Mechanical gradient magnetic field generator

Abstract

Disclosed herein are mechanical gradient magnetic field generators 100, 500, 1600, 1700, 2000, 2112 comprising a magnetic field generating element 102 including at least one generator layer 104. Each of the at least one generator layer includes a stationary divider 106, a movable divider 108 configured to move in one (110) or two (1602) displacement directions, a mechanical element 112 configured to mechanically assist the movement of the movable divider in one or two displacement directions towards an initial position 508, and a set of rotating magnets 114 arranged between the movable divider and the stationary divider. The set of rotating magnets is mechanically coupled to the movable divider and the stationary divider. The mechanical coupling of the set of rotating magnets is such that the movement of the movable divider in one or two displacement directions causes an individual rotation of each of the set of rotating magnets.

Description

[Technical field]

[0001] The present invention relates to magnetic resonance imaging, and more particularly to the generation of magnetic field gradients. [Background technology]

[0002] A large static magnetic field is used by magnetic resonance imaging (MRI) scanners to align the nuclear spins of atoms as part of a procedure to produce images inside a patient's body. This large static magnetic field is called B 0 Various quantities or properties of a subject can be measured spatially using MRI. Spatial encoding in magnetic resonance imaging is achieved by using radio frequency (RF) waveforms (or RF pulses) that are used to control the transmit coils of the MRI scanner, and the B 0 This is accomplished using a combination of a number of spatially selective gradient pulse waveforms (gradient pulses) driving corresponding gradient coil configurations to superimpose the desired spatially encoding magnetic field on top of the field.

[0003] US Patent Application Publication No. 2008 / 054902A1 discloses a method for providing a shim sheet for adjusting a magnetic field in a magnetic resonance device by passive shimming, the method including the steps of magnetic field mapping a region of interest in the MR device to obtain a non-corrected magnetic field distribution including magnetic field inhomogeneities, decomposing the magnetic field inhomogeneities into first and second order spherical harmonic functions, determining a main shim term derived from the second order spherical harmonic function, the main shim term resulting in a passive shim magnetic field that is adapted to a targeted shim magnetic field, scaling the optimized shim term to increase the similarity of the passive shim magnetic field with the targeted shim magnetic field, building a modular shim sheet based on the optimized shim term, and mounting the modular shim sheet on a shim sheet carrier of the magnetic resonance device.

[0004] International application WO2020 / 096855 discloses an apparatus for the creation of a magnetic field, for example for propelling a magnetic device (robot) through biological tissue. The known apparatus comprises a Halbach array of multiple bar-shaped magnets arranged as an interleaved array of bar magnets. Summary of the Invention

[0005] The invention provides in the independent claims a mechanical gradient magnetic field generator, a magnetic resonance imaging system and a magnetic resonance imaging coil. Embodiments are given in the dependent claims.

[0006] Typically, the gradient system is the major cost factor in the manufacture of magnetic resonance imaging systems. A power supply capable of supplying large and varying amounts of current for short durations is often required. An alternative example may provide a means to eliminate or reduce the need for gradient coils and associated power supplies by providing a mechanical gradient field generator. A set of individually rotatable rotating magnets is used to generate gradient fields suitable for magnetic resonance imaging.

[0007] Rotation of the set of rotating magnets is used to turn on, off or adjust the gradient magnetic field. Each of the rotating magnets is, for example, rotatable around an axis passing through the body of the rotating magnet, in particular the axis of rotation of each individual rotating magnet passes through its geometric center. The set of rotating magnets is held or constrained by a stationary divider and a movable divider. The set of rotating magnets is mechanically coupled to the stationary divider and the movable divider such that the magnets of the set of rotating magnets are rotated individually when the movable divider is moved along one or two displacement directions. This allows control of the gradient magnetic field generated by the mechanical gradient magnetic field generator by actuation of the movable divider. The amount of mechanical energy required to actuate the movable divider is reduced by using a mechanical element configured to mechanically assist the movable divider in returning to its initial position.

[0008] In one aspect, the present invention provides a mechanical gradient magnetic field generator having a magnetic field generating element including at least one generator layer, each of the at least one generator layer having a stationary divider, each of the at least one generator layer having a movable divider configured to move in one or two displacement directions relative to the stationary divider, the movable divider having an initial position.

[0009] As used herein, the terms stationary and movable dividers also refer to walls or structures. Stationary and movable dividers are also rigid.

[0010] Each of the at least one generator layer further comprises a mechanical element configured to mechanically assist the movement in one or two displacement directions towards the initial position. The mechanical element takes different embodiments in different configurations. For example, a spring or other elastic element is configured such that when the movable divider is moved in one or two displacement directions, a restoring force is present that assists the movable divider to return to the initial position. The restoring force exerted on the movable divider is generated by the elasticity of the mechanical element. The use of a mechanical element is beneficial as it reduces the amount of energy required to operate the mechanical gradient magnetic field generator.

[0011] Each of the at least one generator layers further comprises a set of rotating magnets arranged between a movable divider and a stationary divider, the movable divider and the stationary divider limiting the movement of the set of rotating magnets, for example. The set of rotating magnets is mechanically coupled to the movable divider and the stationary divider. The mechanical coupling of the set of rotating magnets is such that the movement of the movable divider in one or two displacement directions causes an individual rotation of each of the set of rotating magnets. The rotation of the set of rotating magnets allows the generation of gradient magnetic fields that are individually useful for magnetic resonance imaging or other MR applications such as MR spectroscopy or MR diffusion encoding that does not involve spatial resolution.

[0012] The mechanical element can be used to offset the amount of energy required to produce each rotation of a set of rotating magnets. This allows, for example, operation of gradient magnetic field generators in the main magnetic field of a magnetic resonance imaging system with a reduced amount of energy used. This is beneficial, for example, in that less energy is required to generate the gradient magnetic fields for magnetic resonance imaging relative to conventional gradient coils in a magnetic resonance imaging system.

[0013] The underlying physical phenomena for the generation of magnetic gradient fields according to the present invention are explained below.

[0014] The present invention relates to improving the generation of magnetic gradient fields utilized in magnetic resonance imaging for spatial encoding of magnetic resonance signals and for selection of spatial regions (slices or volumes) in which to manipulate (refocus, invert, dephase) spins. Gradient magnetic fields are excited by electric current waveforms.

[0015] The present invention provides a metamaterial of rotating magnetic elements (spheres) with large angular deflection associated with rotation of a short travel path along the surface of the sphere. Thus, only a low amount of kinetic energy is involved in rotation with high angular deflection (e.g., π or π / 2). The rotating elements are driven by a movable divider displaced by an actuator ((electro, thermo)mechanical actuator, piezoelectric element, electromagnetic coil). The rotating magnetic elements are rotated individually about a rotation axis. Rotation about the rotation axis causes a change in the direction of the magnetic field generated by the magnetic elements. The rotating magnetic elements are each rotated about their individual axis of rotation passing through the magnetic elements, or the magnetic elements are rotated about a common external axis of rotation or about individual external axes of rotation.

[0016] Further, to reorient the rotated magnetic sphere in the main magnetic field of the magnetic resonance examination system, a mechanical element (e.g., a spring, or elastic material) is provided to exert a balancing offset force to compensate for the magnetic field force. This results in a low energy difference between the combination of the meta-material (layer of spheres) and the actuator for different rotational states of the spheres. This allows the magnetic sphere to be rotated by the actuator (gradient coil) while still maintaining the meta-material in the proper position in the applied magnetic field. Thus, the spring (mainly) balances the magnetic field (B 0 The springs may be any mechanical springs (not necessarily coils, but some elasticity in the construction), but they may also be any similar meta-material arranged in a way that does not generate a magnetic field in the field of view, but only provides a "counter-elasticity" to the rest of the meta-material.

[0017] The mechanical gradient field generator of the present invention replaces conventional electrically driven gradient coils. A rotating magnetic sphere generates a magnetic gradient field for rotating the magnetic sphere. The rotation is driven based on an electrical gradient waveform. One or several mechanical gradient field generators are placed adjacent to an examination zone of a magnetic resonance examination system.

[0018] An alternative technical effect of the meta-material and the actuator (forming a mechanical magnetic field generator) is to enhance the magnetic gradient field generated by a (conventional) gradient coil, such that a relatively weak current is applied to the gradient coil. Thus, the mechanical magnetic field generator can be placed between the inner and outer coils of a conventional shielded gradient coil, or the mechanical gradient magnetic field generator can be placed radially outside an unshielded gradient coil. Due to the enhanced magnetic flux transmitted by the meta-material formed by the layer of magnetic spheres, the magnetic gradient field strength is enhanced relative to the gradient field generated by the gradient coil itself.

[0019] That is, the meta-material has extremely high magnetic susceptibility while allowing easy actuator operation and rapid reorientation of the magnetic dipoles. This implementation of the mechanical gradient field generator as an insert gradient augmenter allows efficient transmission and variation of magnetic flux, enhancing the gradient field strength given the applied current. In this implementation, the rotation of the magnetic sphere is driven by the gradient field of the gradient coil, i.e., controlled by the actual gradient waveform, and the force on the divider is balanced by the spring motion. Furthermore, the mechanical gradient field generator is relatively easy to manufacture, because the magnetic sphere is easy and cheap to handle, since the size of the sphere is small but clearly visible to the naked eye. Moreover, the components of the spring parts, the divider, and the magnetic sphere are from a simple mechanical configuration.

[0020] In fact, the mechanical gradient field generator is 40mTm -1 From 200mTm -1 with gradient amplitudes in the range of 0.01 to 0.25 μm for gradient switching. -1 s -1 This can result in a typical slew rate of .

[0021] Various types of magnets can be used, for example, neodymium iron boron magnets, samarium cobalt magnets, or iron platinum magnets would all work well.

[0022] The stationary and movable dividers may be rigid to limit the movement of the rotating magnet set. The use of rigid dividers is beneficial as they provide more reproducible gradient fields.

[0023] The generator layer can be constructed in different ways. In some examples, the generator layer has only a single set of rotating magnets. In this case, the gradient magnetic fields can be controlled by rotating the set of rotating magnets so that the gradient magnetic fields in the field of view are aligned with (or perpendicular to) the main magnetic field. For example, when the gradient magnetic fields are perpendicular to the main magnetic field, they have a negligible effect on the overall magnetic field magnitude. When the gradient magnetic fields are aligned with the main magnetic field, the gradient of the magnetic field magnitude is large enough to perform spatially resolved magnetic resonance imaging.

[0024] In another embodiment, the sets of rotating magnets may each have magnetic poles that are preferably perpendicular to the rotation of the set of rotating magnets about one of one or two displacement directions, which is beneficial as it maximizes the size of the gradient fields that the mechanical gradient field generator can generate.

[0025] In another embodiment, the mechanical element can be an elastic element or spring, which is used, for example, to counter the force of the main magnetic field on the set of rotating magnets. In another embodiment, the mechanical element is an additional magnet whose poles are aligned with the magnetic field lines in the initial position, and which is located away from the set of rotating magnets, for example in a position that does not significantly affect the gradient magnetic fields. This embodiment is beneficial as it obviates the need for additional mechanical components such as springs.

[0026] In another embodiment, the magnetic field generating element may further include an elastic layer attached to the stationary divider and the movable divider. The set of rotating magnets is embedded in the elastic layer. The elastic layer provides the mechanical coupling of the set of rotating magnets. The deformation of the elastic material by the movement of the movable divider causes an individual rotation of each of the set of rotating magnets. This embodiment is beneficial because it provides an effective means to control the initial orientation of the set of rotating magnets, as well as to allow them to rotate in one or two displacement directions. For example, a movable divider and a stationary divider may be provided, so that the elastomer may then be installed while the set of rotating magnets is in the desired orientation. Once the curing process is completed, the movable divider may be moved in a variety of different directions that will individually cause the set of rotating magnets to rotate.

[0027] An additional benefit of this embodiment is that the resilient layer acts as a mechanical element to assist in returning the movable divider to its initial position.

[0028] In another embodiment, the mechanical coupling can be achieved by gear teeth on the rotating magnet set, for example matching gear teeth on the surface of the stationary divider and / or the movable divider. The gear teeth provide a very effective means of controlling the orientation and rotation of the rotating magnet set.

[0029] In another embodiment, the mechanical coupling can be achieved by a high friction layer on the movable divider and / or on the set of rotating magnets. For example, a high friction elastomeric layer such as rubber or otherwise, an additional sticky contact adhesive, etc., are also useful.

[0030] In another embodiment, the mechanical coupling can be achieved by an adhesive layer on the movable divider and / or the set of rotating magnets, which is beneficial as it prevents undesired rotation of the set of rotating magnets.

[0031] In another embodiment, the mechanical coupling may be achieved via a resilient or friction enhancing layer on the movable divider and / or on the set of rotating magnets, for example a rubber layer may be used to provide sufficient friction to effectively control the rotation of the set of rotating magnets.

[0032] In another embodiment, the mechanical coupling may be achieved by contact between the set of rotating magnets and the movable divider, with additional structures, such as cups or fixtures, used to fix the position between the set of rotating magnets and the stationary and / or movable divider.

[0033] In another embodiment, each of the set of rotating magnets can be spherical. Having a spherical magnet allows, for example, movement in two different directions. In some examples, the rotating magnet is spherical, but placed in an additional holder. For example, the spherical magnet is placed in a cylindrical holder with a gear on it. The technical benefit of having a spherical magnet is that it allows a maximum magnet volume below a certain size. For example, when a magnetic field generator is populated from the outside to the inside of a magnetic resonance imaging magnet, there is a very high gradient magnetic field at the entrance, for example at the entrance to the bore of a cylindrical magnet. Limiting the overall size of the magnet, for example by having a diameter force sphere, allows the selection of a magnet that will limit the force of these magnetic field gradients on the magnet.

[0034] In another embodiment, each of the sets of rotary magnets may be cylindrical in shape. This embodiment is beneficial as it provides a high degree of mechanical stability, especially when the direction of motion is a single direction of motion.

[0035] In another embodiment, each of the sets of rotating magnets can be rotationally symmetric about the axis of rotation, for example there are gears or spokes located or formed into the magnets themselves, which provides the magnets with a high degree of rotational stability relative to the stationary and movable dividers.

[0036] In another embodiment, the mechanical gradient field generator may have a flat shape, in this example the stationary and movable dividers may be formed for example from plates, which is a very stable mechanical and easy to mount form for the mechanical gradient field generator.

[0037] In another embodiment, the mechanical gradient magnetic field generator may have a cylindrical shape. This is formed, for example, by making the movable and stationary dividers from concentric tubes. This provides, for example, a very efficient means of creating a gradient magnetic field in a volume. Another advantage is that the movable divider with a cylindrical shape can be moved, for example, along the direction of the rotation axis, as well as rotated around the rotation axis. This provides one or two displacement directions.

[0038] In another embodiment, the mechanical gradient magnetic field generator can be a polygonal tube. The mechanical gradient magnetic field generator includes a plurality of magnetic field generating elements. The polygonal tube is formed from a plurality of magnetic field generating elements. In this embodiment, for example, the magnetic field generating elements can be formed in a flat shape or a rectangular shape. These can then be combined using multiple units to create a polygonal tube. This is particularly efficient in controlling the gradient magnetic field. For example, each of the multiple magnetic field generating elements can be controlled separately. This provides a very high degree of control of the magnetic gradient field generated by the mechanical gradient magnetic field generator.

[0039] In another embodiment, the one or two displacement directions can be a single displacement direction, which is advantageous since it provides not only a simpler mechanical gradient field generator but also a very mechanically stable mechanical gradient field generator.

[0040] In another embodiment, the one or two displacement directions can be two displacement directions. At least one generator has one of the following shapes: flat, spherical section, and cylindrical section. Both the flat, spherical section, and cylindrical section have two degrees of freedom for the dividers to move relative to each other.

[0041] In another embodiment, at least a portion of the set of rotating magnets and the additional set of magnets (if any) may have a maximum dimension between 0.1 mm and 1.2 mm. This embodiment is advantageous because the magnets are large enough to generate an effective gradient field, but are also small enough that the forces on the magnets are limited, especially when the magnets are moved from one position to another during operation. This means that the potential energy stored when the movable divider is moved from one position to another is limited.

[0042] In another embodiment, at least a portion of the rotary magnet set and additional sets of magnets (if any) may preferably have a maximum dimension between 0.2 mm and 1.0 mm. In this embodiment, the forces on the rotary magnet set and additional sets of magnets are even more limited.

[0043] In another embodiment, each of the at least one generator layers may further include an additional divider. The additional divider is stationary relative to the stationary divider. The movable divider is between the additional divider and the stationary divider. Each of the at least one generator layers may further include an additional set of magnets disposed between the movable divider and the additional divider. The additional set of magnets is mechanically coupled to the movable divider and the additional divider.

[0044] The mechanical coupling of the additional set of magnets is such that the movement of the movable divider in one or two displacement directions results in an individual rotation of each of the additional set of magnets. This embodiment is beneficial because a single movement of the movable divider results in a rotation of both the rotating set of magnets as well as the additional set of magnets. This allows the additional set of magnets and the rotating set of magnets to work in concert. For example, they can be arranged such that in certain positions the magnetic fields from the magnets are almost cancelled out. This helps to mount the mechanical gradient field generator to the magnet that is now generating the magnetic field but also has a greater degree of control over the magnetic gradient field that the mechanical gradient field generator produces.

[0045] In another embodiment, the additional set of magnets and the set of rotary magnets may rotate in opposite directions, for example, the two sets of magnets have axes of rotation that are parallel to each other.

[0046] In another embodiment, the at least one generator layer is a plurality of generator layers, and some of the stationary dividers in one layer may be additional dividers in another layer, and similarly, additional dividers in one layer are stationary dividers in another layer of the generator layers.

[0047] In another embodiment, each of the set of rotating magnets and the additional set of magnets may have a dipole moment. In the initial position, the vector sum of the dipole moments of the set of rotating magnets and the additional set of magnets is less than 10% of the sum of the magnitudes of the dipole moments of the set of rotating magnets and the additional set of magnets. In the initial position, the vector sum is preferably less than 1% of the sum of the magnitudes. In other words, the sum of the magnitudes is simply the addition of the respective dipole moments of the set of rotating magnets and the additional set of magnets, ignoring their vector nature. In the initial position, the various magnets as well as the set of rotating magnets and the additional set of magnets are aligned such that the vector sum of all the dipole moments is less than 10% or less than 1% of this sum of the magnitudes.

[0048] This means that in the initial position, the magnets cancel each other's magnetic fields to a very large extent, which essentially blocks or almost eliminates the magnetic gradient fields generated by the mechanical gradient field generators, which has the benefit of not only reducing the gradient fields when not in use, but also making it easier to pull in and out the magnets or main magnet during operation of the magnetic resonance imaging system.

[0049] In another embodiment, the movable divider may have an initial position, and the set of rotatable magnets as well as the set of additional magnets (if any) are configured to generate gradient magnetic fields adjacent the magnetic field generating element when rotated by movement of the movable divider away from the initial position.

[0050] In another embodiment, the mechanical gradient magnetic field generator may further include a locking mechanism for holding the magnetic field generating element in an initial position. This is particularly useful, for example, when placing the magnetic gradient field generator in an operational main magnet of a magnetic resonance imaging system. For example, the mechanical gradient magnetic field generator may be a separate component placed in the main magnet or may further be integrated into a magnetic resonance imaging coil or antenna. The use of the locking mechanism facilitates the movement of the mechanical gradient magnetic field generator into the main magnet.

[0051] In another embodiment, the at least one generator layer can be at least eight generator layers. Using a greater number of generator layers allows for the use of smaller magnets, for example. As previously mentioned, using smaller magnets reduces the forces on the individual magnets, especially when going through regions of very large magnetic field gradients.

[0052] In another embodiment, the at least one generator layer can be at least 15 generator layers. Using 15 generator layers allows for larger magnetic gradient fields to be generated.

[0053] In another embodiment, the at least one generator layer may preferably be more than 20 generator layers, which allows, for example, the use of smaller magnets to generate the same size gradient fields.

[0054] In another embodiment, the mechanical gradient magnetic field generator may further comprise an actuator configured to move each movable divider of at least one generator layer in one or two displacement directions simultaneously, which is advantageous, for example, because it allows automated control of the mechanical gradient magnetic field generator.

[0055] The actuator may in fact be more than one actuator, e.g. one for each displacement direction.

[0056] In another embodiment, the actuator may be a mechanical actuator.

[0057] In another embodiment, the actuator may be a piezoelectric actuator.

[0058] In another embodiment, the actuator can be an electromagnetic actuator. For example, a coil can be wrapped around a mechanical gradient magnetic field generator, and this magnetic field can cause the rotation and movement of a set of rotating magnets. One thing that makes this possible is the use of a mechanical element that mechanically assists the movement in one or two displacement directions toward the initial position. The mechanical element can be selected so that the forces are approximately balanced and only small forces are required. Similarly, the actuator can also be a magnetic field coil system. For example, the actuator is a coil-based magnetic gradient coil system in a standard magnetic resonance imaging system. Instead of actually generating a gradient magnetic field, the gradient coil can be used instead to actuate the mechanical gradient magnetic field generator. This of course has the advantage that no modifications to the magnetic resonance imaging system need to be made and no additional wires or mechanical actuators are required.

[0059] In another aspect, the invention may provide a magnetic resonance imaging system configured to acquire k-space data from a subject at least partially within an imaging zone. The magnetic resonance imaging system includes a mechanical gradient magnetic field generator including an actuator. The mechanical gradient magnetic field generator is configured to generate a gradient magnetic field at least partially within the imaging zone. The magnetic resonance imaging system further includes a memory that stores machine executable instructions and pulse sequence commands. The pulse sequence commands are commands or data that are converted into commands that include individual instructions, and the individual instructions are used to control the magnetic resonance imaging system to acquire the k-space data. For example, the pulse sequence commands are typically displayed as timing diagrams illustrating the control sequences of various components of the magnetic resonance imaging system.

[0060] The magnetic resonance imaging system may further include a computing system configured to control the magnetic resonance imaging system. Execution of the machine executable instructions further causes the computing system to acquire k-space data by controlling the magnetic resonance imaging system with pulse sequence commands. The pulse sequence commands are configured to generate magnetic field gradients by controlling actuators, for example, actual actuators, or possibly a set of existing coils to generate magnetic field gradients, as described above for how this can be used to operate a mechanical magnetic field gradient generator.

[0061] In another embodiment, execution of the machine-executable instructions may further cause the computing system to reconstruct an image or a magnetic resonance image from the k-space data.

[0062] In another embodiment, the magnetic resonance imaging system may further comprise a magnet for generating the main magnetic field. The mechanical gradient field generator is configured to require less energy to generate the gradient fields than a gradient coil system. This is achieved, for example, by having a mechanical element that partially balances the magnetic field force of the main magnet against a set of rotating magnets.

[0063] In another embodiment, the mechanical element may be configured to balance the force on the movable divider by the set of rotating magnets within a predetermined force threshold when the mechanical gradient field generator is in the main magnetic field. This is also true when the mechanical gradient field generator has an additional divider and an additional set of magnets. The mechanical element can be selected such that the force required to move the movable divider is below the predetermined force threshold. This is beneficial since the generation of the gradient field with a minimum amount of force thus allows for large savings in terms of energy.

[0064] In another embodiment, the magnetic resonance imaging system may further include a main magnet, the magnetic resonance imaging system further including a magnetic shield configured to shield the main magnet from the mechanical gradient magnetic field generators, which is beneficial as it reduces the effect of the mechanical gradient magnetic field generators on the main magnet.

[0065] In another embodiment, the magnetic shield may be an active magnetic shield.

[0066] In another embodiment, the magnetic shield can be a mechanical magnetic shield formed from one or more of the magnetic field generating elements, for example, if there are multiple layers, some of the layers facing the main magnet are designed to function as a magnetic shield.

[0067] In another embodiment, the magnetic resonance imaging system may have a subject support configured to support at least a portion of the subject within the imaging zone. The mechanical gradient field generator is at least partially integrated into the subject support. This is particularly beneficial, for example, when the mechanical gradient field generator is flat. By integrating it into the subject support, it provides a means of providing additional space in the bore of the magnet when coils can be eliminated.

[0068] In another embodiment, the movable divider may include an array of temperature sensors and an array of heating elements. The machine executable instructions are configured to control a computing system to regulate the temperature of multiple pairs of adjacent magnets using the array of temperature sensors and the array of heating elements. This is beneficial as it provides a means of greater control of the generated gradient magnetic fields.

[0069] In another embodiment, the computing system may be further configured to magnetically shim the imaging zone by modifying the temperature of multiple pairs of adjacent magnets using the array of temperature sensors and the array of heating elements, thereby providing a means of fine tuning of the main magnetic field and improved image quality when performing magnetic resonance imaging.

[0070] In another embodiment, the movable dividers may include an array of temperature sensors that sense the temperature of the corresponding magnets during system operation. Additionally or alternatively, the movable dividers may include at least one position sensor configured to monitor the current position of the individual magnets or the movable dividers in real time during the acquisition of k-space data. In some examples, data from the array of temperature sensors and / or the one or more position sensors are stored together with the k-space data for use in appropriate model-based MR reconstruction to correct for corresponding runtime effects. This has the benefit of resulting in a more accurate reconstruction of magnetic resonance images from the k-space data.

[0071] In another embodiment, the machine executable instructions may be configured to control a computing system to determine the calibration of a mechanical actuator from one or more test magnetic resonance images, for example, which provides a means of more precise control of a mechanical gradient field generator.

[0072] In another embodiment, determining the calibration of the mechanical actuator may include operating the actuator to determine a desired gradient field for acquiring test k-space data of a predefined object such as a phantom. Determining the calibration of the magnetic actuator further includes checking the deviation of the image from an ideal image that would then be expected to have the desired gradient field. Thus, the step uses this deviation of the image to calculate the actuator to correct the deviation, thereby providing a calibration.

[0073] In another embodiment, the one or more test magnetic resonance images may be phantom magnetic resonance images. Determining the calibration of the magnetic actuator includes receiving a calibration response to input of the one or more test magnetic resonance images to a trained neural network. For example, the neural network may be trained to utilize a desired magnetic field, then input the test image, then output the calibration. The trained neural network may be trained, for example, by utilizing known gradient magnetic fields and generating training data.

[0074] In another aspect, the present invention may provide a magnetic resonance imaging coil including a magnetic gradient field generator according to an embodiment. This embodiment is beneficial because the mechanical gradient field generator is very compact and easily integrated into the magnetic resonance imaging coil, which provides additional flexibility to the magnetic resonance imaging system.

[0075] In another embodiment, the magnetic resonance imaging coil may be a head coil.

[0076] In another embodiment, the magnetic resonance imaging coil may be a body coil.

[0077] It is understood that one or more of the above-mentioned embodiments of the present invention may be combined with each other, unless the combined embodiments are mutually exclusive.

[0078] As will be appreciated by those skilled in the art, aspects of the invention may be embodied as an apparatus, method, or computer program product. Accordingly, aspects of the invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software aspects with hardware aspects, all generally referred to herein as "circuits," "modules," or "systems." Additionally, aspects of the invention may take the form of a computer program product embodied in one or more computer-readable medium(s) having computer-executable code embodied thereon.

[0079] Any combination of one or more computer readable media may be utilized. A computer readable medium may be a computer readable signal medium or a computer readable storage medium. As used herein, a "computer readable storage medium" encompasses any tangible storage medium that stores instructions that are executable by a processor or computer computing system of a computing device. A computer readable storage medium may be referred to as a computer readable non-transitory storage medium. A computer readable storage medium may further be referred to as a tangible computer readable medium. In some embodiments, a computer readable storage medium may also store data that can be accessed by a computer computing system of a computing device. Examples of computer readable storage media include, but are not limited to, floppy disks, magnetic hard disk drives, solid state hard disks, flash memory, USB thumb drives, random access memory (RAM), read only memory (ROM), optical disks, magneto-optical disks, and register files of a computer computing system. Examples of optical disks include compact disks (CDs) and digital versatile disks (DVDs), such as CD-ROM, CD-RW, CD-R, DVD-ROM, DVD-RW, or DVR-R disks. The term computer-readable storage medium also refers to various types of recording media that can be accessed by a computer device over a network or communication link. For example, data may be retrieved over a modem, over the Internet, or over a local area network. The computer executable code embodied on the computer-readable medium may be transmitted using any suitable medium, including but not limited to wireless, wired, fiber optic cable, RF, etc., or any suitable combination of the foregoing.

[0080] A computer-readable signal medium includes a propagated data signal having computer-executable code embodied therein, for example in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including but not limited to electromagnetic, optical, or any suitable combination thereof. A computer-readable signal medium is any computer-readable medium that is not a computer-readable storage medium, which can convey, propagate, or carry a program by or for use in connection with an instruction execution system, apparatus, or device.

[0081] "Computer memory" or "memory" is an example of a computer-readable storage medium. Computer memory is any memory that can be directly accessed by a computer computing system. "Computer storage" or "storage" is a further example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. In some embodiments, computer storage is also computer memory, or vice versa.

[0082] As used herein, a "computing system" encompasses an electronic component capable of executing a program or machine-executable instructions or computer-executable code. References to a computing system, including examples of a "computing system," should be interpreted as including more than one computing system or processing core, as the case may be. A computing system is, for example, a multi-core processor. A computing system also refers to a collection of computing systems, either within a single computing system or distributed among multiple computing systems. The term computing system should also be interpreted as referring to a collection or network of computing devices, each of which includes a processor or computing system, as the case may be. Machine-executable code or instructions are executed by multiple computing systems or processors, either within the same computing device or even distributed across multiple computing devices.

[0083] Machine-executable instructions or computer-executable code include instructions or programs that cause a processor or other computing system to perform aspects of the present invention. Computer-executable code for performing operations related to aspects of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and traditional procedural programming languages ​​such as the "C" programming language or similar programming languages, and compiled into machine-executable instructions. In some cases, the computer-executable code is in the form of a high-level language or in a pre-compiled form used in conjunction with an interpreter that generates the machine-executable instructions on the fly. In other cases, the machine-executable instructions or computer-executable code is in the form of programming for a programmable logic gate array.

[0084] The computer executable code may run entirely on the user's computer as a stand-alone software package, partially on the user's computer, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer via any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or a connection may be made to an external computer (e.g., over the Internet using an Internet Service Provider).

[0085] Aspects of the present invention are described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present invention. It is understood that each block or a portion of a block of the flowchart, illustrations, and / or block diagrams may be implemented by computer program instructions in the form of computer executable code, when applicable. It is further understood that combinations of blocks in different flowchart, illustrations, and / or block diagrams may be combined, when not mutually exclusive. These computer program instructions are provided to a computing system of a general purpose computer, special purpose computer, or other programmable data processing device to generate a machine such that the instructions, executed via the computer or other programmable data processing device computing system, create means for performing the function / acts specified in one or more blocks of the flowchart and / or block diagram.

[0086] These machine-executable instructions or computer program instructions may also be stored in a computer-readable medium that can direct a computer, other programmable data processing apparatus, or other device to function in a particular manner, such that the instructions stored in the computer-readable medium generate an article of manufacture including instructions that perform a function / act specified in one or more blocks of the flowcharts and / or block diagrams.

[0087] Machine-executable instructions or computer program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be executed on the computer, other programmable apparatus, or other device, generating a computer-implemented process, such that the instructions executing on the computer or other programmable apparatus result in a process for performing a function / act specified in one or more blocks of the flowcharts and / or block diagrams.

[0088] A "user interface" as used herein is an interface that allows a user or operator to interact with a computer or computer system. A "user interface" is also referred to as a "human interface device." A user interface provides information or data to an operator and / or receives information or data from an operator. A user interface allows a computer to receive input from an operator and provides output from the computer to a user. In other words, a user interface allows an operator to control or operate a computer, and an interface allows a computer to show the effects of the operator's control or operation. Displaying data or information on a display or on a graphical user interface is an example of providing information to an operator. Receiving data via a keyboard, mouse, trackball, touchpad, pointing stick, graphics tablet, joystick, gamepad, webcam, headset, pedals, wired gloves, remote control, and accelerometer are all examples of user interface components that allow information or data to be received from an operator.

[0089] As used herein, a "hardware interface" encompasses an interface that allows a computing system of a computer system to interact with and / or control external computing devices and / or devices. A hardware interface allows a computing system to send control signals or instructions to external computing devices and / or devices. A hardware interface also allows a computing system to exchange data with external computing devices and / or devices. Examples of hardware interfaces include, but are not limited to, Universal Serial Bus IEEE 1394 ports, parallel ports IEEE 1284 ports, serial ports RS-232 ports, IEEE-488 ports, Bluetooth connections, wireless local area network connections, TCP / IP connections, Ethernet connections, control voltage interfaces, MIDI interfaces, analog input interfaces, and digital input interfaces.

[0090] As used herein, a "display" or "display device" encompasses an output device or user interface adapted to display images or data. A display outputs visual, audio frequency, and / or tactile data. Examples of displays include, but are not limited to, computer monitors, television screens, touch screens, tactile electronic displays, Braille screens, cathode ray tubes (CRTs), storage tubes, bi-stable displays, ePaper, vector displays, flat panel displays, vacuum fluorescent displays (VFs), light emitting diode (LED) displays, electroluminescent displays (ELDs), plasma display panels (PDPs), liquid crystal displays (LCDs), organic light emitting diode displays (OLEDs), projectors, and head mounted displays.

[0091] K-space data is defined herein as the recorded measurements of radio frequency signals emitted by atomic spins using the antenna of a magnetic resonance machine during a magnetic resonance imaging scan.

[0092] A Magnetic Resonance Imaging (MRI) image or MR image is defined herein as a reconstructed two- or three-dimensional visualization of the anatomical data contained within the k-space data, which visualization can be performed using a computer.

[0093] Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings in which: [Brief description of the drawings]

[0094] [Figure 1] FIG. 1 illustrates an example of a mechanical gradient magnetic field generator. [Diagram 2] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Diagram 3] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 4] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Diagram 5] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 6] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 7] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 8] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 9] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 10] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 11] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 12] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 13]FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 14] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 15] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 16] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 17] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 18] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 19] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 20] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Figure 21] FIG. 1 illustrates an example of a magnetic resonance imaging system. [Figure 22] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. [Diagram 23] FIG. 2 illustrates a further example of a magnetic resonance imaging system. [Figure 24] FIG. 24 is a flowchart illustrating a method for using the magnetic resonance imaging system of FIG. 21 or 23. [Diagram 25] FIG. 1 shows an example of a head coil incorporating a mechanical gradient magnetic field generator. [Figure 26] FIG. 13 shows a further example of a mechanical gradient magnetic field generator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0095] Similarly numbered elements in these figures are either equivalent elements or perform the same function. An element previously discussed will not necessarily be discussed in a subsequent figure if the function is equivalent.

[0096] MRI spatial encoding is typically done mostly with magnetic field gradient coils built into the walls of the MR system. These take up a lot of bore space and require expensive amplifiers. Local gradient systems for the brain, for example, have never been commercially available because of the weight and power required.

[0097] The use of many tiny magnets (a set of rotating magnets) can be tuned to go from no gradient to a strong gradient collectively. A permanent magnetic sphere or cylinder is held, for example, between the dividers or plates. Mechanically moving the moving plate rotates the set of rotating magnets, generating a change in the external magnetic field. Using tiny spheres (for the dividers) and light, stiff materials minimizes the kinetic energy during the magnetic change. A spring system (mechanical element) minimizes the energy difference between different positions of the moving plate. The total power required to change and maintain the magnetic field is relatively small, allowing high frequency operation and low cost drive systems, while avoiding or reducing the need for cooling systems.

[0098] FIG. 1 shows an example of a mechanical gradient magnetic field generator 100. The mechanical gradient magnetic field generator 100 is shown to include a magnetic field generating element 102. In this example, the magnetic field generating element 102 includes a single generator layer 104. Multiple layers 104 can be stacked on top of each other. There is a stationary divider 106 that remains stationary or fixed, and a movable divider 108 that can move in a displacement direction 110. For the operation of the mechanical gradient magnetic field generator, the relative positions of the stationary divider 106 and the movable divider 108 determine the magnetic field generated by the mechanical gradient magnetic field generator 100. Although the stationary divider 106 may also move, it is assumed that one of the dividers (the stationary divider 106) is stationary since the relative motion between the stationary divider 106 and the movable divider 108 is of interest.

[0099] There is a mechanical element 112 that assists in moving the movable divider 108 back to its initial position. Between the stationary divider 106 and the movable divider 108 is a set of rotating magnets 114 consisting of rotating magnets 116 each having an orientation of a magnetic dipole 118.

[0100] There is a piezoelectric actuator 120 attached to the movable divider 108. As the piezoelectric actuator 120 moves the movable divider 108, the mechanical element 112, in this case a spring, serves to pull the movable divider 108 back to its initial position. As the movable divider 108 moves, it causes the individual magnets 116 to rotate and reorient the magnetic dipoles 118.

[0101] Fig. 2 shows a further example of a mechanical gradient magnetic field generator 100. The example of Fig. 2 is very similar to the example shown in Fig. 1, except that now the actuator is a mechanical actuator 200. For example, located remotely with respect to the movable divider 108 can be a motor or stepper motor or other mechanical actuator such as a pneumatic or hydraulic motor or actuator. The movable divider 108 is connected to the mechanical actuator 200 by a cable 202.

[0102] Fig. 3 shows a further example of a mechanical gradient magnetic field generator 100. The example shown in Fig. 3 is similar to the one shown in Fig. 1 and Fig. 2, except that in this case the actuator is a thermomechanical actuator 300. There is a voltage source that is used to control the thermomechanical actuator 300 and adjust the position of the movable divider 108 in the displacement direction 110. The thermomechanical actuator 300 can be implemented in several different ways. The thermomechanical actuator 300 can have a heating element for heating, a thermoelectric or Peltier element for heating and / or cooling, and / or a cooling system, such as an air or fluid cooling system.

[0103] Figure 4 shows a further example of a mechanical gradient magnetic field generator 100. The example shown in Figure 4 is very similar to the examples shown in Figures 1, 2 and 3. In this case the actuator is an electromechanical actuator 400. The movable divider 108 is connected to mechanical elements 112 or springs on either side, and the magnetic field generated by the electromechanical actuator 400 rotates the magnets 116 and thereby moves the movable divider 108. The electromechanical actuator 400 may represent an actual coil wound around the magnetic field generating element 102 or it may also be a gradient coil system in a magnetic resonance imaging system.

[0104] FIG. 5 shows a further example of a mechanical gradient magnetic field generator 500. In this example, actuators and mechanical elements are not depicted. In this example, in addition to the stationary divider 106 and the set of rotating magnets 114, there is now an additional divider 502. The movable divider 108 is between the stationary divider 106 and the additional divider 502. The additional divider 502 is stationary relative to the stationary divider 106. Between the movable divider 108 and the additional divider 502 there is an additional set of magnets 504, which further includes individual rotating magnets 116 with a direction of magnetic dipole 118. When the movable divider 108 is moved in the direction of movement 110, it causes the set of rotating magnets 114 and the additional set of magnets 504 to rotate individually. In this example, it can be seen that the magnets 116 in the two layers have their dipole moments 118 in opposite directions. In this case, the magnetic fields will cancel due to the distance from the mechanical gradient magnetic field generator 500. As the movable divider 108 is moved in the direction of movement 110, the dipoles 118 will no longer be aligned, resulting in a net magnetic field. It can be seen that the diameter of the magnets is between 0.2 mm and 1 mm. This helps to reduce the effect of large magnetic fields on the magnets 116, especially as they are being moved in and out of the main magnet.

[0105] 5, the movable divider 108 is in an initial position 508. The mechanical gradient magnetic field generator 500 is also shown to include an optional locking mechanism 506 in the form of a pin that passes through the stationary divider 106, the movable divider 108, and the additional divider 502. This holds the position of the movable divider 108 stationary relative to the stationary divider 106 and the additional divider 502. This is useful, for example, when moving the mechanical gradient magnetic field generator 500 into / out of the main magnet.

[0106] In the configuration of Figure 5, the net magnetic field has near zero magnitude at distances compared to the scale of the magnet spheres. In the above example, a net magnetic field can be generated by adjusting the position and / or orientation of the spheres, by moving the center plate (movable divider 108), and by forcing the dipole arrangement to have the same direction.

[0107] 6 shows a further view of the mechanical gradient magnetic field generator 500 after the movable divider 108 has been moved in the direction 110. This causes the magnet 116 to rotate, and it can be seen that the orientation of the magnetic dipoles 118 has also rotated. The dipoles 118 no longer effectively cancel each other, resulting in the generation of a gradient magnetic field.

[0108] An array of such mechanical gradient field generators 100, 500 can generate gradient fields as an alternative to the strong currents traditionally used to generate magnetic fields. Field shaping can be achieved using variations in the starting angles for the dipoles, multiple layers, asymmetric spacing between dipoles, and various other similar techniques. In this case, canceling forces such as those provided by the mechanical elements 112 can be used to minimize the force and power requirements for switching. Local shimming can also be achieved using such techniques.

[0109] FIG. 7 shows a further view of the mechanical gradient magnetic field generator 500. The example of FIG. 7 is again in the initial position 508 and is a modification of the example shown in FIG. 5. In FIG. 5, the dipoles of the set of rotating magnets 114 and the dipoles of the additional set of magnets 504 are placed opposite each other so as to cancel the magnetic fields as much as possible. In the example shown in FIG. 7, some of the magnetic dipoles are rotated relative to each other. This allows local shimming of the main magnetic field. As the movable divider 108 moves in the displacement direction 110, the magnets 116 rotate further but are no longer aligned as they were in FIG. 5. The rotational positions of the individual magnets 116 can be selected to tailor the desired gradient magnetic field and / or to perform shimming functions.

[0110] As an example of mass, a head gradient system might weigh only 5 kg, including a magnet weighing around 2 kg. Net forces and torques are carefully considered in the design. The amount of magnetic material also affects safety in the event of a failure. The smaller the unit, the lower the risk, for example a single dimensional gradient system for thoracic diffusion can be of low mass.

[0111] The actuation of the device can be realized by any known actuator 112, for example a piezoelectric actuator. However, it is also possible to simply incorporate the device in a conductor coil (such as a gradient coil) and actuate the device by magnetic forces. For this, the magnetic forces in the high B0 field on the intermediate plate can be compensated for by an appropriate spring force. The forces are nonlinear and in some cases nonlinear springs can be used. An elegant way to compensate the forces is to use the same nonlinear magnetic forces as well. This can be combined in the magnet system with the parts of the device used for "active shielding", i.e. to compensate for the magnetic field outside the insert gradient assembly. The mechanical coupling further ensures that the sum of the forces and torques on the device is always sufficiently low. Nevertheless, it is beneficial to include some mechanical springs to compensate for the self-field energy, i.e. to reduce the demagnetization factor. Thus, the power requirements for operating the device can be lowered.

[0112] Since it is beneficial to maintain the field homogeneity of B0, it is advantageous to include heating elements to correct for thermal drift in the hard magnetic spheres (the set of rotating magnets). These heating elements may have a second purpose of correcting the net force on the middle plate, allowing the device to operate at low power.

[0113] Since the mechanical gradient magnetic field generator 100, 500 benefits from precise adjustment, its effect must be measured. For this purpose, a displacement sensor (for the middle plate), e.g. an optical sensor, is used. However, it is convenient to measure the local magnetic field by a suitable sensor. With such a feedback system, the gradient assembly can be divided into many subunits, each containing its own coil for actuation. This makes the design of the gradient assembly simpler and allows more degrees of freedom to correct drifts and nonlinearities encountered in the mechanical gradient magnetic field generator 100, 500.

[0114] Figures 8, 9, 10, and 11 are used to illustrate several means for achieving mechanical coupling between the rotating magnets 116 of the set of rotating magnets 114 and / or between the rotating magnets 116 of the additional set of magnets 504, including the movable dividers 108, the stationary dividers 106, and / or the additional dividers 502. The examples in Figures 8 through 11 are described with respect to the set of rotating magnets 114, the stationary dividers 106, and the movable dividers 108, but they can also be applied to mechanical coupling between the additional set of magnets 504, including the additional dividers 502 and the movable dividers 108.

[0115] FIG. 8 shows a further view of the mechanical gradient magnetic field generator 100. Details regarding the actuators and mechanical elements are not depicted in FIGS. 8 to 11. The example shown in FIG. 8 is similar to the example shown in FIG. 1. To ensure that the magnets 116 rotate when the movable divider 108 is moved in the movement direction 110, there is an additional friction layer 800 mounted on the surfaces of the movable divider 108 and the stationary divider 106 facing the set of magnets 114. This provides additional friction and ensures that when the movable divider 108 is moved, the magnets rotate without slipping, as they should. This friction layer 800 can be, for example, a material such as a sticky adhesive, or the friction layer 800 is an additional layer such as rubber that further increases friction. This friction layer 800 can alternatively be mounted on the surface of the rotating magnets 116. In yet another example, the friction layer 800 is mounted on the magnets 116 and both the movable dividers 108 and the stationary dividers 106 as depicted in FIG.

[0116] FIG. 9 shows an alternative method for coupling the rotary magnet 116 to the stationary divider 106 and the movable divider 108. In this example, there is a plastic material 900 that fills the space between the stationary divider 106 and the movable divider 108. The magnet 116 is embedded within this elastic material 900. As the movable divider 108 is moved in the direction of movement 110, the elastic material 900 deforms and the rotary magnet 116 is caused to rotate. One advantage of this embodiment is that the elastic material 900 inherently functions as the mechanical element 112 or as a spring as shown in other embodiments. Although a spring or other elastic element is also included, the elastic material 900 inherently performs this function. Another advantage of using the elastic material 900 is that the rotary magnet 116 can be any shape. However, although magnet 116 is depicted in this image as being circular 116, it could also be cubic or rectangular in shape, and in fact it would be advantageous if magnet 116 were not round, as this would help reduce the chance of it being inadvertently rotated by the main magnetic field of the magnetic resonance imaging system.

[0117] FIG. 10 shows a further way to mechanically couple the magnet 116 to the stationary divider 106 and the movable divider 108. In this example, the magnet 116 now has gear teeth 100 thereon. There are corresponding gear teeth 1002 on the movable divider 108 and the stationary divider 106. This provides a very effective mechanical coupling, preventing inadvertent rotation of the magnet 116, even in a large main magnetic field. This can be constructed in a number of different ways. In some examples, the rotating magnet 116 has gear teeth formed directly on it. The gear teeth are formed from a magnetic material. In other examples, the magnet 116 can be embedded in a gear formed from plastic or some other material.

[0118] FIG. 11 shows a further way of mechanically coupling the magnet 116 to the movable divider 108 and the stationary divider 106. The magnet 116 does not need to be rotated too much to generate the gradient field. In some instances, a rotation of 15°, 30°, or even less than 45° is sufficient. The embodiment shown in FIG. 11 is similar to FIG. 10, except that in this case there is a ridge 1100 that engages with a notch 1102 in the stationary divider 106 and the movable divider 108. As the movable divider 108 is moved in the direction of motion 110, the magnet 116 rotates by tilting. The spacing between the movable divider 108 and the stationary divider 106 will change, but a spring system can be used, for example, to maintain the proper tension between the two.

[0119] Figures 12, 13, 14 and 15 show alternative examples of how to construct the mechanical element 112 to return the movable divider 108 to the initial position 508. The examples shown in Figures 12 to 15 apply both when there is a single set of rotary magnets 116 as well as when there is a set of rotary magnets 116 and an additional set of magnets 504. In Figure 9, the material 900 at least partially served as the mechanical element 112. Figures 12 and 13 show a modification of the example shown in Figure 9. In Figure 12, the entire volume between the movable divider 108 and the stationary divider 106 is not filled. The elastic material 900 covers the surface of the movable divider 108 and a part of the magnets 116. There is another section of the elastic material 900 that covers the surface of the stationary divider 106 and another part of the magnets 116. An open space 1200 is left to help adjust how elastic the mechanical element 112 is.

[0120] 13 shows a further alternative. In this example, elastic material 900 forms a band connecting the magnets 116. There is then an open space 1200 adjacent the movable divider 108 and the fixed divider 106. This band of elastic material 900 also functions as the mechanical element 112.

[0121] FIG. 14 shows a further example of a mechanical gradient magnetic field generator 500. In this example, the movable divider 108 is used to rotate both the set of rotating magnets 114 and the additional set of magnets 504 simultaneously. To provide a restoring force to return the movable divider 108 to its initial position 508, the magnet 116 is not round but has an oval-shaped profile. The mechanical element 112 is formed by an elastic material or a resilient element such as a spring, which pushes the stationary divider 106 towards the movable divider 108 and the additional divider 502 towards the movable divider 108. Due to the oval shape of the magnet 116, the mechanical element 112 compresses when the magnet 116 rotates. This creates a restoring force to return to the initial position 508.

[0122] FIG. 15 shows an alternative way of providing a restoring force to return the movable divider 108 to its initial position. The arrow 1500 represents the direction of the main magnetic field lines. To provide the restoring force, some magnets act as the mechanical elements 112. As the movable divider 108 is moved in the displacement direction 110, the dipole moment 118 of the magnet 116 that is part of the mechanical element 112 rotates towards the opposite direction of the main magnetic field direction 1500. This creates a restoring force. There are two magnets labeled 1502, which are magnets that are designed not to rotate. They are used, for example, to shim the magnetic field or to correct disturbances in the magnetic field caused by the magnet 116 of the mechanical element 112.

[0123] 16 shows a further example of a mechanical gradient magnetic field generator 1600. In this example, the movable divider 108 can move in two deflection directions 1602. A two-dimensional array of rotating magnets 116 is distributed between the movable divider 108 and the stationary divider 106. In this example, the magnets 116 are held in place by an elastic material 900, which also optionally functions as the mechanical element 112. As the movable divider 108 is moved, the elastic material 900 deforms, thereby causing the rotation of the rotating magnets 116. The orientation of the dipole moment is not shown in this example.

[0124] FIG. 17 shows a further example of a mechanical gradient magnetic field generator 1700. This example is similar to FIG. 16, except that it further has an additional layer including an additional set of magnets 504 distributed between the movable divider 108 and the additional divider 502. To facilitate understanding of the figure, only one row and one column of the set of rotating magnets 114 and the set of additional magnets 504 are shown. It can be seen that the dipole moments 118 of the set of rotating magnets 114 and the set of additional magnets 504 face each other. Then, when the movable divider 108 is moved in any direction, this will generate a controllable gradient magnetic field. Both the set of rotating magnets 114 and the set of additional magnets 504 are embedded at least partially in an elastic material 900 that functions as the mechanical element 112.

[0125] FIG. 18 shows a modification of the mechanical gradient magnetic field generator 1700 depicted in FIG. 17. In FIG. 17, the dividers 106, 108, 502 are flat. These dividers can also be formed in different shapes. In FIG. 18, a cylindrical section 1800 is shown. The dividers 106, 108, 502 can also be formed in cylinders. They can also be formed in spherical sections. In FIG. 18, the movable divider 108 can be moved in two displacement directions 1602.

[0126] 19 shows a further method of manufacturing a mechanical gradient magnetic field generator 1600 that can be moved in two displacement directions 1602. In this example, the magnets 116 have protrusions 1900 that mate with notches or holes 1902. As the movable divider 108 is moved in any displacement direction 1602, the magnets tilt, effectively rotating. The difficulty is that the magnets 116 can spin in the main magnetic field. To prevent this, there is an elastic connection 1904 between each magnet 116 and its nearest neighboring magnets 116. The elastic material 1900 may achieve this function. In other examples, there is an actual mechanical connection or spring between the nearest neighboring magnets.

[0127] FIG. 20 shows a further example of a mechanical gradient magnetic field generator 2000 including multiple generator layers 104. The movable dividers 108 of each layer are connected to actuators 120. There are additional compression elements 2002 to hold all of the generator layers 104 together. In this example, some of the stationary dividers 106 also serve as additional dividers 502 for adjacent layers. The mechanical elements 112 used to provide a restoring force to the initial position are not shown in FIG. 20. The method of mechanically coupling the magnets 116 is also not shown. Any of the previously shown examples may be used.

[0128] FIG. 21 shows an example of a magnetic resonance imaging system 2100. The magnetic resonance imaging system 2100 includes a magnet 2104. The magnet 2104 is a superconducting cylindrical type magnet with a bore 2106 therein. Different types of magnets can be used, for example both split cylindrical magnets and so-called open magnets. Split cylindrical magnets are similar to standard cylindrical magnets, except that the cryostat is split into two sections to allow access to the same plane of the magnet, such magnets are used, for example, in conjunction with charged particle beam therapy. Open magnets have two magnet sections, one above the other, with a space between them large enough to accommodate a subject, the configuration of the two sections being similar to that of a Helmholtz coil. Open magnets are popular because they are not subject-limited. Inside the cryostat of the cylindrical magnet is a bank of superconducting coils.

[0129] Within the bore 2106 of the cylindrical magnet 2104 is an imaging zone 2108 where the magnetic field is strong and uniform enough to perform magnetic resonance imaging. A predefined region of interest 2110 is shown within the imaging zone 2108. K-space data is typically acquired for the region of interest. A subject 2118 is shown supported by a subject support 2120 such that at least a portion of the subject 2118 is within the imaging zone 2108 and the predefined region of interest 2110.

[0130] Instead of conventional gradient coils and power supplies, the magnetic resonance imaging system 2100 includes a mechanical gradient magnetic field generator 2112. In this example, the mechanical gradient magnetic field generator 2112 is provided in two sections. Each section is formed, for example, as a polygonal tube 2113. The mechanical gradient magnetic field generator includes a number of magnetic field generating elements. The polygonal tube is formed by configuring a number of, for example, flat, magnetic field generating elements. For each of the polygonal tubes 2113, a connection to the actuator 120 is shown. However, each of the magnetic field generating elements is individually controlled. This provides more freedom when creating the gradient magnetic fields.

[0131] Adjacent to the imaging zone 2108 is a radio frequency coil 2114 for manipulating the orientation of magnetic spins in the imaging zone 2108 and for receiving radio transmissions from spins also in the imaging zone 2108. A radio frequency antenna includes multiple coil elements. A radio frequency antenna is also referred to as a channel or an antenna. The radio frequency coil 2114 is connected to a radio frequency transceiver 2116. The radio frequency coil 2114 and the radio frequency transceiver 2116 are replaced by separate transmit and receive coils and separate transmitters and receivers. It is understood that the radio frequency coil 2114 and the radio frequency transceiver 2116 are representative. The radio frequency coil 2114 is also intended to represent a dedicated transmit antenna and a dedicated receive antenna. Similarly, the transceiver 2116 also represents a separate transmitter and receiver. The radio frequency coil 2114 also has multiple receive / transmit elements and the radio frequency transceiver 2116 has multiple receive / transmit channels. For example, if a parallel imaging technique such as SENSE is performed, the radio frequency coil 2114 will have multiple coil elements.

[0132] The magnetic resonance imaging system 2100 is further shown to include a computer 2130. The computer 2130 is intended to represent one or more computing or computing devices located at one or more locations. The computer 2130 is shown to include a computing system 2132. The computing system 2132 is intended to represent one or more computing systems, which may be, for example, one or more processing cores located at one or more locations. Various combinations of the computing systems 2132 and / or the computers 2130 may be connected using a network and work in conjunction together. The computing system 2132 is shown to be in communication with a hardware interface 2134, a user interface 2136, and a memory 2138. The hardware interface 2134 is an interface that allows the computing system 2132 to communicate with and / or control other components of the magnetic resonance imaging system 2100, such as the transceiver 2116 and the mechanical gradient magnetic field generator 2112.

[0133] The user interface 2136 is a user interface that allows an operator to control and operate the magnetic resonance imaging system 100. The memory 2138 is intended to represent various types of memory in communication with the computing system 2132.

[0134] The memory 2138 is shown to include machine executable instructions 2140, which are instructions that enable the computing system 2132 to perform various processes and tasks, such as image processing, numerical calculations, and control of the magnetic resonance imaging system 2100. The memory 2138 is further shown to include pulse sequence commands 2142. As used herein, pulse sequence commands are commands or data that are converted into commands that enable the computing system 2132 to control the magnetic resonance imaging system 2100 to acquire k-space data, such as lines of k-space data 2144.

[0135] FIG. 22 shows an exemplary end view of one of the mechanical gradient magnetic field generators 2112. The mechanical gradient magnetic field generator 2112 is formed from multiple layers 104 as depicted in FIG. 17. FIG. 17 depicts a single planar mechanical gradient magnetic field generator 1700. The mechanical gradient magnetic field generator 2112 is formed by using multiple mechanical gradient magnetic field generators 1700 depicted in FIG. 17. For example, shifting all the dividers along the z direction (perpendicular to the plane of the drawing) generates a gradient magnetic field component along the z direction. Shifting the dividers relative to each other at different locations along the x and y directions generates gradient magnetic fields along the x and y directions. Various other combinations of different shifts of the respective dividers generate gradient magnetic fields in other directions.

[0136] FIG. 23 shows a further example of a magnetic resonance imaging system 2300. The example shown in FIG. 23 is similar to the example shown in FIG. 21. However, in this example, there is a mechanical gradient magnetic field generator 1700 disposed within the subject support 2120. In this example, the radio frequency coil is a surface coil 2302 shown as being placed on the surface of the subject 2118. The flat mechanical gradient magnetic field generator 1700 is convenient and uses very little space. The example shown in FIG. 23 provides a magnetic resonance imaging system that includes a larger available bore size 2106. This allows for the construction of a cheaper magnetic resonance imaging system, for example, because a smaller magnet results in a larger bore 2106 size. Another advantage of both examples in FIG. 21 and 23 is that expensive power supplies for the magnetic field gradient coils are no longer required.

[0137] Fig. 24 shows a flow chart illustrating a method using the magnetic resonance imaging system 2100 of Fig. 21 or the magnetic resonance imaging system 2300 of Fig. 23. Initially, in step 2400, the magnetic resonance imaging system is controlled by pulse sequence commands 2142 to acquire k-space data 2114. The k-space data 2114 includes commands used to control the mechanical gradient magnetic field generator 2112 or the mechanical gradient magnetic field generator 1700 to generate gradient magnetic fields during acquisition of the k-space data 2114. Then, in step 2402, the k-space data 2144 is optionally reconstructed into a magnetic resonance image 2146.

[0138] 25 shows an example of a magnetic resonance imaging system 2500 including therein a head coil 2502. The head coil includes a radio frequency coil 2504, for example a birdcage coil, which integrates several mechanical gradient field generators 1700. In this example, four units are used. However, other shapes such as the previously illustrated polygonal tube 2113 may also be used. Each of the mechanical gradient field generators 1700 is operated individually.

[0139] FIG. 26 illustrates the use of mechanical gradient magnetic field generators 100 with a single row or set of rotating magnets 114 to generate magnetic field gradients for measuring a subject 2118. The dipole moment has no appreciable effect on the main magnetic field 1500 (e.g., less than 5 ppm distortion) when not aligned with the main magnetic field 1500. As depicted in FIG. 26, the gradient magnetic fields are turned off. When the movable divider 108 for each mechanical gradient magnetic field generator 100 is moved in the direction 110 shown for that particular mechanical gradient magnetic field generator 100, a gradient magnetic field will be generated for the subject 2118.

[0140] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are illustrative or exemplary and are not to be considered restrictive, and the invention is not limited to the disclosed embodiments.

[0141] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the dependent claims. In the claims, the word "comprises" does not exclude other elements or steps, and singular elements do not exclude a plurality. A single processor or other unit fulfills the functions of several items recited in the claims. The mere fact that certain methods are recited in mutually different dependent claims does not indicate that a combination of these methods cannot be used to advantage. The computer program is stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as part of other hardware, but also distributed in other forms, such as via the Internet or other wired or wireless communication systems. Any reference signs in the claims should not be interpreted as limiting the scope. [Explanation of symbols]

[0142] 100 Mechanical gradient magnetic field generator 102 Magnetic Field Generator 104 Generator Layer 106 Static Divider 108 Movable Divider 110 Displacement direction 112 Mechanical elements (springs) 114 Rotating Magnet Set 116 Rotating Magnet 118 Magnetic Dipole Direction 120 Piezoelectric Actuator 200 Mechanical Actuator 202 Cable 300 Thermomechanical Actuator 400 Electromechanical Actuator 500 Mechanical Gradient Magnetic Field Generator 502 Addition Divider 504 Extra set of magnets 506 Locking mechanism 508 Initial position 800 Friction layer 900 Elastic layer 1000 gear teeth 1002 Gear teeth on the surface 1100 Ridge 1102 Notch 1200 Open Space 1500 Main magnetic field direction 1502 Optional non-rotating magnet 1600 Mechanical Gradient Magnetic Field Generator 1602 Two Displacement Directions 1700 Mechanical Gradient Magnetic Field Generator 1800 Cylindrical Section 1900 Protrusion 1902 Notch 1904 Elastic Connection 1602 Two Displacement Directions 2000 Mechanical Gradient Magnetic Field Generator 2002 Compression Element 2100 Magnetic Resonance Imaging System 2104 Magnet 2106 Magnet bore 2108 Imaging Zone 2110 Area of ​​Interest 2112 Mechanical Gradient Magnetic Field Generator 2113 Polygonal tube 2114 Radio Frequency Coil 2116 Transceiver 2118 Target 2120 Support for those affected 2130 Computer 2132 Computer Calculation Systems 2134 Hardware Interface 2136 User Interface 2138 Memory 2140 Machine executable instructions 2142 Pulse sequence command 2144 k-space data 2146 Magnetic Resonance Imaging 2200 Polygonal tube end view 2300 Magnetic Resonance Imaging System 2400 Pulse sequence commands are used to control the magnetic resonance imaging system to acquire k-space data. 2402 Reconstructing magnetic resonance images from k-space data 2500 Magnetic Resonance Imaging System 2502 Head coil 2504 Radio Frequency Coil (Birdcage Coil)

Claims

1. 1. A mechanical gradient magnetic field generator comprising a magnetic field generating element including at least one generator layer, each of said at least one generator layer comprising: a static divider; a movable divider that moves relative to the stationary divider in one or two displacement directions, the movable divider having an initial position; a mechanical element that mechanically assists the movement of the movable divider in the one or two displacement directions by a restoring force generated by the elasticity of the mechanical element toward the initial position; a set of rotating magnets arranged between the movable divider and the stationary divider, the set of rotating magnets being mechanically coupled to the movable divider and the stationary divider, the mechanical coupling of the set of rotating magnets being such that movement of the movable divider in the one or two displacement directions results in individual rotation of each magnet of the set of rotating magnets.

2. 2. The mechanical gradient magnetic field generator of claim 1, wherein the magnetic field generating element further comprises an elastic layer attached to the stationary divider and the movable divider, the set of rotating magnets being at least partially embedded within the elastic layer, the elastic layer providing the mechanical coupling of the set of rotating magnets, and deformation of an elastic material due to the movement of the movable divider causing individual rotation of each of the set of rotating magnets.

3. The mechanical coupling is gear teeth on the set of rotary magnets; a high friction layer on the movable divider and / or on the set of rotating magnets; an adhesive layer on the movable divider and / or on the set of rotary magnets; a resilient layer on the movable divider and / or on the set of rotary magnets; an interface between the set of rotary magnets and the movable divider; 2. The mechanical gradient magnetic field generator of claim 1, wherein the gradient magnetic field is produced via any one of the following combinations:

4. The mechanical gradient magnetic field generator comprises: A flat shape and A cylindrical shape and a polygonal tube shape, wherein the mechanical gradient magnetic field generator includes a plurality of the magnetic field generating elements, and the polygonal tube is formed from the plurality of magnetic field generating elements; 4. The mechanical gradient magnetic field generator according to claim 1, further comprising:

5. 4. The mechanical gradient magnetic field generator of claim 1, wherein the one or two displacement directions are two displacement directions, and the at least one generator has any one of a flat shape, a spherical section shape, and a cylindrical section shape.

6. Each of the at least one generator layer further comprises: an additional divider that is stationary relative to the stationary divider, the movable divider being between the additional divider and the stationary divider; 4. The mechanical gradient magnetic field generator of claim 1, further comprising: an additional set of magnets arranged between the movable divider and the additional divider, the additional set of magnets being mechanically coupled to the movable divider and the additional divider, the mechanical coupling of the additional set of magnets being such that movement of the movable divider in the one or two displacement directions causes individual rotation of each of the additional set of magnets.

7. 7. The mechanical gradient magnetic field generator of claim 6, wherein the set of rotating magnets and the additional set of magnets each have a dipole moment, and wherein in the initial position a vector sum of the dipole moments of the set of rotating magnets and the additional set of magnets is less than 10% of the sum of the magnitudes of the dipole moments of the set of rotating magnets and the additional set of magnets, and wherein in the initial position the vector sum is preferably less than 1% of the sum of the magnitudes.

8. 4. The mechanical gradient magnetic field generator according to claim 1, further comprising a locking mechanism for holding the magnetic field generating element in the initial position.

9. 4. The mechanical gradient magnetic field generator according to claim 1, further comprising an actuator for simultaneously moving the movable dividers of each of the at least one generator layer in the one or two displacement directions.

10. 9. The mechanical gradient magnetic field generator of claim 8, wherein the actuator is one of a mechanical actuator, a piezoelectric actuator, an electromagnetic actuator, a thermoelectric actuator, and a magnetic field coil system.

11. 1. A magnetic resonance imaging system for acquiring k-space data from a subject at least partially within an imaging zone, the magnetic resonance imaging system comprising:

10. The mechanical gradient magnetic field generator of claim 9, which generates the gradient magnetic fields at least partially within the imaging zone; a memory for storing machine executable instructions and pulse sequence commands; and a computing system that controls the magnetic resonance imaging system, wherein execution of the machine-executable instructions causes the computing system to control the magnetic resonance imaging system using the pulse sequence commands to acquire the k-space data, and the pulse sequence commands control the actuators to generate the gradient magnetic fields.

12. 12. The magnetic resonance imaging system of claim 11, further comprising a magnet for generating a main magnetic field, and wherein the mechanical gradient magnetic field generator is configured such that generation of the gradient magnetic fields requires less energy than a gradient magnetic field coil system.

13. 12. The magnetic resonance imaging system of claim 11, wherein the mechanical element balances the forces exerted by the set of rotating magnets on the movable divider within a predetermined force threshold when the mechanical gradient field generator is within the main magnetic field.

14. A magnetic resonance imaging coil comprising a mechanical gradient field generator according to any one of claims 1 to 3.

15. The magnetic resonance imaging coil of claim 14 , wherein the magnetic resonance imaging coil is a head coil or a body coil.

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