JPH07171125A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To provide a magnetic resonance imaging device capable of reducing the processing load of a CPU and executing the oblique processing on an optional waveform together with the progress of photographing. CONSTITUTION:In a magnetic resonance imaging device in which a sequence controller 11 for controlling the linear gradient magnetic field of each XYZ axis and the generation of transmitting pulse is served also for the oblique processing for converting the magnetic field data for the linear gradient magnetic field of each XYZ axis into the magnetic data for the linear gradient magnetic field of each XYZ axis according to the photographing of an inclined surface inclined at an optional angle to the cross section, a high-speed oblique processing unit 28 exclusive for oblique processing is installed in the sequence controller independently from a CPU 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus capable of photographing an inclined surface inclined at an arbitrary angle with respect to a cross section.

[0002]

2. Description of the Related Art In a magnetic resonance imaging apparatus, it is possible to image an arbitrary inclined surface (hereinafter referred to as "gradient imaging") by changing the direction of a linear gradient magnetic field. The processing required to change the direction of the linear gradient magnetic field is generally called oblique processing. The magnetic field data of the linear gradient magnetic field of each of the XYZ axes used for transverse cross-section imaging is shown as Gx (t), Gy (t), and Gz (t) as a time function, and the tilt angle of the inclined surface around the X axis is θ, When the slew angle around the Y axis of the inclined surface is φ, the magnetic field data Gx0 (t), Gy0 (t), and Gz0 (t) of the linear gradient magnetic field of each of the XYZ axes used for tilt imaging are as follows ( It is expressed by the formula 1).

[0003]

[Equation 1]

Conventionally, the calculation processing for converting the magnetic field data of the transverse cross-section imaging by the equation (1) into the magnetic field data of the tilt imaging (hereinafter this processing is referred to as "oblique processing") is XY.
It is performed by the CPU in the sequence controller for controlling the generation of the linear gradient magnetic field of each Z axis and the transmission pulse according to a predetermined sequence. In addition to the off-line processing, the CPU plays a role of managing input / output of data between the sequence controller and an external device and controlling various memories in the sequence controller.

By the way, the magnetic field data of the linear gradient magnetic field in the phase encode direction is not limited to a general rectangular waveform, but is intentionally shaped into, for example, an arc-shaped arbitrary waveform in consideration of the rising and falling characteristics of the magnetic field generation. There is also.

In the case of an arbitrary waveform, since the oblique processing is repeated at every sampling point sufficient to express this arbitrary waveform, the processing amount becomes enormous as compared with the processing amount in the case of a rectangular waveform. The CPU needs to interrupt the above-described data input / output management and various memory controls at the same time while executing this huge amount of oblique processing, and cannot execute the oblique processing in real time as the shooting progresses. Therefore, conventionally, the oblique processing of all sampling points is completed before photographing, the result is temporarily stored in the memory, and is appropriately read from the memory at the time of photographing to be used to ensure the low processing capability of the CPU. .

Therefore, a huge amount of memory is required, and it is necessary to wait the oblique processing time for all sampling points after the tilt angle and the slew angle of the inclined surface are determined and before the photographing is started.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to address the above-mentioned circumstances, and its purpose is to reduce the processing load on the CPU and to perform oblique processing of arbitrary waveforms in real time as the shooting progresses. It is to provide a magnetic resonance imaging apparatus capable of performing the magnetic resonance imaging.

[0009]

The present invention is a sequence controller for controlling the generation of a linear gradient magnetic field in each of XYZ axes and a transmission pulse according to a predetermined sequence, and crosses the magnetic field data of the linear gradient magnetic field in each of XYZ axes. XYZ according to the shooting of an inclined surface that inclines at an arbitrary angle to the surface
In a magnetic resonance imaging apparatus that also serves as an oblique processing for converting magnetic field data of a linear gradient magnetic field of each axis, a dedicated unit for the oblique processing is provided in the sequence controller independently of the CPU.

[0010]

According to the present invention, since the dedicated unit for the oblique processing is provided in the sequence controller independently of the CPU, the CPU is released from the oblique processing and the processing load is reduced. Further, since the operation control and the oblique processing in the sequence controller can be executed while being shared between the CPU and the dedicated unit, the oblique processing is not interrupted by the interruption of this operational control, and the oblique processing is performed in real time as the photographing progresses. Can be run with.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram of the sequence controller of FIG.

In the gantry 14, a static magnetic field magnet 1, X and Y
A linear gradient magnetic field coil 2 and a transmission / reception coil 3 that form a linear gradient magnetic field in each Z axis are provided. The transmission / reception coil 3 may be directly attached to the subject instead of being embedded in the gantry 14. As the static magnetic field magnet 1 as the static magnetic field generator, for example, a permanent magnet, a normal conducting coil or a superconducting coil is selectively adopted. Linear gradient magnetic field coil 2
Is a coil for generating a linear gradient magnetic field Gx along the X axis, a linear gradient magnetic field Gy along the Y axis, and a linear gradient magnetic field Gz along the Z axis. The transmission / reception coil 3 serves both as a transmitter for generating a radio frequency (RF) pulse as a selective excitation pulse for selecting a slice and as a receiver for detecting a magnetic resonance signal generated by magnetic resonance. The subject P on the bed 13 is inserted into the imaging area in the gantry 14 together with the top plate.

The static magnetic field magnet 1 is driven by the static magnetic field controller 4. The transmit / receive coil 3 is driven by the transmitter 5 during transmission and is coupled to the receiver 6 during reception. The linear gradient magnetic field coil 2 is driven for each axis by an amplifier 7 for an X-axis linear gradient magnetic field, an amplifier 8 for a Y-axis linear gradient magnetic field, and an amplifier 9 for a Z-axis linear gradient magnetic field.

The amplifiers 7, 8, 9 and the transmitter 5 and the receiver 6 are driven by a sequence controller 10 according to a predetermined sequence, and an X-axis linear gradient magnetic field Gx, a Y-axis linear gradient magnetic field Gy, a Z-axis linear gradient magnetic field Gz, Radio frequency (RF) pulses are generated in a predetermined pulse sequence.

The computer system 11 supplies the sequence controller 10 with the data required to create a pulse sequence. In the case of imaging a tomographic plane parallel to the axial plane, the sagittal plane, or the coronal plane shown in FIG. 3 (hereinafter referred to as “simple imaging”), a pulse sequence describing the linear gradient magnetic field of each of the XYZ axes and the generation timing of the transmission pulse. The computer system 11 supplies the data, the magnetic field data indicating the strength of the generated linear gradient magnetic field of each of the XYZ axes, the hardware constant, and the offset data for adjusting the uniform magnetic field to the sequence controller 10. In the case of gradient imaging, pulse sequence data describing the linear gradient magnetic fields of the XYZ axes and the transmission pulse generation timing, and the intensity of the linear gradient magnetic fields of the XYZ axes used for simple imaging of the reference axial surface are shown. Magnetic field data,
The oblique angle of the inclined surface with respect to the reference surface (axial surface), hardware constants, and offset data for uniform magnetic field adjustment are supplied from the computer system 11 to the sequence controller 10. The oblique angle means, as shown in FIG. 4, a tilt angle θ around the X axis of the inclined surface with respect to the axial surface and a slew angle φ around the Y axis of the inclined surface with respect to the axial surface.

The computer system 11 also takes in magnetic resonance signals received by the receiver 6 and reconstructs a tomographic image of the subject P. This tomographic image is sent to the display unit 12,
It is displayed there.

As shown in FIG. 2, the computer system 1
1 is connected to one bus 21 for both data / control via the communication board 20. A CPU 22 that controls the overall operation of the sequence controller 10 is connected to the bus 21. The sequence data supplied from the computer system 11 is sent to the sequence data control unit 23 via the communication board 20 and the bus 21 under the control of the CPU 22, and is held in the sequence data memory 24 under the control of the sequence data control unit 23. . The magnetic field data supplied from the computer system 11 is sent to the arbitrary waveform data control unit 25 via the communication board 20 and the bus 21 under the control of the CPU 22, and is stored in the arbitrary waveform data memory 26 under the control of the arbitrary waveform data control unit 25. Retained. The offset data supplied from the computer system 11 is C
After being held in the internal memory board of the PU 22, it is supplied to one input terminal of the adder 30 via the other bus 27. The hardware constant and the oblique angle supplied from the computer system 11 are held in the internal memory board of the CPU 22 and then supplied to the high-speed oblique processing unit 28 via the other bus 27. The magnetic field data held in the arbitrary waveform data memory 26 is stored in the other bus 2 according to the sequence data under the control of the CPU 22.
7 to the high-speed oblique processing unit 28.

The high-speed oblique processing unit 28 uses the sent magnetic field data, the hardware constant, and the oblique angle to convert the magnetic field data of the simple imaging of the axial surface into the magnetic field data of the tilt imaging according to the following equation (2). To do. XYZ used for simple shooting of the axial surface
The magnetic field data of the linear gradient magnetic field of each axis are shown as Gx (t), Gy (t), and Gz (t) as a time function, respectively, and the tilt angle around the X axis of the inclined surface is θ and around the Y axis of the inclined surface. The slew angle is φ, and XY used for tilted imaging after oblique processing.
Gx0 (t) for the magnetic field data of the linear gradient magnetic field of each Z axis
, Gy0 (t) and Gz0 (t).

[0019]

[Equation 2]

The magnetic field data of the linear gradient magnetic field of each of the XYZ axes used for tilt imaging which is subjected to the oblique processing by the high-speed oblique processing unit 28 is passed through the ECC circuit 29 for correcting the eddy current to the other side of the adder 30. It is supplied to the input terminal.

In the adder 30, the X used for tilt photographing is used.
The magnetic field data of the linear gradient magnetic field of each YZ axis is added to the offset data. As a result, the linear gradient magnetic field on each of the XYZ axes is uniformly corrected. The homogeneity-corrected magnetic field data is sent to the corresponding amplifiers 7, 8, and 9, respectively.

Next, the operation of this embodiment will be described. FIGS. 5A and 5B show pulse sequences before and after oblique processing of magnetic field data of rectangular waveform.
(B) shows pulse sequences before and after oblique processing of magnetic field data of arbitrary waveform. The magnetic field data of the linear gradient magnetic field (here, Gx) in the phase encoding direction is not limited to the rectangular waveform as shown in FIG. 5A, but is deliberately set to, for example, that shown in FIG. In some cases, it may be shaped into an arc-shaped arbitrary waveform as shown in FIG. Here, a case where the magnetic field data of the linear gradient magnetic field Gx in the phase encoding direction is shaped into an arbitrary waveform will be described.

The oblique angle is set in the computer system 11 after being determined by the operator. XY
Pulse sequence data describing the linear gradient magnetic field of each Z axis and the transmission pulse generation timing, magnetic field data indicating the intensity of the linear gradient magnetic field of each XYZ axis used for simple imaging of the reference axial surface, and the reference plane ( Axial surface)
The oblique angle of the inclined surface with respect to, the hardware constant, and the offset data for uniform magnetic field adjustment are supplied from the computer system 11 to the sequence controller 10.

The sequence data is sent to the sequence data control unit 23 via the communication board 20 and the bus 21 under the control of the CPU 22, and is held in the sequence data memory 24 under the control of the sequence data control unit 23. The magnetic field data is sent to the arbitrary waveform data control unit 25 via the communication board 20 and the bus 21 under the control of the CPU 22, and is stored in the arbitrary waveform data memory 26 under the control of the arbitrary waveform data control unit 25. Offset data, hardware constants and oblique angles are held in the internal memory board of the CPU 22.

After the above preparatory work is completed, photographing is immediately started according to the sequence of the sequence data held in the sequence data memory 24. The magnetic field data of each sample point held in the arbitrary waveform data memory 26 is sequentially supplied to the high-speed oblique processing unit 28 along with the sequence together with the hardware constant and the oblique angle. The high-speed oblique processing unit 28 uses the sent magnetic field data, the hardware constant, and the oblique angle to convert the magnetic field data of the simple imaging of the axial surface into the magnetic field data of the tilt imaging in real time according to the above equation (2). If real-time processing of this oblique processing is impossible, the oblique processing start time of the magnetic field data of the linear gradient magnetic field is set earlier than the generation timing of other transmission pulses by the processing time required for the oblique processing. As a result, the sequence as scheduled is executed.

The magnetic field data of the linear gradient magnetic field of each of the XYZ axes used for tilt imaging which is obliquely processed by the high-speed oblique processing unit 28 is supplied to the other side of the adder 30 via the ECC circuit 29 for correcting the eddy current. It is supplied to the input terminal. At this time, offset data is supplied to one input terminal of the adder 30. The magnetic field data is
It is added with the offset data. Thereby, the magnetic field data of each axis is corrected so that the linear gradient magnetic field of each axis of XYZ becomes uniform. The homogeneity-corrected magnetic field data is sent to the corresponding amplifiers 7, 8, and 9, respectively. Amplifiers 7, 8,
9 generates a linear gradient magnetic field of each axis at the timing when each magnetic field data is sent.

As described above, according to this embodiment, the dedicated unit 28 for the oblique processing is provided in the sequence controller 10.
Since the CPU 22 is provided independently of the CPU 22, the CPU 22 is released from the oblique processing and the processing load is reduced. Further, since the operation control and the oblique processing in the sequence controller 11 can be executed while being shared by the CPU 22 and the dedicated unit 22, the oblique processing is not interrupted by the interruption of the operational control, and the oblique processing is performed to advance the photographing. With it can be executed in real time. As a result, after the oblique angle is determined, the shooting can be started immediately. Further, since the dedicated unit 28 for the oblique processing is provided in the sequence controller 10 independently of the CPU 22, modularization is promoted, and the ease of development and maintenance is improved. Furthermore, the memory that holds the magnetic field data after the oblique processing is no longer required,
It is also effective in terms of equipment cost. The present invention is not limited to the above-described embodiments, but can be implemented with various modifications.

[0028]

As described above, according to the present invention, since the dedicated unit for the oblique processing is provided in the sequence controller independently of the CPU, the CPU is released from the oblique processing and the processing load is reduced. Further, since the operation control and the oblique processing in the sequence controller can be executed while being shared between the CPU and the dedicated unit, the oblique processing is not interrupted by the interruption of this operational control, and the oblique processing is performed in real time as the photographing progresses. It is possible to provide a magnetic resonance imaging apparatus that can be executed in.

[Brief description of drawings]

FIG. 1 is a block diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of the sequence controller of FIG.

FIG. 3 is a diagram showing a tomographic plane that can be imaged with magnetic field data having a rectangular waveform.

FIG. 4 is a diagram showing a tilt angle and a slew angle of an inclined surface.

FIG. 5 is a diagram showing pulse sequences before and after oblique processing of magnetic field data having a rectangular waveform.

FIG. 6 is a diagram showing pulse sequences before and after oblique processing of magnetic field data having an arbitrary waveform.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... Linear gradient magnetic field coil, 3 ... Transmitting / receiving coil, 4 ... Static magnetic field control device, 5 ... Transmitter, 6 ... Receiver, 7 ... X-axis linear gradient magnetic field amplifier, 8 ... Y-axis linear gradient Magnetic field amplifier, 9 ... Z-axis linear gradient magnetic field amplifier, 10 ... Sequence controller, 11 ... Computer system, 12
... Display unit, 13 ... Top plate, 14 ... Gantry, 20 ... Communication board, 21, 27 ... Bus, 22 ... CPU, 23 ... Sequence data control unit, 24 ... Sequence data memory, 25 ... Arbitrary waveform data control unit, 26 ... Arbitrary waveform data memory, 28 ... High-speed oblique processing unit,
29 ... ECC circuit, 30 ... Adder.

Claims (1)

[Claims] 1. A sequence controller for controlling the generation of a linear gradient magnetic field in each of the XYZ axes and a transmission pulse according to a predetermined sequence, wherein the magnetic field data of the linear gradient magnetic field in each of the XYZ axes is inclined at an arbitrary angle with respect to a cross section. In a magnetic resonance imaging apparatus that also serves as oblique processing for converting into magnetic field data of a linear gradient magnetic field of XYZ axes according to imaging of an inclined surface, a dedicated unit for the oblique processing is provided in the sequence controller independently of the CPU. A magnetic resonance imaging apparatus characterized by the above.