement and faces the second magnet 14 during the second magnetic resonance measurement). A similar effect can be achieved by continuously rotating the magnetic resonance imaging device 10 relative to the patient 15 while acquiring magnetic resonance image data.

[0151] In step S6, the image of the diagnosis-related body region of the patient 15 is output. Outputting may include saving the image of the diagnosis-related body region to a storage unit of the magnetic resonance imaging device 10, a medical information system, and / or a cloud. However, the image of the diagnosis-related body region may also be output to an operator of the magnetic resonance imaging device 10 via the output unit 25 and / or an output unit positioned on the pole surface of the first magnet 13 or the second magnet 14 facing the patient 15.

[0152] The above embodiments are to be considered as examples. Each embodiment may be expanded by features of other embodiments. In particular, the sequence of steps of the method of the present invention should be understood as exemplary. The individual steps may also be performed in a different order or partially or completely overlap in time.

Claims

1. A magnetic resonance imaging apparatus comprising a field generating unit, wherein: The field generating unit comprises a first magnet and a second magnet, the first magnet and the second magnet delimiting an imaging volume of the magnetic resonance imaging device in two spatial directions, and wherein the field generating unit is configured to provide a static magnetic field within the imaging volume, characterised in that the first magnet and the second magnet are arranged asymmetrically with respect to the imaging volume, and wherein the first magnet and the second magnet are arranged such that access to the imaging volume is provided along at least two perpendicular spatial directions, wherein the direction of the access to the imaging volume is angled with respect to a main magnetic field direction of the magnetic field in the imaging volume, wherein the first magnet comprises a superconducting magnet having a plurality of magnet segments, wherein each magnet segment comprises a magnetic field axis, and wherein the magnetic field axes of the plurality of magnet segments are oriented parallel to the magnetic field axis of the first magnet, wherein each magnet segment comprises a tubular shape, and wherein, the diameter of at least a first magnet segment of the plurality of magnet segments is different from the diameter of at least a second magnet segment of the plurality of magnet segments, and the magnetic field axis of each magnet segment of the plurality of magnet segments is positioned along the magnetic field axis of the first magnet, In this way, the overall shape of the first magnet is made to correspond to a cone, a frustoconical shape or a sequence thereof.

2. The magnetic resonance imaging apparatus according to claim 1, wherein The first magnet includes a superconducting magnet, and the second magnet includes a permanent magnet or an electromagnet.

3. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein: The first magnet comprises a superconducting magnet, and the second magnet comprises a superconducting magnet, wherein the magnetic resonance imaging apparatus comprises one of: a cryostat connected to the combination of the first magnet and the second magnet, or • A first cryostat connected to the first magnet and a second cryostat connected to the second magnet.

4. The magnetic resonance imaging apparatus according to claim 1 or 2, further comprising a support structure configured to provide structural support to the field generating unit, wherein The support structure comprises a positioning unit which is configured to adjust the position and / or orientation of the field generating unit in at least one spatial direction.

5. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein: The first magnet and / or the second magnet comprises a pole face pointing towards the imaging volume, wherein the pole face of the first magnet and / or the second magnet pointing towards the imaging volume comprises a non-planar surface.

6. The magnetic resonance imaging apparatus according to claim 5, wherein The polar surface of the first magnet and / or the second magnet pointing toward the imaging volume comprises a conical, frustoconical or hemispherical shape.

7. The magnetic resonance imaging apparatus according to any one of claims 1, 2, and 6, further comprising a stray field accommodation unit configured to align the magnetic stray field of the field generating unit so that the magnetic field strength and / or magnetic field uniformity in the center of the imaging volume is increased, wherein The stray field accommodating unit includes at least one of the following: a backing plate attached to the first magnet and / or to the second magnet, wherein the backing plate comprises a ferromagnetic material, and wherein the backing plate is attached to a pole face of the first magnet and / or the second magnet facing away from the imaging volume, a yoke attached to the first magnet and the second magnet, wherein the yoke comprises a ferromagnetic material, a shielding coil attached to the first magnet and / or the second magnet, wherein the shielding coil comprises a circular shape and wherein a center of the shielding coil is positioned along a trajectory defined by a center of mass of a projection of the first magnet and / or the second magnet in the direction of the center of the imaging volume.

8. The magnetic resonance imaging apparatus according to any one of claims 1, 2, and 6, wherein: The field generating unit comprises a gradient field system having at least one gradient coil for generating at least one magnetic gradient field, wherein the first magnet and / or the second magnet comprises a pole face pointing towards the imaging volume, and wherein the at least one gradient coil of the gradient field system is as follows: adjacent to the polar face of the first magnet and / or the second magnet pointing towards the imaging volume, and / or • at least partially recessed into the pole face of the first magnet and / or the second magnet pointing towards the imaging volume.

9. The magnetic resonance imaging apparatus according to any one of claims 1, 2, and 6, wherein: The first and second magnets are arranged such that an angle defining a path to the imaging volume exceeds 60°, 75°, 90°, or 105°, wherein the angle is enclosed by a center of the imaging volume, the first and second magnets.

10. The magnetic resonance imaging apparatus according to claim 9, wherein A second distance between the center of the imaging volume and a closest point on the polar face of the second magnet pointing toward the imaging volume exceeds a first distance between the center of the imaging volume and a closest point on the polar face of the first magnet pointing toward the imaging volume, and wherein a ratio of the second distance to the first distance ranges between 1.25 and 8.

11. The magnetic resonance imaging apparatus according to any one of claims 1, 2, 6, and 10, wherein: The imaging volume includes a shape of an ellipsoid, a disk, a star, a polyhedron, a torus, or a combination thereof.

12. A method for acquiring an image of a diagnostically relevant body region of a patient using a magnetic resonance imaging apparatus according to any one of claims 1 to 11, the method comprising the steps of: aligning at least a portion of the diagnostically relevant body region of the patient with the imaging volume (S1), performing (S2) a first magnetic resonance measurement to acquire first magnetic resonance image data from the diagnostically relevant body region, adjusting the relative position and / or orientation of the magnetic resonance imaging device and the patient via rotation of the magnetic resonance imaging device and / or a patient positioning device (S3), performing (S4) a second magnetic resonance measurement to acquire second magnetic resonance image data from the diagnostically relevant body region, reconstructing an image of the diagnosis-relevant body region of the patient based on the first magnetic resonance image data and the second magnetic resonance image data (S5), Outputting the image of the diagnosis-related body region of the patient (S6).

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