JP2009178287A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MRI apparatus capable of photographing a curved face along a skeleton structure and a blood vessel running system of a subject. <P>SOLUTION: Operation of detecting magnetic resonance signals while exciting a predetermined columnar region 63 of the subject and applying an inclined magnetic field in the longitudinal direction of the columnar region is repeated while moving the columnar region 63 into a position along a predetermined curved shape 64 in the subject. An image is composed using a plurality of obtained magnetic resonance signals to obtain an image along the predetermined curved face 64 in the subject. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging method that uses a magnetic resonance imaging (hereinafter referred to as MRI) apparatus to image a predetermined tissue over a wide range such as the whole body in a short time.

  In a conventional MRI apparatus, a method has been proposed in which images of a plurality of partial regions of a subject are taken and these images are connected in order to obtain an image of the entire region along the toe direction from the top of the subject. Yes. For example, in Patent Document 1 or Patent Document 2, a subject is divided into a plurality of regions, a bed is moved, each region is imaged, and the obtained images are combined to obtain a wide range image such as the whole body. Has been proposed.

On the other hand, in Patent Document 3, a rod-shaped region that is thin enough to be regarded as a line is excited, one-dimensional magnetic resonance information along the longitudinal direction is acquired, and the rod-shaped excited region is translated on a predetermined two-dimensional plane. Thus, a method for obtaining a two-dimensional image in which a one-dimensional image is arranged in a short time has been proposed.
JP 2006-21049 A JP 2003-135429 A JP 2006-26311 A

  However, as in the method disclosed in Patent Document 1 or 2 described above, an image obtained by connecting a plurality of images is merely a continuous planar image and is an anatomically continuous image. Absent. That is, in order to obtain an image capable of continuously observing a predetermined skeletal structure or vascular running system to be observed, it is necessary to capture images along a curved skeleton structure or vascular running system. Since the imaging method employed in 1 or 2 is a normal imaging method in which the imaging surface is a flat surface, it is not possible to capture a curved portion that deviates from the imaging surface. On the other hand, if the 3D image can be captured, the shape of the curved portion can be captured. However, since the 3D image requires time for imaging, it takes a very long time when applied to a wide range of imaging such as the whole body. The imaging method disclosed in Patent Document 3 also has a flat imaging surface.

  An object of the present invention is to provide an MRI apparatus capable of imaging a curved surface along a desired tissue such as a skeletal structure of a subject or a vascular running system.

In order to achieve the above object, according to the present invention, the following MRI apparatus is provided. That is, a static magnetic field generating means for generating a uniform static magnetic field space, a gradient magnetic field generating means for applying a gradient magnetic field to the static magnetic field space, and a high frequency magnetic field generating means for irradiating a subject arranged in the static magnetic field space with a high frequency magnetic field And a detecting means for detecting a magnetic resonance signal generated from the subject, a gradient magnetic field generating means, a high-frequency magnetic field generating means and a detecting means to execute a predetermined imaging pulse sequence, and from the acquired magnetic resonance signal, the subject An MRI apparatus having a control means for reconstructing an image of the object, wherein the control means excites a predetermined columnar region of the subject by applying a gradient magnetic field and irradiating the high-frequency magnetic field, and inclines in a longitudinal direction of the columnar region The operation of detecting a magnetic resonance signal while applying a magnetic field is repeated while moving the columnar region, and an image is reconstructed using the obtained plurality of magnetic resonance signals. Thereby, the image imaged along the predetermined shape in the subject can be obtained.
For example, the control means detects the magnetic resonance signal while moving the columnar region to a position along a predetermined curved surface shape in the subject, and uses the obtained magnetic resonance signal as a real space signal along the longitudinal direction of the columnar region. The image is reconstructed by arranging the plurality of real space signals obtained by converting into the above. Thereby, an image captured along a predetermined curved surface in the subject can be obtained.

  When constructing an image by arranging the above real space signals, it is also possible to construct a projected image of a predetermined curved surface by arranging the obtained real space signals on a two-dimensional plane.

  Further, when the MRI apparatus of the present invention has a bed on which the subject is mounted and moves in a predetermined direction in the static magnetic field space at a predetermined speed, the control means sets the longitudinal direction of the columnar region to the main plane of the bed. The columnar region is moved in the direction perpendicular to the bed main plane while the columnar region is moved in the movement direction by moving the bed, and the columnar region is moved in the direction perpendicular to the bed main plane. It can be moved along a curved surface.

  The width of the columnar region in the bed movement direction can be made equal to the distance the bed moves during the time from the start of excitation of one columnar region to the start of excitation of the next columnar region. In this case, it is possible to obtain information about the bed movement direction of the subject without interruption.

  The control means described above can realize moving the columnar region in a direction perpendicular to the bed main plane by changing at least one of the strength of the gradient magnetic field and the frequency of the high frequency.

  Further, the control means can be configured to display a reference image captured in advance for the subject on the display device and accept the setting of the curved surface shape from the operator. In addition, the control unit may be configured to perform image processing on a reference image captured in advance for the subject and automatically set the curved surface shape based on the image processing result. In these cases, the control means includes a curve along the longitudinal direction of the tissue and the reference image is captured by using an image captured on the surface including the longitudinal direction of the tissue to be imaged as the reference image. A curved surface orthogonal to the two-dimensional plane can be set as the curved surface shape.

  For example, the control unit can directly set a part of the curved surface shape based on one or more reference images and set the remaining part by interpolation processing.

  In addition, the control unit may repeatedly display an image reconstructed using a plurality of magnetic resonance signals obtained up to that time while exciting the columnar region and detecting the magnetic resonance signal. Is possible. Thereby, the correction of the position to move the columnar region thereafter can be received from the operator who has seen the real-time image. By continuing the operation while moving the columnar region along the accepted corrected position, an image reflecting the correction can be obtained.

  As an effect of the present invention, imaging is performed by moving the columnar region to a desired curved surface shape. By setting a curved surface shape along a desired tissue, a desired tissue having a shape that cannot be captured by a plane is obtained. It can be acquired as a continuous image without interruption. In addition, imaging can be performed in a short time, and imaging efficiency can be improved.

An embodiment of the MRI apparatus of the present invention will be described with reference to the drawings.
(First embodiment)
As shown in FIG. 1, the MRI apparatus of the present embodiment includes a superconducting coil 1, a gradient magnetic field generating coil 2, a high frequency magnetic field generating coil 3, a receiving coil 4, a gradient magnetic field power source 5, and a high frequency magnetic field power source. 6, a bed 7, a control unit 8, and a console 9.

  The superconducting coil 1 generates a uniform static magnetic field space in the imaging space. The gradient magnetic field generating coil 2 includes three sets of coils for applying a gradient magnetic field (Gx, Gy, Gz) whose magnetic field intensity changes linearly along the three-axis directions of x, y, and z in the imaging space. In the present embodiment, the x, y, and z axes are the origin o at the center of the static magnetic field space formed by the superconducting coil 1, the body axis direction of the subject 10 is the x axis, and the body width direction is the y axis. The thickness direction is z-axis. Gx, Gy, and Gz are all set so that the amount of gradient magnetic field at the origin is zero.

  The high frequency magnetic field generating coil 3 irradiates the subject 10 with a high frequency magnetic field for inducing magnetic resonance. The receiving coil 4 detects a magnetic resonance signal from the subject 10. The bed 7 includes a drive mechanism 7a that conveys the imaging region of the subject 10 to the imaging space. The gradient magnetic field power supply 5 supplies a current for generating a predetermined gradient magnetic field to the gradient magnetic field generating coil 2. The high-frequency magnetic field power source 6 supplies a high-frequency magnetic field generating coil 3 with a high-frequency current having a predetermined waveform for generating a predetermined high-frequency magnetic field. The control unit 8 outputs a control signal to the high-frequency magnetic field power supply 6 and the gradient magnetic field power supply 5, and generates a predetermined gradient magnetic field and a high-frequency magnetic field at a predetermined timing. Further, the control unit 8 detects the reception signal of the reception coil 4 at a predetermined timing, and performs image reconstruction processing by converting it into a real space signal by Fourier transformation. The image reconstructed by the control unit 8 is displayed on the image display unit 9a (see FIG. 10) of the console 9. The control unit 8 receives imaging conditions, image reconstruction conditions, and the like from the operator via the console 9.

  In the MRI apparatus, an image is taken according to a measurement procedure called an imaging pulse sequence that defines the application procedure of a high-frequency magnetic field and a gradient magnetic field and the timing of signal measurement. Known imaging pulse sequences include SE (spin echo) method, GE (gradient echo) method, FSE (fast spin echo) method, EPI (echo planar) method, etc. Is different. In these methods, two-dimensional position information is generally given to magnetic resonance signals by encoding position information with respect to phase and frequency, and a two-dimensional image is directly reconstructed. In contrast, in this embodiment, instead of directly reconstructing a two-dimensional image, a column scan was performed to excite a columnar region and acquire a magnetic resonance signal while giving one-dimensional information. The signal is Fourier transformed to reconstruct a one-dimensional image. This operation is repeated while gradually shifting the columnar excitation region, and the obtained one-dimensional images are arranged to obtain a two-dimensional image.

  Here, the principle of obtaining a two-dimensional image by arranging one-dimensional images will be described. FIG. 2 shows a pulse sequence used in this embodiment, and the horizontal axis is a time axis. High-frequency magnetic field (RF) pulses 51 and 53, an x-direction gradient magnetic field (Gx) pulse 52, a y-direction gradient magnetic field (Gy) pulse 55, and a z-direction gradient magnetic field (Gz) pulse 54 are respectively shown in FIG. Applied. The magnetic resonance signal (echo signal) 56 is detected at the timing shown in FIG. Here, the RF pulses 51 and 53, the Gx pulse 52, and the Gz pulse 54 act to excite the region to be photographed, and Gy serves to encode position information to the frequency of the echo signal.

  Specifically, first, at time t0, the Gx pulse 52 and the RF pulse 51 that excites the magnetization by 90 ° are irradiated, so that the first perpendicular to the x-axis of the subject 10 is obtained as shown in FIG. 1 cross-section 61 is excited. Next, at time t1, the second cross section 62 parallel to the xy plane is excited by irradiating the Gz pulse 54 and the RF pulse 53 that excites the magnetization by 180 °. The second cross section 62 is orthogonal to the first cross section 61. At this time, a quadrangular columnar region 63 along the y-axis where the first cross section 61 and the second cross section 62 intersect with each other is an echo generating region. At time TE, the echo signal 56 is acquired while applying the Gy pulse 55 to give position information to the echo signal 56. The above steps are repeated at a predetermined repetition time (TR).

  In the present embodiment, an image along the curved surface 64 is obtained as shown in FIG. 3B by shifting the region 63 not only in the x-axis direction but also in the z-axis direction for each repetition. The region 63 is shifted in the x-axis direction by moving the bed 7. As shown in FIGS. 4A and 4B, the bed 7 is set so as to move the subject 10 and move in the x direction at a speed v. Assuming that the first coordinate in the x direction of the tip 11 of the subject 10 is x = −L (FIG. 4A), the tip of the subject is at the center of the magnetic field after L / v time after the bed 7 starts moving. x = 0 is reached (FIG. 4B). This time is t = t0.

  The pulse sequence of FIG. 2 is executed at time t0. The Gx pulse 52 and the 90 ° excitation RF pulse 51 are irradiated to excite the first cross section 61. Here, the coordinate in the x direction of the first cross section 61 is 0, and the thickness in the x direction is d. Next, at time t1, the Gy pulse 54 and the 180 ° excitation RF pulse 53 are irradiated to excite the second cross section 62 orthogonal to the first cross section 61. The height of the second cross section 62 is the coordinate z, and the thickness is d. As a result, a region 63 where the first cross section 61 and the second cross section 62 intersect is excited and becomes an area where the echo signal 56 is generated. The Gy pulse 55 is applied to encode position information in the echo signal 56, and the echo signal 56 is acquired at time TE.

  Here, the width in the y direction of the second cross section 62 is FOV. The acquired echo signal 56 is subjected to signal processing by the control unit 8 and reconstructed into a first real space signal. This real space signal corresponds to regions of x = −d / 2 to + d / 2, y = −FOV / 2 to + FOV / 2, and z = (z−d / 2) to (z + d / 2). . Since the above pal sequence is repeated at the repetition time TR, the bed 7, that is, the subject 10 moves by v × TR during TR. Therefore, by adjusting any of d, v, and TR so that the relationship with the desired thickness d of the first cross section 61 satisfies d = v × TR, the thickness of the subject 10 is increased in the x-axis direction. Images can be taken while being shifted by d.

  At the same time as moving the excitation region 63 in the x-axis direction, the z-axis direction is also shifted by a predetermined amount. Thereby, an image along the curved surface 64 can be obtained. At this time, as shown in FIG. 5A, the curved surface 64 is set to a surface including a desired tissue, for example, the blood vessel 21 in the reference image 20 taken in advance for the subject 10. As a result, an anatomically continuous image capable of continuously observing the curved blood vessel 21 is obtained. In order to use the curved surface 64 as an imaging surface, the excitation region 63 is moved in the z-axis direction every time the pulse sequence is repeated.

  A method of moving the excitation region 63 in the z-axis direction will be described by taking as an example a case in which the excitation region 63 is moved along the curved surface 64 to the regions 23, 24, 25, and 26 as shown in FIG. To do. First, when the time when the area 23 is imaged is T0, the times when the areas 24, 25, and 26 are respectively imaged are T0 + TR, T0 + 2TR, and T0 + 3TR. Further, if the center frequency of the second RF pulse 53 of the pal sequence is ω1, ω2, ω3, ω4 and the distance from the center of the static magnetic field is z1, z2, z3, z4, respectively, ω1 = ω + γ × Gz × z1, ω2 = ω + γ × Gz × z2, ω3 = ω + γ × Gz × z3, and ω4 = ω + γ × Gz × z4. Here, ω is the frequency when exciting the center of the static magnetic field, and γ is the gyromagnetic ratio. The control unit 8 stores ω1 to ω4 in a built-in storage device, and at the time T0, T0 + TR, T0 + 2TR, T0 + 3TR, the frequency of the RF pulse 53 to be irradiated is changed to ω1, ω2, ω3, ω4 and the above pulses. When the sequence is performed, the excitation region 63 moves to the regions 23, 24, 25, and 26, and a line-shaped image is obtained from each region. An image 27 obtained by planarly connecting the obtained line-shaped images in the direction opposite to the moving direction of the bed is equivalent to an image obtained by projecting the curved surface 64 on the xy plane as shown in FIG. Therefore, the curved blood vessel 21 is imaged without interruption.

  Based on the above principle, the configuration and operation for the MRI apparatus of the present embodiment to capture a curved surface will be further described with reference to FIGS.

  As illustrated in FIG. 6, the control unit 8 includes a curved surface shape setting unit 601, a columnar region control unit 602, an imaging control unit 603, and an image reconstruction unit 604. The curved surface shape setting unit 601 displays a reference image measured in advance and receives a setting of the shape of the curved surface 64 from an operator on the image, and automatically sets the curved surface 64 by image processing the reference image. And an automatic setting unit 606. The columnar region control unit 602 detects a distance (z coordinate) of the set curved surface 64 from the center of the static magnetic field, and sets the center frequency of the RF pulse 53 from the detected z coordinate to ω1, ω2, ω3, respectively. A calculation unit 608 that calculates ω4 and a storage unit 609 that stores the obtained ω1 and the like are provided.

  The curved surface shape setting unit 601, the columnar region control unit 602, the imaging control unit 603, and the image reconstruction unit 604 of the control unit 8 are read out and executed by the CPU by reading a program stored in a built-in storage device. Realized. The operation of the control unit 8 will be specifically described with reference to the flowchart of FIG. First, the curved surface shape setting unit 605 of the control unit 8 displays an image for accepting the setting of the imaging condition of the reference image on the image display unit 9a of the console 9 in order to capture the reference image before performing the main imaging (step 101). The operator operates the console 9 to set the imaging condition for the reference image. The imaging conditions for accepting the settings are the orientation of the imaging surface of the reference image (eg, cross section, sagittal section, annular section), imaging range (whole body, head, chest, abdomen, legs, etc.), imaging field (FOV), The number of divisions when the entire imaging range cannot be captured with a single reference image, the imaging range after division, the type of imaging sequence (SE method, GE method, etc.), the TR of the imaging sequence, the number of repetitions, and the like.

  The orientation of the imaging plane of the reference image is a plane that intersects the imaging plane (curved surface) of the main imaging, and is a plane along the longitudinal direction of the tissue (skeleton structure or blood vessel) to be captured. For example, when a cross-sectional image of the spine is captured by the main imaging, the imaging surface of the reference image is set to the sagittal cross-section of the spine. In the following description, the body axis direction is the x direction (the movement direction of the bed 7), the width direction of the subject is the y direction, the thickness direction is the z direction, the reference image is imaged with respect to the sagittal section, and the main imaging is The case where the curved surface is parallel to is described.

  The curved surface shape setting unit 601 of the control unit 8 passes the received imaging condition of the reference image to the imaging control unit 603. The imaging control unit 603 captures a reference image according to the imaging conditions set in step 101, and the image reconstruction unit 604 performs image reconstruction. When the reference image is divided into a plurality of images and is captured, they are combined into a single reference image by a known method. The reconstructed reference image 801 is transferred to the curved surface shape setting unit 601 and displayed on the image display unit 9a as a part of the photographing condition setting image 800 as shown in FIG. 8 (step 102). In the main imaging condition setting image 800, in addition to the reference image 801, an imaging position designation cursor 803 for accepting designation of a curved surface position (imaging position trajectory) to be captured in the main imaging on the reference image 801, and a main imaging sequence. Three input sections 807, 808, and 809 for setting the parameters are displayed.

  The operator draws a curve 802 by moving the imaging position designation cursor 803 along the skeleton structure or blood vessel to be imaged on the reference image 801 by operating the mouse of the console 9 or the like. The receiving unit 605 of the curved surface shape setting unit 601 receives this curve 802. The curved surface shape setting unit 601 includes a curved line 802 and sets a curved surface perpendicular to the reference image 801 as the curved surface 64 to be imaged. For example, in the example of FIG. 8, since the reference image 801 is a sagittal section (zx plane) image, a curved surface including the curve 802 and parallel to the transverse section (xy plane) is set as the curved surface 64 to be imaged (step 103). Further, when the operator gives an instruction, the automatic setting unit 606 can automatically extract a pixel for drawing a skeletal structure or a blood vessel by performing image processing on the reference image 801 and set it as a curve 802. is there. The automatically extracted curve 802 is displayed together with the reference image on the image display unit 9a. The curved surface shape setting unit 601 includes a curved line 802 and sets a curved surface perpendicular to the reference image as the curved surface 64 to be imaged.

  The three input units 807 to 809 displayed on the main imaging condition setting image 800 are an TR input unit 807 of the main imaging sequence, an input unit 808 of the moving speed v of the bed 7, and an x of the excitation region 63. This is an input unit 809 having an axial thickness d. Since these parameters d, v, and TR have a relationship of d = v × TR as described above, the curved surface shape setting unit 601 receives input from any of the two (step 104). The remaining one parameter is set by the control unit 8 calculating d = v × TR.

  The columnar region control unit 602 sets the thickness of the excitation region 63 described with reference to FIGS. 3A and 3B in the bed movement direction (x-axis) to the value d set in step 104 in FIG. The gradient magnetic field amount of the Gx pulse 52 in the main imaging sequence is determined based on the relationship with the frequency width of the first RF pulse 51 (step 105).

  The z detection unit 607 of the columnar region control unit 602 obtains the irradiation time of the second RF pulse 53 of each TR in the main imaging, and the z coordinate of the curve 802 at the position of the first cross section 61 at that time, that is, FIG. b1) z1, z2, z3, z4. The coordinate z obtains the pixel on the curve 802 on the reference image 801 and the distance h805 or (FOV-h) 806 from the image end of the pixel, and the actual value of the center of the FOV 804 and FOV 804 of the reference image 801. It can be obtained by calculation from the relationship with the spatial coordinates. The ω calculating unit 608 calculates the center frequencies ω1, ω2, ω3, ω4... for each TR of the second RF pulse 53 from the obtained coordinates z (z1, z2, z3, z4. ω + γ × Gz × z1, ω2 = ω + γ × Gz × z2, ω3 = ω + γ × Gz × z3, and ω4 = ω + γ × Gz × z4 (step 106). Where ω is the frequency when exciting the center of the static magnetic field, and γ is the gyromagnetic ratio. The obtained value such as ω1 is stored in the ω storage unit 609 in correspondence with the irradiation time of the second RF pulse 53.

  The imaging control unit 603 reads ω1, ω2, ω3, ω4, etc. stored in the ω storage unit 609, and uses these together with other imaging parameters set in the curved surface shape setting unit 601, and the pulse of FIG. The main imaging is performed by executing the sequence. That is, by setting the bed speed v, the repetition time TR, and the gradient magnetic field amount of the Gx pulse 52 to the values set or determined in Steps 104 and 105, the excitation region 63 is set by the distance d set in Step 104 by the x axis. Move in the direction. At the same time, by setting the center frequency ω for each TR of the second RF pulse 53 to the center frequencies ω 1, ω 2, ω 3, ω 4... Obtained in step 106, the excitation region 63 is positioned at a position along the curve 802. Move. Thereby, in the main imaging, the excitation region 63 can be set at a position along the curve 802 on the reference image 801.

  The image reconstruction unit 604 reconstructs a one-dimensional image by performing Fourier transform on the magnetic resonance signal obtained for the excitation region 63 in each TR. By arranging the obtained one-dimensional images in the x-axis direction, an image obtained by projecting the subject image of the curved surface 64 onto the zy plane can be obtained. This image is an anatomically continuous image captured without interruption of the skeletal structure and the vascular system located along the curve 802.

  The width and height of the excitation region 63 in the bed movement direction (that is, the thickness d of the first cross section 61 and the second cross section) can both be set to about several mm. For example, when the width of the excitation region 63 in the bed movement direction is set to 1 mm, the whole body of the subject 10 with a height of 180 cm can be imaged with 1800 lines. In the imaging sequence of FIG. 2, since the time (1TR) for imaging one line is usually about 0.1 seconds, the whole body 1800 lines can be imaged in about 180 seconds = 3 minutes. Since the time required for whole-body imaging is a short time, the burden on the subject 10 is small.

  Further, by setting the width and height (z direction) of the excitation region 63 in the bed movement direction (x direction) to about several millimeters, the operator draws a curve 802 on the reference image 801 relatively easily and quickly. Even in this case, the main vascular system can be easily and continuously imaged, and can be imaged efficiently.

  In addition, the moving direction (x direction) of the bed 7 and the second cross section 62 (xy plane) excited by the second RF pulse 53 are parallel, and the bed 7 has a moving distance v × TR and the first distance between 1TR. By making the slice thickness d of one section 61 coincide (d = v × TR), as shown in FIG. 5B, adjacent excitation regions 23 to 26 are in contact with each other in the x-axis direction. Therefore, information about the subject 10 can be acquired as the image 27 without interruption in the x-axis direction.

  Note that the actual imaging range in step 107 can be set to the same range as the imaging range of the reference image 801 in step 101, but it is also possible to perform actual imaging only for a partial range of the reference image 801. is there. For example, it is possible to accept the main imaging range from the operator in step 103 and perform the main imaging only on the curved surface 64 set in the range. Thereby, it is possible to capture an image only in a necessary range in a short time. For example, in step 103, only the range in which the operator has drawn the curve 802 can be set as the main imaging range.

  In the first embodiment described above, a plurality of one-dimensional images acquired by moving the excitation region 63 along the curved surface 64 are arranged on a two-dimensional plane as shown in FIG. However, it is not necessarily a two-dimensional planar image. Of course, a three-dimensional image can be obtained by arranging the one-dimensional images along the curved surface 64.

  When the heights (z coordinates) z1, z2, z3, and z4 of the adjacent excitation regions among the excitation regions 23 to 26 shown in FIG. 5B are the same value, the second cross section having the same height. 62 will be excited continuously. For this reason, when TR is shorter than the recovery time of longitudinal magnetization, the intensity of the magnetic resonance signal from the excitation region is weakened by continuous excitation. Therefore, the columnar region control unit 602 of the control unit 8 is configured to warn the user that the signal intensity is weakened when the z coordinates detected by the z detection unit 607 have the same value in the adjacent excitation regions 23. Is possible. Alternatively, in order to avoid continuously exciting the same section, when exciting adjacent excitation regions having the same coordinate z, the direction of the second section 62 is inclined from the main plane (xy plane) of the bed 7. The imaging control unit 603 can be instructed. Thereby, even if the z coordinates of adjacent excitation regions are the same, it is possible to eliminate the second cross section 62 from becoming the same surface by inclining, so that the phenomenon that the intensity of the magnetic resonance signal is weakened can be solved.

(Second Embodiment)
In the first embodiment described above, a reference image is captured for a skeleton structure or a surface along a blood vessel to be imaged, and the operator manually specifies a curve 802 on the reference image, or the skeleton by image processing. Although the curved surface 802 is set by specifying the curve 802 by extracting a blood vessel or the like, the curved surface shape can be set by other methods. For example, as shown in FIG. 9, a plurality of reference images 31 to 34 are photographed at arbitrary intervals with respect to a skeleton structure to be imaged and a surface crossing a blood vessel, and the region between the reference image and the reference image is The curve 802 can be set by interpolation processing.

  For example, in the reference images 31, 32, 33, and 34 in FIG. 9, the coordinates in the x direction are x31, x32, x33, and x34, and the coordinates in the z direction of the skeleton structure or vascular system to be imaged are z31, z32, and z33. , Z34, the curved surface shape setting unit 601 sets the position of the second cross section 62 to z31 <z <z32 in the section x31 <x <x32, and the second in the section x32 <x <x33. The position of the cross section 62 is set to z32 <z <z33, and in the section of x33 <x <x34, the position of the second cross section 62 is set to z33 <z <z34.

  As an interpolation method, for example, a method of connecting the coordinates to be imaged of the reference images 31, 32, 33, and 34 with a straight line or a predetermined curve, or a predetermined fitting method such as a least square method can be used. Further, data on the skeletal structure and vascular system shape to be imaged is obtained in advance for each sex and age of the subject, stored in a storage unit built in the control unit 8, and the subject to be imaged. It is also possible to use a method in which shape data corresponding to the sex and age of the specimen 10 is read out and fitted to the imaging target coordinates of the reference images 31, 32, 33, and 34.

  By using such an interpolation method, it is possible to set a curve for performing the main imaging even when it is difficult to capture a reference image with respect to a skeleton structure to be imaged or a surface along the blood vessel.

  Since the method other than the setting of the curve 802 is the same as that of the first embodiment, the description thereof is omitted.

(Third embodiment)
As described in the first and second embodiments, in the imaging method of the present invention, a one-dimensional image is acquired every time the columnar excitation region 63 is imaged. By arranging the obtained one-dimensional images, the images picked up to the present time can be displayed on the image display unit 9a in real time. Utilizing this, in the third embodiment, as shown in FIG. 10, a change acceptance for accepting a change in the shape of a curved surface to be imaged after that point in the middle of imaging from an operator who has confirmed the image in real time. A unit 610 is provided, and imaging is continued along the changed curved surface shape.

  The imaging control unit 603 of the control unit 8 performs the imaging sequence of FIG. 2 in step 107 of FIG. 7, and the image reconstruction unit 604 acquires the data line by line and reconstructs it by that time. The image data of each configured line is displayed on the image display unit 9a as an image 41 in FIG. The image reconstruction unit 604 displays, on the display screen, coloration or the like indicating that the line 141 has been reconstructed immediately before in the image 41 to be displayed. In this line 141, as shown in FIG. 11A, the end image of the blood vessel 901 to be imaged does not appear. This is because the blood vessel 901 is out of the excitation region 63 where the image of the line 141 is obtained. When the operator who has viewed the image 41 instructs the correction of the position of the excitation area of the imaging curved surface via the console 9, the change receiving unit 610 will activate the excitation area 420 corresponding to the four lines 42 to be imaged from now on. The z coordinates of .about.450 are received from the columnar region control unit 602 and displayed on the image display unit of the console 9 as shown in FIG. The z-coordinate values of the excitation regions 420 to 450 are the coordinates detected in step 106 in FIG.

  The operator looks at this screen and gives instructions to correct the heights (z coordinates) z1 to z4 of the excitation areas 420, 430, 440 and 450 to z1 ′ to z4 ′ as shown in FIG. 9 through. The change receiving unit 610 transfers the modified z1 ′ to z4 ′ to the columnar region control unit 602. The ω calculation unit 608 of the columnar region control unit 602 sets the z coordinates of the excitation regions 420 to 450 to z1 ′ to z4 ′ by performing Step 106 again based on the corrected z1 ′ to z4 ′. Frequencies ω1 ′ to ω4 ′ are obtained by calculation. The imaging control unit 603 continues the subsequent main imaging using the obtained ω1 ′ to ω4 ′, and the image reconstruction unit 604 sequentially displays the acquired images of the line 42 as illustrated in FIG. In the example of FIG. 11C, by correcting the positions of the excitation regions 420, 430, 440, and 450, an image in which the blood vessel image 901 can be confirmed again on the line 42 is obtained. Note that, except for the correction of the height of the excitation region, it is the same as in the first and second embodiments, and thus description thereof is omitted.

  As described above, in the third embodiment, the imaging method of the present invention uses the fact that a one-dimensional image is obtained in real time, and displays the reconstructed image in real time. The height of the excitation area to be imaged can be corrected. As a result, it is possible to correct the correct position and continue the main imaging, so that the blood vessel once deviated from the excitation region can be captured again in the excitation region and imaged. Therefore, it is possible to obtain an image of an imaging target such as a blood vessel, to prevent the main imaging from being performed again, and to improve imaging efficiency.

Finally, the influence of the movement of the bed 7, that is, the movement of the subject 10 on the magnetic resonance signal is evaluated. In the pulse sequence of FIG. 2, the relationship between the applied gradient magnetic field G and the magnetic resonance signal S is:
S (ky) = ∫ρ (y) ・ exp {j (θ + ky ・ y)} dy = exp (jθ) ∫ρ (y) ・ exp (j ・ ky ・ y) dy
It is represented by
here
ky = γ∫Gy dt
θ = γ∫Gx dt ・ vt = 1/2 (γ ・ v ・ Gx ・ t2)
It is. ρ (y) is the proton density. The magnetic rotation ratio γ, the moving speed of the magnetization (moving speed of the bed 7) v, the gradient magnetic field strength G, and the gradient magnetic field application time t are, for example, γ = 42 MHz / T, G = 10 mT / m, When v = 0.01m / s and t = 0.001s, the amount of phase change due to couch movement θ
= 4.2x10 ^-3 Hz. Since this θ is very small, the influence on the magnetic resonance signal is small. Even if the imaging methods of the first to third embodiments are performed while moving the bed 7, image degradation due to the movement of the bed 7. It can be seen that the image can be reconstructed with almost no occurrence.

  As described above, according to the present invention, it is possible to image a wide range such as the whole body while moving the bed 7 with the MRI apparatus, and it is also possible to image a curved surface along the skeletal structure or vascular system of interest.

1 is a block diagram showing the overall structure of an MRI apparatus according to a first embodiment. Explanatory drawing which shows the imaging pulse sequence of the MRI apparatus of 1st Embodiment. (A) Explanatory drawing which shows the area | region (line) excited by the imaging pulse sequence of FIG. (B) Explanatory drawing which shows moving the excitation area | region and imaging the curved surface 64. FIG. (A) In the MRI apparatus of 1st Embodiment, it is explanatory drawing which shows the state in which the front-end | tip 11 of the subject 10 is located in coordinate x = -L, (b) The front-end | tip 11 of the subject 10 is coordinate x == It is explanatory drawing which shows the state located in 0. FIG. (A) In 1st Embodiment, explanatory drawing which shows making the curved surface 64 in alignment with the blood vessel 21 of the reference image 20 into an imaging surface, (b) Changing height z1-z4 of the excitation area | regions 23-26. Explanatory drawing which shows that the imaging surface along the curved surface 64 is obtained by FIG. The block diagram which shows the detailed structure of the control unit 8 of the MRI apparatus of 1st Embodiment. 5 is a flowchart showing the operation of a control unit at the time of imaging in the MRI apparatus of the first embodiment. Explanatory drawing which shows the example of the image 800 for main imaging condition settings displayed on the image display part of the console 9 in 1st Embodiment. Explanatory drawing which shows the some reference image imaged in the direction which crosses an imaging target in 2nd Embodiment. The block diagram which shows the detailed structure of the control unit 8 of the MRI apparatus of 3rd Embodiment. (A) In 3rd Embodiment, explanatory drawing which shows the reconstructed image 41 displayed in real time in the middle of imaging, (b) In the reconstructed image 41, excitation of four lines to be imaged from now on An explanatory diagram showing xz coordinates of the regions 420 to 450, (c) an explanatory diagram showing a reconstructed image captured by correcting the heights of the excitation regions 420 to 450, and (d) an excitation region 420 to four lines. Explanatory drawing which shows the state which corrected z coordinate of 450. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Superconducting coil, 2 ... Gradient magnetic field generation coil, 3 ... High frequency magnetic field generation coil, 4 ... Reception coil, 5 ... Gradient magnetic field power supply, 6 ... High frequency magnetic field power supply, 7 ... Sleeper, 8 ... Control unit, 9 ... Console 9a ... Image display unit 10 ... Subject, 20 ... Reference image, 21 ... Blood vessel, 23-26 ... Excitation region, 27 ... Image, 31-34 ... Reference image, 41 ... Real-time reconstructed image, 61 ... First 62 ... second cross section, 63 ... excitation region, 64 ... curved surface (imaging surface), 141 ... line imaged at present, 420, 430, 440, 450 ... excitation region, 601 ... curved surface shape setting unit, 602 ... Columnar region control unit, 603 ... Imaging control unit, 604 ... Image reconstruction unit, 605 ... Reception unit on reference image, 606 ... Automatic setting unit by image processing, 607 ... Curved surface height z detection unit, 608 ... ω calculation unit, 609 ω storage unit, 800 ... main shooting condition setting image, 801 ... reference image, 802 ... curve, 803 ... imaging position designation cursor, 804 ... FOV (z direction), 805 ... distance h from image edge, 806 ... FOV-h, 807... TR input unit, 808... Velocity v input unit, 809... X-axis direction thickness d input unit of excitation region, 901.

Claims (11)

Static magnetic field generating means for generating a uniform static magnetic field space, gradient magnetic field generating means for applying a gradient magnetic field to the static magnetic field space, and high frequency magnetic field generating means for irradiating a subject arranged in the static magnetic field space with a high frequency magnetic field And a detection means for detecting a magnetic resonance signal generated from the subject; and the magnetic resonance signal obtained by controlling the gradient magnetic field generation means, the high-frequency magnetic field generation means and the detection means to execute a predetermined imaging pulse sequence. Control means for reconstructing the image of the subject from
The control means excites a predetermined columnar region of the subject by applying the gradient magnetic field and irradiating the high-frequency magnetic field, and detects the magnetic resonance signal while applying a gradient magnetic field in the longitudinal direction of the columnar region. Is performed while moving the columnar region, and an image is reconstructed using the obtained plurality of magnetic resonance signals.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the control unit detects the magnetic resonance signal while moving the columnar region to a position along a predetermined curved surface shape in the subject. A magnetic resonance imaging apparatus that reconstructs the image by converting a magnetic resonance signal into a real space signal along a longitudinal direction of the columnar region and arranging the obtained plurality of real space signals.   The magnetic resonance imaging apparatus according to claim 2, wherein the obtained plurality of real space signals are arranged on a two-dimensional plane to constitute a projection image of the subject image on the predetermined curved surface. Resonance imaging device. The magnetic resonance imaging apparatus according to claim 2, further comprising a bed on which the subject is mounted and moved at a predetermined speed in a predetermined direction in the static magnetic field space,
The control means sets the longitudinal direction of the columnar region in a direction parallel to the main plane of the bed and perpendicular to the moving direction of the bed, and moves the columnar region in the moving direction by moving the bed. However, the magnetic resonance imaging apparatus is characterized in that the columnar region is moved along the curved surface by moving the columnar region in a direction orthogonal to the bed main plane.   5. The magnetic resonance imaging apparatus according to claim 4, wherein the width of the columnar region in the bed movement direction is a distance that the bed moves during a period from the start of excitation of one columnar region to the start of excitation of the next columnar region. A magnetic resonance imaging apparatus characterized by   6. The magnetic resonance imaging apparatus according to claim 4, wherein the control unit moves at least one of the strength of the gradient magnetic field and the frequency of the high frequency in order to move the columnar region in a direction orthogonal to the bed main plane. Magnetic resonance imaging apparatus characterized by changing   7. The magnetic resonance imaging apparatus according to claim 2, wherein the control unit displays a reference image captured in advance for the subject on a display device, and receives the setting of the curved surface shape from an operator. A magnetic resonance imaging apparatus.   7. The magnetic resonance imaging apparatus according to claim 2, wherein the control unit performs image processing on a reference image captured in advance for the subject and sets the curved surface shape based on the image processing result. A magnetic resonance imaging apparatus.   9. The magnetic resonance imaging apparatus according to claim 7, wherein the reference image is an image captured on a surface including a longitudinal direction of a tissue to be imaged, and the control unit is along the longitudinal direction of the tissue. A magnetic resonance imaging apparatus comprising: a curved surface that includes a curve and is orthogonal to a two-dimensional plane on which the reference image is captured.   9. The magnetic resonance imaging apparatus according to claim 2, wherein the control unit sets a part of the curved surface shape based on the one or more reference images, and sets the remainder by interpolation processing. A magnetic resonance imaging apparatus.   10. The magnetic resonance imaging apparatus according to claim 1, wherein the control unit obtains up to that point while repeatedly performing the operation of exciting the columnar region and detecting the magnetic resonance signal. 11. Means for displaying an image reconstructed using the plurality of magnetic resonance signals on a display device, and means for accepting correction of a position to move the columnar region thereafter from an operator who has seen the real-time image; The magnetic resonance imaging apparatus is characterized in that the operation is continued while moving the columnar region along the received corrected position.

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