JPH0215833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to nuclear magnetic resonance
The present invention relates to a magnetic field calibration device for resonance (hereinafter abbreviated as NMR) imaging equipment.

NMR imaging devices and ESR have been known for a long time. By the way, in the case of spectroscopy, it is essentially important to keep the magnitude of the main magnetic field H ₀ constant, as is generally the case with NMR imaging devices, ESR, etc. However, in NMR imaging equipment, the main magnetic field
The stability of H ₀ is not as critical as in spectroscopy and only needs to be maintained at around 10 ⁻⁶ during imaging. If stability is maintained, the absolute value is not so strictly required. This is because the absolute value of the main magnetic field H ₀ is only related to the occurrence of uniform parallel movement in the Fourier transform after periodic detection of the FID (free induction decay) signal, and is not particularly problematic. It is from.

However, whether static or dynamic, the spatial and temporal uniformity of the main magnetic field H ₀ is superior. The main magnetic field H ₀ is affected by changes in the driving power source, the material of the main magnetic field H ₀ coil, the magnetic circuit, etc. (temperature changes, etc.).

The present invention has been made in view of these points, and its purpose is to provide a magnetic field calibration device that detects the main magnetic field H ₀ and automatically stabilizes the main magnetic field H ₀ using a servo.

To achieve such an object, the present invention provides a nuclear magnetic resonance imaging apparatus equipped with a detection coil, which is the main coil for imaging, and is arranged with the axis of the coil orthogonal to the main magnetic field _H0 . In the magnetic field calibration device, a coil surrounding a water capsule is arranged so that the axis of the coil is perpendicular or substantially perpendicular to the main magnetic field H ₀ so that the magnetic flux does not intersect with the detection coil, and the winding surface of the detection coil is It is characterized in that the absolute value of the main magnetic field H ₀ is calibrated by detecting the resonance of the protons of the water.

For servo control of the main magnetic field H ₀ , it is still preferable to use proton absorption lines (γ=4.2576MHz/KG). This is because there is already established technology for proton magnetometers, which have an accuracy of 10 ^-5 for proton absorption lines and a resolution of 10 ^-6 to 10 ^-7 . However, this does not mean that a probe coil containing a water sample for this purpose cannot be brought into the space being imaged for detection or calibration. This is because as long as it is placed near the detection coil for main imaging, it will combine with the detection coil and exert an influence. This effect can be removed by shielding the probe coil by surrounding it with a case made of a non-magnetic conductor, but in this case there is a problem that it interferes with imaging.

Therefore, in the present invention, such a configuration is avoided and a configuration as shown in FIG. 1 is adopted.

In this figure, 1a and 1b are the magnetic poles (N pole and S pole) of the electromagnet for generating the main magnetic field H ₀ , 2a,
2b is a perturbation coil placed between the magnetic poles 1a and 1b for obtaining magnetic field perturbation during imaging;
is a detection coil for detecting FID signals. These are as follows, assuming that the main magnetic field H ₀ is in the z-axis direction.
A magnetic field is applied by the perturbation coils 2a and 2b in the x-axis direction, and a detection coil 3 is arranged so as to be able to detect changes in the magnetic field appearing in the y-axis direction. The subject is placed inside the detection coil 3. On the other hand, the probe coil 10 for magnetic field calibration, which is a feature of the present invention, is arranged on the winding surface of the detection coil 3 so that there is no magnetic coupling with the detection coil 3.

FIG. 2 is a diagram showing details of this probe coil 10 portion. In FIG. 2, a coil 12 is wound around the outer periphery of a water capsule 11. The axial direction of this coil 12 is made to be in the same direction as the winding surface of the detection coil 3, and arranged so as not to be orthogonal to each other. That is, the coil 12 is arranged so that its axis is perpendicular or substantially perpendicular to the main magnetic field H ₀ so that the magnetic flux does not intersect with the detection coil 3 .

The capsule 11 placed in the coil 12 is preferably a glass ampoule or the like, and the water to be sealed is preferably water in which approximately 0.1% of a paramagnetic salt such as Fe ₂ Cl ₃ is dissolved rather than pure water. Furthermore, it is preferable to provide a case 13 for electrostatic shielding on the outside of the coil 12.

On the other hand, the winding of the detection coil 3 is a hollow pipe (such as a copper pipe), and the lead wire of the coil 12 is configured to be guided to the outside through the inside of this pipe.

FIG. 3 shows the main parts of a system that uses this probe coil 10 to continuously measure and stabilize the main magnetic field H ₀ . In the figure, the marginal oscillator 31 oscillates with the probe coil 10, but unlike in the case of a general proton magnetometer, it is not possible to apply a sweep in the direction of H ₀ for this measurement, so the variable capacitance Apply a sweep to the fosc using a diode, etc. The output of the marginal oscillator 31 is amplified and detected by a detector 34, and the resulting DC component is sent to an integrator 35.
and is fed back to the marginal oscillator 31 to optimize the oscillation level, and
The alternating current component of the output of the marginal oscillator 31 passes through a differentiating circuit 36 and an amplifier 37 for observation and analysis of absorption lines, is digitized by an A/D converter 38, and is sent to a microprocessing unit (hereinafter referred to as μPU) 39. can be conveyed to. On the other hand, the same μPU 39 controls the D/A converter 32 and the sweep oscillator 33 to control the average value (center value) and sweep of fosc.

Also, the fosc itself is connected to the counter 41 via the amplifier 40.
is measured and transmitted to the μPU 39. The μPU 39 also controls the current source 42 for the main magnetic field H ₀ . μPU39
The current source 42 for the main magnetic field H ₀ is controlled so that the current source 42 for the main magnetic field H 0 is centered on the peak of the absorption line as shown in FIG. The desired value of the main magnetic field H ₀ is determined by an external command to the μPU 39. The frequency is found by dividing this main magnetic field H ₀ by the value of γ,
Feedback control is performed so that the fosc count value becomes this frequency. During this time, the fosc value is controlled so as to maintain observation and not lose sight of the absorption line.

Since the probe coil 10 does not interfere with the FID signal reception work as an imaging work, the main magnetic field H ₀ and in some cases H ₀ +ΔH
(x, y) (ΔH is the perturbation magnetic field) is constantly measured.

Next, another arrangement example of the probe coil 10 will be described using FIGS. 5 and 6. As another example of arrangement, an example of installing at A or B in FIG. 5 is shown. The probe coil 10 is installed at position A as shown in FIG. 6A, and at position B as shown in FIG. 6B. Here, the main detection coil 3 has its coil axis perpendicular to the direction of the main magnetic field _H0 , and the main purpose detection RF magnetic field _HRF is indicated by the arrow _HRF.
It is in the direction of Also, the probe coil 10
is made of copper or aluminum pipe
The entire probe coil 10 is buried within the pipe of the FID signal detection coil 3. Furthermore, in case A of Fig. 6, the axis of the probe coil 10 is connected to the main magnetic field.
In the case of (b ₎ , the probe coil 10 is composed of a flat coil wound around a cylindrical water-filled capsule, and the axis of the coil is made substantially perpendicular to the main magnetic field H ₀ . In addition, marginal oscillator 3
It would be better if it could be stored in the pipe including the 1st class. The detection coil 3 is not limited to a pipe, but may be a strip (the probe coil 10 is in a shielded shape). The lead wire of the probe coil 10 is taken out from the ground side terminal 3b of the detection coil 3 through the pipe of the detection coil 3 or along the band.

As explained above, according to the present invention, NMR
In the imaging device, at least the main magnetic field
It is possible to realize a magnetic field calibration device that detects H ₀ and automatically stabilizes the main magnetic field H ₀ using a servo.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of the magnetic field detection section of the magnetic field calibration device of the present invention, FIG. 2 is a detailed diagram of a part thereof,
FIG. 3 is a block diagram showing an example of the magnetic field calibration device of the present invention, FIG. 4 is an explanatory diagram showing an example of an absorption line, and FIG. 5 is a diagram showing another installation position of the probe coil.
FIG. 6 is a diagram showing the installation direction at each position in FIG. 5. 1a, 1b... Main magnetic field magnetic pole, 2a, 2b... Perturbation coil, 3... Detection coil, 10... Probe coil, 11... Water capsule, 12...
Coil, 31...Marginal oscillator, 39...
...Microprocessing unit, 41...Counter, 42...Current source for main magnetic field _H0 .

Claims (1)

[Claims] 1. In a magnetic field calibration device in a nuclear magnetic resonance imaging apparatus including a detection coil that is a main coil for imaging and is installed perpendicular to the axis of the coil in the main magnetic field H ₀ , a coil surrounding the capsule, the axis of the coil being aligned with the main magnetic field.
It is installed on the winding surface of the detection coil so as to be perpendicular or substantially perpendicular to H ₀ so that the magnetic flux does not intersect with the detection coil, and detects the resonance of the protons of the water to increase the absolute value of the main magnetic field H ₀ . A magnetic field calibration device for a nuclear magnetic resonance imaging apparatus, characterized in that it calibrates values. 2. A patent characterized in that the water capsule and the coil are arranged inside a pipe of the detection coil formed of a copper or aluminum pipe so that the magnetic axis thereof is substantially orthogonal to the main magnetic field H ₀ A magnetic field calibration device for a nuclear magnetic resonance imaging apparatus according to claim 1.