JP3153573B2 - Magnetic resonance equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium for obtaining spectral information and image information of a subject using a magnetic resonance phenomenon.
It relates to NaSo location, in particular, to a technique for shortening the acquisition time of each piece of information.

[0002]

2. Description of the Related Art In recent years, as the development of a magnetic resonance diagnostic apparatus has progressed, biochemical information (ischemic disease, metabolic abnormality,
Non-invasive methods for collecting and evaluating cancer characteristics, therapeutic effects, etc.) have been put to practical use.

[0003] There therefore spectroscopy also copy is used in such an evaluation, for example, from spectroscopy of phosphorus can be obtained energy metabolism information reflecting the activity of the tissue, from spectroscopy of proton, ischemia Metabolites such as lactic acid, which indicates the degree of the state, and NAA (N-acetylaspartic acid), which is said to have a precise relationship with brain function, can be detected. further,
Imaging these distributions (MRSI: Magnetic Resonance
Spectroscopic Imaging) is said to be able to diagnose normal tissues and diseased sites. To perform advanced preventive diagnosis, etc., the distribution of biochemical information (functional information) provided by multiple nuclides It is desired to obtain respectively.

However, since the concentration of metabolites such as phosphorus in a living body is as low as several millimoles to several tens of millimoles, the measurement requires a long time.

[0005] In addition, since the detection sensitivity differs for each nuclide,
The voxel size of the distribution image obtained for each nuclide cannot be uniform. Therefore, conventionally, when observing magnetic resonance spectra from a plurality of nuclides, it is necessary to change the encoding time in the pulse sequence for each nuclide, or the gradient magnetic field strength for encoding,
Magnetic resonance spectra from a plurality of nuclides cannot be obtained by a series of pulse sequences, and there is a disadvantage that the measurement time is lengthened by the number of nuclides to be observed.

[0006] Further, since the concentration of metabolites such as protons and phosphorus in a living body is extremely low, the resolution of MRSI images is inferior to that of ordinary MRI images. Therefore, MRS
Since it is very difficult to identify the position only by the I image, conventionally, both the MRI image and the MRSI image are obtained, and the position is identified by this. For this reason, the measurement time was significantly long.

[0007]

As described above, in the conventional magnetic resonance diagnostic apparatus, when measuring magnetic resonance spectra from a plurality of nuclides, it is necessary to execute pulse sequences by the number of nuclides. It takes a long time. In order to identify a position in an MRSI image, it is necessary to take an MRI image. In this case, it is necessary to execute a different pulse sequence between the MRSI and the MRI, so that it takes a long time to collect data. There was a disadvantage.

[0008] The present invention has been made to solve such conventional problems, the first object, tinnitus magnetic <br/> both to collect in a short time magnetic resonance spectra from a plurality of nuclides it is to provide the equipment. The second purpose is
Is to provide a magnetic co NaSo location that can be taken in a short time both MRSI images and MRI images.

[0009]

In order to achieve the above object, the present invention provides a subject placed in a uniform static magnetic field,
Apply high frequency magnetic field and gradient magnetic field to
The magnetic co NaSo location to gather the magnetic resonance signals of the plurality of nuclides, magnetic resonance due to a plurality of nuclides in the subject
Owns frequency to excite the nuclide to collect signal
Each high-frequency pulse applied before the gradient magnetic field
Means for identifying the position required for each nuclide.
High-frequency pulses and
And means for applying a gradient magnetic field .

[0010] In another invention, the antenna is arranged in a uniform static magnetic field.
The location is the subject was, the high frequency magnetic field, and, to mark <br/> pressure gradient magnetic field, a magnetic resonance image signals from the subject, and the magnetic co NaSo location to gather the magnetic resonance spectrum signal, The excitation angle θ of the first selective excitation pulse is 90 ° <θ <1
80 [deg.], And the magnetic resonance image signal is obtained before the time when the longitudinal magnetization excited by the first selective excitation pulse becomes substantially zero.
And means for collecting the first selective excitation pulse.
Excited Te longitudinal magnetization and having a means Ru give time or al magnetic resonance spectrum signal as a schematic 0.

[0011]

According to the above-mentioned structure, 180 nuclides can be added to a specific nuclide.
° selective pulse is applied, and before and after this pulse, a gradient magnetic field in the encoding direction is applied. Then, for the nuclides to which the 180 ° pulse is applied, the gradient magnetic fields before and after this are offset from each other, and for the nuclides to which the 180 ° pulse is not applied, both magnetic fields are added. Therefore, by appropriately adjusting the magnitude of the gradient magnetic field, different encodings can be given to different nuclides. As a result, magnetic resonance signals of a plurality of nuclides can be obtained by one pulse sequence.

When obtaining a magnetic resonance spectrum and a magnetic resonance image, a selective excitation pulse having a flip angle θ satisfying 90 ° <θ <180 ° is applied to a target region. Then, magnetic resonance image information is collected by using a field echo method or the like until the longitudinal magnetization becomes zero. After the longitudinal magnetization becomes zero, an RF pulse for observing metabolites is applied to obtain magnetic resonance spectrum information. Therefore, magnetic resonance spectrum information and magnetic resonance image information can be obtained by one pulse sequence.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a magnetic resonance diagnostic apparatus according to one embodiment of the present invention.

The magnetic resonance diagnostic apparatus shown in FIG. 1 has a main magnet 10 for generating a main magnetic field (static magnetic field), a main magnet power supply 11, and linear X-, Y-, and Z-axis directions. A gradient coil system 12 including a plurality of gradient coils for generating a gradient magnetic field having a gradient magnetic field distribution, a gradient coil power supply 13, a shim coil system 14 including a plurality of shim coils,
A high-frequency probe 16 for applying a high-frequency magnetic field and detecting a magnetic resonance signal;
17 for supplying a high-frequency signal to the receiver, a receiver 18 for receiving, detecting and amplifying the magnetic resonance signal detected by the probe 16, a sequence controller 19 and a CPU.
/ Memory 20. Here, transmitter 1
7. The receiver 18 is capable of exciting or receiving multi-nuclide magnetic resonance signals, respectively, and the probe 16 is detuned and decoupled so that the magnetic resonance signals from the multi-nuclides can be simultaneously observed. . Further, the CPU / memory 20 and the sequence controller 19 send control signals to the transmitter 17 and the gradient coil power supply 13, respectively, for the application timing of the high-frequency pulse and the application timing of the gradient magnetic field.

Next, a pulse sequence for simultaneously acquiring MRSI data of metabolites based on a plurality of nuclides using the magnetic resonance diagnostic apparatus shown in FIG. 1 will be described. In this description, an example in which one-dimensional spatial information is mapped in the case of two nuclides A and B is described for convenience.

Now, in order to encode spatial information uniquely into the phase of magnetization, it is necessary to satisfy the conditions shown in the following equations (1) and (2), as is well known.

The _{γ A · ΔG A · R A} · Δt A = 1 ... (1) γ B · ΔG B · R B · Δt B = 1 ... (2) However, gamma nuclear gyromagnetic ratio, .DELTA.G the gradient field Intensity, R is spatial resolution, Δt is gradient magnetic field application time, and A and B of the suffix indicate A nucleus and B nucleus, respectively.

The basic principle for arbitrarily varying the amount of phase encoding will be described with reference to FIG. Same figure
In the sequence shown in (a), after applying an RF pulse 21 of α °, a gradient magnetic field 22 (magnitude G
e, time ΔT), and then apply a 180 ° RF pulse 23 to generate a gradient magnetic field 24 (magnitude Ge, time ΔT).
Is applied. In this case, since the gradient magnetic fields 22, 24 having the same polarity, intensity, and application time are applied before and after the 180 ° RF pulse 23, the gradient magnetic fields 22,
24 offset each other. Therefore, it is not subjected to phase encoding.

In the pulse sequence shown in FIG. 2B, the polarity of the gradient magnetic field differs before and after the 180 ° RF pulse. Therefore, since the respective gradient magnetic fields 27 and 28 are added,
The excited magnetization is encoded twice as large as the gradient magnetic field 27.

Further, in the pulse sequence shown in FIG. 3 (c), a 180 ° RF pulse is not applied, and only the gradient magnetic field 3 is applied.
Since 0 and 31 are continuously applied, the excited magnetization is encoded twice as much as the gradient magnetic field 30.

That is, it is understood that the gradient magnetic field can be arbitrarily changed by using the method shown in FIGS. 2A to 2C while satisfying the above-mentioned equations (1) and (2).

Next, an example in which MRSI data of A nucleus and B nucleus are simultaneously acquired will be described with reference to the pulse sequence shown in FIG.

In the pulse sequence shown in FIG.
An RF pulse 32 for exciting the A nucleus and an RF pulse 34 for exciting the B nucleus are simultaneously applied. Thereafter, a gradient magnetic field 35 in the encoding direction having a magnitude ΔG and an application time Δt is applied.

As a result, the RF pulses 32 and 34 are subjected to phase encoding by the gradient magnetic field 35. Thereafter, the gradient magnetic fields 36 and 37 having the magnitude ΔG ′ and the application time Δt ′ are successively applied, and the 180 ° RF pulse 33 is applied only to the A nucleus at the application interval of the gradient magnetic fields 36 and 37.

Therefore, as described above, the A nucleus is not encoded by the gradient magnetic fields 36 and 37. That gradient .DELTA.G _A of the A nucleus will undergo .DELTA.G _A = .DELTA.G next, only the encoding by the gradient magnetic field 35.

Further, since the 180 ° RF pulse is not applied to the B nucleus, the B nucleus is encoded by the gradient magnetic fields 36 and 37. Since the gradient magnetic fields 36 and 37 have the opposite polarity to the gradient magnetic field 35, The following equations (3) and (4) hold.

The _{ΔG> ΔG B ... (3)} ΔG · Δt-2 · ΔG '· Δt' = ΔG B · Δt B = 1 / (γ B · R B) ... (4) Therefore, the pulse shown in FIG. 3 If a sequence is used, A
Nuclei and B nuclei can each be given a different encoding. And even if the number of nuclides increases, 180
By appropriately applying the ° RF pulse and the gradient magnetic field before and after the 180 ° RF pulse, even if the number of nuclides increases, it is easy to provide encoding corresponding to each nuclide.

In this manner, a plurality of nuclides can be simultaneously excited by one pulse sequence, and data of spatial distribution can be collected at the same time. In the pulse sequence shown in FIG. 3, the magnitudes of the gradient magnetic fields 36 and 37 in one step and the application time need not be equal, but may be determined so as to satisfy the equations (1) and (2). Further, the matrix size of each nuclide is not necessarily required to coincide, to Matrix scan size may ignore data for excess encoding steps that occur to different, or to improve the signal-to-noise ratio An averaging process may be included.

FIG. 4 is a pulse sequence diagram of multi-nuclide simultaneous MRSI when the gradient magnetic field strength is fixed. In this pulse sequence, for the sake of convenience, when exciting two nuclides, a nuclide with a small absolute value of the nuclear magnetic rotation ratio γ is considered as a reference (A nucleus in this example). Then, the A core RF pulse 4
After the 0 and B nuclear RF pulses 41 are applied simultaneously,
The gradient magnetic field pulses 43 to 47 in the encoding direction for the application time Δt (≦ Δt _A ) are sequentially applied. For the B nucleus, a 180 ° RF is applied between the gradient magnetic field pulses 45 and 46.
Pulse 42 is applied.

[0030] Then, Delta] t between the application time Delta] t of each magnetic field pulses 43-47, the gradient magnetic field application time Delta] t _A of the A nucleus
If N = Δt _A (N is the number of gradient magnetic field pulses) holds,
For the A nucleus, the encoding using the gradient magnetic field pulse as one unit is performed a desired number of times m (m = 1, 2,..., M,
However, spatial information can be mapped by performing only M (the matrix size).

On the other hand, for the B nucleus, since the gradient magnetic field pulses are canceled before and after the application of the 180 ° RF pulse, the number of gradient magnetic field pulses to be encoded is N ₁ −N ₂ (where N ₁ is 180 °). number of RF pulses applied before the gradient magnetic field pulses, N ₂ is the number) of the gradient magnetic field pulse after the application. Therefore, by performing the phase encoding while satisfying the following expression (5), the spatial distribution of the B nucleus can be mapped.

Δt (N ₁ −N ₂ ) = Δt _B (5) When the imaging regions of the respective nuclide distribution images obtained by the pulse sequences shown in FIG. 3 and FIG. Is displayed by performing an interpolation operation or the like so as to match, the spatial distribution of information obtained from each nuclide can be comprehensively diagnosed.

Next, a sequence for simultaneously collecting proton MRI and MRSI will be described. In this description, an example in which MRI and MRSI are performed in one plane of the subject will be described for convenience.

FIG. 5 is a basic pulse sequence diagram when performing an N × N matrix proton image and an M × M matrix MRSI. As shown in the figure, RF pulses for exciting the magnetization of the target region of the subject when the slice direction gradient magnetic field G _s is applied 51
Is applied. The flip angle at this time is 90 ° + α (0
° <α <90 °).

Accordingly, the magnetization of the target area is tilted in the negative direction of the Z axis by the RF pulse 51.
Then, the magnetization component _{Mz in the} Z-axis direction is reduced by longitudinal relaxation as shown in FIG.
, Gradually increases, and at time t _1, M _z = 0
Becomes Then, applying an RF pulse 52 for exciting a metabolite at this time t _1. Thereby, spectrum information in which the water signal is suppressed can be obtained.

This method is described in Patt (J. Chem. Phys. (1)
972) ) . In the present invention, after the first RF pulse 51, L = N / M times of phase encoding 57 is performed using the field echo method, and the MRI is performed.
Collect data. Thereafter, applying a high frequency pulse for observing the proton metabolites such as lactic acid at time t ₁ which biological water longitudinal magnetization crosses zero by the vertical relaxation process. The phase encoding is sequentially repeated (M × M) times to advance the pulse sequence, thereby spatially mapping the proton metabolite.

As described above, by using the pulse sequence shown in FIG. 5, MRI and MRSI can be obtained in a series of pulse sequences. As a result, compared to conventional, Ru can be dramatically reduced data acquisition time.

If the obtained metabolite distribution image is different from the proton image in the imaging region, an interpolation operation or the like is performed so as to match the imaging region and displayed. If images of various proton metabolites are superimposed and displayed on the proton image, the disease site diagnosed from the metabolic information can be read from the proton image with good resolution, and the state of the living body can be comprehensively evaluated. Diagnosis is possible.

Further, MR based on nuclides other than protons
If SI is measured at the same time as proton metabolites, advanced diagnosis is possible by superimposing and displaying the MRSI of these polynuclear species on a high-resolution MRI image. Further, if the pulse sequence shown in FIG. 3 is performed from the time t _{1 of the} pulse sequence shown in FIG. 5, MRI and multi-nuclide MRSI can be obtained simultaneously.

[0040]

As described above, according to the present invention,
In the case of performing MRSI of a plurality of nuclides, by exciting a plurality of nuclides before applying the phase encoding , it becomes possible to observe magnetic resonance signals at the same time. A distribution reflecting chemical information can be obtained. Thus, the burden on the patient can be reduced. Further, since biochemical information of a plurality of nuclides can be imaged at the same time, an image which is not affected by positional deviation can be obtained.

In addition, when MRSI with poor resolution is performed, a high-resolution proton image, which is indispensable for identifying a diseased site, can be obtained within the MRSI data collection time, thereby reducing the burden on the subject. In addition, it is possible to suppress the influence of positional deviation due to MRI and MRSI. In addition, since the biological function information and the morphological information can be comprehensively evaluated, the effect of speeding up the diagnosis of a disease or the like can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a magnetic resonance diagnosis apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a principle of canceling a gradient magnetic field in an encoding direction by applying a 180 ° RF pulse.

FIG. 3 is a pulse sequence diagram when acquiring MRSI data of two nuclides simultaneously.

FIG. 4 is a pulse sequence diagram when acquiring MRSI data of two nuclides simultaneously.

FIG. 5 is a pulse sequence diagram for obtaining MRI and MRSI.

[Explanation of symbols]

 Reference Signs List 10 main magnet 11 main magnet power supply 12 gradient coil system 13 gradient coil 14 shim coil system 15 shim coil power supply 16 high-frequency probe 17 transmitter 18 receiver 19 sequence controller 20 CPU / memory

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. An object placed in a uniform static magnetic field,
Apply high frequency magnetic field and gradient magnetic field to
The magnetic co NaSo location to gather the magnetic resonance signals of a plurality of nuclear species, the magnetic resonance signals caused by several species in the subject yield of
Each possessing a frequency to excite the nuclide to collect
Means for applying a high-frequency pulse prior to the gradient magnetic field
And the encoding phase for position identification required for each nuclide
In order to impart high-frequency pulse as well as magnetic co NaSo location, characterized by comprising means for applying a gradient magnetic field, a. 2. An object placed in a uniform static magnetic field ,
Apply high frequency magnetic field and gradient magnetic field to
Magnetic resonance image signals, as well as magnetic resonance spectrum signal
The magnetic co NaSo location to gather the items, excitation angle of the first selective excitation pulse theta is 90 ° <theta <180
縦, and the longitudinal magnetization excited by the first selective excitation pulse is
Means for collecting magnetic resonance image signals by the time the Overview Once the 0, the longitudinal magnetization excited by the first selective excitation pulse
Magnetic co NaSo location, characterized in that from the time when the Overview Once the 0 equipped with resulting Ru means magnetic resonance spectrum signal.