Magnetic Resonance Imaging System

Abstract

To enable imaging corresponding to the movement and free attitude of a subject in an imaging space in an open type magnetic resonance imaging apparatus.SOLUTION: A magnetic resonance imaging apparatus of an embodiment includes: a magnetostatic field magnet equipped with a superconducting coil and generating a magnetostatic field having a magnetostatic field distribution in an open area in the outside of the superconducting coil; a control unit for adjusting the magnetostatic field distribution; and a generation unit for generating a magnetic resonance image based on a magnetic resonance signal emitted from a subject whose at least a part is placed on the open area in the outside of the superconducting coil.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to a magnetic resonance imaging apparatus.

Background Art

[0002] A magnetic resonance imaging apparatus is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with a high-frequency (RF: Radio Frequency) signal at the Larmor frequency, and reconstructs a magnetic resonance signal (MR (Magnetic Resonance) signal) generated from the subject upon excitation to generate an image.

[0003] Many magnetic resonance imaging (MRI) apparatuses have a configuration called a gantry, and a cylindrical space (this space is called a bore) is formed in the gantry. Imaging is performed with the subject (for example, a patient) lying on the top plate being carried into the cylindrical space. Inside the gantry, a cylindrical static magnetic field magnet, a cylindrical gradient magnetic field coil, and a cylindrical transmit-receive coil (i.e., a WB (Whole Body) coil) are housed. In this type of magnetic resonance imaging apparatus, which has been around for a long time, since the static magnetic field magnet, the gradient magnetic field coil, and the transmit-receive coil are cylindrical, hereinafter, this type of magnetic resonance imaging apparatus shall be referred to as a cylindrical magnetic resonance imaging apparatus.

[0004] In a cylindrical magnetic resonance imaging apparatus, imaging is to be performed in a closed space within the bore. Therefore, for some patients, such as those with claustrophobia, imaging may be difficult.

[0005] In contrast, magnetic resonance imaging (MMRI) systems have been proposed and developed that use flat-plate-shaped static magnetic field magnets and gradient magnetic field coils, and are configured to image subjects such as patients in an open space sandwiched between, for example, two flat-plate-shaped static magnetic field magnets. This type of MMRI system will hereafter be referred to as a planar open-type MMRI system (or simply an open-type MMRI system). Because imaging is performed in an open space with an open-type MMRI system, it is possible to image patients with claustrophobia.

[0006] On the other hand, cylindrical magnetic resonance imaging systems are designed to image in a narrow region with high magnetic field uniformity within the bore, whereas open-type magnetic resonance imaging systems image the subject in a relatively wide open space, meaning the subject's position relative to the static magnetic field magnet is not necessarily fixed.

[0007] Magnetic resonance imaging (MRI) imaging takes a relatively long time and exposes the subject to a noisy environment. Therefore, when imaging children or the elderly in a large, open space, for example, there is a higher possibility of movement during imaging, which may result in motion-induced artifacts.

[0008] Furthermore, depending on the patient's condition, it may be difficult for them to lie on their back on the tabletop. In such cases, there is a demand for imaging that can be performed in a position that suits the patient's condition. However, to meet this demand, it is necessary to be able to freely adjust the position and range of the imaging area according to the patient's condition. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Special Publication No. 2022-521391 [Overview of the project] [Problems that the invention aims to solve]

[0010] One of the problems that the embodiments disclosed herein and in the drawings aim to solve is to enable imaging in an open-type magnetic resonance imaging apparatus that responds to the movement of the subject and the subject's free posture within the imaging space. However, the problems that the embodiments disclosed herein and in the drawings aim to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in each embodiment described later can also be positioned as other problems. [Means for solving the problem]

[0011] One embodiment of a magnetic resonance imaging apparatus includes a superconducting coil, a static magnetic field magnet that generates a static magnetic field with a static magnetic field distribution in an open region outside the superconducting coil, a control unit that adjusts the static magnetic field distribution, and a generation unit that generates a magnetic resonance image based on a magnetic resonance signal emitted from a subject, at least a portion of which is placed in the open region outside the superconducting coil. [Brief explanation of the drawing]

[0012] [Figure 1] A diagram showing a first configuration example of a magnetic resonance imaging apparatus according to an embodiment. [Figure 2] A diagram showing a second configuration example of a magnetic resonance imaging apparatus according to the embodiment. [Figure 3] A diagram showing an example of the configuration of a static magnetic field magnet. [Figure 4] A schematic diagram showing the configuration of a superconducting coil in the magnetic resonance imaging apparatus of this embodiment, and a static magnetic field power supply connected to this superconducting coil. [Figure 5] A diagram showing an example configuration of a static magnetic field magnet having three superconducting coils. [Figure 6] A diagram showing an example configuration of a magnetic resonance imaging apparatus according to the first embodiment. [Figure 7] This diagram schematically shows the change in the position of the imaging region when the current supplied to each of the two superconducting coils is varied. [Figure 8] A schematic diagram showing the time-dependent change pattern of current in a superconducting coil. [Figure 9] A diagram showing an example configuration of a magnetic resonance imaging apparatus according to the second embodiment. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments of the present invention will be described based on the attached drawings. (First embodiment) Figure 1 shows a first configuration example of an open-type magnetic resonance imaging apparatus 1 according to an embodiment. As illustrated in Figure 1, the magnetic resonance imaging apparatus 1 has, for example, two circular flat plate-shaped (in other words, thin cylindrical) static magnetic field magnets 10.

[0014] Each static magnetic field magnet 10 is positioned such that its central axis, that is, the axis passing through the centers of the circles on both end faces of the cylindrical shape, is parallel to, for example, the floor. Furthermore, the two static magnetic field magnets 10 are positioned so as to sandwich the subject. This arrangement of the static magnetic field magnets 10 creates a magnetic field in the open space between the two magnets 10. The subject is imaged in this open space, for example, in a standing position.

[0015] Figure 2 shows a second configuration example of the open-type magnetic resonance imaging apparatus 1. While Figure 1 shows a configuration example for imaging a standing subject, Figure 2 shows a configuration example for imaging a supine subject lying on the tabletop 80 of the bed 81. When imaging a supine subject, the two static magnetic field magnets 10 are arranged so that their central axes are in the vertical direction, as shown in Figure 2. For example, one static magnetic field magnet 10 is placed below the tabletop 80, and the other static magnetic field magnet 10 is placed above the tabletop 80.

[0016] As shown in Figures 1 and 2, imaging using the static magnetic field magnet 10 of the embodiment allows the subject to be imaged in an open magnetic field space, so for example, even patients with claustrophobia can be imaged. In FIGS. 1 and 2, although the state where the subject is imaged in the open region outside the static magnetic field magnet 10 including the superconducting coil is shown, imaging may be performed in a state where at least a part of the subject is placed in the open region outside the superconducting coil.

[0017] FIG. 3 is a diagram showing an example of the configuration of the static magnetic field magnet 10. Each static magnetic field magnet 10 incorporates a superconducting coil 101. The static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power source 40 (see FIG. 4 etc.) to the superconducting coil 10 in the excitation mode, and then, when shifting to the persistent current mode, the static magnetic field power source 40 is disconnected. Once shifting to the persistent current mode, the static magnetic field magnet 10 continues to generate a large static magnetic field for a long time, for example, over one year.

[0018] On the other hand, an operation mode in which a current is continuously applied from the static magnetic field power source to the superconducting coil 101 during the operation period including imaging without disconnecting the static magnetic field power source 40 is also possible. This operation mode shall be called the control current mode.

[0019] In the magnetic resonance imaging apparatus 1 of the embodiment, in either the persistent current mode or the control current mode, as schematically indicated by arrows in FIG. 3, the magnetic resonance imaging apparatus 1 is configured such that the position and shape of the static magnetic field distribution in the imaging region R can be adjusted or changed, rather than being fixed.

[0020] FIG. 4 is a diagram schematically showing the configuration of the superconducting coil 101 included in the magnetic resonance imaging apparatus 1 of the embodiment and the static magnetic field power source 40 connected to this superconducting coil 101. The superconducting coil 101 of the embodiment is configured to be divided into a plurality of segments as shown in the lower diagram of FIG. 4.

[0021] In the example shown in FIG. 4, the superconducting coil 101 is configured to be divided into nine segments up to segments 101a, 101b, 101c, 101d, 101e, 101f, 101g, 101h, and 101i.

[0022] In other words, the superconducting coil 101 is divided into multiple segments, and each segment has a superconducting subcoil (hereinafter simply referred to as a subcoil) that is independent of the other segments.

[0023] Each segment's subcoil can be constructed as a multi-core wire structure by embedding numerous thin filaments or thin tapes of superconducting wires, such as niobium-titanium (Nb-Ti), or rare-earth or bismuth-based high-temperature superconducting wires, into a superelectric base material such as copper. The superconducting coil 101, as an assembly of these multiple segments, is immersed in a liquid helium container (not shown) filled with liquid helium, for example.

[0024] Each subcoil in each segment can be connected in parallel to the static magnetic field power supply 40, and each can receive an independent current supply from the static magnetic field power supply 40. By independently controlling the magnitude and direction of the current supplied from the static magnetic field power supply 40 to each subcoil, or by switching the current on or off, the strength of the static magnetic field generated by the superconducting coil 101, as well as the shape of the static magnetic field distribution, such as its magnitude and position, can be adjusted to a desired state.

[0025] Alternatively, some of the subcoils of the multiple segments of the superconducting coil 101 may be connected in parallel to the static magnetic field power supply 40 as described above, while some of the subcoils of other segments may be connected in series, and both ends of the series-connected subcoils may be connected to the static magnetic field power supply 40. In this case, the number of groups of series-connected subcoils may be one or two or more.

[0026] In the example shown in Figure 4, current is supplied to the nine segments 101a, 101b, 101c, 101d, 101e, 101f, 101g, 101h, and 101i that make up the superconducting coil 101 by six feed lines from the static magnetic field power supply 40. In this case, for example, the four segments 101a, 101b, 101c, and 101d can be configured to receive independent current in parallel by four feed lines. On the other hand, segments 101e and 101f are connected in series to form a first series group, and the three segments 101g, 101h, and 101i are also connected in series to form a second series group. The remaining two feed lines of the static magnetic field power supply 40 can then be configured to supply current to the first and second series groups, respectively.

[0027] The magnitude and direction of the current supplied from the static magnetic field power supply 40 to each segment of the superconducting coil 101 may be controlled by the static magnetic field power supply 40 itself, or by a control circuit 42 (see Figure 6) connected to the static magnetic field power supply 40.

[0028] Figures 3 and 4 show a configuration in which the static magnetic field magnet 10 includes one superconducting coil 101, but the static magnetic field magnet 10 can also be configured to include multiple superconducting coils. Figure 5 shows an example configuration in which the static magnetic field magnet 10 has three superconducting coils 101, 102, and 103. In the example shown in Figure 5, three annular superconducting coils 101, 102, and 103, which have different diameters from each other, are arranged coaxially.

[0029] Each superconducting coil 101, 102, and 103 is divided into one or more segments. In the example shown in Figure 5, superconducting coil 101 is divided into nine segments, similar to Figure 4, superconducting coil 102 is divided into eight segments, and superconducting coil 103 is divided into two segments.

[0030] By independently controlling the magnitude and direction of the current supplied not only to the superconducting coil 101 but also to the subcoils of each segment of the other two superconducting coils 102 and 103, as well as the on / off state of the current, it is possible to adjust the strength of the static magnetic field formed by the entire static magnetic field magnet 10, as well as the shape of the static magnetic field distribution, such as its magnitude and position, with a greater degree of freedom.

[0031] Figure 6 shows an example of the configuration of a magnetic resonance imaging apparatus 1 according to the first embodiment, in which the static magnetic field magnets 10 shown in Figure 5 are placed above and below a subject P lying on its side. An imaging region R (or FOV (Field of View)) is formed between the two static magnetic field magnets 10.

[0032] The magnetic resonance imaging apparatus 1 shown in Figure 6 includes, in addition to the two static magnetic field magnets 10 described above, a tabletop 80 on which the subject P lies, a local coil 20 installed close to the subject, a gradient magnetic field coil 60, and an RF (Radio Frequency) coil 62.

[0033] Furthermore, the magnetic resonance imaging apparatus 1 includes a static magnetic field power supply 40, a control circuit 42, an imaging condition setting circuit 50, a sequence controller 51, a gradient magnetic field power supply 52, a transmission circuit 53, a reception circuit 54, and a reconstruction processing circuit 55.

[0034] The imaging condition setting circuit 50 sets imaging conditions such as the type of pulse sequence and the values ​​of various parameters, which are input via a user interface (not shown), to the sequence controller 51.

[0035] The sequence controller 51 performs a scan of the subject by driving the gradient power supply 52 and the transmission circuit 53, respectively, based on the set imaging conditions. The gradient power supply 52 applies a gradient current to the gradient coil 60 based on the drive signal from the sequence controller 51.

[0036] The transmitting circuit 53 generates an RF pulse based on a drive signal from the sequence controller 51 and applies the RF pulse to the RF coil 62. The local coil 20 receives the MR (Magnetic Resonance) signal emitted from the subject P in response to this application. The MR signal received by the local coil 20 is converted from an analog signal to a digital signal by the receiving circuit 54. The MR signal converted to a digital signal is supplied to the reconstruction processing circuit 55 as k-space data. The reconstruction processing circuit 55 performs reconstruction processing such as inverse Fourier transform on the k-space data to generate a magnetic resonance image.

[0037] As mentioned above, the static magnetic field power supply 40 supplies current to the superconducting coils 101, 102, and 103 of the upper and lower static magnetic field magnets 10, respectively, under the control of the control circuit 42. In Figure 6, to avoid diagrammatic complexity, the current is shown as being supplied to each of the superconducting coils 101, 102, and 103 by a single feed line. However, in reality, current is supplied to each of the superconducting coils 101, 102, and 103 by multiple feed lines, which enables individual and independent current control for the subcoils of multiple segments within the superconducting coils 101, 102, and 103.

[0038] As described above, the control circuit 42 can adjust the static magnetic field distribution by independently controlling at least one of the direction and magnitude of the current flowing through each segment of the superconducting coils 101, 102, and 103.

[0039] For example, in all or any of the superconducting coils 101, 102, and 103, multiple segments may be classified into a first group and a second group, and the static magnetic field distribution may be adjusted by passing currents in opposite directions through one or more first subcoils belonging to the first group and one or more second subcoils belonging to the second group.

[0040] Alternatively, instead of independently controlling the current between segments, or in addition to independently controlling the current between segments, the static magnetic field distribution can also be adjusted by independently controlling at least one of the direction and magnitude of the current flowing through each of the superconducting coils 101, 102, and 103. The operating mode of the current supplied from the static magnetic field power supply 40 to the superconducting coils 101, 102, and 103 may be either a persistent current mode or a controlled current mode.

[0041] Here, the persistent current mode refers to the current operation mode in which the current applied to the superconducting coils 101, 102, and 103 is increased from zero to a predetermined value, and then the static magnetic field power supply 40 is disconnected, allowing the current to continue flowing through the superconducting coils 101, 102, and 103. The transient operation mode in which the current applied to the superconducting coils 101, 102, and 103 is increased from zero to a predetermined value is called the excitation mode.

[0042] In the persistent current mode, the direction and magnitude of the current flowing through the superconducting coils 101, 102, and 103 and their respective segments are predetermined at the start of the excitation mode and remain fixed after transitioning to the persistent current mode.

[0043] On the other hand, the control current mode is a current operation mode in which current is continuously applied from the static magnetic field power supply 40 to the superconducting coil 101 during the operation period, including during imaging, without disconnecting the static magnetic field power supply 40. The direction and magnitude of the current flowing to the superconducting coils 101, 102, 103 and their respective segments in the control current mode can be changed at any desired timing, whether before or during imaging.

[0044] The operating mode of the current supplied from the static magnetic field power supply 40 to the superconducting coils 101, 102, and 103 may be assigned to either a persistent current mode or a controlled current mode for all superconducting coils 101, 102, and 103 and all segments, or a mixture of persistent current mode and controlled current mode may be used among multiple superconducting coils 101, 102, and 103, or among multiple segments.

[0045] As described above, the static magnetic field distribution can be adjusted by controlling the current of the static magnetic field power supply 40 by the control circuit 42. By adjusting the static magnetic field distribution, that is, by changing the shape and position of the static magnetic field distribution, at least one of the following can be adjusted: the position of the imaging area of ​​the subject, the range of the imaging area of ​​the subject, and the strength of the static magnetic field.

[0046] Furthermore, the control circuit 42 may acquire imaging conditions from the imaging condition setting circuit 50 and adjust the static magnetic field distribution based on the acquired imaging conditions. In this case, the acquired imaging conditions include, for example, at least one of the position of the imaging area of ​​the subject, the range of the imaging area of ​​the subject, and the strength of the static magnetic field, and the control circuit 42 determines the current to be supplied to each segment of the superconducting coils 101, 102, and 103 to obtain the desired static magnetic field distribution based on these imaging conditions.

[0047] The control circuit 42 maintains a lookup table that associates imaging conditions, such as the position of the imaging area, the range of the imaging area of ​​the subject, and the strength of the static magnetic field, with the current supplied to each segment of the superconducting coils 101, 102, and 103 to obtain the static magnetic field distribution corresponding to these imaging conditions. The control circuit 40 can then determine the current to supply to each segment based on the imaging conditions set in the imaging condition setting circuit 50 by referring to this lookup table.

[0048] Figure 7 schematically shows the change in the position of the imaging region R when parameters such as the current of the static magnetic field power supply and the cross-sectional area of ​​the superconducting coil segment are changed, as an example of adjusting the static magnetic field distribution. For ease of explanation, Figure 7 illustrates a configuration in which the upper static magnetic field magnet 10 is removed from the configuration shown in Figure 6. Figure 7 schematically shows the change in the position of the imaging region R corresponding to the static magnetic field distribution when the cross-sectional areas Sa and Sb are changed, in the case where the static magnetic field magnet 10 has two superconducting coils 101 and 102, with currents Ia and Ib supplied to the superconducting coils 101 and 102 respectively, and the cross-sectional areas Sa and Sb of the segments of the superconducting coils 101 and 102 respectively.

[0049] In the graph shown on the right side of Figure 7, the combinations of cross-sectional area Sa and cross-sectional area Sb are indicated by white squares, and the position of the imaging region R corresponding to each combination is indicated by a black circle. Here, the position of the imaging region R is defined as the distance D from the upper end of the static magnetic field magnet 10 (or superconducting coils 101, 102) to the center of the imaging region R. As can be seen from this graph, the position of the imaging region R can be changed by changing the respective values ​​of cross-sectional area Sa and cross-sectional area Sb. Alternatively, instead of changing the cross-sectional areas Sa and Sb, the position of the imaging region R can also be changed by changing the currents Ia and Ib. Furthermore, the above is just one example of adjusting the static magnetic field distribution; the static magnetic field distribution can also be adjusted by adjusting other parameters besides the current of the static magnetic field power supply 40 and the segment cross-sectional area of ​​the superconducting coil.

[0050] By adjusting the static magnetic field distribution as described above, imaging can be performed even when the subject moves within the imaging space between the two static magnetic field magnets 10. Furthermore, imaging can be performed according to the subject's free posture.

[0051] Incidentally, in the persistent current mode, various parameters must be considered when determining the rate of increase and decrease of the applied current to the superconducting coils 101, 102, and 103, that is, the time-dependent change pattern of the current from zero to a predetermined persistent current, and the time-dependent change pattern of the current from a predetermined persistent current value to zero during demagnetization.

[0052] Furthermore, in the control current mode as well, when determining the time-dependent change pattern of the current applied to the superconducting coils 101, 102, and 103 while maintaining the superconducting state, various parameters must be considered.

[0053] Figure 8 schematically shows the time-dependent current change pattern for superconducting coils 101, 102, and 103, including during excitation and demagnetization. In the example of the time-dependent current change pattern shown in Figure 8, excitation is started at time t0, the current increases from zero to current I(1) from time t0 to time t1, the current is maintained at current I(1) from time t1 to time t2, the current further increases from current I(1) to current I(2) from time t2 to time t3, the current is maintained at current I(2) from time t3 to time t4, the current decreases from current I(2) to current I(3) from time t4 to time t5, the current is maintained at current I(3) from time t5 to time t6, and the current decreases from current I(3) to current zero from time t6 to time t7.

[0054] Here, the time-dependent change pattern of the current of the static magnetic field power supply 40 for exciting the static magnetic field magnet 10 (or for increasing the strength of the static magnetic field), and the time-dependent change pattern of the current of the static magnetic field power supply 40 for demagnetizing the static magnetic field magnet 10 (or for decreasing the strength of the static magnetic field) are determined based on at least one of the shape of the static magnetic field distribution to be realized, the strength of the static magnetic field to be realized, the temperature of the superconducting coil 101, etc., the empirical magnetic field of the superconducting coil 101, etc., and the cooling performance for cooling the superconducting coil 101.

[0055] Here, the temperature of the superconducting coils 101, etc., can be obtained as magnet monitor information from data of temperature sensors provided adjacent to each superconducting coil 101, etc. Furthermore, parameters such as the shape of the static magnetic field distribution to be realized, the strength of the static magnetic field to be realized, and the cooling performance can be provided to the control circuit 42 in advance. Note that the shape of the static magnetic field distribution to be realized and the strength of the static magnetic field to be realized can also be determined based on the imaging conditions set in the imaging condition setting circuit 50.

[0056] (Second embodiment) Figure 9 shows an example of the configuration of a magnetic resonance imaging apparatus 1 according to the second embodiment. The first difference from the first embodiment (see Figure 6) is that the magnetic resonance imaging apparatus 1 of the second embodiment is equipped with a magnetic material 70 for adjusting the static magnetic field distribution. The magnetic material 70 is a component containing a magnetic material such as iron or nickel. The magnetic material 70 is disposed, for example, between the static magnetic field magnet 10 and the top plate 80. Alternatively, the magnetic material 70 may be placed inside a vacuum container called a cryostat. The magnetic material 70 may also be configured as a coil.

[0057] The magnetic material 70 is moved, for example, along the longitudinal or transverse direction of the top plate 80 by a drive mechanism 72 under the control of a control circuit 42. By moving the magnetic material 70, the shape of the static magnetic field distribution and the strength of the static magnetic field can be adjusted, and as a result, the size and position of the imaging area R can be adjusted.

[0058] The second difference from the first embodiment is that the magnetic resonance imaging apparatus 1 of the second embodiment moves at least one of the gradient magnetic field coils 60, the RF coil 62, and the top plate 80 relative to the static magnetic field magnet 10. Similar to the magnetic material 70 described above, the gradient magnetic field coils 60, the RF coil 62, or the top plate 80 can be moved, for example, along the longitudinal or transverse direction of the top plate 80 by the drive mechanism 72 under the control of the control circuit 42. By moving these, the shape of the static magnetic field distribution and the strength of the static magnetic field can be adjusted, and as a result, the size and position of the imaging area R can be adjusted.

[0059] As described above, in the magnetic resonance imaging apparatus 1 of the second embodiment, the size and position of the imaging area R can be adjusted, and imaging can be performed even when the subject moves within the imaging space between the two static magnetic field magnets 10. Furthermore, imaging can be performed according to the subject's free posture.

[0060] (Third embodiment) In the magnetic resonance imaging apparatus 1 of the first embodiment described above (Figure 6), or the magnetic resonance imaging apparatus 1 of the second embodiment (Figure 9), the apparatus is configured to include two static magnetic field magnets 10 facing each other, and the subject is imaged in the space between the two static magnetic field magnets 10.

[0061] In contrast, the third magnetic resonance imaging apparatus 1 is configured to include only one of the two static magnetic field magnets 10. For example, the configuration of the magnetic resonance imaging apparatus 1 of the first and second embodiments shown in Figures 6 and 9 can be modified by removing the static magnetic field magnet 10 located above the top plate 80 to obtain the magnetic resonance imaging apparatus 1 of the third embodiment. In the third embodiment, the static magnetic field magnet consists only of the static magnetic field magnet 10 located below the top plate 80. The same effects as those of the first and second embodiments can be obtained in the magnetic resonance imaging apparatus 1 of the third embodiment.

[0062] The control circuit, imaging condition setting circuit, and reconstruction processing circuit described in each embodiment are examples of the control unit, imaging condition setting unit, and generation unit described in the claims, respectively.

[0063] According to at least one embodiment described above, in an open-type magnetic resonance imaging apparatus, it is possible to perform imaging in accordance with the movement of the subject and the subject's free posture within the imaging space.

[0064] While several embodiments have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of other forms, and various omissions, substitutions, modifications, and combinations of embodiments are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0065] 1. Magnetic Resonance Imaging System 10 Static magnetic field magnet 20 Local Coils 40 Static magnetic field power supply 42 Control circuits 60. Gradient field coils 62 RF coils 70 Magnetic material 72 Drive mechanism 101, 102, 103 Superconducting Coils

Claims

1. A static magnetic field magnet comprising a superconducting coil configured to be divided into a plurality of segments, which generates a static magnetic field having a static magnetic field distribution in an open region outside the superconducting coil, A control unit that adjusts the static magnetic field distribution by independently controlling the current flowing through the superconducting coil for each segment, A generation unit that generates a magnetic resonance image based on a magnetic resonance signal emitted from a subject placed in an open region outside the superconducting coil, at least a portion of which is located. A magnetic resonance imaging system equipped with the following features.

2. The control unit adjusts the static magnetic field distribution by independently controlling at least one of the direction and magnitude of the current flowing through the superconducting coil for each segment. The magnetic resonance imaging apparatus according to claim 1.

3. The superconducting coil comprises at least a first superconducting coil belonging to a first group segment and a second superconducting coil belonging to a second group segment. The control unit adjusts the static magnetic field distribution by setting the direction of the first current flowing through the first superconducting coil and the second current flowing through the second superconducting coil to be opposite, and by independently controlling the magnitudes of the first current and the second current. The magnetic resonance imaging apparatus according to claim 1.

4. The system further comprises a static magnetic field power supply for applying current to the superconducting coil, The control unit controls the static magnetic field distribution by increasing the current applied to the superconducting coil to a predetermined value, and then continuing to supply current to the superconducting coil in a persistent current mode while the static magnetic field power supply is disconnected. The magnetic resonance imaging apparatus according to claim 1.

5. The system further comprises a static magnetic field power supply for applying current to the superconducting coil, The control unit controls the static magnetic field distribution by adjusting the current flowing through the superconducting coil while the static magnetic field power supply is connected to the superconducting coil. The magnetic resonance imaging apparatus according to claim 1.

6. The system further comprises a static magnetic field power supply for applying current to the superconducting coil, The control unit, For the first superconducting coil belonging to the first group of segments among the plurality of segments, the static magnetic field distribution is controlled by a persistent current mode in which the current applied to the first superconducting coil is increased to a predetermined value, and then the static magnetic field power supply is disconnected while the current is continuously supplied to the first superconducting coil. For a second superconducting coil belonging to a second segment other than the first group among the plurality of segments, the static magnetic field distribution is controlled by adjusting the current flowing through the second superconducting coil while the static magnetic field power supply is connected to the second superconducting coil. The magnetic resonance imaging apparatus according to claim 1.

7. The control unit adjusts at least one of the following by adjusting the static magnetic field distribution: the position of the imaging area of ​​the subject, the range of the imaging area of ​​the subject, and the strength of the static magnetic field. The magnetic resonance imaging apparatus according to claim 1.

8. It further includes an imaging condition setting unit for setting imaging conditions, The imaging conditions include at least one of the following: the position of the imaging area of ​​the subject, the range of the imaging area of ​​the subject, and the strength of the static magnetic field. The control unit adjusts the static magnetic field distribution based on the set imaging conditions. The magnetic resonance imaging apparatus according to claim 7.

9. The system further comprises a static magnetic field power supply for applying current to the superconducting coil, The control unit determines the time-dependent change pattern of the current of the static magnetic field power supply for exciting the static magnetic field magnet, and the time-dependent change pattern of the current of the static magnetic field power supply for demagnetizing the static magnetic field magnet, based on at least one of the static magnetic field distribution, the strength of the static magnetic field, the temperature of the superconducting coil, the empirical magnetic field of the superconducting coil, and the cooling performance of the superconducting coil. The magnetic resonance imaging apparatus according to claim 1.

10. A static magnetic field magnet comprising a superconducting coil, which generates a static magnetic field having a static magnetic field distribution in an open region outside the superconducting coil, A control unit for adjusting the static magnetic field distribution, A generation unit that generates a magnetic resonance image based on a magnetic resonance signal emitted from a subject placed in an open region outside the superconducting coil, at least a portion of which is located. A magnetic material that adjusts the static magnetic field distribution, The system includes a drive mechanism for moving the magnetic material, The control unit adjusts the static magnetic field distribution by controlling the drive mechanism to move the magnetic material relative to the static magnetic field magnet. Magnetic resonance imaging device.

11. A gradient magnetic field coil for applying a gradient magnetic field to the subject, An RF coil for applying a high-frequency magnetic field to the subject, A top plate on which the subject lies, The system further comprises the gradient magnetic field coil, the RF coil, and a drive mechanism for moving at least one of the top plates, The control unit adjusts the static magnetic field distribution by controlling the drive mechanism to move at least one of the gradient magnetic field coil, the RF coil, and the top plate relative to the static magnetic field magnet. The magnetic resonance imaging apparatus according to claim 1.

Images