Magnetic resonance imaging equipment

Abstract

To improve spatial resolution and temporal resolution in imaging a part including a tissue with short T2 or T2* relaxation time.SOLUTION: A magnetic resonance imaging apparatus comprises a collection unit. The collection unit applies excitation pulses to a subject at repetition time intervals to acquire echo signals generated at the respective repetition time intervals and uses the echo signals to collect data on a plurality of trajectories set in a k space. The collection unit acquires a plurality of echo signals by setting echo times, which each are a time from application of an excitation pulse to generation of an echo signal, so as to have different lengths in the respective repetition times and uses the plurality of echo signals to collect data on the same trajectory.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, a technology called Ultra Short TE (UTE) is known as a technology related to a magnetic resonance imaging (MRI) apparatus.

[0003] UTE is a technology that acquires an echo signal immediately after applying an excitation pulse to the subject, and uses the echo signal to acquire k-space data by radial acquisition to generate an image. By setting the echo time (TE), which is the time from application of the excitation pulse to generation of the echo signal, to a short time of, for example, less than 0.1 ms, it is possible to obtain images of T2 or T2 * It is possible to visualize tissues with short relaxation times. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-195421 A [Patent Document 2] JP 2016-123865 A [Patent Document 3] JP 2017-225501 A Summary of the Invention [Problem to be solved by the invention]

[0005] One of the problems that the embodiments disclosed in this specification and the drawings are intended to solve is T2 or T2 *The object of the present invention is to improve the spatial and temporal resolution when imaging a site including tissue with a short relaxation time. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0006] The MRI apparatus according to the embodiment includes an acquisition unit. The acquisition unit acquires echo signals generated at intervals of a repetition time by applying an excitation pulse to a subject at the intervals of the repetition time, and acquires data of a plurality of trajectories set in k-space using the echo signals. Here, the acquisition unit acquires a plurality of echo signals by setting an echo time, which is a time from application of the excitation pulse to generation of the echo signal, to different lengths for each of a plurality of repetition times, and acquires data of the same trajectory using the plurality of echo signals. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an MRI apparatus according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a trajectory in k-space used by the acquisition function according to the first embodiment. [Diagram 3] FIG. 3 is a diagram showing a pulse sequence used by the acquisition function according to the first embodiment. [Figure 4] FIG. 4 is a flowchart showing the procedure of the imaging method performed by the MRI apparatus according to the first embodiment. [Diagram 5] FIG. 5 is a diagram showing a pulse sequence used by the acquisition function according to the second embodiment. [Figure 6] FIG. 6 is a diagram showing an example of a trajectory in k-space used by an acquisition function according to a modified example of the second embodiment. [Figure 7]FIG. 7 is a diagram showing an example of contrast-enhanced imaging according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of an MRI apparatus according to the present application will be described in detail with reference to the drawings.

[0009] (First embodiment) FIG. 1 is a diagram showing an example of the configuration of an MRI apparatus according to the first embodiment.

[0010] For example, as shown in FIG. 1, an 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 RF (Radio Frequency) 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 16.

[0011] The static magnetic field magnet 1 generates a static magnetic field in an imaging space in which a subject S is placed. Specifically, the static magnetic field magnet 1 is formed in a hollow, approximately cylindrical shape (including a shape in which the cross section perpendicular to the central axis is elliptical), and generates a static magnetic field in an imaging space formed on its inner periphery. For example, the static magnetic field magnet 1 is a superconducting magnet or a permanent magnet. The superconducting magnet referred to here is composed of, for example, a container filled with a coolant such as liquid helium, and a superconducting coil immersed in the container.

[0012] The gradient coil 2 is disposed inside the static magnetic field magnet 1, and generates a gradient magnetic field in an imaging space in which the subject S is disposed. Specifically, the gradient coil 2 is formed in a hollow, substantially cylindrical shape (including a shape in which the cross section perpendicular to the central axis is elliptical), and has an X coil, a Y coil, and a Z coil corresponding to the X axis, the Y axis, and the Z axis, which are perpendicular to each other. The X coil, the Y coil, and the Z coil generate a gradient magnetic field in the imaging space that changes linearly along each axis direction based on a 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. The X axis is set to be along the horizontal direction perpendicular to the Z axis, and the Y axis is set to be along the vertical direction perpendicular to the Z axis. As a result, the X axis, the Y axis, and the Z axis form an apparatus coordinate system unique to the MRI apparatus 100.

[0013] The gradient magnetic field power supply 3 generates a gradient magnetic field in the imaging space by supplying a current to the gradient magnetic field coil 2. Specifically, the gradient magnetic field power supply 3 generates a gradient magnetic field in the imaging space that changes linearly along the mutually orthogonal readout direction, phase encoding direction, and slice direction, respectively, by supplying currents individually to the X coil, Y coil, and Z coil of the gradient magnetic field coil 2. In the following, the gradient magnetic field along the readout direction is called a readout gradient magnetic field, the gradient magnetic field along the phase encoding direction is called a phase encoding gradient magnetic field, and the gradient magnetic field along the slice direction is called a slice gradient magnetic field.

[0014] Here, the readout gradient magnetic field, the phase encoding gradient magnetic field, and the slice gradient magnetic field are superimposed on the static magnetic field generated by the static magnetic field magnet 1, thereby providing spatial position information to the magnetic resonance signal generated from the subject S. Specifically, the readout gradient magnetic field changes the frequency of the magnetic resonance signal according to the position in the readout direction, thereby providing the magnetic resonance signal with position information along the readout direction. The phase encoding gradient magnetic field changes the phase of the magnetic resonance signal along the phase encoding direction, thereby providing the magnetic resonance signal with position information along the phase encoding direction. The slice gradient magnetic field provides the magnetic resonance signal with position information along the slice direction. For example, when the imaging region is a slice region (2D imaging), the slice gradient magnetic field is used to determine the direction, thickness, and number of slice regions, and when the imaging region is a volume region (3D imaging), the slice gradient magnetic field is used to change the phase of the magnetic resonance signal according to the position in the slice direction. As a result, the axis along the readout direction, the axis along the phase encoding direction, and the axis along the slice direction form a logical coordinate system for defining the slice region or volume region to be imaged.

[0015] The whole-body RF coil 4 is disposed on the inner circumference side of the gradient magnetic field coil 2, applies an RF magnetic field (excitation pulse, etc.) to the subject S disposed in the imaging space, and receives a magnetic resonance signal (echo signal, etc.) generated from the subject S by the RF magnetic field. Specifically, the whole-body RF coil 4 is formed in a hollow, substantially cylindrical shape (including a shape in which the cross section perpendicular to the central axis is elliptical), and applies an RF magnetic field to the subject S disposed in the imaging space located on the inner circumference side thereof based on an RF pulse supplied from the transmission circuit 6. In addition, the whole-body RF coil 4 receives a magnetic resonance signal generated from the subject S due to the influence of the RF magnetic field, and outputs the received magnetic resonance signal to the reception circuit 7.

[0016] The local RF coil 5 receives a magnetic resonance signal generated from the subject S. Specifically, the local RF coil 5 is prepared for each part of the subject S, and is disposed near the surface of the part to be imaged when imaging the subject S. The local RF coil 5 receives a magnetic resonance signal generated from the subject S due to the influence of the RF magnetic field applied by the whole-body RF coil 4, and outputs the received magnetic resonance signal to the receiving circuit 7. The local RF coil 5 may further have a function of applying an RF magnetic field to the subject S. In that case, the local RF coil 5 is connected to the transmitting circuit 6, and applies an RF magnetic field to the subject S based on an RF pulse supplied from the transmitting circuit 6. 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.

[0017] The transmission circuit 6 outputs an RF pulse corresponding to a Larmor frequency specific to the target atomic nucleus placed in the static magnetic field to the whole-body RF coil 4. Specifically, the transmission circuit 6 has a pulse generator, an RF generator, a modulator, and an amplifier. The pulse generator generates a waveform of an RF pulse. The RF generator generates an RF signal at a resonance frequency. The modulator generates an RF pulse 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 generated by the modulator and outputs it to the whole-body RF coil 4.

[0018] The receiving circuit 7 generates magnetic resonance data based on the magnetic resonance signal output from the whole-body RF coil 4 or the local RF coil 5, and outputs the generated magnetic resonance data to the processing circuit 15. For example, the receiving circuit 7 includes a selector, a preamplifier, a phase detector, and an A / D (Analog / Digital) converter. The selector selectively inputs the magnetic resonance signal output from the whole-body RF coil 4 or the local RF coil 5. The preamplifier amplifies the magnetic resonance signal output from the selector. The phase detector detects the phase of the magnetic resonance signal output from the preamplifier. The A / D converter generates magnetic resonance data by converting the analog signal output from the phase detector into a digital signal, and outputs the generated magnetic resonance data to the processing circuit 15. Note that, in the processes described here as being performed by the receiving circuit 7, all of the processes do not necessarily have to be performed by the receiving circuit 7, and some of the processes (e.g., processes by an A / D converter, etc.) may be performed by the whole-body RF coil 4 or the local RF coil 5.

[0019] 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 magnetic field generated by the whole-body RF coil 4. Specifically, the RF shield 8 is formed in a hollow, approximately cylindrical shape (including a cylinder whose cross section perpendicular to the central axis is elliptical), and is disposed in the space on the inner periphery side of the gradient magnetic field coil 2 so as to cover the outer periphery of the whole-body RF coil 4.

[0020] The gantry 9 has a hollow bore 9a formed in a substantially cylindrical shape (including one in which the cross section perpendicular to the central axis has an elliptical shape), 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 houses each of the following in a state in which the whole-body RF coil 4 is disposed on the outer periphery of the bore 9a, the RF shield 8 is disposed on the outer periphery of the whole-body RF coil 4, the gradient magnetic field coil 2 is disposed on the outer periphery of the RF shield 8, and the static magnetic field magnet 1 is disposed on the outer periphery of the gradient magnetic field coil 2. Here, the space within the bore 9a of the gantry 9 becomes an imaging space in which the subject S is disposed during imaging.

[0021] The bed 10 includes a top plate 10a on which the subject S is placed, and when imaging the subject S, the top plate 10a on which the subject S is placed is moved to an imaging space. For example, the bed 10 is installed so that the longitudinal direction of the top plate 10a is parallel to the central axis of the static magnetic field magnet 1.

[0022] Here, an example will be described 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, 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 to face each other across an imaging space in which the subject S is placed. In such an open-type structure, the space sandwiched between the pair of static magnetic field magnets, the pair of gradient magnetic field coils, and the pair of RF coils corresponds to a bore in the tunnel-type structure.

[0023] The input interface 11 accepts input operations of various instructions and various information from an 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 the electrical signal to the processing circuit 17. For example, the input interface 11 is realized by a trackball for setting imaging conditions and a region of interest (ROI), a switch button, a mouse, a keyboard, a touchpad for performing an input operation by touching the operation surface, a touch screen in which a display screen and a touchpad are integrated, a non-contact input circuit using an optical sensor, and a voice input circuit. Note that in this specification, the input interface 11 is not limited to only those having physical operation parts 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 device and outputs the electrical signal to a control circuit is also included as an example of the input interface 11.

[0024] The display 12 displays various information. Specifically, the display 12 is connected to the processing circuit 17, and converts various information data sent from the processing circuit 17 into an electric signal for display and outputs it. For example, the display 12 is realized by a liquid crystal monitor, a CRT monitor, a touch panel, or the like.

[0025] The memory circuitry 13 stores various data. Specifically, the memory circuitry 13 is connected to the processing circuits 14 to 17, and stores various data input and output by each processing circuit. For example, the memory circuitry 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.

[0026] The processing circuitry 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 to move the top board 10a in the longitudinal direction, the up-down direction, or the left-right direction from the operator via the input interface 11, and operates a moving mechanism of the top board 10a of the bed 10 so as to move the top board 10a in accordance with the received instruction.

[0027] The processing circuitry 15 has an acquisition function 15a. The acquisition function 15a executes various pulse sequences to acquire k-space data. Specifically, the acquisition function 15a executes various pulse sequences by driving the gradient magnetic field power supply 3, the transmission circuitry 6, and the reception circuitry 7 according to sequence execution data output from the processing circuitry 17. Here, the sequence execution data is data representing a pulse sequence, and is information that specifies the timing and strength of the current that the gradient magnetic field power supply 3 supplies to the gradient magnetic field coil 2, the timing and strength of the high-frequency pulse that the transmission circuitry 6 supplies to the whole-body RF coil 4, and the timing at which the reception circuitry 7 samples the magnetic resonance signal. Then, the acquisition function 15a receives the magnetic resonance data output from the reception circuitry 7 as a result of executing the pulse sequence, and stores it in the memory circuitry 13. At this time, the magnetic resonance data stored in the memory circuitry 13 is stored as k-space data representing a two-dimensional or three-dimensional k-space by adding position information along each of the readout direction, phase encoding direction, and slice direction by each of the gradient magnetic fields described above.

[0028] The processing circuitry 16 has a generating function 16a. The generating function 16a generates an image from the k-space data collected by the processing circuitry 15. Specifically, the generating function 16a reads out the k-space data collected by the processing circuitry 15 from the storage circuitry 13, and performs reconstruction processing such as Fourier transform on the read out k-space data to generate a two-dimensional or three-dimensional image. Then, the generating function 16a stores the generated image in the storage circuitry 13.

[0029] The processing circuitry 17 has an imaging control function 17a. The imaging control function 17a controls each component of the MRI device 100, thereby controlling the entire MRI device 100. Specifically, the imaging control function 17a displays a GUI (Graphical User Interface) for receiving various instructions and various information from an operator on the display 12, and controls each component of the MRI device 100 in response to an input operation received via the input interface 11. For example, the imaging control function 17a generates sequence execution data based on imaging conditions input by the operator, and outputs the generated sequence execution data to the processing circuitry 15, thereby collecting k-space data. Also, for example, the imaging control function 17a controls the processing circuitry 16 to reconstruct an image from the k-space data collected by the processing circuitry 15. Also, for example, the imaging control function 17a reads an image from the storage circuitry 13 in response to a request from the operator, and displays the read image on the display 12.

[0030] Here, the above-mentioned processing circuits 14 to 17 are realized by, for example, a processor. In this case, the processing functions of each processing circuit are stored in the storage circuit 13 in the form of, for example, a program executable by a computer. Then, each processing circuit realizes the processing function corresponding to each program by reading each program from the storage circuit 13 and executing it. In other words, each processing circuit in a state where each program is read has each function shown in each processing circuit in FIG. 1.

[0031] In this embodiment, each processing circuit is described as being realized by a single processor, but the embodiment is not limited to this, and each processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to realize each processing function. Also, the processing functions of each processing circuit may be appropriately distributed or integrated into a single or multiple processing circuits. In the example shown in FIG. 1, a single storage circuit 13 is described as storing a program corresponding to each processing function, but multiple storage circuits may be distributed and arranged, and the processing circuits may read out corresponding programs from individual storage circuits.

[0032] The configuration example of the MRI apparatus 100 according to the present embodiment has been described above. With such a configuration, the MRI apparatus 100 according to the present embodiment uses a technology called UTE to measure the T2 * It has the function of generating map images.

[0033] UTE is a technology that acquires an echo signal immediately after applying an excitation pulse to the subject, and uses the echo signal to acquire k-space data by radial acquisition to generate an image. By setting the echo time (TE), which is the time from application of the excitation pulse to generation of the echo signal, to a short time of, for example, less than 0.1 ms, it is possible to obtain images of T2 or T2 * It is possible to visualize tissues with short relaxation times.

[0034] Using such a UTE, T2 * When generating a map image, for example, multiple echo signals are acquired while changing the TE at short time intervals immediately after the excitation pulse is applied, and multiple data with different TEs are collected, and T2 * By deriving the value of T2 * A method for generating a map image is conceivable.

[0035] However, in general, in an MRI device, since the switching speed of the gradient magnetic field is restricted by dB / dt, when collecting multiple echo signals at short time intervals, the strength of the gradient magnetic field must be reduced, resulting in low spatial resolution. On the other hand, in order to improve the spatial resolution of an image, the interval between echo signals (Echo Train Spacing: ETS) must be extended, resulting in low temporal resolution.

[0036] For these reasons, the above-mentioned methods may not be able to meet clinical demands that require both high spatial resolution and high temporal resolution.

[0037] For this reason, the MRI apparatus 100 according to this embodiment is configured to detect T2 or T2 * The present invention is configured to improve the spatial resolution and the time resolution when imaging a site including tissue with a short relaxation time.

[0038] Specifically, in this embodiment, the acquisition function 15a of the processing circuitry 15 acquires echo signals generated at intervals of a repetition time (TR) by applying an excitation pulse to the subject at intervals of a repetition time (TR), and acquires data of a plurality of trajectories set in k-space using the echo signals. Here, the acquisition function 15a acquires a plurality of echo signals by setting TE to different lengths for each of the plurality of TRs, and acquires data of the same trajectory using the plurality of echo signals.

[0039] The configuration of the MRI apparatus 100 will be described in detail below. In this embodiment, the acquisition function 15a acquires three-dimensional k-space data by radial acquisition, and the generation function 16a generates three-dimensional T2 * An example of generating a map image will be described.

[0040] FIG. 2 is a diagram showing an example of a trajectory in k-space used by the acquisition function 15a according to the first embodiment.

[0041] For example, as shown in FIG. 2, the acquisition function 15a acquires data along a plurality of linear trajectories 21 extending radially from the center of the k-space by radial acquisition in the three-dimensional k-space.

[0042] Here, if the total number of sampling points p collected along multiple trajectories set in k-space is N, the coordinates (x(p), y(p), z(p)) of each sampling point p are expressed by the following equations (1) to (3).

[0043]

number

number

number

[0044] Furthermore, for multiple trajectories, when the m-th trajectory is represented as Seg(m), each trajectory is defined as follows: Here, multiple elements on the right side correspond to multiple sampling points s collected along each trajectory.

[0045] Seg(0) = 0, m, 2 m, · · ·, N m Seg(1)=1,m+1,2m+1,...,N-m+1 · · Seg(m)=m-1,2m-1,3m-1,...,N-1

[0046] FIG. 3 is a diagram showing a pulse sequence used by the acquisition function 15a according to the first embodiment.

[0047] 3, the acquisition function 15a applies an excitation pulse 31 to the subject multiple times at a constant TR interval, and acquires an echo signal 33 at each TR interval using UTE. At this time, the acquisition function 15a acquires the echo signal 33 while applying a gradient magnetic field 32 including a readout gradient magnetic field, a phase encoding gradient magnetic field, and a slice gradient magnetic field, and then applies a spoiler gradient magnetic field 34 at a timing when a certain time has elapsed since the application of the excitation pulse 31.

[0048] Here, the acquisition function 15a sets TE to different lengths by changing each of the multiple TRs by a predetermined time, and acquires multiple echo signals 33. At this time, the acquisition function 15a acquires the multiple echo signals 33 consecutively or in a time sequence as close as possible.

[0049] For example, the collection function 15a changes TE continuously by a predetermined time. At this time, for example, the collection function 15a increases TE continuously by a predetermined time. Alternatively, the collection function 15a may decrease TE continuously by a predetermined time. Alternatively, the collection function 15a may continuously increase TE by a predetermined time and decrease TE by a predetermined time in a mixed manner.

[0050] For example, the acquisition function 15a applies an excitation pulse 31 n times at a constant TR interval, and changes TE from TE1 to TEn by successively increasing TE from TEmin by Δt at each TR interval, thereby acquiring multiple echo signals 33.

[0051] In this case, for example, the acquisition function 15a acquires T2 or T2 * Depending on the relaxation time, TEmin and Δt are set. For example, the acquisition function 15a acquires T2 or T2 * The shorter the relaxation time, the shorter the TEmin and Δt, and the shorter the T2 or T2 * The longer the relaxation time, the longer TEmin and Δt are set. Also, for example, the acquisition function 15a sets the TR to the shortest length that allows acquisition of an echo signal of TEn, which is the longest TE.

[0052] For example, the acquisition function 15a applies the excitation pulse 31 five times, and changes the TE for each TR to 0.1 ms, 0.12 ms, 0.14 ms, 0.16 ms, and 0.18 ms to acquire five echo signals 33. In the case of UTE, magnetic resonance signals are generated by FLASH (Fast Low-Angle Shot), so that the signal change between these multiple TEs can be suppressed by keeping the flip angle of the excitation pulse at 5 to 10° or less and by controlling the phase of the spoiler gradient magnetic field and RF pulse appropriately. * It is possible to limit the portion depending on the relaxation time.

[0053] Then, the acquisition function 15a acquires a plurality of data with different TEs for the same trajectory among a plurality of trajectories set in the k-space, using a plurality of echo signals 33 acquired by changing the TE.

[0054] Thereafter, the acquisition function 15a repeatedly acquires multiple echo signals 33 while changing the solid angle of the trajectory by changing the distribution of the readout gradient magnetic field, the phase encoding gradient magnetic field, and the slice gradient magnetic field contained in the gradient magnetic field 32, thereby acquiring multiple data with different TEs for all trajectories set in the k-space.

[0055] At this time, for example, the acquisition function 15a may collect data by thinning it out by setting a trajectory at an angle called Golden Angle. Also, for example, the acquisition function 15a may divide the k-space into a plurality of segments by using respiratory gating or the like in combination, and collect data by thinning it out by the number of segments.

[0056] In this embodiment, the generation function 16a of the processing circuit 16 calculates T2 using a known technique such as curve fitting based on multiple data with different TEs collected by the collection function 15a. * By deriving the value, T2 * Generate a map image.

[0057] FIG. 4 is a flowchart showing the procedure of the imaging method performed by the MRI apparatus 100 according to the first embodiment.

[0058] 4, in this embodiment, the imaging control function 17a sets imaging conditions including TE, TR, etc. used in imaging based on an input from an operator (step S11). Then, when the imaging control function 17a receives an instruction to start imaging from the operator (step S12, Yes), it starts the following process.

[0059] First, the acquisition function 15a acquires multiple echo signals by setting the TE to different lengths for each of multiple TRs based on the imaging conditions set by the imaging control function 17a, as described above, and acquires k-space data by using the multiple echo signals to acquire data of the same trajectory (step S13).

[0060] Next, the generation function 16a generates a T2 * A map image is generated (step S14).

[0061] Here, the processes of steps S11 and S12 are realized, for example, by the processing circuitry 17 reading out a predetermined program corresponding to the imaging control function 17a from the storage circuitry 13 and executing it. Also, the process of step S13 is realized, for example, by the processing circuitry 15 reading out a predetermined program corresponding to the acquisition function 15a from the storage circuitry 13 and executing it. Also, the process of step S14 is realized, for example, by the processing circuitry 16 reading out a predetermined program corresponding to the generation function 16a from the storage circuitry 13 and executing it.

[0062] As described above, in the first embodiment, the acquisition function 15a acquires echo signals generated at intervals of TR by applying an excitation pulse to the subject at intervals of TR, and acquires data of a plurality of trajectories set in k-space using the echo signals. Here, the acquisition function 15a acquires a plurality of echo signals by setting TE to different lengths for each of the plurality of TRs, and acquires data of the same trajectory using the plurality of echo signals.

[0063] According to this configuration, by acquiring one echo signal for each TR, a high-intensity gradient magnetic field can be used without being restricted by dB / dt, and the spatial resolution can be improved. Also, by changing the TE at each TR interval, the time difference of the TE can be reduced, and the time resolution can be improved.

[0064] Therefore, according to this embodiment, T2 or T2 * The spatial and temporal resolution can be improved when imaging a site that includes tissue with a short relaxation time.

[0065] Furthermore, according to this embodiment, by varying the TE and acquiring multiple echo signals successively or in as close a time sequence as possible, data of the same trajectory can be collected, thereby minimizing the effects of movement and flow in the area to be imaged.

[0066] Furthermore, the imaging method of this embodiment has the advantage that the waveform of the gradient magnetic field is almost the same between the two TEs. In the conventional method, when imaging a part with movement or flow, the sensitivity to the movement or flow changes significantly due to the effect of GM (Gradient Moment), which is a phase component generated by the gradient magnetic field. In contrast, in the imaging method of this embodiment, the waveform of the gradient magnetic field is almost the same between the two TEs, so that the sensitivity to the movement or flow is maintained.

[0067] Here, T2 *The collection time required to collect data required to generate a map image is compared between a case where multiple echo signals are acquired with one excitation pulse using a general multi-echo method (hereinafter, the conventional method) and a case where multiple echo signals are acquired by changing the TE using the imaging method of this embodiment. Note that the collection time is compared here between a case where the number of echo signals used to collect data for one trajectory is 5 and the echo interval is 1.5 ms using the conventional method and a case where the number of echo signals used to collect data for one trajectory is 5 and the variable range of TE is up to 2.5 ms using the imaging method of this embodiment.

[0068] In this case, in the conventional method, the TR is about 9 ms, and the acquisition time is 180 s if the number of trajectories is 20000. On the other hand, in the imaging method of this embodiment, the TR is about 4 ms, and if the number of trajectories is also 20000, the acquisition time is 80 s*5=400 s, which is more than double the acquisition time of the conventional method.

[0069] However, the T2 * Considering the relaxation time, it is expected that the measurement accuracy will not be high due to signal attenuation in the conventional method, but the imaging method of this embodiment enables highly accurate measurement.

[0070] For example, as a simple comparison, if only two TEs are considered, in the conventional method, the TEs are 0.1 ms and 1.6 ms, and the attenuation between them is imaged, whereas in the imaging method of this embodiment, the first TE is set to 0.1 ms, and the second TE can be freely selected from about 0.2 ms to 1.6 ms, thereby expanding the flexibility of clinical application.

[0071] In this case, if the number of trajectories is 20000, the conventional method requires a TR of about 4 ms, and the acquisition time is 80 s, whereas the method of this embodiment requires a second TE of 0.5 ms and a TR of 2.5 ms, and the acquisition time is 50 s*2=100 s. However, the disadvantage of extending the imaging time with respect to the improvement of accuracy is not considered to be large.

[0072] Furthermore, the multiple echo signals collected by changing the TE using the imaging method of this embodiment have the same collection order and format as the multiple echo signals collected using the conventional method, so the data collection and image reconstruction framework (e.g., the method of using a buffer memory, etc.) used in the conventional method can be used as is.

[0073] Although the first embodiment has been described above, the embodiment of the MRI apparatus according to the present application is not limited to this. Therefore, other embodiments of the MRI apparatus according to the present application will be described below. Note that in the following embodiments, the differences from the first embodiment will be mainly described, and the description of the contents common to the first embodiment will be omitted.

[0074] Second embodiment First, in the above-mentioned first embodiment, an example in which one echo signal is acquired in one TR has been described, but the embodiment is not limited to this.

[0075] For example, the collection function 15a may acquire multiple first echo signals by setting TE to different lengths for each of multiple TRs, and further acquire multiple second echo signals by setting TE to a fixed length for each of multiple TRs, and collect data of the same trajectory using the acquired multiple first echo signals and multiple second echo signals.

[0076] FIG. 5 is a diagram showing a pulse sequence used by the acquisition function 15a according to the second embodiment.

[0077] 5, the acquisition function 15a applies an excitation pulse 51 to the subject multiple times at a constant TR interval, and acquires a first echo signal 53 at each TR interval using UTE. At this time, the acquisition function 15a acquires the first echo signal 53 while applying a gradient magnetic field 52 including a readout gradient magnetic field, a phase encoding gradient magnetic field, and a slice gradient magnetic field, and then applies a rewinder gradient magnetic field 54.

[0078] Here, the acquisition function 15a acquires a plurality of first echo signals 53 by changing TE by a predetermined time for each of the plurality of TRs, in the same manner as in the first embodiment.

[0079] Furthermore, the acquisition function 15a applies a rewinder gradient magnetic field 54 at each TR interval, and then acquires a second echo signal 56 by a GRE (Gradient Echo) method. At this time, the acquisition function 15a applies a gradient magnetic field 55 including a readout gradient magnetic field, a phase encoding gradient magnetic field, and a slice gradient magnetic field to acquire the second echo signal 56, and then applies a spoiler gradient magnetic field 57 at a timing when a certain time has elapsed since the application of the excitation pulse 31.

[0080] Here, the acquisition function 15a sets TE to a fixed length for each of the multiple TRs, and acquires multiple second echo signals 56.

[0081] For example, the collecting function 15a acquires a plurality of first echo signals 53 by changing TE in five steps from 0.1 ms to 2.5 ms, and acquires a plurality of second echo signals 56 by fixing TE at about 4 ms.

[0082] Then, the collection function 15a collects multiple pieces of data with different TE for the same trajectory among multiple trajectories set in k-space, using multiple first echo signals 53 acquired by changing the TE and multiple second echo signals 56 acquired by fixing the TE.

[0083] For example, the acquisition function 15a divides the k-space into a central region and a peripheral region, and for each trajectory, acquires data in the range included in the central region using a first echo signal, and acquires data in the range included in the peripheral region using a second echo signal.

[0084] At this time, for example, the collection function 15a uses an imaging method called the Keyhole method to collect multiple data for each trajectory within the range of the central region of k-space that determines the contrast, using multiple first echo signals 53 acquired by changing the TE, while collecting multiple data within the range of the peripheral region of k-space, using second echo signals acquired by fixing the TE in common within the same trajectory.

[0085] As described above, in the second embodiment, the acquisition function 15a acquires a plurality of first echo signals by setting TE to different lengths for each of a plurality of TRs, and further acquires a plurality of second echo signals by setting TE to a fixed length for each of a plurality of TRs, and acquires data of the same trajectory using the acquired plurality of first echo signals and plurality of second echo signals.Then, the acquisition function 15a divides the k-space into a central region and a peripheral region, and acquires data for each trajectory using the first echo signal in the range included in the central region and the second echo signal in the range included in the peripheral region.

[0086] In this embodiment, the positions of the first echo signal and the second echo signal in the k-space can be controlled independently, so that such an acquisition pattern is possible. Furthermore, for the first echo signal, which has a limited time resolution, it is necessary to use a wide band acquisition band, i.e., a strong gradient magnetic field strength, whereas for the second echo, which has a degree of freedom in setting the TE and TR times, it is possible to adopt a control such as increasing the SNR by using a narrow band acquisition band, i.e., a weaker gradient magnetic field.

[0087] According to this configuration, the second echo signal acquired with the TE fixed is commonly used within the same trajectory, so that T2 * The time required to collect the data required to generate the map image can be reduced.

[0088] For example, if the TR is extended to 6 ms, but the number of trajectories is set to 20,000, it becomes possible to collect echo signals of five TEs in an acquisition time of 120 s. This allows the sampling point density to be increased at short TEs, and the T2 * We can also expect improved accuracy in calculating values.

[0089] (Modification of the second embodiment) The above-described second embodiment can also be applied to an imaging method called PETRA (Pointwise Encoding Time Reduction With Radial Acquisition).

[0090] PETRA is an imaging method that uses UTE, and is capable of improving spatial resolution by collecting data point-by-point in the central region of k-space using Cartesian acquisition, and collecting data in the peripheral region of k-space using radial acquisition.

[0091] FIG. 6 is a diagram showing an example of a trajectory in k-space used by the acquisition function 15a according to a modified example of the second embodiment.

[0092] For example, as shown in FIG. 6, in PETRA, k-space is divided into a central region and a peripheral region, and in the central region, data is collected at each point 61 by Cartesian acquisition, while in the peripheral region, data is collected along straight lines 62 extending radially from the center of k-space by radial acquisition.

[0093] In this case, similar to the second embodiment described above, the collection function 15a acquires multiple first echo signals by setting TE to different lengths for each of the multiple TRs, and further acquires multiple second echo signals by setting TE to a fixed length for each of the multiple TRs, and collects data of the same trajectory using the acquired multiple first echo signals and multiple second echo signals.

[0094] For example, the acquisition function 15a acquires a plurality of echo signals while increasing the TE from 0.1 ms by 0.1 ms for each TR.

[0095] The acquisition function 15a then divides the k-space into a central region and a peripheral region, and in the range included in the central region, data is acquired for each point 61 by Cartesian acquisition using the first echo signal, and in the range included in the peripheral region, data is acquired along a straight line 62 extending radially from the center of the k-space by radial acquisition using the second echo signal.

[0096] At this time, for example, the acquisition function 15a sets the ratio between the central region and the peripheral region in the k-space and the number of sampling points to be set in each region according to the part to be imaged.

[0097] Similarly to the Keyhole method, the collection function 15a collects, for each trajectory, multiple pieces of data within the range of the central region of k-space that defines the contrast, using multiple first echo signals 53 acquired by varying the TE, while collecting multiple pieces of data within the range of the peripheral region of k-space, using second echo signals acquired by fixing the TE in common within the same trajectory.

[0098] In the above-mentioned second embodiment and modified example, an example in which two echo signals are acquired in one TR has been described, but the number of echo signals acquired in one TR is not limited to this. For example, the acquisition function 15a may further acquire one or more echo signals following the second echo signal for each TR. In this case, the acquisition function 15a acquires each echo signal acquired after the second echo signal by fixing the TE for each TR.

[0099] (Third embodiment) The imaging methods described in the above-mentioned embodiments can also be applied to contrast-enhanced imaging, which performs imaging by enhancing or suppressing signals from specific tissues.

[0100] Here, the contrast-enhanced imaging is a method of collecting k-space data at a time when a predetermined waiting time has elapsed after applying a pre-pulse to the subject, which enhances or suppresses the signal of a specific tissue. For example, such a contrast-enhanced imaging method includes a Time-SLIP (time-spatial labeling inversion pulse) method and a fat suppression method. Here, the Time-SLIP method is a method of visualizing the flow and movement of blood, CSF, etc., by applying a labeling pulse that labels blood, CSF, etc., and the like. In addition, the fat suppression method is a method of suppressing the signal of fat to be imaged by applying a fat suppression pulse that selectively saturates the spins of fat.

[0101] In this case, the acquisition function 15a acquires data of multiple trajectories set in k-space after a predetermined waiting time has elapsed after applying a pre-pulse to the subject that enhances or suppresses signals from specific tissues.

[0102] FIG. 7 is a diagram showing an example of contrast-enhanced imaging according to the third embodiment.

[0103] For example, as shown in FIG. 7, the acquisition function 15a applies a pre-pulse (Prep-Pulse) for enhancing or suppressing a signal of a specific tissue to the subject, and then, after a predetermined waiting time has elapsed, continuously executes a loop (TR*n shown in FIG. 7) in which an excitation pulse 72 is applied multiple times at a constant TR interval for each trajectory set in the k-space, and TE is changed at each TR interval to acquire multiple echo signals 73, as described in each of the above-mentioned embodiments.

[0104] Here, when imaging a region to be imaged in multiple time phases, the acquisition function 15a applies a pre-pulse multiple times at a predetermined time interval (Trepeat shown in FIG. 7) and executes the above loop continuously for each time interval.

[0105] (Other embodiments) In the above-mentioned second and third embodiments, examples have been described in which data within a range included in the central region of k-space is collected using the first echo signal, and data within a range included in the peripheral region of k-space is collected using the second echo signal, but the embodiments are not limited to this.

[0106] For example, the imaging methods described in the second and third embodiments can be applied to cases where in-phase images and out-of-phase images are taken in abdominal examinations and the like.

[0107] Here, an in-phase image is an image obtained by setting TE so that the frequency difference between water and fat is in phase, and an out-of-phase image is an image obtained by setting TE so that the frequency difference between water and fat is in anti-phase.

[0108] In this case, similar to the second and third embodiments described above, the collection function 15a acquires multiple first echo signals by setting TE to different lengths for each of the multiple TRs, and further acquires multiple second echo signals by setting TE to a fixed length for each of the multiple TRs, and collects data of the same trajectory using the acquired multiple first echo signals and multiple second echo signals.

[0109] The acquisition function 15a then uses the first echo signal to acquire data for generating an in-phase image, and the second echo signal to acquire data for generating an out-of-phase image. Alternatively, the acquisition function 15a may use the first echo signal to acquire data for generating an out-of-phase image, and the second echo signal to acquire data for generating an in-phase image. This is particularly effective when the time difference between in-phase and out-of-phase is small at a static magnetic field strength of 3T or more (for example, 0.95 ms at 7T), and further, as described above, it is possible to minimize the fluctuation of the influence of the flow due to the GM.

[0110] In addition, in each of the above-mentioned embodiments, the example of collecting three-dimensional k-space data to generate a three-dimensional image is described, but the embodiment is not limited to this. For example, the imaging method described in each embodiment can be similarly applied to the case of collecting two-dimensional k-space data to generate a two-dimensional image.

[0111] In addition, in each of the above-mentioned embodiments, an example has been described in which the collection unit in this specification is realized by the collection function 15a of the processing circuit 15, but the embodiment is not limited to this. For example, the collection unit in this specification may be realized by the collection function 15a described in the embodiment, or may be realized by only hardware, only software, or a combination of hardware and software.

[0112] In the above description, the "processor" reads out and executes a program corresponding to each processing function from a storage circuit, but the embodiment is not limited to this. The term "processor" refers to a circuit such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). When the processor is a CPU, for example, the processor reads out and executes a program stored in a storage circuit to realize each processing function. On the other hand, when the processor is an ASIC, instead of storing a program in a storage circuit, the processing function is directly incorporated as a logic circuit in the circuit of the processor. Note that each processor in this embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining multiple independent circuits to realize its processing function. Furthermore, multiple components in FIG. 1 may be integrated into one processor to realize the processing functions.

[0113] Here, the program executed by the processor is provided in advance in a ROM (Read Only Memory) or a storage circuit. The program may be provided in a format that can be installed in these devices or in a format that can be executed, recorded on a computer-readable storage medium such as a CD (Compact Disk)-ROM, a FD (Flexible Disk), a CD-R (Recordable), or a DVD (Digital Versatile Disk). The program may be provided or distributed by being stored on a computer connected to a network such as the Internet and downloaded via the network. For example, the program is composed of modules including each of the above-mentioned functional units. As actual hardware, a CPU reads out the program from a storage medium such as a ROM and executes it, so that each module is loaded onto a main storage device and generated on the main storage device.

[0114] According to at least one embodiment described above, T2 or T2 * The spatial and temporal resolution can be improved when imaging a site that includes tissue with a short relaxation time.

[0115] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included 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]

[0116] 100 MRI machine 15 Processing circuit 15a Collection Function

Claims

1. A device comprising: an acquisition unit that acquires echo signals generated during a certain repetition time by applying an excitation pulse to a subject at intervals of the repetition time, and collects data of a plurality of trajectories set in k-space using the echo signals; the acquisition unit acquires a plurality of echo signals by setting an echo time, which is a time from application of the excitation pulse to generation of the echo signal, to different lengths for each of a plurality of repetition times, and acquires a plurality of data having different echo time lengths for the same trajectory among the plurality of trajectories by using the plurality of echo signals having different echo time lengths. Magnetic resonance imaging device.

2. the acquisition unit sets the echo time to different lengths by changing each of the plurality of repetition times by a predetermined time, and acquires the plurality of echo signals.

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

3. The collecting unit continuously changes the echo time by a predetermined time.

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

4. The acquisition unit continuously increases the echo time by a predetermined time, continuously decreases the echo time by a predetermined time, or continuously increases the echo time by a predetermined time and decreases the echo time by a predetermined time in a mixed manner.

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

5. the acquisition unit acquires a plurality of first echo signals by setting the echo time to a different length for each of a plurality of repetition times, and further acquires a plurality of second echo signals by setting the echo time to a fixed length for each of a plurality of repetition times, and acquires the plurality of data for the same trajectory using the plurality of first echo signals and the plurality of second echo signals.

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

6. the acquisition unit divides the k-space into a central region and a peripheral region, and acquires data for each trajectory in a range included in the central region by using the first echo signal, and acquires data for a range included in the peripheral region by using the second echo signal.

6. A magnetic resonance imaging apparatus according to claim 5.

7. the acquisition unit divides the k-space into a central region and a peripheral region, and in the range included in the central region, acquires data point by point by Cartesian acquisition using the first echo signal, and in the range included in the peripheral region, acquires data along straight lines extending radially from the center of the k-space by radial acquisition using the second echo signal.

6. A magnetic resonance imaging apparatus according to claim 5.

8. A collecting unit that applies an excitation pulse to a subject at intervals of a repetition time to obtain echo signals generated during the repetition time, and collects data of a plurality of trajectories set in k-space using the echo signals; the acquisition unit acquires a plurality of first echo signals by setting an echo time, which is a time from application of the excitation pulse to generation of the echo signal, to different lengths for each of a plurality of repetition times, and further acquires a plurality of second echo signals by setting the echo time to a fixed length for each of the plurality of repetition times, divides the k-space into a central region and a peripheral region, and acquires data for each of the trajectories using the first echo signal in a range included in the central region and using the second echo signal in a range included in the peripheral region, thereby acquiring data of the same trajectory among the plurality of trajectories using the plurality of first echo signals and the plurality of second echo signals. Magnetic resonance imaging device.

9. A collecting unit that applies an excitation pulse to a subject at intervals of a repetition time to obtain echo signals generated during the repetition time, and collects data of a plurality of trajectories set in k-space using the echo signals; the acquisition unit acquires a plurality of first echo signals by setting an echo time, which is a time from application of the excitation pulse to generation of the echo signal, to different lengths for each of a plurality of repetition times, and further acquires a plurality of second echo signals by setting the echo time to a fixed length for each of the plurality of repetition times, divides the k-space into a central region and a peripheral region, and in a range included in the central region, data is acquired point-by-point by Cartesian acquisition using the first echo signals, and in a range included in the peripheral region, data is acquired along straight lines extending radially from the center of the k-space by radial acquisition using the second echo signals, thereby acquiring data of the same trajectory among the plurality of trajectories using the plurality of first echo signals and the plurality of second echo signals. Magnetic resonance imaging device.

10. The acquisition unit acquires data of the plurality of trajectories at a time when a predetermined waiting time has elapsed after applying a pre-pulse that enhances or suppresses a signal of a specific tissue to the subject.

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

11. The acquisition unit acquires the echo signal using Ultra Short TE (UTE).

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

Images