JPS5957147A - Method and apparatus for inspection utilizing nuclear magnetic resonance - Google Patents

Abstract

PURPOSE:To forcibly bring magnetization to thermal equlibrium, by a method wherein an object to be inspected is excited by a specific angle pulse at the beginging of repeated inspection sequence and the specific angle pulse is again applied at the point of time when the echo signal at the end of sequence becomes max. CONSTITUTION:Gradient magnetic fields in three axis directions crossed at right angles, that is, in an x-, a y- and a z-axes are controlled through a gradient magnetic field control circuit 4 and the applications of various kinds of pulses for exciting an object to be inspected through a gate circuit 61 are controlled by a controller 60. In this case, after an object to be inspected is excited by a 90 deg. pulse at the begining of repeated inspection sequence, an echo signal due to nuclear magnetic resonance is formed by a predetermined gradient magnetic field and an exciting pulse. When the 90 deg. pulse is again applied at the point of time when the echo signal becomes max., the direction of magnetization is forcibly directed to the direction for bring said direction to thermal equilibrium state and rapidly returned to the good initial state for starting the next sequence to form a tomographic image having high S/N and high resolving power.

Description

[Detailed description of the invention]

The present invention is 91 pieces of nuclear magnetism!゛clear ma
g++eLicresonance) (Rishita this r
The present invention relates to an inspection method and an inspection apparatus using nuclear magnetic resonance, in which the current S1 (abbreviated as N M It , 1) is used as the 11th to know the distribution of specific atomic nuclei in the subject from outside the sample. Before explaining the present invention, the principles of NMR will be briefly explained in Sections B and J. The atomic nucleus consists of a proton and one child inside, and these as a whole are considered to be rotating 1 degree with nuclear spin angular momentum ■. Figure 11. -t, shows the hydrogen nucleus ('n), which consists of one proton P as shown in (a) K, and rotates as expressed by the spin quantum number 1/2. Here, the proton I) also has a positive σ) charge of 1, as shown in (b),
Therefore, as the nucleus rotates, a magnetic moment is generated. In other words, each hydrogen nucleus can be seen as a small magnet. Figure 2 is an explanatory diagram schematically showing 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. First. On the other hand, in the case of hydrogen, etc., the direction of the micromagnets (the direction of the 9-shell moment) is f random as shown in the diagram, and no magnetization is observed as a whole. Here, a static magnetic field ++ in the Z direction is applied to such a substance. When is applied, each atomic nucleus is aligned in the I-Io direction (the energy level of the nucleus is magnetized by M in the Z direction). The third (At) shows this hammer for hydrogen J3ij, -r cedar. Since the spin quantum number of the water nucleus is /2, as shown in Figure 5 (b), -1 and +1/! The energy difference ΔE between two energy levels, which is divided into two energy levels, is expressed by equation (1). Δ1 bow = rk+10...
・(1) However, γ: gyromagnetic ratio 1; = h/2π 11 Nyblank constant Here, the static magnetic field +10 is applied to each JJ child nucleus. T-b-
・Since a suspension force of 1 is applied, the atomic nucleus rotates around the Z axis (2
) precesses at a steep angular velocity ω, as shown by the equation. ω−γIIn (Larmor angular velocity) ・・・・・・
(2) In this state σ), when an electromagnetic wave of a frequency corresponding to the angular velocity ω (usually ω, ω) is applied, resonance occurs,
The proto-I nucleus absorbs energy corresponding to the energy difference ΔE shown in equation (1) and transitions to a higher energy level. Even if several fm nuclei with nuclear spin angular momentum coexist, each nucleus has a different gyromagnetic ratio γ, so the resonant frequencies differ, and therefore it is difficult to extract only the resonance of a specific nucleus. It's six. In addition, by measuring the strength of the resonance, it is possible to know the existence phase of the atomic nucleus.Also, after a time period called relaxation time, which is determined by time convergence, the nucleus is excited to a higher level. The atomic nucleus returns to a lower level. Among these relaxation times, the spin-interstitial relaxation time (W relaxation time), which is called 1゛1, is a time constant that depends on the way each compound binds, and is different between normal tissues and malignant tumors. , it is known that the values differ greatly. Here, we have explained the hydrogen nucleus (1■), but it is possible to perform similar measurements with other atomic nuclei with nuclear spin angular motion 171, and in addition to hydrogen nuclei, phosphorus nuclei (B I p ) , carbon nucleus (15C), na)
IJium nucleus (25Na), fluorine nucleus (F),
It is applicable to oxygen nuclei (170), etc. □In this way, by NMR, the past and past existence of a specific atomic nucleus σ) and the relaxation time of the child are determined by g + + -, so the material /
il, 4 in j! Various chemical information' in the I-determined atomic nucleus? By leaving X-Ji, we will be able to conduct multiple tests inside the subject. bt Since then, as a medical examination using such a block <N /-
Resonance signals are obtained in many directions behind the object, and the NMI' corresponding to the
MrL Q'% (There is a method in which the δ intensity is determined by a reconstruction method. Fig. 4 is an operation waveform diagram for explaining an example of an inspection method in such a conventional device 12VC.
First, as shown in Figure 4 (b), there is a Z gradient magnetic field (2) and a thin frequency spectrum (f) as shown in (a).
Apply tF pulse (qu'pulse)'c. In this case, protons are excited only on the surface where the Larmor angular velocity ω = γ (11o + Δ0.), and the magnetization M is expressed as y in a rotating coordinate system rotating at ω as shown in Figure 5 (a). '9 in the axial direction

[J°It is the same as the one whose direction has been changed. Next, as shown in Figure 4 (c), the X gradient magnetic field 0□ is applied for a predetermined time +
1 is added, thereby grading the phase of magnetization M in the X-axis direction as shown in equation (5). γL engineering f+□d+・0. =2π11
・・・・・・(3) However, r: Magnetic rotation ratio ■, d: Length of object in X direction N-N n: Integer (n = -7-7+1, . . . , -1, [1,
+1. ..., H-+) N: Number of divisions in the Z direction Next, as shown in Figure 4 (=), a V gradient magnetic field G is applied, and under this, as shown in Figure 4 (j → Detect the NMR resonance signal.Graduation is performed in the y-axis direction using the Larmor angular velocity. As it gradually disperses in the direction of the raw egg within the / plane, the NMR and resonance signals eventually decrease and disappear after 7 hours as shown in Section 4V). Hereafter, wait one hour until the state returns to thermal equilibrium, and then repeat the next sequence lV = 1V. At this time, the predetermined time for applying the x gradient magnetic field (J) is repeated N times with the value determined by equation (5). .Then, by performing two-dimensional Fourier transformation on the N M 11 resonance signal obtained by N times of 7 times, an in-plane proton density image can be obtained). In the conventional device that operates, in Fig. 4, NMIl, the time τ until the resonance signal disappears is 10~211+ηS, and the time τ' is 10~211+ηS. Relaxation time 1゛, due to 1
sec culmness is required. Therefore, if the division ratio N in the X-axis direction is, for example, about 100, a long time of at least 2 minutes or more is required for the measurement. Here, the present invention aims to eliminate such disadvantages (also σ) in conventional methods and devices. The method according to the invention comprises a 90° pulse of il! After exciting the subject with magnetic waves, an echo signal is created by reversing the gradient magnetic field and anti-gauge, and when this echo signal is at its maximum, a 90° pulse of electromagnetic waves is applied again to return the magnetization M to a thermal equilibrium state, 1
:The feature is that it is set to 5. FIG. 6 is a flowchart showing the number of phases of an embodiment of an apparatus for implementing the method of the present invention. In the figure, 1 is a static magnetic field coil that generates a static 1 NJ4) TO (complicated) magnetic field σ) direction is the Z direction), and 2-digit l
1 i TI magnetic field 1 coil 1 distribution 1 circuit, including the source DC stabilization 11: source + 1) magnetic flux density Ha, 0. at IT culm)
) Su, also - yesterday's 1n-4 was more than Z) is a wishful thinking + 11 and 5 slope? A comprehensive view of the i+7 embankment coil (-Tamoσ)
, 4 is a control circuit for this gradient magnetic field coil 5. TJ', 7 [9: I (A) is a configuration diagram showing an example of the gradient magnetic field coil 5, where the Z gradient magnetic field C S coil Δ1
．． 3/Gradient magnetic field 11 + coil 32.53, shown in the figure 11. Is it the same shape as the magnetic field coil 32.53, rotated 90 degrees and installed? The coil 3 for the X gradient magnetic field, which contains the coil for the X gradient magnetic field 7, this σ)/I, for the eτ field, has a magnetic field of 1, f, in the same direction as the uniform static magnetic field 110.
60 is the controller of the control circuit 4 (Z). 5 is #Jr *R, F of the narrow frequency spectrum f on the body
/ζζsus 11. Force as magnetic waves7. ,) excitation coil, σ) configuration is shown in Figure 7 (r'I)vC.
'I') is an oscillator that generates an electric shock, and the output of the spear is
A gate circuit 61 whose opening/closing is controlled by a signal from a controller 60 is applied to the excitation coil 5 via a power amplifier 62. 7 is the NMR co-p of the first sample
(L (Detection coil for i detection, structure D
V is the same as the excitation coil shown in FIG.
It is desirable to install this coil as close as λ to the subject, but if necessary,
lff1i V? 'l Coil and the previous month] You can also get a rash. 71 is an NMR resonance signal (F
ID: frceir+rlucjion dec
ay); 72 is a phase detection circuit;
73 indicates a phase-detected waveform signal from the amplifier 71.1. Ff wave memory circuit 8, which includes an A/D converter, inputs the signal from the wave memory circuit 73 via a transmission line 74 made of, for example, an optical fiber, and performs predetermined signal processing. A computer that obtains tomographic images,
Reference numeral 9 denotes a tr display, like a television set, which displays the obtained tomographic image. The operation of the device (σ) with l'Dψ in this manner will now be described with reference to FIGS. 8 and 9. First, the control circuit 2 applies a current to the static magnetic field coil 1, and applies a static magnetic field I1. Assume that the state is given. In this state, the controller 60 first sends a current to the X gradient magnetic field coil 31 via the control circuit 4 to generate a Z/I:J magnetic field (1z+11i4) as shown in FIG. Under O1+, the gate circuit 61
is opened, and the signal from the oscillator 6 is applied to the excitation coil 5 via the amplifier 62, resulting in a narrow spectrum as shown in FIG. 8(a). One side of the subject is excited with 90 pulses. In addition, in Figure 8 (b), G21 has a thread (0□,
This is a known method for improving the SIN ratio. At this time, at A11, the magnetization M changes its direction 906 in the l' axis direction as shown in the rotating coordinate system of FIG.
As shown in Figure (c), 5 VC7) P furnace i with constant r
0. A current is applied for a predetermined period of time, and then a current of, for example, positive polarity is carefully applied to the 7th order 1st distribution coil 3, and
Apply gradient magnetism 1+->, -1-rly for a predetermined +1ν period of +v, and detect under this.
As shown in figure (E), Br N Mn・4]・ql! Detected as signal data E1, this NMII and III”,
At the time when the signal is detected (for example, at the time of the seal),
As shown in FIG. 9(b), the magnetization M is in the process of gradually dispersing in the direction of the dashed arrow in the x'IX/ plane. NMR outputted by the detection coil 7, both l'lli
', the signal gradually attenuates over time and eventually disappears. This signal is multiplied by the intensifier 71, phase detected by the phase detection circuit 72, and then detected by the wave memory circuit 73.
The computer Bvc is applied via. Here, NM
Both R and 11β signals are Fourier transformed and have 1 brogiex. signal. The operation up to now is the same as that of the conventional device. After τ time elapses after applying 90 pulses of electromagnetic waves (N
M rt and nl: j signal is absent < 1, (time until it occurs),
The controller 60 reverses the direction of the voltage applied to the y-gradient magnetic field coil 33, flows the 11; Dt
Apply only for a fixed time ly). And, below this, as shown in FIG. 8 G1-) obtained from the detection coil 7? C.N.
Dark signal at MIN-I (the first one is called the echo signal, ζ)
At the point in time when this echo signal is detected as fl (for example, the second point in time), the magnetization M is within the j, %1' plane as shown in FIG. 9(c). It is in the middle of gradually joining 1i in the direction of the dashed arrow. Confusingly, as shown in Figure 8 (c), 15 "on-time 11JI,
Then, as shown in Fig. 8 (b), an X gradient magnetic field -G22, - (7th..) is applied. As shown in Fig. 8 (a), a 90°-r pulse electromagnetic wave is applied.The sequence after applying the electromagnetic wave for τ time after first applying the electromagnetic wave (the sequence in which an echo signal is waited for) ) is a book in which the previous sequence (sequence for detecting data EI) is repeated in reverse 11i order. Therefore, assuming that the state of the sample does not change during the 2i time period, the data obtained in the previous sequence will be 7-data ■・;1.
Data E of the echo signal input in the j-%σ) sequence (means a signal waveform that is symmetrical on the time axis). When a positive magnetic wave of 90°-τ' pulse is applied with tC and lr shields, 1. As shown in Figure 9), the magnetization M is i
Axially φ; strictly oriented. Here, as shown in the figure, the magnetization M does not completely coincide with the 7; axis and is in a slightly dispersed state due to the relaxation time Go2. After a short period of time τ' in this state, the magnetization M-axis coincides with the i-axis due to relaxation. From the time point 15, the recovery time τ' when the magnetization M coincides with the i-axis is as follows: At the time point 130, the magnetization M is 7. Since there is only a slight dispersion from the ′ axis, it is sufficiently short compared to the relaxation time ′1”1, for example, about 4τ. When the rounding time τ′ has elapsed, the first sequence After that, the same sequence is repeated +0 In each sequence, the application time 1 of the X gradient magnetic field Oi applied to the specimen is adjusted according to the conditions of equation (5), so tt so j + σ)
Regarding the sequence, from detection coil 7 N M n J
l: n! ``Obtain + signal -β and echo signal. Combi 1.-E 8 are output in each sequence, for example, N M n 'v'' (data 1'i1. E2...σ) Perform a two-dimensional transposition operation as a group of N γ-tori to obtain an image and display it on the display 9. In the above, the computer 8 is designed not to use echo signals, but in each sequence, it first outputs f1, NMR, JI: ringing signal (this is simply referred to as NM11.signal). ) of each data M1. ! ', 2..., and each data E H + M2... of the echo signal that is output subsequently can be used. be. The average value of the +IINMTL signal and the signal obtained by reversing the time axis of the echo signal is expressed, and this is treated as one data,
Perform a two-dimensional Fourier transform operation to obtain a single tomographic image. (Obtain a proton density image using the II+NM signal, and calculate the difference signal between the NM multiplied signal and the echo signal with the time axis reversed, and use this as one σ) data7 to perform Fourier transform calculation. Transverse relaxation time called T2 (T2 is caused by the interaction of spins of nearby electron nuclei) Vci-; 6 (Obtain both images of 'r2 image. Based on (11), the proton density is 1
Another image is obtained by combining the iTi image and the '1' image. 6v) Average several N M It times signal echo signals of the lr tRσ) sequence and use this as one data. By adopting these methods, it is possible to improve the slN ratio and obtain an image with a quality of 11. However, by selecting one of these methods depending on the purpose of diagnosis, it is possible to obtain a tomographic image suitable for the purpose. FIGS. 10 and 11-1 are operation waveform diagrams showing other examples of the method according to the present invention. The method shown in FIG.
jec+ion rccnn+Nrt+cLion)
It was applied to As shown in Figures 10 (a) and (b), first, while applying a Z gradient magnetic field G2, a 90'' pulse electromagnetic wave is applied, and when at U, in Figure 10 (c), As shown in , X gradient magnetic field Sa and V gradient magnetic field (1,
2 by this? An original gradient magnetic field is created at ', and under this field, the L N M It co-exit signal is detected as shown in (e). # After applying the 9n' pulse, the X gradient P in the Zen direction is shown.
) J% -01 and y gradient magnetic field -Gy are applied simultaneously, and under this, an NM resonance signal (this is called an echo signal) is detected as data 1, as shown in (e). After that, (at the time when 2τ has passed after applying the 9o° pulse, that is, when the echo signal reaches the maximum), the Z
A gradient magnetic field ~(), I is applied, and with this 1, 900. Apply pulsed electromagnetic waves. Thereafter, wait for the recovery time τ' and repeat the following sequence in step 1:5. In each sequence, (1a,
(1) is transformed little by little, thereby making it possible to obtain NM resonance signals and echo signals corresponding to each projection in many directions of the object. The method shown in FIG.
xciJRjinnI applied to the inr+ method, so force) ro. As shown in FIGS. 11(a) and 11(b), while applying the Z gradient magnetic μ2 (12), apply a 90' pulse electromagnetic wave IJl+L,, 121xl (a) iτ. + Subject ITn17ffis, with the surface FJ!l start -1. As shown in Fig. 11 (c) and (a), under the X gradient magnetic field (1□ also applied). , 180' pulse is applied 111 to this (Figure 11 method) VC 87. as shown. Excite only the line Δy on the surface. IN
N M as shown in Fig.
IL J1H Narushin dark light spin echo) is maximum 7) A
A y gradient magnetic field oy is applied, and spin echoes are detected as datat:1 under which. After that (one hour after applying the qo″ pulse), the gradient furnace + −o in the reverse direction
, , Go'! l-G! are applied sequentially, -G2 is applied, and an electromagnetic wave of 90'''-Je pulse is applied at °C. By Fourier transforming the data I': I T Ml, X on the line Δν shown in FIG.
The proton density distribution in the axial direction is taken using the (+J lococoder). After that, the magnitude of o!/ + "!/ is gradually increased and the above sequence is repeated to obtain secondary T data over the entire Sz surface. As mentioned above, the method according to the present invention provides at least two types of pulses, (qo6 pulse, qi
The direction of the magnetization M is forcibly changed by a row of aer pulses, and the magnetization MfX returns to the equilibrium state in a short time. Check out the tomographic images related to this! 1. Wear hakama with rokoto. In addition, the NM multiplied signal and echo signal are #J'
Therefore, by using each of these signals, a tomographic image with a good S/N ratio and high resolution can be obtained.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram for explaining nuclear magnetic moments, Figure 2 is an explanatory diagram for explaining the arrangement of nuclear magnetic moments, and Figure 3 is an explanatory diagram for explaining the arrangement of nuclear magnetic moments due to a static magnetic field. , FIG. 4 is an operation waveform diagram for explaining an example of the conventional method, FIG. 5 is a tth explanatory diagram for explaining the direction of magnetization M by the method of FIG. 4, and FIG. 6 is a diagram according to the present invention. A professional showing an example of a shed to realize the method. Figure fp; Figure y (A) is a configuration diagram showing an example of the gradient magnetic field coil σ) used in the device in Figure 6, and (B) is the same. , 8th
The figure is an operation waveform diagram for explaining one of the methods according to the present invention, and Fig. 9 is a rotation μm in the direction of magnetization M at the first point in time according to the present method. The explanatory diagrams shown on the standard scale, Figures 1n and 11 are the methods of the present invention.
An operational waveform diagram showing an example, FIG. 12 is an explanatory diagram of an excitation surface by an electromagnetic wave pulse button applied in the method of FIG. 11. DESCRIPTION OF SYMBOLS 1... Coil for static magnetic field, 2... h coil control circuit for static magnetic field, 3... Coil for gradient magnetic field, 5... Excitation coil, 6 [1... Controller, 7... detection coil,
8...Combi 7-ta.

Claims (1)

[Claims] (1) Applying a uniform static magnetic field to the subject and marking an electromagnetic wave with a frequency that induces nuclear magnetic resonance in the subject? In addition, a gradient magnetic field is applied to the subject to identify a radiation part of a nuclear magnetic resonance signal from the subject, so as to obtain a nuclear magnetic resonance signal (NMR signal) from a specific part of the subject. In this testing method, the subject is first excited with 90 pulses of electromagnetic waves, then a gradient magnetic field is applied, and then the direction of the gradient magnetic field is reversed and repeated to create an echo signal, and when this echo signal is at its maximum, it is repeated again. An inspection method using nuclear magnetic resonance, characterized in that 90 pulses of electromagnetic waves are applied to return the magnetization to a thermal equilibrium state, and thereafter the above sequence is repeated at predetermined intervals. (2) NMIL obtained in one sequence
An examination method using nuclear magnetic resonance according to claim 1, wherein the average value of the signal and the signal obtained by reversing the time axis of the echo signal is calculated, and the average value is obtained as data of one projection. (5) Calculate the difference signal between the NMrL signal and the signal obtained by inverting the time axis of the echo signal, take the data of 1 project, and perform the specified calculation to obtain 1 and 2 images. An inspection method using nuclear magnetic resonance according to claim 1. (4) Multiple NMIs obtained from multiple sequences
+. σ) An inspection method using nuclear magnetic resonance as claimed in claim 1, wherein the signal and/or a plurality of echo signals are averaged to form data of one projection. (5) Static magnetic field forming means that applies a uniform static magnetic field to the subject, generates magnetic fields having gradients in the two axes of the subject, the X-axis direction, and the Y-axis direction, and generates nuclear magnetic resonance signals from the subject. a magnetic field generating means for specifying a radiation portion of the object, an excitation means for applying a pulsed electromagnetic wave to the object, a control means for controlling the excitation means Vr-t5/, a control means for controlling the radiation part of the object; Nuclear magnetic resonance signal (N M 11 signal) (φ
There is also a rendering means that manually inputs the σ) signal from the detection means and performs predetermined calculations to obtain a tomographic image.
The magnetic field generating means and fljl! The fal1 means first excites the subject with a wave pulse electromagnetic wave, then applies a gradient magnetic field, then reverses the direction of the gradient magnetic field and repeats the process to create an echo signal. At the point in time, a 90° pulse of electromagnetic waves is applied again to return the magnetization to a thermal equilibrium state, and from then on, the operation of repeating the previous sequence at a predetermined interval is blocked. Inspection equipment