Magnetic resonance imaging apparatus, hyperpolarized signal acquisition method, and hyperpolarized signal acquisition program

Abstract

To achieve acquisition of data capable of improving reliability of information acquired on the basis of a super-polarized signal while suppressing attenuation of an MR signal from nuclides in a super-polarized state.SOLUTION: A magnetic resonance imaging device includes an acquisition unit and a magnetic field control unit. In a period from the excitation of a first nuclide in a super-polarized state to a point before the acquisition of a first magnetic resonance signal from the first nuclide, the acquisition unit excites a second nuclide in a non-super-polarized state different from the first nuclide, and acquires a second magnetic resonance signal from the second nuclide. The magnetic field control unit makes both a first total sum indicating a total sum of an amount of application of a gradient magnetic field related to the excitation of the second nuclide and a second total sum indicating a total sum of an amount of application of a gradient magnetic field related to the acquisition of the second magnetic resonance signal close to zero before the acquisition of the first magnetic resonance signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments disclosed in the present specification and drawings relate to a magnetic resonance imaging apparatus, a method for acquiring a hyperpolarized signal, and a program for acquiring a hyperpolarized signal. [Background technology]

[0002] Conventionally, magnetic resonance imaging (MRI) devices acquire magnetic resonance signals (MR signals) from hyperpolarized nuclei (probes). A hyperpolarized state is a state in which the distribution of spin numbers occupying the nuclear spin energy levels of atomic nuclei corresponding to their orientation with respect to a static magnetic field is extremely biased compared to the distribution at thermal equilibrium (Boltzmann distribution). Imaging methods based on MR signals from hyperpolarized nuclei (hyperpolarized signals) (also known as hyperpolarized MRI) are molecular imaging techniques that enable the acquisition of dynamic metabolic information and physiological processes.

[0003] The hyperpolarized signal is dramatically increased compared to the MR signal from non-hyperpolarized nuclides. However, the hyperpolarized signal decays at a rate that depends on the T1 (spin-lattice relaxation time) of the hyperpolarized nuclides. Furthermore, if the acquisition position of the hyperpolarized signal shifts beyond the spatial resolution of the hyperpolarized signal due to the effects of pulsation and / or respiratory motion in the subject, the reliability of metabolic information acquired based on the hyperpolarized signal may be reduced. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2018-514795 Summary of the Invention [Problem to be solved by the invention]

[0005] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to obtain data that can improve the reliability of information obtained based on hyperpolarized signals while suppressing attenuation of MR signals from hyperpolarized nuclides. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0006] A magnetic resonance imaging apparatus according to an embodiment includes an acquisition unit and a magnetic field control unit. The acquisition unit excites a second nuclide in a non-hyperpolarized state different from the first nuclide during a period from excitation of a first nuclide in a hyperpolarized state until acquisition of a first magnetic resonance signal from the first nuclide, and acquires a second magnetic resonance signal from the second nuclide. The magnetic field control unit causes both a first sum indicating the sum of applied amounts of gradient magnetic fields related to the excitation of the second nuclide and a second sum indicating the sum of applied amounts of gradient magnetic fields related to acquisition of the second magnetic resonance signal to approach zero before acquisition of the first magnetic resonance signal. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing an example of a magnetic resonance imaging apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a hyperpolarized navigator sequence for one excitation of a hyperpolarized nuclide according to the embodiment. [Figure 3] FIG. 3 is a diagram showing an example of a hyperpolarized navigator sequence according to a first modified example of the embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a hyperpolarized navigator sequence according to a second modified example of the embodiment. [Figure 5] FIG. 5 is a diagram showing an example in which the balance of slice selection gradient magnetic fields relating to reception of navigator echoes is changed according to a third modified example of the embodiment. [Figure 6]Figure 6 is a diagram showing an example of a sequence in which a flop pulse and a preceding flop pulse for protons are applied to the subject P simultaneously without slice selection when the spin echo method is used as the navigator sequence, according to a fourth modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A magnetic resonance imaging (MRI) device, a hyperpolarized signal acquisition method, and a hyperpolarized signal acquisition program will be described below with reference to the drawings. Note that the technical concept of this embodiment may be applied to other devices that control the MRI device, such as a sequencer (sequence control device), and various modalities combined with an MRI device, such as a PET (Positron Emission Tomography)-MRI device or a SPECT (single photon emission computed tomography)-MRI device.

[0009] (Embodiment) Fig. 1 is a diagram showing an example of an MRI apparatus 100 according to this embodiment. As shown in Fig. 1, the MRI apparatus 100 includes a static magnetic field magnet 101, a gradient magnetic field coil 103, a gradient magnetic field power supply 105, a bed 107, a bed control circuit 109, a transmission circuit 113, a transmission coil 115, a reception coil 117, a reception circuit 119, a sequence control circuit (which may also be referred to as an imaging control circuit, an imaging control unit, or the like) 121, a system control circuit (system control unit) 123, a memory 125, an input interface 127, a display 129, and a processing circuit 131.

[0010] The static magnetic field magnet 101 is a magnet formed in a hollow, approximately cylindrical shape. The static magnetic field magnet 101 generates a substantially uniform static magnetic field in the internal space. For example, a superconducting magnet or the like is used as the static magnetic field magnet 101.

[0011] The gradient coil 103 is a hollow, approximately cylindrical coil and is disposed on the inner surface of the cylindrical cooling vessel. The gradient coil 103 receives current individually from a gradient power supply 105 to generate gradient magnetic fields whose magnetic field strength varies along the mutually orthogonal X, Y, and Z axes. The gradient magnetic fields of the X, Y, and Z axes generated by the gradient coil 103 form, for example, a slice-selective gradient magnetic field, a phase-encoding gradient magnetic field, and a frequency-encoding gradient magnetic field. The slice-selective gradient magnetic field is used to arbitrarily determine an imaging slice. The phase-encoding gradient magnetic field is used to change the phase of a magnetic resonance signal (hereinafter referred to as an MR (Magnetic Resonance) signal) according to a spatial position. The frequency-encoding gradient magnetic field is used to change the frequency of the MR signal according to a spatial position.

[0012] The gradient magnetic field power supply 105 is a power supply device that supplies current to the gradient magnetic field coil 103 under the control of the sequence control circuit 121 .

[0013] The bed 107 is a device equipped with a top plate 1071 on which the subject P is placed. The bed 107 inserts the top plate 1071 on which the subject P is placed into the bore 111 under the control of a bed control circuit 109.

[0014] The bed control circuit 109 is a circuit that controls the bed 107. The bed control circuit 109 drives the bed 107 in response to instructions from the operator via the input / output interface 17, thereby moving the tabletop 1071 in the longitudinal direction, the up-down direction, and in some cases the left-right direction.

[0015] Under the control of the sequence control circuit 121, the transmission circuit 113 supplies radio frequency pulses modulated at the Larmor frequency to the transmission coil 115. For example, the transmission circuit 113 includes an oscillator, a phase selection unit, a frequency conversion unit, an amplitude modulation unit, an RF (Radio Frequency) amplifier, and the like. The oscillator generates an RF pulse at a resonance frequency specific to the target atomic nucleus in a static magnetic field. The phase selection unit selects the phase of the RF pulse generated by the oscillator. The frequency conversion unit converts the frequency of the RF pulse output from the phase selection unit. The amplitude modulation unit modulates the amplitude of the RF pulse output from the frequency conversion unit according to, for example, a sinc function. The RF amplifier amplifies the RF pulse output from the amplitude modulation unit and supplies it to the transmission coil 115.

[0016] The transmission coil 115 is an RF coil arranged inside the gradient magnetic field coil 103. In response to the output from the transmission circuit 113, the transmission coil 115 generates an RF pulse corresponding to a high frequency magnetic field.

[0017] The receiving coil 117 is an RF coil arranged inside the gradient magnetic field coil 103. The receiving coil 117 receives MR signals emitted from the subject P by a high frequency magnetic field. The receiving coil 117 outputs the received MR signals to a receiving circuit 119. The receiving coil 117 is, for example, a coil array having one or more, typically a plurality of coil elements (hereinafter referred to as a plurality of coils). For the sake of concreteness, the receiving coil 117 will be described below as a coil array having a plurality of coils.

[0018] 1, the transmit coil 115 and the receive coil 117 are depicted as separate RF coils, but the transmit coil 115 and the receive coil 117 may be implemented as an integrated transmit / receive coil. The transmit / receive coil corresponds to the imaging region of the subject P and is, for example, a local transmit / receive RF coil such as a head coil.

[0019] The receiving circuit 119 generates a digital MR signal (hereinafter referred to as MR data) based on the MR signal output from the receiving coil 117 under the control of the sequence control circuit 121. Specifically, the receiving circuit 119 performs signal processing such as detection and filtering on the MR signal output from the receiving coil 117, and then performs analog-to-digital (A / D) conversion (hereinafter referred to as A / D conversion) on the data that has undergone this signal processing to generate MR data. The receiving circuit 119 outputs the generated MR data to the sequence control circuit 121. For example, the MR data is generated in each of a plurality of coils and output to the sequence control circuit 121 together with a tag that identifies each of the plurality of coils.

[0020] The sequence control circuit 121 controls the gradient magnetic field power supply 105, the transmission circuitry 113, the reception circuitry 119, etc. in accordance with the imaging protocol output from the processing circuitry 15 to perform imaging of the subject P. The imaging protocol has a pulse sequence according to the type of examination. The imaging protocol defines the magnitude of the current supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the timing at which the gradient magnetic field power supply 105 supplies the current to the gradient magnetic field coil 103, the magnitude and time width of the radio frequency pulse supplied to the transmission coil 115 by the transmission circuitry 113, the timing at which the radio frequency pulse is supplied to the transmission coil 115 by the transmission circuitry 113, the timing at which the MR signal is received by the reception coil 117, etc. The sequence control circuit 121 drives the gradient magnetic field power supply 105, the transmission circuitry 113, the reception circuitry 119, etc. to image the subject P, and then receives MR data from the reception circuitry 119 and transfers the received MR data to the processing circuitry 131.

[0021] For the sake of specificity, the pulse sequence executed by the sequence control circuit 121 is assumed to be a pulse sequence (hereinafter referred to as a hyperpolarized navigator sequence) that acquires a hyperpolarized signal generated by a first nuclide in a hyperpolarized state and a navigator echo that detects the body movement of the subject P. The hyperpolarized state is a state in which the distribution of the number of spins occupying the energy levels of the nuclear spins of atomic nuclei corresponding to the orientation state with respect to the static magnetic field is extremely biased compared to the distribution (Boltzmann distribution) at thermal equilibrium. The hyperpolarized navigator sequence is a pulse sequence that acquires, for example, a first magnetic resonance signal (hereinafter referred to as a hyperpolarized signal) related to metabolic information of the subject P from a first nuclide in a hyperpolarized state (hereinafter referred to as a hyperpolarized nuclide), and also excites a second nuclide in the subject P to acquire a second magnetic resonance signal (hereinafter referred to as a navigator echo) from the protons after excitation of the hyperpolarized nuclide in the hyperpolarized state and before acquisition of the hyperpolarized signal. The second nuclide is, for example, a proton (hydrogen atom). For the sake of concreteness, the following description will be given assuming that the second nuclide is a proton. The hyperpolarized navigator sequence will be described in detail later.

[0022] Hyperpolarized nuclides include, for example, carbon 12 It is an isotope of C 13 C. The hyperpolarized nuclide is 13 The hyperpolarized nuclide is not limited to C, and can be appropriately selected depending on the purpose of the examination on the subject P. The hyperpolarized nuclide is generated by a known hyperpolarization device and injected into the subject P before the execution of the hyperpolarized navigator sequence. 13 The hyperpolarized navigator sequence to acquire hyperpolarized signals using C is 13 The hyperpolarized navigator sequence includes a sequence related to magnetic resonance spectroscopy (MR spectroscopy: MRS) that non-invasively acquires metabolic information in a subject P using C. The pulse sequence for acquiring hyperpolarized signals in the hyperpolarized navigator sequence will be briefly described as being a double spin echo method.

[0023] Note that the pulse sequence for acquiring a hyperpolarized signal in the hyperpolarized navigator sequence is not limited to the double spin echo method, and any pulse sequence may be used as long as it is capable of acquiring a hyperpolarized signal. Furthermore, the sequence for acquiring a navigator echo in the hyperpolarized navigator sequence (hereinafter referred to as the navigator sequence) may be any known method, such as the spin echo method, the field echo method (gradient echo method), or the pencil beam method. Hereinafter, for the sake of specificity, the navigator sequence will be described as being the field echo method.

[0024] The sequence control circuit 121 has, as hardware resources, a processor, memories such as a ROM (Read-Only Memory) and a RAM (Random Access Memory), etc. The term "processor" refers to circuits such as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), an Application Specific Integrated Circuit (ASIC), 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)). The sequence control circuit 121 corresponds to a sequence control unit.

[0025] The sequence control circuit 121 reads out programs related to the acquisition function 21 and the magnetic field control function 23 from its own memory or from a memory 125 described below. The sequence control circuit 121 controls the transmission circuit 113 and the gradient magnetic field power supply 105 in accordance with the read out programs. In this way, the sequence control circuit 121 executes the hyperpolarized navigator sequence.

[0026] The sequence control circuit 121 (or processor) that realizes the acquisition function 21 excites protons and acquires navigator echoes from the protons during the period from the excitation of hyperpolarized nuclei in a hyperpolarized state until the acquisition of a hyperpolarized signal from the hyperpolarized nuclei. The acquisition function 21 controls the transmission circuit 113 to apply multiple RF pulses to the hyperpolarized nuclei. The RF pulses applied to the hyperpolarized nuclei include, for example, a flip pulse (also called an excitation pulse) that excites the hyperpolarized nuclei and multiple flop pulses (also called refocus pulses) that refocus the spins of the hyperpolarized nuclei.

[0027] The acquisition function 21 excites protons between two adjacent flop pulses among the plurality of flop pulses, and acquires a navigator echo. Specifically, the acquisition function 21 excites protons between the application of two gradient magnetic fields related to the application of the plurality of flop pulses, and acquires a navigator echo. More specifically, the acquisition function 21 acquires a hyperpolarized signal after a flop pulse among the plurality of flop pulses that is applied after the acquisition of the navigator echo. The sequence control circuit 121 that realizes the acquisition function 21 corresponds to an acquisition unit.

[0028] The sequence control circuit 121 (or processor) realizing the magnetic field control function 23 brings both a first sum indicating the sum of the applied amount of the gradient magnetic field for proton excitation and a second sum indicating the sum of the applied amount of the gradient magnetic field for acquiring (collecting) navigator echoes closer to zero before the acquisition of a hyperpolarized signal. The applied amount of the gradient magnetic field corresponds to a value obtained by integrating the strength of the gradient magnetic field over the application period of the gradient magnetic field. In other words, the first sum corresponds to a value obtained by adding up, over the number of applications of the gradient magnetic field for proton excitation, a value (also referred to as a gradient moment) obtained by integrating the strength of the gradient magnetic field for proton excitation over the period during which the gradient magnetic field is applied for proton excitation. Furthermore, the second sum corresponds to a value obtained by adding up, over the number of applications of the gradient magnetic field for acquiring the navigator echo, a value obtained by integrating the strength of the gradient magnetic field for acquiring (collecting) navigator echoes over the period during which the gradient magnetic field is applied for acquiring the navigator echoes.

[0029] That is, the magnetic field control function 23 controls the gradient magnetic field power supply 105 so that both the first sum and the second sum approach zero before the hyperpolarized signal is acquired. Since the strengths of the gradient magnetic fields in the first sum and the second sum are set in advance according to the imaging protocol, the magnetic field control function 23 controls, for example, the application time of the gradient magnetic fields in the first sum and the second sum. Note that the magnetic field control function 23 may also control the gradient magnetic field power supply 105 so that both the first sum and the second sum approach zero before the application of the last flop pulse among multiple flop pulses. Preferably, both the first sum and the second sum are zero. In this case, the magnetic field control function 23 controls the gradient magnetic field power supply 105 to make both the first sum and the second sum zero. The sequence control circuit 121 that realizes the magnetic field control function 23 corresponds to a magnetic field control unit.

[0030] The system control circuit 123 has hardware resources such as a processor, memories such as ROM and RAM, and uses a system control function to control the MRI apparatus 100. Specifically, the system control circuit 123 reads a system control program stored in the memory, expands it on the memory, and controls each circuit of the MRI apparatus 100 according to the expanded system control program.

[0031] For example, the system control circuit 123 reads out an imaging protocol from the memory 125 based on imaging conditions input by the operator via the input interface 127. The system control circuit 123 transmits the imaging protocol to the sequence control circuit 121 and controls imaging of the subject P. The system control circuit 123 is realized by, for example, a processor. The system control circuit 123 may be incorporated into the processing circuit 131. In this case, the system control function is executed by the processing circuit 131, and the processing circuit 131 functions as a substitute for the system control circuit 123. The processor that realizes the system control circuit 123 is similar to that described above, and therefore a description thereof will be omitted.

[0032] The memory 125 stores various programs related to the system control functions executed in the system control circuit 123, various imaging protocols, imaging conditions including a plurality of imaging parameters that define the imaging protocols, etc. The memory 125 also stores the acquisition function 21 and the magnetic field control function 23 realized by the sequence control circuit 121, and the interface function 33 and the image generation function 35 realized by the processing circuit 131 in the form of a program executable by a computer.

[0033] The memory 125 also stores various data acquired by the acquisition function 21, various data used in the processing performed by the image generation function 35, and MR images generated by the image generation function 35. The memory 125 also stores MR data acquired by scanning the subject P and an algorithm for reconstructing an MR image based on the MR data.

[0034] The memory 125 may store various data received via a communication interface (not shown). For example, the memory 125 stores information about an examination order for the subject P (such as a region to be imaged, a purpose of the examination, etc.) received from an information processing system in a medical institution, such as a Radiology Information System (RIS).

[0035] The memory 125 is realized by, for example, a semiconductor memory element such as a ROM, a RAM, or a flash memory, a hard disk drive (HDD), a solid state drive (SSD), an optical disk, etc. The memory 125 may also be realized by a drive device that reads and writes various information from and to a portable storage medium such as a CD (Compact Disc)-ROM drive, a DVD (Digital Versatile Disc) drive, or a flash memory.

[0036] The input interface 127 accepts various instructions and information input from an operator. The input interface 127 may be realized by, for example, a trackball, a switch button, a mouse, a keyboard, a touchpad that performs input operations by touching the operation surface, a touchscreen that integrates a display screen and a touchpad, a non-contact input circuit using an optical sensor, and a voice input circuit. The input interface 127 is connected to the processing circuitry 131, converts input operations received from the operator into electrical signals, and outputs the electrical signals to the processing circuitry 131.

[0037] In this specification, the input interface 127 is not limited to an interface having physical operation parts such as a mouse, a keyboard, etc. For example, an example of the input interface 127 also includes an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the MRI apparatus 100 and outputs this electrical signal to a control circuit.

[0038] The input interface 127 inputs an FOV in response to a user instruction for the pre-scan image displayed on the display 129. Specifically, the input interface 127 inputs an FOV in response to a user instruction to set a range in a locator image displayed on the display 129. The input interface 127 also inputs various imaging parameters related to the scan and an instruction to select a pulse sequence in response to a user instruction based on an examination order.

[0039] The display 129 displays various GUIs (Graphical User Interfaces), MR images generated by the processing circuitry 131, and the like under the control of the processing circuitry 131 or the system control circuitry 123. The display 129 also displays imaging parameters related to scans and various information related to image processing. The display 129 is realized by, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display or monitor known in the art.

[0040] The processing circuitry 131 is realized by, for example, the above-mentioned processor. The processing circuitry 131 includes an interface function 33, an image generation function 35, and the like. The processing circuitry 131 that realizes the interface function 33 and the image generation function 35, respectively, corresponds to an interface unit and an image generation unit. Each function, such as the interface function 33 and the image generation function 35, is stored in the memory 125 in the form of a program executable by a computer. For example, the processing circuitry 131 realizes the function corresponding to each program by reading and executing the program from the memory 125. In other words, the processing circuitry 131 in a state in which each program has been read has each function, such as the interface function 33 and the image generation function 35.

[0041] In the above description, an example has been described in which the "processor" reads and executes a program corresponding to each function from memory 125, but the embodiment is not limited to this. If the processor is, for example, a CPU, the processor realizes the function by reading and executing a program stored in memory 125. On the other hand, if the processor is an ASIC, instead of storing a program in memory 125, the function is directly incorporated into the processor circuit as a logic circuit. Note that each processor in this embodiment is not limited to being configured as a single circuit per processor, and multiple independent circuits may be combined to configure a single processor and realize its function. Furthermore, while the description has been given assuming that a single storage circuit stores a program corresponding to each processing function, multiple storage circuits may be distributed and the processing circuit 131 may read the corresponding program from each individual storage circuit.

[0042] The processing circuitry 131 transmits information related to the hyperpolarized navigator sequence to the sequence control circuitry 121 via the interface function 33, and receives MR data related to the hyperpolarized signal (hereinafter referred to as hyperpolarized data) from the sequence control circuitry 120. Upon receiving the hyperpolarized data, the interface function 33 stores the received hyperpolarized data in the memory 125. Furthermore, upon receiving MR data related to the navigator echo (hereinafter referred to as navigator data) from the sequence control circuitry 120, the interface function 33 stores the navigator data in the memory 125.

[0043] The processing circuitry 131 uses the navigator data to perform motion correction on the hyperpolarized data using the image generation function 35, generating an image relating to the metabolism of hyperpolarized nuclides (hereinafter referred to as a hyperpolarized image). Motion correction of the hyperpolarized data associated with motion of the subject P is performed using the navigator data. Motion correction of the hyperpolarized data can be performed using various known techniques as appropriate, and therefore a description thereof will be omitted.

[0044] FIG. 2 is a diagram showing an example of a hyperpolarized navigator sequence HPNS for one excitation of hyperpolarized nuclei. FIG. 2 is not a strict sequence diagram but a schematic diagram. For convenience of explanation, FIG. 2 shows the hyperpolarized navigator sequence HPNS separated into a navigator sequence NS and a sequence for acquiring (collecting) hyperpolarized signals (hereinafter referred to as a hyperpolarized sequence) HPS. That is, in an actual hyperpolarized navigator sequence HPNS, the RF pulses, gradient magnetic fields (Gx, Gy, Gz), and echo signals related to hyperpolarized nuclei (hereinafter referred to as collection echo) related to the navigator sequence NS and the hyperpolarized sequence HPS are arranged on the same axis.

[0045] 2, in the RF pulse, the gradient magnetic field (Gx, Gy, Gz), and the collected echo signal, multiple horizontal axes along the time axis indicate an intensity of 0. The upper region of each of the multiple horizontal axes corresponds to a region of positive intensity, and the lower region of each of the multiple horizontal axes corresponds to a region of negative intensity.

[0046] 2, in the hyperpolarization sequence HPS, the RF pulse has one flip pulse NFI and two flop pulses (NFO1, NFO2). For convenience of explanation, the flop pulse that is applied to the subject P earlier in time of the two flop pulses (NFO1, NFO2) will be referred to as the earlier flop pulse NFO1. Also, the flop pulse that is applied to the subject P later in time of the two flop pulses (NFO1, NFO2) will be referred to as the later flop pulse NFO2.

[0047] 2, a slice selection gradient magnetic field Gz is applied to the subject P together with a flip pulse NFI under the control of the sequence control circuit 121. After the application of the flip pulse NFI, a phase encoding gradient magnetic field Gy and a frequency encoding gradient magnetic field Gx are applied to the subject P under the control of the sequence control circuit 121.

[0048] As shown in FIG. 2, in the double spin echo method, RF pulses, an early flop pulse NFO1 and a late flop pulse NFO2, are applied to the subject P after a flip pulse NFI. A pair of slice selection gradient magnetic fields Gz1 are applied to the subject P before and after the early flop pulse NFO1. In addition, a pair of slice selection gradient magnetic fields Gz2 are applied to the subject P before and after the late flop pulse NFO2. Of the pair of slice selection gradient magnetic fields (Gz1, Gz2), the gradient magnetic field that is earlier in time is used to select slices to which the two flop pulses (NFO1, NFO2) are applied. In addition, of the pair of slice selection gradient magnetic fields (Gz1, Gz2), the gradient magnetic field that is later in time is used to restore the spin state changed by the gradient magnetic field applied for slice selection.

[0049] 2, after application of the subsequent slice-selective gradient magnetic field of a pair of slice-selective gradient magnetic fields Gz2 associated with the subsequent flop pulse NFO2, the sequence control circuit 121 executes an acquisition sequence HPC for acquiring hyperpolarized signals. In the double spin echo method, the acquisition sequence is executed according to, for example, a flyback readout trajectory. Since a known method can be applied to the flyback readout trajectory, a description thereof will be omitted. After execution of the flyback readout trajectory, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to apply a spoiler pulse to the subject P in the acquisition sequence HPC.

[0050] 2, after application of the leading slice selection gradient magnetic field of a pair of slice selection gradient magnetic fields Gz1 associated with the leading flop pulse NFO1, the sequence control circuit 121 controls the transmission circuit 113 to apply to the subject P a flip pulse HFI corresponding to the excitation of protons associated with the navigator echo NE. At the same time, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to generate a slice selection gradient magnetic field SSGz associated with the flip pulse HFI. In addition, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to bring a first sum of the strengths of the gradient magnetic fields in the slice selection gradient magnetic fields SSGz, i.e., a first sum of the application amounts of the gradient magnetic fields associated with the excitation of protons, closer to zero. Preferably, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to bring the first sum to zero.

[0051] 2, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to generate, for example, a phase encoding gradient magnetic field PEGy in relation to the reception of the navigator echo NE. In addition, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to bring a second sum of the strengths of the gradient magnetic fields in the phase encoding gradient magnetic field PEGy, i.e., a second sum of the application amounts of the gradient magnetic fields in relation to the acquisition of the navigator echo, closer to zero. Preferably, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to bring the second sum to zero.

[0052] 2, the sequence control circuit 121 controls the acquisition function 21 to excite protons between two flop pulses and acquire a navigator echo NE. At this time, the sequence control circuit 121 controls the gradient magnetic field power supply 105 using the magnetic field control function 23 so that both the first sum and the second sum approach zero, preferably so that both the first sum and the second sum become zero. More specifically, the sequence control circuit 121 controls the gradient magnetic field power supply 105 using the acquisition function 21 so that protons are excited between a pair of slice selection gradient magnetic fields Gz2 related to the subsequent flop pulse NFO2 and a navigator echo NE is acquired. Furthermore, the sequence control circuit 121 controls the acquisition function 21 to acquire a hyperpolarized signal after the subsequent flop pulse NFO2 after the acquisition of the navigator echo NE.

[0053] 2, the application period of the gradient magnetic field during excitation of hyperpolarized nuclei, the application period of the gradient magnetic field related to the collection of first magnetic resonance signals (hereinafter referred to as the hyperpolarized signal collection period), the application period of the gradient magnetic field during excitation of protons (hereinafter referred to as the proton excitation period), and the application period of the gradient magnetic field related to the collection of second magnetic resonance signals (hereinafter referred to as the navigator echo collection period) are all non-overlapping with one another. That is, the sequence control circuit 121 controls the gradient magnetic field power supply 105 by the magnetic field control function 23 so that the proton excitation period, the hyperpolarized signal collection period, and the navigator echo collection period are all non-overlapping and the first sum and the second sum approach (set to) zero, as shown in FIG.

[0054] The sequence control circuit 121 may control the gradient magnetic field power supply 105 to generate spoiler pulses for the navigator echo NE after the execution of the acquisition sequence HPC, i.e., after the acquisition of the hyperpolarized signal. This causes the acquisition function 21 to generate spoiler pulses for the acquisition of the navigator echo NE after the acquisition of the hyperpolarized signal.

[0055] The MRI apparatus 100 according to the embodiment described above excites protons and acquires navigator echoes NE from the protons during the period from application of a flip pulse to hyperpolarized nuclides until execution of the acquisition sequence HPC, and causes both the first sum and the second sum to approach zero before acquisition of a hyperpolarized signal. Preferably, in the hyperpolarized navigator sequence HPNS, both the first sum and the second sum are zero. Specifically, in this MRI apparatus 100, the multiple RF pulses applied to the hyperpolarized nuclides include a flip pulse and two flop pulses, and the MRI apparatus 100 excites protons and acquires navigator echoes NE between the two flop pulses.

[0056] Furthermore, the MRI apparatus 100 according to the embodiment excites protons and acquires a navigator echo NE between the application of two gradient magnetic fields related to the application of two flop pulses. Furthermore, the MRI apparatus 100 has a hyperpolarized signal acquisition period, a proton excitation period, and a navigator echo acquisition period that do not overlap with one another. Specifically, the MRI apparatus 100 acquires a hyperpolarized signal after the application of the subsequent flop pulse NFO2. At this time, the MRI apparatus 100 may cause the first summation and the second summation to approach zero before the application of the subsequent flop pulse NFO2. Furthermore, the MRI apparatus 100 generates a spoiler pulse related to the acquisition of the navigator echo after the acquisition of the hyperpolarized signal.

[0057] For these reasons, the MRI apparatus 100 according to the embodiment can acquire a navigator echo NE by making both the first sum and the second sum approach zero between a pair of slice-selective gradient magnetic fields Gz2 associated with the subsequent flop pulse NFO2. This allows the navigator echo NE to be acquired while minimizing loss in the intensity of the hyperpolarized signal. That is, the MRI apparatus 100 can acquire a hyperpolarized signal and a navigator echo NE without the application of a gradient magnetic field associated with the acquisition of the subsequent navigator echo NE contributing as a spoiler to the spins of hyperpolarized nuclei, and without the application of a gradient magnetic field associated with the acquisition of a hyperpolarized signal contributing as a spoiler to the spins of protons. For these reasons, even when there is a positional displacement exceeding the spatial resolution associated with the acquisition of a hyperpolarized signal due to the influence of pulsation or respiratory motion, the reliability of metabolic information in a hyperpolarized image can be improved by correcting the body motion of the hyperpolarized signal using the navigator echo NE.

[0058] In addition, as shown in FIG. 2, the MRI apparatus 100 performs excitation of hyperpolarized nuclides and acquisition of navigator echoes (proton excitation and collection of navigator echoes) in parallel, thereby making it possible to acquire a navigator echo immediately before collection of hyperpolarized signals. Therefore, the MRI apparatus 100 can improve the accuracy of body motion correction of the subject P for hyperpolarized data. Furthermore, the hyperpolarized navigator sequence HPNS in the MRI apparatus 100 requires ensuring time (hereinafter referred to as the navigator acquisition period) for inserting a sequence for acquiring navigator echoes NE. However, if the navigator acquisition period exists in a known hyperpolarized signal acquisition sequence, it is possible to generate a hyperpolarized image with improved reliability of metabolic information without extending the hyperpolarized signal acquisition time.

[0059] (First Modification) This modified example involves acquiring navigator echoes NE multiple times during the period from after application of the leading slice selection gradient magnetic field Gz2 of a pair of slice selection gradient magnetic fields Gz2 related to the trailing flop pulse NFO2 to before application of the trailing flop pulse NFO2 (hereinafter referred to as the navigator sequence insertion period).

[0060] FIG. 3 is a diagram showing an example of a hyperpolarized navigator sequence HPNS in the first modified example. FIG. 3 is a schematic diagram, not a strict sequence diagram. In FIG. 3, the navigator sequence NS indicates that a sequence 1NS for acquiring one navigator echo is repeated a required number of times. The required number of times is set in advance based on the navigator insertion period and the time required for sequence 1NS for acquiring one navigator echo. As shown in FIG. 3, according to the MRI apparatus 100 in the first modified example, multiple navigator echoes are acquired for acquiring a hyperpolarized signal.

[0061] According to the MRI apparatus 100 of the first modification, it is possible to perform body motion correction using the navigator echo immediately before acquiring the hyperpolarized signal, thereby further improving the reliability of metabolic information in the hyperpolarized image. Other effects of this modification are similar to those of the embodiment, and therefore will not be described here.

[0062] (Second Modification) This modification uses the spin echo method as a sequence for acquiring a navigator echo in the hyperpolarized navigator sequence HPNS.

[0063] FIG. 4 is a diagram showing an example of a hyperpolarized navigator sequence HPNS in the second modified example. FIG. 4 is a schematic diagram, not a strict sequence diagram. In FIG. 4, the navigator sequence NS applies RF pulses for proton excitation during a period from application of a flip pulse NFI to application of a flop pulse NFO1. More specifically, after application of the leading slice selective gradient magnetic field of a pair of slice selective gradient magnetic fields Gz1 related to the leading flop pulse NFO1, the sequence control circuit 121 controls the transmission circuitry 113 to apply a flip pulse HFI to the subject P. At the same time, the sequence control circuit 121 controls, for example, the gradient magnetic field power supply 105 to generate a frequency encoding gradient magnetic field FEGx related to the flip pulse HFI.

[0064] 4, the sequence control circuit 121 controls the gradient magnetic field power supply 105 so as to make the sum of the intensities of the gradient magnetic fields in the frequency encoding gradient magnetic field FEGx approach zero. Preferably, the sequence control circuit 121 controls the gradient magnetic field power supply 105 so as to make the sum zero.

[0065] 4, after application of the frequency encoding gradient magnetic field FEGx, the sequence control circuit 121 controls the transmission circuit 113 to apply a flop pulse HFO for protons to the subject P. At the same time, the sequence control circuit 121 controls, for example, the gradient magnetic field power supply 105 to generate a phase encoding gradient magnetic field PEGy related to the flop pulse HFO. In addition, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to make the sum of the intensities of the gradient magnetic fields in the phase encoding gradient magnetic field PEGy approach zero.

[0066] 4, the sequence control circuit 121 preferably controls the gradient magnetic field power supply 105 by the magnetic field control function 23 so as to set this sum to zero. That is, the sequence control circuit 121 controls the gradient magnetic field power supply 105 so as to set both the sum of the intensities of the gradient magnetic fields in the frequency encoding gradient magnetic field FEGx related to the flip pulse HFI for protons and the sum of the intensities of the gradient magnetic fields in the phase encoding gradient magnetic field PEGy related to the flop pulse HFO for protons to zero. The sum of the intensities of the gradient magnetic fields in the frequency encoding gradient magnetic field FEGx related to the flip pulse HFI for protons and the sum of the intensities of the gradient magnetic fields in the phase encoding gradient magnetic field PEGy related to the flop pulse HFO for protons correspond to the first sum.

[0067] 4, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to generate, for example, a slice selection gradient magnetic field SSGz in relation to the reception of the navigator echo NE. In addition, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to bring a second sum of the strengths of the gradient magnetic fields in the slice selection gradient magnetic field SSGz, i.e., a second sum of the application amounts of the gradient magnetic fields in relation to the acquisition of the navigator echo, closer to zero. Preferably, the sequence control circuit 121 controls the gradient magnetic field power supply 105 to bring the second sum to zero.

[0068] In this modification, unlike the embodiment, excitation of protons (flip pulse HFI and flop pulse HFO) is performed between application of the leading slice selective gradient magnetic field of a pair of slice selective gradient magnetic fields Gz1 related to the leading flop pulse NFO1 and application of the leading flop pulse NFO1. Next, a navigator echo NE is acquired between application of the leading flop pulse NFO1 and application of the trailing slice selective gradient magnetic field of a pair of slice selective gradient magnetic fields Gz1 related to the leading flop pulse NFO1. That is, according to this modification, even if the excitation of protons is different from that of the embodiment, a navigator echo NE can be acquired. Other effects of this modification are similar to those of the embodiment, and therefore description thereof will be omitted.

[0069] (Third Modification) In this modification, the sum (second sum) of the gradient magnetic fields applied simultaneously to acquire (receive) the navigator echo NE is not set to zero, but is set to an unbalanced state (the second sum is non-zero). The hyperpolarized state of hyperpolarized nuclides transitions to a non-hyperpolarized state over time from the time the hyperpolarized state is generated. As a result, the intensity of the hyperpolarized signal from the hyperpolarized nuclides decays over time. The balance of the intensity of the gradient magnetic fields applied simultaneously to acquire the navigator echo NE is changed so as to suppress the intensity of the hyperpolarized signal that decays over time. For example, the sequence control circuit 121 controls the gradient magnetic field power supply 105 by using the magnetic field control function 23 to set the second sum to a non-zero value so as to suppress the decay of the intensity of the hyperpolarized signal.

[0070] Fig. 5 is a diagram showing an example in which the balance of the slice-selective gradient magnetic field SSGz relating to the reception of the navigator echo NE in Fig. 4 is changed. Fig. 5 is not a strict sequence diagram but a schematic diagram. As shown in Fig. 5, at the rear end AG of the slice-selective gradient magnetic field SSGz, the sum of the intensities of the slice-selective gradient magnetic fields is larger than that in Fig. 4. The sequence control circuit 121 adjusts, for example, the intensity of the gradient magnetic field at the rear end AG using the magnetic field control function 23.

[0071] As a result, in this modification, it is possible to suppress the intensity of the hyperpolarized signal, which decays over time. The second summation can be adjusted as appropriate to suppress the intensity of the hyperpolarized signal, which decays over time. As a result, this modification can suppress the decay over time of the intensity of the hyperpolarized signal, thereby further improving the reliability of metabolic information in hyperpolarized images. Other effects of this modification are similar to those of the embodiment, and therefore will not be described here.

[0072] (Fourth Modification) In this modification, a flop pulse HFO for proton excitation and a preceding flop pulse NFO1 for hyperpolarized nuclei are simultaneously applied to the subject P without slice selection. For example, when the hyperpolarized nuclei are13 C, the sequence control circuit 121 controls the acquisition function 21 to, for example, 13 A conduit pulse that simultaneously excites hyperpolarized nuclides and protons is applied to the subject P. The application of the conduit pulse is performed without slice selection. Note that simultaneous excitation of hyperpolarized nuclides and protons is not limited to a composite pulse, and various known methods can be applied.

[0073] 6 is a diagram showing an example of a sequence in which a flop pulse HFO and a preceding flop pulse NFO1 for protons are simultaneously applied to the subject P without slice selection when the spin echo method is used as the navigator sequence NS. FIG. 6 is not a strict sequence diagram but a schematic diagram. As shown in FIG. 6, the sequence control circuit 121 controls the transmission circuit 113 so that, for example, the acquisition function 21 generates flop pulses for protons and hyperpolarized nuclides with simultaneous excitation and without slice selection. As a result, the acquisition function 21 simultaneously excites hyperpolarized nuclides and protons.

[0074] According to the MRI apparatus 100 of this modification, for example, when the spin echo technique is applied as the navigator sequence NS, the flop pulse HFO and the preceding flop pulse NFO1 for protons can be applied to the subject P simultaneously without slice selection. Therefore, according to the MRI apparatus 100 of this modification, for example, the navigator acquisition period can be shortened, and the hyperpolarized navigator sequence HPNS can be executed without increasing the imaging time. Since other effects of this modification are similar to those of the embodiment, description thereof will be omitted.

[0075] In the above-described embodiments and modifications, the waveform of the gradient magnetic field to be controlled by the magnetic field control function 23 has been described as being continuous in time as shown in Fig. 2 to Fig. 6, but is not limited to this. That is, the waveform of the gradient magnetic field to be controlled may be discontinuous in time, in other words, separated in time.

[0076] When the technical idea of ​​the embodiments is realized in a hyperpolarized signal acquisition method, the hyperpolarized signal acquisition method excites a first nuclide in a hyperpolarized state, excites a second nuclide in a non-hyperpolarized state different from the first nuclide during a period before a first magnetic resonance signal (hyperpolarized signal) from the first nuclide is acquired, brings a first sum indicating the sum of applied amounts of gradient magnetic fields related to the excitation of the second nuclide closer to zero before the first magnetic resonance signal is acquired, acquires a second magnetic resonance signal (navigator echo) from the second nuclide, brings a second sum indicating the sum of applied amounts of gradient magnetic fields related to the acquisition of the second magnetic resonance signal closer to zero before the first magnetic resonance signal is acquired, and acquires the first magnetic resonance signal after bringing the second sum closer to zero. The processing procedures and effects of this hyperpolarized signal acquisition method are similar to those described in the embodiments, and therefore will not be described again.

[0077] When the technical idea of ​​the embodiment is realized by a hyperpolarized signal acquisition program, the hyperpolarized signal acquisition program causes a computer to control the transmission circuitry 113 to excite a first nuclide in a hyperpolarized state, control the transmission circuitry 113 to excite a second nuclide in a non-hyperpolarized state different from the first nuclide during a period before a first magnetic resonance signal (hyperpolarized signal) from the first nuclide is acquired, control the gradient magnetic field power supply 105 to make a first sum indicating the sum of the applied amounts of gradient magnetic fields related to the excitation of the second nuclide approach zero before the first magnetic resonance signal is acquired, control the gradient magnetic field power supply 105 to acquire a second magnetic resonance signal from the second nuclide, control the gradient magnetic field power supply 105 to make a second sum indicating the sum of the applied amounts of gradient magnetic fields related to the acquisition of the second magnetic resonance signal approach zero before the first magnetic resonance signal is acquired, and control the gradient magnetic field power supply 105 to acquire the first magnetic resonance signal after the second sum has approached zero.

[0078] For example, the hyperpolarized signal acquisition method can be realized by installing a hyperpolarized signal acquisition program in the MRI apparatus 100 or a modality having the MRI apparatus 100 and expanding the program in memory. In this case, the program that can cause a computer to execute the method can also be stored and distributed on a storage medium such as a magnetic disk (such as a hard disk), an optical disk (such as a CD-ROM or DVD), or a semiconductor memory. The procedure and effects of the process for acquiring hyperpolarized signals and navigator echoes using the hyperpolarized signal acquisition program are the same as those in the embodiment, and therefore will not be described here.

[0079] According to at least one of the embodiments described above, it is possible to obtain data that can improve the reliability of information obtained based on hyperpolarized signals while suppressing attenuation of MR signals from hyperpolarized nuclides.

[0080] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various 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 modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0081] 21 Acquisition Function 23 Magnetic field control function 33 Interface Functions 35 Image generation function 100 Magnetic resonance imaging device 101 Static Magnetic Field Magnet 103 Gradient magnetic field coil 105 Gradient magnetic field power supply 107 Sleeper 109 Bed control circuit 111 Bore 113 Transmitting Circuit 115 Transmitting Coil 117 Receiving Coil 119 Receiving circuit 121 Sequence control circuit 123 System Control Circuit 125 memory 127 input interface 129 Display 131 Processing circuit

Claims

1. an acquisition unit that excites a second nuclide in a non-hyperpolarized state different from the first nuclide and acquires a second magnetic resonance signal from the second nuclide during a period from after excitation of a first nuclide in a hyperpolarized state until before acquisition of a first magnetic resonance signal from the first nuclide; a magnetic field control unit that controls the waveforms of the gradient magnetic fields so that a first sum indicating a sum of application amounts of the gradient magnetic fields related to the excitation of the second nuclide and a second sum indicating a sum of application amounts of the gradient magnetic fields related to the acquisition of the second magnetic resonance signal both approach zero before the acquisition of the first magnetic resonance signal; A magnetic resonance imaging apparatus comprising:

2. the plurality of RF pulses applied to the first nuclide include a flip pulse and a plurality of flop pulses; the acquiring unit acquires the second magnetic resonance signal between two adjacent flop pulses among the plurality of flop pulses.

2. The magnetic resonance imaging apparatus according to claim 1.

3. the acquisition unit excites the second nuclide and acquires the second magnetic resonance signal between applications of two gradient magnetic fields related to the application of the plurality of flop pulses.

3. The magnetic resonance imaging apparatus according to claim 2.

4. the acquiring unit acquires the first magnetic resonance signal after a flop pulse after acquiring the second magnetic resonance signal, among the plurality of flop pulses.

4. A magnetic resonance imaging apparatus according to claim 2 or 3.

5. the acquisition unit applies an RF pulse for exciting the second nuclide during a period from after application of the flip pulse to before application of the flop pulse; 3. The magnetic resonance imaging apparatus according to claim 2.

6. the magnetic field control unit causes the first sum and the second sum to approach zero before applying a final flop pulse among the plurality of flop pulses.

6. A magnetic resonance imaging apparatus according to claim 2.

7. the first sum and the second sum are both zero; 7. A magnetic resonance imaging apparatus according to claim 1.

8. an application period of a gradient magnetic field during excitation of the first nuclide, an application period of a gradient magnetic field related to acquisition of the first magnetic resonance signal, an application period of a gradient magnetic field during excitation of the second nuclide, and an application period of a gradient magnetic field related to acquisition of the second magnetic resonance signal are all non-overlapping with each other; 8. A magnetic resonance imaging apparatus according to claim 1.

9. the acquiring unit acquires the second magnetic resonance signal a plurality of times; 9. A magnetic resonance imaging apparatus according to claim 1.

10. the acquisition unit simultaneously performs excitation of the first nuclide and excitation of the second nuclide.

10. A magnetic resonance imaging apparatus according to claim 1.

11. the acquisition unit generates a spoiler pulse related to acquisition of the second magnetic resonance signal after acquisition of the first magnetic resonance signal; 11. A magnetic resonance imaging apparatus according to any one of claims 1 to 10.

12. the second nuclide is a proton; 12. A magnetic resonance imaging apparatus according to any one of claims 1 to 11.

13. Exciting the first species in a hyperpolarized state, exciting a second nuclide in a non-hyperpolarized state different from the first nuclide during a period before a first magnetic resonance signal is acquired from the first nuclide; before acquiring the first magnetic resonance signal, a first sum indicating a sum of application amounts of gradient magnetic fields related to excitation of the second nuclide is made to approach zero; acquiring a second magnetic resonance signal from the second nuclide; before the acquisition of the first magnetic resonance signal, a second sum indicating a sum of application amounts of gradient magnetic fields related to the acquisition of the second magnetic resonance signal is brought close to zero; acquiring the first magnetic resonance signal after making the second sum approach zero; A method for acquiring a hyperpolarized signal comprising:

14. On the computer, controlling a transmitter circuit to excite the first species in a hyperpolarized state; controlling the transmission circuit to excite a second nuclide in a non-hyperpolarized state different from the first nuclide during a period before a first magnetic resonance signal is acquired from the first nuclide; controlling a gradient magnetic field power supply so that a first sum indicating a sum of application amounts of gradient magnetic fields related to excitation of the second nuclide approaches zero before the first magnetic resonance signal is acquired; controlling the gradient power supply to acquire a second magnetic resonance signal from the second nuclide; controlling the gradient magnetic field power supply so that a second sum indicating a sum of application amounts of gradient magnetic fields related to acquisition of the second magnetic resonance signal approaches zero before acquisition of the first magnetic resonance signal; controlling the gradient magnetic field power supply to acquire the first magnetic resonance signal after making the second sum approach zero; A hyperpolarized signal acquisition program that realizes this.

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