JP4610010B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a magnetic resonance imaging method and apparatus for taking a tomographic image of a desired region of a human body as a subject using a nuclear magnetic resonance (hereinafter referred to as “NMR”) phenomenon. The present invention relates to a technique for drawing dynamic characteristics, that is, viscoelastic characteristics.

For diseases associated with degeneration of living tissue, pathomechanical diagnosis of living tissue is useful. For example, it is useful for detecting microsclerotic lesions of breast cancer, determining benign / malignant cancer by measuring the degree of sclerosis of prostate cancer, diagnosing arteriosclerosis and cirrhosis, arthropathy, and brain softening. In addition, due to the increase in rigidity based on the muscle tension, pathomechanical diagnosis of tissue is useful for evaluating muscle strength and determining the effect of rehabilitation.
In addition, some of the malignant tumors in the intracranial neoplastic lesions show changes in the degree of sclerosis. If the hardness of the tissue can be presented to the doctor as an image, the surgeon can quickly make a judgment on the operation by increasing the information when performing the surgical operation.

  Although there are still few devices for imaging the pathological mechanical properties of living tissue, one method is to measure the elastic modulus of living tissue with a magnetic resonance imaging (hereinafter referred to as “MRI”) device (Patent Document 1). And is recognized as MR Elastography in the field of MRI apparatus.

In this method, mechanical vibrations of about 50 to 1000 Hz are applied to a desired living tissue by a shaker or the like, and the polarity of the gradient magnetic field is reversed and applied to the subject in synchronization with this, and the initial conditions are different. Collect two images. Next, a phase image representing the amount of displacement of the living tissue is created from each image, and a difference image between them is obtained. From this phase difference image, the propagation wavelength of longitudinal waves or transverse waves in the living body is measured. Then, the elastic modulus and Young's modulus, which are mechanical characteristics of the living tissue, are obtained by calculation from the change in the propagation wavelength of the wave and displayed as a still image. This image is an image showing the hardness and softness of each living tissue.
US Pat. No. 5,825,186

  However, as described above, in order to ensure and measure the elasticity of elasticity and Young's modulus, which are mechanical properties of living tissue, the gradient magnetic field can be reliably synchronized with the excitation frequency of the shaker. The polarity must be changed. Alternatively, the excitation frequency and phase of the shaker must be accurately controlled in accordance with the change in the polarity of the gradient magnetic field.

Further, since the polarity of the gradient magnetic field is switched in accordance with the excitation frequency of the shaker after the high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) excitation of the imaging pulse sequence in the MRI apparatus, A certain amount of time is required until NMR signal (echo signal) measurement. Therefore, the signal strength reduction due to T ₂ decay of the NMR signal can not be avoided. That is, the NMR signal is measured in a state where the SN ratio is poor.
For the above reasons, it is not easy to measure the elastic modulus of living tissue simply and with an improved SN ratio. Solutions for these problems are not disclosed in the above document.

  The present invention simplifies control of pressurization or excitation and imaging pulse sequence, particularly control of gradient magnetic field application, and easily obtains a stiffness distribution image representing the hardness / softness (viscoelasticity) of a living tissue. With the goal. It is another object of the present invention to make it possible to grasp the hardness and softness of a living tissue by dynamically improving the SN ratio by measuring the stiffness distribution image in near real time.

In order to achieve the above object, a method for acquiring a hardness distribution image of the present invention for imaging a hardness distribution of a desired region of a subject using a magnetic resonance imaging apparatus,
(A) placing a desired region of the subject in a static magnetic field space of the magnetic resonance imaging apparatus;
(B) applying a high frequency magnetic field pulse and a gradient magnetic field pulse to the desired region, receiving an echo signal, and obtaining a first image including the desired region;
(C) repeating the step (b) to obtain a second image;
(D) obtaining a displacement distribution in the desired region from the first image and the second image;
(E) obtaining a third image representing a hardness characteristic of the desired region from the displacement distribution;
(F) displaying the third image;
And at least one of between step (a) and step (b) and between step (b) and step (c),
(G) The method includes a step of applying a displacement to the desired region, and the displacement is applied to the desired region also in the image acquisition step immediately after the step (g).
In particular, the step (g) is included between the step (a) and the step (b), and between the step (b) and the step (c) (h) the step (g ), And a different displacement is applied to the desired region in steps (b) and (c).
As a result, only two images with different pressurization or vibration states are acquired, so that control of pressurization or vibration and imaging pulse sequence, particularly control of gradient magnetic field application, can be simplified. In addition, since a general-purpose imaging pulse sequence that does not need to do anything from RF pulse application to echo signal measurement is used, it is possible to improve the SN ratio of an image by measuring an echo signal with a good SN ratio. As a result, a hard distribution image (third image) with a good SN ratio can be easily acquired.

In a preferred embodiment of the present invention, the application of the displacement is performed by pressurizing or vibrating the desired region.
Thereby, a desired displacement can be easily applied to a desired region of the subject.
In a preferred embodiment of the present invention, the step (e) obtains a strain distribution of the desired region by obtaining a spatial differential of the displacement amount distribution, and obtains an image representing the strain distribution of the desired region. The third image is used.
Thereby, the strain distribution image expressing the hardness and softness of the living tissue as strain due to pressurization or vibration can be easily acquired from two images that are simply different in pressurization or vibration state.

In a preferred embodiment of the present invention, the step (e) is characterized in that an image representing a displacement distribution in the desired region is the third image.
Thereby, the displacement amount distribution image expressing the hardness / softness of the living tissue as the displacement amount due to pressurization or vibration can be easily acquired from two images having different pressurization or vibration states.

In a preferred embodiment of the present invention, the step (e) is characterized in that the third image is subjected to gradation processing according to the value of each point to obtain a pseudo color display.
Thereby, the hardness and softness of the living tissue in a desired region can be made clear at a glance.

In a preferred embodiment of the present invention, the step (f) displays the pseudo-color-displayed third image superimposed on the corresponding first image or the second image. To do.
Thereby, the hardness and softness of the living tissue in a desired region can be easily grasped in association with the position and shape of the living tissue.

Also, one preferred embodiment of the present invention is the step (f),
(I) setting the second image as the first image;
(J) applying a displacement different from the previous time to the desired region;
(K) repeating the steps (c), (d), (e), (f), (i) and (j) to obtain a plurality of the third images and displaying the moving images;
It is characterized by having.
As a result, it is possible to dynamically grasp the displacement amount or the change in strain at each point in the desired region in accordance with the progress of the pressurization or vibration state.

According to a preferred embodiment of the present invention, in step (c) during execution of step (k), the k space is divided into a plurality of partial areas, and data of only one partial area is measured. Each time it is updated, an image is reconstructed using k-space data updated for only one of the partial areas, and the partial area to be measured / updated is changed for each repetition. Alternatively, in step (c) during execution of step (k), k-space is divided into a low spatial frequency region including the origin and a surrounding high spatial frequency region, and the measurement frequency of the low spatial frequency region is Each time one of the areas is measured and updated more than the measurement frequency of the high spatial frequency area, image reconstruction is performed using k-space data updated for only one of the partial areas. Features.
Accordingly, the number of images acquired per unit time can be improved and the time resolution between images can be improved, so that the moving image can be displayed more smoothly. Further, if each image is photographed using a high-speed pulse sequence described later, each image can be acquired in near real time, and therefore a stiffness distribution image can also be acquired in near real time.

In a preferred embodiment of the present invention, the first image, the second image, and the pseudo-color-displayed third image are all three-dimensional images.
Alternatively, at any point before step (f),
(L) The method includes a step of acquiring a three-dimensional morphological image including the desired region, and the step (f) displays the moving image of the third image superimposed on the three-dimensional morphological image. To do.
Thereby, the hardness and softness of the living tissue in a desired region can be easily grasped three-dimensionally in association with the position and shape of the living tissue.

In one preferred embodiment of the present invention, in the step (d), a correlation window of a predetermined size surrounding a displacement measurement point is set in each of the first image and the second image, and one correlation window is set as a predetermined. The correlation coefficient between the two correlation windows is obtained while moving at intervals, and the movement direction and the movement amount that are the largest correlation coefficient among the correlation coefficients are set as the displacement direction and the displacement amount of the displacement measurement point, respectively. It is characterized by doing.
In particular, the step (d) is characterized by obtaining the correlation coefficient by moving the correlation window only in the pressurizing or exciting direction, and obtaining the displacement amount only in the direction.
Thereby, the displacement amount and the displacement direction can be easily obtained.

In a preferred embodiment of the present invention, in the step (f), the horizontal axis represents the depth of each point in the desired region of the third image from the surface of the subject, and the value of the point A point value on a desired line is plotted and displayed on a two-dimensional plane having a vertical axis.
Thereby, since the displacement amount or strain distribution at each point on the desired line is represented as a graph, the hardness and softness of the living tissue on the line can be grasped in detail.

In a preferred embodiment of the present invention, the first image and the second image have the same pressure or vibration state before and after.
Thereby, since the time resolution of the rigid distribution image can be improved, the moving image display can be performed more smoothly.

In a preferred embodiment of the present invention, the first image and the second image are acquired by an imaging pulse sequence in which the magnetization of the desired region is in a steady state.
Thereby, since each image can be image | photographed at high speed, it becomes possible to acquire a rigid distribution image in near real time. In particular, it is possible to shorten the time from the RF excitation pulse to echo signal measurement, can be reduced T ₂ decay of the echo signal, it is possible to obtain a good image SN ratio.

In a preferred embodiment of the present invention, the excitation frequency is 1000 Hz or less.
Thereby, since the effect of pressurization or vibration can be exerted to the deep part of the living body, it is possible to acquire a hardness distribution image of the deep part region.

Further, the present invention is configured as follows from the viewpoint of the magnetic resonance imaging apparatus. That is,
A static magnetic field generating means for generating a static magnetic field in a measurement space; a measurement control means for controlling measurement of an echo signal from a desired region of the subject arranged in the measurement space; and the subject using the echo signal In the magnetic resonance imaging apparatus, comprising: a signal processing means for reconstructing the image; a display means for displaying the image; and a means for pressurizing or vibrating a desired region of the subject. An echo signal for capturing two or more images having different pressurization or vibration states from the desired region that has been pressurized or vibrated is measured, and the signal processing means is configured to detect from two of the images. At least one of a displacement amount distribution in the desired region or a strain distribution by spatial differentiation of the displacement amount distribution is obtained, and the display means displays at least one of the displacement amount distribution or the strain distribution. And wherein the door.
As a result, two or more images having different pressurization or vibration states are simply acquired, so that control of pressurization or vibration and imaging pulse sequence, particularly control of gradient magnetic field application can be simplified. Become. As a result, a displacement amount distribution image or a strain distribution image can be easily obtained as the stiffness distribution image (third image).

In a preferred embodiment of the present invention, the pressurization or vibration means transmits a pressurization or vibration from the drive means to the desired region, and a drive means disposed outside the static magnetic field generation means. The transmission means has one end portion in contact with the surface of the adjacent body in the desired region, the other end portion connected to the driving means, and the driving means includes the transmission means. And applying pressure or vibration to the desired region.
Thus, even if the driving means includes a magnetic member that distorts the static magnetic field, the driving means can be disposed outside the static magnetic field space, thereby preventing deterioration of the image quality of the rigid distribution image due to the static magnetic field distortion. be able to.

In one preferred embodiment of the present invention, the static magnetic field generating means is configured such that a pair of static magnetic field generation sources are arranged to face each other with the measurement space in between, and a direction perpendicular to the facing direction is opened. The transmission means transmits pressure or vibration from the opened side to the desired region.
As a result, in the so-called open type MRI apparatus, the subject can be easily accessed from the opened subject side surface, so that pressure or vibration can be applied from the subject side surface.
In a preferred embodiment of the present invention, the pressurizing or vibrating means is arranged below a contact surface with the subject in a table on which the subject is placed.
Thereby, the spinal column or spinal cord region of the subject can be pressurized or vibrated.
Further, the pressurizing or vibrating means is arranged below a contact surface with the subject in a receiving coil that receives the echo signal.
Thereby, it is possible to easily perform pressurization or vibration to a desired region and alignment of image acquisition.

In a preferred embodiment of the present invention, the pressurizing or vibrating means pressurizes or presses a plurality of locations of the subject so that the phases of pressurizing or vibrating substantially coincide with each other in the desired region. It is characterized by vibration.
As a result, even if the desired region is in the deep part of the living body, or the burden on the subject is reduced by reducing the amount of pressure or vibration applied from each location, the desired region can be added efficiently. It becomes possible to apply pressure or vibration.

In a preferred embodiment of the present invention, the pressurizing or vibrating means is arranged so that the desired area is pressurized or vibrated in a different direction within the photographing section including the desired area. A plurality of locations of the subject are pressurized or vibrated, the signal processing means obtains at least one of the displacement amount or strain distribution for each direction, and the display means for each direction At least one of the displacement amount distribution and the strain distribution is displayed.
As a result, even when the displacement or strain of the living tissue varies depending on the direction, a displacement amount distribution image or a strain distribution image can be acquired for each direction.

It is a figure which shows one Example of the MRI apparatus to which this invention is applied. It is a figure which shows one Example of a structure of the test object periphery in the MRI apparatus to which this invention is applied. (A) is sectional drawing seen from the side surface direction of the test object inserted in the cylindrical MRI apparatus gantry. (B) is a cross-sectional view of the subject inserted into the opposing MRI apparatus gantry as seen from the top of the head. It is a figure which shows the outline | summary of the processing flow of the 1st Embodiment of this invention. It is a figure which shows an example of the high-speed imaging | photography pulse sequence in connection with this invention. It is a figure which shows the mode of the displacement and distortion of each local area | region under the body surface which exists on one specific line, and a body surface. It is a figure which shows the Example of the method of improving the image acquisition number per unit time. (A) is a figure which shows the timing which acquires a time-sequential image. (B) is a figure which shows the mode of the division | segmentation of k space in a sequential exchange imaging | photography method. (C) is a figure which shows the mode of the division | segmentation of k space in the Keyhole imaging method. It is a figure which shows schematic structure of the pressurization and vibration apparatus concerning this invention. It is a figure which shows the method of estimating the position of the largest displacement using correlation information. It is a figure which shows the example of a display which superimposes and displays a pseudo color display on a background image.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments of the invention, and the repetitive description thereof is omitted.

  FIG. 1 is a block diagram showing the overall configuration of an MRI apparatus to which the present invention is applied. This MRI apparatus uses an NMR phenomenon to obtain an image of a subject. As shown in FIG. 1, a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, and a reception system 6 , A signal processing system 7, a sequencer 4, and a central processing unit (hereinafter referred to as “CPU”) 8.

  The static magnetic field generation system 2 generates a uniform static magnetic field in the body axis direction or the direction perpendicular to the body axis in the space around the subject 1 placed on the table 21. Further, a permanent magnet type, normal conducting type or superconducting type static magnetic field generating means 210 (not shown) is arranged. In addition, a shim coil 211 (not shown) is provided, and a non-uniform static magnetic field is corrected by flowing a current so as to improve the uniformity of the static magnetic field.

  The gradient magnetic field generation system 3 includes a gradient magnetic field coil 9 wound in the three-axis directions of X, Y, and Z, which is a coordinate system (stationary coordinate system) of the MRI apparatus, and a gradient magnetic field power source 10 that drives each gradient magnetic field coil. It consists of. Gradient magnetic fields Gx, Gy, and Gz are applied in the three axial directions of X, Y, and Z by driving the gradient magnetic field power supply 10 of each coil in accordance with a command from the sequencer 4 described later. At the time of imaging, gradient magnetic fields Gx, Gy, and Gz are combined according to the angle of the slice plane (imaging cross section). Specifically, a slice direction gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane to set a slice plane for the subject 1, and the remaining two directions orthogonal to the slice plane and orthogonal to each other A phase encoding direction gradient magnetic field pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied to the echo signal, and position information in each direction is encoded with respect to the echo signal.

  The sequencer 4 is a control unit that repeatedly applies an RF pulse and a gradient magnetic field pulse based on a predetermined imaging pulse sequence. The sequencer 4 operates under the control of the CPU 8 and transmits various commands necessary for collecting image data of the subject 1. This is sent to the system 5, the gradient magnetic field generation system 3, and the reception system 6.

  The transmission system 5 irradiates an RF pulse in order to cause an NMR phenomenon to the nuclear spin of atoms constituting the biological tissue of the subject 1. The high-frequency oscillator 11, the modulator 12, the high-frequency amplifier 13, and transmission on the transmission side And coil 14a. The high-frequency pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 at a timing according to a command from the sequencer 4, and after the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13, the high-frequency pulse approaches the subject 1. Thus, the subject 1 is irradiated with electromagnetic waves (RF pulses).

  The receiving system 6 detects an NMR signal (echo signal) emitted by the NMR phenomenon of the nuclear spin of the atoms constituting the living tissue of the subject 1, and receives the receiving coil 14b on the receiving side, the amplifier 15, and quadrature detection. And an A / D converter 17. An electromagnetic wave (NMR signal) of the response of the subject 1 induced by the RF pulse irradiated from the transmission coil 14 a on the transmission side is detected by the reception coil 14 b disposed in the vicinity of the subject 1 and amplified by the amplifier 15. After that, the signals are divided into two orthogonal signals by the quadrature phase detector 16 at a timing according to a command from the sequencer 4, and each signal is converted into a digital quantity by the A / D converter 17, and the signal processing system 7 Sent to.

The signal processing system 7 includes an external storage device such as a magnetic disk 18 and an optical disk 19 and a display 20 such as a CRT or LCD (liquid crystal display). When data from the reception system 6 is input to the CPU 8, The CPU 8 executes processing such as signal processing and image reconstruction. An image of the subject 1 as a result of the processing is displayed on the display 20 and recorded on the magnetic disk 18 of the external storage device.
In FIG. 1, the transmission coil 14 a, the reception coil 14 b, and the gradient magnetic field coil 9 are installed so as to face or surround the subject 1 in the static magnetic field space of the static magnetic field generation system 2.

  Next, a first embodiment of the present invention will be described. In the present embodiment, the body surface of the subject is pressurized or vibrated using a pressurizer / vibrator so that a direct current or alternating current displacement is applied to a desired region of the subject. During the pressurization or vibration, two or more images including a desired area and different pressurization or vibration states for the desired area are taken. Next, the displacement distribution of each point in a desired area is obtained between the two captured images. Further, a strain distribution is obtained from the spatial differential of the displacement amount. These displacement amount distribution or strain distribution is displayed as a hardness distribution image representing the hardness / softness of a desired region.

  FIG. 2 shows a first example of this embodiment. 2A and 2B are diagrams detailing the configuration around the subject 1 in FIG. 1, where FIG. 2A shows an example of a cylindrical MRI apparatus gantry, and FIG. 2B shows an example of an opposing MRI apparatus gantry. (A) and (b), in order from the outside, the static magnetic field generating means 210 constituting the static magnetic field generating system 2, the shim coil 211 disposed inside the static magnetic field generating means 2, and the gradient magnetic field coil 10 disposed further inside, A transmitting coil 14a disposed inside and a receiving coil 14b disposed inside thereof are shown. Since these functions are the same as those in FIG.

  FIG. 2A is a cross-sectional view of the subject 1 inserted into the cylindrical MRI apparatus gantry from the side surface direction. The static magnetic field is generated in the cylindrical axis direction, that is, in the horizontal direction. FIG. 2A shows a subject 1 placed on the innermost table 21 and a pressurizing / vibrating device (201 to 203) for pressurizing or vibrating the subject 1. . It should be noted that the pressurizing / vibrating drive unit (actuator) is shown only for the pressurizing / vibrating machine 202, and the other driving units are not shown. The pressurizer / vibrator (201 to 203) can apply a pressure at a portion in contact with a living body. The pressure may be slowly increased or decreased in a direct current manner, or may be periodically increased or decreased with a low frequency alternating current. In this way, the desired region is imaged by the MRI apparatus in near real time as described later, while the desired region is pressurized or vibrated.

The pressurizer / vibrator 201 vibrates the head of the subject 1 by vibrating the contact surface with the head of the headrest or the receiving coil for the head from below. For this reason, a pressurizing or vibrating unit, which is a vibrator or an equivalent actuator, is incorporated under the contact surface with the head in the headrest for head or in the receiving coil for head. It should be noted that the pressurization or excitation unit can be similarly incorporated in the reception coils for other parts so that the pressurization or excitation can be applied to that part as well.
The pressurizer / vibrator 202 is intended to apply pressure to the breast from above, for example. For example, a support (not shown) is provided on the table 21, and this is used as a fulcrum for the surface layer of the breast based on the principle of leverage. Apply pressure gradually. Or you may pressurize the surface of a breast manually.
The pressurizer / vibrator 203 pressurizes or excites the spinal column or spinal cord region. Therefore, a pressurizing or vibrating unit that is a vibrator or an equivalent actuator is built in the table 21 below the contact surface with the subject 1 in the same manner as the pressurizing / vibrating machine 201. It is desirable to be able to apply pressure or vibration in a wider range than in the case of the head.

  When the subject 1 is vibrated using the pressure / vibrator (201 to 203) as described above, the vibration frequency is desirably 1000 Hz or less. This is because the living tissue has viscoelastic properties, and the higher the frequency, the less the vibration action penetrates into the living body. By setting the frequency to 1000 Hz or less, the excitation action can reach the deep part of the living body.

  The pressurizer / vibrator (201 to 203) in FIG. 2 (a) can operate independently of the MRI apparatus. Specifically, as shown in FIG. 7, the pressurization / vibration device 701 includes a pressurization / vibration control unit 702 so as to operate independently of the MRI apparatus. A voltage or current having a stimulation pattern as described above is applied to an actuator (703 to 705), which is a drive unit 702, and the stimulation pattern is changed as a pressure change via a pressurizing / vibrating device (201 to 203). Join to the subject 1. In FIG. 7, the actuators (706 to 708) corresponding to the pressure / vibration units (204 to 206) are not shown.

  Alternatively, the pressurizer / vibrator (201 to 203) may be operated in conjunction with the imaging pulse sequence under the control of the MRI apparatus. In this case, for example, as indicated by a dotted line in FIG. 7, the control information from the sequencer 4 enters the pressurization / vibration control unit 702, and the imaging pulse sequence is activated after the pressurization or excitation is activated. Then, after a desired number of images are acquired, the imaging pulse sequence is completed, and pressurization or vibration is also completed, and the actuators (703 to 705) are returned to the initial positions. The control of the pressurizer / vibrator is the same in the pressurizer / vibrator (204 to 206) described below.

  FIG. 2B is a cross-sectional view of the subject 1 inserted into the opposing type (so-called open type) MRI apparatus gantry from the top of the head. A pair of static magnetic field generation means 210 are arranged opposite to each other with the subject 1 interposed therebetween, and generates a static magnetic field in the opposite direction. However, it is assumed that the struts connecting the upper and lower static magnetic field generating means 210 are connected to the side surfaces of the upper and lower static magnetic field generating means 210 on the foot side of the subject 1. The other configuration is the same as that shown in FIG. In this case, the direction perpendicular to the facing direction, that is, the front / rear / right / left direction of the subject 1 is opened, so that the pressurizer / vibrator (204 to 206) is arranged close to the place to be pressurized or vibrated. be able to. Therefore, pressurization or excitation can be performed from a direction perpendicular to the facing direction, that is, from the front, rear, left, and right directions of the subject.

Furthermore, as shown in FIG. 2B, it is possible to pressurize or vibrate from a plurality of directions. For example, when the pressurizing / vibrating device 204 and the pressurizing / vibrating device 205 which are on the straight line 207 passing through the desired region 220 and face each other are used, the phase of the pressurizing or exciting in the desired region 220 is used. Are applied in the direction of the straight line 207 from both sides.
Also, the pressurizer / vibrator 204 (or 205) that pressurizes or vibrates in the direction of the straight line 207 and the pressurizer / vibrator 206 that pressurizes or vibrates in a direction different from the straight line 207 are used simultaneously or separately. You can also In the case of simultaneous use, there is no particular need to match the pressure or vibration phase in the desired region 220. The angle formed by the two directions is preferably 90 °.
In particular, when the displacement or strain of a living tissue varies depending on the direction, by applying pressure or vibration from multiple directions, the displacement or strain in each direction can be obtained separately and displayed, or they can be combined into a vector The obtained displacement amount or distortion can be obtained and displayed.

Next, the outline of the processing flow of this embodiment will be described with reference to FIG.
In step 301 , the subject is placed in the static magnetic field space of the MRI apparatus. Generally, the subject is placed on the table 21 outside the static magnetic field generation system 2, and the table 21 is sent into the static magnetic field generation system 2 so that a desired region is at the center of the static magnetic field space. The subject is placed in the static magnetic field space.

In step 302 , as shown in FIG. 2, a desired region of the subject is pressurized or vibrated. When the pressurization / vibration apparatus 701 is operated independently of the MRI apparatus, a desired region of the subject is pressurized with a predetermined pressure or with a predetermined amplitude and period before the imaging pulse sequence is activated. Then, the pressure / vibration device 701 is adjusted and operated. Alternatively, when the pressurization / vibration device 701 is operated in conjunction with the imaging pulse sequence under the control of the MRI apparatus, the desired region of the subject is set to a predetermined pressure before the imaging pulse sequence is activated. The sequencer 7 activates the pressurizing / vibrating device 701 so as to pressurize or vibrate at a cycle that can be regarded as being substantially constant within the imaging time. To control.

In step 303 , in a state where the desired region of the subject is pressurized or vibrated, the desired region is imaged with a predetermined imaging pulse sequence, and a first image is acquired. Details of the imaging pulse sequence will be described later. The acquired first image data is temporarily stored in the magnetic disk 18, for example.
In step 304 , a desired region of the subject is pressurized or vibrated in a pressure or vibration state different from that in step 302. The method of pressurization or vibration is the same as in step 302.

In step 305 , in a state where the desired region of the subject is pressurized or vibrated, the desired region is imaged with the same imaging pulse sequence as in step 303, and a second image is acquired. The acquired second image data is temporarily stored, for example, on the magnetic disk 18 as with the first image.
In step 306 , a displacement amount distribution of a desired region is obtained from the first image and the second image. The first image data and the second image data are loaded from the magnetic disk 18 into the memory in the CPU 8, and the CPU 8 calculates and obtains the displacement distribution. The obtained displacement distribution may proceed to Step 309 and be displayed as a displacement distribution image. Further, the obtained displacement amount distribution data is temporarily stored in the magnetic disk 18, for example.

In step 307 , a strain distribution in a desired region is obtained from the displacement amount distribution. Displacement amount distribution data is loaded from the magnetic disk 18 into the memory in the CPU 8, and the CPU 8 calculates and obtains a strain distribution. The obtained strain distribution may proceed to step 308 and be displayed as a strain distribution image. Further, the obtained strain distribution data is temporarily stored in, for example, the magnetic disk 18.
In step 308 , a pseudo color display of the displacement amount distribution image or the distortion distribution image is obtained. Displacement amount distribution data or strain distribution data is loaded from the magnetic disk 18 into the memory in the CPU 8, and the CPU 8 calculates and obtains a pseudo color display thereof. The obtained pseudo color display data is temporarily stored in, for example, the magnetic disk 18.

In step 309 , the displacement amount distribution or the strain distribution or their pseudo color display is displayed on the display 20, for example, as a rigid distribution image (third image). Displacement amount distribution data, distortion distribution data, or pseudo color display data thereof is read from the magnetic disk 18 and displayed as an image.

The above is the outline of the processing flow of the present embodiment, but pressurization or vibration may be omitted in any one of (Step 302 to Step 303) and (Step 304 to Step 305). This is because in order to obtain the displacement amount distribution or the strain distribution, it is sufficient that the pressurization or vibration state of a desired region is simply different between the two.
Hereinafter, various basic elements in each step will be described in detail. Note that the pressurization or vibration in steps 302 and 304 has already been described in the description of FIG. 2, and thus detailed description thereof will be omitted together with steps 301 and 309.

Next, a preferable imaging pulse sequence in steps 303 and 305 will be described. The deformation of the biological tissue in order to measure the high-speed while oscillating pressure and pressure, in longitudinal relaxation time of magnetization relating to the living tissue T ₁ and the transverse relaxation time T ₂ shorter repetition time than (TR), repeated RF pulse application Then, imaging is performed based on an imaging pulse sequence that changes the behavior of magnetization to a steady state free precession state (SSFP). Such imaging pulse sequence, _{T 2} enhancement type Gradient Echo method is useful. For example, Steady State Acquisition with Rebound Gradient Echo as shown in FIG. 4 can be used. This is because a gradient magnetic field is applied so that the phase of transverse magnetization is returned to zero for each axis in the slice direction, the phase encoding direction, and the frequency encoding direction in the repetition time (TR) of the imaging pulse sequence. It is a pulse sequence. In FIG. 4, RF is an RF pulse, Gs is a slice direction gradient magnetic field, Gp is a phase encode direction gradient magnetic field, Gr is a frequency encode direction gradient magnetic field, A / D is an echo signal readout timing and sampling period, and echo is an echo signal. Represents.

  In the imaging pulse sequence of FIG. 4, the RF pulse 401 is applied to the subject 1 placed in a static magnetic field while applying the slice gradient magnetic field 402 to excite magnetization in a desired region. Next, after the rephase gradient magnetic field 403 in the slice direction, the phase encode gradient magnetic field 405 in the phase encode direction, and the dephase gradient magnetic field 407 in the frequency encode direction are applied, the read gradient magnetic field 408 is applied and A / An echo signal 411 is measured during the D interval 410. After the echo signal 411 is measured, the gradient magnetic field 404 and the phase encoding direction are set in each axis so that the gradient magnetic field amount (time integral value of the gradient magnetic field waveform) applied between the RF pulses 401 is returned to zero. A gradient magnetic field 406 and a frequency encoding direction gradient magnetic field 409 are applied to rewind the transverse magnetization phase. Finally, when the repetition time (TR) elapses, the RF pulse 401 is applied again to excite magnetization in a desired region. The above is the operation of the imaging pulse sequence within one repetition time (TR).

Since echo signals to which all the phase encoding amounts necessary for image reconstruction are added are collected, the phase encoding amount 405 added to the echo signal 411 is sequentially changed between two adjacent RF pulses 401. The imaging pulse sequence for one repetition time (TR) is repeated. The SSFP type pulse sequence this rewind, the T ₂ weighted images can be acquired at high speed. For example, when a repetition time (TR) is 4 ms and one image is reconstructed by 256 phase encoding, the shooting time is about 1 second.

As another example of a high-speed imaging pulse sequence, a known EPI (Echo Planer Imaging) method can also be used. The EPI method includes a single shot type in which all k-space data is acquired by one excitation (shot), and a multi-shot type in which all k-space data is acquired by being divided into a plurality of shots, both of which are used. be able to. The present invention does not depend on the imaging pulse sequence, and any general-purpose imaging pulse sequence that is generally used can be used. Preferably, a high-speed imaging pulse sequence with a short imaging time may be used.
As described above, in the general-purpose high-speed imaging pulse sequence, the time from the RF pulse application to the echo signal measurement can be shortened to reduce the T ₂ attenuation of the echo signal. As a result, the SN ratio of the image can be improved.

Next, a method for obtaining the displacement amount distribution in step 306 will be described. FIG. 5 shows an outline of a method for calculating a displacement amount of a local region from two images (hereinafter referred to as “adjacent images”) of a first image and a second image that are different in pressure or vibration state. Here, it is preferable that these adjacent images are images in which the pressurization or vibration state acquired during a short time Δt is in succession.
FIG. 5A shows a displacement amount (that is, a change in position) 501 of the body surface on a specific line passing through a desired region, with time on the horizontal axis and displacement on the vertical axis. Is. It is shown that the amount of displacement of the body surface gradually increases with time by applying pressure.
On the other hand, in a living tissue below the body surface, displacement due to deformation occurs according to its mechanical characteristics. At this time, the amount of displacement in the depth direction from the surface of the living body locally varies depending on the degree of hardening of the organs and lesions of the living body, that is, hardness and softness.

Therefore, in order to pay attention to the minute displacement of the local region between two points in the depth direction with high correlation, the pixel values of the local region on the same line where the distances from the body surface are d1 to d7 are shown in FIG. As shown in (b). The pixel value 502 at time t = t ₁ of each local region on the same line is shown in the upper part of FIG. 5B, and the pixel value 503 at time t = t ₁ + Δt is shown in the lower part of FIG. 5B. It is understood that the width and interval of each local region change slightly as the pressurization proceeds.

  At this time, as shown in FIG. 5C, when the horizontal axis is in the depth direction and the vertical axis is the displacement, the change rate of the displacement (that is, the slope of the graph) is small and soft in the hard region. In the area, it is possible to visually indicate that the change rate of the displacement amount is large. The change rate of this displacement amount represents distortion. Accordingly, FIG. 5C shows that the local regions d2, d3, d6, and d7 are hard, so that the distortion is small, and conversely, the local regions d4, d5 are soft, so that the distortion is large.

Here, a method of estimating the direction of displacement and its amount (displacement amount) will be described with reference to FIG. As shown in FIG. 8, a displacement measurement point 803 is shown in each of two adjacent images, an image 801 when the pressure or vibration state is t = t ₁ and an image 802 when the time t = t ₁ + Δt. A two-dimensional correlation window (mask image) 804 is set. The two-dimensional correlation window 804 can be, for example, 8 pixels × 8 pixels or 16 pixels × 16 pixels when the two-dimensional images 801 and 802 are considered to be composed of 256 pixels × 256 pixels.

During a short time Δt, even in the local region, there is little change even in the local region. Therefore, there are portions having high correlation in the correlation window 804 provided in each of the two adjacent images. Therefore, the correlation between the images 801 and 802 is obtained in the two-dimensional correlation window 804. For example, a correlation window 804 is provided in the search range 805 of the adjacent image 802, and only the correlation window 804b on the image 802 side is moved freely to obtain the correlation between the correlation windows. The moving direction and moving amount of the correlation window 804b having the highest correlation with respect to the correlation window 804a are set as the displacement direction and the displacement amount at the displacement measurement point 803. FIG. 8 shows that the correlation window 804a of the image 801 has the maximum correlation with the correlation window 804b of the image 802. In this case, it is understood that the displacement measurement point 803a of the image 801 is displaced to the position of 803b of the image 802. The above correlation processing is repeated while the displacement measurement point 803 and the search range 805 are sequentially moved in the y (vertical) direction or the x (horizontal) direction, and the displacement amount distribution of the entire image is calculated.
Thereafter, by obtaining the variation or spatial differentiation of the displacement amount in the x direction and the y direction, the strain distribution in each direction can be obtained.

ここで、Ｌ_ｘ、Ｌ_ｙは画像のｘ、ｙ方向のサンプリング間隔、ｋ、ｌは画像のｘ軸、ｙ軸方向のサンプリング変数、ｘ_０、ｙ_０は相関窓の範囲、すなわち、相関窓のｘ，ｙ方向のサイズを示す。ｋ、ｌを変化させたときの相関Ｃ（ｘ，ｙ，ｋ，ｌ）が最大値をとる（ｋ，ｌ）を（ｍ，ｎ）とし、変位計測点（ｘ，ｙ）におけるｘ方向とｙ方向の変位量をそれぞれｗ_ｘ、ｗ_ｙとすると、

と表わすことができる。全変位量は、これら２方向の変位量をベクトル合成した次の（３）式となる。

（３）式の変位量を全ての変位計測点（ｘ，ｙ）について求めて画像として表示したものが変位量分布となる。一般的に、ＭＲＩ画像の場合はｘ方向とｙ方向のサンプリング間隔は同等であるので、推定精度もｘ方向とｙ方向共に同等となる。More specifically, when the image 801 is f ₁ (x, y) and the image 802 is f ₂ (x, y), the correlation C (x, y, k, l) between them is (1) It is expressed by a formula.

Here, L _{x and} L _y are sampling intervals in the x and y directions of the image, k and l are sampling variables in the x and y directions of the image, and x ₀ and y ₀ are correlation window ranges, that is, correlation windows. Indicates the size in the x and y directions. The correlation C (x, y, k, l) when k and l are changed has the maximum value (k, l) as (m, n), and the x direction at the displacement measurement point (x, y) If the displacement in the y direction is w _{x and} w _y respectively,

Can be expressed as The total displacement is expressed by the following equation (3) obtained by vector synthesis of the displacements in these two directions.

A displacement amount distribution is obtained by obtaining the displacement amount of equation (3) for all displacement measurement points (x, y) and displaying them as images. In general, in the case of an MRI image, the sampling intervals in the x direction and the y direction are the same, so the estimation accuracy is also the same in both the x direction and the y direction.

と表すことができる。全歪みはこれら２方向の歪みをベクトル合成した次の（５）式となる。

（５）式の歪みを全ての変位計測点（ｘ，ｙ）について求めて画像としたものが歪み分布となる。各点の歪みをこのように計測すれば加圧前と加圧後の比較（この場合は、（１）式のｆ_１（ｘ，ｙ）のを加圧前の画像とし、ｆ_２（ｘ，ｙ）を加圧後の画像とする）、あるいは加圧中の微小時間間隔Δｔでの組織の変位又は歪みの状態を把握することが出来る。Next, a method for obtaining the strain distribution in step 307 will be described. The obtained displacement distribution is measured from two adjacent images during a minute time Δt, and the displacement (distribution) in that direction is obtained by spatially differentiating the displacement distribution in the x and y directions, respectively. Differential coefficient). That is, if the distortion in the x and y directions at the displacement measurement point (x, y) is ε _x and ε _y , respectively,

It can be expressed as. The total distortion is expressed by the following equation (5) obtained by vector synthesis of distortions in these two directions.

The distortion distribution is obtained by obtaining the distortion of the equation (5) for all the displacement measurement points (x, y) and forming an image. If the strain at each point is measured in this way, comparison between before and after pressurization (in this case, f ₁ (x, y) in the equation (1) is regarded as an image before pressurization and f ₂ (x , Y) is an image after pressurization), or the state of tissue displacement or strain at a minute time interval Δt during pressurization can be grasped.

However, in the above estimation method, when a desired region of the subject is pressurized or vibrated only in one of the x direction and the y direction, or the pressurizing or exciting direction is set in advance. In this case, it is only necessary to obtain the displacement amount or distortion in that direction, and it is not necessary to obtain the displacement amount or distortion in a plurality of directions at the same time. Therefore, it is not necessary to obtain the total displacement or total distortion by vector synthesis as in equation (5), and only the displacement or distortion in the pressurizing or exciting direction may be obtained.
This is because pressurization or vibration is applied only in one specific direction, so the displacement of the biological tissue due to pressurization or vibration is almost all of the translational motion component, and the rotational motion component is the target strain measurement. This is because the amount becomes negligibly small. However, in the area where the pressure / vibrator does not affect, especially in the peripheral area where pressure cannot be applied by the pressure / vibrator, the influence of the rotational motion cannot be ignored, but this is the target of this embodiment. Since it is within the range affected by the pressurizer / vibrator, there is no problem.

Or, conversely, when the displacement or strain of the living tissue varies depending on the direction, pressurize or vibrate a plurality of locations on the subject so that the desired region is pressurized or vibrated in different directions. It is also possible to obtain a displacement amount or strain distribution for each direction and display the displacement amount distribution or strain distribution for each direction. As a result, the displacement amount distribution or strain distribution for each direction can be grasped in detail.
As described above, the method of obtaining the correlation in the x direction and the y direction and estimating the displacement amount or the distortion can be called a spatial correlation method.

  Next, the pseudo color display in step 308 will be described. If the displacement distribution or distortion distribution is displayed in pseudo color corresponding to the pixel value, the doctor can easily visually recognize the degree of cure of the local area obtained by palpation, that is, hardness and softness. Become. For example, a pixel value with a large distortion (or displacement) is displayed in red, and a blue display is assigned to a pixel value with a small distortion (or displacement). In addition, a color is assigned to each intermediate pixel value so that the red pixel changes from orange to yellow to green and then to blue. If the color processing is performed by gradation processing in this way, a region with a large distortion (or displacement) is displayed in red and a region with a small amount is displayed in blue. That is, it is possible to easily recognize that the red region is soft and the blue region is hard.

  As described above, according to the first embodiment of the present invention, since only two images having different pressurization or vibration states are acquired using a general-purpose imaging pulse sequence, the conventional technique is complicated. It is possible to simplify the control of pressurization or vibration and imaging pulse sequence, particularly control of gradient magnetic field application, which required control. In addition, since a general-purpose imaging pulse sequence that does not need to do anything from RF pulse application to echo signal measurement is used, it is possible to improve the SN ratio of an image by measuring an echo signal with a good SN ratio. Further, since only the displacement amount distribution or the strain distribution in the desired region or the pseudo color display thereof is obtained from these two images, the rigid distribution image can be easily obtained.

  Next, a second embodiment of the present invention will be described. As shown in FIG. 3, if the gradient echo method under a steady state is used, it is possible to speed up the imaging pulse sequence and shorten the imaging time. However, in this embodiment, the image per unit time is further reduced. Increase the number of acquisitions. That is, this embodiment increases the apparent number of acquired images by reconstructing an image intermediately using data during measurement, and measures the displacement amount distribution or the distortion distribution in near real time. In this embodiment, the displacement amount distribution or the distortion distribution is displayed as a moving image. For this purpose, the present embodiment divides the k space into a plurality of partial areas, measures one partial area data, and updates the partial area data every other area data measured so far. And reconstruct the image. As a result, the number of images acquired per unit time is increased, and the time resolution between images in the time-series image is improved.

  FIG. 6 shows an example of this embodiment. FIG. 6A shows a technique for increasing the apparent number of acquired images as described above. The horizontal axis represents time, and FIG. 6 shows that one image can be obtained in 0.5 seconds. Normally, after the image 1 is obtained, the next image is not reconstructed until the next full set of phase encoding information is obtained, so the next image is obtained as the image 7. In this case, an image can be obtained only every 0.5 seconds. Therefore, in order to obtain an intermediate image, as shown in FIGS. 6B and 6C, the k-space is divided into several partial areas, and image reconstruction is performed while replacing measurement data for each partial area. carry out.

  The method shown in FIG. 6B divides the k-space 601 into a plurality of partial areas in the phase encoding direction, and performs image reconstruction while replacing the phase encoding data for each partial area. Here, this method is referred to as a photographing method that is sequentially replaced. In the method shown in FIG. 6C, the k-space 601 is divided into a low spatial frequency region 602 including the origin and a surrounding high spatial frequency region 603, and the low spatial frequency region 602 is divided into a high spatial frequency region. Image reconstruction is performed by measuring and updating more frequently than the area 603. This method is the same as the Keyhole Imaging method.

  First, the sequential replacement photographing method in FIG. 6B will be described in detail. First, the entire k space is divided into, for example, six partial regions. Then, after the image 1 is reconstructed, a phase encoding amount corresponding to the partial region 1 in FIG. 6B is given and an echo signal is measured, and the portion in the k-space data used for the reconstruction of the image 1 The image 2 is obtained by reconstructing the image after the data of only the region 1 is replaced with the measurement data. Next, a phase encoding amount corresponding to the partial region 2 in FIG. 6B is given, an echo signal is measured, and the data of only the partial region 2 in the k-space data used for the reconstruction of the image 2 is The image 3 is obtained by reconstructing the image after the measurement data is replaced.

  Thereafter, an image 4-6 is obtained by the same procedure. When the partial area 6 in FIG. 6B is replaced with newly measured data, all of the partial areas 1-6 are replaced with new measured data. become. Thereafter, images 7 to 12 are obtained by the same repetition. In this example, the entire k-space data to be measured is divided into six partial areas. However, the intermediate image can be easily generated with the same concept even when the number of divisions is not limited to six.

The sequential replacement imaging method is applicable not only to the gradient echo method shown in FIG. 4 but also to other general imaging pulse sequences such as the high-speed spin echo method and the EPI method.
In particular, in the case of performing a sequential replacement imaging method using a multi-shot type EPI pulse sequence, if the number of shots is equal to the number of divisions, an intermediate image can be acquired for each shot. For example, when divided so as to acquire all k-space data in 6 shots, phase encoding amounts corresponding to the partial areas 1 to 6 are given to the first to sixth shots, respectively. The echo signal is measured. Then, for each shot, the k-space data of the corresponding partial area is updated with the measurement data so that the intermediate image is reconstructed. Even if such a multi-shot EPI method is used, the apparent number of acquired images can be increased.

Next, the Keyhole Imaging method of FIG. 6C will be described in detail. The k-space 601 is divided into a low spatial frequency region 602 including the origin and a surrounding high spatial frequency region 603, and first, data of all regions (602 and 603) of the k space are measured to reconstruct the image 1 Is done. After this, the measurement / update frequency of the low spatial frequency region 602 is increased more than the measurement / update frequency of the high spatial frequency region 603, and every time any region is measured / updated, the data of the entire k space 601 is obtained. The images are reconstructed by using them, and the images after the image 2 are sequentially acquired. In particular, only the measurement / update of the low spatial frequency region 602 may be performed, and the measurement / update of the high spatial frequency region 603 may not be performed. Since the data measurement in the low spatial frequency region 602 is completed in a short time, this method can increase the apparent number of acquired images.
The keyhole imaging method described above is applicable not only to the gradient echo method shown in FIG. 4 but also to other general imaging pulse sequences such as a fast spin echo method and an EPI method.

  As described above, it is possible to acquire an image of a desired region in near real time by the method of shortening the time interval between image capturing and image acquisition using a high-speed pulse sequence. In addition, since the current electronics technology can sufficiently perform the calculations of the above formulas (1) to (5) at high speed, the displacement amount distribution or the strain distribution or pseudo color display thereof can be obtained in near real time. Can do. Therefore, the displacement amount distribution image, the distortion distribution image, or their pseudo color display can be obtained in synchronization with image acquisition or after acquisition of a large number of time-series images and displayed as a moving image.

In order to display the displacement amount distribution image, the distortion distribution image, or the pseudo color display thereof as a moving image, for example, the following manner is performed.
The simplest moving image display mode is a mode in which a displacement amount distribution image, a distortion distribution image, or a pseudo color display thereof is displayed as a moving image as it is. However, in this case, it is difficult to visually identify a specific place where the hard part is not soft and where the soft part is not soft. Therefore, as shown in FIG. One of the two adjacent images (original image) from which the distortion distribution image is acquired is set as a background image (black and white image) 901, and the background image 901 has a coordinate correspondence relationship and a pseudo color display 902. Are superimposed and displayed. At this time, only a specific original image may be displayed as a stationary background image, or the original image as a background image may be displayed as a moving image in conjunction with moving image pseudo color display. If the interlocking moving image display is stopped at a desired timing, a still image in which the pseudo color display and the background image are superimposed in a coordinate-corresponding state can be acquired. Since the background image is a black and white morphological image, it is easy to see how each tissue is deformed along with information on the hardness and softness of each living tissue by superimposing the image displayed in pseudo color on it. Can be recognized.

As described above, according to the second embodiment of the present invention, the number of images acquired per unit time can be improved, and the time resolution between images can be improved. As a result, it is possible to display a displacement amount distribution or a distortion distribution, or a moving image with pseudo color display thereof alone, or more smoothly by superimposing the original image as a background image. In particular, by superimposing and displaying the original image, it is possible to easily grasp the hardness and softness of the living tissue in a desired region in association with the position and shape of the living tissue.
Further, if a high-speed imaging pulse sequence is used in combination, each image can be acquired in near real time, and therefore a stiffness distribution image can also be acquired in near real time.

In the above, each embodiment in which the present invention is applied to a two-dimensional image has been described. However, an MRI apparatus having a method for obtaining a stiffness distribution image using the MRI apparatus of the present invention or means capable of realizing the method is described in the above embodiment. It is not limited and various changes are possible. For example, as shown in FIGS. 9B and 9C, the present invention can be similarly applied to a case where a three-dimensional image is acquired. In the case of acquiring a three-dimensional image, the displacement amount and distortion calculation and the pseudo color display are expanded to three dimensions. (B) The figure is an example in which the two-dimensional pseudo color display 904 is superimposed on the three-dimensional original image (monochrome morphological image) 903, and (c) the figure is displayed on the three-dimensional original image 903. This is an example in which the three-dimensional pseudo color display 905 is superimposed and displayed. If a moving image or a still image is displayed in association with each other, the spatial positional relationship of the living tissue can be grasped more clearly.
Further, instead of the strain distribution, the displacement distribution and its pseudo color display can be simply obtained and displayed in the same manner as the strain distribution image.

Claims (12)

Using a static magnetic field generating means for generating a static magnetic field, a measurement control means for controlling measurement of an echo signal based on a predetermined pulse sequence from a desired region of a subject arranged in a static magnetic field space, and using the echo signal A magnetic resonance imaging apparatus comprising: signal processing means for reconstructing an image of the subject; display means for displaying the image; and means for pressurizing or vibrating a desired region of the subject.
The measurement control means includes a first echo signal and a second pressure or vibration state from the desired region that is in a first pressure or vibration state by the pressure or vibration means. A second echo signal from the desired area being measured, and
The signal processing means reconstructs a first morphological image from the first echo signal and a second morphological image from the second echo signal, and uses the two morphological images to perform the desired morphological image. Find at least one of the displacement distribution in the region or the strain distribution by the spatial differentiation of the displacement distribution,
The magnetic resonance imaging apparatus characterized in that the display means displays at least one of the displacement amount distribution or the strain distribution . The magnetic resonance imaging apparatus according to claim 1.
The magnetic resonance imaging apparatus according to claim 1, wherein the pressurizing or vibrating means is in a substantially constant pressurizing or vibrating state during the execution of the pulse sequence . The magnetic resonance imaging apparatus according to claim 1 or 2,
The magnetic resonance imaging apparatus, wherein the pressurizing or vibrating means performs the pressurizing or vibrating asynchronously with the pulse sequence . The magnetic resonance imaging apparatus according to claim 1.
The pressurization or vibration means has a drive means and a transmission means for transmitting pressure or vibration from the drive means to the desired region,
The transmission means has one end in contact with the body surface of the desired region and the other end connected to the driving means.
The magnetic resonance imaging apparatus, wherein the driving unit applies pressure or vibration to the desired region via the transmission unit . The magnetic resonance imaging apparatus according to claim 4.
The static magnetic field generating means has a portion where a pair of static magnetic field generation sources are opposed to each other with the static magnetic field space in between, and open in a direction perpendicular to the facing direction,
The driving means is disposed at the opening location,
The magnetic resonance imaging apparatus, wherein the transmission means transmits pressure or vibration from the open portion to the desired region . The magnetic resonance imaging apparatus according to claim 1.
A table on which the subject is placed;
The magnetic resonance imaging apparatus according to claim 1, wherein the pressurizing or vibrating means is disposed below a contact surface with the subject in the table . The magnetic resonance imaging apparatus according to claim 1.
A receiving coil for receiving the echo signal;
The magnetic resonance imaging apparatus, wherein the pressurizing or vibrating means is disposed below a contact surface with the subject in the receiving coil . The magnetic resonance imaging apparatus according to claim 1.
The pressurizing or vibrating means includes a plurality of the transmitting means, and pressurizes or vibrates a plurality of portions of the subject so that the phases of pressurizing or vibrating substantially coincide with each other in the desired region. A magnetic resonance imaging apparatus . The magnetic resonance imaging apparatus according to claim 1.
The pressurizing or vibrating means pressurizes or applies a plurality of locations on the subject so that the desired area is pressurized or vibrated in different directions within an imaging section including the desired area. Shake,
The signal processing means obtains at least one of the displacement or strain distribution for each direction,
The magnetic resonance imaging apparatus characterized in that the display means displays at least one of the displacement amount distribution and the strain distribution for each direction . The magnetic resonance imaging apparatus according to claim 1.
The display means is a value of a point on a desired line on a two-dimensional plane with the horizontal axis representing the depth of each point in the desired region from the surface of the subject and the vertical axis representing the value of the point. Is plotted and displayed . A magnetic resonance imaging apparatus characterized by: The magnetic resonance imaging apparatus according to any one of claims 1 to 10,
The signal processing means sets a correlation window of a predetermined size surrounding a displacement measurement point in each of the first image and the second image, and moves the one correlation window at a predetermined interval while moving the two correlation windows. A magnetic resonance imaging apparatus characterized in that a correlation coefficient is obtained, and a movement direction and a movement amount that are the largest correlation coefficient among the correlation coefficients are set as a displacement direction and a displacement amount of the displacement measurement point, respectively. . The magnetic resonance imaging apparatus according to any one of claims 1 to 11,
The magnetic resonance imaging apparatus, wherein the display means displays at least one of the displacement amount distribution and the strain distribution in color .

Images