JP6985737B2 - Shooting device - Google Patents

Description

The present invention relates to an imaging device, and more particularly to an imaging device capable of photographing an MR elastography (MRE) for measuring the hardness of a tissue and a diffusion-weighted image of water molecules.

In the medical field, an MRI apparatus (Magnetic Resonance Imaging apparatus: magnetic resonance imaging apparatus) having less influence on a patient such as radiation exposure is used. In an MRI device, hydrogen nuclei (protons) contained in each cell of the human body are excited by applying a high-frequency magnetic field according to the spin of the protons, and the excited protons are emitted when they return to their original state (relaxation). Based on electromagnetic waves, it is possible to obtain images showing the parts having different proton densities (for example, water and fat) in shades.
MRE (Magnetic Resonance Elastography) is a difference in the "hardness" inside the object by taking an image with an MRI device while applying vibration (about 50 Hz in the case of the trunk) to the object. This is an imaging method for imaging hardness by utilizing the difference in propagation of vibration waves due to magnetic resonance elastography (see Patent Documents 1 and 2).

In general, lesions become harder as the malignancy increases, and "palpation" for diagnosing the malignancy has been performed for a long time. Although palpation is a simple and effective diagnostic method, it is difficult to palpate deep parts of the body or parts surrounded by bones. In MRE, forced vibration is generated on the surface of the human body, and the difference in local hardness is imaged from the appearance of the vibration wave propagating in the body. This makes it possible for MRE to measure the hardness of parts that were difficult to palpate, and may be able to provide images with completely different diagnostic value.
When the hardness of an object changes, the speed of sound and wavelength of the wave propagating inside the object (propagating wave) change. Therefore, in the MRE, an image is taken while applying vibration synchronized with the MRI apparatus to the image pickup target. This makes it possible to visualize the propagating wave inside the image pickup target. The image of the propagating wave obtained at this time is called Wave Image. Since the Wave Image images the wavelength of the locally propagated wave, it is possible to calculate an image that reflects the hardness of the local area. The image obtained by calculation is called Elastogram.

Diffusion weighted imaging (DWI) incorporates a motion proving gradient (MPG) to reflect the phenomenon of water molecule diffusion in MRI images. This is a technology for imaging the diffusion of water molecules in living tissues. DWI is mainly used for tumor imaging and diagnosis of acute cerebral infarction. In general, malignant tumors repeatedly grow in a disorderly manner, so that the cell density may be higher than that of normal tissue. As the cell density increases, the diffusion of water molecules is restricted, resulting in a lower diffusion coefficient (difficulty in diffusion) in the tumor area. When such a site is imaged with DWI, DWI forms an image contrast reflecting the diffusion coefficient, so that normal tissue and tumor can be imaged with clear contrast. On the other hand, in the area of acute cerebral infarction, cytotoxic edema occurs due to the interruption of blood flow (the interruption of blood flow causes the energy supply and the circulation of waste products to stop, and the cells swell significantly). As a result, the diffusion coefficient of the acute cerebral infarction region is reduced, and a clear contrast can be formed with respect to normal tissue.

As a technique for simultaneously acquiring MRE and DWI, the technique described in Non-Patent Document 1 below is known.
In Non-Patent Document 1, the diffusion detection gradient magnetic field (motion proving gradient: MPG) used when photographing the DWI is referred to as the vibration detection gradient magnetic field (MEG) applied when the MRE is photographed. A technique for simultaneously capturing both an MRE image and a DWI image by using it is described.

Special Table 2005-507691 (“0008”, “0014” to “0023”) Japanese Unexamined Patent Publication No. 2011-98158 (“0003” to “0018”, “0026” to “0029”)

Yin Zl, Magin RL, Klatt D. Simultaneous MR elastography and diffusion acquisitions: diffusion-MRE (dMRE). Magn Reson Med 2014; 71: 1682-1688

(Problems of conventional technology)
In a general MRE, an image is taken in synchronization with a vibration gradient magnetic field (MEG) for detecting vibration and vibration from the outside. At this time, if the intensity of MEG is too strong, a false image (artifact) is generated on the intensity image (an image used in normal diagnosis. DWI also uses this intensity image). Since the MRE uses the MR phase image instead of the intensity image, it is not easily affected by this artifact.
However, in the method of Non-Patent Document 1, since the DWI imaging method (pulse sequence) is used as it is, the diffusion detection gradient magnetic field (motion proving gradient: MPG) is the vibration detection gradient magnetic field (MEG). It also plays a role.
In general DWI, MPG is applied relatively strongly in order to reflect the diffusion phenomenon in the image. Therefore, in the method described in Non-Patent Document 1, since MPG is diverted as MEG, the application strength as MEG is strong. Since DWI uses an intensity image, the method of Non-Patent Document 1 has a problem that an artifact is easily generated in a diffusion-weighted image.

The technical subject of the present invention is to obtain an image without artifacts when observing MRE and DWI at the same time.

In order to solve the technical problem, the photographing apparatus of the invention according to claim 1 is used.
A magnetic field generator that generates a static magnetic field, a gradient magnetic field in which the magnetic field changes depending on the position, and an alternating magnetic field preset based on the magnetic resonance conditions of protons for the subject to be inspected.
An alternating magnetic field applying means for applying the alternating magnetic field at a preset repetition time, and a means for applying the alternating magnetic field.
A receiving means for receiving the electromagnetic wave based on the echo time, which is the time for receiving the electromagnetic wave emitted when the proton of the part to be inspected excited by the alternating magnetic field relaxes.
A first gradient magnetic field that applies a first gradient magnetic field for MRE to any or a plurality of slice directions, lead-out directions, and phase encoding directions, which are three intersecting axes set for an inspected portion. And the application means of
A vibration-imparting member that imparts vibration to the part to be inspected and is capable of imparting multiple vibrations having different phases.
Based on the electromagnetic wave acquired according to the echo time, an MR phase image according to the phase of the electromagnetic wave signal is acquired for each phase of vibration applied by the vibration imparting member, and an MR phase image acquisition means for acquiring the MR phase image.
A means for applying a second gradient magnetic field for applying a second gradient magnetic field for enhancing diffusion to the subject, and a pair of waveforms having the same magnitude and opposite directions at intervals according to the period of the vibration. The means for applying the second gradient magnetic field, and the means for applying the second gradient magnetic field.
A diffusion-weighted image acquisition means for acquiring a diffusion-weighted image based on the phase dispersion of molecules that have moved in response to the second gradient magnetic field.
It is characterized by being equipped with.

The invention according to claim 2 is the photographing apparatus according to claim 1.
The second gradient magnetic field applied in a direction different from the direction in which the first gradient magnetic field is applied,
It is characterized by being equipped with.

The invention according to claim 3 is the photographing apparatus according to claim 1 or 2.
It is characterized in that the strength of the second gradient magnetic field can be changed according to the desired diffusion-weighting effect.

The invention according to claim 4 is the photographing apparatus according to any one of claims 1 to 3.
It is characterized in that the duration of applying the second gradient magnetic field can be changed according to the desired diffusion-weighted effect.

According to the first aspect of the present invention, by separately applying the first gradient magnetic field and the second gradient magnetic field, it is possible to obtain an image without artifacts when observing MRE and DWI at the same time. can.
According to the second aspect of the present invention, by applying the second gradient magnetic field in a direction different from that of the first gradient magnetic field, a diffusion-weighted image in a direction different from that of MRE can be obtained.
According to the third aspect of the present invention, by changing the strength of the second gradient magnetic field, the b value can be changed without adversely affecting the measurement of MRE and DWI.
According to the invention of claim 4, by changing the duration of the second gradient magnetic field, the b value can be changed without adversely affecting the measurement of MRE and DWI.

FIG. 1 is an explanatory diagram of the magnetic resonance imaging apparatus according to the first embodiment of the present invention. FIG. 2 is a functional block diagram of a computer body in the magnetic resonance imaging apparatus of Example 1. FIG. 3 is an explanatory diagram of application of a magnetic field and application of vibration of Example 1, and is a graph in which time is taken on the horizontal axis. FIG. 4 is an explanatory diagram when the gradient magnetic field of Example 1 is applied to each of the vibration phases of 0 °, 90 °, 180 °, and 270 °. FIG. 5 is an explanatory diagram of a process for creating an MR image of the first embodiment. FIG. 6 is an explanatory diagram of the prior art described in Non-Patent Document 1. FIG. 7 is an explanatory diagram of problems of the prior art described in Non-Patent Document 1. FIG. 8 is an explanatory diagram of the effect of the magnetic resonance imaging apparatus of Example 1. FIG. 9 is an example of an MRE image (Wave Image and Elastogram) obtained by the configuration of Example 1, the configuration described in Non-Patent Document 1, and a general MRE technique. FIG. 10 is an explanatory diagram of a diffusion-weighted image obtained by the configuration described in Non-Patent Document 1 and Example 1.

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 addition, in the explanation using the following drawings, the illustrations other than the members necessary for the explanation are omitted as appropriate for the sake of easy understanding.

FIG. 1 is an explanatory diagram of the magnetic resonance imaging apparatus according to the first embodiment of the present invention.
In FIG. 1, the magnetic resonance imaging device 1 of the first embodiment as an example of the imaging device of the present invention has a magnet unit 2 as an example of a magnetic field generator. The magnet portion 2 is formed with a through hole 3 that penetrates the inside in the horizontal direction. A sleeper 6 on which the subject 4 in a sleeping state is supported can penetrate through the through hole 3.
The magnet unit 2 has a magnet 11 for generating a static magnetic field as an example of a member for applying a static magnetic field. As the static magnetic field generating magnet, a superconducting magnet or a permanent magnet can be used. Inside the static magnetic field generating magnet 11, a gradient magnetic field generating coil 12 as an example of a gradient magnetic field applying member is arranged. Inside the gradient magnetic field generation coil 12, a high frequency magnetic field generation coil 13 as an example of an excitation magnetic field application member is arranged. Inside the high-frequency magnetic field generating coil 13, a receiving coil 14 for receiving an electromagnetic wave is arranged as an example of a receiving unit.

Further, in the first embodiment, for the MRE measurement, the subject 4 has a diaphragm (passive driver) as an example of a vibration imparting member on a portion of the body surface corresponding to the position of the liver as an example of the part to be inspected. ) 16 is supported. The diaphragm 16 is a member that gives vibration to the subject 4 at a preset frequency, and for example, a conventionally known arbitrary configuration described in Patent Document 2 or the like can be adopted.

A computer device 21 as an example of the 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 a control signal of the static magnetic field generating magnet 11 and the like, a detection signal of the receiving coil 14, and the like to and from the magnet unit 2. The computer device 21 includes a computer main body 22, a display 23 as an example of a display unit, and a keyboard 24 and a mouse 25 as an example of an input unit. In Example 1, the configuration in which the computer device 21 and the magnet unit 2 are connected by a cable Cb is illustrated, but the present invention is not limited to this, and any wireless such as a mobile phone line, Bluetooth (registered trademark), wireless LAN, etc. is used. It is also possible to send and receive information by communication method.

(Explanation of the control unit of the computer main body 22 of the first embodiment)
FIG. 2 is a functional block diagram of a computer 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 performs I / O (input / output interface) for inputting / outputting signals to / from the outside and adjusting the input / output signal level, and performs necessary activation processing. Performs processing according to the ROM (read-only memory) in which the programs and data of the above are stored, the RAM (random access memory) for temporarily storing the necessary data and programs, and the startup program stored in the ROM or the like. It is composed of a computer device having a CPU (central processing unit), a clock oscillator, and the like, and various functions can be realized by executing a program stored in the ROM, RAM, and the like.
The control unit 41 stores basic software that controls basic operations, a so-called operating system OS, a photographing device control program AP1 as an example of an application program, and other software (not shown).

(Elements connected to the control unit 41 of the first embodiment)
Output signals from signal output elements such as the keyboard 24, the mouse 25, and the receiving coil 14 are input to the control unit 41.
Further, the control unit 41 of the first embodiment outputs a control signal to controlled elements such as the display 23, the static magnetic field generating magnet 11, the gradient magnetic field generating coil 12, and the high frequency magnetic field generating coil 13.

(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 58.

The magnetic field control means 51 controls the magnet portion 2 to control the magnetic field for MR imaging the inspected portion of the subject 4. The magnetic field control means 51 of the first embodiment is an example of a repeating time storage means 51a, an echo time storage means 51b, a static magnetic field application means 51c, a first gradient magnetic field application means 51d, and an alternating magnetic field application means. It has a high-frequency magnetic field applying means 51e and a second gradient magnetic field applying means 51f.

FIG. 3 is an explanatory diagram of application of a magnetic field and application of vibration of Example 1, and is a graph in which time is taken on the horizontal axis.
The repetition time storage means 51a stores the repetition time TR, which is an interval in which a high-frequency magnetic field is applied as an example of an alternating magnetic field applied to excite a proton contained in a portion to be inspected of the subject 4.

The echo time storage means 51b stores the echo time TE, which is the interval from the application of the high frequency magnetic field to the acquisition of the electromagnetic wave emitted when the excited proton returns (relaxes) to the original state. In FIG. 3, in the first embodiment, the echo time storage means 51b stores the echo time TE, which is the period from the application of the high frequency magnetic field to the acquisition of the electromagnetic wave.
In the first embodiment, the repetition time TR and the echo time TE are set in advance, but the user of the magnetic resonance imaging apparatus 1 can manually input the repeat time TR and the echo time TE so that they can be set and changed. be.
In order to carry out the MRE, a plurality of imaging images synchronized with the vibrations having different phases applied from the diaphragm 16 are required. In the first embodiment, four types of vibrations whose phases are shifted by 90 ° are applied from the vibrating plate 16, and when the vibration phases are divided into four, each image pickup has vibration phase 1 (0 °) and vibration phase. It can be defined as 2 (90 °), vibration phase 3 (180 °), and vibration phase 4 (270 °).

The static magnetic field applying means 51c controls the static magnetic field generating magnet 11 to generate a static magnetic field. The static magnetic field applying means 51c of Example 1 generates a static magnetic field of 3 [T] as an example.
The first gradient magnetic field application means 51d controls the gradient magnetic field generation coil 12 to generate a first gradient magnetic field (gradient magnetic field) 61 for MRE whose magnetic field changes depending on the position. Therefore, the first gradient magnetic field 61 is a magnetic field called a vibration detection gradient magnetic field MEG (motion encoding gradient). As shown in FIG. 3, the first gradient magnetic field applying means 51d of the first embodiment slices in three axial directions, that is, the slice direction, the read out direction, and the phase direction, which are orthogonal to each other. A first gradient magnetic field 61 is generated in the direction (slice axis).

The high-frequency magnetic field applying means 51e controls the high-frequency magnetic field generating coil 13 to generate a high-frequency magnetic field 63, which is an alternating magnetic field corresponding to the frequency for exciting protons. As an example, the high-frequency magnetic field application means 51e of the first embodiment has a magnetic field (90 ° RF pulse signal 63a) that tilts the spins aligned in the direction of the static magnetic field by 90 ° and a magnetic field that cancels the angular velocity of the nuclear spin (180 ° RF). The pulse signal) 63b is applied at a predetermined interval (TE / 2). The high-frequency magnetic field application means 51e of the first embodiment generates the high-frequency magnetic field 63 (63a, 63b) at a time corresponding to the repetition time TR. An echo signal is observed 2 hours after the 180 ° RF pulse signal 63b.

The second gradient magnetic field application means 51f controls the gradient magnetic field generation coil 12 to generate a second gradient magnetic field (gradient magnetic field) 62 for diffusion-weighted imaging. As shown in FIG. 3, the second gradient magnetic field application means 51f of the first embodiment is a magnetic field in which the second gradient magnetic field 62 is called a diffusion detection gradient magnetic field MPG (motion proving gradient). As shown in FIG. 3, the second gradient magnetic field applying means 51f of the first embodiment has a first inclination in the three axial directions of the slice direction, the read out direction, and the phase direction. Magnetic field: A second gradient magnetic field 62 is generated in a phase direction (phase axis), which is an example of an axial direction different from MEG61. The second gradient magnetic field 62 of the first embodiment can be generated in an arbitrary axis (direction) according to the direction to be observed, and is generated in the same slice direction as the first gradient magnetic field 61. It is also possible to generate it in the lead-out direction.

Further, in the second gradient magnetic field applying means 51f of the first embodiment, the second gradient magnetic field 62 is applied so as to have different "b values" at the vibration phases of 0 °, 90 °, 180 ° and 270 °. .. Here, the b value is a value used when obtaining a diffusion-weighted image, and the gradient of the observed signal intensity with respect to the b value is the mass diffusivity (when the target is a living body, the diffusion phenomenon and perfusion at the observation target site). Since the phenomena are mixed, it becomes an apparent diffusion coefficient (ADC). For the b value, γ is the gyromagnetic ratio of protons, G is the strength of the MPG, δ is the duration of MPG: MPG lobe duration, and Δ is the pair of MPGs. Interval: When the duration between the MPG pairs is set, it is expressed by the following equation (1).
b = γ ² G ² δ ² (Δ−δ / 3)… Equation (1)
Here, γ is a value that cannot be changed, Δ is a value determined by the vibration 66 described later, but G and δ are variable values. In the embodiment, the b value of MPG62 is changed by changing the value of G. Therefore, it is possible to make observations while changing the value of b according to the four vibration phases (0 °, 90 °, 180 °, 270 °), and to derive the diffusion coefficient from the observation results for the four b values. be. It is also possible to change δ when changing the b value. It is also possible to change the vibration frequency.

The vibration applying control means 52 controls the diaphragm 16 to apply vibration 66 to the inspected portion. In FIG. 3, the period T of the vibration 66 applied by the vibration applying control means 52 of the first embodiment is synchronized with the period T of the first gradient magnetic field 61. In the first embodiment, the vibration applying control means 52 has a function of arbitrarily changing the phase of the vibration 66 with respect to the vibration 66 shown in FIG. 3, and using this function, for example, the number of vibration phase divisions. When there are four, vibration 66 having a phase shifted by 0 °, 90 °, 180 °, and 270 ° with respect to the phase of the first gradient magnetic field 61 can also be applied.

FIG. 4 is an explanatory diagram when the gradient magnetic field of Example 1 is applied to the vibration phases of 0 ° 90 °, 180 °, and 270 °, respectively.
In FIGS. 3 and 4, in the first embodiment, the first gradient magnetic field 61 applies a gradient magnetic field corresponding to a waveform for one cycle to the front and back with the 180 ° RF pulse signal 63b interposed therebetween. At this time, the MEG61a on the front side (early time) of the 180 ° RF pulse signal 63b and the MEG61b on the back side (late time) of the 180 ° RF pulse signal 63b are applied with waveforms that strengthen each other with respect to the vibration phase of the vibration 66. do. For example, when the front MEG61a and the rear MEG61b are applied at a timing in which the vibration frequency is out of phase by one cycle (T), the positive and negative of the waveform are reversed between the front MEG61a and the rear MEG61b (the peak of the front MEG61a is). When it coincides with the peak of vibration 66, the first gradient magnetic field 61 is applied so that the peak of the posterior MEG61b coincides with the valley of vibration 66).

Further, in the first embodiment, the second gradient magnetic field: MPG62 is applied at symmetrical timings in the front-rear direction with the 180 ° RF pulse signal 63b interposed therebetween. As an example of the timing different from that of the first gradient magnetic field MEG61, the MPG62 is applied with the front side MPG62a at a timing earlier than the front side MEG61a and is applied with the rear side MPG62b at a timing later than the rear side MEG61b. Here, the front side MPG62a and the rear side MPG62b are applied with an interval Δ, and the interval Δ is set to be an integral multiple of the period T of the vibration 66. That is, Δ = n · T. Therefore, the anterior MPG62a on the front side (early time) of the 180 ° RF pulse signal 63b and the posterior MPG62b on the rear side (late time) of the 180 ° RF pulse signal 63b are the waveforms (peaks and valleys) of the vibration 66. On the other hand, the phases are applied at the same timing. For example, when the peak of the front MPG62a coincides with the peak of vibration 66, the second gradient magnetic field 62 is applied so that the peak of the rear MPG62b coincides with the peak of vibration 66.
The 180 ° RF pulse signal 63b has the effect of reversing and inverting the positive and negative of the waveforms of the magnetic fields 61 and 62. Therefore, the fact that two identical MPGs 62a and 62b are applied before (before inversion) and after (after inversion) the 180 ° RF pulse signal 63b means that gradient magnetic fields of the same magnitude are applied in opposite directions to each other. It is equivalent to being.

As an example of the receiving means, the signal acquiring means 53 acquires an electromagnetic wave signal generated when the proton of the subject 4 is relaxed through the receiving coil 14 at the time of the echo time TE. Therefore, in the first embodiment, the signal was measured by the receiving coil 14 in the echo time TE in the state where the vibration shown in FIG. 3 was applied by the vibration applying control means 52, and the vibration 66 having a phase shift of 90 ° was applied. In this state, the signal is measured by the receiving coil 14 at the echo time TE, and the signal is measured in the same manner even when the frequency is 180 ° and 270 °, so that the phase of the vibration 66 is changed and the MR image is captured a plurality of times.

FIG. 5 is an explanatory diagram of a process for creating an MR image of the first embodiment.
The MR image acquisition means 54 includes a signal processing means 54a, an MR intensity image creating means 54b, an MR phase image creating means 54c, and a diffusion-weighted image creating means 54d, and is acquired by the signal acquiring means 53. An MR image is created based on the generated electromagnetic signal.
The signal processing means 54a performs signal processing on the received electromagnetic wave signal. In the signal processing means 54a of the first embodiment, the signal acquired by the signal acquisition means 53 is a real part r (real part), and the signal acquired by the signal acquisition means 53 is the imaginary part i (the signal whose phase is delayed by π / 2). imaginary part). That is, a complex number based on the received electromagnetic wave signal, that is, a so-called k-space (frequency space) signal in the technical field of MRI is generated. Then, the inverse Fourier transform (fast Fourier transform in the embodiment) is performed on the real part r and the imaginary part i to convert them into the signals R and I in the real space. Then, based on the real part R and the imaginary part I in the real space, the intensity M = (R ² + I ² ) ^1/2 in the complex plane and the phase φ = tan ^-1 (I / R) are calculated.

The MR intensity image creating means 54b creates an MR intensity image based on the intensity M calculated by the signal processing means 54a. The MR intensity image (for example, diffusion-weighted image) is an image generally used for diagnosis as an MRI image. Since the method for creating an MR intensity image is conventionally known (for example, the Dixon method) and any method can be adopted, further detailed description thereof will be omitted.

The MR phase image creating means 54c creates 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 creating means 54c of the first embodiment creates an MR phase image based on the phase φ calculated from the electromagnetic wave signal measured by the echo time TE. Further, an MR phase image is created in each case where the phase of the vibration applied by the vibration applying control means 52 is 0 °, 90 °, 180 °, and 270 °.

Diffusion-weighted image creation means (an example of diffusion-weighted image acquisition means) 54d is a diffusion based on the phase dispersion of molecules (mainly water molecules in cells) that have moved in response to a second gradient magnetic field: MPG62. Highlighted image: Create a DWI image. That is, a diffusion-weighted image is created based on the diffusion coefficient derived from the acquired signal. In the diffusion-weighted imaging method, a signal observed and acquired in a static magnetic field is measured as a one-dimensional molecular movement in the direction of the second gradient magnetic field MPG62. The quiescent molecule is offset by the spin phase change due to the two MPG62a, 62b and is not affected as a whole, but the molecule that has moved (diffused) in the direction of the MPG62a, 62b has a disordered spin phase. Then, the phase disturbance of the spin caused by the diffusion is observed as a signal drop. Since the diffusion-weighted imaging method (DWI) is conventionally known and is described in, for example, Japanese Patent Application Laid-Open No. 2005-253802, further detailed description will be omitted.

The wavelength acquisition means 55 acquires the wavelength λ of the vibration wave propagating inside the subject 4 by the vibration applied by the diaphragm 16. The wavelength acquisition means 55 of the first embodiment has a phase φ that fluctuates according to the vibration wave for each pixel of the image based on the MR phase image in each case of vibration phase 0 °, 90 °, 180 °, and 270 °. The wavelength λ of the oscillating wave is obtained from the transition of. Specifically, the wavelength λ of the vibration wave is estimated for each local region of the image from the state of propagation of the vibration wave obtained from the images having vibration phases of 0 °, 90 °, 180 °, and 270 °.

The hardness estimating means 56 estimates the hardness μ of the inspected portion based on the wavelength λ of the vibrating wave, the frequency f of the vibrating wave applied by the diaphragm 16, and the density ρ of the inspected portion. .. The frequency f of the vibrating wave is known from the frequency f of the vibrating wave applied by the vibrating plate 16, and the density ρ of the inspected portion is that the density of the human body is approximately 1 [g / cm ³ ]. Then, the hardness (elastic modulus) μ is calculated from ^{μ = ρ · (λ · f) 2.}
The MRE image creating means 57 creates an MR Elastogram image (MRE image) in which the hardness is imaged by utilizing the MR phenomenon. The MRE image creating means 57 of the first embodiment creates an MRE image color-coded according to the hardness μ calculated for each local region (pixel). As an example, a hard part (a pixel with a large value of hardness μ) is displayed in red, and as it becomes softer (a value of hardness μ becomes smaller), it is displayed so as to change to yellow, green, blue, and purple. It is possible.

The image display means 58 displays the image created by the MR image acquisition means 54 or the MRE image creation means 57 on the display 23. That is, the MR intensity image (image used in normal diagnosis), MR phase image (used as Wave Image in MRE), Elastogram image (MRE image), and diffusion-weighted image, which are cross-sectional images of the part to be inspected, are It is displayed on the display 23. In Example 1, since the anatomical structure is difficult to understand only from the Wave Image image and the Elastogram image, a display mode in which the MR intensity image and the Wave Image image or the Elastogram image are superimposed and displayed is also provided. It is also possible to display the MR image and the Wave Image image or the Elastogram image by switching between the MR intensity image and the Wave Image image or the Elastogram image according to the input without displaying the images in an overlapping manner or displaying all the images on the display 23. Further, it is possible to arrange the MR intensity image and the Elastogram image side by side in the same cross section, or to display the Elastogram images in different cross sections side by side.

(Action of Example 1)
In the magnetic resonance imaging apparatus 1 of the first embodiment having the above configuration, the first gradient magnetic field 61 for MRE and the second gradient magnetic field 62 are separately applied during one repetition time TR. .. Here, in the first gradient magnetic field (MEG) 61, the waveform for one cycle is applied twice, but since the waveform is for one cycle and the application time is extremely short, as a result, The positive area and the negative area cancel each other out, which has little effect on DWI. Further, in the second gradient magnetic field (MPG) 62, as described above, magnetic fields having the same intensity are applied in opposite directions, but they cancel each other out with respect to the vibration phase of the vibration 66, and the MRE has a shape. Will have less impact.
Therefore, in the magnetic resonance imaging apparatus 1 of Example 1, an MRE image using the first gradient magnetic field 61 and a diffusion-weighted image using the second gradient magnetic field 62 can be obtained by one measurement.

FIG. 6 is an explanatory diagram of the prior art described in Non-Patent Document 1.
FIG. 7 is an explanatory diagram of problems of the prior art described in Non-Patent Document 1.
In FIG. 6, in the configuration in which the MPG described in Non-Patent Document 1 is also used as the MEG, that is, in the technique in which the MPG and the MEG are integrated, in order to measure different b values, as shown in FIG. It is necessary to take pictures with different intensities (G) of MPG (MEG). In DWI, it is essential to change the intensity (G) of MPG, but for MRE, when the intensity (G) of MPG becomes smaller, the effect of MEG becomes weaker. This causes a problem that the vibration enhancing effect cannot be unified even after several shootings in which the vibration phase required by MRE is changed. Therefore, as shown in FIG. 7, when the b value is low (when the phase is 0 °), the vibration enhancing effect cannot be sufficiently obtained, and the MRE image may not be obtained.

If the intensity (G) is set so that the b value is such that a sufficient vibration enhancement effect can be obtained even when the b value is small in DWI (imaging of vibration phase 0 ° in MRE), the b value is set in DWI. When it is raised (in MRE, imaging with a vibration phase of 270 °), the intensity (G) becomes too strong, and there is a problem that the magnetic field becomes too strong to be used by the human body from the viewpoint of safety. Further, if the intensity (G) is increased in order to increase the b value, the effect of enhancing the vibration is too strong, and there is a problem that an artifact (false image) is generated in the diffusion-weighted image.
In MRE, in order to maximize the effect of the gradient magnetic field (MEG), it is necessary to synchronize the MEG with the vibration. Therefore, in the technique described in Non-Patent Document 1, the value of δ is fixed to the vibration. The value (δ = T / 2) does not change, and the b value cannot be changed by changing the value of δ. Also, f cannot be changed.
Therefore, the technique described in Non-Patent Document 1 has a problem that if the strength of the gradient magnetic field is weak, the sensitivity to vibration in the MRE image cannot be sufficiently obtained, and if the gradient magnetic field is too strong, an artifact is generated in DWI. It is difficult to obtain sufficient accuracy for both MRE and DWI, and there is a big problem in practicality.

On the other hand, in Example 1, a second gradient magnetic field 62 for DWI is applied separately from the first gradient magnetic field 61 for MRE, and they do not adversely affect each other. Therefore, the first gradient magnetic field 61 can be applied at an intensity, period, timing, and period suitable for MRE, and the second gradient magnetic field 62 can be applied at an intensity, period, timing, and period suitable for DWI. Can be done. Therefore, as shown in FIG. 4, in the second gradient magnetic field 62, the diffusion is emphasized and the MRE is not affected, so that stable observation is possible.

FIG. 8 is an explanatory diagram of the effect of the magnetic resonance imaging apparatus of Example 1.
FIG. 9 is an example of an MRE image (Wave Image and Elastogram) obtained by the configuration of Example 1, the configuration described in Non-Patent Document 1, and a general MRE technique.
FIG. 10 is an explanatory diagram of a diffusion-weighted image obtained by the configuration described in Non-Patent Document 1 and Example 1.
Therefore, as shown in FIG. 8, since the vibration enhancing effect of the first gradient magnetic field 61 is secured even when the b value is low, an image can be obtained and the second gradient magnetic field is obtained even when the b value is high. Since 62 does not contribute to the sensitization of vibration, no artifact is generated on the intensity image (diffusion weighted image).
Further, in FIG. 9, even if the first gradient magnetic field 61 and the second gradient magnetic field 62 are separately applied as in the first embodiment, the MRE image is the same as that of the general MRE method. Has been obtained, and there is no problem. Further, in FIG. 10, when the b value becomes high, in the configuration in which the MEG and the MPG are integrated (Unit) as in the technique described in Non-Patent Document 1, the artifact is shown in the region surrounded by the broken line in FIG. Is seen, but not in Example 1 (Separate). The ADC map shown in FIG. 10 is an image obtained by obtaining an apparent diffusion coefficient (ADC) from the measurement results, and is called an apparent diffusion (coefficient) image (ADC map). In the technique described in Non-Patent Document 1, artifacts can be seen in the ADC map, but not in Example 1.

Therefore, in the magnetic resonance imaging apparatus 1 of the first embodiment, MRE and DWI can be photographed at the same time, and high-precision MRE images and DWI images without artifacts can be obtained. At this time, since it is not necessary to increase the strength (G) of MEG and MPG, it is possible to prevent a strong magnetic field that adversely affects the human body from being applied. Therefore, in the magnetic resonance imaging apparatus 1 of the first embodiment, a new imaging method (pulse sequence) that combines the MRE technique for imaging the hardness and the DWI technique for imaging the diffusion of water molecules can be put into practical use. Therefore, the hardness (≈malignancy) of the tumor tissue and the state of water molecule diffusion (≈cell density) can be evaluated at the same time.

Further, in the technique described in Non-Patent Document 1, since MEG and MPG are integrated (Unit), each magnetic field cannot be applied in different directions (slice, lead-out, face). Therefore, it is limited to the case where the directions to be photographed by MRE and DWI are the same, and it is not possible to photograph in different directions by MRE and DWI. When a malignant tumor is present, water molecules move from the outside of the cell to the inside of the cell, making it difficult for the water molecules to move freely. It is desirable to apply a second gradient magnetic field 62 in various axial directions for measurement. However, if it is possible to shoot in only one direction as in the technique described in Non-Patent Document 1, it is necessary to shoot a plurality of times in order to shoot from a plurality of directions, and it takes a long time to shoot. There is also a problem that it is burdensome.
On the other hand, in the first embodiment, the second gradient magnetic field 62 can be applied in a direction (axis) different from that of the first gradient magnetic field 61. Therefore, when it is desired to see a diffusion-weighted image in a direction different from the direction to be photographed by the MRE, it is possible to photograph the inspected portion from an arbitrary direction to be photographed by the DWI method.

(Change example)
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are made within the scope of the gist of the present invention described in the claims. It is possible. Examples of modifications (H01) to (H03) of the present invention are illustrated below.
(H01) In the above embodiment, a so-called tunnel-type magnetic resonance imaging apparatus in which the magnet portion 2 has a ring shape is exemplified, but the present invention is not limited thereto. For example, the magnet portion 2 can be applied to a U-shaped, so-called open type magnetic resonance imaging apparatus.
(H02) The specific numerical values exemplified in the above embodiment can be arbitrarily changed according to the design, use, and the like. For example, since the resonance frequency changes depending on the strength of the static magnetic field, when the strength of the static magnetic field is changed, the echo time, the frequency of the diaphragm 16 and the like are also changed in conjunction with each other.

(H03) In the above embodiment, the vibration frequency is exemplified, but is not limited to 60 Hz. Vibration at 75 Hz or 100 Hz is also possible.

1 ... Shooting device,
2 ... Magnetic field generator,
16 ... Vibration applying member,
51d ... First gradient magnetic field application means,
51e ... Means for applying an alternating magnetic field,
51f ... Means for applying a second gradient magnetic field,
53 ... Receiving means (signal acquisition means),
54b ... Intensity image acquisition means,
54c ... MR phase image acquisition means,
54d ... Diffusion-weighted image acquisition means,
61 ... First gradient magnetic field,
62 ... Second gradient magnetic field,
G ... The strength of the second gradient magnetic field,
T ... Vibration cycle,
TE ... Echo time,
TR ... Repeat time,
δ… Duration to apply the second gradient magnetic field,
Δ… Interval.

Claims (4)

A magnetic field generator that generates a static magnetic field, a gradient magnetic field whose magnetic field changes depending on the position, and an alternating magnetic field preset based on the magnetic resonance conditions of protons for the subject to be inspected.
An alternating magnetic field applying means for applying the alternating magnetic field at a preset repetition time, and a means for applying the alternating magnetic field.
A receiving means for receiving the electromagnetic wave based on the echo time, which is the time for receiving the electromagnetic wave emitted when the proton of the part to be inspected excited by the alternating magnetic field relaxes.
A first gradient magnetic field that applies a first gradient magnetic field for MRE to any or a plurality of slice directions, lead-out directions, and phase encoding directions, which are three intersecting axes set for an inspected portion. And the application means of
A vibration-imparting member that imparts vibration to the part to be inspected and is capable of imparting multiple vibrations having different phases.
Based on the electromagnetic wave acquired according to the echo time, an MR phase image corresponding to the phase of the electromagnetic wave signal is acquired for each phase of vibration applied by the vibration imparting member, and an MR phase image acquisition means for acquiring the MR phase image.
A means for applying a second gradient magnetic field for applying a second gradient magnetic field for enhancing diffusion to the subject, and a pair of waveforms having the same magnitude and opposite directions at intervals according to the period of the vibration. The means for applying the second gradient magnetic field, and the means for applying the second gradient magnetic field.
A diffusion-weighted image acquisition means for acquiring a diffusion-weighted image based on the phase dispersion of molecules that have moved in response to the second gradient magnetic field.
A shooting device characterized by being equipped with. The second gradient magnetic field applied in a direction different from the direction in which the first gradient magnetic field is applied,
The photographing apparatus according to claim 1, wherein the image pickup apparatus is provided with. The imaging device according to claim 1 or 2, wherein the strength of the second gradient magnetic field can be changed according to the desired diffusion-weighting effect. The imaging device according to any one of claims 1 to 3, wherein the duration of applying the second gradient magnetic field can be changed according to the desired diffusion-weighting effect.

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