JPS5855741A - Inspecting device using nuclear magnetic resonance - Google Patents

Abstract

PURPOSE:To correct the degradation in resproduced pictures occuring in magnetic field drifts completely and to obtain picture of good quality by placing plural reference samples around an object to be examined, and reconstituting the picture by using the signals from the respective reference samples as references for positions. CONSTITUTION:Coils 24, 17-19, 13 for generating static magnetic fields, inclined magnetic fields and high frequency magnetic fields, a coil 13 which detects the nuclear magnetic resonance signal from an object 21, and a signal processing unit 16 which constitutes pictures according to the results of operations by operating the detection signals of the coils are provided. Reference samples 26- 28 are placed around the object 21, and the pictures are reconstituted by using the signals from the respective reference samples as references for positions.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inspection apparatus using nuclear magnetic resonance, and more particularly to an inspection apparatus using nuclear magnetic resonance that corrects deterioration of a reproduced image caused by magnetic field drift during the inspection time. .

Conventionally, X-ray beams and ultrasonic imaging devices have been widely used as methods for semi-destructively inspecting internal structures of human bodies and the like. In recent years, attempts to perform similar tests using nuclear magnetic resonance phenomena have been successful, and it has become clear that information that could not be obtained with XMO'R or ultrasonic imaging devices can be obtained.

In an inspection apparatus using nuclear magnetic resonance (hereinafter simply referred to as an "inspection apparatus"), it is necessary to separate and identify signals from an object to be inspected in correspondence with each part of the object. Normally, positional information is obtained by applying a gradient magnetic field to the object to be inspected, varying the static magnetic field placed on each part of the object, and thereby varying the resonance frequency of each part.

Figure 1 is for explaining the W7L principle. Considering only parts 2 and 3 of the object to be inspected 1, under the signal gradient magnetic field G from this part, the resonance curve 4.5 Since they are separated, it is possible to identify the difference in resonance frequency by varying the direction of application of the gradient magnetic field G and obtaining similar resonance curves, that is, projections.1) SXIIIO'l
'The concentration distribution of nuclear spins in the target object can be used to reconstruct the relaxation time distribution using an algorithm exactly similar to can be expressed as f-r(H0+GX)/(2K)--(1). Here, γ is the nuclear gyromagnetic ratio and is a value specific to nuclear spin. It also represents the coordinates where the X-nucleus spin is located. The static magnetic field H6 may fluctuate over time (magnetic field drift) due to ambient temperature changes, power supply fluctuations, external magnetic field fluctuations, etc. Due to fluctuations in the static magnetic field H6, the resonant frequency f expressed by the above equation (1) fluctuate. If this amount of variation is Δf, then when focusing on the same frequency even after the variation, the signal component will be a signal from a portion shifted by ΔX−Δf·2π/(Gγ). Therefore, if the projections obtained in this manner are re-articulated, a problem arises in that the image contains blur.

The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned problems in conventional inspection devices, and to provide an inspection device that corrects the deterioration of reproduced images caused by magnetic field drift. Our goal is to provide the following.

The above-mentioned object of the present invention is to provide magnetic field generating means for 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 of a test subject, a computer for calculating the detected signal, and the computer. Achieved by an inspection apparatus having a means for outputting the calculation results according to the method, in which a plurality of reference samples are placed around the inspection target, and image reconstruction is performed using signals from the reference samples as a position reference. be done.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. fl12 shows the configuration of an inspection device that is an embodiment of the present invention. In the figure, 24 static magnetic field generating coils, 21 objects to be inspected (in this case, a human body), 1
3 is a coil for generating a high frequency magnetic field, and 17, 18, and 19Fi are coils for generating gradient magnetic fields in the x, y, and z directions, respectively.

The output of the high frequency pulse generator 11 is amplified by a power amplifier 12 and excites the high frequency magnetic field generating coil 13. applicable)
The coil 13 also serves as a receiving coil, and the signal component passes through an amplifier 1114, is detected by a detector i 15, and is converted into an image by a signal processing device 16.

The gradient magnetic field is generated by the coil IT, 18.19.
These coils are driven by a power source 20.

A human body 21 to be examined is placed on a ped 22 and moved on a support base 23. A static magnetic field is generated by the coil A/24, which is driven by a power source 25.

FIG. 3 is a diagram showing the arrangement of a reference sample, which is the main point of the present invention. As shown in the figure, 21 is the target object, 26, 2
7.28 is a reference sample.

Three reference samples 26, 27, 28+1, and a regular hexagon that further circumscribes the circle that circumscribes the three reference samples 26, 27, 28+1, and the target object 2 so that the signals from the reference samples and the signals from the target object 21 do not overlap. They are placed every other corner of the square B.

A gradient magnetic field G1. G.

The projection when applying is also shown in FIG. The arrows represent the direction of the gradient magnetic field.

From the projection when the gradient magnetic field G0 is applied, the resonance *l[ti29 of the reference sample 26 is obtained, and the gradient magnetic field G.

The resonance curve Fi30 of the reference sample 27 is separated and output from the projection (g) when .

Static magnetic field ■ for some reason during the examination. Consider the case where the drift occurs. If the static magnetic field H0 is increased by Δ■, it will be translated in parallel by Δf-1ΔB/2, as shown by the broken line (to) in Figure 3 of Keioisha in this case. At this time, the resonance direction III of the reference sample 26 also shifts to a shifted position as shown at 31.

At that ζ, the correct position of the resonance direction 6131 of the reference sample 26 (
By determining Δf from the deviation from the position shown by 29, the projection of the target object can also be easily corrected.

The selection of the reference sample and the calibration method will be specifically explained below.

Considering the coordinate system XY shown in the upper left corner of FIG. 5, let α be the angle that the gradient magnetic field G makes with the X axis. Also, the center 0 of the target object 21 is the center of the gradient magnetic field - that is, at the 0 point H0+C)1. ”-Ho always holds true. In this case, 0 α≦π
/3, the reference sample 27 is π/3≦α≦2π/3
By selecting the reference sample 26 as the reference sample when 2π/3≦α≦π and selecting the reference sample 28 as the reference sample when 2π/3≦α≦π, a reference signal completely separated from the target object 21 can be obtained. Here, the frequency fr at which the reference signal is generated can be expressed as follows, assuming that the radius of the circle C circumscribing the regular hexagonal shadow B is R. That is, 0 α≦π/3
Then trw-to-,5-R-cog (-g-α)π
/3≦α≦2π/3 then t −t + −R・008 (100−α)r・2
and for 2/3≦α≦π, f = f −−1−aos (base π − α) r ・ 2
It is expressed as π 6 . Here, f is the resonance frequency at the zero point.

As described above, if the positions of the reference samples 26, 27, and 28 are fixed and ψ, the position where the reference signal is generated is determined by the direction in which the gradient magnetic field is applied, so that the signal can be corrected. The angle α between the gradient magnetic fields and the X-axis is G, ? G, when g
-tan (GY/GK). Further, the magnitude of the gradient magnetic field must always be constant G, which can be achieved by giving Gy-G@ts1na Gx Qoao11g.

FIG. 4 shows a gradient magnetic field generation section and a signal detection processing section extracted from FIG. 2. Signal processing bag ff116
When the angle α is specified from the angle α to the power source 2o, current is supplied to the carp /'-17 and 18 accordingly.

Also, based on the angle α of the signal processing device 16, the amplifier 1
4. Image reconstruction is performed by correcting the projection movement caused by magnetic field drift in the signal that has passed through the detector 15.

Figure 6 shows the processing process of the signal processing bag [16]. In this processing process, the detected signal is received and subjected to 7-lier transform, and then a reference signal 31 as shown in FIG. 3 is obtained and the frequency shift Δf is calculated. Based on this, the projection is translated by Δf, and the result is used to reconstruct the image.

Although ↓j in the above embodiment has been explained by taking as an example the case where 3 @ reference samples are used, the number of reference samples is not limited to this. Also, when using n reference samples,
The samples can be placed at every other vertex of the 2n-gon, and the reference samples can be changed depending on the direction of application of the gradient magnetic field.Of course, the reference samples do not need to be placed strictly at the vertices of the 211-gon. , it goes without saying that changes can be made as appropriate depending on the cedar shape of the transmitter/receiver coil, etc.

As described above, according to the present invention, magnetic field generating means for 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 examination object, and a computer for calculating the detected signal are provided. In the inspection apparatus having means for outputting calculation results by the computer, a plurality of reference samples are placed around the inspection target, and image reconstruction is performed using signals from the reference samples as a position reference. This has the remarkable effect of realizing an inspection device that can completely compensate for the deterioration of reproduced images caused by magnetic field drift and obtain high-quality images.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between a gradient magnetic field and a resonance curve, and Figure 2 is a diagram showing the configuration of an apparatus according to an embodiment of the present invention. Figure 3 is a diagram for explaining the arrangement of the target object and the reference sample and the projection correction method, and Figure 4 is a diagram showing the part related to gradient magnetic field generation and signal processing of the configuration shown in Figure 2V. , FIG. 5 is a diagram showing the operation of the signal processing device. 13: High frequency magnetic field generation coil, 16: Signal processing device,
IT, 18, 19: Gradient magnetic field generation coil, 21: Target object, 24: Static magnetic field generation coil, 26.2), 28:
Reference sample. Patent applicant: Hitachi Seisakusho Co., Ltd. Figure 1 Figure 3 Figure 4

Claims (1)

[Claims] It has magnetic field generating means for 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 object to be examined, a computer for calculating the detection signal, and a means for outputting the calculation results by the computer. An inspection device using nuclear magnetic resonance, characterized in that the inspection device uses nuclear magnetic resonance.