JPH11347011A - Magnetic resonance imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a quality image of high time resolution and high space resolution by equipping a first signal processing system to reconstitute an image using data measured from the start to an arbitrary time point and a second signal processing system to reconstitute an image using the whole measured data and displaying obtained images in parallel. SOLUTION: A calculation system of CPU 8 of an MRI device has two CPUs 8a, 8b for a reconstituting calculation system and phase-encoded echo signals are stored in RAMs of CPUs 8a, 8b. CPU 8a carries out two dimensional Fourier transform on p echo signals measured at first and reconstitutes the image and makes the image displayed on one screen of a display device 20. Image reconstitution is repeated every new p echo signals to update the display screen. On the other hand, CPU 8b stores the whole measured signals until the end of one measurement into a memory before similarly reconstituting the image of the whole echo signals and makes the image displayed on the other screen.

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 desired part of a subject by utilizing a magnetic resonance phenomenon, and particularly to an IVR (Interventional Radiology). The present invention relates to an MRI apparatus suitable for continuous imaging.

[0002]

2. Description of the Related Art IVR is a technique for performing surgery and treatment while confirming a surgical site or the like using various image acquisition apparatuses during surgery. IVMR using an MRI apparatus has been put to practical use as an image acquisition apparatus. FIG. 6 is a diagram showing image acquisition in IVMR. When data for one measurement is collected by a high-speed imaging sequence, the image is reconstructed, the steps of displaying images are repeated, and the displayed image is sequentially updated. In this way, the information (position, tissue state) of the tissue to be collected when performing a biopsy or the like and the information such as the position of the catheter are monitored in real time.

[0003]

As described above, in the IVMR, it is necessary to obtain tissue information and information on the position of a catheter or the like in real time (high time resolution).
Moreover, the obtained image is required to have high spatial resolution or high S / N.

As a high-speed imaging method using an MRI apparatus, E
There are a PI (echo planar) sequence and an FSP (high-speed spin echo) sequence. In each case, it is necessary to increase the phase encoding and the number of sample points in order to obtain high spatial resolution. Decrease. In addition, integration is effective for obtaining a high S / N image, and in this case, the shooting time is extended. Conversely, in order to achieve real-time performance, a phase encoding and a sequence that reduces the number of sample points are performed. Time resolution and spatial resolution are in a trade-off relationship, and it is difficult to obtain an image with the desired high spatial resolution and high temporal resolution. is there.

[0005] Therefore, the present invention provides a time resolution with one measurement,
The purpose is to obtain an image with high spatial resolution.

[0006]

In order to solve the above-mentioned problems, an MRI apparatus according to the present invention provides a static magnetic field generating means for generating a static magnetic field in a space where a subject is placed, and applies a gradient magnetic field to the space. A gradient magnetic field generating means, a transmitting system for irradiating a high frequency pulse for causing nuclear magnetic resonance to the nuclei of the atoms constituting the living tissue of the subject, and detecting an echo signal emitted from the subject by nuclear magnetic resonance A receiving system, a signal processing system for processing a received echo signal and reconstructing an image,
The signal processing system includes means for displaying a reconstructed image, and the signal processing system repeats a process of reconstructing an image using data measured from the start of one measurement to an arbitrary time before the end until the measurement is completed. A first signal processing system; and a second signal processing system for reconstructing an image using all data measured by the measurement at the end of the measurement. The display means is composed of the first and second signal processing systems. A means for displaying the obtained images in parallel is provided.

Here, one measurement includes the measurement of m echo signals when one image is measured by m phase encodings and the case of adding them.

[0008] In the first signal processing system, an image can be reconstructed and updated at short time intervals without waiting for completion of measurement, and an image with high time resolution can be obtained. In the second signal processing system, a high-definition image with high S / N and high spatial resolution is reconstructed. Since these are displayed side by side on the display means, the operator can simultaneously obtain the position information and the tissue information of the catheter tip with high precision by viewing them simultaneously.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an MRI according to the present invention.
1 is an overall schematic block diagram showing an embodiment of the device.
This MRI apparatus mainly includes a static magnetic field generating magnet 2, a magnetic field gradient generating system 3, a transmitting system 4, a receiving system 5, a signal processing system 6, a sequencer 7, and a central processing unit (CPU) 8. ing.

The static magnetic field generating magnet 2 generates a uniform static magnetic field around the subject 1 in the direction of the opposite axis or in a direction perpendicular to the opposite axis, and has a certain spread around the subject 1. A permanent magnet type, normal conduction or superconducting type magnetic field generating means is arranged in the space. Magnetic field gradient generation system 3
Is a gradient magnetic field coil 9 wound in three directions of X, Y and Z.
And a gradient magnetic field power supply 10 for driving the respective gradient magnetic field coils. By driving the gradient magnetic field power supplies 10 for the respective coils in accordance with an instruction from the sequencer 7 described later, the gradients in the X, Y, and Z axes are provided. Magnetic fields Gx, Gy, G
z is applied to the subject 1. A slice plane for the subject 1 can be set by this method of applying a gradient magnetic field, and positional information can be added to the echo signal.

The sequencer 7 repeatedly applies a high-frequency magnetic field pulse for causing nuclear magnetic resonance to the nuclei of the atoms constituting the living tissue of the subject 1 in a predetermined pulse sequence. Various commands necessary for data collection of tomographic images of the specimen 1 are sent to the transmission system 4, the magnetic field gradient generation system 3, and the reception system 5.

The transmitting system 4 irradiates a high-frequency magnetic field to cause a nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject 1 by the high-frequency pulse sent from the sequencer 7. , A high-frequency amplifier 13 and a high-frequency pulse 14a. The high frequency pulse output from the high frequency oscillator 11 is
The amplitude is modulated by the modulator 12 in accordance with the instruction, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13 and then supplied to the high-frequency coil 14a arranged close to the subject 1. Is irradiated.

The receiving system 5 includes an NM emitted from the subject 1
A receiving coil 14b for receiving the R signal, an amplifier 15,
A quadrature phase detector 16 and an A / D converter 17 are provided. The echo signal received by the receiving coil 14b is amplified, subjected to quadrature detection as two-sequence data, digitized by the A / D converter 17, and sent to the CPU 8. .

The CPU 8 sends commands to the sequencer 7 to control the entire apparatus, and performs various operations such as image reconstruction of data transmitted from the receiving system 5 as a part of the signal processing system 6. The signal processing system 6 includes a storage device such as a ROM or a RAM for storing data in the middle of calculation or data necessary for calculation, a storage device such as a magnetic disk 18 or a magnetic tape 19 for storing calculation results, and a display device for displaying calculation results. 20 and C
An operation console 21 for giving instructions to the PU 8 is provided.

The arithmetic processing system of the CPU 8 comprises two independent reconstruction arithmetic processing systems CPU 8a and CPU 8b. The CPU 8a performs a reconstruction arithmetic processing based on data collected from the start of measurement to an arbitrary time. While repeating such processing until the measurement is completed, the image as the calculation result is sequentially displayed on the display device. The CPU 8b performs a reconstruction calculation process based on the data collected for each measurement,
The image is displayed on the display device 20.

The display device 20 may be provided with two CRT display devices for displaying image data from two reconstruction processing systems in parallel. However, as shown in FIG.
It is preferable to have a function of displaying two sets of image data in parallel on the T screen. FIG. 2 shows the MRI having the above configuration.
FIG. 5 is a diagram showing the status of IVR by the device, in which the operator performs M biopsy or the like on the subject and displays M on the display device.
The position of the catheter tip and the state of the tissue are confirmed on the R image.

Next, I by the MRI apparatus having such a configuration is described.
The shooting procedure at the time of VR will be described with reference to FIG. As an example, a case where a predetermined slice is continuously photographed in a single shot EPI sequence will be described.

First, when the measurement is started, the EPI sequence shown in FIG. 4 is started (301). That is, the high-frequency magnetic field 23 for spin excitation constituting the tissue of the subject is applied together with the gradient magnetic field Gz24 for slice selection, then the readout gradient magnetic field Gx26 is applied, and then the polarity of the readout gradient magnetic field Gx27 is inverted. While repeating, m echo signals S1 to Sm are generated. At this time, a gradient magnetic field Gy25 for encoding the echo signal in the phase direction is applied. Although only 14 echo signals are shown in the drawing for simplicity, a single shot EPI sequence measures, for example, 64 or 128 echo signals. At this time, the amount of phase encoding is not sequentially increased or decreased from the echo signals S1 to Sm, but the echo signals S1 to Sm.
When Sm is divided into n, S1 to Sp (p = m / n),
Sp ~ S2p, S2p ~ S3p ... S (n-1) p ~
Sm is provided so as to appropriately include both high-frequency data and low-frequency data in k-space. For this reason, for example, when m = 64 and n = 4, in S1 to S16, 1, 5,
16 phase encodings from 9 to 61 are given, and S
In 17 to S32, 16 phase encodings of 2, 6, 10... 62 may be provided. Alternatively, the phase encoding can be given at all at random.

The echo signal thus phase-encoded is converted into data of, for example, 64 samples by the CPU 8.
a, stored in the RAM of the CPU 8b (disposed in k-space). The CPU 8a first performs a two-dimensional Fourier transform on the p measured echo signals to reconstruct an image (302, 303). At this time, in order to simplify the calculation, the number of data in the kx direction of the k space may be thinned out in accordance with the number of data in the ky direction (= the number p of phase encodes).

The image reconstructed in this way is displayed on one screen 20a of the display device 20 (304). Although this image has a low spatial resolution, it is reconstructed by data including both high-frequency data and low-frequency data, so that it is possible to sufficiently recognize the outline of the position of the catheter, for example, and furthermore, a very short time from the start of measurement. Is obtained by

The CPU 8a receives the next p echo signals Sp
To S2p, the image reconstruction operation is performed in the same manner, and the image reconstruction is sequentially repeated each time new p echo signals are measured, and the screen 20a of the display device 20 is updated (30).
4). Therefore, the screen 20a shows 1/1 of the time required for one measurement.
A new image is displayed with a time resolution of n.

On the other hand, after all the echo signals S1 to Sm measured up to the end of one measurement are stored in the memory, the CPU 8b performs two-dimensional Fourier transform on all the echo signals to reconstruct an image (305). This image is displayed on the other screen 20b of the display device 20 (306). Since this image is reconstructed using all the echo signals, an image with high spatial resolution can be obtained. The operator operates the two screens 20a and 20a of the display device 20 as shown in FIG.
By simultaneously viewing the high-precision image and the high-time-resolution image displayed on 20b, it is possible to confirm the position information and the tissue information of the catheter as real-time and high-precision information.

In the case of performing continuous shooting as in IVR,
The above-described shooting sequence is repeated. In the next measurement, C
The PU 8a repeats image reconstruction and image update each time p (= m / n) echo signals are measured, and the CPU 8b performs an image reconstruction operation using all echoes measured in the next measurement. The image of the previous measurement is updated and displayed on the screen 20b. In this case, if necessary, an addition process may be performed on the echo obtained in the previous measurement. As a result, an image with a high S / N can be obtained.

Next, as a second embodiment of the present invention, a high S / N
A photographing method for obtaining the image will be described. In this embodiment, as shown in FIG.
A single shot EPI sequence in which the number of measurement data points is reduced as compared with the PI sequence is adopted. In the illustrated embodiment, only four signals are shown in a simplified manner,
Actually, the number m of echo signals measured in one measurement (the number of phase encodes) is a number that can reconstruct one image, for example, 3
2 or 64. In addition, the number of samples is set small in accordance with this, and the time required for measurement is greatly reduced.

The echo signals measured by the photographing sequence are stored in the memories of the CPUs 8a and 8b. The CPU 8a performs image reconstruction using the m echo signals, and displays this on the screen 20a of the display device 20. The image reconstruction is repeated each time the measurement is repeated, whereby the image displayed on the screen 20a is updated. Since this image is reconstructed using a small amount of data, the spatial resolution is low. However, since the measurement time for one measurement is considerably shorter than that of a normal single-shot EPI, an image with a high time resolution can be obtained.

On the other hand, when a plurality of (n) measurements are completed, the CPU 8b performs a Fourier transform process on the data obtained by adding and integrating the n-time measurement data, and displays the reconstructed image on the display device 20. It is displayed on the screen 20b. The higher the number of additions n, the higher the S / N image can be obtained.
As described above, in the present embodiment, an image having a high time resolution and a high S
/ N images can be displayed simultaneously.

[0026]

As described above, the MRI apparatus of the present invention reconstructs an image of measured data with two signal processing systems and displays the measured data in parallel on two display screens, thereby achieving high S / N and high S / N. A high-resolution image such as a high spatial resolution and an image with a high temporal resolution can be simultaneously viewed. Therefore IV
In MR, the operator can confirm the position of the tip of the catheter and the state information of the tissue desired at that time in real time and with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an MRI apparatus according to the present invention.

FIG. 2 is a schematic diagram showing the situation of IVMR using the MRI apparatus of the present invention.

FIG. 3 is a flowchart of data processing by the MRI apparatus of the present invention.

FIG. 4 is a diagram showing an embodiment of an imaging sequence by the MRI apparatus of the present invention.

FIG. 5 is a diagram showing another embodiment of an imaging sequence by the MRI apparatus of the present invention.

FIG. 6 is a flowchart of data processing by a conventional MRI apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 subject 2 static magnetic field generator 3 magnetic field gradient generating system 4 transmitting system 5 receiving system 6 signal processing system 8 CPU 8a CPU (first signal processing system) 8b CPU (second signal processing system) 20 display device 20a, 20b screen

Claims (1)

[Claims] 1. A static magnetic field generating means for generating a static magnetic field in a space in which a subject is placed, a gradient magnetic field generating means for applying a gradient magnetic field to the space, and a nucleus for nuclei of atoms constituting a living tissue of the subject A transmitting system for irradiating a high-frequency pulse for causing magnetic resonance, a receiving system for detecting an echo signal emitted from the subject by the nuclear magnetic resonance, and a signal processing system for processing the received echo signal to reconstruct an image And a means for displaying a reconstructed image, wherein the signal processing system reconstructs an image using data measured from the start of one measurement to an arbitrary time before the end. A first signal processing system that repeats processing until the measurement is completed, and a second signal processing system that reconstructs an image using all data measured by the measurement when the measurement is completed; Stage magnetic resonance imaging apparatus characterized by comprising means for parallel display an image obtained by the first and second processing processing system.