Imaging device and imaging method

Abstract

To perform imaging in a short time and improve accuracy of elastogram as compared to a conventional technology.SOLUTION: An imaging device (1) calculates distortion in a second imaging method on the basis of a reference pattern (131a) appearing in a first MR image (131) and a reference pattern (132a) appearing in a second MR image (132), acquires multiple times an MR phase image of a part to be inspected in a state where the reference pattern (132a) is not added in the second imaging method, corrects the distortion in the MR phase image acquired multiple times in the state where the reference pattern (132a) is not added in the second imaging method, and creates an MR elastography image (212) on the basis of the plurality of MR phase images in which distortion has been corrected.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an imaging device and imaging method for imaging an examination area of ​​a subject's body, and more particularly to an imaging device and imaging method capable of performing MR elastography (Magnetic Resonance Elastography: MRE) imaging for measuring tissue stiffness. [Background technology]

[0002] Magnetic resonance imaging (MRI) devices are used in medical settings because they have minimal effects on patients, such as exposure to radiation. MRI devices excite the hydrogen nuclei (protons) contained in each cell of the human body by applying an alternating (high-frequency) magnetic field that corresponds to the proton's spin, and based on the electromagnetic waves emitted when the excited protons return to their original state (relaxation), it is possible to obtain images that show the longitudinal and transverse relaxation times of protons and areas with different densities (for example, water and fat) using gray levels. MRE (Magnetic Resonance Elastography) is an imaging method that uses differences in the propagation of vibration waves due to differences in "hardness" within the target area to image the hardness by applying vibrations to the target area (approximately 50 Hz to 100 Hz in the case of the trunk) and imaging it with an MRI device (see Patent Documents 1 and 2).

[0003] However, because MRE scans are performed while applying vibration, it is necessary to hold the subject's breath (temporarily hold their breath) during scanning. Therefore, the longer the period during which breathing is held, the more strain the subject will have to endure, so scanning must be performed at high speed. In particular, MRE requires multiple scans (at vibration phases of 0°, 90°, 180°, and 270°), so the longer the scan time, the more strain the subject will have to endure. Several types of imaging methods have been proposed for performing MRE imaging, and spin echo-echo planar imaging (SE-EPI) is known as a high-speed imaging method (see, for example, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2005-507691 (“0008”, “0014” ~ “0023”) [Patent Document 2] JP 2011-98158 A ("0003" to "0018", "0026" to "0029") [Non-patent literature]

[0005] [Non-Patent Document 1] Andreas Fehlner et al., "Increasing the Spatial Resolution and Sensitivity of Magnetic Resonance Elastography by Correcting for Subject Motion and Susceptibility-induced Image Distortions," International Society for Magnetic Resonance in Medicine, J.MAGN.RESON.IMAGING 2017;46:134-141 Summary of the Invention [Problem to be solved by the invention]

[0006] (Problems with the prior art) However, although the SE-EPI method allows for ultrafast imaging at less than one second per slice, it is prone to image distortion.MRE calculates elastograms using the wavelength of wave images from multiple MR phase images, so image distortion reduces the accuracy of the elastogram.

[0007] The present invention has as its technical object to perform imaging in a short time and to improve the accuracy of elastograms compared to conventional techniques. [Means for solving the problem]

[0008] In order to solve the above technical problem, the photographing device of the invention described in claim 1 comprises: a magnetic field generating device that generates, for a part to be examined of a subject, a static magnetic field, a gradient magnetic field that changes depending on the position, and an alternating magnetic field that is set in advance based on the magnetic resonance conditions of protons; a vibration applying member that applies vibration to the inspection target portion; an MR intensity image acquisition means for acquiring an MR intensity image according to the distribution of protons based on the electromagnetic waves acquired according to the timing of application of the gradient magnetic field; an MR phase image acquisition means for acquiring an MR phase image according to the phase of the electromagnetic wave signal based on the electromagnetic wave acquired according to the timing of application of the gradient magnetic field; an MRE image creating means for creating an MR elastography image based on the MR phase image; Equipped with When generating a magnetic field by the magnetic field generating device based on a predetermined first imaging method, a magnetic field corresponding to a predetermined reference pattern for strain detection is added to acquire a first MR intensity image; a second MR intensity image is acquired by adding a magnetic field corresponding to the reference pattern when generating a magnetic field with the magnetic field generator based on a second imaging method that can acquire the MR intensity image and the MR phase image faster than the first imaging method and that produces larger distortion in the MR intensity image and the MR phase image; Calculating distortion in the second imaging method based on a reference pattern reflected in the first MR intensity image and a reference pattern reflected in the second MR intensity image; acquiring the MR phase images of the subject a plurality of times using the second imaging method without adding the reference pattern; Correcting distortions in the MR phase images acquired multiple times without adding the reference pattern by the second imaging method using the calculated distortions; generating the MR elastography image based on the plurality of distortion-corrected MR phase images; It is characterized by:

[0009] The invention described in claim 2 is the photographing device described in claim 1, the reference pattern being configured as a grid pattern; The present invention is characterized by the following features.

[0010] The invention described in claim 3 is the photographing device described in claim 1, The first imaging method is a single-shot fast spin echo method. It is characterized by:

[0011] The invention described in claim 4 is the photographing device described in claim 1, The second imaging method is a spin-echo echo-planar imaging method. It is characterized by:

[0012] In order to solve the above technical problem, the photographing method of the invention described in claim 5 comprises: An imaging method for generating a static magnetic field, a gradient magnetic field that changes depending on the position, and an alternating magnetic field that is preset based on the magnetic resonance conditions of protons while applying vibration to an examination part of a subject, and acquiring an MR intensity image according to the distribution of protons and an MR phase image according to the phase of the electromagnetic wave signal based on the electromagnetic waves acquired depending on the timing of application of the gradient magnetic field, and creating an MR elastography image based on the MR phase image, a magnetic field according to a predetermined reference pattern for strain detection is added when a magnetic field is generated by a magnetic field generating device based on a predetermined first imaging method, thereby acquiring a first MR intensity image; a second MR intensity image is acquired by adding a magnetic field corresponding to the reference pattern when generating a magnetic field with the magnetic field generator based on a second imaging method that can acquire the MR intensity image and the MR phase image faster than the first imaging method and that produces larger distortion in the MR intensity image and the MR phase image; Calculating distortion in the second imaging method based on a reference pattern reflected in the first MR intensity image and a reference pattern reflected in the second MR intensity image; acquiring the MR phase images of the subject a plurality of times using the second imaging method without adding the reference pattern; Correcting distortions in the MR phase images acquired multiple times without adding the reference pattern by the second imaging method using the calculated distortions; generating the MR elastography image based on the plurality of distortion-corrected MR phase images; It is characterized by: [Effects of the Invention]

[0013] According to the inventions described in claims 1 and 5, the distortion of the second MR intensity image is calculated based on the reference pattern reflected in the first MR intensity image and the reference pattern reflected in the second MR intensity image, the distortion in the acquired MR intensity / phase image is corrected with the calculated distortion, and an MR elastography image is created based on multiple MR phase images with corrected distortion, thereby allowing imaging to be performed in a short time as before while improving the accuracy of the elastogram compared to conventional technology. According to the invention as set forth in claim 2, the distortion can be calculated whether the main direction of the distortion is the vertical direction or the horizontal direction. According to the invention of claim 3, the distortion of the second MR phase image can be calculated based on the first MR magnitude image with little distortion acquired by the single-shot fast spin echo method. According to the invention of claim 4, MR phase images can be acquired at high speed by the spin echo type echo planar method, and the burden on the subject can be reduced. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram of a magnetic resonance imaging apparatus according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a functional block diagram of the computer main body in the magnetic resonance imaging apparatus of the first embodiment. [Figure 3] FIG. 3 is an explanatory diagram of the application of a magnetic field and vibration during imaging by the spin echo type echo planar method in the magnetic resonance imaging apparatus of the first embodiment, and is a graph with time on the horizontal axis. [Figure 4] FIG. 4 is an explanatory diagram of a case where a reference pattern is applied during imaging by the spin echo type echo planar method in the magnetic resonance imaging apparatus of the first embodiment, and corresponds to FIG. [Figure 5] FIG. 5 is an explanatory diagram of a case where a reference pattern is applied during imaging by the single-shot type fast spin echo method in the magnetic resonance imaging apparatus of the first embodiment, and corresponds to FIG. [Figure 6] FIG. 6 is an explanatory diagram of an example of an MR image to which a reference pattern of Example 1 has been added, where FIG. 6A is a diagram of an image obtained by the SE-EPI method, FIG. 6B is a diagram of an image obtained by the SSFSE method, and FIG. 6C is a diagram of an image after correction of the image of FIG. 6A. [Figure 7] FIG. 7 is an explanatory diagram of the wave image of Experimental Example 1, where FIG. 7A is a wave image created from the MR phase image before correction, and FIG. 7B is a wave image created from the MR phase image after correction. [Figure 8] FIG. 8 is an explanatory diagram of MRE lastogram images of Experimental Example 1, where FIG. 8A is an MRE lastogram image before correction and FIG. 8B is an MRE lastogram image after correction. DETAILED DESCRIPTION OF THE INVENTION

[0015] Next, specific examples of embodiments of the present invention (hereinafter referred to as examples) will be described with reference to the drawings, but the present invention is not limited to the following examples. In the following description using the drawings, illustrations of components other than those necessary for the description are omitted as appropriate to facilitate understanding. [Example]

[0016] FIG. 1 is an explanatory diagram of a magnetic resonance imaging apparatus according to a first embodiment of the present invention. 1, a magnetic resonance imaging apparatus 1 of Example 1, which is an example of an imaging apparatus of the present invention, has a magnet section 2, which is an example of a magnetic field generator. The magnet section 2 has a through-hole 3 that passes through the interior in the horizontal direction. A bed 6, which supports a lying subject 4, can pass through the through-hole 3. The magnet section 2 has a static magnetic field generating magnet 11 as an example of a static magnetic field applying member. Note that a superconducting electromagnet or a permanent magnet can be used as the static magnetic field generating magnet. A gradient magnetic field generating coil 12 as an example of a gradient magnetic field applying member is arranged inside the static magnetic field generating magnet 11. An alternating (high frequency) magnetic field generating coil 13 as an example of an excitation magnetic field applying member is arranged inside the gradient magnetic field generating coil 12. A receiving coil 14 as an example of a receiving section for receiving electromagnetic waves is arranged inside the alternating magnetic field generating coil 13.

[0017] In Example 1, a vibration pad 16, which is an example of a vibration applying member, is supported on the body surface of the subject 4 on the spine side to perform MRE measurement of the psoas major muscle, which is an example of a part to be examined. The vibration pad 16 is generally of a sound pressure type (a method of transmitting sound pressure generated by a voice coil to a target), but is not limited to this. For example, a mechanical type using a rod or a vibration method using an induction coil can be used.

[0018] A computer device 21, which is an example of an information processing device, is electrically connected to the magnet unit 2 via a cable Cb. Therefore, the computer device 21 is configured to be able to transmit and receive control signals for the static magnetic field generating magnet 11 and the like, detection signals from the receiving coil 14, and the like, to and from the magnet unit 2. The computer device 21 has a computer main body 22, a display 23, which is an example of a display unit, and a keyboard 24 and a mouse 25, which are examples of an input unit. Note that, although Example 1 illustrates a configuration in which the computer device 21 and the magnet unit 2 are connected via a cable Cb, the present invention is not limited to this, and it is also possible to transmit and receive information via any wireless communication method, such as a mobile phone line, Bluetooth (registered trademark), or wireless LAN.

[0019] (Explanation of the control unit of the computer main body 22 in the first embodiment) FIG. 2 is a functional block diagram of a computer main body in the magnetic resonance imaging apparatus of the first embodiment. . In FIG. 2, the control unit 41 of the computer main body 22 of the first embodiment is composed of a computer device having an I / O (input / output interface) that inputs and outputs signals from and to the outside and adjusts input / output signal levels, a ROM (read-only memory) that stores programs and data for performing necessary startup processing, a RAM (random access memory) for temporarily storing necessary data and programs, a CPU (central processing unit) that performs processing in accordance with the startup program stored in the ROM, etc., and a clock oscillator, etc., and can realize various functions by executing the programs stored in the ROM and RAM, etc. The control unit 41 stores basic software for controlling basic operations, a so-called operating system OS, an imaging device control program AP1 as an example of an application program, and other software (not shown).

[0020] (Elements connected to the control unit 41 in the first embodiment) The control unit 41 receives output signals from signal output elements such as the keyboard 24, mouse 25, and receiving coil 14. Furthermore, the control unit 41 of the first embodiment outputs control signals to controlled elements such as the display 23, the static magnetic field generating magnet 11, the gradient magnetic field generating coil 12, and the alternating magnetic field generating coil 13.

[0021] (Function of control unit 41) The imaging device control program AP1 of the control unit 41 of the first embodiment has the following functional means (program modules) 51 to 63.

[0022] The magnetic field control means 51 controls the magnet unit 2 to control the magnetic field for MR imaging of the examination area of ​​the subject 4. The magnetic field control means 51 of the first embodiment includes a repetition time storage means 51a, an echo time storage means 51b, a static magnetic field application means 51c, a gradient magnetic field application means 51d, and an alternating magnetic field application means 51e.

[0023] FIG. 3 is an explanatory diagram of the application of a magnetic field and vibration during imaging by the spin echo type echo planar method in the magnetic resonance imaging apparatus of the first embodiment, and is a graph with time on the horizontal axis. FIG. 4 is an explanatory diagram of a case where a reference pattern is applied during imaging by the spin echo type echo planar method in the magnetic resonance imaging apparatus of the first embodiment, and corresponds to FIG. FIG. 5 is an explanatory diagram of a case where a reference pattern is applied during imaging by the single-shot type fast spin echo method in the magnetic resonance imaging apparatus of the first embodiment, and corresponds to FIG. The repetition time storage means 51a stores a repetition time TR, which is the interval at which a high frequency magnetic field is applied as an example of an alternating magnetic field that excites protons contained in the examination area of ​​the subject 4. In other words, the repetition time TR is the time corresponding to the interval between one cycle (a series of imaging operations).

[0024] The echo time storage means 51b stores the echo time TE, which is the interval from when the alternating magnetic field is applied to when the electromagnetic waves emitted when excited protons return to their original state (relaxation) are acquired. Note that, although the repetition time TR and the echo time TE are set in advance in the first embodiment, they may also be configured so that they can be set and changed by manual input by the user of the magnetic resonance imaging apparatus 1.

[0025] The static magnetic field applying means 51c generates a static magnetic field by controlling the static magnetic field generating magnet 11. The static magnetic field applying means 51c of the first embodiment generates a static magnetic field of 3 [T], for example. The gradient magnetic field application means 51d controls the gradient magnetic field generating coil 12 to generate a gradient magnetic field (gradient magnetic field) that changes depending on the position. When performing imaging using a spin-echo echo-type echo-planar imaging method, which is an example of a second imaging method, the gradient magnetic field application means 51d of the first embodiment generates a gradient magnetic field 91 in the slice direction to identify an imaging cross section in response to a 90-degree pulse 101 or a 180-degree pulse 102, with respect to three mutually orthogonal axial directions: a slice direction, a readout direction, and a phase direction, as shown in FIGS. 3 and 4 . The gradient magnetic field application means 51d also generates a gradient magnetic field 92 for MRE in the readout direction. While the gradient magnetic field 92 for MRE is generated in the readout direction in FIGS. 3 and 4 , it is not actually restricted from being generated in the slice direction or the phase direction. The gradient magnetic field 92 for MRE is generated in response to vibration 93, and is a magnetic field called a motion encoding gradient magnetic field (MEG). In the first embodiment, a gradient magnetic field 92a for one cycle synchronized in phase with the oscillation 93 is generated after a 90-degree pulse 101, and a gradient magnetic field 92b for one cycle 180 degrees out of phase with the oscillation 93 is generated after a 180-degree pulse 102. After the gradient magnetic field 92 for MRE, a gradient magnetic field 94 for echo is generated at predetermined intervals in the readout direction. Furthermore, in the phase direction, a gradient magnetic field 96 for determining a position in k-space (measurement space) is generated according to the position, synchronized with the gradient magnetic field 94 for echo.

[0026] 5, when imaging is performed using a single-shot fast spin echo method as an example of the first imaging method, a gradient magnetic field 91′ for specifying an imaging cross section is generated in the slice direction in response to a 90-degree pulse 101 or a 180-degree pulse 102. A gradient magnetic field 94′ for an echo is generated multiple times at a predetermined timing in the readout direction. A gradient magnetic field 96′ for determining a position in k-space (measurement space) is generated before the gradient magnetic field 94′ for an echo, and a magnetic field 97′ for canceling the gradient magnetic field 96′ is generated after the gradient magnetic field 94′ for an echo. The magnetic fields 96′ and 97′ are generated for each gradient magnetic field 94′ for an echo, and the strengths of the magnetic fields 96′ and 97′ are different each time (they are weakened over time, then the polarity is reversed and they are strengthened over time), thereby changing the position in k-space. In addition, in the single-shot fast spin echo imaging of Example 1, only MR images (MR intensity images and MR phase images) are captured and MRE images are not captured, so vibration 93 and MEG gradient magnetic fields 92a and 92b do not appear in Figure 5.

[0027] The alternating magnetic field application means 51e controls the alternating magnetic field generating coil 13 to generate radio frequency magnetic fields (also referred to as RF, RF pulse, or radio frequency pulse) 101, 102, which are alternating magnetic fields corresponding to a frequency that excites protons (based on the magnetic resonance conditions of protons). When imaging using the spin echo echo planar method, the alternating magnetic field application means 51e of the first embodiment generates a 90-degree pulse 101, which is a radio frequency magnetic field that rotates the magnetization vector of protons by 90 degrees, and a 180-degree pulse 102 that rotates the magnetization vector by 180 degrees. Furthermore, a gradient magnetic field 94 for echoes is applied to the magnetization vector rotated by each pulse 101, 102, thereby generating a large number of echo signals 103. In the spin-echo echo planar method, the echo signals 103 are composed of a spin-echo (SE) signal 103a of relatively high image quality generated by a 90-degree pulse 101 and a 180-degree pulse 102, and a gradient-echo (GE) signal 103b of relatively low image quality generated before and after the SE signal 103a by a gradient magnetic field 94 for the echo. When imaging using the single-shot fast spin echo method, after generating one shot (single shot) of a 90-degree pulse 101, a 180-degree pulse 102 is generated multiple times at predetermined time intervals. This generates multiple echo signals (spin echo signals) 103' (the number of times the 180-degree pulses 102 are generated). Since spin echo signals have relatively high image quality compared to gradient echo signals, there is less image distortion in the single-shot fast spin echo method.

[0028] The reference pattern applying means 52 applies a predetermined reference pattern to the captured image. In Figures 4 and 5, the reference pattern applying means 52 of the first embodiment applies an additional magnetic field 111 corresponding to the reference pattern via the magnetic field control means 51.

[0029] In the first embodiment, when performing imaging with a reference pattern applied, the reference pattern applying means 52 controls the magnetic field control means 51 so as to spatially control (select) the location where an RF pulse (excitation pulse) is applied according to the reference pattern. Specifically, when a reference pattern is applied, an additional magnetic field 111 is applied before the alternating magnetic fields 101, 102 and gradient magnetic fields 91, 92 for imaging. Therefore, at the location of the examination part where the additional magnetic field 111 is applied (location of the pattern), the signal obtained during imaging is forcibly made a specific signal (for example, signal intensity zero, or black in terms of an image).

[0030] As a method for adding a reference pattern, although the purpose of the image to be captured differs, known techniques such as tagging imaging of the myocardium can be applied. In Example 1, a horizontal stripe pattern in which bands extending horizontally appear at equal intervals in the vertical direction is used as the reference pattern. The reference pattern is not limited to a horizontal stripe pattern. For example, the reference pattern can be changed to any pattern, such as a vertical stripe pattern, a grid pattern, a diagonal stripe pattern, or a polka dot pattern, depending on the user's settings, the size and type of the area to be examined (organs, muscles, etc.), the design and specifications of the device, etc. That is, depending on the imaging conditions, the main direction of distortion may be vertical or horizontal (this can be known in advance), so it is possible to select a horizontal stripe pattern when the main direction of distortion is vertical, or a vertical stripe pattern when the main direction of distortion is horizontal. Furthermore, a grid pattern is preferable because it can be used whether the main direction of distortion is vertical or horizontal.

[0031] The vibration application control means 53 applies vibrations of a predetermined frequency (for example, 50 Hz or 60 Hz) to the part to be inspected by the vibration pad 16. The signal acquiring means 54, which is an example of a receiving means, acquires an electromagnetic wave signal generated when protons in the subject 4 relax via the receiving coil 14 at the time of the echo signal 103. Therefore, in the first embodiment, in a state where the vibration shown in Fig. 3 is applied by the vibration application control means 53, a signal is measured by the receiving coil 14 at the echo time TE, thereby capturing an MR image while applying vibration.

[0032] The MR image acquiring means 55 creates an MR image based on the electromagnetic wave signals (echo signals) acquired by the signal acquiring means . The signal processing means 55a performs signal processing on the received electromagnetic wave signal. The signal processing means 55a of the first embodiment regards the signal acquired by the signal acquiring means 54 as a real part r, and a signal obtained by delaying the signal acquired by the signal acquiring means 54 by a phase of π / 2 as an imaginary part i. That is, the signal processing means 55a generates a complex number based on the received electromagnetic wave signal, that is, a signal in k-space (frequency space) in the technical field of MRI. Then, the signal processing means 55a performs an inverse Fourier transform (inverse fast Fourier transform in the embodiment) on the real part r and the imaginary part i to convert them into signals R and I in the real space. Then, the signal processing means 55a calculates an intensity M=(R 2 +I2 ) 1 / 2 and phase φ=tan -1 (I / R). Note that this calculation is introduced in conventional MRI apparatuses and is well known, so further detailed explanation will be omitted.

[0033] The MR intensity image creating means (MR intensity image acquiring means) 55b creates an MR intensity image based on the intensity M calculated by the signal processing means 55a. Note that the MR intensity image is generally an image used for diagnosis as an MRI image.

[0034] The MR phase image generating means (MR phase image acquiring means) 55c generates an MR phase image (used as a wave image in MRE) based on the phase φ calculated from the electromagnetic wave signal. Here, the MR phase image generating means 55c of the first embodiment generates an MR phase image based on the phase φ calculated from the electromagnetic wave signal measured at the echo time TE.

[0035] The first imaging method control means 56 controls imaging by a single shot fast spin echo method (SSFSE method) as an example of the first imaging method. The first imaging method control means 56 of the first embodiment controls the magnetic resonance imaging apparatus 1 via the above-mentioned means 51 to 55 to perform MR imaging by the SSFSE method. As shown in FIG. 5, the first imaging method control means 56 performs MR imaging by the SSFSE method to which a reference pattern is added. Note that in the first embodiment, MR imaging by the SSFSE method is performed by imaging for one phase of vibration of the vibration pad 16 (for example, phase 0°), that is, one MR imaging session.

[0036] The second imaging method control means 57 controls imaging by a spin echo-echo planar imaging method (SE-EPI method) as an example of the second imaging method. The second imaging method control means 57 of the first embodiment controls the magnetic resonance imaging apparatus 1 via the above-mentioned means 51 to 55 to perform MR imaging by the SE-EPI method. The second imaging method control means 57 performs MR imaging by the SE-EPI method with the addition of a reference pattern as shown in FIG. 4 and MR imaging by the normal SE-EPI method (without the addition of a reference pattern) as shown in FIG. 3. In the first embodiment, in the MR imaging by the SE-EPI method with the addition of a reference pattern, imaging is performed for one phase of vibration of the vibration pad 16 (for example, phase 0°). In addition, in the MR imaging without the addition of a reference pattern, imaging is performed for four phases of vibration of the vibration pad 16 (for example, phases 0°, 90°, 180°, and 270°) for MRE.

[0037] FIG. 6 is an explanatory diagram of an example of an MR image to which a reference pattern of Example 1 has been added, where FIG. 6A is a diagram of an image obtained by the SE-EPI method, FIG. 6B is a diagram of an image obtained by the SSFSE method, and FIG. 6C is a diagram of an image after correction of the image of FIG. 6A. The distortion calculation means 58 calculates the distortion of the second MR image 132 based on a first MR image 131 (see FIG. 6B), which is an MR image captured by the first imaging method control means 56, and a second MR image 132 (see FIG. 6A), which is an MR image captured with a reference pattern added by the second imaging method control means 57. That is, the distortion calculation means 58 compares the reference pattern 131a reflected in the first MR image 131 with the reference pattern 132a reflected in the second MR image 132, and calculates the deviation of the reference pattern 132a reflected in the second MR image 132 as distortion, using the reference pattern 131a reflected in the first MR image 131 as a reference. In general, the SSFSE method is known as an imaging method with little distortion, and the SE-EPI method can capture images faster (about 0.2 seconds per shot) than the SSFSE method (about 0.8 seconds per shot), but is known to produce more distortion (artifacts). Therefore, in the first embodiment, the distortion occurring in the imaging results of the SE-EPI method, which involves a lot of distortion, is calculated based on the imaging results of the SSFSE method, which involves a little distortion.

[0038] The distortion correction means 59 corrects the normal imaging results obtained by the second imaging method control means 57 based on the distortion calculated by the distortion calculation means 58. The distortion correction means 59 corrects the distortion of each of the MR images for four phases obtained by the second imaging method control means 57 without a reference pattern.

[0039] The wavelength acquisition means 60 acquires the wavelength λ of the vibration wave propagating within the body of the subject 4 due to the vibration applied by the vibration pad 16 for each region of interest (ROI) based on the MR phase image 133 (see Figure 6C) corrected by the distortion correction means 59. The hardness estimation means 61 estimates the hardness μ of the part to be inspected based on the wavelength λ of the vibration wave, the frequency f of the vibration wave applied by the vibration pad 16, and the density ρ of the part to be inspected. Note that the frequency f of the vibration wave is known from the frequency f of the vibration wave applied by the vibration pad 16, and the density ρ of the part to be inspected is calculated based on the density of the human body, which is approximately 1 [g / cm 3 ]. And the hardness (elastic modulus) μ is μ = ρ·(λ·f) 2 It is calculated from

[0040] The MRE image creation means 62 creates an MRElastogram image (MRE image) that visualizes stiffness using the MR phenomenon. The MRE image creation means 62 of the first embodiment creates an MRE image that is color-coded according to the stiffness μ calculated for each target region (pixel). As an example, it is possible to display stiff parts (pixels with a large stiffness μ value) in red, and change the color to yellow, green, blue, and purple as the stiffness becomes softer (as the stiffness μ value becomes smaller).

[0041] The image display means 63 displays on the display 23 the images created by the MR image acquisition means 55 and corrected by the distortion correction means 59, and the images created by the MRE image creation means 62. That is, the display 23 displays an MR intensity image (an image used in normal diagnosis), an MR phase image (used as a Wave Image in MRE), and an elastogram image (MRE image), which are cross-sectional images of the area to be examined. In the first embodiment, since it is difficult to understand the anatomical structure with only the Wave Image image or the elastogram image, a display mode in which the MR intensity image is superimposed on the Wave Image image or the elastogram image can also be provided. It is also possible to display the images superimposed, or to switch between the MR intensity image and the Wave Image image or the elastogram image according to input, without displaying all images on the display 23. In addition, it is also possible to arrange the MR intensity image and the elastogram image, etc., side by side on the same cross section, or to display elastogram images, etc., on different cross sections side by side, and other arbitrary modifications are possible.

[0042] (Function of Example 1) In the magnetic resonance imaging apparatus 1 of the first embodiment having the above configuration, imaging is performed for one phase each using the SSFSE method and the SE-EPI method with a reference pattern. At this time, the imaging time for each is less than one second, which reduces the burden on the subject. Also, it is possible to provide a rest period of several tens of seconds to several minutes between the SSFSE method imaging and the SE-EPI method imaging, which reduces the burden on the subject. Note that the SSFSE method imaging and the SE-EPI method imaging can be performed in either order. Note that there is no particular need to synchronize the vibration phase of the vibration pad 16 between the SSFSE method imaging and the SE-EPI method imaging. Distortion is calculated from the imaging results obtained by the SSFSE method and the SE-EPI method with the reference pattern. Then, imaging (normal imaging) for four phases is performed using the SE-EPI method without the reference pattern. Therefore, imaging for four phases using the SSFSE method takes several tens of seconds in total, whereas in Example 1, imaging for four phases using the SE-EPI method can be completed in just a few seconds in total. This shortens the time that the subject has to temporarily hold their breath during imaging, reducing the burden on the subject.

[0043] Then, distortion correction is performed from the imaging results for four phases using the SE-EPI method to create an elastogram image. Therefore, it is possible to improve the accuracy of the elastogram image compared to the conventional case where an elastogram image is created using the SE-EPI method without distortion correction. In particular, when imaging a liver suspected of having cirrhosis, the liver has a difference in magnetic susceptibility near the stomach, which makes it prone to artifacts, and therefore the accuracy of the elastogram image is likely to decrease unless distortion correction is performed. However, this is reduced in Example 1. Therefore, the magnetic resonance imaging apparatus 1 of the first embodiment can perform imaging in a shorter time than the conventional technology, and can improve the accuracy of the elastogram.

[0044] FIG. 7 is an explanatory diagram of the wave image of Experimental Example 1, where FIG. 7A is a wave image created from the MR phase image before correction, and FIG. 7B is a wave image created from the MR phase image after correction. FIG. 8 is an explanatory diagram of MRE lastogram images of Experimental Example 1, where FIG. 8A is an MRE lastogram image before correction and FIG. 8B is an MRE lastogram image after correction. In Experimental Example 1, a uniform phantom was subjected to vibration at 60 Hz using vibration pad 16, and an experiment was conducted with MEG at 90 Hz. Because the phantom was uniform, its stiffness was also uniform, and the wavelength of the waves generated by the vibration was also uniform. In FIG. 7, in Wave Image 201 created from the uncorrected MR phase image of FIG. 7A, the wavelength (vertical width of the wave) at the top is shorter than the wavelength at the bottom, whereas in Wave Image 202 (FIG. 7B) after correction, the wavelengths at the top and bottom are almost the same. Therefore, accuracy is improved. 8, in the MRE lastogram image 211 (FIG. 8A) created from the MR phase image before correction, a distribution bias was observed at the bottom, even though the phantom was uniform and had no bias in distribution, whereas the MRE lastogram image 212 (FIG. 8B) after correction has less bias, resulting in higher accuracy.

[0045] (Example of change) Although the embodiments of the present invention have been described above in detail, the present invention is not limited to the above embodiments and various modifications can be made within the scope of the gist of the present invention as set forth in the claims. Modifications (H01) to (H04) of the present invention are exemplified below. (H01) In the above embodiment, the magnet unit 2 is ring-shaped, i.e., a so-called tunnel-type magnetic resonance imaging apparatus is illustrated, but this is not limited thereto. For example, the present invention can also be applied to a so-called open-type magnetic resonance imaging apparatus in which the magnet unit 2 is U-shaped. (H02) In the above-described embodiments, the specific numerical values ​​exemplified, such as frequencies, can be changed arbitrarily according to the design, specifications, and the like.

[0046] (H03) In the above embodiment, the specific shape, length, width, etc. of the vibration pad 16 can be changed according to the design, specifications, etc. (H04) In the above embodiment, the SSFSE method is exemplified as the first imaging method, but is not limited to this. For example, imaging methods with less distortion, such as the HASTE (Half Fourier Acquisition Single Shot Turbo Spin Echo) method and the RARE (Rapid Acquisition with Refocused Echoes) method, can be used. Furthermore, the SE-EPI method is exemplified as the second imaging method, but is not limited to this. For example, imaging methods that enable high-speed imaging, such as the high-speed gradient echo method and the gradient echo type multi-echo method, can be used. [Explanation of symbols]

[0047] 1...photographic device, 2...magnetic field generator, 4...Subject, 16...Vibration imparting member, 55c... Means for creating MR phase images; 62...MRE image generation means, 91,92...Gradient magnetic field 101...alternating magnetic field, 131a, 132a...standard pattern, 131...first MR image, 132...second MR image, 212...MR elastography image.

Claims

1. a magnetic field generating device that generates, for a part to be examined of a subject, a static magnetic field, a gradient magnetic field that changes depending on the position, and an alternating magnetic field that is set in advance based on the magnetic resonance conditions of protons; a vibration applying member that applies vibration to the inspection target portion; an MR intensity image acquisition means for acquiring an MR intensity image according to the distribution of protons based on the electromagnetic waves acquired according to the timing of application of the gradient magnetic field; an MR phase image acquisition means for acquiring an MR phase image according to the phase of an electromagnetic wave signal based on the electromagnetic wave acquired according to the timing of application of the gradient magnetic field; an MRE image creating means for creating an MR elastography image based on the MR phase image; Equipped with When generating a magnetic field by the magnetic field generating device based on a predetermined first imaging method, a magnetic field corresponding to a predetermined reference pattern for strain detection is added to acquire a first MR intensity image; a second MR intensity image is acquired by adding a magnetic field corresponding to the reference pattern when generating a magnetic field with the magnetic field generating device based on a second imaging method that can acquire the MR intensity image and the MR phase image faster than the first imaging method and that produces larger distortion in the MR intensity image and the MR phase image; calculating a distortion in the second imaging method based on a reference pattern reflected in the first MR intensity image and a reference pattern reflected in the second MR intensity image; acquiring the MR phase images of the subject a plurality of times using the second imaging method without adding the reference pattern; correcting distortions in the MR phase images acquired multiple times by the second imaging method without adding the reference pattern, using the calculated distortions; generating the MR elastography image based on the plurality of distortion-corrected MR phase images; An imaging device characterized by:

2. the reference pattern being configured as a grid pattern; 2. The photographing device according to claim 1, further comprising:

3. The first imaging method is a single-shot fast spin echo method.

2. The imaging device according to claim 1.

4. The second imaging method is a spin-echo echo-planar imaging method.

2. The imaging device according to claim 1.

5. An imaging method for generating a static magnetic field, a gradient magnetic field that changes depending on the position, and an alternating magnetic field that is preset based on a magnetic resonance condition of protons while applying vibration to an examination part of a subject, and acquiring an MR intensity image according to the distribution of protons and an MR phase image according to the phase of the electromagnetic wave signal based on the electromagnetic waves acquired depending on the timing of application of the gradient magnetic field, and creating an MR elastography image based on the MR phase image, a magnetic field according to a predetermined reference pattern for strain detection is added when a magnetic field is generated by a magnetic field generating device based on a predetermined first imaging method, and a first MR intensity image is acquired; a second MR intensity image is acquired by adding a magnetic field corresponding to the reference pattern when generating a magnetic field with the magnetic field generating device based on a second imaging method that can acquire the MR intensity image and the MR phase image faster than the first imaging method and that produces larger distortion in the MR intensity image and the MR phase image; calculating a distortion in the second imaging method based on a reference pattern reflected in the first MR intensity image and a reference pattern reflected in the second MR intensity image; acquiring the MR phase images of the subject a plurality of times using the second imaging method without adding the reference pattern; correcting distortions in the MR phase images acquired multiple times by the second imaging method without adding the reference pattern, using the calculated distortions; generating the MR elastography image based on the plurality of distortion-corrected MR phase images; A photographing method characterized by:

Images