JPH0236841A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To make it possible to always attain a precise resonant condition irrespective of a change in environment or the like by automatically adjusting the capacitance of a capacitor part or an inductive capacitance of an inductance part in accordance with a result of determination by a resonant condition determining means. CONSTITUTION:An autotuning controller 10 controls the adjustment of capacitance by an actuator 9 so that the capacitance of a capacitor part 5 is changed steppingly slight by slight by a predetermined range. A computing part 8 computes an impedance of a parallel circuit consisting of the capacitor part 5 and an inclined filed coil 4. The computing part 8 recognizes a step at which the impedance is maximum, and delivers the number of the step to the autotuning controller 1 which therefore controls the operation of the actuator 9 in accordance with the number of the step. With this process, the resonant condition of the parallel circuit consisting of the capacitor part 5 and the inclined field coil 4 is precisely realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic resonance imaging apparatus, and more particularly to a gradient magnetic field generation system for a magnetic resonance imaging apparatus that collects image information at ultra-high speed.

(Prior Art) A magnetic resonance imaging apparatus (MRI) obtains physiological and anatomical information of a subject by the following method.

That is, a radio frequency magnetic field for excitation is applied while a gradient magnetic field for slicing is applied to the specimen placed in a --like static magnetic field, and the magnetic field strength has a predetermined value, and Slicing is performed by selectively exciting target nuclides within the fault whose Larmor frequency is equal to the frequency of the excitation radiofrequency magnetic field. Then, in order to encode spin position coordinate information, for example, into the phase of a magnetic resonance signal to be described later, gradient magnetic fields are applied perpendicularly to the slicing gradient magnetic field and in two directions perpendicular to each other.

After that, the free induction decay (FI
The electromagnetic wave radiation generated by D) is received as a magnetic resonance (MR) signal by a receiving coil.

The received MR multiplied signal is reconstructed into tomographic image information l\ by a computer system consisting of an interface, a central information processing unit (CPU), a storage device, etc., and is also stored in the storage device. Furthermore, the tomographic image information is displayed on a monitor and viewed, providing physiological and anatomical information regarding the subject.

Some MRIs perform imaging using an ultra-high-speed imaging method in order to shorten the imaging time. This is to take one tomographic image in several Qms.

The gradient magnetic field generation system in this ultra-high-speed imaging MRI consists of a gradient magnetic field with a predetermined capacity of two coils between the gradient magnetic field for generating the gradient magnetic field = 1 coil and the gradient magnetic field amplifier that supplies power for generating the gradient magnetic field to the gradient magnetic field coil. A device having a configuration in which one capacitor is connected in series or in parallel is known.

This creates resonance between the inductance of the gradient magnetic field coil, etc. and the main 11 passitance of the gradient magnetic field, thereby suppressing the amount of power supplied from the gradient magnetic field amplifier and providing a strong and excellent transient response. The aim is to generate a gradient magnetic field that

(Problems to be Solved by the Invention) However, such conventional resonance methods have the following problems.

In other words, the capacitance C of the capacitor and the inductance L of the gradient magnetic field coil change due to changes in temperature, etc., and the inductance of the gradient magnetic field coil changes depending on the arrangement of the conductors around the coil. It's also changing.

Therefore, due to the inductance l- of the gradient magnetic field = 1 il and the capacitance C of the capacitor, the resonant frequency fr determined by the following formula, fr = 1 / 2π, /'-C1- changes in accordance with the change of the M boundary. When fr does not match the frequency tg of the gradient magnetic field necessary for ultra-high-speed imaging, it becomes necessary to increase the output of the gradient magnetic field amplifier, and if it exceeds the rated capacity of the gradient magnetic field amplifier, Although the necessary power cannot be supplied to the gradient magnetic field coils, a situation arises in which the necessary gradient magnetic field strength cannot be obtained.

Conventionally, in order to prevent this kind of situation from occurring, when the capacitance of the capacitor or the inductance of the gradient magnetic field coil changes, it is manually compensated for and the resonance is precisely adjusted at the required gradient magnetic field frequency fjJ. Ta.

However, this manual adjustment takes a long time, and MRI
There is a problem in that the throughput or operability of the system decreases.

It is an object of the present invention to solve such problems in conventional MRTs using a resonance method, and to provide an MRI that copes with environmental changes and automatically achieves resonance conditions.

[Structure of the Invention] (Means for Solving the Problems) Magnetic resonance imaging of the present invention [& refers to a gradient magnetic field coil for generating a gradient magnetic field, and a gradient magnetic field coil connected in parallel or series to the gradient magnetic field coil. The capacitance is variable = 1 A resonance state determining means for determining the resonant state of the sensor section, the gradient magnetic field coil, and the capacitor section, and the determination results are input from the resonance state determining means to determine the accurate resonant state. It has a capacitor part capacity adjustment means etc. for adjusting the capacitance of the capacitor part so that the capacitance of the capacitor part is realized.

Or, tilt! A gradient magnetic field coil for i-field generation, an inductor section connected in series to the gradient magnetic field coil and whose inductance is variable, and a capacitor section connected in parallel or series to a series circuit consisting of the gradient magnetic field coil and the inductor section. , a resonance state determining means for determining a resonant state between a series circuit consisting of a gradient magnetic field coil and an inductor section, and a capacitor section, and inputting the determination result from the resonance state determining means so that an accurate resonant state is realized. It has an inductor part inductance adjustment means etc. which adjust the inductance of an inductor part.

(Function) Based on the determination result of the resonance state determining means, the capacitor part capacitance adjusting means or the inductor part inductance adjusting means automatically adjusts the capacitor part capacitance or inductance part inductance, respectively, in spite of changes in the environment. Accurate resonance conditions are always achieved.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a gradient magnetic field generation system 1 in an MRI according to an embodiment of the present invention. It has a magnetic field amplifier 2 and a sine wave signal generation function, a sequence controller that sends control signals to each part of the device at predetermined timing, a sequence controller roller 3, a gradient magnetic field coil 4 that generates a gradient magnetic field for reading, etc. In accordance with the spirit of the invention, a capacitor section 5 whose main 11 passitance is adjustable and connected in parallel with the gradient magnetic field coil 4, a voltage measuring means 6 for measuring the output voltage of the gradient magnetic field amplifier 2, and a gradient magnetic field The measurement results of the current measuring means 7, voltage measuring means 6, and voltage measuring means 7 that measure the output current of the amplifier 2 are input, and the capacitor section 5 and the slope! a calculation unit 8 having a function of calculating the impedance of a parallel circuit consisting of an i-field co-coil, storing the results, comparing the stored calculation results, and recognizing which calculation result is the minimum; As a driving source, it has an ultrasonic motor that is not affected by the magnetic field (or does not affect the magnetic field distribution), and the capacitance is adjusted by changing the insertion amount between the dielectric plates of the capacitor in the capacitor section 5. and an auto-tuning controller 10 that controls the adjustment of the insertion distance between the polar plates of the dielectric of the capacitor by the actuator 9. Although not shown, it also includes a static magnetic field generator, an RF transmitting/receiving coil, and a CPU for RF receiving. It has a computer system that processes MR multiplied signals received through the coil to form tomographic image information, a storage device that stores processing programs and the formed image information, and an image display device that displays tomographic images.

The operation of the gradient magnetic field generation system 1 covering each of these elements will be described below.

Adjustment of the capacitance of the capacitor unit 5 to achieve the resonance condition, that is, auto-tickoning, is performed during a so-called pre-scan in which processing such as tuning of the RF system and frequency locking is performed prior to actual photographing of the cross-sectional H image of the subject.

At this time, a sine wave signal having the same frequency [Q] of the gradient magnetic field necessary for imaging and having a lower level than the signal input during imaging is input from the sequence controller 3 to the gradient magnetic field amplifier 2 and amplified, and the gradient magnetic field is Amplifier 2 output)
is supplied to the gradient magnetic field coil 4, and the gradient magnetic field coil 4 is
WJ generates an extremely low level gradient magnetic field compared to when it is in the shadow.

That is, first, the auto tuning controller 10
controls the capacitance adjustment by the actuator 9 so that the capacitance of the capacitor section 5 changes stepwise by minute amounts within a predetermined range.

Then, at each step, the impedance of the parallel circuit consisting of the capacitor section 5 and the gradient magnetic field coil 4 at that time is computed in the computing section 8. After the capacitance has changed within a predetermined range in the adjustment, the calculation section 8 recognizes at which step the impedance becomes maximum, and sends the step number, which is the recognition result, to the A-Tochikoning controller 10.

Based on the sent step number, the autoconing roller 10 controls the actuator 9 so that the capacitance of the capacitor section 5 becomes the value it had at the step of that number when adjusting the capacitance in the stepwise change. control the behavior of

Through this series of processing, the resonance conditions of the parallel circuit consisting of the capacitor section 5 and the gradient magnetic field coil 4 are accurately realized.

This is because, through the above process, the impedance of this parallel circuit is set to be maximum, which only indicates that accurate resonance conditions have been achieved in this parallel circuit. Thereafter, the auto-tuning controller 10 sends a signal to the sequence controller 3 indicating that tuning has been completed, and the sequence controller 3 then performs the following steps to perform the actual tomography imaging of the subject.
The process moves to a stage in which a sine wave signal is generated with an intensity greater than the intensity generated during the autochoning and is output to the gradient magnetic field amplifier 2.

Subsequent signal processing such as MR multiplied signal reception and image reconstruction is performed in a conventionally known manner.

Embodiments of the present invention are not limited to those described above. For example, as an installation mode of a capacitor used to generate resonance with a gradient magnetic field coil, a gradient magnetic field coil as shown in FIG. It is also possible to install the sensor in series with the sensor, and in this case, for example, the determination as to whether the resonance condition has been achieved can be made based on the case where the impedance of the series circuit becomes the minimum.

Furthermore, in order to achieve the resonance condition, the inductance of the adjusting inductor connected in series with the gradient vAs coil may be varied by, for example, adjusting the magnetic core entrance in the coil or the air gap length.

As an example of this, a configuration in which a capacitor is connected in parallel or in series to a series circuit consisting of a gradient magnetic field coil and an adjusting inductor is shown in FIGS. 3 and 4, respectively.

In addition, in order to achieve the resonance condition, in other words, detecting the resonance state does not necessarily depend on detecting impedance, but detecting current or voltage and determining whether resonance has been achieved by detecting the current or voltage and assuming that the amount thereof becomes maximum or minimum. You may. For example, in the case of FIG. 1, even if the achievement of the resonance condition is determined as the case where the output current of the gradient magnetic field amplifier 2 is minimum or the ratio of the current flowing through the gradient magnetic field coil 4 to the output current of the gradient magnetic field amplifier 2 is maximum. good.

[Effects of the invention] Resonance conditions are automatically achieved, the burden on the operator is reduced, and the time required for adjustment is significantly shortened, so the overall time required for imaging, including the preparation process, is shortened. will be made.

In addition, since accurate resonance conditions are achieved regardless of changes in the usage environment, the characteristic of the resonance method is always utilized in that the capacity of the gradient magnetic field amplifier can be small.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a gradient magnetic field generation system used in MRI according to an embodiment of the present invention, and FIGS. FIG. 3 is a diagram showing an example of a configuration of a gradient magnetic field coil, an inductor, and a capacitor for implementing the invention. '1 Gradient magnetic field generation system 2 Gradient magnetic field amplifier 3 Sequence controller 4 Gradient magnetic field coil 5 Capacitor section 6 Voltage measuring means 7 Current measuring means 8 ...Arithmetic unit 9...Actuator

Claims (2)

[Claims] (1) A magnetic resonance imaging apparatus having a gradient magnetic field generation system for applying a gradient magnetic field to a subject, the gradient magnetic field generation system including a gradient magnetic field coil for generating a gradient magnetic field,
A capacitor unit connected in parallel or series with the gradient magnetic field coil and having a variable capacitance, a resonance state determining means for determining a resonance state between the gradient magnetic field coil and the capacitor unit, and inputting the determination results from the resonance state determining means. 1. A magnetic resonance imaging apparatus comprising: a capacitor section capacitance adjusting means for adjusting the capacitance of the capacitor section so that an accurate resonance state is achieved. (2) A magnetic resonance imaging apparatus having a gradient magnetic field generation system for applying a gradient magnetic field to a subject, the gradient magnetic field generation system including a gradient magnetic field coil for generating a gradient magnetic field,
It consists of an inductor part connected in series to a gradient magnetic field coil and whose inductance is variable, a capacitor part connected in parallel or in series to a series circuit consisting of the gradient magnetic field coil and the inductor part, and a gradient magnetic field coil and an inductor part. Resonant state determining means for determining the resonant state between the series circuit and the capacitor section; and an inductor section inductance for inputting the determination result from the resonance state determining means and adjusting the inductance of the inductor section so that an accurate resonant state is achieved. A magnetic resonance imaging apparatus characterized by having an adjustment means and the like.