JP2001161659A - Magnetic resonance imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging system for imaging a cross section of a subject by using a magnetic resonance, which reconstitutes an image by making a space k without reference to the order of reception of NMR signals, corresponding to a sequence such as a synchronous measuring or the like whose parameter for imaging is changed in real time. SOLUTION: NMR information obtained based on the NMR signal and the parameter for imaging for generating the NMR signal are combined and stored as information on environmental conditions. The NMR information is specified when the information on environmental conditions are designated, and a required space k is reconstituted and displayed.

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 (hereinafter, referred to as "MRI") apparatus for obtaining a tomographic image of a subject using a nuclear magnetic resonance phenomenon, and in particular, an MRI apparatus reconstructs an image based thereon. The present invention relates to an MRI apparatus having a new arrangement method in k-space.

[0002]

2. Description of the Related Art In an MRI apparatus, a gradient magnetic field and a high-frequency (hereinafter, referred to as "RF") pulse are applied to a subject in a static magnetic field to select and excite a cross section of a specific portion, and one of the cross sections is excited.
The axial position information is encoded into the phase of the RF pulse, and the other axial position information is encoded into the frequency of the RF pulse. The obtained NMR signal is a magnetic resonance echo signal from the nucleus of the living tissue at a specific site. By decoding the signal by Fourier transform and reconstructing using the above position information,
Imaging is performed to obtain a cross-sectional image representing a cross section of the site.

[0003] In order to obtain such a cross-sectional image, a predetermined specific sequence called, for example, high-speed spin echo, three-dimensional measurement, or the like in which a gradient magnetic field and an RF pulse are generated and changed at a certain timing is repeated. Image information (hereinafter, referred to as “NMR information”) based on the NMR signal detected corresponding to the gradient magnetic field and the RF pulse, which represents each pixel constituting the image, is arranged in k-space in a predetermined phase encoding order and slice encoding order. Need to be done.

For this reason, NMR information necessary for image reconstruction is stored in a phase encoding order / slice encoding order or a phase encoding / slicing of a detected signal as disclosed in, for example, JP-A-6-285041. It is arranged in the memory corresponding to the k-space in the order of the encoding size.

[0005]

Even in the above-mentioned conventional apparatus, no problem occurs in the imaging sequence in which the order in which the NMR information is stored in the k space, that is, the arrangement in the k space is uniquely determined. However, in the case of a sequence called synchronous measurement in which imaging parameters, which are environmental conditions when an NMR signal is generated while analyzing biological information such as an electrocardiographic waveform and a respiratory state of a subject during the sequence execution, are changed in real time. Since the NMR signals are acquired in an order depending on the ever-changing biological information, the order of phase encoding and slice encoding is not uniquely determined for each measurement, and the order of storage in the memory cannot be uniquely determined. And the image cannot be reconstructed as a result.

An object of the present invention is to provide an MRI apparatus which arranges images in a predetermined k-space and reconstructs an image irrespective of the actual acquisition order of NMR signals in any sequence.

[0007]

According to a first aspect of the present invention, there is provided an MRI apparatus which excites a static magnetic field generating means, a gradient magnetic field generating means, and an atomic nucleus constituting a tissue of a subject. Transmission system for generating an RF pulse for generating magnetic resonance by using the same, a reception system for detecting an NMR signal from a subject by magnetic resonance, and a signal processing system for reconstructing an image using the NMR signal detected by the reception system Means for storing image information based on the detected NMR signal and environmental condition information when the NMR signal is detected as one data, and a k-space based on the environmental condition information. Is provided.

According to the first aspect of the present invention, an image information based on an NMR signal from a subject in an MRI apparatus and an imaging parameter or the like when the NMR signal from which the image information is obtained is detected. Since the condition information is stored as one structured NMR signal, the image information can be specified by specifying the environmental condition information, and even if the imaging parameter is changed in real time, the actual NMR signal Images can be reconstructed by arranging them in a predetermined k space regardless of the order of acquisition.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an MRI apparatus according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram schematically showing the overall configuration of an MRI apparatus to which the present invention is applied, FIG. 2 is a configuration diagram of a signal processing apparatus of the MRI apparatus of the present invention, and FIG. 3 is a structuring used in an embodiment of the present invention. NM
FIG. 4 is a configuration diagram of an R signal, FIG. 4 is a data flow diagram in the MRI apparatus of the present invention, and FIG. 5 is a diagram showing an example of arrangement in k-space in an embodiment of the present invention.

FIG. 1 is a block diagram showing the overall configuration of an MRI apparatus to which the present invention is applied. This MRI apparatus comprises a static magnetic field generating means 1, a gradient magnetic field generating means 2, a transmitting system 3, a receiving system 4, a signal processing system 5, a sequencer 6, a central processing unit 7, and an operation unit (not shown). A tomographic image of the subject is displayed using the phenomenon.

The static magnetic field generating means 1 is composed of any one of a permanent magnet, a normal conducting magnet, and a superconducting magnet arranged in a certain space around the subject 8. A uniform static magnetic field is generated in a direction or a direction perpendicular to the body axis of the subject.

The gradient magnetic field generating means 2 comprises a gradient magnetic field coil 9 wound in three directions of X, Y and Z, and a gradient magnetic field power supply 10 for magnetizing each of these coils. By magnetizing each coil of the gradient magnetic field power supply 10 according to the above, gradient magnetic fields Gs, Gp, and Gf in three directions of X, Y, and Z are applied to the subject 8. The imaging section of the subject 8 is set by the way of applying the gradient magnetic field.

The transmission system 3 includes a high-frequency oscillator 11 and a modulator 1
2. An output from the high-frequency oscillator 11 which includes a high-frequency amplifier 13 and a high-frequency irradiation coil 14 and causes nuclear magnetic resonance to occur in nuclei of atoms constituting a section of the subject 8 set by the gradient magnetic field generating means 2 After the amplified RF pulse is amplified by the high-frequency amplifier 13, the amplified RF pulse is supplied to the high-frequency irradiation coil 14 installed close to the subject 8 and
Irradiation.

The receiving system 4 includes a high-frequency receiving coil 15, a receiving circuit 16, and an analog / digital (hereinafter, “A / D”).
An echo signal, which is an NMR signal due to nuclear magnetic resonance of the nucleus of the subject 8 due to the electromagnetic wave irradiated from the high-frequency irradiation coil 14 of the transmission system 3, is disposed close to the subject 8. Data detected by the high-frequency receiving coil 15, input to the A / D converter 17 via the receiving circuit 16, converted into a digital signal, and further sampled at a timing according to a command from the sequencer 6 (hereinafter “sampling data”) Is sent to the signal processing system 5.

The signal processing system 5 includes a CPU 7 for performing processing such as Fourier transformation, correction coefficient calculation, image reconstruction, and the like on the sampled data, and controlling the sequencer 6. A signal processing device 18, whose structure and functions will be described in detail below, A program for a sequence of image analysis processing over time and a designated measurement, a parameter used when the program is executed, and the like are stored, and a measurement parameter obtained by a preliminary measurement performed on the subject and detected by the reception system 4. The memory 19 temporarily stores sampling data from the NMR signal and an image used for setting a region of interest, and stores parameters for setting the region of interest, and a data storage unit for storing image data reconstructed by the CPU 7. The magnetic disk 20, the optical disk 21, and the image data read from these disks are visualized and cut off. Display 22 for displaying as an image
Consists of The CPU 7 reads out the pulse application pattern of the specified sequence from the memory 19 and reads out the sequencer 6
Is operated to perform an image reconstruction operation using the NMR information that is the image information based on the NMR signal detected by the reception system 4, and displays the image on the display 22 as a tomographic image.

The sequencer 6 operates under the control of the CPU 7 to repetitively generate an RF magnetic field pulse for exciting nuclear nuclei of atoms constituting the subject 8 to cause nuclear magnetic resonance in a predetermined pulse sequence. Various commands, which will be a part of environmental condition information described in detail below when a tomographic image of the subject 8 is created, are sent to the gradient magnetic field generating means 2, the transmission system 3, and the reception system 4. The operation unit includes a trackball, a mouse, a keyboard, and the like, and inputs control information of processing performed by the signal processing system 5.

In the MRI apparatus of this embodiment, the image information based on the detected NMR signal and the NM
Means for storing the environmental condition information when the R signal is detected as one data is provided in the signal processing device 18 described in detail below.

FIG. 2 is a block diagram showing a configuration of the signal processing device 18 of the MRI apparatus to which the present invention is applied. The signal processing device 18 includes a buffer memory 23, digital signal processors (hereinafter referred to as “DSPs”) 24 and 2
6. From the bank memory 25 and the large memory 27 which are means for storing image information based on the detected NMR signal in this embodiment and environmental condition information when the NMR signal from which the image information was obtained is detected as one data. Has become.

The buffer memory 23 includes an A / D converter 17
And stores the sampling data converted into a digital quantity.

The DSP 24 is of a type having an internal memory. The DSP 24 performs QD detection, resampling, Fourier transform and correction calculation on the sampling data stored in the buffer memory 23, and creates a structured NMR signal to be described later.
The data is stored in the bank memory 25.

In this embodiment, the bank memory 25 is of a type having two banks, and the connection destination of each surface is set to DS.
The bank can be switched to the P24 and the DSP 26 by bank switching (hereinafter referred to as “bank change”). The structured NMR signal stored in bank memory 25 by DSP 24 is
Access by the SP 26 becomes possible.

The DSP 26 is arranged in the k-space based on the environmental condition information of the structured NMR signal stored in the bank memory 25, stored in the large memory 27, and performs a reconstruction process and a correction calculation based on it to perform image processing. Memory 19
Transfer to

FIG. 3 shows an example of the structure of a structured NMR signal used in an embodiment of the present invention. This structured NMR signal is created by the procedure described below.

FIG. 4 is a diagram showing a flow of data acquired from a subject in an MRI apparatus to which the present invention is applied. The sampling data converted into a digital amount by the A / D converter 17 of the receiving system 4 is stored in the buffer memory 23 of the signal processing device 18. DSP2
4 performs QD detection / resampling / Fourier transform / correction calculation, creates NMR information, and stores the information in the internal memory of the DSP 24. Sequence type, scan number, phase encode number, slice encode number, echo number, cardiac time phase,
A unique parameter of the environmental condition at the time of detecting the NMR information which is the created image information such as the segment number is acquired from the sequencer 6 and separately obtained as the DSP 24 as the environmental condition information.
In the internal memory.

[0025]

[Table 1]

Table 1 shows a list of items of environmental condition information used in this embodiment. Reserve 1-9 is an empty space for a new item to be used as environmental condition information in the future. In addition to the parameters specified in the table, any imaging parameters for acquiring image information for forming a tomographic image, as long as they are used for specifying the image information, are adopted as environmental condition information, and a preliminary 1 -9 can be used.

Next, in this embodiment, the DSP 24 creates a structured NMR signal as one data by simply writing the environmental condition information and the NMR information held in the internal memory, and accumulates them in the bank memory 25. This accumulation is repeated until the number of structured NMR signals reaches the limit that can be accumulated in one bank of the bank memory 25, or until signal acquisition ends. At either time, the bank memory 25 performs a bank change, and the DSP 26
Can access the stored structured NMR signal.

The DSP 26 sequentially fetches the accessible structured NMR signals, and in this embodiment, the slice encoding order number m • contained in the environmental condition information.
Based on the phase encoding order number n, the NMR information is arranged on the large memory 27 and arranged in the k space, as shown in FIG. 5, regardless of the actual acquisition order of the NMR signals. Then C
The PU 7 reconstructs and corrects the NMR information of the arranged k-space, forms an image, transfers the image to the memory 19, and displays the image.
This is iteratively continued until the reconstruction of the image is completed.

In this example, the structured NMR signal is created as one data by simply writing the environmental condition information and the NMR information, but any known technique can be applied as long as the digital signal is stored in combination. In this case, a known signal handling method such as a method for improving the accuracy of a digital signal such as error suppression and error correction can be added and adopted.

[0030]

Since the present invention is configured as described above, it has the following effects. According to the MRI apparatus of the first aspect, the image information based on the detected NMR signal and the imaging parameter that is the environmental condition information when the NMR signal from which the image information is obtained is detected are stored as one data. By specifying the environmental condition information, the NMR information can be specified, and even in a sequence in which the imaging parameter which is a part of the environmental condition information is changed in real time, for example, in a ROPE imaging or a SSFP imaging in synchronous measurement. The image can be reconstructed irrespective of the respiratory state or cardiac phase, and the image information can be arranged in a predetermined k-space regardless of the actual acquisition order of the NMR signals to reconstruct the image.

[Brief description of the drawings]

FIG. 1 is a block diagram of an MRI apparatus.

FIG. 2 is a configuration diagram of a signal processing device of the MRI apparatus.

FIG. 3 is a configuration diagram of a structured NMR signal.

FIG. 4 is a data flow diagram in the MRI apparatus.

FIG. 5 is a diagram showing an example of an arrangement of a k-space.

[Explanation of symbols]

 17 A / D converter 18 Signal processing device 19 Memory 23 Buffer memory 24 DSP 25 Bank memory 26 DSP 27 Large memory

Claims (1)

[Claims] 1. A static magnetic field generating means, a gradient magnetic field generating means, a transmission system for generating high-frequency pulses for exciting magnetic nuclei constituting a tissue of a subject to generate magnetic resonance, A receiving system for detecting an NMR signal;
In a magnetic resonance imaging apparatus having a signal processing system for reconstructing an image using an NMR signal detected by the reception system, image information based on the detected NMR signal and environmental condition information when the NMR signal is detected A magnetic resonance imaging apparatus provided with a unit for storing data as one data, and a unit for arranging in a k-space based on the environmental condition information.