JP3120111B2 - High-speed magnetic resonance imaging system using single excitation spin echo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to nuclear magnetic resonance (NM)
R). This technology is applied to physical engineering, fluid engineering, biology, medicine,
In the field of pharmacy, the inside of a living body or a substance can be nondestructively imaged and used for visualization of morphological structure, chemical bonding state, flow, examination during surgery, and the like.

[0002]

2. Description of the Related Art A conventional apparatus for imaging the spatial distribution of a substance by NMR has a magnet for generating a static magnetic field and a magnetic field gradient coil around a substance to be measured, and a very strong uniform magnetic field is generated by the magnet for generating a static magnetic field. A magnetic field gradient coil is used to locally control the strength of the magnetic field. MR ((Magnetic Resona
nce) imaging (nuclear magnetic resonance imaging)
In a spatially constant static magnetic field H0, R
An F (electromagnetic) wave is applied to the substance to be measured. To image the spatial distribution of the density and chemical structure of resonant elements, x,
A gradient magnetic field having a spatially different magnetic field strength is superposed in the y and z directions.

In a conventional imaging method, after selective excitation by an RF wave, a gradient magnetic field for phase encoding and readout is applied to change the phase of magnetic resonance spins according to the three-dimensional position of a measurement area. The behavior of the magnetic moment derived from the spin induced by this is in-phase, and the gradient echo and spin echo are observed.

[0004] The resonance frequency ν of the spin when the substance to be measured is placed in a static magnetic field H0 and a gradient magnetic field G (X) in the x direction is applied.
i is given by the following equation. νi = γi (H0 + G (x)) (1−σ) (1) Here, γi and σ are the gyromagnetic ratio and shielding constant of element i that magnetically resonate, respectively. In the equation (1), if the echo signal measured by applying a gradient magnetic field G (x) linearly in the x direction to change the resonance frequency is subjected to Fourier transform,
x and νi correspond. This is the principle of imaging.

[0005]

However, in the case of an imaging method in which a gradient echo is measured, it takes only a short time (for example, several seconds) to obtain an image. When such a device exists, the static magnetic field is deformed due to the influence, and the obtained image may be unclear. It is conceivable to use the MRI apparatus in combination with a patient's treatment apparatus in the medical field, but such a case is not preferable because the treatment apparatus adversely affects the MRI image. On the other hand, in the case of the imaging method in which the spin echo is measured, it takes a long time of at least several minutes to obtain an image for the same region, but the obtained image is clear.

[0006] From the above, it is possible to obtain a clear image while realizing a further high-speed imaging in MRI, and to use an ultra-high-speed MRI apparatus in which equipment for localization and treatment can be used. Development of MR imaging technology is desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to obtain a clear image while realizing a further high-speed imaging in MRI.
It is an object of the present invention to provide an ultra-high-speed MR imaging apparatus in which equipment for localization and treatment can be used.

[0008]

SUMMARY OF THE INVENTION In response to this object, a high-speed magnetic resonance imaging apparatus using single excitation spin echo according to the present invention places a substance to be measured in a static magnetic field H0, and moves it in an x-direction or a y-direction in a rectangular coordinate system. and applying an RF wave having a resonance frequency [nu ^w i corresponding to the temporally constant magnetic field gradient G (x, y) and a number of points w in the z direction as the excitation pulse, the magnetic field H0 is orthogonal coordinate system Is characterized by a linear gradient magnetic field in the z direction.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings showing an embodiment. First, an MR imaging apparatus used in the imaging apparatus of the present invention will be described.

In FIG. 1, reference numeral 1 denotes an MR imaging apparatus.
The MR imaging device 1 includes an excitation device 2. The excitation device 2 partitions the measurement area 3 and excites the measurement substance 4 in the measurement area 3. An RF pulse is supplied from an RF pulse generator 9 to the excitation device 2. This RF pulse (excitation pulse) has a resonance frequency ν corresponding to a number of points w in the z direction.
^w i. As shown in FIG. 2, a magnet 5 and a gradient magnetic field coil 6 are arranged outside the excitation device 2 in a concentric cylindrical shape. The magnet 5 is a magnet for forming a static magnetic field, and desirably forms a stable and high magnetic field. A normal conducting magnet, a superconducting magnet, or a permanent magnet is used. 0.02 to 0.25 T, and 0.35 to 2 T for a superconducting magnet. The static magnetic field H0 formed here is a gradient magnetic field (magnetic field intensity G) which forms a linear change in the z direction (the center direction of the static magnetic field generating coil) in the orthogonal coordinate system.
(Z)). When the magnet 5 is a normal conducting magnet, a current is supplied from the excitation power supply 7. The gradient of the gradient magnetic field G (z) of the static magnetic field H0 formed by the magnet 5 is determined according to the z-direction resolution of the spectral width of a signal obtained by resonance. As shown in FIG. 3, the static magnetic field strength is 2 tesla.
And the frequency of the RF applied to the measurement substance 4 is temporarily
₁ , ω ₂ and the spectrum width of the obtained resonance signal is sw
₁ and sw ₂ , when sw ₁ = sw ₂ = ± 32 KHz, ω ₁ = 85.51616 MHz, ω ₂ ≧ ω ₁ +1
Since it is 5 gauss, it is necessary to incline by 15 gauss between both points. When sw ₁ = sw ₂ = ± 2 MHz, ω ₁ = 85.51616 MHz, ω ₂ ≧ ω ₁ +94
Since it is gauss, it is necessary to incline by 94 gauss between both points. The gradient magnetic field coil 6 is a coil that forms a gradient magnetic field in the measurement region 3 in the x direction or the y direction. The current controlled by the control device 8 is supplied from the power supply 11 to the gradient magnetic field coil 6 to form a magnetic field gradient. The gradient G (x) of the magnetic field gradient is, for example, G (x) = 20 gauss / cm. A signal processing device 1 for processing a signal from the measurement substance 4
2. An image processing device 13 is provided, and the image is displayed.
14 is displayed.

The imaging apparatus according to the present invention has the above-mentioned MR.
This is performed using the imaging device 1 as follows. The measurement substance 4 including a living body is placed in a magnet of a static magnetic field H0. When detecting information about the element i in the living body to be measured, the RF of νi is given to the static magnetic field H0 and the gradient magnetic field G (x) as the gradient magnetic field as given by the equation (1).
Irradiate waves. At this time, the resonance frequency νi changes by varying the intensity of the gradient magnetic field G (x), and resonance occurs at different frequencies depending on the spatial position. This allows spatial separation. Conversely, a temporally constant gradient magnetic field G (x)
Is applied to irradiate a large number of νi, the element i can be spatially separated. That is, the static magnetic field H0 which is a gradient magnetic field
In resonates temporally constant spatial position of the gradient given in (x) G (x) corresponds to corresponds to the number of points w in the z-direction frequency [nu ^w i mid to produce an echo signal Become. Therefore, if the frequency of the RF wave is selected as the resonance frequency of many points corresponding to the region to be imaged, an effect similar to the change in the resonance frequency obtained by varying G (x) can be provided. In order to provide w, the frequency of the RF wave is applied as a number of resonance frequencies v ^w i.

Regarding the detection of information in the z direction, a gradient magnetic field G (x) is applied in the x direction of the measurement area,
RF (Ra with a frequency ν ^W i equal to the resonance frequency at point w)
When a dioFrequency (wave) is applied, nuclear magnetic resonance (NMR) defined by the following equation at point w in the z direction
ance) phenomenon occurs. ν ^W i = γ i (H 0 + G (x)) (1−σ) (2) Echo signal (or F
The ID signal (free induction damping signal) includes a frequency component of ν ^W i, and by subjecting this signal to Fourier transform, x
And νi correspond to each other, and a two-dimensional image on the xz plane can be formed. In the above, x, y, and z can be set arbitrarily. That is, if x is replaced with y, imaging on the yz plane is possible, and if z is replaced with x, imaging on the xy or xz plane is possible.

Next, the above operation will be described with reference to the drawings.
In FIG. 4, when the measurement object 4 is measured to obtain an image of a vertical section of the human head, the resonance frequency νi at the position (x, y, z) of the point P is νi = γi (H0 + Gx + G
y + Gz) (1-.sigma.). Assuming that the plane including the point P is an image plane which is a measurement area, a gradient magnetic field G (z) which makes a linear change in the z direction is applied as a static magnetic field H0. If
Simultaneously applying a gradient magnetic field G (x) in the x direction of the image plane 15, RF waves having a resonance frequency [nu ^w i corresponding to the number of points w and z direction shown in FIG. 4 (RF1, RF2 ··
.) Is applied in the pulse sequence shown in FIG. 5 or FIG. This RF wave contains many frequency components of RF1, RF2,..., And a large number of resonances observed simultaneously under the condition of the above equation (2) occur simultaneously, and the magnetic moment of the nucleus excited by each frequency component is obtained. As shown in FIG. 4, rotation is performed at a corresponding angle, and a large number of signals are obtained at the same time.
These many signals are received and signal-processed by the signal processing device 12 shown in FIG.
Image 15 is reconstructed and displayed on the display 14. That is, the signal processing device 12 includes a receiving system 16.
Can be used. The broadband receiving system 16a includes a real part measurement channel 17a and an imaginary part measurement channel 17b. The real part measurement channel 17a is a channel for measuring the real part where the phase of the signal is zero, and is a demodulator (demodu).
lator) 18a, low-pass filter 21a and A /
A D converter 22a is provided. Imaginary part measurement channel 1
7b is a channel for measuring an imaginary part in which the phase of the signal is shifted by 90 °, and is a demodulator (demodul).
attor) 18b, low-pass filter 21b and A / D
A converter 22b is provided. When the frequency bandwidth of all RFs is particularly large, it is possible to use a narrow band receiving system 16b shown in FIG. 8B having a real part measurement channel 17a and an imaginary part measurement channel 17b for each RF frequency bandwidth. it can. In the demodulators 18a and 18b, the fundamental frequency portion of the signal is deleted, and the low-pass filter 2
1a and 21b determine the measurement bandwidth, and the A / D converter 2
A / D conversion of the signal is performed in 2a and 22b. On the other hand, the image processing device 13 includes a data processing device 23 and a one-dimensional fast Fourier transformer 24. The signal received and processed by the signal processing device 12 is then subjected to data rearrangement in the data processing device 23 of the image processing device 13 in accordance with the RF order. A one-dimensional fast Fourier transform is performed in the
An x-plane image 15 is reconstructed. Thus, imaging can be performed with one excitation.

[0014]

The resonance phenomenon is generated at different frequencies by the low-speed driving of the gradient magnetic field and the single excitation of the radio wave having the modulated resonance frequency, and the ultra-high-speed MRI is enabled by frequency-separating the obtained signal. As a result, the image becomes clear, and a therapeutic device or the like can be used in the NMR apparatus. Further, since the influence of the eddy current is suppressed, further higher speed can be expected in the future. Further, according to the present invention, imaging can be performed by one-time excitation with modulated RF waves in a large number of bands, so that inspection can be performed at high speed. As is apparent from the above description, according to the present invention, it is possible to obtain a clear image while realizing a further high-speed imaging in MRI, and an apparatus for localization and treatment in an MRI apparatus. Can be obtained.

[Brief description of the drawings]

1 is an explanatory diagram showing the configuration of an MR imaging device. FIG. 2 is a perspective explanatory diagram showing a static magnetic field generating magnet and a gradient magnetic field coil. FIG. 3 is an explanatory diagram showing a spectrum width. FIG. 4 is an explanatory diagram showing a measurement region. FIG. 5 is a pulse sequence for imaging. FIG. 6 is an explanatory diagram showing a pulse sequence for imaging. FIG. 7 is an explanatory diagram showing a signal processing device. FIG. 8 is an explanatory diagram showing a signal processing system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 MR imaging device 2 Exciting device 3 Measurement region 4 Measurement substance 5 Magnet 6 Gradient magnetic field coil 7 Excitation power supply 8 Drive device 9 RF pulse generator 11 Control device 12 Signal processing device 13 Image processing device 14 Display 15 Reconstructed image 16 Receiving system 16a Broadband receiving system 16b Narrow band receiving system 17a Real part measurement channel 17b Imaginary part measurement channel 18a Demodulator 18b Demodulator 21a Low pass filter 21b Low pass filter 22a A / D converter 22b A / D converter 23 Data processing device 24 High-speed one-dimensional FFT device

──────────────────────────────────────────────────続 き Continuation of the front page Examiner Kosen Ito (56) References JP-A-59-105550 (JP, A) JP-A-7-79954 (JP, A) JP-A-61-275646 (JP, A) JP-A-63-317143 (JP, A) JP-A-4-15039 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 3/055 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A substance to be measured is placed in a static magnetic field H0, a gradient magnetic field G (x, y) which is temporally constant in the x direction or the y direction in a rectangular coordinate system, and a number of points w in the z direction as excitation pulses.
A high-frequency magnetic resonance imaging by a single-excitation spin echo, wherein an RF wave having a resonance frequency ν ^w i corresponding to the following is applied, and the magnetic field H 0 is a gradient magnetic field linear in the z direction in a rectangular coordinate system. apparatus 2. A method according to claim 1, wherein the measuring substance is placed in a magnetic field H0 which is a linear gradient magnetic field G (z) in the z direction in the rectangular coordinate system, and a temporally constant gradient magnetic field G in the x direction or the y direction in the rectangular coordinate system. (x, y) of the RF wave is applied with a resonance frequency [nu ^w i corresponding to the number of points w in the z direction as the excitation pulse ^{and, ν w i = γi {H0} + G (x, y)} (1-σ Here, γi: gyromagnetic ratio of element i G (x, y): gradient magnetic field strength in x or y direction σ: shielding constant A spin echo signal observed under the above condition is processed to form a two-dimensional image. High-speed magnetic resonance imaging apparatus using single excitation spin echo 3. A high-speed magnetic resonance imaging apparatus using a single-excitation spin echo according to claim 2, wherein the spin echo signal is Fourier-transformed into a two-dimensional image.