JPH02243133A - Magnetic resonance imaging apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic resonance imaging apparatus for capturing arbitrary tomographic images of a subject using magnetic resonance phenomena, and in particular, to The present invention relates to a magnetic resonance imaging apparatus that can reconstruct a normal tomographic image based on image data before the interruption even if imaging is interrupted.

[Prior art] Conventionally, it has been well known that hydrogen atoms in a living body enter a resonance state at a unique frequency in a static magnetic field to reconstruct an arbitrary tomographic image of a subject and use it for medical diagnosis. Are known.

Figure 5 shows, for example, Mitsubishi Electric Technical Report (Vol. 60, No.
5. 1986, pp. 37-42) by Tsuji et al. [Mitsubishi Superconducting Magnetic Resonance Imaging System J] is a block diagram showing a conventional magnetic resonance imaging apparatus.

In the figure, (1) is a cylindrical magnet made of a superconducting magnet that generates a stable static magnetic field in the Z-axis direction, and a gradient magnet that generates gradient magnetic field pulses in three orthogonal axes (X, Y, Z) directions. It is equipped with a magnetic field coil and an RF coil (not shown) that generates a high-frequency magnetic field pulse (RF pulse).

(2) indicates a subject (for example, a human body) placed within the magnet (1); (3) indicates an examination table for moving and inserting the subject (2) into the magnet (1); and (4) is a gradient magnetic field power source that drives the gradient magnetic field coil in a predetermined sequence, (5) is a transceiver that drives the RF coil and receives the magnetic resonance signal from the subject (2), and (6) is a gradient magnetic field power source (4). ) and transmission/reception 1 (5).

(10) is the transmitting/receiving R (5) and the sequence control device (6).
) is a computer connected to CPU (11) and
A main memory W (1) stores processing program data of the CPU 11) and control data of the sequence control device (6).
2) and a high-speed calculation device that reconstructs a tomographic image based on the magnetic +113 signal from the transceiver (5)! ff1(13
), and a bus B that connects a CPU (11), a main storage device (12), a high-speed arithmetic device (13), and a sequence control device (6).

The high-speed calculation device (13) has a built-in AD converter that converts magnetic resonance signals into digital signals, and another main storage device that stores digital signals, and the sequence control device (6) has a built-in computer. (10) has a built-in interface for transmitting and receiving control data to and from the controller.

Figure 6 shows the object (2) designated by gradient magnetic field pulses.
is an explanatory diagram showing a tomographic plane (2a), in which a gradient magnetic field pulse in the Z-axis direction is used as a slice magnetic field, a gradient magnetic field in the X-axis direction is used as a phase encoding magnetic field, and a gradient magnetic field in the Y-axis direction is used as a frequency for signal readout. It is used as an encoding magnetic field.

FIG. 7 is an explanatory diagram showing the phase encode magnetic field strength (phase encode amount) that changes each time a magnetic resonance signal is repeatedly acquired for one imaging. signal N times (for example, 256 times)
When acquiring the phase encoding, the maximum magnetic field strength G
Gauss/C#] to -G is divided into N equal intervals (-
2G/N) and is changed N times.

Next, the operation of the conventional magnetic resonance imaging apparatus shown in FIG. 5 will be described with reference to FIGS. 6 and 7.

First, the subject (2) placed on the examination table (3) is inserted into the magnet (1), and control data for obtaining a predetermined tomographic image is transmitted from the CPU (11) to the sequence via bus B. Input to control device (6).

The sequence control device (6) drives the tilt [power source (4) and transceiver (5)] based on the control data, and controls the subject (
2), a gradient magnetic field pulse and an RF pulse are applied in a predetermined sequence.

As a result, the position and direction of the tomographic plane (2&) are specified by the gradient magnetic field pulse, and the predetermined tomographic plane (2&) is specified by the RF pulse.
The atomic nucleus (eg a hydrogen atom) in 2a) is excited. For example, a magnetic resonance signal is received from the subject (2) via a receiving coil that also serves as an RF coil, and a transceiver (5) receives the magnetic resonance signal.
) is input to the high-speed arithmetic unit (13).

At this time, as shown in FIG. 6, magnetic resonance excitation occurs in a specific tomographic plane (2a), and the number of pixels in the X-axis direction of the tomographic image is adjusted so that the tomographic image of this tomographic plane (2a) can be reconstructed. A phase encode magnetic field whose intensity is changed by the corresponding number of projections (N times) is applied to the subject (2). That is, the seventh
As shown in the figure, the phase encode amount G at the i-th signal acquisition
If i is Gi=[N2(i-1)IQ/N, then the 1st to Nth phase encodes iG and ~GN decrease at regular intervals (-2G/N), and G = G G2 =(N-2)G/NG, =(N-4)G/NG GN=(N-2)G/N.

Under the control of the CPU (11), the high-speed arithmetic unit (13) samples the magnetic resonance signals for N times, converts them into digital signals (image data), and calculates the image of the subject (2) based on this digital signal. A tomographic image of the tomographic plane (2a) is reconstructed. At this time, the change sequence of each phase encode amount Gi is unique, and during addition mode imaging in which this change sequence is further repeatedly acquired, the number of times magnetic resonance signals are collected for each phase encode amount becomes constant. That's what I do.

But one r! Subject (2) in the Ijl image of the R layer image.
If the imaging is interrupted due to significant movement or trouble with the magnetic resonance imaging device, the magnetic resonance signal for a specific amount of phase encoding after medium rM will not be collected, and it will not be possible to reconstruct a normal sectioned NgA. Can not.

Furthermore, even during addition mode imaging, the number of additions for each phase encode amount (projection) is not uniform, so it is still not possible to reconstruct a normal tomographic image.

[Problem 1M to be Solved by the Invention] As described above, conventional magnetic resonance imaging apparatuses do not have a means for compensating image data when imaging is interrupted, so when imaging is interrupted, normal I! There was a problem in that the 7i layer image could not be reconstructed, making inspection difficult.

This invention was made to solve the above problems, and even if imaging is interrupted, a normal tomographic image can be reconstructed based on the collected image data and the history of the amount of phase encoding. The purpose is to obtain a magnetic resonance imaging device.

[Means for Solving the Problems] The magnetic resonance imaging apparatus according to the present invention has ll! regarding the amount of phase encoding. 2 is provided in the computer for storing a history table for each tomographic image taken.

[Operation] In the present invention, even if imaging is interrupted before the acquisition of magnetic resonance signals is completed, image data is compensated based on the acquired magnetic resonance signals and history for each phase encode amount.

Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram showing one embodiment of the present invention, and (I
OA) is compatible with the calculator (10), and (1) to (6
) and (11) to (13) are the same as described above.

(20) is a history table provided in the main storage device (12) in the computer (IOA), and is a history table provided in the main storage device (12) in the computer (IOA).
Control data for 6) and history regarding each phase encode are stored.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be described with reference to FIGS. 2 and 3. Note that the normal imaging operation and tomographic image reconstruction operation are as described above, and will not be described here.

First, control data including a sequence of changes in phase encode amount, etc. is stored in a history table (20) via a CPU (11) in a computer (IOA). The phase encode amount (magnetic field strength) for the Nth time is 0.2G/N, 2G/N,
4G/N, -40/N, ..., (N-2)G/N, (
N-2) Vary G/N, G, and collect in order from the smallest absolute value to the largest absolute value. This is because the intensity of the acquired magnetic resonance signal is greater for a phase encode amount having a smaller absolute value, and this has a greater effect on the quality of the finally obtained tomographic image.

In this way, the image data D (D,, D2, D3,...) based on the collected magnetic resonance signals are as shown in FIG.
Each is stored in the corresponding history table (20) in order. That is, the zz-th image data D2j is stored in the memory location corresponding to the phase encode amount 23G/N on the Mll child table 20), and the 2j+1st image data D,j
+ is the amount of phase encoding on the history table (20) -
Each is stored in a memory location corresponding to 2jG/N as a history regarding the phase encode amount. At this time, the control data in the history table (20) is transmitted and received with the sequence control device (6), and is also transferred to the high-speed calculation device (13) as basic data for tomographic image reconstruction.

Now, if imaging is interrupted after the 2Mth signal acquisition with a phase encode amount of 2MG/N, then 2M+1~
Image data for the Nth phase encode amount can no longer be obtained. At this time, the CPU (11) sorts the image data D1 to D2N in the history table (20), and sorts the image data D2N+, to D2N that were not collected.
The image data 411 is sent in the same manner as when signal acquisition is performed a predetermined number of 10 executions (N times) (see FIG. 3, with N being all 0).

In this way, N (for example, 256) series of compensated image data D1 to DN are obtained while referring to the history regarding the amount of phase encoding, and a tomographic image is reconstructed based on this. At this time, since the phase encode amount at the memory location where the image data is 0 has a large absolute value and a small contribution to image quality, a nearly normal tomographic image is reconstructed.

In the above embodiment, the signals were collected in order from the phase encode amount with the smallest absolute value, but even if the signals were collected in order from the maximum phase encode amount as in the conventional example shown in FIG. 7, the image quality would deteriorate slightly. It has the same effect. In this case, as shown in FIG. All you have to do is perform a reconstruction process.

Moreover, the same effect can be obtained even when applied during addition mode imaging. In this case, if imaging is interrupted after the P-th signal collection during the L-th addition, the number of additions of image data D1 to DP to the phase encode amount corresponding to the 1st to P-th signal collection will be L times, and P+1 Image data DP, ... DN for the phase encode amount corresponding to ~Nth signal acquisition
The number of additions is L-1 times. Therefore, each of the image data DP+l to DN whose addition number is insufficient is L/(L-1
), the signal intensity becomes substantially uniform and a normal tomographic image can be reconstructed.

Furthermore, in this case, if the change sequence of the phase encode amount is fixed, the number of times of application of the phase encode magnetic field corresponding to each phase encode amount can be stored in the history table (20) without storing the value of each phase encode amount in the history table (20). You can store it as .

[Effects of the Invention] As described above, according to the present invention, a history table for storing a history regarding the amount of phase encoding each time a tomographic image is captured is provided in the computer. Even if the magnetic resonance imaging apparatus is interrupted, the magnetic resonance imaging apparatus can compensate for the image data based on the acquired magnetic resonance signals and history for each phase encode amount and reconstruct a normal tomographic image.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a sequence of changes in phase encoding amount according to an embodiment of the invention, and FIG. 3 shows a history table in FIG. 1. An explanatory diagram, FIG. 4, shows IlI according to another embodiment of the present invention.
An explanatory diagram showing a history table, FIG. 5 is a block diagram showing a conventional magnetic resonance imaging apparatus, FIG. 6 is an explanatory diagram showing a tomographic plane of a subject, and FIG. 7 shows a conventional change sequence of phase encoding amount. It is an explanatory diagram. (2)... Subject (4)... Gradient magnetic field power source (5)... Transmitter/receiver (6)... Sequence control device (10^)... Computer (20)... History table D1~ DN... Image data (fi history) In the drawings, the same reference numerals indicate the same or corresponding parts. Broom 1 diagram

Claims (1)

[Scope of Claims] A sequence control device for applying gradient magnetic field pulses and RF pulses to a subject in a predetermined sequence; and a tomographic image of the subject based on magnetic resonance signals obtained from the subject. A magnetic resonance imaging apparatus comprising: a computer for reconstruction; and a history table for storing a history regarding the amount of phase encoding of the gradient magnetic field pulses for each imaging of the tomographic image; The magnetic resonance imaging apparatus according to claim 1, wherein the computer reconstructs the normal tomographic image based on the history even if the imaging is interrupted.