Magnetic Resonance Imaging Apparatus

Abstract

To improve contrast of CSF in an image.SOLUTION: A magnetic resonance imaging device includes a setting unit and a collection unit. The setting unit sets a pulse sequence for applying a refocus pulse several times after applying an excitation pulse once and collecting a plurality of echo signals. The collection unit executes the pulse sequence several times and collects data on a plurality of slices parallel to each other. The setting unit sets the pulse sequence so that the slice thickness of the refocus pulse is larger than the slice thickness of the excitation pulse. The collection unit executes the pulse sequence so as not to continuously collect data on adjacent slices of the plurality of slices, and collects data on each slice.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, in the examination of the cervical spine using a magnetic resonance imaging (MRI) apparatus, generally, images of a plurality of slices set in parallel along the cervical spine of a subject are captured using the fast spin echo (FSE) method. In this case, in the captured images, the contrast of cerebrospinal fluid (CSF) is important.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve the contrast of CSF in the image. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. The problems corresponding to the respective effects of each configuration shown in the embodiments described later can also be positioned as other problems.

Means for Solving the Problems

[0005] The MRI apparatus according to the embodiment includes a setting unit and a collection unit. The setting unit sets a pulse sequence for collecting a plurality of echo signals by applying a refocusing pulse a plurality of times after applying an excitation pulse once. The collection unit executes the pulse sequence a plurality of times to collect data of a plurality of slices parallel to each other. The setting unit sets the pulse sequence such that the slice thickness of the refocusing pulse is greater than the slice thickness of the excitation pulse. The collection unit executes the pulse sequence so as not to continuously collect data of adjacent slices among the plurality of slices, and collects data of each slice.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0007] Hereinafter, embodiments of the MRI apparatus according to the present application will be described in detail with reference to the drawings.

[0008] (Embodiment) FIG. 1 is a diagram showing a configuration example of an MRI apparatus according to this embodiment.

[0009] For example, as shown in FIG. 1, the MRI apparatus 100 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power supply 3, a whole-body radio frequency (RF) coil 4, a local RF coil 5, a transmission circuit 6, a reception circuit 7, an RF shield 8, a gantry 9, a bed 10, an input interface 11, a display 12, a memory circuit 13, and processing circuits 14 to 17.

[0010] The static magnetic field magnet 1 generates a static magnetic field in an imaging space where the subject S is placed. Specifically, the static magnetic field magnet 1 is formed in a hollow substantially cylindrical shape (including those having an elliptical shape in a cross section orthogonal to the central axis), and generates a static magnetic field in the imaging space formed on the inner peripheral side thereof. For example, the static magnetic field magnet 1 is a superconducting magnet, a permanent magnet, or the like. The superconducting magnet mentioned here is composed of, for example, a container filled with a coolant such as liquid helium and a superconducting coil immersed in the container.

[0011] The gradient magnetic field coil 2 is disposed inside the static magnetic field magnet 1 and generates a gradient magnetic field in the imaging space where the subject S is placed. Specifically, the gradient magnetic field coil 2 is formed in a hollow substantially cylindrical shape (including those having an elliptical shape in a cross section orthogonal to the central axis), and has an X coil, a Y coil, and a Z coil corresponding to the X axis, the Y axis, and the Z axis that are orthogonal to each other. The X coil, the Y coil, and the Z coil generate a gradient magnetic field that linearly changes along each axial direction in the imaging space based on the current supplied from the gradient magnetic field power supply 3. Here, the Z axis is set to be along the magnetic flux of the static magnetic field generated by the static magnetic field magnet 1. Further, the X axis is set to be along the horizontal direction orthogonal to the Z axis, and the Y axis is set to be along the vertical direction orthogonal to the Z axis. Here, the X axis, the Y axis, and the Z axis constitute a device coordinate system unique to the MRI apparatus 100.

[0012] The gradient magnetic field power supply 3 generates a gradient magnetic field in the imaging space by supplying current to the gradient magnetic coil 2. Specifically, the gradient magnetic field power supply 3 supplies current to the X coil, Y coil, and Z coil of the gradient magnetic coil 2 individually, thereby generating a gradient magnetic field that linearly changes along the readout direction, phase encoding direction, and slice direction that are orthogonal to each other in the imaging space. Here, the axis along the readout direction, the axis along the phase encoding direction, and the axis along the slice direction constitute a logical coordinate system for defining the slice region or volume region to be imaged.

[0013] Specifically, the gradient magnetic fields along the readout direction, phase encoding direction, and slice direction are superimposed on the static magnetic field generated by the static magnetic field magnet 1, thereby imparting spatial position information to the nuclear magnetic resonance (NMR) signal generated from the subject S. Specifically, the gradient magnetic field in the readout direction imparts the position information in the readout direction to the NMR signal by changing the frequency of the NMR signal according to the position in the readout direction. Also, the gradient magnetic field in the phase encoding direction imparts the position information in the phase encoding direction to the NMR signal by changing the phase of the NMR signal according to the position in the phase encoding direction. Also, the gradient magnetic field in the slice direction imparts the position information in the slice direction to the NMR signal. For example, the gradient magnetic field in the slice direction is used to determine the direction, thickness, and number of slices when the imaging region is a slice region (2D imaging), and is used to change the phase of the NMR signal according to the position in the slice direction when the imaging region is a volume region (3D imaging).

[0014] The whole-body RF coil 4 is arranged on the inner peripheral side of the gradient magnetic field coil 2, applies an RF pulse (excitation pulse, etc.) to the subject S arranged in the imaging space, and receives an NMR signal (echo signal, etc.) generated from the subject S due to the influence of the RF pulse. Specifically, the whole-body RF coil 4 is formed in a hollow substantially cylindrical shape (including those with an elliptical cross-sectional shape perpendicular to the central axis), and based on the RF pulse signal supplied from the transmission circuit 6, applies an RF pulse to the subject S arranged in the imaging space located on its inner peripheral side. Then, the whole-body RF coil 4 receives the NMR signal generated from the subject S due to the influence of the RF pulse, and outputs the received NMR signal to the reception circuit 7. For example, the whole-body RF coil 4 is a birdcage coil or a TEM (Transverse Electromagnetic) coil.

[0015] The local RF coil 5 is arranged near the subject S during imaging and receives the NMR signal generated from the subject S. Specifically, the local RF coil 5 is prepared for each part of the subject S, is arranged near the part to be imaged when imaging of the subject S is performed, receives the NMR signal generated from the subject S due to the influence of the RF pulse applied by the whole-body RF coil 4, and outputs the received NMR signal to the reception circuit 7. For example, the local RF coil 5 is a surface coil or a phased array coil configured by combining a plurality of surface coils as coil elements. Note that the local RF coil 5 may further have a transmission function for applying an RF pulse to the subject.

[0016] The transmission circuit 6 outputs an RF pulse signal corresponding to the resonance frequency (Larmor frequency) specific to the target atomic nucleus placed in the static magnetic field to the whole-body RF coil 4 or the local RF coil 5. Specifically, the transmission circuit 6 includes a pulse generator, an RF generator, a modulator, and an amplifier. The pulse generator generates the waveform of the RF pulse signal. The RF generator generates an RF signal at the resonance frequency. The modulator generates an RF pulse signal by modulating the amplitude of the RF signal generated by the RF generator with the waveform generated by the pulse generator. The amplifier amplifies the RF pulse signal generated by the modulator and outputs it to the whole-body RF coil 4 or the local RF coil 5.

[0017] The reception circuit 7 generates NMR data based on the NMR signal output from the whole-body RF coil 4 or the local RF coil 5, and outputs the generated NMR data to the processing circuit 15. Specifically, the reception circuit 7 includes a selector, a pre-stage amplifier, a phase detector, and an A / D (Analog / Digital) converter. The selector selectively inputs the NMR signal output from the whole-body RF coil 4 or the local RF coil 5. The pre-stage amplifier amplifies the NMR signal output from the selector. The phase detector detects the phase of the NMR signal output from the pre-stage amplifier. The A / D converter generates NMR data by converting the analog signal output from the phase detector into a digital signal, and outputs the generated NMR data to the processing circuit 15. Here, it should be noted that not all of the processes described as being performed by the reception circuit 7 necessarily need to be performed by the reception circuit 7, and some processes (for example, the process by the A / D converter, etc.) may be performed by the whole-body RF coil 4 or the local RF coil 5.

[0018] The RF shield 8 is disposed between the gradient magnetic field coil 2 and the whole-body RF coil 4, and shields the gradient magnetic field coil 2 from the RF pulse generated by the whole-body RF coil 4. Specifically, the RF shield 8 is formed in a hollow substantially cylindrical shape (including those having an elliptical cross-sectional shape perpendicular to the central axis of the cylinder), and is disposed in the space on the inner peripheral side of the gradient magnetic field coil 2 so as to cover the outer peripheral surface of the whole-body RF coil 4.

[0019] The gantry 9 has a hollow bore 9a formed in a substantially cylindrical shape (including those with an elliptical cross-sectional shape perpendicular to the central axis), and houses the static magnetic field magnet 1, the gradient magnetic field coil 2, the whole-body RF coil 4, and the RF shield 8. Specifically, the gantry 9 arranges the whole-body RF coil 4 on the outer peripheral side of the bore 9a, arranges the RF shield 8 on the outer peripheral side of the whole-body RF coil 4, arranges the gradient magnetic field coil 2 on the outer peripheral side of the RF shield 8, and arranges the static magnetic field magnet 1 on the outer peripheral side of the gradient magnetic field coil 2, and houses each of them in this state. Here, the space inside the bore 9a of the gantry 9 becomes the imaging space where the subject S is placed during imaging.

[0020] The couch 10 includes a top plate 10a on which the subject S is placed, and when imaging of the subject S is performed, the top plate 10a on which the subject S is placed is moved into the imaging space. For example, the couch 10 is installed such that the longitudinal direction of the top plate 10a is parallel to the central axis of the static magnetic field magnet 1.

[0021] Here, an example in which the MRI apparatus 100 has a so-called tunnel-type structure in which the static magnetic field magnet 1, the gradient magnetic field coil 2, and the whole-body RF coil 4 are each formed in a substantially cylindrical shape will be described, but the embodiment is not limited to this. For example, the MRI apparatus 100 may have a so-called open-type structure in which a pair of static magnetic field magnets, a pair of gradient magnetic field coils, and a pair of RF coils are arranged so as to face each other with the imaging space where the subject S is placed interposed therebetween. In such an open-type structure, the space sandwiched by the pair of static magnetic field magnets, the pair of gradient magnetic field coils, and the pair of RF coils corresponds to the bore in the tunnel-type structure.

[0022] The input interface 11 receives input operations of various instructions and various information from the operator. Specifically, the input interface 11 is connected to the processing circuit 17, converts the input operation received from the operator into an electrical signal, and outputs it to the processing circuit 17. For example, the input interface 11 is realized by a trackball, a switch button, a mouse, a keyboard, a touch pad for performing 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, a voice input circuit, and the like for setting imaging conditions and a region of interest (ROI). Note that in this specification, the input interface 11 is not limited to only those provided with physical operation components such as a mouse and a 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 apparatus and outputs this electrical signal to the control circuit is also included in the example of the input interface 11.

[0023] The display 12 displays various information. Specifically, the display 12 is connected to the processing circuit 17, converts data of various information sent from the processing circuit 17 into a display electrical signal, and outputs it. For example, the display 12 is realized by a liquid crystal monitor, a CRT monitor, a touch panel, or the like.

[0024] The storage circuit 13 stores various data. Specifically, the storage circuit 13 is connected to the processing circuits 14 to 17, and stores various data input and output by each processing circuit. For example, the storage circuit 13 is realized by a semiconductor memory element such as a RAM (Random Access Memory) or a flash memory, a hard disk, an optical disk, or the like.

[0025] The processing circuit 14 has a bed control function 14a. The bed control function 14a controls the operation of the bed 10 by outputting a control electrical signal to the bed 10. For example, the bed control function 14a receives an instruction from the operator to move the top plate 10a in the longitudinal direction, vertical direction, or lateral direction via the input interface 11, and operates the moving mechanism of the top plate 10a of the bed 10 so as to move the top plate 10a according to the received instruction.

[0026] The processing circuit 15 has a collection function 15a. The collection function 15a collects k-space data by executing various pulse sequences. Specifically, the collection function 15a executes various pulse sequences by driving the gradient magnetic field power supply 3, the transmission circuit 6, and the reception circuit 7 according to the sequence execution data output by the imaging control function 17b of the processing circuit 17. Here, the sequence execution data is data representing a pulse sequence, and is information defining the timing at which the gradient magnetic field power supply 3 supplies current to the gradient magnetic field coil 2 and the strength of the supplied current, the timing at which the transmission circuit 6 supplies an RF pulse signal to the whole-body RF coil 4 and the strength of the supplied RF pulse signal, the timing at which the reception circuit 7 samples the NMR signal, etc. Then, the collection function 15a receives the NMR data output from the reception circuit 7 as a result of executing the pulse sequence, and stores it in the storage circuit 13. At this time, the NMR data stored in the storage circuit 13 is stored as k-space data representing a two-dimensional or three-dimensional k-space by being given position information along each of the readout direction, phase encoding direction, and slice direction by the above-described respective gradient magnetic fields.

[0027] The processing circuit 16 has a generation function 16a. The generation function 16a generates an image from the k-space data collected by the collection function 15a of the processing circuit 15. Specifically, the generation function 16a reads out the k-space data collected by the collection function 15a of the processing circuit 15 from the storage circuit 13, and performs a reconstruction process such as Fourier transform on the read k-space data to generate a two-dimensional or three-dimensional image. Then, the generation function 16a stores the generated image in the storage circuit 13.

[0028] The processing circuit 17 has a setting function 17a and an imaging control function 17b. The setting function 17a receives an input of imaging conditions from an operator via the input interface 11, and based on the input imaging conditions, sets a pulse sequence for collecting k-space data of the subject S. The imaging control function 17b generates sequence execution data representing the pulse sequence set by the setting function 17a, and outputs the generated sequence execution data to the processing circuit 15, thereby causing the collection function 15a of the processing circuit 15 to execute the pulse sequence. Further, the imaging control function 17b controls the processing circuit 16 to cause the processing circuit 15 to reconstruct an image from the k-space data collected by the processing circuit 15. Also, the imaging control function 17b reads out the image stored in the memory circuit 13 in response to a request from the operator, and causes the read image to be displayed on the display 12.

[0029] The configuration example of the MRI apparatus 100 according to the present embodiment has been described above. Under such a configuration, the MRI apparatus 100 according to the present embodiment has a function of imaging a plurality of slices parallel to each other using the Fast Spin Echo (FSE) method.

[0030] Specifically, the setting function 17a of the processing circuit 17 sets a pulse sequence of the FSE method for collecting a plurality of echo signals by applying a refocusing pulse a plurality of times after applying an excitation pulse once. Here, the setting function 17a is an example of a setting unit.

[0031] FIG. 2 is an example of a pulse sequence of the FSE method set by the setting function 17a according to the present embodiment.

[0032] In FIG. 2, “RF” indicates the timing at which the RF pulse is applied. Also, “Gs” indicates on the horizontal axis the application timing and application time of the slice gradient magnetic field, and indicates on the vertical axis the intensity of the slice gradient magnetic field. Also, “Gr” indicates on the horizontal axis the application timing and application time of the readout gradient magnetic field, and indicates on the vertical axis the intensity of the readout gradient magnetic field. Also, “Gp” indicates on the horizontal axis the application timing and application time of the phase encoding gradient magnetic field, and indicates on the vertical axis the intensity of the phase encoding gradient magnetic field.

[0033] For example, as shown in FIG. 2, in the pulse sequence of the FSE method, after an excitation pulse (Flip) is applied, a plurality of refocusing pulses (Flop0, Flop1, Flop2 ···) are continuously applied. Here, for example, the excitation pulse is a 90° pulse, and the refocusing pulse is a 180° pulse. By continuously applying a plurality of refocusing pulses in this way, an echo signal (Echo0, Echo1, Echo2 ···) is generated each time a refocusing pulse is applied.

[0034] Also, at the timing when the excitation pulse and each refocusing pulse are applied, a slice gradient magnetic field is applied. Also, at the timing immediately after each refocusing pulse is applied, a phase encoding gradient magnetic field is applied while changing the intensity step by step for each refocusing pulse. Also, at the timing when each echo signal is generated, a readout gradient magnetic field is applied. As a result, positions in the readout direction, phase encoding direction, and slice direction are imparted to the echo signals generated by each refocusing pulse, and k-space data is collected.

[0035] Then, the collection function 15a of the processing circuit 15 executes the pulse sequence of the FSE method set by the setting function 17a a plurality of times to collect data of a plurality of slices parallel to each other. Here, the collection function 15a is an example of a collection unit.

[0036] For example, in the examination of the cervical vertebrae using an MRI apparatus, generally, T1-weighted images and T2-weighted images of a plurality of slices set in parallel along the cervical vertebrae of a subject are captured using the FSE method. In this case, in the captured images, the contrast of the CSF becomes important.

[0037] FIG. 3 is a diagram showing an example of a T1-weighted image captured in the examination of the cervical vertebrae. Further, FIG. 4 is a diagram showing an example of a T2-weighted image captured in the examination of the cervical vertebrae.

[0038] For example, as shown in FIG. 3, in the T1-weighted image captured in the examination of the cervical vertebrae, it is desirable that the luminance of the CSF in the image is low (there are many flow voids). Further, as shown in FIG. 4, in the T2-weighted image captured in the examination of the cervical vertebrae, it is desirable that the luminance of the CSF in the image is high (there are few flow voids).

[0039] However, in imaging using the FSE method, there are cases where sufficient contrast of the CSF cannot be obtained in the T1-weighted image and the T2-weighted image. Specifically, in the T1-weighted image, there are cases where the luminance value of the CSF does not become sufficiently low, or in the T2-weighted image, there are cases where the luminance value of the CSF does not become sufficiently high.

[0040] For this reason, the MRI apparatus 100 according to the present embodiment is configured to be able to improve the contrast of the CSF in the image.

[0041] Specifically, in the present embodiment, the setting function 17a sets the pulse sequence of the FSE method so that the slice thickness of the refocusing pulse is larger than the slice thickness of the excitation pulse.

[0042] For example, the setting function 17a sets the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse by adjusting the intensity of the slice-direction gradient magnetic field applied together with the refocusing pulse.

[0043] Thus, in the case of imaging conditions for obtaining a T1-weighted image, since the TR (repetition time) is sufficiently short with respect to the T1 value of the CSF, the longitudinal magnetization of the CSF component excited in one slice flows into the adjacent slice without sufficient recovery between slices and is excited. Therefore, the saturation effect becomes high, and the luminance of the CSF in the T1-weighted image can be lowered. On the other hand, in the case of imaging conditions for obtaining a T2-weighted image, since the refocusing pulse is applied over a wide range to the CSF component flowing out of the slice while the refocusing pulse is continuously applied after the excitation pulse is applied, the flow void of the CSF in the T2-weighted image can be suppressed.

[0044] Here, when the slice thickness of the refocusing pulse is set larger than the slice thickness of the excitation pulse in this way, a wider range is selectively excited by the refocusing pulse, so it is considered that interference is likely to occur between adjacent slices.

[0045] Therefore, in the present embodiment, the collection function 15a executes the pulse sequence of the FSE method so as not to continuously collect the data of adjacent slices among the plurality of slices, and collects the data of each slice.

[0046] For example, the collection function 15a divides the plurality of slices into a plurality of groups so that adjacent slices are included in different groups, and sequentially collects the data of the slices included in each group for each group.

[0047] Furthermore, for example, the collection function 15a repeats collecting the data of the selected slices in order by selecting every other slice in the direction in which the slices are arranged for each group, thereby collecting the data of the slices included in each group.

[0048] FIGS. 5 and 6 are diagrams showing an example of data collection performed by the collection function 15a according to the present embodiment.

[0049] For example, as shown in FIG. 5, when a cervical vertebra examination is performed, the collection function 15a collects data of nine slices S1 to S9 that are set to be parallel to each other along the cranio-caudal direction with respect to the head of the subject.

[0050] In this case, for example, the collection function 15a divides the nine slices S1 to S9 into a plurality of groups such that adjacent slices are included in different groups according to the imaging division number (also called coverage) specified by the operator.

[0051] For example, as shown in FIG. 6, when the imaging division number specified by the operator is "2", the collection function 15a divides the nine slices S1 to S9 into two groups. Specifically, the collection function 15a divides the nine slices S1 to S9 into a first group of every other slice S1, S3, S5, S7, and S9 (FIG. 6(A)) and a second group of every other slice S2, S4, S6, and S8 (FIG. 6(B)).

[0052] Then, for example, the collection function 15a repeats the process of selecting every other slice in the direction in which the slices are arranged, as indicated by the numbered parentheses in FIG. 6, for each group, and sequentially collecting the data of the selected slices, thereby collecting the data of the slices included in each group. Specifically, the collection function 15a collects the data of the slices included in the first group in the order of slices S1, S5, S9, S3, S7, and then collects the data of the slices included in the second group in the order of slices S2, S6, S4, S8.

[0053] In this way, by dividing a plurality of slices into groups of every other slice so that adjacent slices are included in different groups respectively, and collecting the data of each slice in order for each group, it is possible to increase the distance between continuously collected slices and to widen the time interval at which the data of adjacent slices are collected. Further, for each group, by repeating the operation of selecting every other slice in the direction in which the slices are arranged and collecting the data of the selected slices in order, it is possible to further increase the interval between continuously collected slices. As a result, even when the slice thickness of the refocusing pulse is set to be larger than the slice thickness of the excitation pulse, interference is less likely to occur between adjacent slices.

[0054] And in this case, for example, the setting function 17a sets the slice thickness of the refocusing pulse according to the slice intervals of a plurality of slices.

[0055] For example, the setting function 17a sets the slice thickness of the refocusing pulse according to the slice intervals of a plurality of slices specified by the operator.

[0056] FIG. 7 is a diagram showing an example of setting the slice thickness of the refocusing pulse performed by the setting function 17a according to the present embodiment.

[0057] For example, assume that the slice interval specified by the operator is “0.8 mm” and the slice thickness is “4 mm”.

[0058] In this case, in a general FSE method, for example, as shown in FIG. 7(A), the slice thicknesses of the excitation pulse and the refocusing pulse are each set to 4 [mm]. Also, when collecting data by dividing a plurality of slices into groups of every other slice as in the example shown in FIG. 6, the slice interval of the refocusing pulse is set to 4 [mm]×2 + 0.8 [mm]×2 = 9.6 [mm].

[0059] In contrast, in the present embodiment, the setting function 17a sets the slice thickness of the excitation pulse to 4 [mm], but sets the slice thickness of the refocusing pulse to 4 [mm] + α, which is greater than 4 [mm], as shown in FIG. 7(B). At this time, the setting function 17a sets the slice interval of the refocusing pulse in the same manner as in the example of FIG. 7(A), and then sets the value of α according to the slice interval. For example, the setting function 17a sets, as the value of α, a value obtained by multiplying the slice interval of the refocusing pulse by a predetermined ratio. Here, the value of α is set to a value within an allowable range of the magnitude of interference generated between the slices of the refocusing pulse.

[0060] Although the processing functions of the processing circuits 14 to 17 have been described above, for example, each processing circuit is realized by a processor. In this case, the processing functions of each processing circuit are stored in the storage circuit 13 in the form of a program executable by a computer, for example. Then, each processing circuit reads out and executes each program from the storage circuit 13 to realize the processing function corresponding to each program. In other words, each processing circuit in the state of having read out each program has each function shown in each processing circuit of FIG. 1.

[0061] FIG. 8 is a flowchart showing the processing procedure of the processing performed by the MRI apparatus 100 according to the present embodiment.

[0062] For example, as shown in FIG. 8, in the present embodiment, the setting function 17a sets the pulse sequence of the FSE method so that the slice thickness of the refocusing pulse becomes larger than the slice thickness of the excitation pulse in response to a start instruction from the operator (step S101, Yes) (step S102). The processing of steps S101 and S102 is realized, for example, by the processing circuit 17 reading out and executing a predetermined program corresponding to the setting function 17a from the storage circuit 13.

[0063] Thereafter, while the collection function 15a does not continuously collect data of adjacent slices, the pulse sequence of the FSE method is executed multiple times to collect data of a plurality of slices parallel to each other (step S103). The process of this step S103 is realized, for example, by the processing circuit 15 reading out a predetermined program corresponding to the collection function 15a from the storage circuit 13 and executing it.

[0064] Then, the generation function 16a generates an image of each slice based on the data collected by the collection function 15a (step S104). The process of this step S104 is realized, for example, by the processing circuit 16 reading out a predetermined program corresponding to the generation function 16a from the storage circuit 13 and executing it.

[0065] In the above description, it is assumed that the processing circuits 14 to 17 are each realized by a single processor, but the embodiment is not limited to this. For example, each processing circuit may be configured by combining a plurality of independent processors, and each processor may realize each processing function by executing a program. Also, the processing functions of each processing circuit may be appropriately distributed or integrated into a single or a plurality of processing circuits. Further, in the above description, it is assumed that a single storage circuit 13 stores programs corresponding to each processing function, but the embodiment is not limited to this. For example, a plurality of storage circuits may be distributed and arranged for each processing circuit, and each processing circuit may read out the corresponding program from an individual storage circuit.

[0066] As described above, in the present embodiment, the setting function 17a sets a pulse sequence of the FSE method that collects a plurality of echo signals by applying a refocusing pulse a plurality of times after applying an excitation pulse once. Further, the collection function 15a executes the pulse sequence of the FSE method set by the setting function 17a a plurality of times to collect data of a plurality of slices parallel to each other. Here, the setting function 17a sets the pulse sequence of the FSE method so that the slice thickness of the refocusing pulse is larger than the slice thickness of the excitation pulse. Further, the collection function 15a executes the pulse sequence of the FSE method so as not to continuously collect data of adjacent slices among the plurality of slices, and collects data of each slice.

[0067] According to such a configuration, by making the slice thickness of the refocusing pulse larger than the slice thickness of the excitation pulse, as described above, it is possible to lower the luminance of the CSF in the T1-weighted image and increase the luminance of the CSF in the T2-weighted image. Further, by collecting the data of each slice while not continuously collecting the data of adjacent slices, as described above, even when the slice thickness of the refocusing pulse is set larger than the slice thickness of the excitation pulse, interference is less likely to occur between adjacent slices. Therefore, according to the present embodiment, the contrast of the CSF in the image can be improved.

[0068] Further, in the present embodiment, the setting function 17a sets the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse by adjusting the intensity of the slice-selection gradient magnetic field applied together with the refocusing pulse. Thereby, the characteristics of the refocusing pulse can be improved without extending the ETS (Echo Train Space) or increasing the SAR (Specific Absorption Rate).

[0069] (Modification of the embodiment) Although the embodiments of the MRI apparatus 100 have been described above, it is also possible to implement the above-described embodiments by appropriately changing a part of the configuration of the MRI apparatus 100. Therefore, hereinafter, some modification examples according to the above-described embodiments will be described. In the following, the description will focus on the points different from the above-described embodiments, and the common content will be omitted.

[0070] For example, in the above-described embodiment, an example in which the collection function 15a divides a plurality of slices into groups of every other slice so that adjacent slices are included in different groups, and then repeatedly collects the data of the slices selected every other slice for each group has been described. However, the embodiment is not limited to this.

[0071] For example, when the collection function 15a divides a plurality of slices into a plurality of groups, the interval between the slices included in each group is not limited to one, and may be two or more. For example, when the imaging division number specified by the operator is "3", the collection function 15a divides a plurality of slices into groups of every other slice, divides them into three groups, and collects the data of each slice.

[0072] Also, the interval between the slices when selecting slices for each group is not limited to one, and may be two or more. For example, the collection function 15a may repeatedly collect the data of the slices included in each group by selecting every other slice in the direction in which the slices are arranged for each group and collecting the data of the selected slices in order.

[0073] Also, for example, the collection function 15a may repeatedly collect the data of the slices selected at least every other slice for the entire plurality of parallel slices without grouping the slices. In this case, for example, the collection function 15a may collect the data of each slice by repeatedly selecting every other slice in the direction in which the plurality of slices are arranged and collecting the data of the selected slices in order.

[0074] In the above-described embodiment, an example has been described in which the setting function 17a sets the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse by adjusting the intensity of the slice-direction gradient magnetic field applied together with the refocusing pulse. However, the embodiment is not limited to this.

[0075] For example, the setting function 17a may set the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse while adjusting the bandwidth of the refocusing pulse.

[0076] When setting the slice thickness of the refocusing pulse by adjusting the intensity of the slice-direction gradient magnetic field, if the intensity of the slice-direction gradient magnetic field differs too much between the excitation pulse and the refocusing pulse, the influence of magnetic field inhomogeneity may increase.

[0077] Therefore, for example, the setting function 17a adjusts the intensity of the slice-direction gradient magnetic field applied together with the refocusing pulse and the bandwidth of the refocusing pulse according to the magnitude of the magnetic field inhomogeneity at each position for each position of a plurality of slices, so that the slice thickness of the refocusing pulse can be set to be larger than the slice thickness of the excitation pulse without significantly changing the ratio between the slice gradient magnetic field of the excitation pulse and the slice gradient magnetic field of the refocusing pulse. In this case, for example, the setting function 17a uses the B0 map imaged in a preparatory imaging performed before this imaging to obtain the magnetic field inhomogeneity at the position of each slice, and adjusts the bandwidth of the RF pulse according to the degree of this magnetic field inhomogeneity. This is because if the refocusing pulse is uniformly made broadband, a significant increase in SAR is inevitable, but if the magnetic field is uniform to a certain extent and not affected by inhomogeneity, it is considered that it can be dealt with only by changing the slice thickness of the refocusing pulse as in the above-described embodiment.

[0078] In the above-described embodiment, an example has been described in which the setting function 17a sets the slice thickness of the refocusing pulse according to the slice interval of a plurality of slices. However, the embodiment is not limited to this.

[0079] For example, the setting function 17a may change the slice thickness of the refocus pulse according to the imaging conditions (image contrast).

[0080] (Other embodiments) In the above-described embodiments, an example in which the setting unit and the collection unit in this specification are realized by the setting function 17a of the processing circuit 17 and the collection function 15a of the processing circuit 15 has been described. However, the embodiments are not limited to this. For example, the setting unit and the collection unit in this specification may realize the same functions not only by the setting function 17a and the collection function 15a described in the embodiments, but also by only hardware, only software, or a combination of hardware and software.

[0081] In the above description, an example has been described in which the "processor" reads and executes a program corresponding to each processing function from the storage circuit. However, the embodiments are not limited to this. The term "processor" means, for example, a circuit such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), or a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)). When the processor is, for example, a CPU, the processor realizes each processing function by reading and executing a program stored in the storage circuit. On the other hand, when the processor is an ASIC, instead of storing a program in the storage circuit, the processing function is directly incorporated as a logic circuit in the circuit of the processor. Note that each processor according to the present embodiment is not limited to being configured as a single circuit for each processor, and may be configured as one processor by combining a plurality of independent circuits to realize its processing function. Further, a plurality of components in FIG. 1 may be integrated into one processor to realize its processing function.

[0082] Here, the program executed by the processor is provided by being pre - incorporated into a ROM (Read Only Memory), a storage circuit, etc. This program may be provided by being recorded on a computer - readable storage medium such as a CD (Compact Disk) - ROM, an FD (Flexible Disk), a CD - R (Recordable), a DVD (Digital Versatile Disk) in a file in a form installable or executable on these devices. Further, this program may be stored on a computer connected to a network such as the Internet and provided or distributed by being downloaded via the network. For example, this program is composed of modules including the above - described respective functional units. As actual hardware, the CPU reads the program from a storage medium such as a ROM and executes it, whereby each module is loaded onto the main storage device and generated on the main storage device.

[0083] According to at least one of the embodiments described above, the contrast of the CSF in the image can be improved.

[0084] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations of the embodiments can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0085] 100 MRI apparatus 15 Processing circuit 15a Acquisition function 17 Processing circuit 17a Setting function

Claims

1. A setting unit that sets a pulse sequence for collecting a plurality of echo signals by applying a refocusing pulse a plurality of times after applying an excitation pulse once; A collection unit that executes the pulse sequence a plurality of times to collect data of a plurality of slices parallel to each other; The setting unit sets the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse by setting, as the slice thickness of the refocusing pulse, a thickness obtained by adding a value within an allowable range of the magnitude of interference generated between slices of the refocusing pulse to the slice thickness of the excitation pulse, thereby setting the pulse sequence; The collection unit executes the pulse sequence so as not to continuously collect data of adjacent slices among the plurality of slices, and collects data of each slice; A magnetic resonance imaging apparatus.

2. The collection unit divides the plurality of slices into a plurality of groups such that adjacent slices are included in different groups, and sequentially collects data of the slices included in each group for each group; The magnetic resonance imaging apparatus according to Claim 1.

3. The collection unit collects data of the slices included in each group by repeating, for each group, selecting slices at every other slice in the direction in which the slices are arranged and sequentially collecting data of the selected slices; The magnetic resonance imaging apparatus according to Claim 2.

4. The collection unit collects data of each slice by repeating selecting slices at every other slice in the direction in which the plurality of slices are arranged and sequentially collecting data of the selected slices; The magnetic resonance imaging apparatus according to Claim 1.

5. The setting unit sets the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse by adjusting the intensity of a slice-selection gradient magnetic field applied together with the refocusing pulse; The magnetic resonance imaging apparatus according to any one of Claims 1 to 4.

6. The setting unit sets the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse while adjusting the bandwidth of the refocusing pulse; The magnetic resonance imaging apparatus according to any one of Claims 1 to 4.

7. The setting unit adjusts, for each position of each of the plurality of slices, the intensity of the slice-direction gradient magnetic field applied together with the refocusing pulse and the bandwidth of the refocusing pulse according to the magnitude of the magnetic field inhomogeneity at each position, so that the ratio of the slice-direction gradient magnetic field of the excitation pulse to the slice-direction gradient magnetic field of the refocusing pulse is made substantially constant while setting the slice thickness of the refocusing pulse to be larger than the slice thickness of the excitation pulse. The magnetic resonance imaging apparatus according to any one of claims 1 to 4. Claim 8 The setting unit changes the slice thickness of the refocusing pulse according to imaging conditions. The magnetic resonance imaging apparatus according to any one of claims 1 to 7. Claim 9 The setting unit sets the slice thickness of the refocusing pulse according to the slice interval of the plurality of slices. The magnetic resonance imaging apparatus according to any one of claims 1 to 8.

Images