JPH07184872A - System for inspection using nuclear magnetic resonance and inspection method therefor - Google Patents

Abstract

PURPOSE:To observe an image during photographing time by time and to perform judgement of the quality of the image by a method wherein the image of the static part of an examinee is eliminated and a max. strength projecting processing is performed and a processing procedure for displaying an angio image obtd. is stored in a memory device. CONSTITUTION:When image sensing is started (100), at first, a rephase image on which a serum information is reflected is sensed and reformation of the image is performed (101). Then, a dephase image on which the serum information is not reflected is sensed and reconstitution of the image is performed (102). After two images are obtd., by performing a subtraction processing on the two images (103) to eliminate a signal from the static part, an image on which blood flow parts are extracted can be obtd. Then, an MIP (max. intensity projection) processing is performed and, after a projection processing of a blood vessel image is performed (106), the obtd. angio image is displayed (107). While judging whether or not the above described processing is to be continued on the predetermined region (105), the processing is repeated to complete the angio image sensing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures nuclear magnetic resonance (hereinafter referred to as "NMR") signals from hydrogen, phosphorus, etc. in a living body and visualizes nuclear density distribution and relaxation time distribution. NM
The present invention relates to an inspection device using the R phenomenon.

[0002]

2. Description of the Related Art Conventionally, X-ray CT and ultrasonic imaging devices have been widely used as devices for nondestructively inspecting internal structures such as the head and abdomen of a human body. In recent years, an attempt to perform the same examination using the NMR phenomenon has succeeded, and it has become possible to acquire various kinds of information that could not be obtained by the X-ray CT or the ultrasonic imaging apparatus.

First, the basic principle of the NMR phenomenon will be briefly described below. An atomic nucleus is composed of protons and neutrons, and is regarded as a nuclear spin that rotates with angular momentum I as a whole. Now, let's take a look at the atomic nucleus of hydrogen.
The hydrogen nucleus consists of one proton and rotates in the spin quantum number 1/2. Since the proton has a positive charge, a magnetic moment μ is generated as the nucleus rotates,
Each nucleus can be thought of as a very small magnet. (For example, in a ferromagnetic material such as iron, magnetization occurs as a whole because the directions of the magnets described above are aligned.
With hydrogen or the like, the directions of the magnets described above are different, and magnetization does not occur as a whole. However, even in this case, when the static magnetic field H is applied, the respective atomic nuclei are aligned in the direction of the static magnetic field. ) In the case of hydrogen nucleus, the spin quantum number is 1/2
Therefore, it is divided into two energy levels of -1/2 and +1/2. The difference ΔE between the energy levels is generally expressed by the following equation.

[0004]

## EQU1 ## ΔE = γhH / 2π where γ: gyromagnetic ratio, h: Planck's constant, and H: static magnetic field strength.

In general, since a static magnetic field H exerts a force of μ × H on an atomic nucleus, the atomic nucleus precesses around the axis of the static magnetic field at an angular velocity ω (Larmor angular velocity) shown by the following equation.

[0006]

[Equation 2] ω = γH When an electromagnetic wave (radio wave) of frequency ω is applied to a system in such a state, a nuclear magnetic resonance phenomenon occurs, and in general, the nucleus absorbs the energy corresponding to the energy difference ΔE represented by Equation 1. However, it shifts to a higher energy level. At this time, even if many various nuclei exist, not all the nuclei cause the nuclear magnetic resonance phenomenon. This is because the gyromagnetic ratio γ is different for each atomic nucleus, so that the resonance frequency expressed by the equation 2 is different for each atomic nucleus and only a specific atomic nucleus corresponding to the applied frequency resonates.

Next, the nucleus that has been transferred to a higher level by radio waves returns to the original level after a time determined by a certain time constant (called relaxation time). At this time, the angular frequency ω is changed from the nuclei transferred to the high level by radio waves.
The nuclear magnetic resonance signal of is emitted.

[0008] Here, the relaxation time mentioned above is
It is divided into a lattice relaxation time (longitudinal relaxation time) T1 and a spin-spin relaxation time (transverse relaxation time) T2. Generally, in the case of a solid, the spin-spin relaxation time T2 becomes short because the interaction between spins is likely to occur. Further, the absorbed energy first transfers to the spin system and then to the lattice system, so that the spin-lattice relaxation time T1 is the spin-spin relaxation time T2.
It is a very large value compared to. However, in the case of a liquid, since the molecules are freely moving, the spin-spin and spin-lattice energy exchanges are about the same in ease. The phenomenon described above is the same for phosphorus nuclei, carbon nuclei, sodium nuclei, fluorine nuclei, oxygen nuclei, and the like other than hydrogen nuclei.

In the inspection apparatus using the NMR phenomenon based on the above-mentioned basic principle, the signal from the inspection object is separated and separated.
It is necessary to identify, but one of them is to apply a gradient magnetic field to the inspection object, make the magnetic field placed on each part of the object different, and then make the resonance frequency or phase encode amount of each part different There is a way to get. The basic principle of this method is described in JP-A-55-20495 and Journal of Magnetic Resonance (J. Magn. Reson.) Vol. 18, pp. 69-83 (1975), Physics of. Second edition of Medicine and Biology (Phys. Med. & Biol.)
Volume 5, pages 751 to 756 (1980), etc., and detailed description thereof is omitted.

Further, as a method of displaying the MRI image thus obtained, for example, US Pat.
There is a method as disclosed in 8,786. In this method, in spectroscopic imaging, images of P1, H, and P4 are simultaneously displayed on one screen together with spectra.

[0011]

The above-mentioned prior art is a very useful method for determining the active site because it is possible to simultaneously compare the respective image information by spectroscopic imaging and the distribution of each nucleus. Is. However, the above-mentioned prior art is limited to spectroscopic imaging, and does not take into consideration general MRI image display and man-machine interface in image processing, and image display during MRA (Magnetic Resonance Angiography) imaging. Although not described in the above-mentioned related art, in the case of MRA imaging, the conventional MRI apparatus displays the cross-sectional image by performing the image reproduction processing after imaging similarly to the case of general MRI imaging. However, in the case of MRA, each cross-sectional image is not very necessary, and the purpose is to obtain a final blood vessel image.

An object of the present invention is to sequentially display an angio image as a final result according to the progress of examination in MRA.
An object is to provide an MRI apparatus that can be monitored and an inspection method thereof.

[0013]

Basically, an inspection apparatus using nuclear magnetic resonance according to the present invention comprises a magnetic field generating means for generating a magnetic field of a static magnetic field, a gradient magnetic field and a high frequency magnetic field, and an inspection target. Signal detecting means for detecting the nuclear magnetic resonance signal of the computer, an electronic computer for performing a predetermined operation on the detection signal from the signal detecting means, and outputting the result, and a predetermined memory previously stored in a storage device in the electronic computer. A control device for controlling the operation timing of each of the above means is provided in accordance with the procedure. The storage device stores, as a processing procedure, a processing procedure of removing a still portion image of an inspection target, performing maximum intensity projection processing, and displaying the obtained angio image.

[0014]

As apparent from the above procedure, in the present invention,
The maximum intensity projection process is always performed before the angio image for all of the predetermined regions is obtained, that is, immediately after the process of removing the static image is performed, and the obtained angio image is displayed.

Therefore, the image can be seen every moment during the shooting, and the quality of the image can be judged.

[0016]

EXAMPLES In order to facilitate understanding of the present invention, the principle of the conventional spin echo technique will be briefly described before the description of the examples.

FIG. 2 is a schematic block diagram of an inspection apparatus using NMR which is an embodiment of the present invention. Since the external configuration shown in the figure is similar to that of a conventional apparatus, this figure is used. The principle of the conventional spin echo method will be briefly described with reference to FIG.

As shown in the overall configuration diagram of FIG. 2, the subject 20 has X, Y and Z gradient magnetic field coils 16 for generating gradient magnetic fields in three directions orthogonal to the coil 18 for generating a static magnetic field H. , 17, 15 (see FIG. 4) are installed in a high frequency magnetic field coil 8 for generating a high frequency magnetic field. Here, since the direction of the static magnetic field is generally the Z axis, the X and Y axes are as shown in FIGS. 2 and 4. Here, in order to image the transverse cross section (XY plane) of the subject 20, the gradient magnetic field and the high frequency magnetic field are driven according to the spin echo sequence shown in FIG. This will be described below with reference to FIG. 3. In period A, the high frequency power amplitude-modulated in the state in which the gradient magnetic field Gz is applied to the subject 20 is applied to the high frequency coil 8.
The magnetic field strength of the cross section is the static magnetic field H and the gradient magnetic field strength z at the position z.
It is represented by the sum of Gz, H + zGz. On the other hand, since the amplitude-modulated high frequency power of the frequency ω has a specific frequency band ω ± Δω,

[0019]

Ω ± Δω = γ (H + zG
By selecting the frequency ω or the gradient magnetic field strength Gz so as to satisfy z), the hydrogen nuclear spins in the cross section will be excited. Here, γ represents the gyromagnetic ratio of hydrogen nuclei. In the period B, the nuclear spin previously excited by applying the gradient magnetic field Gy for Δt changes depending on the position of y.

[0020]

## EQU00004 ## A frequency shift represented by Δω '= γyGyΔt is caused in the resonance signal. Period D
At, the resonance signal is collected while the gradient magnetic field Gx is applied.
At this time, the nuclear spin excited in the period A is changed by the position x.

[0021]

[Mathematical formula-see original document] A frequency difference represented by Δω ″ = γxGx is obtained. In the period C, a high-frequency magnetic field of 180 degrees and a gradient magnetic field Gz are applied to obtain spin echoes of excited nuclear spins. The period E is the waiting time until the nuclear spin returns to equilibrium. If the amplitude value of the gradient magnetic field Gy in the period B is changed by 256 steps and the resonance signals are repeatedly collected, data of 256 × 256 can be obtained. An image is obtained by subjecting these data to two-dimensional Fourier transform.

Embodiments of the present invention will be described below in detail with reference to the drawings. In FIG. 2, reference numeral 5 is a control device,
6 is a high frequency pulse generator, 7 is a power amplifier, 8 is a coil for both transmission and reception for generating a high frequency magnetic field and detecting a signal generated from the target object 20, 9 is an amplifier, 10 is a detector, and 11 is a signal processing device. Shows. In this embodiment, the coil 8 is used as a transmission / reception coil, but transmission and reception may be performed by separate coils. Also, 12, 13,
14, respectively, in the z direction and the direction (x
Coil for generating a gradient magnetic field in the y-direction)
5, 16 and 17 are the coils 12, 13, 1 respectively
4 shows a power supply unit for driving the drive unit 4. The gradient magnetic field generated by these coils causes the magnetic field distribution in the space in which the inspection object is placed to have a desired gradient. In FIG. 4, the coils 13, 14, and 8 are drawn in order of decreasing size, but this is for convenience of showing the overall configuration, and it is not necessary to stick to this size and order.
The control device 5 has a function of outputting various commands to each device at a constant timing. The output of the high frequency pulse generator 6 is amplified by the power amplifier 7,
Excite. The signal component received by the coil 8 passes through the amplifier 9, is detected by the wave detector 10, and is then converted into an image by the signal processing device 11. The static magnetic field is generated by the coil 18 driven by the power supply 19. In this embodiment, the static magnetic field is generated by the normal conducting method using the coil 18, but it may be a superconducting method that does not require the power source 19 except during excitation. A subject 20 to be inspected is placed on a bed 21, and the bed 21 is configured to be movable on a support 22. Figure 4
2 is an example showing the configuration of the gradient magnetic field coil that can be placed in FIG. An example is shown in which the coil 12 generates a z-direction gradient magnetic field, the coil 13 generates an x-direction gradient magnetic field, and the coil 14 generates a y-direction gradient magnetic field. The coil 13 and the coil 14 have the same shape and are rotated by 90 degrees around the z axis. Actually the coils 12, 13, 1
4 is wound around one cylindrical bobbin and used. These gradient magnetic field coils generate a magnetic field in the same direction as the static magnetic field (z-axis direction), and generate magnetic fields having linear gradients (gradients) along the z, x, and y axes, respectively.

The present invention relates to improvement of the content and procedure of signal processing performed by the signal processing device 11. FIG. 1 shows a simplified procedure of calculating and displaying angio images according to the present invention by taking a subtraction method as an example. Figure 5
Is a conventional diagram corresponding to FIG. 1. Subtract the rephased image and the dephased image shown in FIG.
A case where an angio image is calculated and displayed by performing projection processing by IP (Maximum Intensity Projection) processing will be described in comparison with the processing shown in FIG. First, an example of the conventional calculation / display procedure of the angio image shown in FIG. 5 will be described. When imaging is started (step 100), first, a rephase image in which blood flow information is reflected is taken and image reconstruction is performed (step 101). Next, a dephase image which is not reflected with blood flow information is picked up and image reconstruction is performed (step 102). In this conventional example, the images were collected in the order of imaging the rephase image (step 101) and imaging the dephase image (step 102), but the order of this imaging need not be particular. After the two images are obtained, subtraction processing of the two images is performed in order to remove the signal from the stationary portion (step 103), and an image in which the blood flow portion is depicted can be obtained and displayed. (Step 104). In the conventional processing, the above processing is repeated until the imaging of all the preset areas is completed. Finally, MIP processing is performed to project a blood vessel image (step 106), and the obtained angio image is displayed (step 107). Then, angio imaging is completed (step 108).

Next, in the embodiment of the present invention shown in FIG. 1, when the imaging is started (step 100), the rephase image in which the blood flow information is first reflected as in the conventional method shown in FIG. Is imaged and image reconstruction is performed (step 101). Next, similarly to the conventional method shown in FIG. 5, a dephase image in which blood flow information is not reflected is captured and image reconstruction is performed (step 102). In the present embodiment, the images are collected in the order of the imaging of the rephase image (step 101) and the imaging of the dephase image (step 102), but the order of this imaging need not be particular. After the two images are obtained, subtraction processing of the two images is performed in order to remove the signal from the stationary portion (step 1
By 03), an image in which the blood flow part is depicted can be obtained. In one embodiment of the present invention, MIP processing is performed next, and blood vessel image projection processing is performed (step 106), and then the obtained angio image is displayed (step 107). While determining whether or not to continue the above processing for a predetermined area (step 105), the processing is repeated and then the angio imaging is ended (step 108). It is also possible to end with an intermediate result (step 108) by selecting the end before the final angio image is obtained for the predetermined area (step 105). As described in the above embodiment, the image captured by the MRA is not reproduced and displayed, but the image after MIP processing is displayed each time each image is obtained. By doing so, it becomes possible to judge pass / fail in the middle of the process, so that in the case of a defect, it is possible to interrupt without capturing the image to the end. Also,
Since the final image is displayed moment by moment, the progress of the inspection can be easily grasped. Furthermore, since the imaging can be stopped when the desired portion is displayed, an efficient examination can be performed. In the above description, the subtraction of the rephase image and the dephase image is taken, and MIP (Maximum
Intensity projection processing calculates angio images
Although the case of displaying is described, in addition to the method described in the present embodiment, when the angio image is calculated and displayed by various other methods such as imaging by the TOF (Time Of Flight) method and MIP (Minimum Intensity Projection) method. Needless to say, it is also applicable.

[0025]

According to the present invention, an angio-processed image can be displayed each time an image is obtained in MRA.
By doing so, it is possible to see the images moment by moment during the shooting and judge whether the image is good or bad. Therefore, if the image is defective or the image is not the desired image, it is possible to interrupt without capturing the image to the end.

[Brief description of drawings]

FIG. 1 is a schematic flowchart of processing according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an inspection apparatus using NMR that is an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a spin echo method sequence.

FIG. 4 is a diagram showing a configuration of a gradient magnetic field coil and a direction of a flowing current.

FIG. 5 is a schematic flowchart of processing showing an example of a conventional method.

[Explanation of symbols]

 5 ... ・ Control device 6 ・ ・ ・ High frequency pulse generator 7 ・ ・ ・ ・ Power amplifier 8 ・ ・ ・ ・ Transmit / receive coil 9 ・ ・ ・ ・ ・ ・ Amplifier 10 ・ ・ ・ ・ ・ ・ Detector 11 ・ ・ ・Processing device 12, 13, 14 ... Coil for generating gradient magnetic field 15, 16, 17, 19, ... Power supply unit 18 ... Coil for generating static magnetic field 20 ... Subject

Claims (3)

[Claims] 1. A magnetic field generating means for generating respective magnetic fields of a static magnetic field, a gradient magnetic field and a high frequency magnetic field, a signal detecting means for detecting a nuclear magnetic resonance signal from an inspection object, and a predetermined detection signal from the signal detecting means. Using a nuclear magnetic resonance having an electronic computer that performs an operation and outputs the result, and a control device that controls the operation timing of each of the above means in accordance with a predetermined procedure stored in advance in a storage device in the electronic computer In the inspection apparatus, as the above-mentioned processing procedure, the procedure of processing for removing the still part image of the inspection object, performing predetermined processing for obtaining the angio image, and displaying the obtained angio image is stored. An inspection device using nuclear magnetic resonance. 2. The inspection apparatus according to claim 1, wherein the procedure stored in the storage device further includes the step of repeatedly performing the series of processes on a predetermined area, thereby providing a final step. An inspection apparatus using nuclear magnetic resonance characterized by obtaining an angio image. 3. An inspection method using nuclear magnetic resonance,
An inspection method comprising removing a static image of an inspection object, performing maximum intensity projection processing, and displaying the obtained angio image.