Magnetic resonance imaging apparatus, magnetic resonance imaging method, and program

Abstract

To shorten an echo time.SOLUTION: A magnetic resonance imaging device includes a design unit and a collection unit. The design unit designs a pulse sequence so as to superpose at least part of a first crusher gradient magnetic field applied after a first refocus pulse and a second crusher gradient magnetic field applied before a second refocus pulse after the first refocus pulse on the basis of a LASER (localization by adiabatic selective refocusing) pulse sequence including six refocus pulses. The collection unit collects magnetic resonance spectroscopy signals by executing the designed pulse sequence.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As imaging sequences for magnetic resonance spectroscopy (MRS), mainly methods such as the PRESS (point resolved spectroscopy) system, the ISIS (image-selected in vivo spectroscopy) system, and the LASER (localization by adiabatic selective refocusing) system can be mentioned. Among them, the LASER system, which has less contamination of unnecessary signals outside the region of interest to be excited, has high selection accuracy for the region of interest. However, in the LASER method, it is necessary to transmit a total of six refocusing pulses, two times each for the respective gradient magnetic fields Gx, Gy, and Gz, and there is a problem that the TE becomes long.

[0003] Therefore, semi-LASER, which applies a total of four refocusing pulses, is often used as an alternative to LASER. However, for the gradient magnetic field corresponding to a certain slice, semi-LASER only applies the gradient magnetic field related to normal slice selection. Therefore, there is a problem that the slice characteristics deteriorate in the axial direction in which the gradient magnetic field related to normal slice selection is applied.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

[0005] One of the problems that the embodiments disclosed herein and in the drawings aim to solve is to reduce echo time. 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 the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0006] The magnetic resonance imaging apparatus according to this embodiment includes a design unit and an acquisition unit. The design unit designs a pulse sequence based on a LASER (localization by adiabatic selective refocusing) pulse sequence including six refocus pulses, such that at least a portion of the first crusher gradient magnetic field applied after the first refocus pulse and the second crusher gradient magnetic field applied before the second refocus pulse following the first refocus pulse overlap. The acquisition unit acquires a magnetic resonance spectroscopy signal by executing the designed pulse sequence. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a block diagram showing a magnetic resonance imaging apparatus according to this embodiment. [Figure 2] Figure 2 is a flowchart showing the operation of the magnetic resonance imaging apparatus according to this embodiment. [Figure 3] Figure 3 shows a first design example of a pulse sequence according to this embodiment. [Figure 4] Figure 4 shows a second design example of the pulse sequence according to this embodiment. [Figure 5] Figure 5 shows a third design example of the pulse sequence according to this embodiment. [Modes for carrying out the invention]

[0008] The magnetic resonance imaging apparatus, magnetic resonance imaging method, and program according to this embodiment will be described below with reference to the drawings. In the following embodiments, parts with the same reference numerals perform similar operations, and redundant explanations will be omitted as appropriate. One embodiment will be described below with reference to the drawings.

[0009] Figure 1 is a block diagram showing an example configuration of a magnetic resonance imaging apparatus 1 according to this embodiment. As shown in Figure 1, the magnetic resonance imaging apparatus 1 includes a stand 11, a bed 13, a gradient magnetic field power supply 21, a transmitting circuit 23, a receiving circuit 25, a bed drive device 27, a sequence control circuit 29, and a medical information processing device (host computer) 50.

[0010] The mounting base 11 includes a static magnetic field magnet 41 and a gradient magnetic field coil 43. The static magnetic field magnet 41 and the gradient magnetic field coil 43 are housed in the casing of the mounting base 11. The casing of the mounting base 11 has a hollow bore. A transmitting coil 45 and a receiving coil 47 are arranged inside the bore of the mounting base 11.

[0011] The static magnetic field magnet 41 has a hollow, approximately cylindrical shape and generates a static magnetic field inside the approximately cylindrical body. For example, a permanent magnet, a superconducting magnet, or a normal conducting magnet can be used as the static magnetic field magnet 41. Here, the central axis of the static magnetic field magnet 41 is defined as the Z-axis, the axis perpendicular to the Z-axis is defined as the Y-axis, and the axis perpendicular to the Z-axis horizontally is defined as the X-axis. The X-axis, Y-axis, and Z-axis constitute an orthogonal three-dimensional coordinate system.

[0012] The gradient magnetic field coil 43 is mounted inside the static magnetic field magnet 41 and is a hollow, substantially cylindrical coil unit. The gradient magnetic field coil 43 generates a gradient magnetic field by receiving current from the gradient magnetic field power supply 21. More specifically, the gradient magnetic field coil 43 has three coils corresponding to the mutually orthogonal X, Y, and Z axes. These three coils form a gradient magnetic field in which the magnetic field strength changes along each of the X, Y, and Z axes. The gradient magnetic fields along each of the X, Y, and Z axes are combined to form mutually orthogonal frequency-encoded gradient magnetic field Gr, phase-encoded gradient magnetic field Gp, and slice-selection gradient magnetic field Gs in the desired direction. The frequency-encoded gradient magnetic field Gr is used to change the frequency of the magnetic resonance signal (hereinafter referred to as the MR signal) according to the spatial position. The phase-encoded gradient magnetic field Gp is ​​used to change the phase of the MR signal according to the spatial position. The slice-selection gradient magnetic field Gs is used to arbitrarily determine the imaging cross-section (slice). In the following explanation, the gradient direction of the frequency-encoded gradient magnetic field Gr is assumed to be the X-axis, the gradient direction of the phase-encoded gradient magnetic field Gp is ​​assumed to be the Y-axis, and the gradient direction of the slice-selection gradient magnetic field Gs is assumed to be the Z-axis.

[0013] The gradient power supply 21 supplies current to the gradient coil 43 according to the sequence control signal from the sequence control circuit 29. By supplying current to the gradient coil 43, the gradient power supply 21 generates gradient magnetic fields along the X, Y, and Z axes. These gradient magnetic fields are superimposed on the static magnetic field formed by the static magnetic field magnet 41 and applied to the subject P.

[0014] The transmitting coil 45 is, for example, positioned inside the gradient magnetic field coil 43 and receives current from the transmitting circuit 23 to generate high-frequency pulses (hereinafter referred to as RF pulses).

[0015] The transmitting circuit 23 supplies current to the transmitting coil 45 in order to apply an RF pulse to the subject P via the transmitting coil 45 in order to excite the target proton present in the subject P. The RF pulse oscillates at a resonant frequency unique to the target proton, thereby exciting the target proton. An MR signal is generated from the excited target proton and detected by the receiving coil 47. The transmitting coil 45 is, for example, a whole-body coil (WB coil). A whole-body coil may also be used as a transmitting and receiving coil.

[0016] The receiving coil 47 receives MR signals emitted from target protons present in the subject P in response to the RF pulse. The receiving coil 47 has multiple receiving coil elements capable of receiving MR signals. The received MR signals are supplied to the receiving circuit 25 via wired or wireless connection. Although not shown in Figure 1, the receiving coil 47 has multiple receiving channels implemented in parallel. Each receiving channel has a receiving coil element that receives the MR signal and an amplifier that amplifies the MR signal. The MR signal is output for each receiving channel. The total number of receiving channels and the total number of receiving coil elements may be the same, or the total number of receiving channels may be greater than or less than the total number of receiving coil elements.

[0017] The receiving circuit 25 receives the MR signal generated from the excited target proton via the receiving coil 47. The receiving circuit 25 processes the received MR signal to generate a digital MR signal. The digital MR signal can be represented in k-space, which is defined by the spatial frequency. Therefore, the digital MR signal will be referred to as k-space data below. k-space data is an example of an MR acquisition signal. The k-space data is supplied to the medical information processing device 50 via wired or wireless connection.

[0018] The transmitting coil 45 and receiving coil 47 described above are merely examples. Instead of the transmitting coil 45 and receiving coil 47, a transmitting and receiving coil equipped with both transmitting and receiving functions may be used. Furthermore, the transmitting coil 45, receiving coil 47, and the transmitting and receiving coil may be combined.

[0019] A bed 13 is installed adjacent to the gantry 11. The bed 13 has a top plate 131 and a base 133. The subject P is placed on the top plate 131. The base 133 supports the top plate 131 so as to be slidable along each of the X-axis, Y-axis, and Z-axis. A bed drive device 27 is housed in the base 133. The bed drive device 27 moves the top plate 131 in response to control from the sequence control circuit 29. The bed drive device 27 may include any motor such as a servo motor or a stepping motor.

[0020] The sequence control circuit 29 has, as hardware resources, a processor such as a CPU (Central Processing Unit) or MPU (Micro Processing Unit) and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The sequence control circuit 29 synchronously controls the gradient magnetic field power supply 21, the transmission circuit 23, and the reception circuit 25 based on the data collection conditions set by the processing circuit 51, subjects the subject P to data collection according to the data collection conditions, and collects k-space data regarding the subject P. The sequence control circuit 29 is an example of a sequence control unit.

[0021] The sequence control circuit 29 according to this embodiment executes data collection for magnetic resonance spectroscopy (hereinafter referred to as MRS), which is a type of chemical shift measurement. Chemical shift measurement is a technique for measuring chemical shift, which is a minute difference in the resonance frequency of target protons such as hydrogen atomic nuclei that occurs according to differences in chemical environments. MRS has a single voxel method for collecting data for a single voxel and a multi-voxel method for collecting data for multiple voxels, and this embodiment is applicable to any of these methods. The multi-voxel method is also called chemical shift imaging (CSI) or MRS imaging (MRSI). Note that the voxels in the measurement target region are also called voxels of interest (VOI). In this embodiment, for example, the two-dimensional region and the voxels of interest specified by MRSI are also included in the region of interest (ROI).

[0022] The sequence control circuit 29 executes data collection for MRS on the subject P. By executing data collection for MRS, a free induction decay (FID) signal or a spin echo signal is generated from the voxel of interest of the subject P. The reception circuit 25 receives the FID signal or the spin echo signal via the reception coil 47, signal-processes the received FID signal or spin echo signal, and collects k-space data regarding the voxel of interest. The k-space data to be collected is assumed to be digital data representing the signal intensity value emitted from the voxel of interest as a function of time. The pulse sequence for MRS is repeated the number of excitation (NEX) times, and k-space data for the number of excitations is collected. Hereinafter, the k-space data collected by MRS will be referred to as MRSk data. MRSk data is an example of an MRS signal.

[0023] In this embodiment, the LASER (localization by adiabatic selective refocusing) method is used as the MRS pulse sequence. Hereafter, the MRS pulse sequence using the LASER method will also be referred to as the LASER pulse sequence.

[0024] As shown in Figure 1, the medical information processing device 50 is a computer having a processing circuit 51, memory 53, display 55, input interface 57, and communication interface 59.

[0025] The processing circuit 51 has a processor such as a CPU as a hardware resource. The processing circuit 51 functions as the central hub of the magnetic resonance imaging apparatus 1. For example, the processing circuit 51 realizes setting functions 511, design functions 512, and acquisition functions 513 by executing various programs.

[0026] The processing circuit 51 sets the Region of Interest (ROI) using the setting function 511. The processing circuit 51, using the design function 512, designs the pulse sequence by designing it so that at least a portion of the first crusher gradient magnetic field applied after the first refocus pulse and the second crusher gradient magnetic field applied before the second refocus pulse after the first refocus pulse overlap, based on the LASER pulse sequence. The acquisition function 513 allows the processing circuit 51 to control the sequence control circuit 29 and execute the pulse sequence designed by the design function 512, thereby acquiring the MRS signal in the region of interest.

[0027] Memory 53 is a storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or integrated circuit memory that stores various types of information. Alternatively, memory 53 may be a drive device that reads and writes various types of information to and from portable storage media such as CD-ROM drives, DVD drives, or flash memory. For example, memory 53 stores previously collected medical data, MRS signals, control programs, etc.

[0028] The display 55 displays various information. As the display 55, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in the art can be used as appropriate.

[0029] The input interface 57 includes an input device that receives various commands from the user. Possible input devices include keyboards, mice, various switches, touchscreens, and touchpads. However, the input device is not limited to those with physical operating components such as mice and keyboards. For example, an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device separate from the magnetic resonance imaging apparatus 1 and outputs the received electrical signals to various circuits is also an example of the input interface 57. Furthermore, the input interface 57 may also be a speech recognition device that converts audio signals collected by a microphone into instruction signals.

[0030] The communication interface 59 is an interface that connects the magnetic resonance imaging apparatus 1 to workstations, PACS (Picture Archiving and Communication System), HIS (Hospital Information System), RIS (Radiology Information System), etc., via a LAN (Local Area Network) or the like. The communication interface 59 transmits and receives various types of information between the connected workstation, PACS, HIS, and RIS.

[0031] Next, an example of the operation of the magnetic resonance imaging apparatus 1 according to this embodiment will be described with reference to the flowchart in Figure 2. In step SA1, the processing circuit 51 sets a region of interest for the subject using the setting function 511. For example, the 3D region to be measured can be set by user input via the input interface 57. Alternatively, the processing circuit 51 may automatically set the region of interest depending on the imaging target area, case, etc.

[0032] In step SA2, the processing circuit 51, using the design function 512, designs the pulse sequence by adjusting the time interval between refocus pulses and the crusher gradient magnetic field in the LASER pulse sequence according to the size of the region of interest. The crusher gradient magnetic field is a gradient magnetic field applied to reduce or eliminate residual transverse magnetization. Specific examples of the pulse sequence design method will be described later with reference to Figure 3 and subsequent figures.

[0033] In step SA3, the processing circuit 51, using the acquisition function 513, acquires the MRS signal by executing the pulse sequence designed in step SA2. The processing circuit 51 displays the spectrum based on the acquired MRS signal on a display 55 or the like. The pulse sequence is repeatedly executed to acquire the MRS signal, and the number of times the pulse sequence is repeated can be determined, for example, based on the number of times the MRS signal is integrated.

[0034] Next, a first design example of the pulse sequence according to this embodiment will be described with reference to Figure 3. Figure 3 is a pulse sequence diagram for a first design example, which uses six adiabatic pulses as refocus pulses, similar to the LASER pulse sequence. From top to bottom, it shows the sequences of RF, x-axis gradient magnetic field Gx, y-axis gradient magnetic field Gy, z-axis gradient magnetic field Gz, and MRS signal.

[0035] After applying the excitation pulse 31, the region of interest is localized in the x, y, and z axes using six refocus pulses 32, thereby collecting the MRS signal shown in the bottom row. In the example in Figure 3, for the sake of explanation, the refocus pulses 32 are numbered from "Refocus Pulse 1" to "Refocus Pulse 6" according to the order in which they are applied. Furthermore, the time interval between the excitation pulse 21 and refocus pulse 1 is defined as "Time Interval T0", the time interval between refocus pulse 1 and refocus pulse 2 as "Time Interval T1", the time interval between refocus pulse 2 and refocus pulse 3 as "Time Interval T2", the time interval between refocus pulse 3 and refocus pulse 4 as "Time Interval T3", the time interval between refocus pulse 4 and refocus pulse 5 as "Time Interval T4", the time interval between refocus pulse 5 and refocus pulse 6 as "Time Interval T5", and the time interval between refocus pulse 6 and the MRS signal as "Time Interval T6".

[0036] As shown in Figure 3, the processing circuit 51, using the design function 512, designs a crusher gradient magnetic field 33 in which at least a portion of the first crusher gradient magnetic field applied after the first refocus pulse and the second crusher gradient magnetic field applied before the second refocus pulse immediately following the first refocus pulse overlap. Specifically, during a time interval T1, a crusher gradient magnetic field 33 is applied in which the first crusher gradient magnetic field and the second crusher gradient magnetic field overlap (combined into one). For example, during the time interval T1 between refocus pulse 1 and refocus pulse 2, one crusher gradient magnetic field 33 is applied to each axis. During the time interval T3 between refocus pulse 3 and refocus pulse 4, one crusher gradient magnetic field 33 is applied to the x axis and z axis, respectively. During the time interval T5 between refocus pulse 5 and refocus pulse 6, one crusher gradient magnetic field 33 is applied to each axis.

[0037] In the example shown in Figure 3, time intervals T3 and T5 also show the design of a single crusher gradient magnetic field 33. However, two first and two second crusher gradient magnetic fields may be placed independently at time intervals T3 and T5 without overlap. In other words, in the pulse sequence shown in Figure 3, it is sufficient to design at least one crusher gradient magnetic field 33 in which at least a portion of the first and second crusher gradient magnetic fields overlap.

[0038] Furthermore, the design function 512 causes the processing circuit 51 to design time intervals T2 and T4 to be shorter than any of time intervals T1, T3, and T5, or shorter than the average value of time intervals T1, T3, and T5. Time intervals T2 and T4 are designed to satisfy a temporal constraint from the excitation pulse 31 until the MRS signal is collected. The temporal constraint is that the sum of the time intervals T0, T2, T4, and T6 is equal to the sum of the time intervals T1, T3, and T5. This sum can also be expressed as half the echo time (TE / 2). Furthermore, as shown in Figure 3, the design function 512 causes the processing circuit 51 to continuously apply the region-selection gradient magnetic field 34 for refocus pulses 2 and 3 at a time interval T2. Similarly, the design function 512 causes the processing circuit 51 to continuously apply the region-selection gradient magnetic field 34 for refocus pulses 4 and 5 at a time interval T4.

[0039] Specifically, the x-axis gradient magnetic field Gx is designed to continuously apply the region-selection gradient magnetic field 34 for a time interval T2. Similarly, the y-axis gradient magnetic field Gy is designed to continuously apply the region-selection gradient magnetic field 34 for a time interval T4.

[0040] In other words, a combined gradient magnetic field is applied at time intervals T2 and T4, which combines the crusher gradient magnetic fields that should be applied. That is, the region-selection gradient magnetic field 34 can be said to be applied in a combined state, combining the crusher gradient magnetic field that should be applied after the refocus pulse 2 and the crusher gradient magnetic field that should be applied before the refocus pulse 3. By doing so, the time required to apply the crusher gradient magnetic field at time intervals T2 and T4 can be shortened while reducing or eliminating residual transverse magnetization, thereby shortening the echo time (TE).

[0041] Furthermore, for refocus pulse 1 and refocus pulse 6, a gradient magnetic field 35 for region selection is applied in accordance with refocus pulse 1 and refocus pulse 6, similar to the general LASER method, and a crusher gradient magnetic field is applied before and after the refocus pulse (before and after the gradient magnetic field 35).

[0042] Furthermore, the processing circuit 51 may design the time intervals T2 and T4 according to the required strength of the crusher gradient magnetic field using the design function 512. For example, if the size of the region of interest is large, the strength of the crusher gradient magnetic field will be higher (the area will be larger in the pulse sequence), so at least one of the time intervals T2 and T4 should be designed to be longer. Specifically, if the region of interest is 1 cm for the y and z axes and 2.5 cm for the x axis, the length of the region of interest on the x axis is longer than that of the other axes, so in the example in Figure 3, the time interval T2 should be designed to be longer than the time interval T4 for the gradient magnetic field Gx on the x axis. Furthermore, the processing circuit 51 may design the gradient magnetic field 35 using the design function 512 such that the axis with the longest axial length of the region of interest is excited by the refocus pulse 1 and refocus pulse 6 using a general LASER method for region selection.

[0043] When the processing circuit 51 adjusts the time intervals T2 and T4 according to the size of the region of interest using the design function 512, a lower limit may be set on the size of the region of interest to avoid a situation where the time intervals T2 and T4 are too short and the transverse magnetization cannot be sufficiently eliminated. Furthermore, when the processing circuit 51 sets a lower limit on the time intervals T2 and T4 using the design function 512 and adjusts the time intervals T2 and T4 according to the size of the region of interest, even if it is possible to set the time intervals T2 and T4 shorter than the lower limit, the processing circuit 51 may set the time intervals T2 and T4 to the lower limit.

[0044] Note that time intervals T0 to T6 may be different time intervals. Alternatively, at least one set of time intervals T1, T3, and T5 may be the same time interval. Time intervals T2 and T4 may be the same time interval.

[0045] Next, a second example of setting the MRS pulse sequence according to this embodiment will be described with reference to Figure 4. A smaller crusher gradient magnetic field 40 may be added to the MRS pulse sequence shown in Figure 3. In the example in Figure 4, a smaller crusher gradient magnetic field 40 is designed to be applied before and after refocus pulses 2 and 4, respectively. This allows for further reduction or elimination of residual transverse magnetization and suppression of unwanted signals.

[0046] Next, a third example of setting the MRS pulse sequence according to this embodiment will be described with reference to Figure 5. The MRS pulse sequence shown in Figure 5 is based on the pulse sequence of the MEGA-LASER method, which includes the MEGA pulse, a frequency-selective pulse.

[0047] When using the MEGA pulse 70, the design function 512 is used to design the processing circuit 51 to apply the MEGA pulse 70 (180-degree pulse) without applying a gradient magnetic field between the refocus pulse 3 and the refocus pulse 4, and after the refocus pulse 6. By calculating the difference signal between a pulse sequence including the MEGA pulse 70 shown in Figure 5 and a pulse sequence without the MEGA pulse 70, as shown in Figure 3 or Figure 4, it is possible to improve the identification accuracy for some types of molecules (e.g., GABA) that have signals for different frequency shift values.

[0048] Furthermore, the processing circuit 51 may use the design function 512 to set the pulse length of each adiabatic pulse used as refocus pulses 1 to 6 to, for example, 2.6 milliseconds to 3.4 milliseconds. Also, the pulse bandwidth of the adiabatic pulse may be designed to be, for example, between 2.0 kilohertz (kHz) and 5 kilohertz (kHz).

[0049] According to the embodiment described above, the first crusher gradient magnetic field applied after the first refocus pulse and the second crusher gradient magnetic field applied before the second refocus pulse after the first refocus pulse are designed to overlap by at least a portion of each. Furthermore, the time interval T2 between the second and third refocus pulses, and the time interval T4 between the fourth and fifth refocus pulses are designed to be shorter than the time intervals T1, T3, and T5 between the other refocus pulses. This allows for the use of two refocus pulses in each of the x, y, and z axes, without reducing the number of refocus pulses to four, as in semi-LASER. This reduces the echo time (TE) of the pulse sequence while maintaining high excitation accuracy.

[0050] In the above description, the term "processor" refers to circuits such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an Application Specific Integrated Circuit (ASIC), or a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). When the processor is a CPU, for example, it performs its functions by reading and executing a program stored in a memory circuit. On the other hand, when the processor is an ASIC, for example, instead of the program being stored in a memory circuit, the function is directly incorporated as a logic circuit within the processor's circuit. In this embodiment, each processor is not limited to being configured as a single circuit; multiple independent circuits may be combined to form a single processor and perform its functions. Furthermore, multiple components shown in the figure may be integrated into a single processor to perform its functions.

[0051] In addition, each function according to the embodiment can also be realized by installing a program that performs the processing on a computer such as a workstation and loading it into memory. In this case, the program that can cause the computer to execute the method can also be stored and distributed on a storage medium such as a magnetic disk (hard disk, etc.), optical disk (CD-ROM, DVD, etc.), or semiconductor memory.

[0052] 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 can be made 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]

[0053] 1. Magnetic Resonance Imaging System 11. Stand 13 berths 21 Gradient magnetic field power supply 23 Transmitter Circuit 25 Receiving Circuit 27 Bed drive mechanism 29 Sequence control circuit 31 Excitation pulse 32 Refocus Pulses 33,40 Crusher gradient magnetic field 34. Gradient magnetic fields for region selection 35 Gradient magnetic field 41 Static magnetic field magnet 43. Gradient field coil 45 Transmitter coil 47 Receiving coil 50 Medical Information Processing Devices 51 Processing Circuit 53 memory 55 displays 57 Input Interfaces 59 Communication Interface 70 MEGA pulses 131 Top plate 133 Base 511 Settings function 512 Design functions 513 Collection function

Claims

1. A design unit designs a pulse sequence based on a LASER (localization by adiabatic selective refocusing) pulse sequence containing six refocus pulses, such that at least a portion of the first crusher gradient magnetic field applied after the first refocus pulse and the second crusher gradient magnetic field applied before the second refocus pulse following the first refocus pulse overlap. A magnetic resonance imaging apparatus comprising: an acquisition unit that acquires a magnetic resonance spectroscopy signal by executing the designed pulse sequence; The first refocus pulse is the second and fourth refocus pulses among the six refocus pulses. The second refocus pulse is the third and fifth refocus pulses among the six refocus pulses. The time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse are shorter than the time intervals between other refocus pulses. Magnetic resonance imaging device.

2. The magnetic resonance imaging apparatus according to claim 1, wherein the design unit continuously applies, as the first crusher gradient magnetic field and the second crusher gradient magnetic field, region-selection gradient magnetic fields for the second refocus pulse and the third refocus pulse during the time interval between the second refocus pulse and the third refocus pulse.

3. The magnetic resonance imaging apparatus according to claim 1, wherein the design unit continuously applies, as the first crusher gradient magnetic field and the second crusher gradient magnetic field, a gradient magnetic field for region selection with respect to the fourth refocus pulse and the fifth refocus pulse, during the time interval between the fourth refocus pulse and the fifth refocus pulse.

4. The magnetic resonance imaging apparatus according to claim 1, wherein the design unit designs the time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse, such that the time interval increases as the required crusher intensity increases.

5. The magnetic resonance imaging apparatus according to claim 1, wherein the design unit designs the time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse to be longer as the axial size of the region of interest increases.

6. The magnetic resonance imaging apparatus according to any one of claims 1 to 5, wherein the design unit adjusts the time interval between refocus pulses in the LASER pulse sequence and the first crusher gradient magnetic field and the second crusher gradient magnetic field according to the size of the region of interest.

7. The magnetic resonance imaging apparatus according to any one of claims 1 to 5, wherein the design unit applies a MEGA pulse, which is a frequency-selective pulse, between the third and fourth refocus pulses and after the sixth refocus pulse among the six refocus pulses.

8. The magnetic resonance imaging apparatus according to any one of claims 1 to 5, wherein each of the six refocus pulses is set to have a pulse length between 2.6 milliseconds and 3.4 milliseconds and is designed to have a pulse bandwidth between 2 kilohertz and 5 kilohertz.

9. A magnetic resonance imaging method performed in a magnetic resonance imaging apparatus, The design means designs a pulse sequence based on a LASER (localization by adiabatic selective refocusing) pulse sequence including six refocus pulses, such that at least a portion of the first crusher gradient magnetic field applied after the first refocus pulse and the second crusher gradient magnetic field applied before the second refocus pulse following the first refocus pulse overlap. A magnetic resonance imaging method comprising an acquisition means that acquires a magnetic resonance spectroscopy signal by executing the designed pulse sequence, The first refocus pulse is the second and fourth refocus pulses among the six refocus pulses. The second refocus pulse is the third and fifth refocus pulses among the six refocus pulses. The time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse are shorter than the time intervals between other refocus pulses. Magnetic resonance imaging method.

10. The magnetic resonance imaging method according to claim 9, wherein the design means continuously applies a region-selection gradient magnetic field for the second refocus pulse and the third refocus pulse as the first crusher gradient magnetic field and the second crusher gradient magnetic field, during the time interval between the second refocus pulse and the third refocus pulse.

11. The magnetic resonance imaging method according to claim 9, wherein the design means continuously applies a region-selection gradient magnetic field for the fourth refocus pulse and the fifth refocus pulse as the first crusher gradient magnetic field and the second crusher gradient magnetic field, during the time interval between the fourth refocus pulse and the fifth refocus pulse.

12. The magnetic resonance imaging method according to claim 9, wherein the design means is designed such that the time interval between the second refocus pulse and the third refocus pulse and the time interval between the fourth refocus pulse and the fifth refocus pulse become longer as the required crusher intensity increases.

13. The magnetic resonance imaging method according to claim 9, wherein the design means is designed to increase the length of the time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse, as the axial size of the region of interest increases.

14. On the computer, A design function that designs a pulse sequence based on a LASER (localization by adiabatic selective refocusing) pulse sequence containing six refocus pulses, such that at least a portion of the first crusher gradient magnetic field applied after the first refocus pulse and the second crusher gradient magnetic field applied before the second refocus pulse following the first refocus pulse overlap, A program that implements an acquisition function for acquiring magnetic resonance spectroscopy signals by executing the aforementioned designed pulse sequence, The first refocus pulse is the second and fourth refocus pulses among the six refocus pulses. The second refocus pulse is the third and fifth refocus pulses among the six refocus pulses. The time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse are shorter than the time intervals between other refocus pulses. program.

15. The program according to claim 14, wherein the design function continuously applies, as the first crusher gradient magnetic field and the second crusher gradient magnetic field, a gradient magnetic field for region selection with respect to the second refocus pulse and the third refocus pulse, during the time interval between the second refocus pulse and the third refocus pulse.

16. The program according to claim 14, wherein the design function continuously applies, as the first crusher gradient magnetic field and the second crusher gradient magnetic field, a gradient magnetic field for region selection with respect to the fourth refocus pulse and the fifth refocus pulse, during the time interval between the fourth refocus pulse and the fifth refocus pulse.

17. The program according to claim 14, wherein the design function designs the time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse, such that the time interval increases as the required crusher intensity increases.

18. The program according to claim 14, wherein the design function designs the length of the time interval between the second refocus pulse and the third refocus pulse, and the time interval between the fourth refocus pulse and the fifth refocus pulse to be longer as the axial size of the region of interest increases.

Images