JPH08299299A - Method for simultaneously photographing plural slices for magnetic resonance diagnostic device - Google Patents

Abstract

PURPOSE: To make it possible to simultaneously embody excitation and to set the slice intervals to be simultaneously excited freely to some extent by forming the plural waveforms formed by multiplying a basic waveform by a desired function as the waveform of amplitude modulation and executing photography by impression of the high-frequency magnetic fields subjected to the amplitude modulation with the respective waveforms. CONSTITUTION: The photographing for one encoding-component is executed by using an amplitude modulation waveform RF1(t) for a 90 deg. pulse 101 by initially setting the encoding value of photographing sequence and the photographing for the one encoding-component is executed by using an amplitude modulation waveform RF2(t) for the 90 deg. pulse 101. Further, the photographing for the one encoding-component is executed by using an amplitude modulation waveform RF3(t) for the 90 deg. pulse 101 and the photographing for one encoding component is executed by using an amplitude modulation waveform RF4(t) for the 90 deg. pulse 101. The photographing operation is ended if the encoding value attains the prescribed value. The signals are then separated to the signals of the respective slices by executing sepn. calculation 104. The images of the respective slices are obtd. by executing image reconstitution with each of the respective separated signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simultaneously imaging a plurality of slices in a magnetic resonance diagnostic apparatus, that is, a method for efficiently measuring data in the magnetic resonance diagnostic apparatus.

[0002]

2. Description of the Related Art As prior art relating to the present invention, the techniques described in the following documents (1) to (5) are known. References (1) Author: AA Maudsley Title: "Multiple-Line-Scanning Spin Densit
y Imaging "Journal: Journal of Magnetic Resonance, vol.41,
pp.112-126 (1980). Reference (2) Author: CH Oh, HW Park, and ZH Cho Title: "Line-Integral Projection Reconstruc
tion (LPR) with Slice Encoding Techniques: Multislice R
egional Imaging inNMR Tomography "Papers: IEEE Transaction on Medical Imagin
g, vol.MI-3, no.4 (1984). Reference (3) Authors: SP Souza, J. Szumowski, CL Dumouli.
n, DP Plewes, and G. Glover Title: "SIMA: Simultaneous Multislice Ac
quisition of MRImages by Hadamard-Encoded E
xcitation Journal: Journal of Computer Assoced Tomograph
y, vol.12, no.6 (1988).

Reference (4) Author: GH Glover, and A. Shimakawa Title: "POMP (Phase Offset Multi-Plana)
r) Imaging: A newhight efficiency technique. Proceedings of the conference: Society of Magnetic Resonance i
n Medicine, 7-th Annual Scientific Meeting and
Exhibition, Brook of Abstracts, p. 241 (1988). Reference (5) Author: J. Taguchi, K. Sano, and T. Yokoyama Title: "Double Slice Imaging by Using Two"
Type of 90 ° RF Pulse Shape "Conference Meeting Reprint: Society of Magnetic Resonance i
n Medicine, 10-th Annual Scientific Meeting and
Exhibition, Brook of Abstracts, wip, p.1177 (199
1).

The above-mentioned document (1) describes a method of exciting a plurality of slices at the same time for measurement in the case of imaging by the line scan method, and then performing image reconstruction by separating each line by a subsequent calculation. . Then, as a means for exciting the lines at the same time, a method of performing 4-channel type amplitude modulation is described. That is, a single vibration wave vibrating at a predetermined reference frequency is shunted into four channels, each channel has a phase of 0 °, 90 °, 180 °, 270 °, and an independent amplitude for each channel. Modulation is performed.
As described in the above reference (1), the 0 ° channel is 180
Basically, the same function is achieved only by different signs from the 0 ° channel, and the 90 ° channel and the 270 ° channel also have the same function.
And 90 ° two-channel amplitude modulation. In the above reference (2), when a slice image is obtained by imaging with the line integral scan method, a plurality of slices are excited and measured at the same time, and the image is reconstructed by dividing each slice by a subsequent calculation. The method is described.
The method of creating the high-frequency magnetic field used for the simultaneous excitation means of each slice is the same as in the above-mentioned document (1).

The above-mentioned document (3) is a method of simultaneously exciting each slice by imaging by the two-dimensional Fourier transform method and similarly to the above-mentioned document (2). For the method of simultaneous excitation, refer to the above document.
Similar to (1) and (2), the two-channel modulation method is specifically described in an easy-to-understand manner. In reference (3), 0
The ° channel is called the I channel, and the 90 ° channel is called the Q channel.
° The term channel is briefly described below. For example, when simultaneously exciting two slices, amplitude modulation of sinc (at) cos (ω ₀ t) is performed only on the 0 ° channel in the first measurement, and −si is applied only to the 90 ° channel in the next measurement.
It is described that amplitude modulation of nc (at) sin (ω ₀ t) is performed. Here, the function sinc (x) = sinx / x. Four
If two slices are excited at the same time, sinc (at) ・ cos (ω ₀ t)
Amplitude modulation of (2ω ₀ t) is performed, and in the second measurement, amplitude modulation of −sinc (at) ・ sin (ω ₀ t) ・ sin (2ω ₀ t) is performed only for the 0 ° channel and the third measurement is performed. Then, the amplitude modulation of −sinc (at) · cos (ω ₀ t) · sin (2ω ₀ t) is performed only on the 90 ° channel, and −sinc (a
It is described that it can be understood that amplitude modulation of t) · sin (ω ₀ t) · cos (2ω ₀ t) is performed.

Further, in the above-mentioned document (4), the above-mentioned (1) to (3)
Is a modification of the Hadamard-type simultaneous excitation, and the excitation method of the simultaneous excitation is devised so that the image of each slice can be separated and reproduced only by arranging the signals and performing Fourier transform. However, the method for realizing simultaneous excitation requires two-channel type amplitude modulation or a special high-frequency magnetic field generation mechanism as in the documents (1) to (3). The methods of the above literatures (1) to (4) are all
It cannot be realized by one-channel type amplitude modulation having only 0 ° channel. On the other hand, the above-mentioned document (5) describes one method for realizing the function of simultaneous excitation by limiting the number of slices to two even with one-channel type amplitude modulation. In the first excitation, the amplitude modulation mainly having the cos component is performed, and in the second excitation, the amplitude modulation mainly having the sin component is performed. This technique has the drawback that only two slices can be excited simultaneously and that the interval between the two slices cannot be set freely.

[0007]

From the above prior art (1)
In (4), realization means such as performing 2-channel type amplitude modulation, having a high frequency magnetic field generating mechanism similar to it, or having a special high frequency magnetic field generating function limited to that function is necessary. However, there is a problem that it cannot be realized by a device that performs only one-channel type amplitude modulation, which is the minimum required for a magnetic resonance diagnostic device. In addition, the above conventional technology (5)
However, as in the above-mentioned conventional techniques (1) to (3), there is a problem that simultaneous excitation of four, eight, etc. cannot be performed and the interval between two simultaneously excited slices cannot be freely set. The present invention has been made in view of the above circumstances, and an object thereof is to solve the above-mentioned problems in the conventional art,
Even in a device that only performs 1-channel type amplitude modulation, simultaneous excitation similar to the Hadamard type simultaneous excitation described in the related arts (1) to (3) was realized, and simultaneous excitation of 4, 8, etc. was realized. , Slice intervals for simultaneous excitation can be set to some extent,
An object of the present invention is to provide a simultaneous imaging method for a plurality of slices in a magnetic resonance diagnostic apparatus.

[0008]

The above object of the present invention is to generate static magnetic field, gradient magnetic field and high frequency magnetic field, detecting means for measuring a magnetic resonance signal from an object to be inspected, and various detected signals. In a magnetic resonance diagnostic apparatus having a calculation means for performing a calculation, a high-frequency magnetic field generation means for performing one-channel type amplitude modulation, and a means for controlling execution of each of the means,
As the waveform of the amplitude modulation, a plurality of waveforms created by multiplying a predetermined basic waveform by a desired function is created, and a high-frequency magnetic field amplitude-modulated with each waveform of the plurality of waveforms is applied to obtain an image. By simultaneously exciting a plurality of slice portions, to obtain each measurement signal that changed the way of excitation of the plurality of slices according to each waveform, to the signal of each slice using the plurality of measurement signals A signal for each slice is created by performing a separation operation for separation, and based on the signal for each slice,
This is achieved by a method for simultaneously imaging a plurality of slices in a magnetic resonance diagnostic apparatus, which is characterized by reconstructing each slice image.

More specifically, the following waveform RF _k (t) is used as the amplitude modulation waveform for one channel.

(Equation 5) Where t is time, T is high-frequency magnetic field application time, and k is 1
To (n to the power of 2), RF ₀ (t) is a predetermined basic waveform, RF _k (t) is the k-th desired function, and ω k is k
Is a constant that represents the desired frequency, n is an integer, the number of slices to be simultaneously imaged is (2 to the nth power), and j is 1 to n.
Up to an integer, b _j is an integer that takes either 0 or 1,
A value when k is expressed by the following equation 2 which is similar to a binary number.

(Equation 6)

As an example, the case of simultaneously exciting four slices will be shown below. For four slices,
When n = 2, k takes a value from 1 to 4, and the equation (1) takes four forms from the following equations (3) to (6).

(Equation 7)

(Equation 8)

[Equation 9]

[Equation 10] Signal data is measured by irradiating a high-frequency magnetic field amplitude-modulated using the amplitude modulation waveforms RF1 (t) to RF4 (t) described above. In the first measurement, amplitude modulation of RF1 (t) is performed and 2
RF2 (t) in the third measurement, RF3 (t) in the third measurement,
Amplitude modulation of RF4 (t) is performed in the fourth measurement.

Assuming that the measurement data obtained by the four measurements are data1, data2, data3, and data4, respectively, the separation calculation shown in the following equations (7) to (10) is performed, and each slice is processed. Separated data slice1, slice2, slice3, sli
get ce4

[Equation 11]

(Equation 12)

(Equation 13)

[Equation 14] The separation operation of the above equations (7) to (10) is performed to create the separated data for each slice, and the image is reconstructed to obtain the image of each slice. The measurement data and the data separated into each slice are complex numbers, and in the magnetic resonance diagnostic apparatus, one of the measurement data of two channels obtained by quadrature detection or the like is associated with real number data and the other is associated with imaginary number data. There is. I in the above formulas (7) to (10) is an imaginary unit. As above, when the number of slices is 4, the formula (3) to the formula
Measurement is performed with a high frequency magnetic field using the amplitude modulation waveform shown in (6), and based on the obtained measurement data, separation data is obtained by performing the separation calculation shown in Expressions (7) to (10). , The separated data is image-reconstructed to obtain each slice image.

[0012]

The operation of the simultaneous multi-slice imaging method according to the present invention is as follows. When a high-frequency magnetic field is applied assuming a uniform object, a signal amount calculated from each value in the slice direction is calculated and called a slice profile. Magnetization is a vector having a magnitude and a direction, and when the static magnetic field direction is taken as the Z axis, it initially faces the Z axis direction and changes its direction by the application of a high frequency magnetic field, and has a component on the XY plane. The XY plane component of the magnetization is proportional to the signal amount of the magnetization. The manner in which the magnetization changes direction as described above can be described by the Bloch equation. The Bloch equation can be numerically solved by giving a waveform of a high frequency magnetic field, and the slice profile can be calculated. A method for solving the Bloch equation and optimizing the high frequency magnetic field waveform is described in the following document (6), for example. Reference (6) Author: Steven Conolly, Dwight Nishimur
a, Albert Macovski Title: Optimal Control Solutions to the Mag
netic ResonanceSelective Excitation Problem Paper: IEEE Trans. on Medical Imaging, vo
l.MI-5, No.2 (1986).

FIG. 10 shows an example in which a slice profile obtained by applying a high-frequency magnetic field waveform according to the present invention is calculated based on the method of the above-mentioned document. The slice profile 110 of FIG. 10 is a case where a waveform based on the following equation (11) is used as the predetermined basic waveform RF ₀ (t).

(Equation 15) Using the basic waveform RF ₀ (t) shown in equation (11), the above equation
When n = 2, ω ₁ = 4π, and ω ₂ = 8π in (1), that is, the formula (11) is used for RF ₀ (t) in the formulas (3) to (6),
When ω ₁ = 4π and ω ₂ = 8π, four types of amplitude modulation waveforms are described as RF1 (t) to RF4 (t), and
It is shown in (12) to equation (15).

[Equation 16]

[Equation 17]

(Equation 18)

[Formula 19]

Using the amplitude modulation waveforms RF1 (t) to RF4 (t) of the high-frequency magnetic field shown in the above equations (12) to (15), the magnetizations are respectively excited with an applied strength that excites the desired magnetization by 90 degrees. The slice profile when excited is shown in FIG. Vertical numbers 1 to 4 in FIG. 10 are amplitude modulation waveforms RF1.
(t) to RF4 (t), and the horizontal axis corresponds to the slice direction position. The slice profile 110 is
It is a plot of how much the magnetization uniformly distributed in the slice axis direction produces a signal amount by the application of a high-frequency magnetic field. It depends on which direction on the XY plane the projected component of the XY plane of the magnetization is. , The phase of the emitted electromagnetic wave signal becomes different. Here, the signal emitted when the magnetization is directed to the X axis is defined as a real number (Real), and the case where the magnetization is directed to the Y axis is an imaginary number (Imaginaly) (abbreviated below,
Defined as "Imag") and treats the signal as a complex number.

In FIG. 10, the slice profile 112 in the Real direction and the slice profile 122 in the Imag direction are shown, and the absolute value is calculated from the two to show the slice profile 102 of the absolute value. From the figure, the first and fourth high-frequency magnetic fields have many components in the Real direction 112, and the second and third high-frequency magnetic fields are Imag.
It can be seen that there are many components in the direction 122. Here, the profile was calculated by setting the applied intensity for exciting the desired magnetization by 90 °, but the high frequency magnetic field for exciting the desired magnetization by 90 ° is called a 90 ° pulse. FIG. 1 shows each pulse waveform and a slice profile 102 of an absolute value when the pulse is applied, when the high-frequency magnetic field waveforms of the above equations (12) to (15) are used as the 90-degree pulse 101. FIG. 6 shows a slice profile 103 of absolute values when the separation calculation 104 using the above formulas (7) to (10) is performed to separate each slice.

When RF1 (t) is applied, a slice profile of P1 (z) is obtained, and similarly P2 (z), P3 (z),
A slice profile of P4 (z) is obtained. Further, when the separation calculation 104 is performed, the separated slice profiles of S1 (z) to S4 (z) can be obtained. As described above, as an example is shown in the simulation, it is possible to simultaneously excite a plurality of slices by using the high-frequency magnetic field of the equation (1) and separate them into each slice by the subsequent calculation. The following is a brief summary to clarify the difference between the present invention and the prior art.
The amplitude modulation waveform is represented by the following equation (16) by comparing the method of the prior art document (3) with the present invention.

(Equation 20)

A formula representing an amplitude modulation waveform in the prior art
(16) is different from Expression (1) of the amplitude modulation waveform according to the present invention only in that the term of sin is added with i representing an imaginary unit. However, the imaginary unit i indicates that the high-frequency magnetic field is treated as an imaginary number, the real part corresponds to the amplitude modulation waveform of the 0 ° channel, and the imaginary part corresponds to the amplitude modulation waveform of the 90 ° channel. As will be understood from the calculation of the slice profile, if such 2-channel type amplitude modulation is performed, as described in the above reference (3), for example, 4
When exciting two slices simultaneously, (1,1,1,1), (1,1,
Four types of excitation are possible: (-1, -1), (1, -1,1, -1), (1, -1, -1,1). However, (1,1,1,1), etc. are the order of excitation of the four slices, and (1,1,1,1) is the magnetization of all four slices after excitation. 1: 1 in the positive direction of the axis
Excitation at a ratio of 1: 1 means (1,1, -1, -1)
Means to be excited at a ratio of 1: 1: -1: -1. The -1 excitation is excitation in which the magnetization is in the negative direction of the X axis.

In the present invention, when four slices are simultaneously excited, the slice profile is simply expressed as
Excitation of (1,1,1,1), (-i, -i, i, i), (-i, i, -i, i), (-1,1,1, -1) There is. However, the excitation of i means that the magnetization is oriented in the positive direction of the Y axis. (1,1,1,1), (-i, -i, i,
i), (-i, i, -i, i), (-1,1,1, -1) excitations are
Multiplying by 1, i, i, -1, (1,1,1,1), (1,1, -1,-
1), (1, -1,1, -1), (1, -1, -1,1), which is the same pattern as the conventional one. As described above, the present invention uses the amplitude modulated wave of the formula (1) in which the imaginary unit i attached to the sin term of the amplitude modulated wave of the conventional technique (3) expressed by the formula (16) is used, and as a result, simultaneous excitation is performed. Although the magnetization directions afterward are different, the pattern similar to that of the prior art (3) can be realized by appropriately multiplying by i or the like. By taking the imaginary number unit i attached to the amplitude modulation wave of the high frequency magnetic field as described above, the advantage that the same simultaneous excitation imaging function as that described in the related art (3) can be realized even in an apparatus that can only perform amplitude modulation of one channel. Occurred.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the following description, the magnetic resonance diagnostic apparatus according to one embodiment of the present invention will be described by dividing it into three parts, <configuration>, <procedure>, and <imaging sequence>. First, the <configuration> of the magnetic resonance diagnostic apparatus according to this embodiment will be described. As described above, the present invention can be implemented by a commercially available ordinary magnetic resonance diagnostic apparatus. FIG. 2 shows a block diagram of the magnetic resonance diagnostic apparatus, which will be briefly described below. Figure 2
The magnetic resonance diagnostic apparatus shown in FIG.
Gradient magnetic field generator 203, high frequency magnetic field generator 204,
It includes a receiving device 205, a sequence control device 206, a processing device 207, and a display device 208. Static magnetic field generator 20
2 creates a strong and uniform magnetic field,
To generate magnetization. The gradient magnetic field generation device 203 uses x,
It has a gradient magnetic field generator for the y and z3 directions and can operate independently, and generates a gradient magnetic field having an arbitrary strength and direction at any time by setting the application timing and applied strength of the gradient magnetic field in each direction. it can. When a gradient magnetic field is applied, the magnetic field strength changes according to the position in the direction of the gradient magnetic field, the Larmor frequency of the magnetization of the inspection object 201 changes accordingly, and the magnetization of the inspection object 201 is distinguished in position.

The high-frequency magnetic field generator 204 can generate a desired high-frequency magnetic field and, if necessary, resonantly excites the magnetization of the inspection object 201 so that only the magnetization satisfying the resonance condition emits an electromagnetic wave. By combining a gradient magnetic field and a high frequency magnetic field, it is possible to generate an electromagnetic wave only from a region satisfying the resonance condition and enable imaging of the region. The receiving device 205 measures an electromagnetic wave generated by the resonance excitation of the magnetization of the inspection object 201, and processes it as a signal data to the processing device 207.
Pass to. The processing device 207 stores the signal data,
Image reconstruction is performed on the signal data to generate image data. The display device 208 displays image data. The sequence display device 206 controls the operations of the gradient magnetic field generation device 203, the high frequency magnetic field generation device 204, the reception device 205, and the processing device 207. The sequence control device 206 has a function of an ordinary computer, and has a program for sending a command to operate each device and data describing an operation state of each device referred to by the program. Further, the processing device 207 is composed of dedicated hardware that performs computation at high speed, and computation of data processing is performed by creating and executing a program described in a programming language specific to the dedicated hardware. Processor 207
Can also use an ordinary computer because of its function.

The configuration of the magnetic resonance diagnostic apparatus has been described above. There are various types of high-frequency magnetic field generator 204,
This is shown in FIGS. The present invention can be implemented with any of the types of Figures 3-6. Conventional technology (1)-
In (4), the high-frequency magnetic field generator 204 requires the mechanism shown in FIGS. 4 to 6, but the present invention is characterized in that it can be implemented by the magnetic resonance diagnostic apparatus having the simplest mechanism shown in FIG. Hereinafter, FIGS. 3 to 6 will be briefly described. FIG. 3 has the simplest mechanism as the high-frequency magnetic field generator 204. The single-oscillation-wave oscillator 300 transmits a single-oscillation reference oscillatory wave, and the amplitude-modulated-wave generator 320 generates an amplitude-modulated wave. Both are mixed by the mixer 330 to amplitude-modulate the reference vibration wave. The high frequency after amplitude modulation is enlarged by the amplifier 340 and electromagnetically irradiated by the coil 350 to obtain a high frequency magnetic field. The amplitude modulation wave generation device 320 reads the data from the memory that stores the value of the amplitude modulation waveform based on the command of the sequence control device 206, and DA-converts the data to generate the amplitude modulation wave. As the waveform data of the amplitude modulation waveform, a predetermined waveform may be created in advance and stored in a predetermined memory, and the sequence control device 206 calculates the waveform data each time as necessary, and stores it in a predetermined memory. It may be remembered.

FIG. 4 shows a mechanism for performing a two-channel type amplitude modulation as the high-frequency magnetic field generator 204. The reference vibration wave generated by the single vibration wave oscillator 300 is shunted, and the phase of one channel is shifted by 90 ° by the 90 ° phase shifter 311. Each channel has an independent amplitude modulation wave generator 321 and 322, and the mixer 3
Independent amplitude modulation is performed on each channel at 30 and then combined. Since it is possible to electrically have components with different phases, it is possible to create a high-frequency magnetic field represented by a complex number. FIG. 5 shows a mechanism capable of simultaneously changing the phase and the amplitude independently of each other as the high-frequency magnetic field generator 204. After modulating the phase of the simple vibration wave by the phase modulator 315,
It is amplitude-modulated, and as the addition theorem of trigonometric functions shows, it can generate exactly the same high-frequency magnetic field as that having the 2-channel type mechanism of FIG. FIG. 6 shows a case where a plurality of reference frequencies are provided, and the single-frequency wave transmitter 1 (306) to the single-frequency wave transmitter 4 (309) each independently make a plurality of reference frequency waves having different frequencies. , The respective reference oscillatory waves are independently phase-shifted using the phase shifters 316 to 319. As for the phase shift, a fixed phase shift is performed during one irradiation of the high frequency magnetic field, but another phase can be shifted during the next irradiation of the high frequency magnetic field. In this way, the high frequencies in which the respective reference frequencies have the respective phases are combined and then the amplitude is modulated. The mechanism of FIG. 6 has less degrees of freedom in the obtained high-frequency magnetic field than the mechanisms of FIGS. 4 and 5,
This mechanism is sufficient for simultaneous excitation with multiple frequencies.

The various mechanisms of the high frequency magnetic field generator 204 have been described above. Here, the high-frequency magnetic field realized by using the simplest mechanism of FIG. 3 can be easily realized by the device having the mechanism of FIGS. For example, in the case of FIG. 4, if the amplitude modulation waveform of the 90 ° channel is set to 0 so that a high frequency is not obtained from the 90 ° channel, the mechanism becomes exactly the same as that of FIG. In the case of FIG. 5, if the modulation phase data of the phase modulator 315 is fixed to 0 and phase modulation is not performed, the mechanism of FIG. 3 is obtained. In the case of FIG. 6, the single vibration waves generated by the single vibration wave transmitter 1 (306) to the single frequency transmitter 4 (309) are all the same, and the phase shifted by the phase shifters 316 to 319 is set to 0. Then, the mechanism becomes the same as that of FIG. Since the present invention can be implemented by an apparatus having the mechanism shown in FIG.
It can also be implemented by a device having a mechanism as shown in FIG.

Next, the <procedure> of the present invention will be described. Figure 7
FIG. 6 is a flowchart showing the imaging procedure of the present invention in the case of simultaneously exciting four slices. Below, FIG.
The number of each block is described in correspondence with the step number. Step 701: Start a series of shooting operations. Step 702: Initialize the encoding value of the photographing sequence. There are various shooting sequences, and a typical one will be described later in the section of the shooting sequence. Step 703: For the 90 ° pulse 101, the above equation (1
The amplitude modulation waveform RF1 (t) shown in 2) is used to capture one encode. Step 704: For the 90 ° pulse 101, the above equation (1
The amplitude modulation waveform RF2 (t) shown in 3) is used to capture an image for one encoding. Step 705: For the 90 ° pulse 101, the above equation (1
The amplitude modulation waveform RF3 (t) shown in 4) is used to capture an image for one encoding.

Step 706: For 90 ° pulse 101,
Using the amplitude modulation waveform RF4 (t) shown in the above equation (15), one-encoding photographing is performed. Step 707: It is judged whether or not the encoded value has reached a predetermined value, and if it has reached the predetermined value, the operation proceeds to step 709 to end the photographing operation, and if it has not reached the predetermined value, the operation proceeds to step 708. . Step 708: Increment the encoding value by 1 and step 7
Return to 03. After obtaining the measurement signal by taking a picture with the above procedure,
The separation calculation 104 shown in (7) to (10) is performed to separate the signals of each slice, and image reconstruction is performed on each of the separated signals to obtain an image of each slice. The image reconstruction method depends on the imaging sequence, but at present, the method of imaging so that the image can be reconstructed by the two-dimensional Fourier transform is most often used. Since the two-dimensional Fourier transform is a linear operation, a separation operation 104 for adding or subtracting signals is performed.
Even if the two-dimensional Fourier transform is performed after performing the above, the two-dimensional Fourier transform is performed on each signal to generate each original image data and then the same operation as the separation operation 104 is performed. The result does not change.

In addition to the image reconstruction method, the half Fourier method may be used, and the image capturing method is an image capturing method having an encoding order for capturing a small amount of data unique to the half Fourier method. In this case, since the operation of the half Fourier method is a non-linear operation, it is necessary to first perform the separation operation 104 to separate each signal and then to perform image reconstruction by the half Fourier method. When image reconstruction by the half Fourier method is performed before the separation calculation 104, an original image in which the phase estimation of the image does not work appears, and even after the separation calculation 104 is performed, the separated image may be blurred. The half Fourier method is described in the following document (7), for example. Reference (7) Author: K. Sano, K. Suzuki, T. Yokoyama,
H. Koizumi Title: "Image Reconstruction from Half of D
ata Using a Phase Map "Conference Proceedings: Society of Magnetic Resonance i
n Medicine, 6th Annual Scientific Meeting and
Exhibition, Book of Abstracts, p.809 (1987).

Next, the <imaging sequence> of the present invention will be shown. There are various imaging sequences in which the present invention can be used.
Two typical examples are given in FIG. 8 and FIG. FIG. 8 shows a pulse sequence based on the gradient echo method. The horizontal axis of the figure shows time, and the vertical axis shows the operating state of each device. The high-frequency magnetic field 801 is generated by the high-frequency magnetic field generator 204, and X
The gradient magnetic field generation device 203 generates a directional gradient magnetic field 802, a Y-direction gradient magnetic field 803, and a Z-direction gradient magnetic field 804.
The reception gate 805 is a gate signal issued by the sequence control device 206. When the gate signal is in the ON state, the reception device 205 operates to receive a magnetic resonance signal and obtain signal data. In the Y-direction encoding 810, the intensity of the gradient magnetic field changes stepwise at regular intervals for each encoding, and the series of operations in FIG. 8 shows the operation for one encoding. The number of encoding times required for a series of shootings depends on the shooting matrix. For example, 256 * 25
In the case of 6 matrices, it usually has 256 times of encoding. In half shooting, the number of times used for phase estimation (for example, 16 times) is added to 128 times of half, and the number of times is slightly higher than 128 times.
(For example, 144 times) encoding times are required.

The 90-degree pulse 101 shown in FIG. 1 is used as the 90-degree pulse 101 in FIG. This is the above equation (1
As described in <Procedure> above, images are taken by sequentially using the pulses of these four trees, as described in the above <Procedure>. It should be noted that the time from the image pickup for one encoding to the image pickup for the next one encoding is called a repetition time TR, which can be freely set by the user. Figure 9
Is an imaging sequence based on the spin echo method.
The most important feature of the spin echo method is that the 180-degree pulse 820 is applied, and the phase of the magnetization excited by the 180-degree pulse 820 is inverted, and imaging that cancels the influence of magnetic field inhomogeneity is possible. 180 degree pulse 8
A pulse waveform used for normal imaging may be used for 20, or the pulse waveform described in the formula (11) may be used with an applied intensity twice as high as that used for a 90-degree pulse.

The embodiment of the present invention has been described above in the order of <configuration>, <procedure>, <imaging sequence>. <Procedure> and <
In the imaging sequence>, the case where four slices are simultaneously excited has been described as an example, but the present invention similarly uses the pulse waveform shown in the above formula (1) for simultaneous excitation of the n-th power of 2. You can Ωk in the equation (1) is a parameter value that determines the slice interval for simultaneous excitation, and the slice interval is proportional to ωk. Therefore, when it is desired to increase the slice interval, ωk is increased. Further, for k = 2 to n, if ωk = ω ₁ * (2 ** (k-1)), the intervals between all simultaneously excited slices are the same. However, 2 ** (k-1) represents 2 to the power of k-1.

It is needless to say that the above embodiment shows one example of the present invention, and the present invention should not be limited to this. For example, there are many other shooting sequences in which the present invention can be used,
For example, there are many such as a multi-echo sequence, a fast SE sequence, and a water-fat separation sequence. Regarding the shooting sequence as described above, for example,
Many articles are listed in the magazine: Magnetic Resonance in Medicine and the like. The present invention can be implemented by using the pulse of the present invention for the 90-degree pulse of those imaging sequences. Further, the present invention can be carried out by using the pulse of the present invention as long as it is a pulse for excitation purpose, even if it is an α-degree pulse instead of the 90-degree pulse.

[0031]

As described above in detail, according to the present invention, even a magnetic resonance diagnostic apparatus having a high-frequency magnetic field generator having only a function of performing one-channel type amplitude modulation has two functions.
It is possible to realize the simultaneous imaging method for a plurality of slices in the magnetic resonance diagnostic apparatus capable of simultaneously exciting the n-th power of n, and improving the imaging efficiency by the well-known simultaneous excitation.

[Brief description of drawings]

FIG. 1 is a pulse waveform and slice profile of the present invention,
It is a figure which shows the slice profile after a separation calculation.

FIG. 2 is a diagram showing a configuration example of a magnetic resonance diagnostic apparatus.

FIG. 3 is a configuration diagram of a high-frequency magnetic field generator that performs 1-channel type amplitude modulation.

FIG. 4 is a configuration diagram of a two-channel type high-frequency magnetic field generator that performs amplitude modulation.

FIG. 5 is a configuration diagram of a high-frequency magnetic field generator that simultaneously performs phase modulation and amplitude modulation.

FIG. 6 is a configuration diagram of a high-frequency magnetic field generator that simultaneously performs phase modulation and amplitude modulation.

FIG. 7 is a flowchart showing the procedure of the present invention.

FIG. 8 is an imaging sequence diagram based on a gradient echo method according to an embodiment.

FIG. 9 is an imaging sequence diagram based on the spin-entry echo method according to the embodiment.

FIG. 10 is a diagram showing a slice profile when four slices are simultaneously excited according to an example.

[Explanation of symbols]

 101 90-degree pulse 102 Slice profile of absolute value 103 Separation slice profile of absolute value 104 Separation operation 112 Slice profile in the Real direction 122 Slice profile in the Imag direction 300,306 to 309 Single oscillator generator 311 90-degree phase shifter 315 Phase modulation Machine 316 to 319 Phase shifter 320 to 322, 325, 326 Amplitude modulated wave generator 801 High frequency magnetic field 802 X direction gradient magnetic field 803 Y direction gradient magnetic field 804 Z direction gradient magnetic field 805 Consultation gate 810 Y direction encode 820 180 degree pulse

Claims (7)

[Claims] 1. A static magnetic field, a gradient magnetic field, a high frequency magnetic field generating means, a detecting means for measuring a magnetic resonance signal from an inspection object, an arithmetic means for performing various operations on the detected signal, and 1.
High-frequency magnetic field generating means for performing channel-type amplitude modulation,
In a magnetic resonance diagnostic apparatus having means for controlling execution of each of the means, a plurality of waveforms created by multiplying a predetermined basic waveform by a desired function are created as the amplitude modulation waveforms, and the plurality of waveforms are created. Each of the measurement signals obtained by exciting a plurality of slice portions at the same time by applying a high-frequency magnetic field amplitude-modulated with each waveform of the waveform of FIG. 1 and changing the excitation method of the plurality of slices according to each waveform. To obtain a signal for each slice by performing a separation operation for separating the signal for each slice using the plurality of measurement signals, and reconstructing each slice image based on the signal for each slice. Multiple-slice simultaneous imaging method in a magnetic resonance diagnostic apparatus characterized by. 2. The method for simultaneously imaging multiple slices in a magnetic resonance diagnostic apparatus according to claim 1, wherein the following function RF _k (t) is used as a desired function for multiplying the predetermined basic waveform. [Equation 1] Where t is time, T is application time of high frequency magnetic field, k is an integer from 1 to (2 to the nth power), RF ₀ (t) is a predetermined basic waveform, and RF _k (t) is the k-th desired signal. , Ωk is a constant representing the desired frequency depending on k, n is an integer, and the number of slices to be simultaneously imaged is (2 to the nth power)
Number of sheets, j is an integer from 1 to n, b _j is an integer that takes a value of either 0 or 1, and is a value when k is represented by the following formula similar to a binary number. [Equation 2] 3. The method of claim _{2, ωk = ω 1 * (} 2 ** (k-
1)), (k is an integer from 2 to n), the multi-slice simultaneous excitation method in the magnetic resonance diagnostic apparatus.
However, 2 ** (k-1) represents 2 to the power of k-1. 4. The multiple-slice simultaneous excitation method in a magnetic resonance diagnostic apparatus according to claim 1, wherein an imaging method using a half Fourier method is performed as the calculation of the image reconstruction. 5. A static magnetic field, a gradient magnetic field, a high frequency magnetic field generating means, a detecting means for measuring a magnetic resonance signal from an inspection object, an arithmetic means for performing various calculations on the detected signal, and 1.
High-frequency magnetic field generating means for performing channel-type amplitude modulation,
In a magnetic resonance diagnostic apparatus having means for controlling execution of each of the above means, a plurality of waveforms created by multiplying a predetermined basic waveform by a desired function are created as the amplitude modulation waveforms. By applying a high-frequency magnetic field amplitude-modulated with each waveform of the waveform of, the multiple slices are excited at the same time, and each measurement signal that changes the way of exciting the multiple slices according to the waveform Magnetic resonance diagnosis characterized in that the image of each slice is obtained by performing image reconstructing of the plurality of measurement signals to create respective original image data and performing slice separation calculation on the original image data. Simultaneous imaging of multiple slices in a device. 6. The simultaneous imaging of multiple slices in a magnetic resonance diagnostic apparatus according to claim 5, wherein the desired function for multiplying the predetermined basic waveform is a function RF _k (t) of the following equation. Method. (Equation 3) Where t is time, T is application time of high frequency magnetic field, k is an integer from 1 to (2 to the nth power), RF ₀ (t) is a predetermined basic waveform, and RF _k (t) is the k-th desired signal. , Ωk is a constant representing the desired frequency depending on k, n is an integer, and the number of slices to be simultaneously imaged is (2 to the nth power)
Number of sheets, j is an integer from 1 to n, b _j is an integer that takes a value of either 0 or 1, and is a value when k is represented by the following formula similar to a binary number. [Equation 4] 7. The method of claim _{6, ωk = ω 1 * (} 2 ** (k-
1)), (k is an integer from 2 to n), the multi-slice simultaneous excitation method in the magnetic resonance diagnostic apparatus.
However, 2 ** (k-1) represents 2 to the power of k-1.