JPS6184549A - Inspecting device using nuclear magnetic resonance - Google Patents

Abstract

PURPOSE:To obtain a tomographic image with high quality by picking up an optional section in addition to a lateral and a longitudinal section without being influenced by the rising nor falling of a slanting magnetic field. CONSTITUTION:A controller 1 outputs various instructions to respective devices at constant timing. The output of a high frequency pulse generator 2 is amplified by an amplifier 3 to excite a coil 4. The coil 4 serves as a receiving coil, whose received signal is passed through an amplifier 5 and detected by a detector 6, and then converted into an image by a signal processor 7. Slanting magnetic fields in the Z direction and directions perpendicular to it are produced by coils 8, 9, and 10. The coils 9 and 10 establish the magnetic fields which cross each other at right angles. Then, respective components of a slanting magnetic field generated for inspecting a plane which cross none of the respective coordinate axes at right angles and respective components of a slanting magnetic field applied when a plane crossing the magnetic field at right angles is inspected are put together and applied without overlapping.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an inspection device using nuclear magnetic resonance (NMR),
In particular, it measures nuclear magnetic resonance signals such as hydrogen and phosphorus in living organisms, and analyzes nuclear density distribution and relaxation time distribution.

This relates to equipment that visualizes chemical shifts, etc.

[Background of the invention]

2. Description of the Related Art Conventionally, X-ray CT and ultrasonic imaging devices have been widely used as devices for nondestructively inspecting the internal structure of the head, rear region, and the like of a human body. In recent years, attempts to perform similar tests using nuclear magnetic resonance phenomena have been successful.

It has become clear that information that cannot be obtained with XMCT or ultrasound imaging devices can be obtained. In an inspection device that uses nuclear magnetic resonance phenomena, it is necessary to separate and identify signals from an inspection object in correspondence with each part of the object. One of them is
There is a method of obtaining positional information by applying a gradient magnetic field to an object to be inspected, varying the static magnetic field placed on each part of the object, and thereby varying the resonant frequency or phase shift of each part.

FIG. 1 is a diagram for explaining the principle.

This method is named the Fourier-zoogmatography method (hereinafter simply referred to as the FT method) by Kumar et al., and its basic principle is described in the Journal of
Magnetic Re5onance (IL 6
9 (1975)).

Now, although the above-mentioned document assumes a three-dimensional case, for convenience's sake, we will limit the discussion to a two-dimensional case. First, slicing is performed by simultaneously applying a band-limited high-frequency magnetic field and a gradient magnetic field G. Subsequently, a gradient magnetic field G is applied, and finally, the signal is observed while applying the gradient magnetic field G. By changing the application time of G for each sequence and performing two-dimensional Fourier transform on the observed signal, it is possible to know the two-dimensional structure of the inspection object.

In addition to the method described here, there is a spin warp method proposed by Edalstein et al., but the principle is exactly the same as the Fourier-Zoogmatography method, with the only difference being the method of applying G. (Phys, Mad.

Biol, 25.751 (1980)) By the way, one of the major features of NMR inspection equipment is that it
It is said that the advantage of this method is that it can image any cross section, whereas line CT can only image a cross section. To achieve this, instead of driving each gradient magnetic field independently, it is necessary to apply a composite gradient magnetic field that weights each component according to the inclination of the imaging plane. However, a desired magnetic field cannot be generated simply by combining the inputs to the gradient magnetic field generator. This is because it is difficult to change the waveform of the rising and falling portions of the gradient magnetic field according to the input waveform, and the waveform is determined by the characteristics of the gradient magnetic field generating section.

In other words, in the transient response portion of the gradient magnetic field, the input and output are in a nonlinear region, and therefore cannot be controlled from the outside.

Therefore, the gradient magnetic field synthesized by weighting each component is
The resulting waveform differs from the input waveform, causing image deterioration.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and its purpose is that when inspecting a plane that is not orthogonal to any of the gradient magnetic fields, the magnetic field that is synthesized by weighting each component is
An object of the present invention is to provide an imaging device using nuclear magnetic resonance that can generate an input waveform almost faithfully.

[Summary of the invention]

In an NMR inspection system, three sets of orthogonal gradient magnetic fields G,
,G,,G, are used. However, each G, = 2H/
It is defined as 2X, G, ==2H/2y, G, =2H/2z, where H represents the magnetic field strength. Now, X+V
When imaging a plane perpendicular to either of the +1 axes,
a,,G,,G,have completely independent roles. In accordance with the example shown in FIG. 1, G1 has the role of slice selection, jGll has the role of phase encoding, and G has the role of signal detection. Therefore, when generating these gradient magnetic fields, it is sufficient to set the application timing and amplitude so that each magnetic field can fulfill its role by itself. However, when imaging a plane that is not orthogonal to any of x, y, and z, it is necessary to generate a combined magnetic field by weighting each component. For example, when imaging a plane perpendicular to the arrow in FIG. 2, it is necessary to apply a magnetic field for slice selection, a magnetic field for phase encoding, and a magnetic field for signal detection. Here, the arrow is on the xz plane and makes an angle θ with the Z axis, G.

represents the magnitude of the gradient magnetic field. Also, 1( changes depending on the stage of phase encoding. What is shown here is
This is the case when the imaging plane is parallel to y#, but of course the same argument can be made for any plane.In any case, G=
It can be seen that at least two of ,G, ,G must be applied at the same time, and that they must be weighted according to the angle of the imaging plane. However, as described above, the waveform of the rising and falling portions of the gradient magnetic field does not accurately reflect the input waveform, causing an error in the output. This is caused by ignoring the transient response part when synthesizing the input waveforms of each component.

In order to solve this problem, we have found that when combining a plurality of components, it is sufficient to apply the components so that they do not overlap, except when selecting a slide. That is, in NMR, the magnetic field for phase encoding or the magnetic field for signal detection only needs to be applied between the 90° radio frequency magnetic field (rj) and 180″ rf, or between 180° rf and the peak of the signal. , taking advantage of the property that it can be located anywhere.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3 shows the configuration of an inspection device that is an embodiment of the present invention.

The control device 1 outputs various commands to each device at constant timing. The output of the high frequency pulse generator 2 is amplified by the amplifier 3, and the six coils 4 that excite the coil 4 also serve as receiving coils at the same time.The received signal component passes through the amplifier 5, and after being detected by the detector 6, The signal processing device 7 converts it into an image. The output of the high frequency pulse generator 2 is also used as a reference signal when the detector 6 performs quadrature phase detection. The generation of gradient magnetic fields in the Z direction and in the direction perpendicular thereto is carried out by coils 8, 9.10, respectively, which are driven by amplifiers 11, 12.13, respectively. A static magnetic field is generated by a coil 14, and the coil 14 is driven by a power source 15. The coil 9 has almost the same shape as the coil 10, is rotated 90'' around the Z axis, and generates mutually orthogonal gradient magnetic fields.The human body 16 to be examined is placed on the bed 17. Placed, bet 17
moves on the support stand 18.

Figure 4 shows an example of the application sequence of the high-frequency magnetic field H1, gradient magnetic field G, , G, , G, etc. when the imaging plane is not tilted. is similar to that shown in Figure 4.

Now, if we assume that the imaging plane is tilted as shown in Figure 2, a new sequence shown by the dotted line in Figure 5 will be added to this sequence, and the combined magnetic field will be the one that should be generated in the end. becomes. However, since the magnetic field to be combined includes a nonlinear region except when selecting a slice, the actually generated magnetic field is not simply the sum of the two.

FIG. 6 shows an example of a sequence for the deformed spin warp used in the present invention. In order to tilt the imaging plane, new additional pulses are applied as shown by dotted lines. traditional pal,
That is, each gradient magnetic field pulse G, , G when imaging a plane perpendicular to two directions.

The pulse is set to be applied to obtain a tilted imaging surface at a time that does not overlap with (shown by the solid line).
It is possible to generate the desired composite magnetic field shown in equations 1), (2), and (3).

FIG. 7 shows a second embodiment of the invention.

The sequence is the same as that shown in FIG. 6, except that the phase encoding magnetic field is set in the section opposite to the 180' rf pulse. In addition, in the modified spin warp method, if the rising and falling edges of the gradient magnetic field have the same waveform, the pulses 19 in FIGS. 6 and 7 are not necessarily necessary, so the present invention can be applied even when this is omitted. is clear. In addition, Fig. 8 shows a case where a magnetic field with the polarity reversed from that applied at the time of slice selection is then applied to align the phases of the nuclear spins, but instead of applying a magnetic field with the polarity reversed, 180@ A similar effect can be obtained by applying a magnetic field of the same polarity after the rf pulse, so
The sequence for it is shown below.

Furthermore, as a fifth embodiment of the present invention, unlike the imaging of a plane parallel to the y-axis as shown in FIG. 9, a sequence for a plane that is not parallel to all axes is shown. .

In the figure, α, α', α' indicate gradient magnetic field pulses for slice selection, and when selecting slices in a plane perpendicular to two directions as in the example in Fig. 4, only the gradient magnetic field pulses shown by solid lines are used for slice selection. Whereas only the Z-direction gradient magnetic field pulse β was applied for selection.

In this example, in addition to this, it is necessary to apply gradient magnetic field pulses α' and α' in the X direction and the X direction, respectively. At this time, if selected as follows, the slice performed by applying a gradient magnetic field obtained by combining pulses α, α', α' and the arrow ( 10th
(shown in the figure). Also, β in the figure is used as a gradient magnetic field pulse for phase encoding in the Z, X, and y directions, respectively.

Apply pulses β′ and β′. This β, β′.

β' may be determined so as to satisfy the following equation.

Of course, in equation (5), β, β', and β' are indeterminate, but this is because there is no condition as to which direction of the tomographic plane to be displayed should be taken as the phase encoding direction.

゛This condition can be specified by the value of β/β′, for example, and in this case,
The solution to equation (5) is unique. Further, the magnitude of the pulses γ, γ', and γ' shown in the figure to be applied in the Z, X, and 7 directions, respectively, as gradient magnetic field pulses for signal detection may be determined to satisfy the following. In any case, in this example as well, the gradient magnetic field pulse shown by the solid line.

The additional magnetic field pulses required for tilting the imaging surface shown by dotted lines do not overlap with each other.

Note that when imaging a plane that is not parallel to either X, y+z411, the sequences shown in Figs. 6, 7, and 8 can be used in addition to the sequence shown in Fig. 9. It is clear that the effects described in the present invention can be obtained even if the present invention is expanded and used as shown in FIG.

Although the embodiments described above are for deformed spin warp, it is clear from the above description that the present invention is not limited to this and can also be applied to the Fourier-Zugmatography method or the projection-reconstruction method.

〔Effect of the invention〕

According to the present invention, an inspection apparatus using nuclear magnetic resonance can image any cross section in addition to a cross section or a longitudinal section without being affected by the rise and fall of a gradient magnetic field. It was possible to obtain images.

A simple explanatory diagram of the screen is a diagram showing the pulse sequence of the conventional method, No. 6゜7.8.
．． Figure 9 shows the pulse sequence used in the present invention. 1! No. 3

Claims (1)

[Scope of Claims] 1. Magnetic field generating means for a gradient magnetic field in each coordinate axis direction of a three-dimensional orthogonal coordinate system, a static magnetic field in one direction of each coordinate axis, and a high-frequency magnetic field, and a nuclear magnetic resonance signal from an object to be examined. In an inspection apparatus using nuclear magnetic resonance comprising a signal detection means for detecting and a calculation means for calculating the detection signal, a gradient magnetic field generated for inspecting a plane that is not orthogonal to any of the coordinate axes is used. An inspection apparatus using nuclear magnetic resonance, characterized in that each component is combined and applied so as not to overlap each component of a gradient magnetic field applied when inspecting a plane perpendicular to the magnetic field.