Magnetic resonance imaging device and magnetic resonance imaging method
Patent Information
- Application Number
- JP2023133145
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-08-17
- Publication Date
- 2025-02-28
Smart Images
Figure 2025027903000001_ABST
Abstract
Description
[Technical field]
[0001] The embodiments disclosed in this specification and the drawings relate to a magnetic resonance imaging apparatus and a magnetic resonance imaging method. [Background technology]
[0002] When a subject is placed in a strong magnetic field, the nuclear spins of the molecules that make up the subject are aligned and the nuclear spins precess at the Larmor frequency. When a radio frequency (RF) signal at the Larmor frequency is irradiated to the subject in this state, the nuclear spins of the molecules resonate with the RF signal and are excited, and then when the molecules return to their original stable state, a magnetic resonance (MR) signal is generated from the subject.
[0003] Known techniques that utilize magnetic resonance include magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS).
[0004] MRI is a technology that uses MR signals generated from a subject to generate images of the subject. In MRI, the frequency and phase of the MR signals are slightly changed for each spatial position of the subject, and images of the subject are generated by associating positions inside the subject with the intensity of the MR signals.
[0005] On the other hand, MRS is a technology that detects, analyzes, or displays the spectrum of a substance in a specific region of a subject using MR signals generated from the subject. It is known that metabolic substances contained in the subject, such as choline, creatine, NAA (N-acetylaspartic acid), etc., have slightly different magnetic resonance frequencies for each type of substance due to differences in chemical bonds of various molecules. The deviation of the magnetic resonance frequency of each substance from the magnetic resonance frequency of a certain reference substance (reference magnetic resonance frequency) is called chemical shift.
[0006] In MRI and MRS using this MRI device, the homogeneity of the static magnetic field is required to maintain the image quality of the MR image. Therefore, in order to increase the homogeneity of the static magnetic field when the subject is carried into the static magnetic field, there is a magnetic field adjustment technology called active shimming that controls the current value of the magnetic field correction coil. [Prior art documents] [Patent documents]
[0007] [Patent Document 1] JP 2020-22572 A [Patent Document 2] JP 2019-195588 A Summary of the Invention [Problem to be solved by the invention]
[0008] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to suppress the deterioration of the quality of MR data due to the decrease in the homogeneity of the static magnetic field during MR data collection. 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 later can also be positioned as other problems. [Means for solving the problem]
[0009] A magnetic resonance imaging apparatus according to an embodiment includes a shim data acquisition unit, a correction control unit, an MR data acquisition unit, and a shim necessity determination unit. The shim data acquisition unit acquires data for magnetic field adjustment to correct static magnetic field inhomogeneity. The correction control unit controls a current value of a magnetic field correction coil to increase the homogeneity of the static magnetic field based on the data for magnetic field adjustment. The MR data acquisition unit acquires data for MR image generation by an imaging scan to image a subject. The shim necessity determination unit determines whether or not to acquire data for magnetic field adjustment again during the imaging scan based on the data for MR image generation acquired by the MR data acquisition unit. When the shim necessity determination unit determines that the data for magnetic field adjustment is to be acquired again, the shim data acquisition unit acquires data for magnetic field adjustment again during the imaging scan, and the correction control unit controls a current value of the magnetic field correction coil during the imaging scan based on the data for magnetic field adjustment acquired again. [Brief description of the drawings]
[0010] [Figure 1] 1 is a schematic diagram showing an example of the overall configuration of a magnetic resonance imaging apparatus according to an embodiment; [Diagram 2] An explanatory diagram of the chemical shift of water and fat when the homogeneity of the static magnetic field is different. [Diagram 3] 1 is a block diagram showing an example of the arrangement of a magnetic resonance imaging apparatus according to a first embodiment. [Figure 4] 4 is a flowchart showing an example of processing performed by the magnetic resonance imaging apparatus according to the first embodiment. [Diagram 5] FIG. 2 is a block diagram showing an example of the configuration of a magnetic resonance imaging apparatus according to a first modified example of the first embodiment. [Figure 6] 6 is a flowchart showing an example of processing by the magnetic resonance imaging apparatus according to the first modification of the first embodiment. [Figure 7] FIG. 13 is a diagram illustrating a case where the evaluation criteria regarding artifacts are not met. [Figure 8] FIG. 2 is a block diagram showing an example of the configuration of a magnetic resonance imaging apparatus according to a second modification of the first embodiment. [Figure 9]FIG. 11 is a block diagram showing an example of the arrangement of a magnetic resonance imaging apparatus according to a second embodiment. [Figure 10] 10 is a flowchart showing an example of processing performed by a magnetic resonance imaging apparatus according to the second embodiment. [Figure 11] FIG. 11 is a diagram showing an example of a display screen of a spectrum based on MR spectrum data of the magnetic resonance imaging apparatus according to the second embodiment. [Figure 12] FIG. 11 is a first explanatory diagram for evaluation of the quality of a spectrum of a magnetic resonance imaging apparatus according to the second embodiment. [Figure 13] FIG. 2 is a second explanatory diagram for evaluation of the quality of a spectrum of the magnetic resonance imaging apparatus according to the second embodiment. [Figure 14] FIG. 11 is a third explanatory diagram for evaluation of the quality of a spectrum of the magnetic resonance imaging apparatus according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] Hereinafter, embodiments of a magnetic resonance imaging apparatus and a magnetic resonance imaging method will be described in detail with reference to the drawings.
[0012] (Overall configuration of magnetic resonance imaging device) A magnetic resonance imaging apparatus (MRI (Magnetic Resonance Imaging) apparatus) 1 according to an embodiment can utilize magnetic resonance imaging technology. FIG. 1 is a schematic diagram showing an example of the overall configuration of the MRI apparatus 1 according to an embodiment. The MRI apparatus 1 includes a magnet stand 100, a control cabinet 300, an image processing apparatus 400 such as a console, and a bed 500.
[0013] The magnet gantry 100 and the bed 500 are arranged, for example, in a shielded room called an examination room. On the other hand, the control cabinet 300 is arranged, for example, in a machine room, and the image processing device 400 is arranged, for example, in an operation room. Note that the image processing device 400 may be connected to the MRI apparatus 1 via a network and installed in a remote location away from the operation room.
[0014] The magnet gantry 100 includes a static magnetic field magnet 10, a gradient magnetic field coil 11, a WB (Whole Body) coil 12, and a magnetic field correction coil 13. The static magnetic field magnet 10 of the magnet gantry 100 is broadly classified into a cylindrical type in which the magnet has a cylindrical magnetic structure, and an open type in which a pair of magnets are arranged above and below with an imaging space in between. Here, an MRI device 1 with a cylindrical magnet gantry 100 will be described, but an open type MRI device may also be used. Note that the open type MRI device has the same configuration as the cylindrical type MRI device 1, except that the static magnetic field magnet, gradient magnetic field coil, and WB coil that constitute the magnet gantry are parallel plate-shaped.
[0015] The static magnetic field magnet 10 has a roughly cylindrical shape and generates a static magnetic field in a bore into which the subject P is transported. The bore is the space inside the cylinder of the magnet gantry 100. The static magnetic field magnet 10 is composed of, for example, a housing for holding liquid helium, a refrigerator for cooling the liquid helium to an extremely low temperature, and a superconducting coil inside the housing. The static magnetic field magnet 10 may be composed of a permanent magnet. Below, a case where the static magnetic field magnet 10 has a superconducting coil will be described.
[0016] The static magnetic field magnet 10 has a built-in superconducting coil, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, the static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply to the superconducting coil. After that, when the mode is switched to the persistent current mode, the static magnetic field power supply is disconnected. Once in the persistent current mode, the static magnetic field magnet 10 continues to generate a static magnetic field for a long time, for example, for more than one year.
[0017] The magnetic field correction coil 13 performs magnetic field adjustment to correct static magnetic field inhomogeneity and increase the homogeneity of the static magnetic field by controlling the current value of the magnetic field correction coil 13 based on the magnetic field adjustment data. The magnetic field correction coil 13 may be a gradient magnetic field coil 11. The gradient magnetic field coil 11 can adjust the correction magnetic field by applying a shim coil or offset current that can adjust the correction magnetic field up to the higher order term of the coil spherical harmonic function, for example. The gradient magnetic field coil 11 can perform magnetic field adjustment to correct static magnetic field inhomogeneity and increase the homogeneity of the static magnetic field based on the magnetic field adjustment data.
[0018] The gradient magnetic field coil 11 has a roughly cylindrical shape like the static magnetic field magnet 10, and is placed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 is composed of three gradient magnetic field coils for the X-axis, Y-axis, and Z-axis. Each gradient magnetic field coil is supplied with a gradient magnetic field current (power) from a gradient magnetic field power supply 31 (31x for the X-axis, 31y for the Y-axis, and 31z for the Z-axis), thereby generating gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions and applying them to the subject P. Here, the Z-axis direction is the direction along the static magnetic field, the Y-axis direction is the vertical direction, and the X-axis direction is the direction perpendicular to the Z-axis and Y-axis.
[0019] The WB coil 12 is also called a whole-body coil, and is disposed inside the gradient magnetic field coil 11 in a generally cylindrical shape so as to surround the subject P. The WB coil 12 functions as a transmitting coil. That is, the WB coil 12 transmits RF pulses to the subject P in accordance with radio frequency (RF) signals transmitted from the RF transmitter 32. Meanwhile, the WB coil 12 may also function as a receiving coil in addition to functioning as a transmitting coil that transmits RF pulses. In that case, the WB coil 12 serves as a receiving coil to receive MR signals emitted from the subject P due to excitation of atomic nuclei.
[0020] The MRI apparatus 1 may include a local coil 20 in addition to the WB coil 12. The local coil 20 is placed close to the body surface of the subject P. The local coil 20 may include a plurality of coil elements. There are several types of local coils 20, such as a head coil, a chest coil, an abdominal coil, a spine coil, and a knee coil. Note that, although FIG. 1 shows a case where the local coil 20 is a chest coil, the present invention is not limited to this case.
[0021] The local coil 20 functions as a receiving coil. That is, the local coil 20 receives the above-mentioned MR signal. The local coil 20 may be a transmitting / receiving coil having a function as a transmitting coil that transmits RF pulses in addition to the function as a receiving coil that receives MR signals. That is, the local coil 20 may be a transmitting-only coil, a receiving-only coil, or a coil for both transmitting and receiving.
[0022] The bed 500 includes a bed body 50 and a tabletop 51. The bed body 50 can move the tabletop 51 in the vertical and horizontal directions, and moves the subject P placed on the tabletop 51 to a predetermined height before imaging. Thereafter, during imaging, the tabletop 51 is moved horizontally to move the subject P into the bore.
[0023] The control cabinet 300 includes gradient magnetic field power supplies 31 (for the X-axis 31x, for the Y-axis 31y, and for the Z-axis 31z), an RF transmitter 32, an RF receiver 33, and a sequence controller .
[0024] The gradient magnetic field power supply 31 includes gradient magnetic field power supplies 31x, 31y, and 31z for each channel that drive coils that generate gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The gradient magnetic field power supplies 31x, 31y, and 31z output required currents independently for each channel in response to a command from a sequence controller 34.
[0025] The RF transmitter 32 generates a high-frequency signal based on an instruction from a sequence controller 34. The RF transmitter 32 transmits the generated high-frequency signal to the WB coil 12 and the local coil 20.
[0026] The MR signals received by the WB coil 12 and the local coil 20 are transmitted to the RF receiver 33. The RF receiver 33 performs analog-to-digital (AD) conversion on the MR signals from the WB coil 12 and the local coil 20 and outputs them to a sequence controller 34. The digitally converted MR signals are sometimes called raw data.
[0027] The sequence controller 34, under the control of the image processing device 400, drives the gradient magnetic field power supply 31, the RF transmitter 32, and the RF receiver 33 to image the subject P. When raw data is received from the RF receiver 33 by imaging, the sequence controller 34 transmits the raw data to the image processing device 400.
[0028] The sequence controller 34 includes a processing circuit (not shown). The processing circuit is configured with hardware such as a processor that executes a predetermined program, a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC).
[0029] Next, a description will be given of the image processing device 400. The image processing device 400 includes a processing circuit 40, a memory circuit 41, a display 42, an input interface 43, and a communication circuit 44.
[0030] The processing circuitry 40 has a dedicated or general-purpose processor, and realizes various functions by software processing by executing a program stored in the storage circuitry 41 or directly built into the processing circuitry 40. The processing circuitry 40 realizes the function of controlling the operation of the sequence controller 34, and performing imaging according to a pulse sequence to generate an MR image. The processing circuitry 40 may be configured with hardware such as an FPGA or an ASIC. Various functions described later can also be realized by such hardware. Moreover, the processing circuitry 40 may realize various functions by combining software processing and hardware processing.
[0031] The storage circuitry 41 includes semiconductor memory elements such as a random access memory (RAM) and a flash memory, a hard disk, an optical disk, etc. The storage circuitry 41 may include a portable medium such as a universal serial bus (USB) memory and a digital video disk (DVD). The storage circuitry 41 stores various processing programs used in the processing circuitry 40, data required for executing the programs, and medical images.
[0032] The display 42 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display. The display 42 displays various information under the control of the processing circuit 40. The display 42 is a display device, and may also be a GUI (Graphical User Interface) capable of receiving various operations from a user, such as a touch panel.
[0033] The input interface 43 includes an input device that can be operated by a user, and an input circuit that inputs a signal from the input device. The input device can be realized by a trackball, a switch, a mouse, a keyboard, a touchpad, a touchscreen, a non-contact input device using an optical sensor, a voice input device, etc. When the input device is operated by a user, the input circuit generates a signal according to the operation and outputs it to the processing circuit 40.
[0034] The communication circuit 44 includes an interface for performing communication connected to a network via a wired or wireless connection. The communication circuit 44 can exchange various data between the network and the memory circuit 41, for example.
[0035] The image processing device 400 controls the entire MRI apparatus 1 using these components. Specifically, imaging conditions and other various information and instructions are received by a user such as an examiner operating an input interface 43 such as a mouse and a keyboard. The processing circuitry 40 then causes the sequence controller 34 to execute a scan based on the input imaging conditions, while reconstructing an image based on data transmitted from the sequence controller 34. The reconstructed image is displayed on a display 42 or stored in a memory circuitry 41.
[0036] (active shimming) In imaging by an MRI device, the homogeneity of the static magnetic field is required to maintain the image quality of the MR image. For example, the homogeneity of the static magnetic field may be particularly required in areas where air is present in the imaging area, such as the neck, heart, breast, lungs, elbows, and fingers, or in areas that are out of the center of the static magnetic field magnet. In addition, the homogeneity of the static magnetic field may be particularly required in imaging methods such as fat suppression, magnetic resonance spectroscopy (MRS), CEST (Chemical Exchange Saturation Transfer) MRI, EPI (Echo Planar Imaging), and SSFP (Steady State Free Precession).
[0037] Specifically, the effect of static magnetic field inhomogeneity in the case of fat suppression method will be explained with reference to Fig. 2. As shown in Fig. 2(a), when the static magnetic field is highly homogeneous, the water signal and the fat signal are separated due to the difference in chemical shift, so that the fat can be frequency-selectively suppressed by the suppression pulse. On the other hand, as shown in Fig. 2(b), when the static magnetic field is inhomogeneous, the water signal and the fat signal are not separated due to the difference in chemical shift, but are superimposed, so that the fat cannot be frequency-selectively suppressed by the suppression pulse.
[0038] In order to maintain the image quality of MR images, there is a magnetic field adjustment technique called active shimming, which improves the uniformity of the static magnetic field. In active shimming, with the subject accommodated in the static magnetic field, magnetic field adjustment data for adjusting the static magnetic field nonuniformity is automatically or manually collected before collecting MR data for imaging. The magnetic field adjustment data is acquired by, for example, actually collecting signals to measure the magnetic field distribution in the target region for magnetic field adjustment using a predetermined pulse sequence for acquiring magnetic field adjustment data, and expanding the magnetic field distribution for each magnetic field component that is the target of magnetic field adjustment.
[0039] As described above, the magnetic field correction coil 13 performs magnetic field adjustment to correct the static magnetic field inhomogeneity and increase the homogeneity of the static magnetic field by controlling the current value of the magnetic field correction coil 13 based on the magnetic field adjustment data. The magnetic field correction coil 13 may be, for example, the gradient magnetic field coil 11.
[0040] By performing active shimming before acquiring imaging MR data, the homogeneity of the static magnetic field is increased, and the image quality of the MR image generated from the imaging MR data is maintained. However, the magnetic field adjustment by active shimming may become poor due to the movement of the subject during acquisition of imaging MR data, and the homogeneity of the static magnetic field may decrease. As a result, the image quality of the MR image may deteriorate. A process for suppressing the deterioration of the quality of MR data due to the decrease in the homogeneity of the static magnetic field during MR data acquisition will be described below using an embodiment.
[0041] (First embodiment) FIG. 3 is a block diagram showing an example of the configuration of the MRI apparatus 1 according to the first embodiment. As shown in FIG. 3, the processing circuitry 40 of the MRI apparatus 1 according to the first embodiment realizes each of the functions of a shim data acquisition function F1, a correction control function F2, an MR data collection function F3, and a shim necessity determination function F4. Each function and operation of the processing circuitry 40 of the MRI apparatus 1 according to the first embodiment will be described with reference to the flowchart of FIG. 4. First, the subject P is placed on the top board 51 of the bed 500 and is accommodated in a static magnetic field. In addition, in the MRI apparatus 1, for example, imaging conditions used in the imaging scan are set by a user's operation from the input interface 43 or by reading out an imaging protocol stored in the memory circuitry 41.
[0042] In step ST10, the shim data acquisition function F1 acquires magnetic field adjustment data D1 for correcting static magnetic field inhomogeneity. For example, the magnetic field adjustment data D1 is acquired by actually collecting signals for measuring the magnetic field distribution in the target region of magnetic field adjustment using a predetermined pulse sequence for acquiring magnetic field adjustment data, and expanding the magnetic field distribution for each magnetic field component that is the target of shimming.
[0043] The target region of the magnetic field adjustment may be the entire imaging region or a local region in the imaging region. That is, the shim data acquisition function F1 acquires magnetic field adjustment data D1 for correcting static magnetic field inhomogeneity for at least one of the entire imaging region and the local region in the imaging region.
[0044] In step ST20, the correction control function F2 controls the current value of the magnetic field correction coil 13 for increasing the homogeneity of the static magnetic field, based on the magnetic field adjustment data D1.
[0045] In step ST30, the MR data acquisition function F3 acquires MR image generation data D2 by performing an imaging scan to image the subject. The MR image generation data D2 is obtained by acquiring MR signals in the imaging region using a pulse sequence and various imaging conditions for the imaging scan that are set in advance.
[0046] In step ST40, the shim necessity determination function F4 determines whether or not to acquire the magnetic field adjustment data D1 again during the imaging scan based on the MR image generation data D2 collected by the MR data collection function F3. The MR image generation data D2 collected by the MR data collection function F3 includes the MR image generation data already collected during the imaging scan and the MR image generation data being collected.
[0047] Here, the collected MR image generation data is data for which collection has been completed. On the other hand, the MR image generation data being collected is data for which collection has not been completed. In other words, the collected MR image generation data and the collected MR image generation data include data in which the image quality of the MR image is maintained and data in which the image quality of the MR image is not maintained.
[0048] The determination of whether to acquire the magnetic field adjustment data D1 again during the imaging scan is performed, for example, by determining whether the image quality satisfies a predetermined evaluation standard. Then, the shim necessity determination function F4 acquires the magnetic field adjustment data D1 again when the quality of the image based on the MR image generation data already collected during the imaging scan and the MR image generation data being collected does not satisfy the predetermined evaluation standard (i.e., NO in step ST40).
[0049] The shim necessity determination function F4 may determine whether the image quality satisfies a predetermined evaluation standard by using at least one index among SSIM (Structural Similarity Index Measure), PSNR (Peak Signal to Noise Ratio), NMSE (Normalized Mean Squared Error), and MSE (Mean Squared Error). For example, it may be determined whether at least one index among SSIM, PSNR, NMSE, and MSE satisfies a predetermined reference value set in advance.
[0050] If the shim necessity determination function F4 determines that the magnetic field adjustment data D1 should be acquired again (i.e., if the image quality does not satisfy the predetermined evaluation standard in step ST40, the answer is NO), the shim data acquisition function F1 acquires the magnetic field adjustment data D1 again during the imaging scan. That is, the process proceeds to step ST10. Then, the correction control function F2 controls the current value of the magnetic field correction coil 13 during the imaging scan based on the magnetic field adjustment data D1 acquired again (i.e., step ST20). Furthermore, the MR data acquisition function F3 acquires a part or all of the MR image generation data D2 again (i.e., step ST30).
[0051] Moreover, when the shim necessity determination function F4 determines not to acquire the magnetic field adjustment data D1 again (that is, YES in step ST40 where the image quality satisfies a predetermined evaluation standard), the flowchart in FIG. 3 ends.
[0052] According to the MRI apparatus 1 of the first embodiment, when the image quality of the MR image based on the data for generating the MR image is not maintained, the magnetic field adjustment is performed again, thereby suppressing deterioration of the quality of the MR data due to a decrease in the homogeneity of the static magnetic field.
[0053] (Modification 1 of the first embodiment) FIG. 5 is a block diagram showing a configuration example of the MRI apparatus 1 according to the first modification of the first embodiment. As shown in FIG. 5, the processing circuit 40 of the MRI apparatus 1 according to the first modification of the first embodiment is different from the MRI apparatus 1 according to the first embodiment in that it further realizes a data recollection determination function F5. Other configurations and functions are not substantially different from those of the MRI apparatus 1 according to the first embodiment shown in FIG. 3, so the same configurations are denoted by the same reference numerals and the description thereof is omitted. The functions and operations of the processing circuit 40 of the MRI apparatus 1 according to the first modification of the first embodiment will be described with reference to the flowchart of FIG. 6.
[0054] Steps ST10, ST20, and ST30 of the MRI apparatus 1 according to the first modification of the first embodiment are not substantially different from steps ST10, ST20, and ST30 of the MRI apparatus 1 according to the first embodiment, and therefore the same configurations and operations are denoted by the same reference numerals and description thereof is omitted. After step ST30, the process proceeds to step ST35.
[0055] In step ST35, the data recollection determination function F5 evaluates artifacts of an image based on the MR image generation data D2 collected by the MR data collection function F3 during the imaging scan, and determines whether to collect a part or all of the MR image generation data D2 again. If the data recollection determination function F5 determines that the evaluation criterion for artifacts is not met, the MR data collection function F3 collects a part or all of the MR image generation data D2 again.
[0056] Here, a case where the data for generating MR images being collected does not satisfy the evaluation criteria for artifacts will be described with reference to Fig. 7. Fig. 7 shows an example of the cases (1) to (3) where the collected data for generating MR images satisfies the evaluation criteria for artifacts and the data for generating MR images being collected does not satisfy the evaluation criteria for artifacts.
[0057] (1) is an example of an image in an imaging region where the K-space is filled with Cartesian data by, for example, the spin echo method, when the subject P moves during the collection of data for generating an MR image. It shows how a motion artifact caused by the movement of the subject P appears as a ghost displaced in the phase encoding direction.
[0058] (2) is an example of an image in the K-space region in which the K-space is filled with Cartesian data, for example, by the spin echo method, in the case where there is an effect of chemical shift during collection of data for generating an MR image.
[0059] (3) is an example of an image in the imaging region where the K-space is filled with data by the EPI method using a data filling trajectory with a "single stroke zigzag" shape specific to EPI when there is an effect of chemical shift during the collection of data for generating MR images. It shows how the chemical shift artifact appears as a positional shift in the phase encoding direction.
[0060] Specifically, the EPI method is a high-speed imaging method, and the gradient magnetic field in the frequency encoding direction is large, and the bandwidth per pixel is wide, for example, 1000 Hz or more, so that the chemical shift is contained within one pixel. In other words, the pixel shift in the frequency encoding direction due to the chemical shift is unlikely to occur in the image. In addition, the gradient magnetic field in the phase encoding direction is smaller than the gradient magnetic field in the frequency encoding direction, and the frequency band is narrow, for example, about 10 Hz. However, since the EPI method uses a "single-stroke zigzag" data filling trajectory, even if the phase shift in one phase encoding row in the K space is small, the phase shift is accumulated when moving to the next phase encoding row, and a large position shift in the phase encoding direction appears.
[0061] In addition to the cases (1) to (3), if the subject P moves during the collection of data for generating an MR image, a spiral motion artifact appears in the imaging area where the K-space is filled with data in a spiral. In this way, the direction and pattern in which the artifact is detected differ depending on the imaging method, the filling trajectory of the K-space, etc. Also, the direction and pattern in which the artifact is detected tend to have a certain tendency depending on the imaging method, the filling trajectory of the K-space, etc.
[0062] Although the spin echo method and the EPI method are exemplified as imaging methods used in the imaging scan, the imaging method is not limited to these, and known two-dimensional and three-dimensional imaging methods such as the FSE method, the GRE method, the SSFP method, the fat suppression method, etc. may be used. In addition, although the Cartesian, the "one-stroke zigzag" shape, and the spiral are exemplified as filling trajectories of the K-space, the filling trajectory is not limited to these, and known filling trajectories such as the radial trajectory may be used.
[0063] As described above, in the MR image generation data, the direction and pattern in which artifacts are detected differ depending on the imaging method, the filling trajectory of the K space, etc. That is, in the cases of (1) to (3), the background variance differs between the MR image generation data that has already been collected and the MR image generation data that is still being collected.
[0064] Therefore, in step ST35, the data re-collection determination function F5 calculates the background variance in an image of at least one of the imaging region and the K-space region based on the MR image generation data D2 collected by the MR data collection function F3, and determines whether to collect part or all of the MR image generation data D2 again.
[0065] More specifically, as described above, the direction and pattern in which artifacts are detected tend to have a certain tendency depending on the imaging method, the filling trajectory of the K-space, and the like. Therefore, it is possible to evaluate artifacts based on the variance of the background of the image. For example, an evaluation of artifacts may be performed from the variance of the background of the image using a trained model, etc. From the evaluation result of artifacts, it can be determined whether or not to collect a part or all of the MR image generation data D2 again.
[0066] The determination is made after a certain time has elapsed since the start of acquisition of MR image generation data. The determination can be made if there is both acquired MR image generation data and MR image generation data being acquired. For example, the determination may be made before acquiring MR image generation data for addition. Also, for example, the determination may be made for each slice or for each plurality of slices in a multi-slice imaging scan.
[0067] When the data recollection determination function F5 determines that the evaluation criteria for artifacts are satisfied (i.e., YES in step ST35), the flowchart in Fig. 3 ends. On the other hand, when the data recollection determination function F5 determines that the evaluation criteria for artifacts are not satisfied (i.e., NO in step ST35), the process proceeds to step ST45. The evaluation criteria for artifacts may be stored in the storage circuitry 41 in advance.
[0068] In step ST45 of the MRI apparatus 1 according to the first modification of the first embodiment, if the shim necessity determination function F4 determines not to acquire the magnetic field adjustment data D1 again (i.e., YES in step ST45), the MRI apparatus 1 proceeds to step ST30. In other words, the MR data acquisition function F3 again acquires a part or all of the MR image generation data D2 without acquiring the magnetic field adjustment data D1 again.
[0069] Other than that, there is no substantial difference from step ST40 of the MRI apparatus 1 according to the first embodiment, and therefore the same configuration and operation will not be described. That is, in step ST45, the shim necessity determination function F4 determines whether or not to acquire the magnetic field adjustment data D1 again during the imaging scan based on the MR image generation data D2 acquired by the MR data acquisition function F3. Then, when the shim necessity determination function F4 determines that the magnetic field adjustment data D1 is to be acquired again (that is, in the case of NO in step ST45), the shim data acquisition function F1 acquires the magnetic field adjustment data D1 again. That is, the process proceeds to step ST10. Then, the correction control function F2 controls the current value of the magnetic field correction coil 13 based on the magnetic field adjustment data D1 acquired again (that is, step ST20). Furthermore, the MR data acquisition function F3 again acquires a part or all of the MR image generation data D2 (that is, step ST30).
[0070] (Modification 2 of the first embodiment) FIG. 8 is a block diagram showing a configuration example of the MRI apparatus 1 according to the second modification of the first embodiment. As shown in FIG. 8, the processing circuit 40 of the MRI apparatus 1 according to the second modification of the first embodiment is different from the MRI apparatus 1 according to the first modification of the first embodiment in that it further realizes a presentation function F7 and an integration function F8. Other configurations and functions are not substantially different from those of the MRI apparatus 1 according to the first modification of the first embodiment shown in FIG. 5, so the same configurations are given the same reference numerals and the description is omitted. In addition, the operation of the presentation function F7 of the processing circuit 40 of the MRI apparatus 1 according to the second modification of the first embodiment and other functions of the integration function F8 is not substantially different from the flowchart of the MRI apparatus 1 according to the first modification of the first embodiment shown in FIG. 6, so the overlapping description is omitted.
[0071] In the MRI apparatus 1 according to the second modification of the first embodiment, the presentation function F7 may present at least two of the following: (a) recollection of the MR image generation data D2 and integration of the recollected data and the collected data are automatically performed; (b) recollection of the MR image generation data D2 is automatically performed, but integration of the recollected data and the collected data is selected after recollection of the MR image generation data D2; and (c) recollection of the MR image generation data D2 is not automatically performed. In accordance with this presentation, the user may preliminarily decide on collection of the MR image generation data D2 again (i.e., step ST30) and integration of the recollected data and the collected data. The user makes the decision, for example, via the input interface 43. Note that registration may be performed between the data before integration of the data. The presentation by the presentation function F7 is performed, for example, before the start of the flowchart in FIG. 6.
[0072] Specifically, for example, when it is determined to automatically perform recollection of the MR image generation data D2, a part or all of the MR image generation data D2 is collected again (i.e., step ST30) in the flowchart of Fig. 6. On the other hand, when it is determined not to automatically perform recollection of the MR image generation data D2, step ST30 is not performed.
[0073] The integration function F8 also integrates the recollected data and the collected data. The integration of data by the integration function F8 is performed after the recollection of the MR image generation data D2, for example, after the end of the flowchart in FIG. 6. As described above, the integration of the recollected data and the collected data may be performed automatically depending on the user's decision. After the recollection of the MR image generation data D2, the presentation function F7 may further present whether or not to integrate the recollected data and the collected data, and the user may decide.
[0074] According to the MRI apparatus 1 according to the first modification of the first embodiment and the second modification of the first embodiment, when the image quality of the MR image based on the data for generating the MR image is not maintained, the magnetic field adjustment is performed again, so that the deterioration of the quality of the MR data due to the decrease in the homogeneity of the static magnetic field can be suppressed. Also, when the quality of the MR data is deteriorated due to, for example, a movement or a chemical shift that is not caused by the decrease in the homogeneity of the static magnetic field, the magnetic field adjustment is not performed again, and the data for generating the MR image is recollected. Therefore, the deterioration of the quality of the MR data can be suppressed without unnecessary extension of the imaging time.
[0075] Second embodiment FIG. 9 is a block diagram showing an example of the configuration of the MRI apparatus 1 according to the second embodiment. As shown in FIG. 9, the processing circuitry 40 of the MRI apparatus 1 according to the second embodiment realizes each of the functions of a SIM data acquisition function F1, a correction control function F2, an MR data collection function F3, a SIM necessity determination function F4, a data recollection determination function F5, an adjustment spectrum collection function F6, and a presentation function F7. The processing circuitry 40 of the MRI apparatus 1 according to the second embodiment may further realize an integration function F8. The functions and operations of the processing circuitry 40 of the MRI apparatus 1 according to the second embodiment will be described with reference to the flowchart of FIG.
[0076] In the first embodiment, an imaging scan is performed to acquire data D2 for generating an MR image, but in the second embodiment, an MRS scan is performed to acquire data D3 for an MR spectrum.
[0077] The results of the MRS scan are represented by a spectrum with the horizontal axis representing the chemical shift (frequency) from a reference substance and the vertical axis representing the signal intensity. In the MRS scan, for example, the type and concentration of metabolites in a living body can be investigated by analyzing the frequency difference of atomic nuclei due to differences in molecular structure. Below, a case will be described in which the collected MR spectrum data D3 is data for metabolite spectra, but the collected MR spectrum data D3 may be data for a water reference spectrum, or both. The water reference spectrum is a spectrum without water suppression.
[0078] First, the subject P is placed on the top board 51 of the bed 500 and is accommodated in a static magnetic field. In addition, in the MRI apparatus 1, imaging conditions for an MRS scan are set, for example, by a user's operation.
[0079] In step ST110, the shim data acquisition function F1 acquires magnetic field adjustment data D1 for correcting static magnetic field inhomogeneity. For example, the magnetic field adjustment data D1 is acquired by actually collecting signals for measuring the magnetic field distribution in the target region of magnetic field adjustment using a predetermined pulse sequence for acquiring magnetic field adjustment data, and expanding the magnetic field distribution for each magnetic field component that is the target of shimming.
[0080] The target region of the magnetic field adjustment may be the entire imaging region, a local region in the imaging region, or both. That is, the shim data acquisition function F1 acquires magnetic field adjustment data D1 for correcting static magnetic field inhomogeneity for at least one of the entire imaging region and the local region in the imaging region.
[0081] In step ST120, the correction control function F2 controls the current value of the magnetic field correction coil 13 for increasing the homogeneity of the static magnetic field, based on the magnetic field adjustment data D1.
[0082] In step ST130, the adjustment spectrum acquisition function F6 acquires an adjustment spectrum D4 of the water suppression pulse by an MRS scan that detects the spectrum of the subject. The signal intensity of metabolites such as choline, creatine, and NAA (N-acetylaspartic acid) in the subject observed in the MRS scan is smaller than that of free water. Therefore, in order to reduce the influence of free water in detecting weak metabolite signals, there is a technique for lowering the signal intensity of free water by using a water suppression pulse. For good water suppression, an adjustment spectrum of the RF intensity of the water suppression pulse is acquired.
[0083] In step ST140, the MR data acquisition function F3 acquires MR spectrum data D3 by an MRS scan that detects the spectrum of the subject. The MR spectrum data D3 is obtained by acquiring MR signals in the imaging region using a pulse sequence and various imaging conditions for the MRS scan that are set in advance.
[0084] In step ST150, the data recollection determination function F5 evaluates the defects of the spectrum based on the MR spectrum data collected by the MR data collection function F3 during the MRS scan. The evaluation of the defects of the spectrum is performed on the spectrum generated based on the collected MR spectrum data and the MR spectrum data being collected.
[0085] Here, the collected MR spectrum data is data for which collection of the MR spectrum data has been completed. On the other hand, the MR spectrum data being collected is data for which collection of the MR spectrum data has not been completed. In other words, the collected MR spectrum data and the MR spectrum data being collected include data with a good spectrum and data with a bad spectrum.
[0086] The evaluation of the spectrum defect in step ST150 is performed, for example, by the data recollection determination function F5 calculating the variance of the spectrum based on the MR spectrum data D3 collected by the MR data collection function F3.
[0087] In an MRS scan, a plurality of pieces of MR spectrum data are generally collected and added together to improve a signal-to-noise ratio (SNR). Therefore, whether or not a spectrum is defective may be evaluated by the variance of a spectrum based on MR spectrum data currently being collected relative to a spectrum based on a plurality of collected MR spectrum data or all collected MR spectrum data. Alternatively, the spectrum may be evaluated by the variance of a spectrum based on MR spectrum data currently being collected relative to a spectrum based on at least one collected MR spectrum data. The evaluation of whether a spectrum is defective may be performed, for example, using a trained model.
[0088] The evaluation of the spectral defects in the MR spectrum data is performed after a certain time has elapsed since the start of collection of the MR spectrum data. The evaluation can be performed if there is both the collected MR spectrum data and the MR spectrum data being collected.
[0089] In step ST160, the data recollection determination function F5 determines whether to collect a part or all of the MR spectrum data D3 again based on the evaluation of the spectrum defect. The evaluation of the spectrum defect is indicated, for example, by the number of the defective spectrum (i.e., the number of additions in the addition of the MR spectrum data), the total number of the defective spectra, etc.
[0090] Fig. 11 is a diagram showing an example of a display screen during collection of a spectrum based on the data for MR spectra D3. As shown in Fig. 11, during collection of the data for MR spectra D3, for example, a spectrum obtained by adding collected data for MR spectra or a spectrum indicating that the data for MR spectra being collected is the Nth spectrum (N: natural number) that has been added. The spectrum is displayed on the display 42, for example.
[0091] Furthermore, when it is determined that the MR spectrum data collected by the MR data collection function F3 does not satisfy the evaluation criterion for spectrum defects, the presentation function F7 may present that fact. In Fig. 11, an example is shown in which M (M: a natural number less than the total number of collected MR spectrum data) pieces of MR spectrum data that are defective spectra are detected.
[0092] In this case, when the data recollection determination function F5 determines that the evaluation criterion for the spectrum defect is not satisfied, the MR data collection function F3 collects a part or all of the MR spectrum data D3 again. The determination of whether the evaluation criterion for the spectrum defect is satisfied or not may be determined, for example, by whether the ratio of the MR spectrum data (M pieces in FIG. 11) that becomes a defective spectrum to the total number of collected MR spectrum data exceeds a predetermined reference value, thereby determining whether to collect the MR spectrum data again.
[0093] Also, the user may decide whether or not to collect M pieces of MR spectrum data that are bad spectra again. In this case, the presentation function F7 presents at least two of the following options: (a) automatically perform recollection of the MR spectrum data D3 and automatically integrate the recollected data and the collected data; (b) automatically perform recollection of the MR spectrum data D3, but select integration of the recollected data and the collected data after recollection of the MR spectrum data D3; and (c) do not automatically perform recollection of the MR spectrum data D3. The user may preliminarily decide on collection of the MR spectrum data D3 (i.e., step ST140) and integration of the recollected data and the collected data according to this presentation. The user makes the decision, for example, via the input interface 43. Note that registration may be performed between the data before integration. Presentation by the presentation function F7 is performed, for example, before the start of the flowchart in FIG. 10.
[0094] Specifically, for example, when it is determined to automatically perform recollection of the MR spectrum data D3, a part or all of the MR spectrum data D3 is collected again (i.e., step ST140) in the flowchart of Fig. 10. On the other hand, when it is determined not to automatically perform recollection of the MR spectrum data D3, step ST140 is not performed.
[0095] As described above, the collected MR spectrum data D3 may be data for metabolite spectra, data for water reference spectra, or both. In step ST160, when the MR data collection function F3 collects a part or all of the MR spectrum data again, data for metabolite spectra may be collected, data for water reference spectra may be collected, or both may be collected.
[0096] 10, in step ST170, the shim necessity determination function F4 determines whether or not to acquire the magnetic field adjustment data D1 again during the MRS scan based on the MR spectrum data D3 acquired by the MR data acquisition function F3. The MR spectrum data D3 acquired by the MR data acquisition function F3 includes the MR spectrum data already acquired during the MRS scan and the MR spectrum data being acquired.
[0097] The determination of whether to acquire the magnetic field adjustment data D1 again during the MRS scan is performed, for example, by determining whether the quality of the spectrum satisfies a predetermined evaluation criterion. Then, the shim necessity determination function F4 acquires the magnetic field adjustment data D1 again when the quality of the spectrum based on the MR spectrum data already collected in the MRS scan and the MR spectrum data being collected does not satisfy the predetermined evaluation criterion (i.e., NO in step ST170).
[0098] The shim necessity determination function F4 may determine whether the quality of the spectrum satisfies a predetermined evaluation criterion using at least one index of, for example, the signal-to-noise ratio, the half-width, and the accuracy of curve fitting.
[0099] 12 to 14 are explanatory diagrams for evaluating the quality of a spectrum based on the MR spectrum data D3 being collected. Cases in which the signal-to-noise ratio, the half-width, and the accuracy of curve fitting are used to determine whether the quality of the spectrum satisfies a predetermined evaluation standard will be described in order.
[0100] Fig. 12 shows a case where the quality of a spectrum is determined to satisfy a predetermined evaluation criterion using an index of signal-to-noise ratio. As shown in Fig. 12, the SNR is the peak height in a metabolite spectrum relative to twice the root mean square of the noise width in a region without peaks or artifacts in the metabolite spectrum in the frequency domain. Depending on whether the SNR satisfies a predetermined reference value set in advance, it may be determined whether the quality of a spectrum satisfies a predetermined evaluation criterion.
[0101] Fig. 13 shows a case where the full width at half maximum index is used to determine whether the quality of the spectrum meets a predetermined evaluation standard. The full width at half maximum (FWHM) of the spectrum peak is expressed by, for example, Equation (1). Here, T2 is the transverse relaxation time, γ is the gyromagnetic ratio, ΔB0 is the amount of change in the static magnetic field, and (Window Function) is a window function.
[0102]
number
[0103] Since a spectrum is obtained by Fourier transforming an MR signal (e.g., MR spectrum data D3), the full width at half maximum of the spectrum peak changes depending on the speed of the free induction decay. For example, when the static magnetic field is inhomogeneous due to poor shimming, the free induction decay becomes faster and the full width at half maximum becomes wider as shown in formula (1) compared with the case where the static magnetic field is homogeneous. FIG. 13 illustrates a case where the same subject is imaged in a state where the spectrum in FIG. 13(a) has a higher degree of uniformity of the magnetic field than the spectrum in FIG. 13(b). Whether the quality of the spectrum satisfies a predetermined evaluation criterion may be determined depending on whether the full width at half maximum satisfies a predetermined reference value.
[0104] FIG. 14 shows a case where the quality of a spectrum satisfies a predetermined evaluation criterion using an index of the accuracy of curve fitting. FIG. 14(a) shows a spectrum based on an actually collected MR signal, FIG. 14(b) shows a spectrum obtained by linearly combining the spectra of each known metabolite for the target metabolite, and FIG. 14(c) shows an example of the accuracy when the spectrum of FIG. 14(a) is curve-fitted to the spectrum of FIG. 14(b). For the curve fitting, a known technique for accurate curve fitting, such as correction of baseline distortion, can be used. Depending on whether the accuracy of the curve fitting satisfies a predetermined reference value set in advance, it may be determined whether the quality of the spectrum satisfies a predetermined evaluation criterion.
[0105] Returning to Fig. 10, if the shim necessity determination function F4 determines that the magnetic field adjustment data D1 should be acquired again (i.e., if the result is NO in step ST170 in which the quality of the spectrum does not satisfy the predetermined evaluation criterion), the shim data acquisition function F1 acquires the magnetic field adjustment data D1 again during the MRS scan. That is, the process proceeds to step ST110. Then, the correction control function F2 controls the current value of the magnetic field correction coil 13 during the MRS scan based on the magnetic field adjustment data D1 acquired again (i.e., step ST120). Furthermore, the process follows the flowchart of Fig. 10.
[0106] Also, when the shim necessity determination function F4 determines not to acquire the magnetic field adjustment data D1 again (i.e., YES in step ST170 where the quality of the spectrum meets a predetermined evaluation standard), the process proceeds to step ST140. That is, the MR data collection function F3 collects a part or all of the MR spectrum data D3 again without acquiring the magnetic field adjustment data D1 again.
[0107] Also, for example, after recollection of the MR spectrum data D3, such as after the end of the flowchart in FIG. 10, the recollected data and the collected data may be integrated. The integration function F8 integrates the recollected data and the collected data. As described above, the presentation function F7 presents the integration of the data and the collected data, and the user may decide, for example, via the input interface 43. The integration of the recollected data and the collected data may be automatically performed by the user's decision. Also, after recollection of the MR spectrum data D3, the presentation function F7 may further present whether or not to integrate the recollected data and the collected data, and the user may decide.
[0108] According to the MRI apparatus 1 of the second embodiment, when the quality of the spectrum based on the MR spectrum data is not maintained, the magnetic field adjustment is performed again, so that the deterioration of the quality of the MR data due to the decrease in the homogeneity of the static magnetic field can be suppressed. Also, when a bad spectrum, for example, that is not caused by the decrease in the homogeneity of the static magnetic field is detected, the magnetic field adjustment is not performed again, and the data for the MR spectrum that is lacking due to the bad spectrum is recollected. Therefore, the deterioration of the quality of the MR data can be suppressed without unnecessary extension of the imaging time.
[0109] According to at least one of the embodiments described above, it is possible to suppress deterioration of the quality of MR data due to a decrease in the homogeneity of the static magnetic field during MR data acquisition.
[0110] In the above embodiment, the term "processor" refers to a circuit such as a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit) or Application Specific Integrated Circuit (ASIC), programmable logic device (e.g. Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and FPGA), etc. The processor realizes various functions by reading and executing a program stored in a storage medium.
[0111] In addition, although the above embodiment shows an example in which a single processor of a processing circuit realizes each function, a processing circuit may be configured by combining multiple independent processors, and each processor may realize each function. In addition, when multiple processors are provided, a storage medium for storing a program may be provided separately for each processor, or a single storage medium may collectively store programs corresponding to the functions of all the processors.
[0112] In addition, the SIM data acquisition function F1, the correction control function F2, the MR data collection function F3, the SIM necessity determination function F4, the data re-collection determination function F5, the adjustment spectrum collection function F6, the presentation function F7, and the integration function F8 in the description of the embodiments are examples of the SIM data acquisition unit, the correction control unit, the MR data collection unit, the SIM necessity determination unit, the data re-collection determination unit, the adjustment spectrum collection unit, the presentation unit, and the integration unit in the description of the claims, etc.
[0113] Although several embodiments of the present invention 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, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]
[0114] 1...MRI device 13...Magnetic field correction coil F1...Shim data acquisition function F2...Correction control function F3...MR data collection function F4...Shim necessity determination function F5...Data recollection determination function F6...Adjustment spectrum collection function F7...Presentation function F8...Integration function
Claims
1. a shim data acquisition unit for acquiring data for adjusting a magnetic field to correct static magnetic field inhomogeneity; a correction control unit that controls a current value of a magnetic field correction coil for increasing the uniformity of the static magnetic field based on the magnetic field adjustment data; an MR data acquisition unit that acquires data for generating an MR image by performing an imaging scan of an object; a shim necessity determination unit that determines whether or not to acquire the magnetic field adjustment data again during the imaging scan based on the MR image generation data collected by the MR data collection unit, When the shim necessity determination unit determines that the magnetic field adjustment data is to be acquired again, the shim data acquisition unit acquires the magnetic field adjustment data again during the imaging scan, and the correction control unit controls the current value of the magnetic field correction coil during the imaging scan based on the magnetic field adjustment data acquired again. Magnetic resonance imaging device.
2. The MR image generation data collected by the MR data collection unit includes MR image generation data that has already been collected during the imaging scan and MR image generation data that is currently being collected.
2. A magnetic resonance imaging apparatus according to claim 1.
3. The MR data acquisition unit further acquires a part or all of the MR image generation data again.
2. A magnetic resonance imaging apparatus according to claim 1.
4. When the quality of an image based on the MR image generation data already collected during the imaging scan and the MR image generation data being collected does not satisfy a predetermined evaluation standard, the shim necessity determination unit acquires the magnetic field adjustment data again.
2. A magnetic resonance imaging apparatus according to claim 1.
5. The SIM necessity determination unit determines whether or not the quality of the image satisfies a predetermined evaluation criterion using at least one index of SSIM (Structural Similarity Index Measure), PSNR (Peak Signal to Noise Ratio), NMSE (Normalized Mean Squared Error), and MSE (Mean Squared Error).
5. A magnetic resonance imaging apparatus according to claim 4.
6. a data recollection determination unit that evaluates an artifact of an image based on the MR image generation data collected by the MR data collection unit during the imaging scan and determines whether or not to collect a part or all of the MR image generation data again, When the data recollection determination unit determines that the evaluation criterion regarding the artifact is not satisfied, the MR data acquisition unit again collects a part or all of the MR image generation data.
2. A magnetic resonance imaging apparatus according to claim 1.
7. the data recollection determination unit calculates background variance in at least one of an imaging region and a K-space region based on the MR image generation data collected by the MR data collection unit, and determines whether or not to collect a part or all of the MR image generation data again.
7. A magnetic resonance imaging apparatus according to claim 6.
8. a shim data acquisition unit for acquiring data for adjusting a magnetic field to correct static magnetic field inhomogeneity; a correction control unit that controls a current value of a magnetic field correction coil for increasing the uniformity of the static magnetic field based on the magnetic field adjustment data; an MR data acquisition unit that acquires MR spectrum data by MRS scanning to detect a spectrum of a subject; and a shim necessity determination unit that determines whether or not to acquire the magnetic field adjustment data again during the MRS scan based on the MR spectrum data acquired by the MR data acquisition unit, When the shim necessity determination unit determines that the magnetic field adjustment data is to be acquired again, the shim data acquisition unit acquires the magnetic field adjustment data again during the MRS scan, and the correction control unit controls the current value of the magnetic field correction coil during the MRS scan based on the magnetic field adjustment data acquired again. Magnetic resonance imaging device.
9. The MR spectrum data collected by the MR data collection unit includes MR spectrum data already collected during the MRS scan and MR spectrum data currently being collected.
9. A magnetic resonance imaging apparatus according to claim 8.
10. The MR data acquisition unit further acquires a part or all of the MR spectrum data again.
9. A magnetic resonance imaging apparatus according to claim 8.
11. The shim necessity determination unit acquires the magnetic field adjustment data again when the quality of the spectrum based on the MR spectrum data already collected in the MRS scan and the MR spectrum data being collected does not satisfy a predetermined evaluation criterion.
9. A magnetic resonance imaging apparatus according to claim 8.
12. the shim necessity determination unit determines whether or not the quality of the spectrum satisfies a predetermined evaluation criterion using at least one index of a signal-to-noise ratio, a half-width, and an accuracy of curve fitting; 12. A magnetic resonance imaging apparatus according to claim 11.
13. a data recollection determination unit that evaluates a spectrum defect based on the MR spectrum data collected by the MR data collection unit during the MRS scan and determines whether to collect a part or all of the MR spectrum data again, When the data recollection determination unit determines that the evaluation criterion regarding the spectrum defect is not satisfied, the MR data acquisition unit again collects a part or all of the MR spectrum data.
9. A magnetic resonance imaging apparatus according to claim 8.
14. the data recollection determination unit calculates a variance of the MR spectrum data being collected relative to the MR spectrum data collected by the MR data collection unit, and determines whether or not to collect a part or all of the MR spectrum data again.
14. A magnetic resonance imaging apparatus according to claim 13.
15. The shim data acquisition unit acquires the magnetic field adjustment data for correcting the static magnetic field inhomogeneity for at least one of the entire imaging region and a local region within the imaging region.
9. A magnetic resonance imaging apparatus according to claim 1 or 8.
16. The MR data acquisition unit reacquires a part or all of the data for at least one of the MR spectrum of the metabolite spectrum and the water reference spectrum; 11. A magnetic resonance imaging apparatus according to claim 10.
17. A display unit, the presenting unit presents a message to the effect that the spectrum based on the MR spectrum data collected by the MR data collecting unit does not satisfy an evaluation criterion regarding a defect in the spectrum when the spectrum is determined not to satisfy the evaluation criterion regarding a defect in the spectrum.
14. A magnetic resonance imaging apparatus according to claim 13.
18. A display unit, The presentation unit presents at least two of the following: (a) the execution of recollection by the MR data collection unit and the integration of the recollected data and the collected data are automatically performed; (b) the execution of recollection of data by the MR data collection unit is automatically performed, but the integration of the recollected data and the collected data is selected after the data is recollected; and (c) the execution of recollection of data by the MR data collection unit is not automatically performed.
11. A magnetic resonance imaging apparatus according to claim 3 or 10.
19. an integration unit; The integration unit integrates the recollected data and the collected data.
20. A magnetic resonance imaging apparatus according to claim 18.
20. The magnetic field correction coil is a gradient magnetic field coil.
9. A magnetic resonance imaging apparatus according to claim 1 or 8.
21. Acquire data for adjusting the magnetic field to correct static magnetic field inhomogeneity; Based on the magnetic field adjustment data, a current value of a magnetic field correction coil for increasing the uniformity of the static magnetic field is controlled; acquiring data for generating an MR image by performing an imaging scan of the subject; determining whether or not to acquire the magnetic field adjustment data again during the imaging scan based on the collected MR image generation data; when it is determined that the magnetic field adjustment data is to be acquired again, the magnetic field adjustment data is acquired again during the imaging scan, and the current value of the magnetic field correction coil is controlled during the imaging scan based on the magnetic field adjustment data acquired again. Magnetic resonance imaging methods.
22. Acquire data for adjusting the magnetic field to correct static magnetic field inhomogeneity; Based on the magnetic field adjustment data, a current value of a magnetic field correction coil for increasing the uniformity of the static magnetic field is controlled; acquiring data for an MR spectrum by performing a spectral detection MRS scan of the subject; determining whether to reacquire the magnetic field adjustment data during the MRS scan based on the collected MR spectrum data; when it is determined that the magnetic field adjustment data is to be acquired again, the magnetic field adjustment data is acquired again during the MRS scan, and the current value of the magnetic field correction coil is controlled during the MRS scan based on the magnetic field adjustment data acquired again. Magnetic resonance imaging methods.
Citation Information
Patent Citations
Magnetic resonance imaging apparatus and multi-slice imaging method
JP2019195588A
Magnetic resonance imaging apparatus
JP2020022572A