JPH01214356A - Magnetic resonance imaging method - Google Patents

Abstract

PURPOSE:To prevent the lowering of image quality even when an electrocardiographic waveform is varied by repeating exciting/collecting procedure, wherein a region to be imaged is excited at the point of time when a predetermined time is elapsed after saturation procedure is executed and data are collected, at every electrocardiographic waveform to obtain a data group for imaging the region to be imaged. CONSTITUTION:For example, when an image is composed of 256 matrice, saturation procedure and exciting/collecting procedure are repeated 256 times in such a state that a time TD is provided at every R-wave of an electrocardiographic waveform and a repeating time TR1 is provided between both procedures. The data corresponding to 256 lines can be collected and the reconstitution of an electrocardiographic synchronous image becomes possible and the image is displayed on a display system. Since the time between the saturation procedure and the exciting/collecting procedure corresponding to the repeating time TR1 is fixed and the magnetization of a region to be imaged is saturated by the execution of the saturation procedure, the recovery degree of magnetization within the fixed time becomes always same even when the saturation procedure and the exciting/collecting procedure are repeated at every electrocardiographic waveform. Therefore, even when an electrocardiographic waveform is varied, the repeating time TR1 is constant and electrocardiographic synchronous imaging not lowering image quality can be performed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic resonance system that utilizes magnetic resonance phenomena to obtain diagnostic information such as slice images of specific parts of a subject. The present invention relates to a magnetic resonance imaging method that performs electrocardiogram-gated imaging using a diagnostic device, and particularly relates to a magnetic resonance imaging method that can obtain high-quality images without artifacts even when an electrocardiogram waveform fluctuates.

(Prior art) Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only electromagnetic waves of a specific frequency. The angular frequency ω shown in (ωo−s2πν., ν0
; Larmor frequency).

ω01γHO Here, γ is the gyromagnetic ratio specific to the type of atomic nucleus,
Further, Ho is the static magnetic field strength.

An apparatus that performs biological diagnosis using the above-mentioned principle processes the electromagnetic waves of the same frequency as the above induced after the above-mentioned resonance absorption, and calculates the nuclear density, longitudinal relaxation time TI, transverse relaxation time T2. Diagnostic information that reflects information such as flow and chemical shift, such as slice images of a subject, can be obtained non-invasively.

Collecting diagnostic information by magnetic resonance can excite all parts of a subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical requirements for imaging images. Therefore, the actual device is designed to excite a specific region and collect its signals.

Such a magnetic resonance diagnostic apparatus can perform electrocardiogram-gated imaging. That is, in electrocardiogram-gated imaging, a subject is fitted with, for example, an electrocardiograph, and scanning is performed using an electrocardiogram waveform, for example, a QR8 waveform, from the electrocardiograph as a reference for synchronization.

Here, an example of a pulse sequence for electrocardiographic gated imaging of one slice image according to the conventional method will be described with reference to FIG. That is, FIG. 4(a) is an electrocardiogram waveform diagram, and FIG. 4(b) is an electrocardiogram waveform diagram.
is a diagram showing an RF pulse and an echo signal. That is, the peak of an R wave in the electrocardiographic waveform shown in FIG. 4(a) is set as time to, and after a predetermined time TD is obtained from this time to, a 90° pulse in the spin echo method, for example, is applied,
A further 180° pulse is applied. Execution of this excitation procedure induces an echo signal at echo time TE, which is collected to obtain one line of data. To generate an image, for example, if the image is a 256 matrix, the above procedure is repeated 256 times with a repetition time TR. As a result, we were able to collect data for 256 lines.
Images can now be reconstructed.

Here, the relationship between the R wave-to-R wave interval TRR and the repetition time TR will be explained. That is, the R wave-R wave interval TRR
If is constant, the time TD from the R-wave peak time to will also be constant, and the repetition time TR will also be constant. In contrast,
When the R wave-R wave interval TRR changes, the R wave peak time to
The time TD from then on changes, and the repetition time TR also changes.

Expressing the above mathematically, the echo signal S-p (1-exp (-TR/Tl)Φ
e x p (-TE/T2) ρ is the density of the imaging target nuclide, especially protons.

Therefore, when TR changes, the echo signal S also changes. This fluctuation in the echo signal S means that data on the image fluctuates in the encoding direction, leading to deterioration in image quality due to artifacts in the encoding direction.

(Problem to be Solved by the Invention) In this way, in the conventional technology, the excitation/collection procedure is executed in synchronization with a specific point of the electrocardiogram waveform, so if the electrocardiogram waveform fluctuates, artifacts etc. This resulted in a decrease in image quality.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic resonance imaging method that prevents image quality from deteriorating even when an electrocardiogram waveform fluctuates during electrocardiogram-gated imaging.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized by taking the following measures in order to solve the above problems and achieve the objects. That is, the present invention provides a method for performing magnetic resonance imaging of a desired region of a subject in synchronization with an electrocardiogram waveform, including a saturation procedure for saturating a region to be imaged in synchronization with a specific point of the electrocardiogram waveform, and a method for performing magnetic resonance imaging on a desired region of a subject in synchronization with an electrocardiogram waveform. A data group for imaging the imaging target region is obtained by repeating an excitation/collection procedure for each electrocardiogram waveform, in which the imaging target region is excited and data is collected a predetermined time after the execution of the imaging target region. shall be.

(Function) According to such a method, the time between the saturation procedure and the excitation/collection procedure, which corresponds to the repetition time, is fixed, and by performing the saturation procedure, the magnetization of the imaging target region is Since the magnetization is saturated, the degree of magnetization recovery at the fixed time is determined by the saturation procedure and excitation/excitation for each electrocardiogram waveform.
Even if the collection procedure is repeated, it will always be the same. Therefore, even when the electrocardiogram waveform fluctuates, the repetition time is constant, and electrocardiogram-gated imaging can be performed with the constant repetition time without deterioration of image quality.

(Example) An example of the magnetic resonance imaging method according to the present invention will be described below. FIG. 1 is a diagram showing an example of the configuration of a magnetic resonance diagnostic apparatus capable of implementing the method of this embodiment, and FIG. 2 is a diagram showing a configuration example of a magnetic resonance diagnostic apparatus capable of implementing the method of this embodiment, and FIG. FIG. 2 is a diagram showing the pulse sequence of FIG.
FIG. 3 is a diagram showing pulse and echo signals.

As shown in FIG. 1, as a magnet assembly capable of accommodating a subject P,
A static magnetic field magnet (a shim coil for static magnetic field correction may be added) 1 made of a permanent magnet, a normal conducting magnet, a superconducting magnet, or a combination thereof, and position information is given to the magnetic resonance signal induction site. The gradient magnetic field for x, y
, a gradient magnetic field generating coil 2 for generating gradient magnetic fields in the z-axis direction, a transmitting coil 3A for transmitting RF pulses (90° pulse, 180'' pulse) and detecting the induced magnetic resonance signal, and a receiving coil 2 for generating magnetic resonance signals in the z-axis direction. It has a coil 3B. Here, the transmitting coil 3A is illustrated as a large-sized coil for whole body use, and the receiving coil 3B is illustrated as a small-sized surface coil. It may be something.

In the case of the superconducting system, there is a static magnetic field control system 4 which includes refrigerant supply control and mainly controls energization of the static magnetic field power source, and an X-axis, Y-axis, and Z-axis gradient magnetic field power source 5.6.7.
It is equipped with

Furthermore, the signals from the transmitter 8, which supplies power for generating RF pulses for excitation to the transmitter coil 3A, and the receiver coil 3B are amplified to the extent that they can be applied to subsequent processing, and the outputs are phase-shifted into real and imaginary parts, respectively. It is equipped with a receiver 9 that performs wave detection, converts the phase detection output into a digital signal, and outputs an A/D conversion output.

The apparatus also includes a sequencer 10 that performs a saturation procedure and an excitation collection procedure as shown in FIG. 2(b) using, for example, protons as the nuclide to be imaged. And receiver 9
The raw data is taken into a computer system 11, where a slice image of, for example, 256 matrices is reconstructed by, for example, a two-dimensional Fourier transform method, and displayed on a display system 12.

The present device also includes an electrocardiograph 13 that generates a signal synchronized with an electrocardiogram waveform. This electrocardiograph 13
The synchronizing signal generating section 13b generates a signal synchronized with the peak value of the R wave, and supplies this to the computer system 11, which performs the saturation procedure and excitation collection. It is used as a starting signal to carry out the procedure.

With the apparatus configuration as described above, the imaging method of this embodiment is performed as follows. That is, Fig. 2(a)
As shown in , the electrocardiograph 13 provides the computer system 11 with a synchronization signal based on the peak value of the R wave of the electrocardiogram waveform of the subject P, and the computer system 11 performs saturation based on this synchronization signal. A start signal is provided to the sequencer 10 to carry out the procedure and excitation/acquisition procedure. That is, the peak of an R wave in the electrocardiogram waveform shown in FIG. 2(a) is set at time t.
o, and after obtaining a predetermined time TD from this time to, a 90'' pulse is applied as a saturation procedure to saturate the magnetization in the imaging target region (slice cross section).
As a collection procedure, a 90' pulse and a 180° pulse are applied using the normal spin echo method. Execution of this excitation/collection procedure induces an echo signal at echo time TE, which is collected to obtain one line of data.

Here, in order to generate an image, for example, if the image is a 256 matrix, the above-mentioned saturation procedure and excitation/acquisition procedure are performed by setting a time TD for each R wave of the electrocardiogram waveform and performing the saturation procedure and excitation/acquisition procedure. 25 with a repetition time TRL in between.
Repeat 6 times. This means that 256 lines of data have been collected, and it is now possible to reconstruct an electrocardiogram gated image. This image is displayed on the display system 12.

According to the method of this embodiment, the time between the saturation procedure and the excitation/collection procedure, which corresponds to the repetition time TRI, is fixed, and by executing the saturation procedure, the imaging target region can be Since the magnetization of is saturated, the degree of magnetization recovery at the fixed time is always the same even if the saturation procedure and the excitation/collection procedure are repeated for each electrocardiogram waveform. Therefore, even when the electrocardiogram waveform fluctuates, the repetition time TRI remains constant, and electrocardiogram-gated imaging can be performed with the repetition time TRI constant without deterioration in image quality.

In other words, if the above is expressed mathematically, the echo signal S-p (1-exp (-TRI/TI
)-exp (-TE/T2) Therefore, the repetition time TRI is the R wave-R wave interval TR
Even if R changes, it remains constant, so the echo signal S does not change. Therefore, <5 does not result in deterioration of image quality due to artifacts and the like.

The method described above is an example of capturing a single slice, but
For example, three multi-slice images can be taken as shown in FIG. 3 in the same manner as the above method. FIG. 3 is a diagram showing a pulse sequence for obtaining one line data of electrocardiographic gated imaging of three slice images by the same method,
FIGS. 3(a) and 3(d) are diagrams showing RF pulses and echo signals on the third surface.

In this method, the saturation procedure and excitation/collection procedure for the second surface are delayed by TRI /3 from the first surface, and the saturation procedure and excitation and collection procedure for the third surface are delayed by TRI /3 from the second surface. I'm trying to delay it. Generally, in the case of N slices, TRI is performed between each slice plane.
/N delay.

The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the gist of the present invention.

[Effects of the Invention] As described above, the present invention includes a saturation procedure for saturating an imaging target region in synchronization with a specific point of an electrocardiogram waveform, and excitation of the imaging target region after a predetermined time after execution of this saturation procedure. Furthermore, the data group for imaging the imaging target region is obtained by repeating the excitation/collection procedure for data collection for each electrocardiogram waveform, so the saturation procedure and excitation/collection procedure corresponding to the repetition time are repeated for each electrocardiogram waveform. The time between procedures is fixed, and the magnetization of the imaging target area is saturated by performing the saturation procedure, so the degree of magnetization recovery at the fixed time varies for each electrocardiogram waveform. Even if the saturation procedure and excitation/collection procedure are repeated, the result will always be the same.

Therefore, even when the electrocardiogram waveform fluctuates, the repetition time is constant, and it is possible to provide a magnetic resonance imaging method capable of performing electrocardiogram-gated imaging without degrading the image quality when the repetition time is constant.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a magnetic resonance diagnostic apparatus capable of carrying out an embodiment of the magnetic resonance imaging method according to the present invention, and FIG. Figure 3 is a diagram showing a pulse sequence for obtaining one line of data to be photographed. Figure 3 is a diagram showing a pulse sequence for obtaining one line of data for electrocardiographically synchronized photographing of three slice images using the same method. FIG. 3 is a diagram showing a pulse sequence for obtaining one line data of electrocardiographic gated imaging of one slice image using a conventional method. 1... Static magnetic field magnet, 2... Gradient magnetic field generating coil, 3
A... Transmitting coil, 3B... Receiving coil, 4...
Static magnetic field control system, 5...X-axis gradient magnetic field power supply, 6...Y
Axial gradient magnetic field power supply, 7... 2-axis gradient magnetic field power supply, 8...
Transmitter, 9...Receiver, 10...Sequencer, 11
...Computer system, 12...Display system, 13
···Electrocardiograph. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A method for magnetic resonance imaging of a desired region of a subject in synchronization with an electrocardiogram waveform includes a saturation procedure for saturating the imaging target region in synchronization with a specific point of the electrocardiogram waveform, and a predetermined time after execution of this saturation procedure. A magnetic resonance imaging method characterized in that a data group for imaging the imaging target region is obtained by repeating an excitation/collection procedure for exciting the imaging target region and collecting data after a period of time for each electrocardiogram waveform. .