JPH0833617A - Magnetic resonance imaging system - Google Patents

Abstract

PURPOSE:To change a parameter required for sequence in real time by providing the system with at least two or more processors which fetch, decode, execute or write back an instruction and a sequence controller provided with shared memory for them. CONSTITUTION:The sequence controller 2 is operated under the control of a central processing unit 1, and sends various kinds of instructions required for the data collection of the tomographic image of an examinee 7 to a transmission system 3, a gradient magnetic field generating system 21 and a reception system 5. At least two or more processors which fetch, decode, execute or write back the instruction are installed in the sequence controller 2, and the shared memory for them is installed. A parameter input value from an operator, etc., via a central processing unit interface 31 is set on the processors A32, B33 and the shared memory 34, and the operator executes designated sequence as controlling I/O event memory 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a magnetic resonance imaging apparatus for imaging a desired portion of a subject by utilizing magnetic resonance.

[0002]

2. Description of the Related Art Magnetic resonance imaging apparatus (hereinafter referred to as MRI
Device) is used to measure the nuclear spin density density distribution, relaxation time distribution, chemical shift, etc. at the inspection site in the subject using the nuclear magnetic resonance phenomenon, and display the cross section of the subject as an image from the measured data. It is a thing. The outline of the principle will be described below.

Nuclear spins of a subject placed in a uniform static magnetic field perform precession about the direction of the static magnetic field at the Larmor frequency corresponding to the magnetic field strength. When an electromagnetic wave having a frequency equal to this Larmor frequency is applied to the subject from the outside, the nuclear spins in the subject are excited and transit to a high energy state. When this irradiation is cut off, the nuclear spins return to a low energy state with a relaxation time constant depending on the binding state. At this time, nuclear magnetic resonance (hereinafter referred to as NM
Signal) is emitted. This NMR signal is detected by a high frequency receiving coil tuned to its resonance frequency.
At this time, a gradient magnetic field of three axes of X, Y and Z is applied to the static magnetic field space in order to add position information to this signal. As a result, position information in the space is detected as a signal of frequency information, and data processing by a computer is performed to form an image.

By the way, recently, a sequence for generating the above-mentioned NMR signal is an EPI (Echo Planer Image).
ging) etc., there is an increasing tendency toward complication. To control these sequences, for example, Japanese Patent Laid-Open No.
A sequence controller as disclosed in Japanese Patent No. 277085 has been proposed. According to this controller, when changing various event memories for executing an event, the architecture allows unnecessary rewriting to be omitted. Rewriting is possible. Therefore, it is possible to control a complicated sequence, that is, a sequence having many event change points within the TR time.

[0005]

However, when the event memory is rewritten by the sequence controller described above, the table value to be referred to for changing various events, the incremental value of the gradient magnetic field strength, and the like are preliminarily set by the operator. It is calculated from the sequence parameter input value and can only be supported if it is set in the processor memory. That is, during the sequence execution, unexpected movements of the subject, electrocardiographic waveforms, etc. (hereinafter referred to as biometric information)
While analyzing, it is not possible to change the table value or increment value itself to a value different from the initial setting in real time.

The main reason for this is that the above sequence controller has only one processor. Generally, it is considered that the special processing as described above may be processed by using an interrupt. However, in the MRI sequence, since it is necessary to control the irradiation of the gradient magnetic field and the electromagnetic wave on the order of 1 μs, the time allowed for interrupt processing is limited, or the arbitration between sequence control and interrupt processing becomes complicated. Therefore, interrupt processing is not preferable, and improvement of this point has been conventionally demanded.

The present invention has been made in view of the above demands, and can control a complicated sequence and change parameters required for the sequence in real time while analyzing biological information during execution of the sequence. An object of the present invention is to provide an MRI apparatus capable of performing sequence control that can follow the biological information of the subject while the sequence is being executed.

[0008]

The object is to apply an electromagnetic wave and a gradient magnetic field to a subject placed in a uniform magnetic field according to a desired sequence, detect a nuclear magnetic resonance signal from the subject, and obtain data by a computer. In a nuclear magnetic resonance imaging apparatus for imaging by processing, a processor (CP that fetches, decodes, executes, or writes back instructions
U, MPU, or DSP (Digital Signal Processe)
r) and the like) are provided, and a sequence controller provided with a shared memory thereof is provided.

[0009]

One of the above processors controls the sequence, and the other processors analyze the biometric information and the like, and change the parameters required for the sequence in real time via the shared memory. This makes it possible to control a complex sequence and to change the parameters required for the sequence in real time while analyzing the biometric information during the execution of the sequence.
It becomes possible to perform sequence control that follows the biological information of the subject during execution of the sequence.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the MRI apparatus according to the present invention. This MRI apparatus obtains a tomographic image of the subject 7 by utilizing the NMR phenomenon, and includes a static magnetic field generation system 4, a central processing unit 1, a sequence controller 2, a transmission system 3, a gradient magnetic field generation system 21, and a reception system 5. , Signal processing system 6.

The static magnetic field generating system 4 is for generating a uniform static magnetic field around the subject 7 and is provided with a permanent magnet type, normal conducting type or superconducting type magnetic field generating means. The sequence controller 2 operates under the control of the central processing unit 1 and sends various commands necessary for collecting data of a tomographic image of the subject 7 to the transmission system 3, the gradient magnetic field generation system 21, and the reception system 5. . As will be described in detail later, the sequence controller 2 is provided with at least two processors for fetching, decoding, executing, or writing back instructions, and a shared memory thereof.

The transmission system 3 comprises a high frequency oscillator 8, a modulator 9, a high frequency amplifier 10 and a high frequency transmission coil 11, and an amplitude of the high frequency signal output from the high frequency oscillator 8 output by a command from the sequence controller 2. The amplitude is modulated by the modulator 9 with the value of, and the high frequency pulse thus amplitude-modulated is amplified by the high frequency amplifier 10 and then supplied to the high frequency transmitting coil 11 arranged in the vicinity of the subject 7, whereby an electromagnetic wave is generated. It is supposed to be irradiated to 7.

The gradient magnetic field generating system 21 is composed of a gradient magnetic field coil 13 wound in three directions of X, Y and Z, and a gradient magnetic field power source 12 for driving each coil, and an instruction from the sequence controller 2 is given. By driving the gradient magnetic field power source 12 of each coil according to
Gradient magnetic fields Gx, Gy, Gz in the three Y-axis directions are applied to the subject 7. By the method of applying the gradient magnetic field, the slice plane for the subject 7 can be set.

The receiving system 5 comprises a high frequency receiving coil 14, an amplifier 15, an A / D converter and a detector 16,
The NMR signal of the subject 7 caused by the electromagnetic wave emitted from the high frequency transmitting coil 11 is detected by the high frequency receiving coil 14 and converted into a digital amount through the amplifier 15 and the A / D conversion and detector 16, and the signal is a signal. It is sent to the processing system 6.

The signal processing system 6 includes a central processing unit 1 and
A recording device such as the magnetic disk 20 and the optical disk 19;
It is composed of a display 18 such as a CRT, and is obtained by performing processing such as Fourier transform, correction coefficient calculation, image reconstruction, etc. in the central processing unit 1 and performing appropriate calculation on a signal intensity distribution of an arbitrary cross section or a plurality of signals. The distribution is imaged and displayed on the display 18.

In FIG. 1, the high-frequency coils (high-frequency transmitting coil 11 and high-frequency receiving coil 14) on the transmitting side and the receiving side and the gradient magnetic field coil 13 are the static magnetic field generating system 4 arranged in the space around the subject 7. It is located in the magnetic field space.

FIG. 2 is a block diagram showing a concrete example of the sequence controller 2. The sequence controller 2 includes a central processing unit interface 31, a processor A 32, a processor B 33, a shared memory 34, a clock generator 35, and an I / O event memory 36.

The operation of the sequence controller 2 will be described. Via the central processing unit interface 31, the parameter input values from the operator and the parameter values and programs calculated based on them are shared by the processor A 32, the processor B 33, and the shared. It is set in the memory 34.

In response to a sequence start command from the central processing unit 1, the processor A32 refers to the parameters and the shared memory 34 according to the program, and specifies the operations of the clock generator 35, the transmission / reception systems 3 and 5, the gradient magnetic field generation system 21, and the like. The sequence specified by the operator is executed while controlling the I / O event memory 36. During the execution of this sequence, the processor B33 analyzes the biometric information and rewrites the parameter value on the shared memory 34. As a result, the processor A32 can reflect this information in real time during execution of the sequence without analyzing the biological information by itself.

Next, details of the above-described operation by the sequence controller 2 will be described with reference to FIGS. 3, 4 and 5. FIG. 3 is a model diagram of a cross-sectional image, of which (a) is in the slice direction (here, a transformer),
(B) shows the xy cross section, (c) shows the xy cross section when the subject 7 rotates about the z axis by an angle θ in the xy plane. FIG. 4 is a time chart showing a spin echo sequence for obtaining a transformer cross-sectional image by a conventional device (sequence controller), and FIG. 5 is an example of a spin echo sequence for obtaining a transformer cross-sectional image by the device of the present invention (sequence controller 2). It is a time chart shown.

In the conventional device (sequence controller), the number of echoes is changed according to the parameter input value from the operator.
Irradiation pulse waveform, gradient magnetic field amplitudes G _x0 , G _y0 and increment value Δ
G _{y0 and the} like are set in the parameter memory, and the processor refers to them and controls the sequence, but these cannot be changed in real time according to the biological information. Therefore, for example, when the subject 7 rotates as shown in FIG. 3, in order to obtain a cross-sectional image designated by the operator, it is necessary to change the phase encoding direction and the readout direction according to the movement, Since this cannot be done, an increase in artifacts and a decrease in S / N occur.

On the other hand, according to the device of the present invention (sequence controller 2), information from the position sensor (ultrasonic position sensor, laser position sensor, etc.) is executed by a processor other than the sequence control, for example, the processor B33, and the shared memory is used. To change the parameters on 34 in real time,
Sequence control processor, eg processor A32
Can be controlled according to the movement of the subject 7.

For example, in the present embodiment, a processor other than the above sequence control, for example, the processor B33 determines the amplitudes G _x1 , G _y1 , the increment values ΔG _x1 , ΔG _y1 , and the actually output amplitudes G _x , G _y . The following equations (1), (2), (3), respectively

[Equation 1] And the parameter value of the shared memory 34 is rewritten before the next slice. The sequence control processor, for example, the processor A32, immediately reflects these parameter values changed in real time in the sequence, and the processor A32 can control the movement of the subject 7.

In the above embodiment, the spin echo method of the trans section is mentioned as the sequence, but the sequence is not limited to this sequence and can be applied to other sequences. Further, although the analysis of the movement of the subject has been described as the function of the processor other than the sequence control, the present invention is not limited to this analysis, and may be applied to, for example, pattern analysis of an electrocardiographic waveform.

[0025]

As described above, according to the present invention, one of the processors of the sequence controller controls the sequence, and the other processors analyze the biometric information and are required for the sequence via the shared memory. Since various parameters can be changed in real time, there is an effect that sequence control that follows the biological information of the subject becomes possible during execution of the sequence.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a device of the present invention.

FIG. 2 is a block diagram showing a specific example of a sequence controller in FIG.

FIG. 3 is a model diagram of a transformer cross-sectional image.

FIG. 4 is a time chart showing a spin echo sequence of a conventional device.

FIG. 5 is a time chart showing an example of a spin echo sequence by the device of the present invention.

[Explanation of symbols]

 1 central processing unit 2 sequence controller 3 transmission system 4 static magnetic field generation system 5 reception system 6 signal processing system 7 subject 8 high frequency oscillator 9 modulator 10 high frequency amplifier 11 high frequency transmission coil 12 gradient magnetic field power supply 13 gradient magnetic field coil 14 high frequency reception Coil 15 Amplifier 16 A / D converter and detector 18 Display 19 Optical disk 20 Magnetic disk 21 Gradient magnetic field generation system 31 Central processing unit interface 32 Processor A 33 Processor B 34 Shared memory 35 Clock generator 36 I / O event memory

Claims (1)

[Claims] 1. Nuclear magnetic resonance in which an electromagnetic wave and a gradient magnetic field are applied to a subject placed in a uniform magnetic field according to a desired sequence, a nuclear magnetic resonance signal is detected from the subject, and imaged by data processing by a computer. The magnetic resonance imaging apparatus, wherein the imaging apparatus includes a sequence controller in which at least two processors for fetching, decoding, executing, or writing back instructions are provided, and a shared memory thereof is provided.