JPH04126132A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To offer an MRI image being effective for an articulatory disease, etc., since a repeated motion image in an actual moving state can be obtained by constituting a period of a synchronous image pickup so that a body to be examined can be recognized by an acoustical or optical means. CONSTITUTION:A timing generator 1 for controlling a pulse sequence is connected to a sequencer 12. From a timing generator 1, three kinds of pulses of a trigger pulse, a pulse (a) and a pulse (b) are outputted. By the trigger pulse, the repeating period of a measuring instrument is determined, and by the pulses (a), (b) outputted alternately in its half period, the sound signals of each different tone quality are outputted from oscillators 2a, 2b, amplified by an amplifier 3, and thereafter, outputted to the body as period recognition voice information from a loudspeaker 4. Also, the pulses (a), (b) connect alternately relays 5a, 5b, and by current supplied from a power source 6, two lamps 7a, 7b whose colors are different emitting light, and the signal is outputted as period recognition optical information.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic resonance imaging apparatus that images a desired location of a subject using magnetic resonance.

In particular, the present invention relates to a magnetic resonance imaging apparatus suitable for synchronous imaging of repetitively moving parts of a subject.

[Conventional technology]

Magnetic resonance imaging family M (hereinafter referred to as MRI equipment) utilizes the nuclear magnetic resonance phenomenon to measure the density distribution of atomic nuclear spins at a desired inspection site in a subject.

It measures the relaxation time distribution, etc., and displays an image of the cross section of the subject based on the measured data.

The nuclear spins of an object placed in a uniform and strong static magnetic field generator precess around the direction of the static magnetic field at a frequency determined by the strength of the static magnetic field (Larmor frequency). When a high-frequency magnetic field with a frequency equal to the frequency is externally irradiated, spin is recalled and transitions to a higher energy state (nuclear magnetic resonance phenomenon). When this irradiation is stopped, the spin returns to its original low state with a time constant corresponding to each state. It returns to its energy state, and at this time it emits electromagnetic waves to the outside. This is detected by a high-frequency receiving coil tuned to that frequency. At this time, a three-axis gradient magnetic field is applied to the static magnetic field space for the purpose of adding positional information in the space. As a result, it becomes possible to capture positional information in space as frequency information.

The information obtained differs depending on the timing of application of the above-described high-frequency magnetic field and gradient magnetic field, and this application method is called a pulse sequence. FIG. 4 shows a sequence diagram of the spin echo method, which is a typical pulse sequence. In the spin echo method, first, a high frequency magnetic field for excitation is irradiated. At this time, a slice gradient magnetic field for determining the slice position is simultaneously applied. This irradiation power is set to be such that macroscopically viewed nuclear spins are tilted 90 degrees to a plane perpendicular to the static magnetic field. Each spin is a sphere that starts rotating at its own unique speed, and over time a phase difference occurs between each spin. When a high-frequency magnetic field with enough power to tilt the spins 180 degrees is applied again, each spin is reversed and one phase difference converges to form an echo signal. This is the echo time (Te
).

Further, for the purpose of adding two-dimensional positional information within the slice plane, an encoding gradient magnetic field is applied between two high-frequency magnetic irradiations as a readout gradient magnetic field when detecting an echo signal. A tomographic image can be obtained by repeatedly detecting echo signals by changing this encoding gradient magnetic field little by little (this repetition time is called Tr) and finally performing two-dimensional Fourier transform processing on all detected signal data. can.

This example uses a single section and one echo, but it is also possible to obtain multiple echo signals (multi-echo) by simultaneously imaging multiple sections (multi-slice) or by further applying a high-frequency magnetic field. It is.

[Problem to be solved by the invention]

Since MHI devices require a relatively long time for imaging, it is difficult to image moving parts.For example, when diagnosing arthropathy.

Obtaining images of the joint in motion is clinically effective, so conventionally the joint was moved little by little and fixed, several images were captured, and these images were displayed repeatedly at high speed. By doing so, a cross-sectional image of a moving image was obtained in a pseudo manner. This is called animation display. Figure 2 is an example of animation display at the temporomandibular joint. Five images are displayed for each state, from image 1 with the temporomandibular joint closed to image 5 with the temporomandibular joint fully open. The temporomandibular joint is fixed and imaged, and these images are repeatedly displayed at high speed in the order of images 1-5, 1-5, and so on. In this way, it is possible to obtain a moving image of repetitive motion that looks as if it were captured in real time. However, this method cannot image the detailed movement of a clinically important joint, and the appearance of the joint differs between when the joint is actually moving and when it is fixed, which poses diagnostic problems.

An object of the present invention is to provide an MHI device having an imaging means that solves the problem of the above-mentioned inconsistencies in animation images of repetitive motions of joints produced by the conventional method.

[Means to solve the problem]

The above-mentioned problem is due to the fact that the image of the joint that performs one repetitive motion is not taken in the actual state of motion, but in a fixed state. In order to solve this problem, the present invention The present invention provides a method that enables imaging while the object is in motion.

As mentioned above, it is difficult for the MHI device to image a moving part, but if the part moves repeatedly with a certain degree of periodicity, the synchronous imaging method can be applied. This activates a pulse sequence in synchronization with the repetitive movement cycle of the target area, and is particularly effective for imaging the heart. Imaging of the heart is synchronized with the electrocardiogram waveform; details of this can be found in Circulation 67
(2) (1983) pp251-257J.

A conceptual diagram of the synchronous imaging method is shown in Figure 3. This is an example of synchronous imaging during the opening and closing of the temporomandibular joint as before, but the subject is moved from the intermaxillary state of state 1 through the intermaxillary state of state 5 again. Assume that the repetitive motion of returning to state 1 is repeated at a constant cycle. A pulse sequence is always started from state 1 in synchronization with this cycle. Also, if you divide the cycle into 8 time points as shown in the figure and collect image data at each time point, you can actually move 8 types of temporomandibular joint images from state 1 to state 8. It is possible to simultaneously image the state. In this case, one important point is that the repetitive motion of the subject must be repeated at exactly constant intervals. In order to achieve this, each time the MRI apparatus starts repeatedly collecting image data, synchronization information is emitted to the subject by acoustic means such as a voice synthesis signal or a buzzer sound, or by optical means such as the brightness of a lamp. Allow the subject to recognize the cycle of repetitive motion. Furthermore, in order to provide the subject with more accurate periodicity, the synchronization information is emitted by dividing the period into a plurality of periods.

For example, at the turning point of a repetitive motion (state 5 in Figure 3),
Change the tone of the buzzer. It does things like change the color of the lamp's light.

By repeatedly displaying captured images of each state at high speed, it is possible to reproduce a moving image of a joint, etc., in a state in which a repetitive motion is actually performed.

In the example shown in FIG. 3, one cycle is divided into eight, but if the number of divisions is further increased and images are taken in many states, smoother moving images can be reproduced.

[Effect]

According to the present invention, the problems of pseudo moving images of animation display caused by the conventional method have been solved. This is possible by obtaining moving images of actual operation, and therefore clinically effective MHI images can be obtained.

〔Example〕

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

FIG. 6 is a configuration diagram showing an example of the overall configuration of an MHI device according to the present invention. This MHI device uses nuclear magnetic resonance (NMR)
It uses the phenomenon to obtain a tomographic image of the subject 30, and includes a static magnetic field generating magnet 10 and a central processing bag! ! (hereinafter referred to as CPU) 11, a sequencer 12, a transmission system 13, a gradient magnetic field generation system 14, a reception system 15, and a signal processing system 16. The static magnetic field generating magnet 10 generates a strong and uniform static magnetic field around the subject 30.
Magnetic field generating means of a permanent magnet type, a normal conduction type, or a superconducting type is arranged in a spacious space around the magnetic field. The sequencer 12 operates under the control of the CPU II and sends various commands necessary for data collection of tomographic images of the subject 30 to the transmission system 13, the gradient magnetic field generation system 14, and the reception system 15. The transmission system 13 includes a high frequency generator 17, a modulator 18, a high frequency amplifier 19, and a high frequency coil 20a on the transmission side. After amplitude modulating and amplifying this amplitude modulated high frequency pulse with a high frequency amplifier 19, the subject 30
By supplying electromagnetic waves to a high-frequency coil 20a placed close to the electromagnetic wave, the subject 30 is irradiated with electromagnetic waves. The gradient magnetic field generation system 14 consists of gradient magnetic field coils 21 wound in the three axes of x, y, and z, and a gradient magnetic field power supply 22 that drives each coil. By driving the gradient magnetic field power supply 22, a gradient magnetic field Gx is generated in the three axis directions of x, y, and z.

Gy and Gz are applied to the subject 30.

Depending on how this gradient magnetic field is applied, a slice plane for the subject 30 can be set. The receiving system 15 includes a receiving coil 20b, a preamplifier 23, and a quadrature phase detector 24.
and an A/D converter 25, and the electromagnetic wave (NMR signal) of the response of the subject 30 due to the electromagnetic wave irradiated from the high-frequency coil 20a on the transmitting side is received by the receiving coil 20b placed close to the subject 30. Two systems are detected, input to the A/D converter 25 via the preamplifier 23 and the quadrature phase detector 24, converted into digital quantities, and further sampled by the quadrature phase detector 24 at the timing according to the command from the sequencer 12. The signal is sent to the signal processing system 16. The signal processing system 16 includes a CPU 11, a recording device such as a magnetic disk 26 and a magnetic tape 27, and a display 28 such as a CRT.
Correction coefficient calculation 9 Processing such as image reconstruction is performed, and the signal intensity distribution of an arbitrary cross section or the distribution obtained by performing appropriate calculations on a plurality of signals is converted into an image and displayed on the display 28. In this figure, the transmitting-side high-frequency coil 20a, the receiving coil 20b, and the gradient magnetic field coil 21 are arranged in the magnetic field space of the static magnetic field generating magnet 10 arranged in the space around the subject 30.

Here, a timing generator 1 for pulse sequence control according to the present invention is connected to a sequencer 12. From the timing generator 1, a trigger pulse (t) and a pulse a (,) are generated as shown in FIG.

Three types of pulses, pulse b (b), are output.

The measurement repetition period is determined by the trigger pulse, and the pulses a and b are output alternately during the half period, and audio signals of different sound quality are output from the oscillators 2a and 2b.After being amplified by the amplifier 3, the audio signals are output from the speaker 4. This is output to the subject 30 as period recognition audio information. In addition, the pulses a and b alternately connect and disconnect the relays 5a and b, and the power supply 6
The two lamps 7a and 7b of different colors emit light due to the electric current supplied from the lamps 7a and 7b, which are outputted as optical information for period recognition.

In a normal spin-22 pulse sequence, as shown in Figure 4, echo signal data is repeatedly collected while changing the amount of the encoding gradient magnetic field little by little by a constant amount of change, and the repetition period is Tr. , this is 128
A two-dimensional echo signal data table is created by repeating the process a number of times, such as 256 times, or 256 times, and the image is reconstructed by performing two-dimensional Fourier transform processing on this data table. On the other hand, in the cine mode sequence used in the synchronous imaging method, as shown in Figure 5, echo signal data is collected multiple times under the same encoding gradient magnetic field (in the figure, data is collected 8 times). Furthermore, as in the normal sequence, the amount of encoding gradient magnetic field is varied and data is sequentially collected to create eight two-dimensional echo signal data tables. and,
By reconstructing each image, eight images can be captured simultaneously. In this case, as is clear from the figure, if the cine mode sequence is performed using the same Tr as the normal sequence, the imaging time will be extended by the number of images simultaneously captured.

When imaging the repeated opening and closing movements of the temporomandibular joint, it is only necessary that the opening and closing of the jaw match the encoding repetition period of the cine mode sequence, as shown in Figure 5. When collecting each echo signal data, the positional state of the temporomandibular joint can always be made equal, and since temporomandibular joint images in eight different states are generated by movement, it is possible to obtain them simultaneously without signal influence.

The trigger pulse from the timing generator 1 gives the change period of the encode gradient magnetic field, and the trigger pulse from the sequencer 1
2 controls the cine mode sequence in response to this. This trigger pulse is also the period of the anti-movement, so the fifth
Pulses a and b in the logic states shown in the figure are output for the purpose of making the subject 30 recognize the repetitive motion cycle. In the case of opening and closing movements of the jaw, the final encoding gradient magnetic field is used to open the jaw during tone a or luminescent color a given at the timing of pulse a, and close the jaw during tone suma j±luminescent color. You can repeat until.

In this example, the interval between trigger pulses is divided into two and two types of cognitive information are given to the subject 30, but if the trigger pulse is further divided and detailed cognitive information is given, it is possible to further stabilize the cycle of repetitive movements. .

If the joint images taken at each point in time are repeatedly displayed at high speed, it is possible to reproduce a moving image of repetitive motion in an actual motion state, and it is possible to provide an MRI image that is effective in diagnosing arthropathy and the like.

The synchronized imaging method in a dynamic state according to the present invention can be combined with multi-slice imaging or multi-echo imaging, and can also be applied not only to spin echo methods but also to other sequences such as gradient echo methods. be.

〔Effect of the invention〕

As described above, by using the imaging means of the present invention, it is possible to obtain repetitive motion images during actual exercise, and therefore it is possible to provide MRI images that are effective in diagnosing arthropathy, etc. It has the effect of becoming

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a timing generator and cognitive information output device according to the present invention, FIG. 2 is an explanatory diagram showing pseudo video imaging using a conventional method, and FIG. 3 is an explanatory diagram showing a synchronous imaging method according to the present invention. , FIG. 4 is an explanatory diagram showing a pulse sequence based on the spin echo method, FIG. 5 is an explanatory diagram showing a cine mode sequence according to the present invention, and FIG. 6 is a configuration diagram showing the overall configuration of an MRI apparatus. 1... Timing generator, 2... Oscillator, 3...
...Amplifier, 4...Speaker, 5...Relay 6.
...Power supply, 7 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. Means for applying a static magnetic field to a subject; a means for applying a slicing direction gradient magnetic field, a readout gradient magnetic field, and a phase encoding gradient magnetic field to the subject; and a means for applying a magnetic field to the nuclei of atoms constituting the tissue of the subject; means for repeatedly applying high-frequency pulses that cause resonance in a predetermined pulse sequence; means for detecting magnetic resonance signals; and image reconstruction means for obtaining an image representing physical properties of a target object using the detected signals. A part that performs repetitive motion in synchronization with the period by repeatedly applying the same amount of phase encoded gradient magnetic field multiple times within an arbitrary period in the pulse sequence and detecting the signal. Magnetic resonance has a synchronized imaging function that enables signal detection at the same point in time, minimizes the influence of false signals associated with movement, and simultaneously captures multiple images at different points in time of repetitive motion. A magnetic resonance imaging apparatus, characterized in that the imaging apparatus is configured such that a subject can recognize the period of the synchronous imaging by acoustic or optical means. 2. More accurate synchronization timing can be recognized by the subject by generating multiple pieces of recognition information for the subject by acoustic or optical means at any given time and by changing its properties. A magnetic resonance imaging apparatus according to claim 1. 3. The magnetic resonance imaging apparatus according to claims 1 and 2, which has a function of displaying a pseudo moving image by repeatedly displaying a plurality of images at high speed.