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

Abstract

To acquire magnetic resonance data at high speed while reducing the effects of chemical shift. [Solution] The magnetic resonance imaging apparatus according to this embodiment includes a batch readout unit and a setting unit. The batch readout unit reads out magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space, in a batch without applying a refocus pulse, when reading out magnetic resonance data for imaging of a subject. The setting unit resets the reading position of the magnetic resonance data by applying the refocus pulse and performing phase encoding. The batch readout unit reads out the magnetic resonance data in a batch so that the total reading time for reading the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution.

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 magnetic resonance imaging program.

Background Art

[0002] Conventionally, there is a high-speed imaging method called echo planar imaging (hereinafter referred to as EPI) that collects all data in the k-space without a refocusing pulse (rephasing pulse). In EPI, since no refocusing pulse is used, the B0 shift including the chemical shift accumulates. Therefore, in EPI, chemical shift artifacts appear in the phase encoding direction.

[0003] Also, there is a high-speed imaging method called fast spin echo (hereinafter referred to as FSE). In FSE, a refocusing pulse is applied for each line along the frequency encoding direction in the k-space, and magnetic resonance data is collected. Therefore, in FSE, the B0 shift is reset for each collection of one line of magnetic resonance data. However, FSE requires a longer imaging time than EPI because of the application of the refocusing pulse.

[0004] Also, as another high-speed imaging method, there is GRASE (GRAdient and Spin Echo). GRASE is an imaging method that, for example, applies a refocusing pulse every N lines (N is a natural number of 2 or more) in the phase encoding direction and collects magnetic resonance data while interleaving. At this time, the B0 shift is reset for each collection of N lines of magnetic resonance data. GRASE is in an intermediate position between EPI and FSE.

[0005] EPI is necessary to quickly image a subject. However, EPI introduces a chemical shift in the phase encoding direction. Because this chemical shift causes fat to appear in separate pixels, a clean image cannot be obtained with EPI unless fat is suppressed. In other words, in normal EPI, the sampling period in the phase encoding direction is longer (slower) than the sampling period in the frequency encoding direction, so a chemical shift artifact dependent on the phase encoding direction appears in the magnetic resonance image. As mentioned above, the chemical shift artifact is reduced in GRASE compared to EPI because the sampling period in GRASE is inversely proportional to the interleaving factor (a factor that determines the alternating arrangement of readouts in the phase encoding direction).

[0006] However, even in GRASE, the sampling period in the phase encoding direction is shorter than that in the frequency encoding direction, so a chemical shift appears in the phase encoding direction. In GRASE, the fundamental reason for the short sampling period is that the total readout time in the frequency encoding direction (the time interval between two temporally adjacent refocus pulses) is too long. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-173397 [Overview of the project] [Problems that the invention aims to solve]

[0008] One of the problems that the embodiments disclosed herein and in the drawings aim to solve is to collect magnetic resonance data at high speed while reducing the effects of chemical shift. 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]

[0009] The magnetic resonance imaging apparatus according to this embodiment includes a batch readout unit and a setting unit. The batch readout unit reads magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space, in a batch without applying a refocus pulse during the reading of magnetic resonance data for imaging of a subject. The setting unit resets the reading position of the magnetic resonance data by applying the refocus pulse and performing phase encoding. The batch readout unit reads the magnetic resonance data in a batch so that the total reading time for reading the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a block diagram showing the configuration of an MRI apparatus according to an embodiment. [Figure 2] Figure 2 shows an example of reading MR data in a single batch according to an embodiment. [Figure 3] Figure 3 shows an example of FSE and EPI readout as a comparative example. [Figure 4] Figure 4 shows an example of sequence information (sequence) according to the embodiment. [Figure 5] Figure 5 is a flowchart showing an example of the procedure for sampling period reduction imaging according to the embodiment. [Modes for carrying out the invention]

[0011] The following describes embodiments of a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), a magnetic resonance imaging method, and a magnetic resonance imaging program with reference to the drawings. In principle, the contents described in each embodiment can also be applied to other embodiments. In the following embodiments, parts with the same reference numerals perform similar operations, and redundant explanations will be omitted as appropriate.

[0012] (Embodiment) Figure 1 is a block diagram showing the configuration of an MRI apparatus 100 according to an embodiment. As shown in Figure 1, the MRI apparatus 100 comprises a static magnetic field magnet 101, a static magnetic field power supply 102, a gradient magnetic field coil 103, a gradient magnetic field power supply 104, a patient table 105, a patient table control circuit 106, a transmitting coil 107, a transmitting circuit 108, a receiving coil 109, a receiving circuit 110, a sequence control circuit 120, and a computer 130 (also referred to as an image processing device). Note that the MRI apparatus 100 does not include a subject P (e.g., a human body). Furthermore, the configuration shown in Figure 1 is merely an example. For example, the parts within the sequence control circuit 120 and the computer 130 may be integrated or separated as appropriate.

[0013] The static magnetic field magnet 101 is a hollow, substantially cylindrical magnet that generates a static magnetic field in its internal space. The static magnetic field magnet 101 is, for example, a superconducting magnet and is excited by the supply of current from the static magnetic field power supply 102. The static magnetic field power supply 102 supplies current to the static magnetic field magnet 101. The static magnetic field magnet 101 may also be a permanent magnet, in which case the MRI device 100 does not need to have the static magnetic field power supply 102. The static magnetic field power supply 102 may also be provided separately from the MRI device 100.

[0014] The gradient coil 103 is a hollow, substantially cylindrical coil positioned inside the static magnetic field magnet 101. The gradient coil 103 is formed by combining three coils corresponding to the mutually orthogonal X, Y, and Z axes. These three coils receive current individually from the gradient power supply 104 to generate gradient magnetic fields whose magnetic field strength changes along the X, Y, and Z axes. The gradient magnetic fields in the X, Y, and Z axes generated by the gradient coil 103 are, for example, a slicing gradient magnetic field Gs, a phase encoding gradient magnetic field Ge, and a readout gradient magnetic field Gr. The gradient power supply 104 supplies current to the gradient coil 103.

[0015] The bed 105 is equipped with a top plate 105a on which the subject P is placed. Under the control of the bed control circuit 106, the top plate 105a is inserted into the cavity (imaging port) of the gradient magnetic field coil 103 with the subject P placed on it. Normally, the bed 105 is installed so that its longitudinal direction is parallel to the central axis of the static magnetic field magnet 101. Under the control of the computer 130, the bed control circuit 106 drives the bed 105 to move the top plate 105a in the longitudinal and vertical directions.

[0016] The transmitting coil 107 is positioned inside the gradient coil 103 and receives RF pulses from the transmitting circuit 108 to generate a high-frequency magnetic field. The transmitting circuit 108 supplies RF pulses to the transmitting coil 107 that correspond to the Larmor frequency, which is determined by the type of atom being targeted and the magnetic field strength.

[0017] The receiving coil 109 is positioned inside the gradient magnetic field coil 103 and receives magnetic resonance signals (hereinafter referred to as MR (Magnetic Resonance) signals) emitted from the subject P due to the influence of the high-frequency magnetic field. When the receiving coil 109 receives an MR signal, it outputs the received MR signal to the receiving circuit 110.

[0018] Note that the above-described transmission coil 107 and reception coil 109 are merely examples. The transmission coil 107 and reception coil 109 may be configured by combining one or more of a coil having only a transmission function, a coil having only a reception function, or a coil having both transmission and reception functions.

[0019] The reception circuit 110 detects the MR signal output from the reception coil 109 and generates MR data based on the detected MR signal. Specifically, the reception circuit 110 generates MR data by digitally converting the MR signal output from the reception coil 109. Further, the reception circuit 110 transmits the generated MR data to the sequence control circuit 120. Note that the reception circuit 110 may be provided on the gantry device side including the static magnetic field magnet 101, the gradient magnetic field coil 103, etc.

[0020] The sequence control circuit 120 performs imaging of the subject P by driving the gradient magnetic field power supply 104, the transmission circuit 108, and the reception circuit 110 based on the sequence information transmitted from the computer 130. Here, the sequence information is information that defines the procedure for performing imaging, and is also referred to as sequence conditions. The sequence information defines the strength of the current supplied by the gradient magnetic field power supply 104 to the gradient magnetic field coil 103 and the timing of supplying the current, the intensity of the RF pulse supplied by the transmission circuit 108 to the transmission coil 107 and the timing of applying the RF pulse, the timing at which the reception circuit 110 detects the MR signal, etc.

[0021] For example, the sequence control circuit 120 is an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA), or an electronic circuit such as a central processing unit (CPU) or a micro processing unit (MPU). The sequence control circuit 120 corresponds to the sequence control unit.

[0022] The sequence control circuit 120 drives the gradient magnetic field power supply 104, the transmission circuit 108, and the reception circuit 110 to image the subject P. After that, when the sequence control circuit 120 receives MR data from the reception circuit 110, it transfers the received MR data to the computer 130.

[0023] The computer 130 performs overall control of the MRI apparatus 100, generation of images, etc. The computer 130 includes a memory circuit 132, an input device 141, a display 143, and a processing circuit 150. The processing circuit 150 includes an interface function 131, a control function 133, a bulk read function 134, a setting function 136, a correction function 140, and an image generation function 142.

[0024] The memory circuit 132 stores the MR data received by the processing circuit 150 having the interface function 131, various data collected by the bulk read function 134 and the collection function 138, various image data generated by the image generation function 135, etc. Also, the memory circuit 132 stores the MR data arranged in the k-space (also referred to as k-space data) by the control function 133. For example, the memory circuit 132 is realized by a semiconductor memory element such as a RAM (Random Access Memory), a flash memory, a hard disk, an optical disk, etc. The memory circuit 132 may be referred to as a memory.

[0025] The input device 141 receives various instructions and information inputs from the user. The input device 141 is realized by, for example, a trackball, a switch button, a mouse, a keyboard, a touch pad that performs an input operation by touching an operation surface, a touch screen in which a display screen and a touch pad are integrated, a non-contact input circuit using an optical sensor, and a voice input circuit, etc. The input device 141 is electrically connected to the processing circuit 150, converts the input operation received from the user into an electrical signal, and outputs it to the processing circuit 150. The input device 141 corresponds to the input unit.

[0026] In this specification, the input device 141 is not limited to those equipped with physical operating components (input interfaces) such as a mouse or keyboard. For example, 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 device 100 and outputs this electrical signal to a control circuit is also included as an example of the input device 141. The input device 141 corresponds to the input section and may also be referred to as an input interface, operating device, etc.

[0027] The display 143, under the control of the processing circuit 150 having a control function 133, displays a GUI (Graphical User Interface) for accepting inputs such as imaging conditions, and images generated by the processing circuit 150 having an image generation function 142. The display 143 also displays the analysis results described later by the analysis function 137. The display 143 can be implemented by a display device such as a CRT display, liquid crystal display, organic EL display, LED display, plasma display, or any other display or monitor known in the art. The display 143 corresponds to the display unit.

[0028] The processing functions performed by the interface function 131, control function 133, batch read function 134, setting function 136, correction function 140, and image generation function 142 are stored in the memory circuit 132 in the form of programs that can be executed by the computer 130. The processing circuit 150 is a processor that reads the programs from the memory circuit 132 and executes them to realize the functions corresponding to each program. In other words, the processing circuit 150, in the state where each program has been read, will have the functions shown in the processing circuit 150 in Figure 1.

[0029] In Figure 1, the processing functions performed by the interface function 131, control function 133, batch readout function 134, setting function 136, correction function 140, and image generation function 142 are described as being realized by a single processing circuit 150. However, the processing circuit 150 may be configured by combining multiple independent processors, and each processor may realize the functions by executing a program. In other words, each of the above functions may be configured as a program, and one processing circuit 150 may execute each program, or a specific function may be implemented in a dedicated, independent program execution circuit.

[0030] In the above description, the term "processor" refers to circuits such as CPUs, GPUs (Graphical Processing Units), application-specific integrated circuits, and programmable logic devices (e.g., Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), and Field Programmable Gate Arrays (FPGAs)). The processor functions by reading and executing programs stored in the memory circuit 132.

[0031] Alternatively, instead of saving the program in the memory circuit 132, the program may be directly incorporated into the processor's circuitry. In this case, the processor functions by reading and executing the program incorporated into the circuitry. Similarly, the bed control circuit 106, transmission circuit 108, reception circuit 110, etc., are also composed of the above-mentioned processor and other electronic circuits.

[0032] The processing circuit 150 transmits sequence information to the sequence control circuit 120 via the interface function 131 and receives MR data from the sequence control circuit 120. Furthermore, when the processing circuit 150, which has the interface function 131, receives MR data, it stores the received MR data in the storage circuit 132. The processing circuit 150 that implements the interface function 131 corresponds to the interface section.

[0033] The processing circuit 150, through its control function 133, performs overall control of the MRI device 100, controlling imaging, image generation, image display, etc. For example, the processing circuit 150 with the control function 133 receives input of imaging conditions (imaging parameters, etc.) via a GUI and generates sequence information according to the received imaging conditions. The processing circuit 150 with the control function 133 also transmits the generated sequence information to the sequence control circuit 120. The sequence information related to this embodiment will be described later.

[0034] Hereafter, the three axes in k-space will be referred to as kx, ky, and kz. The processing circuit 150, using the batch readout function 134, batch reads out magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space, without applying a refocus pulse, when reading out magnetic resonance data for imaging of the subject P. The first direction is, for example, the kx direction in k-space. In this case, the second direction is the ky direction in k-space. Note that the first direction may also be, for example, the ky direction in k-space. In this case, the second direction will be the kx direction in k-space.

[0035] To make the explanation more concrete, the first direction will be assumed to be the kx direction and the second direction to be the ky direction. In this case, the batch readout function 134 reads out the MR data for the position along the kx direction and the position along the ky direction in a batch, without applying a refocus pulse after the refocus pulse has been applied.

[0036] In other words, the batch readout function 134 performs GRASE under conditions where, for example, the total readout time between two adjacent refocus pulses is small. Specifically, the batch readout function 134 slightly fluctuates the readout in the ky direction during GRASE.

[0037] In this embodiment, batch reading involves, for example, in a plane where there are 256 reading positions in the kx direction (kx=256) and 3 reading positions in the ky direction (ky=3), the reading positions are fluctuated in the ky direction. This fluctuation of the reading positions may be horizontal and vertical with respect to the kx direction, or it may be diagonal.

[0038] For example, in the batch readout in this embodiment, each of the multiple readout lines in k-space fluctuates in the ky direction and therefore has a predetermined width in the ky direction. That is, each of the multiple readout lines in this embodiment corresponds to several readout lines in the FSE. For this reason, the batch readout function 134 reads the MR data in a batch over a predetermined width corresponding to several readout lines in the FSE.

[0039] As a result, each of the multiple readout lines in this embodiment corresponds to several readout lines in the FSE, depending on the amplitude of the fluctuation in the ky direction. Furthermore, each of the multiple readout lines in this embodiment is treated in the same way as several readout lines in the FSE.

[0040] Each of the multiple readout lines in this embodiment is imaged in a k-space order similar to that of FSE (for example, if it is T1W (T1-weighted), it is imaged in a centric order (centric view ordering: a method of sequentially obtaining high-frequency phase encodings from the phase encodings of lines containing low-frequency components at the center of k-space), and if it is T2W (T2-weighted), it is imaged so that the desired TE (echo time) is positioned at the center of k-space.

[0041] Figure 2 shows an example of reading MR data in a single step. As shown in Figure 2, there are four MR data reading positions along the ky direction on a single readout line RL (for example, in the region including the center of k-space, ky = 0.5, 0, 1, 1.5). Note that the MR data reading positions in the ky direction are not limited to four points, but may be two to five points. Also, as shown in Figure 2, the MR data reading positions in the ky direction do not have to be equally spaced (a constant gradient).

[0042] The MR data readout line (hereinafter referred to as the readout line) is oscillated, for example, as shown in Figure 2, so that the sampling period of the MR data in the kx direction and the sampling period of the MR data in the ky direction are approximately the same. As a result, the shape of one readout line (frequency encoding direction) becomes zigzag (S-shaped or inverted S-shaped) so that the sampling periods in the kx and ky directions are approximately the same.

[0043] Furthermore, as shown in Figure 2, the diagonal directions with respect to the kx direction in a single readout line RL are not limited to two points (ky = -1.5, 0.5), but may be one or three points. Also, although the shape of the readout line RL shown in Figure 2 is angular, the actual MR data readout positions are set, for example, on a curve that is S-shaped along the kx direction. Note that the magnetic resonance data readout line formed by the first and second directions is not limited to an S-shape in k-space, but may also be an inverted S-shape. The magnetic resonance data readout line along an S-shape or inverted S-shape in k-space corresponds to frequency encoding. In addition, in Figure 2, half-integer grid points are set as MR data readout positions in addition to integer grid points in k-space. This can shorten the imaging time. Note that half-integer grid points are not essential as MR data readout positions and may be omitted.

[0044] The batch readout function 134 reads out magnetic resonance data in a batch so that the total readout time for reading the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution. The reference time is set in advance to a time that does not cause chemical shift to appear in the MR image. In the comparative example, FSE resets the phase error due to chemical shift with a refocus pulse each time. In the comparative examples GRASE and EPI, the phase error accumulates over the length of the readout time.

[0045] Figure 3 shows an example of readout between FSE and EPI as a comparative example. In FSE, the phase error accumulated in one line for k-space readout (cumulative phase error) is the product of the chemical shift, the duel rate, and the MR data acquisition point on one readout line. Here, the duel rate is also called the duel time or duel unit, and corresponds to the MR data acquisition time per sample in readout.

[0046] In FSE, the chemical shift along the frequency encoding direction is so small that it can be considered zero. In EPI and GRASE, the cumulative phase error in frequency encoding is the total acquisition time multiplied by the chemical shift. Furthermore, the amount of chemical shift in the frequency encoding direction in EPI and GRASE is the product of the chemical shift and the total acquisition time divided by the number of readout samples in the frequency encoding direction (hereinafter referred to as readout samples).

[0047] For example, if the division value obtained by dividing the total imaging time by the number of readout samples in the frequency encoding direction exceeds 1, chemical shift artifacts will appear in the MR image. The larger this division value becomes, the more prominent the chemical shift artifacts will be in the MR image. Therefore, in this embodiment, the total imaging time is controlled so that this division value is less than the design threshold. The design threshold (also referred to as a predetermined reference time) is, for example, 1, but is not limited to this and may be 2 or 3.

[0048] The design threshold is pre-set and stored in the memory circuit 132. The total imaging time is controlled, for example, by the number of readout positions along the readout line RL shown in Figure 2. This allows the batch readout function 134 to read out the magnetic resonance data in a batch so that the total readout time for reading the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution. The processing circuit 150 that implements the batch readout function 134 corresponds to the batch readout unit. The batch readout function 134 may also be implemented in the sequence control circuit 120.

[0049] Figure 4 shows an example of sequence information (sequence) according to this embodiment. The sequence shown in Figure 4 shows an example where the interleaving factor is 3. In the trapezoidal SP showing the application of the readout gradient magnetic field in Gx shown in Figure 4, in this embodiment, the width of the upper base of the trapezoid is represented by a series of pulses shorter than GRASE.

[0050] The processing circuit 150 resets the reading position of the magnetic resonance data by applying a refocus pulse and performing phase encoding using the setting function 136. After the batch reading of MR data by the batch reading function 134, the setting function 136 applies a refocus pulse to the subject P and performs phase encoding. As a result, after the batch reading of MR data, the setting function 136 resets the reading position of the MR data on the reading line. The processing circuit 150 that implements the setting function 136 corresponds to the setting unit. Note that the setting function 136 may also be incorporated into the sequence control circuit 120.

[0051] The processing circuit 150, using the acquisition function 138, acquires first correction data for positions along a first direction in a region including the center of k-space, all at once without applying a refocus pulse. The readout line for the first correction data is, for example, along the kx direction. At this time, the acquisition function 138 acquires first correction data for a region including the center of k-space (for example, the center of k-space). The readout line for the first correction data along the kx direction corresponds to frequency encoding.

[0052] The acquisition function 138 stores the first correction data in the memory circuit 132. The acquisition of the first correction data is performed before or after the main scan. The first correction data corresponds to, for example, MR data acquired by repeatedly reading a read line along kx=0 a predetermined number of times.

[0053] Alternatively, the data acquisition function 138 may acquire second correction data by performing a first encoding for the first direction and then a second encoding for the second direction. In this case, the readout line for the second correction data corresponds to the S-shaped readout line shown in Figure 2. The entire S-shaped readout line corresponds to frequency encoding and corresponds to one readout.

[0054] The acquisition function 138 may acquire the second correction data for positions along the first direction and positions along the second direction in a region including the center of k-space, all at once without applying a refocus pulse. In this case, the read line of the second correction data formed by the positions along the first direction and positions along the second direction has an S-shape and an inverted S-shape in the region including the center of k-space. Specifically, the read line of the second correction data corresponds to an S-shaped or inverted S-shaped read line in the region including the center of k-space shown in Figure 2. The entire S-shaped and inverted S-shaped read line corresponds to frequency encoding and corresponds to a single readout. The acquisition function 138 stores the second correction data in the memory circuit 132. The acquisition of the second correction data is performed before or after the main scan.

[0055] Furthermore, the acquisition function 138 may acquire at least one of the first correction data and the second correction data multiple times in a region including the center of k-space. In this case, the setting function 136 resets the read position of at least one of the first correction data and the second correction data by applying a refocus pulse and performing phase encoding during each of the multiple acquisitions of at least one of the first correction data and the second correction data.

[0056] Furthermore, the collection function 138 may collect at least one of the first and second correction data at a higher density than the collection density of the MR data read out by the batch readout function 134 in k-space. Since known methods can be applied to such high-density collection, a detailed explanation is omitted.

[0057] Furthermore, the acquisition function 138 acquires at least one of the first and second correction data. The processing circuit 150 that implements the acquisition function 138 corresponds to the acquisition unit. The acquisition function 138 may be implemented in the sequence control circuit 120 or implemented by the batch readout function 134.

[0058] The processing circuit 150 corrects the position of the magnetic resonance data in k-space using either the first or second correction data via the correction function 140. Alternatively, the correction function 140 may use both the first and second correction data to correct the position of the magnetic resonance data in k-space. The correction of the MR data position by the correction function 140 corresponds to, for example, gridding. Since known methods (e.g., JIJackson, CHMeyer, DGNishimura, A.Macovski, “Selection of a convolution function for Fourier inversion using gridding (computerised tomography application)”, in IEEE Transactions on Medical Imaging, vol. 10, no.3, pp. 473-478, Sept. 1991) can be applied to the gridding process, a detailed explanation is omitted.

[0059] The correction may also be performed when the MR image is reconstructed by the image generation function 142. In this case, the processing realized by the correction function 140 is executed by the image generation function 142. The processing circuit 150 that realizes the correction function 140 corresponds to the correction unit.

[0060] The processing circuit 150 reads the corrected MR data (k-space data) from the storage circuit 132 using the image generation function 142, and generates an MR image by applying reconstruction processing such as a Fourier transform to the read k-space data. Since known methods can be applied to the generation of the MR image, a detailed explanation is omitted. The processing circuit 150 that implements the image generation function 142 corresponds to the image generation unit.

[0061] The overall configuration of the MRI apparatus 100 according to the embodiment has been described above. Under the above configuration, the MRI apparatus 100 according to the embodiment performs a process to image the subject P by reducing the sampling period in the phase encoding direction to the same extent as the sampling period in the frequency encoding direction (hereinafter referred to as the sampling period reduction imaging process). The procedure for the sampling period reduction imaging process will be described below with reference to Figure 5. Figure 5 is a flowchart showing an example of the procedure for the sampling period reduction imaging process.

[0062] (Sampling period reduction imaging process) (Step S501) The sequence control circuit 120 applies an excitation pulse (RF pulse) to the subject P. At this time, the sequence control circuit 120 applies a gradient magnetic field (Gz) related to slice selection to the subject P along with the excitation pulse. Next, after a predetermined time has elapsed, the sequence control circuit 120 applies a refocus pulse (RF pulse) to the subject P. At this time, the sequence control circuit 120 applies a gradient magnetic field (Gz) related to slice selection to the subject P along with the refocus pulse.

[0063] (Step S502) The sequence control circuit 120 applies a gradient magnetic field to the subject P to realize a single readout line as shown in Figure 2 for the acquisition of MR data. The timing of the application of the gradient magnetic field for MR data readout is preset so that the total readout time for MR data readout does not exceed a predetermined reference time that depends on the spatial resolution. The receiving circuit 110 receives the MR data via the receiving coil 109 and outputs it to the sequence control circuit 120.

[0064] As a result, the processing circuit 150 reads out MR data for positions along the first direction and positions along the second direction in a single batch using the batch readout function 134, without applying a refocus pulse. For example, the batch readout function 134 reads out MR data in a single batch along the magnetic resonance data readout line (S-curve or inverted S-curve in k-space) formed by the positions along the first direction and positions along the second direction, without applying a refocus pulse. The batch readout function 134 stores the batch readout MR data in the storage circuit 132. The processing in this step corresponds to the collection of multiple readout lines between two adjacent refocus pulses, for example, in one line in FSE as a comparative example or in GRASE as a comparative example.

[0065] (Step S503) The processing circuit 150 determines whether all MR data related to the target to be collected, i.e., all MR data placed in k-space for image reconstruction, has been collected. If the collection of all MR data related to the target to be collected is not complete (No in step S503), the process in step S504 is executed. This repeatedly reads out MR data and resets the readout position over a predetermined range in k-space. The predetermined range corresponds to a pre-set imaging range. If the collection of all MR data related to the target to be collected is complete (Yes in step S503), the process in step S505 is executed.

[0066] (Step S504) The processing circuit 150 resets the MR data readout position by applying a refocus pulse and performing phase encoding via the setting function 136. The resetting of the MR data readout position corresponds to the readout position of a different readout line (an S-shape in k-space) than the readout line RL (for example, the S-shape in k-space shown in Figure 2) read out in step S502. For example, the setting function 136 applies a refocus pulse (180° pulse) to the subject P via the sequence control circuit 120. Next, the setting function 136 applies a gradient magnetic field related to phase encoding to the subject P via the sequence control circuit 120 to set the readout position. Then, the processing from step S502 onward is repeated.

[0067] (Step S505) The processing circuit 150, using the acquisition function 138, acquires first correction data for the position along the first direction in a region including the center of k-space, all at once without applying a refocus pulse. For example, the acquisition function 138 acquires the first correction data by repeatedly frequency encoding the readout line along kx=0 a predetermined number of times.

[0068] The data collection function 138 stores the collected first correction data in the memory circuit 132. Note that the collection of the first correction data may be performed before the processing related to this scan (steps S501 to S504). Furthermore, if the MR data is corrected using only the second correction data described later, this step is unnecessary.

[0069] (Step S506) The processing circuit 150, using the acquisition function 138, acquires second correction data for positions along the first direction and positions along the second direction in a region including the center of k-space, all at once without applying a refocus pulse. The readout line of the second correction data formed by the positions along the first direction and positions along the second direction has an S-shape and an inverted S-shape in the region including the center of k-space.

[0070] For example, the acquisition function 138 acquires second correction data by frequency encoding S-shaped and inverted S-shaped readout lines in a region including the center of k-space (kx=0, ky=0). The acquisition function 138 stores the acquired second correction data in the memory circuit 132. Note that the acquisition of the second correction data may be performed before the processing related to this scan (steps S501 to S504). Also, if the MR data is corrected using only the first correction data, this step is unnecessary. Furthermore, the acquisition of the second correction data may be performed before the acquisition of the first correction data.

[0071] The acquisition function 138 may acquire at least one of the first correction data and the second correction data multiple times in a region including the center of k-space. In this case, the setting function 136 applies a refocus pulse and performs phase encoding during each of the multiple acquisitions of at least one of the first correction data and the second correction data. As a result, the setting function 136 resets the readout position of at least one of the first correction data and the second correction data. The acquisition function 138 may also acquire at least one of the first correction data and the second correction data at a density higher than the acquisition density of magnetic resonance data in k-space.

[0072] (Step S507) The processing circuit 150 corrects the position of the MR data in k-space using the first correction data and the second correction data via the correction function 140. Alternatively, the correction function 140 may correct the position of the MR data in k-space using either the first correction data or the second correction data. In this case, since the collection of correction data not used for correction is unnecessary, the step of collecting correction data not used for correction is not required in the sampling period reduction imaging process.

[0073] The processing circuit 150 reads the corrected MR data (k-space data) from the storage circuit 132, performs reconstruction processing such as a Fourier transform on the read k-space data, and generates an MR image. When the correction is performed by the image generation function 142, the image generation function 142 corrects the position of the MR data in k-space using at least one of the first correction data and the second correction data (i.e., using the first correction data and / or the second correction data), and generates an MR image based on the corrected MR data (k-space data).

[0074] The MRI apparatus 100 according to the embodiment described above reads out MR data for a subject P in an imaging scenario, reading out MR data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space, all at once without applying a refocus pulse. Then, by applying the refocus pulse and performing phase encoding, the readout position of the MR data is reset, and the MR data is read out all at once so that the total readout time for the MR data does not exceed a predetermined reference time that depends on the spatial resolution. For example, in the MRI apparatus 100 according to the embodiment, the readout line of magnetic resonance data formed by the position along the first direction and the position along the second direction has an S-shape or an inverted S-shape in k-space.

[0075] As a result, according to the MRI apparatus 100 of this embodiment, by setting the S-shaped readout line such that the value obtained by dividing the product of the chemical shift and the total imaging time by the number of readout samples in the frequency encoding direction is smaller than the reference time, it is possible to acquire images with a sampling period in the phase encoding direction that is approximately the same as the sampling period in the frequency encoding direction.

[0076] Furthermore, the MRI apparatus 100 according to the embodiment collects first correction data for positions along a first direction in a region including the center of k-space without applying a refocus pulse, and corrects the position of the MR data in k-space using the first correction data. Furthermore, the MRI apparatus 100 according to the embodiment collects second correction data for positions along a first direction and positions along a second direction in a region including the center of k-space without applying a refocus pulse, and the readout line of the second correction data formed by the positions along the first direction and positions along the second direction has an S-shape and an inverted S-shape in the region including the center of k-space, and corrects the position of the MR data in k-space using at least one of the first correction data and the second correction data.

[0077] Furthermore, the MRI apparatus 100 according to the embodiment collects at least one of the first correction data and the second correction data multiple times in a region including the center of k-space, and resets the readout position of at least one of the first correction data and the second correction data by applying a refocus pulse and performing phase encoding in each of the multiple collections of at least one of the first correction data and the second correction data. In addition, the MRI apparatus 100 according to the embodiment collects at least one of the first correction data and the second correction data at a density higher than the density of MR data collection in k-space.

[0078] Based on these findings, the MRI apparatus 100 according to this embodiment can collect various correction data in accordance with the MR data readout line shown in Figure 2, thereby correcting the MR data.

[0079] From the above, the MRI apparatus 100 according to the embodiment can image the subject P quickly, like EPI and GRASE, without the influence of chemical shift, like FSE. Furthermore, the MRI apparatus 100 according to the embodiment can correct the MR data using correction data collected in accordance with the readout line, thereby generating an MR image with reduced influence of chemical shift. As a result, the MRI apparatus 100 according to the embodiment can reduce the burden on the subject P by shortening the examination time, and improve the throughput of the examination by generating an MR image with reduced chemical shift artifacts.

[0080] When the technical concept of the embodiment is realized by a magnetic resonance imaging method, the magnetic resonance imaging method reads out magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space, all at once without applying a refocus pulse, applies a refocus pulse and performs phase encoding to reset the read position of the magnetic resonance data, and repeats the reading of the magnetic resonance data and resetting the read position over a predetermined range in k-space, so that the total read time for reading the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution. The procedure and effects of the sampling period reduction imaging process performed by the magnetic resonance imaging method are the same as in the embodiment, so a description is omitted.

[0081] When the technical concept in the embodiment is realized in a magnetic resonance imaging program, the program enables the computer to read out magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space, all at once without applying a refocus pulse, then apply the refocus pulse and perform phase encoding to reset the reading position of the magnetic resonance data, and repeat the reading of the magnetic resonance data and resetting the reading position over a predetermined range in k-space. The reading out of the magnetic resonance data all at once is done in such a way that the total reading time for the reading of the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution.

[0082] For example, sampling period reduction imaging can be achieved by installing an acquisition program on a computer in an MRI device and loading it into memory. In this case, the magnetic resonance imaging program that can cause the computer to execute the sampling period reduction imaging can 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. Furthermore, the distribution of the magnetic resonance imaging program is not limited to the above-mentioned media, and may also be distributed using telecommunications functions, such as downloading via the internet. The procedure and effects of sampling period reduction imaging using the magnetic resonance imaging program are the same as in the embodiment, so a description will be omitted.

[0083] According to the embodiments described above, magnetic resonance data can be collected at high speed while reducing the effects of chemical shift.

[0084] While 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 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 variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0085] 100 Magnetic Resonance Imaging System 101 Static Magnetic Field Magnet 102 Static magnetic field power supply 103 Gradient field coil 104 Gradient magnetic field power supply 105 berths 105a Top plate 106 Bed control circuit 107 Transmitter coil 108 Transmitter Circuit 109 Receiving coil 120 Sequence control circuit 130 Computers 131 Interface Functions 132 Memory circuit 133 Control Functions 134 Batch Read Function 136 Settings Function 138 Collection Functions 140 Correction function 141 Input device 142 Image generation function 143 displays 150 Processing Circuits

Claims

1. In reading magnetic resonance data during imaging of a subject, a batch readout unit reads magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space, all at once without applying a refocus pulse. A setting unit that resets the reading position of the magnetic resonance data by applying the refocus pulse and performing phase encoding, Equipped with, The batch reading unit reads the magnetic resonance data in a batch so that the total reading time for reading the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution. Magnetic resonance imaging device.

2. The magnetic resonance data readout line formed by the position along the first direction and the position along the second direction has an S-shape or inverted S-shape in the k-space. The magnetic resonance imaging apparatus according to claim 1.

3. A collection unit that collects first correction data for a position along the first direction in a region including the center of the k-space without applying a refocus pulse, A correction unit that corrects the position of the magnetic resonance data in the k-space using the first correction data, The magnetic resonance imaging apparatus according to claim 1 or 2, further comprising:

4. The collection unit collects second correction data for positions along the first direction and positions along the second direction in a region including the center of the k-space, all at once without applying a refocus pulse. The second correction data readout line, formed by the position along the first direction and the position along the second direction, has an S-shape and an inverted S-shape in the region including the center of the k-space. The correction unit corrects the position of the magnetic resonance data in the k-space using at least one of the first correction data and the second correction data. The magnetic resonance imaging apparatus according to claim 3.

5. The collection unit collects at least one of the first correction data and the second correction data multiple times in a region including the center of the k space. The setting unit resets the read position of at least one of the first and second correction data by applying the refocus pulse and performing phase encoding during each of multiple acquisitions of at least one of the first and second correction data. The magnetic resonance imaging apparatus according to claim 4.

6. The collection unit collects at least one of the first correction data and the second correction data at a density higher than the density of collection of the magnetic resonance data in the k-space. The magnetic resonance imaging apparatus according to claim 4.

7. In reading out magnetic resonance data during imaging of a subject, magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space are read out simultaneously without applying a refocus pulse. By applying the refocus pulse and performing phase encoding, the reading position of the magnetic resonance data is reset. The process involves repeatedly reading out the magnetic resonance data and resetting the reading position over a predetermined range in the k-space. Equipped with, The process of reading out the magnetic resonance data in a batch is performed such that the total reading time for reading out the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution. Magnetic resonance imaging method.

8. On the computer, In reading out magnetic resonance data during imaging of a subject, magnetic resonance data for a position along a first direction in k-space and a position along a second direction different from the first direction in k-space are read out simultaneously without applying a refocus pulse. By applying the refocus pulse and performing phase encoding, the reading position of the magnetic resonance data is reset. The process involves repeatedly reading out the magnetic resonance data and resetting the reading position over a predetermined range in the k-space. To make it happen, Reading the magnetic resonance data in a batch means reading the magnetic resonance data in a batch such that the total reading time for reading the magnetic resonance data does not exceed a predetermined reference time that depends on the spatial resolution. Magnetic resonance imaging program.

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