JPS60146140A - Method and apparatus of inspection using nuclear magnetic resonance - Google Patents

Abstract

PURPOSE:To form a method and an apparatus of inspection using nuclear magnetic resonance, by suppressing extra signals by homogenity spoil pulses in nuclear magnetic resonance (NMR). CONSTITUTION:A 90 deg. (x) pulse is imparted in order to give NMR to the atomic nucleus of a body to be inspected. TS1 time after this, a 180 deg. (y) pulse is applied. Before and after the 180 deg. (y) pulse, homogenity spoil pulses are applied at GX, GY and GZ as shown by (a) and (b) in the waveform. By the pulse (b), each magnetization can suppress the yield of a signal A when the 180 deg. (y) pulse is not accurate. When TS2 time have elapsed after the application of 180 deg. (y) pulse, the NMR signal 5 becomes the maximum. After TS3 time a 180 deg. (y) pulse is further supplied. A homogenity spoil pulse is applied to GX, GY and GZ as shown by (c). Thus extra signals caused by the inaccuracy of the 180 deg. pulses can be suppressed, and only the necessary NMR signal can be generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field to which the invention pertains] The present invention relates to nuclear magnetic resonance (nuclear mag++c
tiGresonance) (hereinafter referred to as f'N
Abbreviated as M RJ.

) phenomenon, the distribution of specific atomic nuclei inside the subject can be known from outside the subject. This invention relates to improvements in suitable NMR imagers.

First of all, let us give an overview of the principle of NMR.
I will clarify.

The atomic nucleus consists of protons and neutrons, which are considered to be rotating as a whole with a nuclear spin angular motion ff1l.

Figure 1 shows the hydrogen atomic nucleus (H), which is an IC type, and as shown in (a), it consists of one proton p, and the spin quantum number is 1.
It has a rotation expressed as /2.

Here, since the proton p has a positive charge e+ as shown in (b), the magnetic moment i follows the rotation of the atomic nucleus.
occurs. In other words, each hydrogen nucleus can be thought of as a small magnet.

Figure 2 is an explanatory diagram that schematically shows this point. In a ferromagnetic material such as iron, the directions of these micromagnets are aligned as shown in (a), and magnetization is observed as a whole. . On the other hand, in the case of hydrogen, etc., the direction of the micromagnet (or the direction of the magnetic moment 1-) is random as shown in (1), and no magnetization is observed as a metal body.

Here, a static magnetic field 110 in the Z 7'J direction is applied to such a substance.
When is applied, each atomic nucleus aligns in the direction of H6. In other words, the energy level of the nucleus is set to 17>1 in seven directions.

Figure 3 (a) shows this situation for hydrogen nuclei. Since the spin quantum number of the hydrogen nucleus is 1/2, J, uni, -1/2 and + as shown in Figure 3 (1)
It is divided into two energy levels of 1/2. 2
energy 4 (position J 1''-difference ΔF is (
1) It is expressed by the formula.

Δ[-γFL l-1o ... (1) where γ is the gyromagnetic ratio 9-h/2ych h is the blank constant where each nucleus has a static magnetic field of 1-10 J, and -C1μ
XH.

As a result of this force, the atomic nucleus precesses around two axes at an angular velocity ω as shown in equation (2).

ω-γhl o (Larmor angular velocity)...(2) When electromagnetic waves (usually radio waves) with a frequency corresponding to the angular velocity ω are applied to the system in this state, resonance occurs, and the atomic nucleus has the energy shown by equation (1). It absorbs energy corresponding to the difference E and transitions to a higher energy level.Even if several types of nuclei with nuclear spin angular momentum are mixed, each nucleus has a different gyromagnetic ratio γ, so The resonance frequencies are different, so it is possible to extract only the resonance of a specific atomic nucleus.Also, by measuring the strength of the resonance, it is possible to know the existence of the nucleus.Also, it is possible to determine the existence of the nucleus by measuring the strength of the resonance. After resonance, the nucleus returns to a lower unit after a time determined by the relaxation time and the realized time constant.

This relaxation time is the spin-lattice relaxation time (longitudinal relaxation time)
It is classified into T+ and spin-spin relaxation time (transverse relaxation time>T2), and data on material distribution can be obtained by observing this relaxation time.In general, in a solid, spin is determined on the crystal lattice. Since the positions are almost fixed, interactions between spins are likely to occur.Therefore, the relaxation time T2 is short, and in nuclear magnetic resonance, 1q equals 1 energy tJ
1. First, we move to spin systems and then to lattice systems. Therefore, the crowd was much larger at time T1 than at time T2. On the other hand, in a liquid, molecules move freely, so
The ease of energy exchange between spins and between spins and the molecular system (lattice) is about the same. Therefore, time - ", and T2 are equal in number to 11". In particular, time ""
1 is a time constant that depends on the way each compound binds, and it is known that the value differs greatly between normal tissue and malignant 11F tumor.

Here, we have explained the hydrogen nucleus ('l-1), but in addition to this, it is possible to perform similar measurements with a nucleus with a nuclear spin angular motion m of 1.
It is applicable to phosphorus nucleus (''P), carbon nucleus <C>, sodium nucleus (Na), fluorine nucleus ('F), oxygen nucleus (0), etc.

In this way, by using NMR, it is possible to measure the presence of a specific atomic nucleus and its relaxation time, so by obtaining various chemical information about a specific atomic nucleus within a substance,
Various tests can be performed within the subject.

Conventionally, as an inspection device using such NMR, based on the same principle as the X-ray C-ray, 101 hens of a virtual cross section of the subject are excited, and the NMR corresponding to each projection is excited.
There is a method in which MR resonance signals are measured in many directions of the subject and the N M II resonance signal intensity at each position of the subject is determined by a reconstruction method.

Figure 4 shows the two-dimensional stage Jl Yore H8 no Recon method, which uses the spin echo method.
structtonmetl+od) (hereinafter two-dimensional P
FIG. 2 is an operation waveform diagram for explaining an example of an inspection means of a conventional apparatus to which the R method is applied.

First, a two-gradient magnetic field Gz as shown in FIG. 4(B) and an RF pulse (9o6 pulse) with a narrow frequency spectrum f as shown in FIG. 4(B) are applied to the subject. As a result, an NMR resonance signal as shown in FIG. 5(e) is generated. When Ts+time has elapsed until this NMR resonance signal 23 disappears, a 180° pulse is applied. As a result, the dispersed magnetization M begins to gather again, and as shown in (e), the NMR
Faith y3 gradually increases. Spin echo 1
Call it No. 5.

After the 180° pulse is applied, the spin echo signal reaches its maximum after a time period of 21+-S has elapsed. Then 1-53
During the period, the gradient magnetic fields Gx and Gy shown in (c) and (d) of the same figure are applied, and the signal is increased by 1q. Perform processing such as main conversion on this signal /7 [! In particular, it is possible to obtain block data for reconstructing cross-sectional images.

After the TS3 period, LJ is held for a predetermined period of time.
, Gy little by little, 11 in many directions of one tree under test.
”The extraction data is 11. In this way,
The surface data of the relevant cross section can be stored.

However, such a device has the following problems.

(2) If the 180° pulse has even a slight irregularity, a component will occur, resulting in an extra signal like J: shown in (Bo) in FIG. 4.

(2) In the so-called multi-slice method in which a plurality of planes are sequentially excited, when there is a correlation between views, disturbances in the movement of magnetized planes and incorrect signals occur.

■When the period TS3 ends, the magnetization vector at the boundary of the slice plane is directed in the negative direction of the l axis, and the thermal equilibrium state is not returned unless the recovery time Td is made sufficiently long, resulting in an insufficient recovery time 1-d.
In this case, the following sequence is obtained (i becomes smaller).

[Object of the Invention] In view of the above points, the object of the present invention is to provide a spin-one-cow method that suppresses the generation of unnecessary signals in the NMR signal and generates only the necessary signals. 2D P
It is an object of the present invention to provide an inspection method using R-method nuclear magnetic resonance and an apparatus therefor.

[Summary of the Invention] The present invention for achieving the first objective is to apply a first 90° pulse to impart a nuclear magnetic sound to the nuclei of atoms constituting the tissue of the subject. J-ru” two pieces, this first one.
After Ts + time has elapsed since the application of the 90° pulse, the first 180° pulse is applied to 110 IJ: a step of applying a second 1806 pulse after 53 hours have elapsed from the start point 115 of the measurement of the nuclear magnetic resonance signal; , wait for 1 d time to pass after applying this second 180° pulse, and then proceed to the next step. 1806 pulses before and after the first 1806 pulse and (also) the second 1806 pulse.
In the 180'' pulse, homogeneity spoil pulses are applied in the X, y, J, and Z magnetic field gradient directions.

[Example] The present invention will be described in detail below with reference to the drawings. FIG. 5 is a block diagram showing the configuration of an embodiment of a device for implementing the method of the present invention. In the figure, 1 is a static magnetic field coil for generating a uniform static magnetic field Ho (in this case, in 7 directions), and 2 is this static magnetic field coil 1.
The control circuit includes, for example, a DC stabilized power supply. The density Ho of the magnetic flux generated by the static magnetic field coil 1 is 0
．． It is desirable that the uniformity is about 1T and the uniformity is 10-4 or more.

Reference numeral 3 generally indicates a gradient magnetic field coil, and 4 indicates a control circuit for this gradient magnetic field coil 3.

FIG. 6(a) is a dimensional configuration diagram of an example of the gradient magnetic field coil 3, in which the Z gradient magnetic field coil 31, the Y gradient magnetic field coil 32 are shown.
．． 33. Although not shown, a y-gradient magnetic field coil 32.
It has the same shape as 33 and includes an X-gradient magnetic field coil that is rotated by 90°.

This gradient magnetic field coil is arranged in the same direction as the uniform static magnetic field Ho in the x, y, and z axes directions (la
Create a place. The control circuit 4 has a 21st part 1-1-ra 20 (
(details will be described later) is controlled by υ11.

5 is an excitation = 1 il which gives a narrow frequency spectrum 1 Hz pulse as an electromagnetic wave to the subject, and its configuration is shown in FIG. 6 (b).

6 is the NMR resonance line '1 of the atomic nucleus to be measured.
Frequencies corresponding to
(iMl-12/T) oscillator (・
, and its output)j are applied to the excitation coil 5 via a gate circuit 30 (details will be described later) whose opening and closing are controlled by signals from the controller 20, and a power amplifier 7. 8 is a detection coil for detecting a 83 kN noise signal on the subject; its configuration is shown in Figure 6 (
It is the same as the excitation coil shown in b), and is installed at 906 rotations with respect to the excitation coil 5. Note that this detection coil is preferably installed as close as possible to the subject, but may also be used as the C1 excitation coil if necessary.

9 is an amplifier for amplifying the N M l (, Jt olfactory multiplier signal obtained from the detection coil 8, 10 is a phase detection circuit, and 11 is a signal from a wave memory circuit 11 that stores the phase-detected waveform signal from the amplifier 9. For example, a computer receives the input via a transmission line 12 made up of an optical fiber and performs predetermined signal processing to obtain a tomographic image, and 14 is a display device such as a television monitor that displays the obtained Ii layer image. .

Further, necessary information is transmitted from the controller 20 to the computer 13 via a signal line 21.

The controller 20 generates gradient magnetic fields Gz and Gx.

It was configured to be able to output signals necessary for controlling Gy and RF modulation signals (alley-log signals) and control signals (digital signals) necessary for transmitting RF pulses and receiving NMR signals. It is something.

The gate circuit 30 receives the R signal from the oscillator 6, and generates four types of signals with 90° different phases in response to the R signal.
One of the four types is selected based on instructions from the controller 20, and this is further modulated with an RF modulation signal to obtain a drive signal for the exciting coil 5.

The bow movement 1 of the present invention constructed in this way will now be described with reference to FIG. 7.

1) As before, apply a 90'x pulse (this pulse is modulated by, for example, the QalJSS function so that it has a narrow frequency spectrum), and as shown in Fig. 7 (a), this J: 1-51 hours later 1
Apply 80°y pulse. Here, the subscript X + 3' of 906 or 180° indicates the phase of the RF pulse, and X and y
The phase difference was 90'.

There are J and 5 before and after this 180' y pulse, and as shown in the waveforms (eco) and 2) in Figure 17, there are small modinines, r, spoil, and Add pulse.

1806y pulse application ■Te magnetization IVH, center of slice plane (90° pulse application stops magnetization M and 410'
rotating part), slice plane boundary (when 90° pulse is applied, M rotates θ°, and 180° pulse IIJ jJII
I+ij has G2=O, so the part rotates 180°) and the magnetization outside the slice plane (the part that is not affected by the application of a 90° pulse and the direction of magnetization M is reversed by the 1806 pulse) The directions of M are as shown in sections a) and c) of Fig. 7, respectively.

By applying pulse b immediately after applying this 180°y pulse, each magnetization M becomes as shown in the figure, and the signal A (as shown by the dotted line in the same figure (e)) that occurs when the 180''y pulse is inaccurate (If this remains for a long time, it will affect the observation of echo signals) can be suppressed.

Note that if only the pulse b is applied, the magnetization plane 1H will be disturbed, so just before the 180°y pulse, (b) in Figure 7 will be generated.
As shown in ~(d), pulses like a are applied. The pulses a and b are used in pairs, and the products of intensity and time of a and b are equal in each of Gx, Gy, and Gz.

2) When T52 hours have passed after applying the 180°y pulse, N
The MR signal reaches its maximum, and G in the subsequent TS3 section.
Observe NMR Shintan while applying x and Gy.

At the end of the 53rd period, the two magnetization vectors at the slice boundary are below (/l1lllnh
11 slices are sliced on the cone facing
Outside 01 is facing Ito.

3) After the Ts3 interval, apply a 180°y pulse to move the slice boundary and the magnetization edges 1 to 1 outside the slice plane upward as shown. To this, J, Su, 9. iii) The magnetization vector at the slice boundary approaches the thermal equilibrium state ta:. The magnetization vector outside the slice plane is in a state close to the thermal I iρ1 state.

4) Next, for Gx, Gy and Gz -C (b) in Figure 7
~ (d) As shown by C, ho[zinnia r spoiled
Pulse hl G). This eliminates the correlation between the yicws, and even if the 180' y pulse is uncertain, it immediately reduces the signal caused by it.

5) Then wait 16 hours and move on to the next yicw sequence.

In this manner, the generation of extra signals caused by the incorrect 141° of the 180° pulse is suppressed, and the necessary NMR
Only the signal can be avoided.

Note that the present invention is not limited to the embodiment shown in FIG. 7, and may include other embodiments as listed below.

1) The RF pulse sequence shown in Figure 7 is (90°X.

1'sI・180'y, ding S2. TS3. 18
0°y・Td), but the phase of the RF pulse is limited to this. For example, (90°, 'l'-5,, 180
°-months, Ts2, 1-53, 180°-x,
-1'd) may be used.

2) In the embodiment of FIG. 7, Gx and Gy are only within the section of TS3.
Although not limited to this, as shown in Figure 8, Gx and G
You may also write y. However, in this case, a legal relationship must be established.

Qx+Xim+=CIX2Xim2 g'/I XT, ro+ = gV2 Also, TS+ and 1-52 can be shortened.

3) It is applicable not only to the two-dimensional PR method but also to the Fourier method and the spin warp method.

4) It is also possible to apply a so-called invirgini silica 91 which adds a 1+(0° pulse) before the sequence, which is not shown in FIG.

5> It is also possible to set the 180° pulse in the sequence to 33 pulses. For example, instead of 180°X, 90°x
, 180°7, 90°X Sg: Instead of 180°, 90'y, 1806x, 90°y etc.

As a result, in particular, the out-of-plane magnetized hexagonal is reversed to jl(, TF, so that the disturbance of the extra it number X5 + a-formed hexagonal) is reduced.

6) During the waiting time of d, other planes are excited and their information is also collected (multi-slice method), and the apparent
It is possible to perform fast imaging.

As explained above, according to the present invention, components of the magnetization vector are eliminated by the spoil pulse, redundant signals are reduced, correlation between views is reduced, disturbance of the magnetization vector is eliminated, and the extra 4T signal is removed. It can prevent the occurrence of redness.

In addition, the second 180° pulse causes the magnetization vector at the slice boundary to point upward, thereby making it possible to approach a thermal equilibrium state with a short Td. Also, in this case, insufficient Ta
However, the effect is that a large signal can be obtained in the next sequence.

Furthermore, by using three optical pulses, the vector rotates accurately, so unnecessary signals are less likely to be generated, and the necessary large signal can be obtained.

Furthermore, by using multi-slice, many images can be acquired in the same time as it takes to acquire one image ( ), which apparently reduces the imaging time. Since the spoil pulse, the second i ao' pulse, or three pulses as described above are used, the movement of the magnetization vector is accurate, and the vector moves correctly even during the full-nare slice.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the spin of a hydrogen atom, Figure 2 is a schematic diagram of the magnetic moment of a hydrogen atom being 1, and Figure 3 is a diagram explaining the state in which the nucleus of a hydrogen atom is aligned in the h direction of the magnetic field. Zuru diagram,
Fig. 4 is a diagram that does not show an example of the test pulse waveform by NMR, Fig. 5 is a configuration diagram of an embodiment of the device of the present invention, Fig. 6 is a structural diagram showing an example of a magnetic field coil, and Fig. m7 is a diagram of the present invention. FIG. 8 is an operation waveform diagram showing another embodiment of the present invention. 110. Static magnetic field coil, 2, 4. ,, Long spell system. control circuit, 351. Gradient magnetic field coil, 511. Excitation coil, 6610 oscillator, 880. Detection: 1il, 10,...
, phase detection circuit, 11. ,, one]-bu memory circuit, 13
．． ,,computer,20. ,. controller, 30. ,,gate circuit.

Claims (3)

[Claims] (1) Applying the first 90° pulse to give nuclear magnetic resonance to the nucleus of the atom that describes the tissue of the subject, and after TS1 hours have passed from the application of this first 90' pulse. a step of applying a first 180° pulse to the atomic nucleus; and a step of applying a gradient magnetic field to the atomic nucleus after TS2 hours have elapsed from the first 180° pulse and measuring the resulting nuclear magnetic resonance (ft). , after T53 hours have elapsed from the start of the measurement of the nuclear magnetic resonance signal, the second
applying a 180° pulse and this second 180° pulse;
While repeating the thetance including the elapsed time Td after the application of the pulse -C to move to the next one culm, an image related to the tissue of the subject is reconstructed based on the nuclear magnetic resonance signal. J3J, and (or) the second 180° pulse before and after the first 180° pulse.
0°l< )Lt Suni43 b' T is X, ri'J3
An inspection method using nuclear magnetic resonance in which a homogeneity spoil pulse is applied in the direction of the magnetic field gradient of Nibi-2. (2) The first and second 180° pulses have the same phase and are 9 in phase with respect to the 180° pulse.
2. The nuclear magnetic resonance inspection method according to claim 1, wherein the pulse is provided with two 90' pulses before and after the two 90' pulses, which differ by 0°. (3) The nuclear magnetic resonance examination method according to claim 1Jn, characterized in that the multi-slice can be performed by exciting another slice plane during the waiting time Td. (4-) means for applying a high-frequency pulse for imparting nuclear magnetic resonance to the atomic nucleus of an atom that depicts the tissue of the subject; a magnetic field applying means for imparting a gradient magnetic field to the atomic nucleus; and nuclear magnetic resonance occurring in the atomic nucleus. In a nuclear magnetic resonance inspection apparatus equipped with a means for measuring a signal, the means for applying a high-frequency pulse applies a first 90' pulse and then, after a predetermined time, a first 180° pulse and further a predetermined pulse from this. If a second 180° pulse is applied after a predetermined time after the application of the second 180° pulse, the i41-
, ) ” (Includes 4 means 4!- for transitioning to the next sequence, and the tIFJ magnetic field applying means is the first 180
°To apply a gradient magnetic field a predetermined time after the pulse (
111 before and after the first 180° pulse and/or after the second 1806 pulse,
The means for measuring the nuclear magnetic field is configured to apply a small magnitude spoil pulse in the gradient magnetic field directions of y and l, and the means for measuring the nuclear magnetic field is configured to apply a nuclear magnetic resonance signal generated when the gradient magnetic field is applied to Lj. An examination by nuclear magnetic resonance configured to measure and use for reconstructing images related to a single tissue under examination and characterized by %f/! /.