JP2006026311A - Two-dimensional magnetic resonance imaging method, three-dimensional magnetic resonance imaging method and magnetic resonance imaging program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-dimensional magnetic resonance imaging method capable of acquiring magnetic resonance information necessary for imaging in a short period of time without lowering spatial resolution. <P>SOLUTION: A plurality of different lines aligned on a measurement cross section whose image is intended to be acquired are excited by selectively exciting a plane non-parallel to the measurement cross section and observing signals emitted by the excited respective lines, so that one-dimensional resonance information of the plurality of different lines is acquired while avoiding the overlapping of the excitation planes. The image of the measurement cross section is formed by the one-dimensional resonance information of the acquired plurality of lines. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides a two-dimensional magnetic resonance imaging method capable of acquiring magnetic resonance information necessary for imaging in a short time without reducing spatial resolution, a three-dimensional magnetic resonance imaging method using the same, and magnetic resonance It relates to an imaging program.

  MRI (Magnetic Resonance Imaging), which has been developed mainly in the medical field so far, is characterized by being a noninvasive measurement method for a living body. In many cases, MRI is a technique for imaging a two-dimensional or three-dimensional distribution of water (protons) in a living body. Therefore, it is used exclusively for image diagnosis.

  This technique can also be applied to the field of botany, which lacked a decisive method for exploring the internal water distribution and water movement of living plants. At this time, in order to obtain an image with high spatial resolution and good image quality, it is necessary to increase the number of pixels necessary for expressing a range to be drawn. However, as the number of pixels increases, an enormous amount of measurement time is required for each pixel, and this often becomes a limitation when applied to a medical field or a technology such as research.

  In a conventional imaging method, a two-dimensional SE method (Spin Echo method) is generally used. The two-dimensional SE method is a technique that should be called the basis of the imaging method. FIG. 20 shows a two-dimensional SE method pulse sequence. In the two-dimensional SE method, first, magnetization is inclined to the XY plane using a 90 ° pulse. At the same time, a gradient magnetic field is applied in the Z direction to selectively excite the slice region in the Z direction. Thereafter, a gradient magnetic field is applied to the magnetization developed on the XY plane from the Y axis (phase encoding). At the same time, a refocus gradient magnetic field is applied in the X-axis direction to generate a normal echo signal. Thereafter, the magnetic field developed by the 180 ° pulse is recombined, and at the same time, a gradient magnetic field for obtaining positional information in the X-axis direction is applied. A two-dimensional image can be obtained by Fourier transforming the obtained information. As shown in FIG. 21, in the two-dimensional SE method, position information (image) is captured as a plane using two gradient magnetic fields of X and Y.

In the two-dimensional SE method, the measurement time (AT) is generally given by AT = TR * N _p * A _v (TR: repetition time, N _p : number of phase encoding steps, A _v : Integration count). Therefore, if any of these three parameters is reduced, the imaging time can be shortened. However, if the repetition time TR is extremely shortened, it is difficult to obtain a sufficient signal depending on the measurement target. Further, since the phase encoding step number N _p is an important parameter for determining the image resolution, shortening N _p means a decrease in the image resolution as a result. Integration number A _v is a number in the case of obtaining a plurality of times the same signal in order to improve the S / N ratio. If the same signal is taken twice, the measurement time is simply doubled (normally, the number of integrations is 4 to 16 times). In order to shorten the measurement time, it is a common method to reduce the number of integrations. However, in a biological sample in which a difference in magnetic susceptibility is noticeable depending on the part, the S / N ratio is remarkably reduced, and if the number of integration is reduced, it is strongly influenced by noise.

  Several methods for shortening the time required for imaging have been devised, and some have already been put into practical use (Non-Patent Documents 1 to 21). However, both impose a considerable compromise (deterioration) on the image itself. In particular, when a measurement of a small sample is attempted, the superiority or inferiority of the spatial resolution becomes a big problem in analyzing a fine tissue. This has been a major obstacle in investigating changes in water dynamics in vivo that occur in a short time.

Purcell EM, Torrey HC, Pound RV. Phys Rev 69:37, 1946 Bloch F, Hansen WW, Packard ME.Phys Rev 69: 127, 1946 Hahn EL.Phys Rev 80: 580, 1950 Lauterbur PC. Nature 242: 190, 1973 Damadian R. US patent 3789832, 1972 Kumar A, Welti D, Ernst RR. J Magn Reson 18:69, 1975 Manfield P, Pykett LL. J Magn Reson 29: 355, 1978 Hounsfield GN Brit J Radiol 46: 1016, 1973 R. Damadian: Science, 171, 1151, 1971. W.A.EdelsteJn et al .: Phys. Mad. Biol .. 25. 751. 1980. AoN. Garroway, et al .: JoPhys. C, 7, L458, 1974. P. Mansfield, et al .. Phys. E, 9, 271, 1976. P. Mansfield, et al .: Brit. J. Radiol., 51, 921, 1978. P. Mansfield: J. Phys. C, 10, L55, 1977. W.S.Hinshaw: Phys. Letters, 48A, 87, 1974. W.S.Hinshaw: J. Appl.Phys., 47, 3709, 1976. W.S.Hinshaw, et al .: Nature, 270, 722, 1977. W.S.Hinshaw, et al .: Brit. Jr. Radiol., 51, 273, 1978. W.S.Hinshaw, et al .: Brit. J. Radiol., 52, 36, 1979. P. Mansfield, P.R.Harvey .: Magnetic Resonance in Medicine. 29 (6). 1993. 746-758. Nobuaki Ishida, Hiromi Kano, Shujiro Ogawa Analytical Chemistry, Vol 41, 561-566, 1992

  The present invention has been made in view of the above, and a two-dimensional magnetic resonance imaging method and three-dimensional magnetic resonance capable of acquiring magnetic resonance information necessary for imaging in a short time without reducing the spatial resolution. It is an object to provide an imaging method and a magnetic resonance imaging program.

  In order to solve the above problems, the present inventors have focused on the one-dimensional measurement method that has been used for the purpose of calibration before imaging as a result of intensive research and adjusted the excitation surface in the one-dimensional measurement method. By acquiring one-dimensional magnetic resonance information, it has been found that it is possible to measure one-dimensional magnetic resonance information of a plurality of lines arranged on a measurement section from which an image is to be acquired in a short time. I came up with it.

That is, the present invention is as follows.
[1] A two-dimensional magnetic resonance imaging method for obtaining an image of a cross section of a measurement object,
A one-dimensional magnetic resonance information acquisition step of acquiring one-dimensional magnetic resonance information of each line using a one-dimensional measurement method for a plurality of different lines arranged on a measurement cross section to acquire an image;
Forming an image of the measurement cross section from one-dimensional magnetic resonance information of the plurality of lines, and
In the one-dimensional magnetic resonance information acquisition step,
Each line is excited by selectively exciting a plane that is non-parallel to the measurement cross section and intersects the measurement cross section on a line from which one-dimensional magnetic resonance information is to be acquired, and a signal emitted from each excited line. By observing
A two-dimensional magnetic resonance imaging method characterized by measuring one-dimensional magnetic resonance information of a plurality of different lines while avoiding overlapping of excitation surfaces.

[2] In the one-dimensional magnetic resonance information acquisition step,
Selectively exciting a first plane that is non-parallel to the measurement cross section and intersects the measurement cross section on a line from which one-dimensional magnetic resonance information is to be acquired;
Selectively exciting a second plane that is non-parallel to the measurement section and the first plane and intersects the measurement section and the first plane on a line from which the one-dimensional magnetic resonance information is to be acquired;
2. The two-dimensional magnetic resonance imaging method according to [1], wherein magnetic resonance information of an intersection line portion between the first plane and the second plane is acquired as one-dimensional magnetic resonance information of the line. .

[3] Exciting the first plane by a 90 ° pulse and a gradient magnetic field orthogonal to the first plane,
The two-dimensional magnetic resonance imaging method according to [2], wherein the second plane is excited by a 180 ° pulse and a gradient magnetic field orthogonal to the second plane.

[4] The two-dimensional magnetic resonance imaging method according to any one of [1] to [3], wherein the one-dimensional magnetic resonance information is magnetic resonance information of proton nuclei.

[5] The one-dimensional magnetic resonance information acquisition step of acquiring one-dimensional magnetic resonance information of each line by a multi-plane method, according to any one of [1] to [4] 2D magnetic resonance imaging method.

[6] Using the two-dimensional magnetic resonance imaging method according to any one of [1] to [5], acquiring images of a plurality of cross sections for the measurement object,
3. A three-dimensional magnetic resonance imaging method, wherein three-dimensional magnetic resonance information of the measurement object is formed from a plurality of acquired cross-sectional images.

[7] A magnetic resonance imaging program that causes a computer to execute the method according to any one of [1] to [6].

  According to the present invention, since the one-dimensional magnetic resonance information of a plurality of different lines is measured while avoiding overlapping of excitation planes, the next line can be excited immediately without waiting for the T1 relaxation time. . For this reason, it is possible to greatly shorten the imaging time without reducing the spatial resolution.

  In addition, since an image can be formed using the obtained one-dimensional magnetic resonance information as it is, the image forming processing time can be shortened.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the outline of the present invention will be described, and then the configuration, processing, and the like of the present invention will be described in detail while showing specific embodiments.

(Outline of the present invention)
FIG. 1 is a flowchart for explaining the outline of the two-dimensional magnetic resonance imaging method of the present invention. The two-dimensional magnetic resonance imaging method of the present invention is a method for acquiring an image of a cross section of a measurement object, and is arranged on a measurement cross section using a novel one-dimensional measurement method developed by the present inventors. After acquiring one-dimensional magnetic resonance information on a plurality of different lines (step S10), an image of a measurement cross section is formed using the acquired one-dimensional magnetic resonance information (step S20).

  In the present invention, a measurement object to be subjected to two-dimensional magnetic resonance imaging is an object having an atomic nucleus capable of causing a nuclear magnetic resonance phenomenon. Usually, people, animals, plants, and the like are the measurement objects.

The two-dimensional measurement method such as the two-dimensional SE method that is generally used captures position information in a plane, whereas the one-dimensional measurement method used in the present invention captures position information as a line. It is. Since the one-dimensional measurement method does not use phase encoding, one-dimensional magnetic resonance information can be obtained in a very short measurement time compared to the two-dimensional measurement method. For example, when the observation nucleus is ¹ H, the measurement can usually be performed in several seconds to several tens of seconds.

  Hereinafter, a one-dimensional measurement method will be described by taking a spin echo method as a typical spin sequence as an example. FIG. 2 is an example of a pulse sequence of the one-dimensional spin echo method. In the case of the spin echo method, a combination of the first 90 ° selective excitation pulse and the Z axis gradient magnetic field selectively excites the Z = 0 plane (first plane), and the next 180 ° selective excitation pulse and the Y axis. A plane of Y = 0 (second plane) is selectively excited by the gradient magnetic field. Therefore, what is finally observed with a spin echo formed is an intersection portion of Z = 0 (first plane) and Y = 0 (second plane). Here, if an X-axis gradient magnetic field is applied at the time of observing the spin echo signal, one-dimensional magnetic resonance information in the X direction of the intersection line portion of Z = 0 and Y = 0 can be obtained. The plane to be selectively excited (hereinafter sometimes referred to as the excitation plane) actually has a slight thickness, and this thickness is determined by the strength of the gradient magnetic field to be applied. The surface can be made thin. In the one-dimensional spin echo method, a region that emits a spin echo signal is a rod-like region in which the first plane and the second plane overlap as shown in FIG. In order to improve the spatial resolution, the cross section of the rod-like excitation region may be narrowed down by using a strong gradient magnetic field. The size of the cross section of this rod-shaped region varies depending on the measurement conditions, but is usually about 10 μm to 500 μm in both the vertical and horizontal directions.

  The feature of the one-dimensional measurement method developed by the present inventors is that when measuring the one-dimensional magnetic resonance information of each line arranged on the measurement section, the one-dimensional magnetic resonance information is acquired in parallel with the measurement section. By exciting each line by selectively exciting a plane that intersects the measurement cross section on the line, the one-dimensional magnetic resonance information of a plurality of different lines is measured while avoiding overlapping of excitation planes. For example, the above-described spin echo method is a measurement method that selectively excites two planes (Z = 0, Y = 0), but the one-dimensional measurement method developed by the present inventors is applied to the spin echo method. Selectively excites two different planes that are non-parallel to the measurement cross section.

The difference between the one-dimensional measurement method developed by the present inventors and the prior art will be described by taking as an example the case of imaging the cross section of the Z = 0 plane by the spin echo method. As shown in FIG. 4, the lines for acquiring the one-dimensional magnetic resonance information by the one-dimensional measurement method are a plurality of lines X _{1 to} X _n arranged on the measurement cross section (Z = 0). In FIG. 4, the lines X _{1 to} X _n are arranged in parallel at regular intervals on the measurement cross section.

In the conventional one-dimensional measurement method, firstly, one-dimensional magnetic resonance information is acquired for the line X ₁ , and as shown in FIG. 5A, the first plane A ₁ (Z = 0) that is the same plane as the measurement cross section. , And a second plane B ₁ (Y = n _1, where n ₁ is a real number) orthogonal to the measurement cross section is selectively excited, and is a line that is an intersection of the first plane A ₁ and the second plane B ₁ observing the spin echo signal emitted by the X _1. Similarly, for the next line X ₂ , as shown in FIG. 5B, the first plane A ₂ (Z = 0) which is the same plane as the measurement cross section and the _second plane orthogonal to the measurement cross section. The plane B ₂ (Y = n ₂ : n ₂ is a real number) is selectively excited to observe a spin echo signal emitted from the line X ₂ that is the intersection of the first plane A ₂ and the second plane B _2. .

  However, it should be noted that it is necessary to wait for the T1 relaxation time in order to excite the surface once excited. In the conventional one-dimensional measurement method, the Z = 0 plane which is the first plane is repeatedly excited every time one-dimensional magnetic resonance information of each line is measured. For this reason, before measuring the next line, the nuclei on the Z = 0 plane excited during the measurement of the previous line must be returned to the stable state of the base. This has caused a long measurement time.

  On the other hand, according to the novel one-dimensional measurement method developed by the present inventors, a plane that is not parallel to the measurement cross section is selectively excited, so that one-dimensional of a plurality of different lines is avoided while avoiding overlapping of excitation planes. It is possible to measure magnetic resonance information. For this reason, it is not necessary to wait for T1 time before measuring the next line, and the measurement time can be greatly shortened.

A novel one-dimensional measurement method developed by the present inventors will be described with reference to FIGS. First, since the line X ₁ to obtain a one-dimensional magnetic resonance information, as shown in Figure 6-1, the measurement cross-section and a non-parallel, and the first plane A ₁ intersects with the measurement section on line X _1, and the measurement section and the first plane a ₁ and non-parallel, and to selectively excite the second plane B ₁ intersecting the plane a ₁ measurement section and the first in line X _1. Then, the spin echo signal emitted from the line X ₁ that is the intersection of the first plane A ₁ and the second plane B ₁ is observed. Here, the first plane A ₁ can be selectively excited by applying a gradient magnetic field perpendicular to the first plane A ₁ when the 90 ° pulse is irradiated. Further, the second plane B ₁ can be selectively excited by applying a gradient magnetic field perpendicular to the second plane B ₁ when irradiating the 180 ° pulse.

Then, also obtains one-dimensional magnetic resonance information about line X _2. That is, as shown in Figure 6-2, the measurement cross-section and a non-parallel, and the first plane A ₂ which intersects the measuring section on line X _2, and the measurement section and the first plane A ₂ nonparallel in, and, to selectively excite the second plane B ₂ intersecting the measuring section and the first plane a ₂ on line X _2. Then, the spin echo signal emitted from the line X ₂ that is the intersection of the first plane A ₂ and the second plane B ₂ is observed. To translate the excitation plane from the first plane A ₁ to the first plane A _{2 and} to translate from the second plane B ₁ to B ₂ , it is only necessary to change the RF frequency. That is, the excitation plane is changed by changing the frequency of the 90 ° pulse to the resonance frequency corresponding to the first plane A ₂ and changing the frequency of the 180 ° pulse to the resonance frequency corresponding to the second plane B _2. It can be translated.

Thereafter, in the same manner, while changing the RF frequency, as shown in FIG. 6-3, the line X _n is also non-parallel to the measurement cross section and intersects the measurement cross section on the line X _{n. n} and the second plane B _n are selectively excited, and the spin echo signal emitted from each line is observed.

  In this way, by selectively exciting a plane that is not parallel to the measurement cross section, it is possible to avoid overlap of excitation planes that occur during measurement of each line. According to the one-dimensional measurement method developed by the present inventors, the excitation planes (the first plane A and the second plane B) do not overlap at all in the measurement of different lines. Therefore, without waiting for the T1 relaxation time. The next line can be excited immediately and the measurement time can be shortened.

The thus spin echo signals of the respective lines X ₁ to X _n obtained by performing a Fourier transform, to obtain a one-dimensional magnetic resonance information of each line X ₁ to X _n. An image of the measurement cross section can be formed by arranging the one-dimensional magnetic resonance information of each line X _{1 to} X _n in association with the position of each line on the measurement cross section.

  The one-dimensional measurement method developed by the present inventors can be applied to all pulse sequences using selective excitation pulses. That is, any pulse sequence that applies an RF pulse having a specific width in frequency with a linear gradient magnetic field applied can be applied without particular limitation. Therefore, in addition to the above-described spin echo method, for example, it can be applied to a gradient echo method, a stimulated echo method, and the like. Unlike the spin echo method, the gradient echo method and the stimulated echo method are sequences of only a 90 ° selective excitation pulse, but the 90 ° selective excitation pulse selectively excites a plane non-parallel to the measurement cross section, By observing a signal emitted from the intersection of the excited plane and the measurement cross section, it is possible to measure one-dimensional magnetic resonance information of a plurality of different lines while avoiding overlapping of the excitation planes.

  In addition, by combining the one-dimensional measurement method developed by the present inventors and the multi-fault method (multi-plane method), it becomes possible to measure a large number of measurement lines almost simultaneously, and the measurement time can be further increased. . FIG. 7 shows a conceptual diagram of a pulse sequence of the multiplane method. According to the multi-plane method, the excitation of the first line is completed, and the next line is excited during TR waiting for the recovery of magnetization, thereby acquiring one-dimensional magnetic resonance information of a large number of lines almost simultaneously. be able to. The multi-plane method is a method used when, for example, measuring several to several tens of images in the Z-axis direction almost simultaneously in a two-dimensional image on the XY plane. In the conventional one-dimensional measurement method, as described above, The multiplane method could not be applied because of the overlap of excitation planes. However, according to the one-dimensional measurement method developed by the present inventors, it is possible to avoid the overlap of the excitation planes, so that it can be used in combination with the multiplane method.

  Also, using the two-dimensional magnetic resonance imaging method of the present invention, a plurality of cross-sectional images are acquired for the measurement object, and the three-dimensional magnetic resonance imaging of the measurement object is performed by combining the acquired plurality of cross-sectional images. You can also.

As described above, by using the one-dimensional measurement method developed by the present inventors, the imaging time can be greatly shortened. For this reason, it is possible to perform two-dimensional imaging using an nuclide that is difficult to measure in the past as an observation nucleus. Since the measurement time was long in the conventional method, the observation nuclei were mainly proton nuclei with a relatively short measurement time. However, since high-speed measurement is possible in the present invention, the observation nucleus is not particularly limited as long as it is an atomic nucleus that causes a nuclear magnetic resonance phenomenon. In addition to proton nuclei, for example, ¹¹ B, ¹³ C, ¹⁴ N, ¹⁵ N , ¹⁷ O, ¹⁹ F, ³¹ P, ³³ S, ¹²⁹ Xe and the like can be measured. For this reason, the range of the in-vivo substance used as a measuring object spreads and it is useful for the diagnosis and treatment with respect to various diseases. In addition, since the time resolution can be improved, for example, it is possible to image in vivo metabolic dynamics in real time.

  Further, by using the one-dimensional measurement method developed by the present inventors, it is possible to shorten the processing time required for image analysis. In the conventional two-dimensional measurement method, when forming an image of the Z = 0 cross section from the obtained signal, it is necessary to Fourier transform the observed signal for both the X axis and the Y axis. Data obtained by Fourier transforming the signal observed for the line only to the X axis can be used for image analysis as it is. That is, the method of the present invention can reduce the processing time required for the image forming process because the Fourier transform process is uniaxially less than the two-dimensional measurement method.

(Embodiment 1)
The first embodiment is an example in which one-dimensional magnetic resonance information of each line on the measurement section Z = 0 is acquired by the spin echo method, and two-dimensional magnetic resonance imaging of the measurement section Z = 0 is performed.

In the first embodiment, the measurement section Z = 0 on the constant of each line y = a _n arranged in parallel with the X-axis direction at a pitch (a _n is a real number), by measuring the line by line one-dimensional magnetic resonance information Go. Figure 8 is a schematic diagram of a plane which is excited when measuring line y = a _n. Embodiment 1, the measurement section Z = 0 45 ° with respect to inclined planes Z + Y = a _n, and, by exciting the plane Y = a _n inclined 90 °, 1-dimensional magnetic line y = a _n Resonance information is acquired. Here, Z + Y = a _n planes, can be excited by a combination of the 90 ° pulse and ZY gradient magnetic field, Y = a _n plane can be excited by the combination of the 180 ° pulse and the Y-axis gradient magnetic field.

  One-dimensional magnetic resonance information can be acquired using a known MRI apparatus. An MRI apparatus (not shown) used for one-dimensional magnetic resonance measurement is controlled by a control device 30. FIG. 9 is a diagram showing a configuration of a control device 30 for controlling the MRI apparatus. The control device 30 includes a control unit 301 including a CPU, a memory 302, a display unit 303, an input unit 304, a Fourier transform unit 305, an image forming unit 306, a CD-ROM drive unit 307, and a disk unit 308. Are connected via a system bus A.

  The control unit 301 controls the operation of the MRI apparatus to execute a pulse sequence based on the one-dimensional measurement method developed by the present inventors. The memory 302 includes a memory such as a RAM and a ROM, and stores a program to be executed by the control unit 301 and necessary information obtained in the measurement process. The display unit 303 includes a CRT, an LCD (liquid crystal display panel), and the like, and displays various screens such as a pulse sequence setting screen and a measurement cross-section image to the user. The input unit 304 includes a keyboard, a mouse, and the like, and is used by the user to input various information such as pulse sequence measurement conditions. The Fourier transform unit 305 performs Fourier transform on the signal generated by each line observed by the MRI apparatus and converts the signal into one-dimensional magnetic resonance information of each line. The image forming unit 306 forms an image of the measurement cross section from the one-dimensional magnetic resonance information of each line.

  The illustrated CD-ROM 40 stores a program describing the magnetic resonance imaging program of the present embodiment. First, a program is installed in the disk unit 306 from the CD-ROM 40 set in the CD-ROM drive unit 305. A program read from the disk unit 106 when the MRI control apparatus is started up is stored in the memory 302. In this state, the control unit 301 (CPU) controls the static magnetic field and the gradient magnetic field applied to the measurement object and the electromagnetic wave to be irradiated according to the program stored in the memory 302, and controls the MRI apparatus. A pulse sequence based on the one-dimensional measurement method developed by the inventors is executed.

  In the present embodiment, the magnetic resonance imaging program of the present invention is provided by the CD-ROM 40. However, the recording medium of this program is not limited to this, and depends on the computer constituting the system. For example, it is also possible to use other recording media such as a magnetic disk such as a flexible disk, a magneto-optical disk, and a magnetic tape.

  Next, the processing of this embodiment will be described. First, before photographing, the user sets various measurement conditions from the input unit 304. In the first embodiment, the observation nucleus is a proton nucleus, and the measurement conditions are set as follows. It should be noted that the setting values of the measurement conditions shown below are merely examples, and it is needless to say that the setting values can be adjusted as appropriate according to the measurement purpose.

90 ° pulse width of observation nucleus: 48 [us]
Modulation of pulse attenuator value frequency domain: x_domain
Offset for frequency modulation: x_offset
Pulse width of selective excitation pulse: 1000 [us]
Attenuator value of selective excitation pulse: 23.1 [dB]
Definition of 180 ° pulse: 17.1 [dB]
180 ° pulse movement: Possible setting RF pulse modulation Movement distance per 1ppm: 0.25 [mm]
Selective excitation pulse function: Gaussian function slice height direction can be specified and moved: 5 [ppm]
X-axis magnetic field gradient refocus value (grad_1): 29.5 [%]
Z-axis magnetic field gradient (selective excitation) refocus value (grad_2): 11 [%], 0 [%] → 60 [%]: 0.1 [%];
Z axis magnetic field gradient refocus value (grad_3): -6 [%]
Y axis magnetic field gradient (selective excitation) refocus value (grad_4): -3.5 [%]
Specified time (grad_recover time): 0.3 [ms]
T2 time and its limit values: 0.2 [ms], 0.1 [ms] → 300 [s]: 0.1 [ms]
Waiting time to start measurement: 1.0 [s]
Relaxation time and its limit values: 1.0 [s], 0.1 [s] → 300 [s]: 0.1 [s]

After defining the measurement _{conditions, y = a 1, y =} a 2, y = a 3, in the order of ··· y = a _n, we obtain the one-dimensional magnetic resonance information of each line. FIG. 10 is a flowchart for executing a pulse sequence for measuring one-dimensional magnetic resonance information of each line. First, a predetermined waiting time is waited until the measurement is started (step S111).

Then, to excite the Z + Y = a _n plane 90 ° pulse and ZY gradient fields. First, a Z-axis gradient magnetic field is applied at grad2, waits for 100 μsec (step S121), a Y-axis gradient magnetic field is applied at grad2, waits for grad_recover (step S122), and a selective excitation pulse (90 ° pulse) is applied (step) S123). Here, RF frequency of the selected excitation pulses is set to a predetermined resonant frequency to excite the Z + Y = a _n plane. Next, after turning off the Z-axis gradient magnetic field and waiting for 100 μsec (step S124), the Y-axis gradient magnetic field is turned off and waiting for T2 time (step S125).

After exciting the Z + Y = a _n plane, in order to obtain a normal spin echo signal, applying a refocusing gradient field. The X-axis gradient magnetic field is applied at grad1, the Y-axis gradient magnetic field is applied at grad4, the Z-axis gradient magnetic field is applied at grad3, and a half of the signal acquisition time is awaited (step S131). Next, the X, Y, and Z axis gradient magnetic fields are turned off, and a grad_recover time is awaited (step S132).

After applying the refocus gradient field to excite Y = a _n plane 180 ° pulse and Y-axis gradient magnetic field. First, a Y-axis gradient magnetic field is applied at grad2, waits for grad_recover time (step S141), and a selective excitation pulse (90 ° pulse) is applied (step S142). RF frequency of the selected excitation pulses for irradiating here is set to a predetermined resonant frequency to excite the Y = a _n plane. Next, the Y-axis gradient magnetic field is turned off, and the process waits for T2 time (step S143). Then, it waits for grad_recover time (step S144).

After exciting the Z + Y = a _n plane and Y = a _n plane, y = a ₁ as the intersection section of the two planes observes spin echo signals emanating. First, in order to capture data, an X-axis gradient magnetic field is applied, and 40 μsec is waited (step S151). Then, captures the spin echo signals generated by the y = a _n, wear X-axis gradient magnetic field (step S152).

Thus, the spin echo signals for each line on the measurement cross-section _{Z = 0, y = a 1} , y = a 2, y = a 3, will get in the order of ··· y = a _n. To measure the next line by shifting the measurement line by one pitch, the RF frequency of selective excitation may be changed. The pitch (slice thickness) of each line can be set as appropriate, but is set to 0.5 mm in the present embodiment.

  The Fourier transform unit 305 performs Fourier transform on the observed spin echo signal of each line and stores it in the memory 302 as one-dimensional magnetic resonance information of each line.

  The image forming unit 306 reads the one-dimensional magnetic resonance information of each line from the memory 302 and arranges the position of each line and the one-dimensional magnetic resonance information of each line in association with each other, thereby arranging the measurement cross section (Z = 0). Form an image. The obtained image is displayed on the display unit 303 and can be confirmed by the user.

  As described above, in the first embodiment, the 90 ° pulse is inclined by 45 ° and the 180 ° pulse is inclined by 90 ° with respect to the measurement cross section, thereby avoiding the overlap of excitation planes. Dimensional magnetic resonance information measurement is possible.

(Embodiment 2)
The second embodiment is an application example of the first embodiment, and is an example in which a 90 ° pulse and a 180 ° pulse are respectively inclined by 45 ° to acquire a cross-sectional image of Z = 0. In the second embodiment, since the configuration and processing other than the pulse sequence are the same as those in the two-dimensional magnetic resonance imaging method of the first embodiment, the description thereof is omitted.

FIG. 11 is a schematic diagram of a plane excited in the second embodiment. In the second embodiment, the measurement section Z + 45 ° inclined plane Z with respect to = 0 Y = a _n, and, by exciting the plane Z-Y = a _n inclined 45 °, on the measurement cross-section Z = 0 and obtaining the 1-dimensional magnetic resonance information for each line y = a _n. Here, Z + Y = a _n planes, can be excited by a combination of the 90 ° pulse and ZY gradient magnetic field, Y = a _n plane can be excited by the combination of the 180 ° pulse and ZY gradient fields.

FIG. 12 shows a pulse sequence used for measuring one-dimensional magnetic resonance information in the second embodiment. FIG. 13 is a flowchart for executing the pulse sequence of the second embodiment. In the same manner as the first embodiment, firstly, waits for a predetermined waiting time until the start of the measurement (step S 111), exciting the Z + Y = a _n plane 90 ° pulse (step S121～125), a refocusing gradient (Steps S131 to 132).

In the second embodiment, after applying the refocus gradient field, as it follows, to excite the Z-Y = a _n plane 180 ° pulse. First, a Y-axis gradient magnetic field is applied at grad2, waits for 100 μsec (step S201), a Z-axis gradient magnetic field is applied at −grad2, waits for grad_recover time (step S202), and a selective excitation pulse (180 ° pulse) is applied ( Step S203). Next, after turning off the Y-axis gradient magnetic field and waiting for 100 μsec (step S204), the Z-axis gradient magnetic field is turned off and waiting for T2 time (step S205). Then, it waits for grad_recover time (step S206).

After exciting the Z + Y = a _n plane and Z-Y = a _n plane, in the same manner as in the first embodiment, y = a ₁ as the intersection section of the two planes observes spin echo signals emanating (step S151, 152).

In this way, the one-dimensional magnetic resonance information for each line on the measurement cross-section _{Z = 0, y = a 1} , y = a 2, y = a 3, will get in the order of ··· y = a _n be able to.

  As described above, in the second embodiment, the 90 ° pulse and the 180 ° pulse are inclined by 45 ° with respect to the measurement cross section, thereby avoiding the overlap of the excitation planes and performing one-dimensional magnetic resonance of a plurality of different lines. Information measurement is possible.

(Embodiment 3)
The third embodiment is an example in which a 90 ° pulse and a 180 ° pulse are inclined 45 °, respectively, and an image of a cross section of Y = 0 is acquired. In the third embodiment, since the configuration and processing other than the measurement cross section and the pulse sequence are the same as those in the two-dimensional magnetic resonance imaging method of the first embodiment, description thereof will be omitted.

FIG. 14 is a schematic diagram of a plane excited in the third embodiment. In the third embodiment, the measurement cross-section Y = 0 on the constant of each line arranged parallel to the X-axis direction at a pitch z = a _n (a _n is a real number), 45 ° respectively inclined with respect to the measured cross-section Y = 0 by exciting the plane Z + Y = a _n and the plane Z-Y = a _n was, and obtains one-dimensional magnetic resonance information. Here, Z + Y = a _n planes, can be excited by a combination of the 90 ° pulse and ZY gradient magnetic field, ZY = a _n plane can be excited by the combination of the 180 ° pulse and ZY gradient .

  FIG. 15 shows a pulse sequence used for measuring one-dimensional magnetic resonance information in the third embodiment. FIG. 16 is a flowchart for executing the pulse sequence of the third embodiment.

In the same manner as the first embodiment, firstly, waits for a predetermined waiting time until the start of the measurement (step S 111), exciting the Z + Y = a _n plane 90 ° pulse (step S121～125), a refocusing gradient (Steps S131 to 132).

In the third embodiment, after applying the refocus gradient field, as it follows, to excite the Z-Y = a _n plane 180 ° pulse. First, a Y-axis gradient magnetic field is applied at -grad2, waits for 100 μsec (step S301), a Z-axis gradient magnetic field is applied at grad2, waits for grad_recover time (step S302), and a selective excitation pulse (180 ° pulse) is applied ( Step S303). Next, after turning off the Y-axis gradient magnetic field and waiting for 100 μsec (step S304), the Z-axis gradient magnetic field is turned off and waiting for T2 time (step S305). Then, it waits for grad_recover time (step S306).

After exciting the Z + Y = a _n plane and Z-Y = a _n plane, in the same manner as in the first embodiment, z = a _n which is a intersection section of the two planes observes spin echo signals emanating (step S151, 152).

In this way, the one-dimensional magnetic resonance information for each line on the measurement cross-section _{Y = 0, z = a 1} , z = a 2, z = a 3, will get in the order of ··· z = a _n be able to.

  As described above, the third embodiment enables one-dimensional magnetic resonance information measurement of a plurality of different lines while avoiding overlapping of excitation planes even when the measurement cross section Y = 0.

(Embodiment 4)
Embodiment 4 is an example of application of the second embodiment, the multi-plane method, substantially simultaneously measures the one-dimensional magnetic resonance information measuring section Z = 0 on the line y = a _n of (a _n is a real number) This is an example. In the fourth embodiment, the configuration and processing other than using the multi-plane method are the same as those in the two-dimensional magnetic resonance imaging method of the second embodiment, and thus the description thereof is omitted.

FIG. 17 is a flowchart for executing the pulse sequence of the fourth embodiment. In the fourth embodiment, by applying the multi-plane method, measuring cross the line y = a ₁ on _{Z = 0, y = a 2} , y = a 3, 1 -dimensional magnetic ··· y = a _n The resonance information is continuously measured.

  First, a predetermined waiting time is waited until the measurement is started (step S111).

In the fourth embodiment, by applying a selected excitation pulse with modulation frequency, continuously exciting the Z + Y = a _n plane. First, a Z-axis gradient magnetic field is applied at grad2, waits for 100 μsec (step S401), a Y-axis gradient magnetic field is applied at grad2, waits for grad_recover (step S402), and a selective excitation pulse (90 ° pulse) is modulated while modulating the frequency. Is applied (step S403). By applying a selected excitation pulse with modulation _{frequency, Z + Y = a 1,} Z + Y = a 2, ···, it is possible to substantially simultaneously excite Z + Y = a _n plane. Here, for example, the frequency is set to be modulated in steps of −20 ppm to 1 ppm. Next, after turning off the Z-axis gradient magnetic field and waiting for 100 μsec (step S404), the Y-axis gradient magnetic field is turned off and waiting for T2 time (step S405).

After continuously excites the Z + Y = a _n plane, as in the second embodiment, applying a refocusing gradient (step S131～132), to excite the Z-Y = a _n plane 180 ° pulse (step S201~206), Z + Y = a n plane and Z-Y = a _n a intersection section of the plane y = a _n observes spin echo signals emanating (step S151,152).

Thus, the pulse sequence using a multi-plane method, measuring cross the line y = a ₁ on _{Z = 0, y = a 2} , y = a 3, 1 -dimensional magnetic resonance ··· y = a _n Information can be acquired at once.

  As described above, the fourth embodiment can measure the one-dimensional magnetic resonance information of a plurality of different lines on the measurement cross section almost simultaneously by applying the multi-plane method. It can be shortened.

(Embodiment 5)
The fifth embodiment is an application example of the third embodiment, the multi-plane method, substantially simultaneously measures the one-dimensional magnetic resonance information measuring section Y = 0 on each line z = a _n of (a _n is a real number) This is an example. In the fifth embodiment, the configuration and processing other than using the multi-plane method are the same as those in the two-dimensional magnetic resonance imaging method of the third embodiment, and thus the description thereof is omitted.

FIG. 18 is a flowchart for executing the pulse sequence of the fifth embodiment. In the fifth embodiment, by applying the multi-plane method, the measurement cross-section Y = 0 the on line _{z = a 1, z = a} 2, z = a 3, 1 -dimensional magnetic ··· z = a _n The resonance information is continuously measured.

  First, a predetermined waiting time is waited until the measurement is started (step S111).

Then, as in the fourth embodiment, by applying a selected excitation pulse with modulation frequency, continuously exciting the Z + Y = a _n planes (step S401~405).

After continuously excites the Z + Y = a _n plane, as in the third embodiment, applying a refocusing gradient (step S131～132), to excite the Z-Y = a _n plane 180 ° pulse (step S301~306), Z + Y = a n plane and Z-Y = a _n a intersection section of the plane y = a _n observes spin echo signals emanating (step S151,152).

Thus, the pulse sequence using a multi-plane method, measuring cross the line z = a ₁ on _{Y = 0, z = a 2} , z = a 3, 1 -dimensional magnetic resonance ··· z = a _n Information can be acquired at once.

  As described above, in the fifth embodiment, the measurement time can be shortened even when the measurement cross section Y = 0 and by applying the multi-plane method to the measurement cross section Y = 0.

  As mentioned above, although the example of embodiment of the two-dimensional magnetic resonance imaging method of this invention was shown, a measurement cross section and a pulse sequence are not limited to these embodiment.

  That is, the measurement cross section is not limited to Z = 0 and Y = 0, and any cross section can be measured as long as it is planar. For example, Z = 1, X + Y + Z = 3 plane, etc. Two-dimensional imaging is possible.

Moreover, since various planes can be selectively excited by a combination of the RF frequency and the gradient magnetic field, various variations can be considered for the pulse sequence. For example, when making a ZY gradient magnetic field in the 90 ° pulse, if the gradient magnetic field strength in the Y-axis direction to half of the gradient magnetic field strength in the Z-axis direction can selectively excite the Z + (Y / 2) = a n plane. At this time, the gradient magnetic field intensity in the Y-axis direction is halved, and the selection width in the Y-axis direction (the thickness of the excitation surface in the Y-axis direction) is doubled. The same operation is possible for the 180 ° pulse.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following Example.

<Example 1>
Using the pulse sequence described in Embodiment 2, one-dimensional magnetic resonance information was acquired by a one-dimensional measurement method, and two-dimensional magnetic resonance imaging was performed. The measurement apparatus, measurement sample, and measurement conditions are as follows. The time required for the measurement in Example 1 was 22 seconds.

(a) Measuring device JNM-ECA500WB manufactured by JEOL Ltd.
Imaging probe DOTY 20mm probe
(b) Measurement sample Phantom CuSO ₄ aqueous solution
(c) Measurement conditions
FOV = 20 * 20
Number of measurement points: 256
Slice thickness: 0.5mm
RG (receiver gain) = 36
TE (echo time) = 0.2msec
TR (repetition time) = 5 sec
90 ° pulse = 49μsec
Integration count: 2 times

<Example 2>
Using the pulse sequence described in the fourth embodiment, one-dimensional magnetic resonance information was acquired by a one-dimensional measurement method using a multiplane method, and two-dimensional magnetic resonance imaging was performed. The measurement conditions are as follows. The same measurement apparatus and measurement sample as in Example 1 were used. The time required for the measurement in Example 2 was 20 seconds. The measurement results are shown in FIG. The upper figure of FIG. 19-1 is the obtained cross-sectional image, and the lower figure is the signal intensity on the AA ′ line in the cross-sectional image.

FOV = 20 * 20
Number of measurement points: 256
Slice thickness: 0.5mm
RG (receiver gain) = 36
TE (echo time) = 0.2msec
TR (repetition time) = about 5 seconds
90 ° pulse = 49μsec
Integration count: 2 times

<Comparative Example 1>
Two-dimensional magnetic resonance imaging was performed by the two-dimensional SE method. The measurement conditions are as follows. The same measurement apparatus and measurement sample as in Example 1 were used. The time required for the measurement in Example 2 was 42 minutes 45 seconds. The measurement results are shown in Fig. 19-2. The upper figure of FIG. 19-2 is the obtained cross-sectional image, and the lower figure is an image analysis software (Scion Image By Scion Corporation URL: http://www.scioncorp.com/index.htm) from the cross-sectional image. Is the signal intensity on the BB ′ line analyzed using.

FOV = 20 * 20
Number of measurement points: 256 * 256 (2D)
Slice thickness: 0.5mm
RG (receiver gain) = 36
TE (echo time) = 0.2msec
TR (repetition time) = 5 sec
90 ° pulse = 49μsec
Integration count: 2 times

  In Examples 1 and 2, it was possible to capture an image with a measurement time of 1/100 or less compared to Comparative Example 1 using the two-dimensional SE method. In Examples 1 and 2, the signal obtained using the one-dimensional measurement method was completely inferior to the signal extracted from the two-dimensional image of Comparative Example 1. When comparing FIG. 19-1 and FIG. 19-2, a slight difference in signal intensity is seen between the one-dimensional measurement method and the two-dimensional SE method. This is because Comparative Example 1 is analyzed after performing Fourier transform on both the X axis and Y axis, whereas in Example 2, data obtained by performing Fourier transform only on the X axis can be used for immediate signal analysis. It is thought to be caused by. That is, in Comparative Example 1, it is considered that there is a difference in data because Fourier transformation is performed by one axis. Therefore, it is more accurate to directly analyze the signal intensity by the one-dimensional measurement method as in the present invention than to analyze the signal intensity after obtaining the image by the two-dimensional SE method as in Comparative Example 1. It is thought that data can be acquired.

  As described above, the nuclear magnetic imaging method according to the present invention can acquire magnetic resonance information necessary for imaging in a short time without lowering the spatial resolution, and therefore requires a measurement speed in the medical field or research. Can be widely used in various fields.

It is a flowchart for demonstrating the outline | summary of the two-dimensional magnetic resonance imaging method of this invention. It is a pulse sequence of the one-dimensional spin echo method. It is a schematic diagram which shows the excitation surface and signal observation area | region by a one-dimensional spin echo method. It is a schematic diagram which shows an example of the line which acquires 1-dimensional magnetic resonance information. Is a schematic view showing a state when the excitation of the line X ₁ by a conventional one-dimensional measurement. Is a schematic view showing a state when the excitation of the line X ₂ by the conventional one-dimensional measurement. Is a schematic view showing a state when the excitation of the line X ₁ by 1-dimensional measurement method of the present invention. Is a schematic view showing a state when the excitation of the line X ₂ by a one-dimensional measurement method of the present invention. It is a schematic diagram which shows the state at the time of the excitation of the line _Xn by the one-dimensional measuring method of this invention. It is a conceptual diagram of the pulse sequence of a multiplane method. 3 is a schematic diagram of a plane excited in the first embodiment. FIG. It is a block diagram of the control apparatus 30 which controls an MRI apparatus. 3 is a flowchart for executing the pulse sequence of the first embodiment. 6 is a schematic diagram of a plane excited in the second embodiment. FIG. 6 is a pulse sequence used for measurement of one-dimensional magnetic resonance information in the second embodiment. 6 is a flowchart for executing a pulse sequence according to the second embodiment. FIG. 10 is a schematic diagram of a plane excited in the third embodiment. 6 is a pulse sequence used for measuring one-dimensional magnetic resonance information in the third embodiment. 10 is a flowchart for executing the pulse sequence of the third embodiment. 10 is a flowchart for executing the pulse sequence of the fourth embodiment. 10 is a flowchart for executing the pulse sequence of the fifth embodiment. It is a table | surface which shows the signal strength on the AA 'line in the cross-sectional image obtained by Example 2, and the said cross-sectional image. It is a graph which shows the signal strength on the BB 'line in the cross-sectional image obtained by the comparative example 1, and the said cross-sectional image. It is a pulse sequence of the two-dimensional SE method. It is a conceptual diagram of two-dimensional SE method.

Claims (7)

A two-dimensional magnetic resonance imaging method for obtaining a cross-sectional image of a measurement object,
A one-dimensional magnetic resonance information acquisition step of acquiring one-dimensional magnetic resonance information of each line using a one-dimensional measurement method for a plurality of different lines arranged on a measurement cross section to acquire an image;
Forming an image of the measurement cross section from one-dimensional magnetic resonance information of the plurality of lines, and
In the one-dimensional magnetic resonance information acquisition step,
Each line is excited by selectively exciting a plane that is non-parallel to the measurement section and intersects the measurement section on a line from which one-dimensional magnetic resonance information is to be acquired, and a signal generated by each excited line By observing
A two-dimensional magnetic resonance imaging method characterized by measuring one-dimensional magnetic resonance information of a plurality of different lines while avoiding overlapping of excitation surfaces. In the one-dimensional magnetic resonance information acquisition step,
Selectively exciting a first plane that is non-parallel to the measurement cross section and intersects the measurement cross section on a line from which one-dimensional magnetic resonance information is to be acquired;
Selectively exciting a second plane that is non-parallel to the measurement section and the first plane and intersects the measurement section and the first plane on a line from which the one-dimensional magnetic resonance information is to be acquired;
2. The two-dimensional magnetic resonance imaging method according to claim 1, wherein magnetic resonance information of an intersection line portion between the first plane and the second plane is acquired as one-dimensional magnetic resonance information of the line. . Exciting the first plane with a 90 ° pulse and a gradient magnetic field orthogonal to the first plane;
The two-dimensional magnetic resonance imaging method according to claim 2, wherein the second plane is excited by a 180 ° pulse and a gradient magnetic field orthogonal to the second plane.   The two-dimensional magnetic resonance imaging method according to claim 1, wherein the one-dimensional magnetic resonance information is magnetic resonance information of proton nuclei.   5. The two-dimensional magnetic resonance according to claim 1, wherein, in the one-dimensional magnetic resonance information acquisition step, the one-dimensional magnetic resonance information of each line is acquired by a multi-plane method. Imaging method. Using the two-dimensional magnetic resonance imaging method according to any one of claims 1 to 5, acquiring images of a plurality of cross sections for the measurement object,
3. A three-dimensional magnetic resonance imaging method, wherein three-dimensional magnetic resonance information of the measurement object is formed from a plurality of acquired cross-sectional images.   A magnetic resonance imaging program that causes a computer to execute the method according to claim 1.

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