JPH0528139B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention uses magnetic resonance imaging techniques to
The present invention relates to a magnetic resonance imaging apparatus that can image the heart while performing heartbeat synchronization, and particularly relates to a magnetic resonance imaging apparatus that can image the heart from the systolic phase to the diastolic phase.

(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. It resonates at the angular frequency ω ₀ (ω ₀ =2πν ₀ , ν ₀ ; Larmor frequency) shown in .

ω ₀ =γH ₀ where γ is the gyromagnetic ratio specific to the type of atomic nucleus, and H ₀ is the static magnetic field strength.

The device that performs biological diagnosis using the above principles is
The electromagnetic waves of the same frequency as above that are induced after the above-mentioned resonance absorption are signal-processed to produce diagnostic information that reflects information such as nuclear density, longitudinal relaxation time T1, transverse relaxation time T2, flow, chemical shift, etc. The aim is to obtain slice images, etc., 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. from,
The actual device excites a specific region and collects its signals.

Such a magnetic resonance imaging apparatus can perform heartbeat (electrocardiogram) synchronized imaging.
That is, in electrocardiogram-gated imaging, an electrocardiograph is attached to the subject, and the R-R interval (T _RR ) is divided into, for example, 16, using the electrocardiogram waveform, for example, the QRS waveform, as a reference for synchronization. However, scanning is performed for each divided time phase. Specifically, the fourth
As shown in the figure, the R wave of a certain heartbeat is set as a reference t0, and a predetermined time interval Δt (R-R interval time
At t1 after T _RR /16), the same slice plane of the heart is scanned to obtain data at this time phase. Next, at t2 after a time interval Δt, the same slice plane of the heart is scanned to obtain data at this time phase. If this is repeated until t16 until the next heartbeat, data for one line of 16 time phases can be obtained. To generate an image, for example, if there are 256 matrices, the above procedure is repeated 256 times with the repetition time TR set to T _RR /16. As a result, we were able to collect data for 256 lines of 16 time phases, and by combining the data for each time phase, we were able to generate a 16 time phase image of the same slice plane of the heart. By cyclically displaying the temporal image (cinematic display), dynamic changes in the heart can be expressed using the R wave as the beginning of the image.

However, although the above method assumes that T _RR during 256 data collections is universal, in reality T _RR fluctuates to a degree that cannot be ignored. Therefore, in general, a standard T _RR value is determined and data collection is often performed only for a shorter period of time than this value. Therefore, in the case of subjects whose T _RR fluctuates significantly, it is not possible to obtain images from the early to the end of diastole, making it difficult for the observer to clearly understand changes in cardiac dynamics. Can not.

Also, by using R waves as the standard,
Similar to the above-mentioned situation, it is not possible for the observer to clearly understand the dynamic changes in the heart position. In other words, as shown in Figure 5, the heart enters the diastolic phase from the Q wave to the R wave, reaches maximum diastole at the peak of the R wave, and enters the systolic phase after the S wave after the R wave. In the cine display of phase images, the image begins at the end of diastole and ends at the systole.

In general, dynamic changes in the heart can be grasped smoothly by changing the image from the beginning of diastole to the peak, from the peak of diastole to the end of diastole, and then to systole. With cine display, dynamic changes cannot be grasped smoothly.

(Problem to be Solved by the Invention) As described above, in the conventional method, since the image begins after the R wave, that is, at the end of diastole, especially in the case of a subject whose _TRR fluctuates greatly,
There is a problem in that it is not possible for an observer to clearly understand changes in cardiac dynamics.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic resonance imaging apparatus that allows an observer to better understand changes in cardiac dynamics.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized by having the following means in order to solve the above problems and achieve the objects. That is, the present invention provides a static magnetic field generating means,
A gradient magnetic field generating means, a high frequency magnetic field generating means, and a magnetic resonance signal detecting means are provided, and each magnetic field generated by each of these means is applied to the subject to perform magnetic resonance excitation on a desired imaging region of the subject. a main body that collects magnetic resonance signals from the imaging region at the same time; an electrocardiogram synchronization signal generation section that generates signals at predetermined intervals and repeats this operation every two heartbeats; A magnetic resonance signal collection unit that collects magnetic resonance signals; and a magnetic resonance signal collection unit that selects the magnetic resonance signals collected by the magnetic resonance signal collection unit in accordance with the collection order of each cycle, and reconstructs the selected magnetic resonance signal group. The present invention is characterized by comprising: an image generation section that generates a plurality of images having different time phases by performing processing; and an image display section that displays the plurality of images generated by the image generation section.

(Function) According to the magnetic resonance imaging apparatus having such a configuration, when the heart is to be imaged, data groups at predetermined intervals from the early diastole, peak, and end of the heart's diastole to the systole between two heartbeats are collected. If you select the data for each time phase to generate multiple time phase images and display them as cine,
This provides a good representation of changes in cardiac dynamics.

Furthermore, since one piece of data for each time phase is collected in units of two adjacent heartbeats, even if the R-wave to R-wave interval fluctuates greatly during repeated data collection, the data in the data group Each time phase data therein corresponds to the dynamics of the heart. Therefore, even if the R wave-R wave interval varies greatly,
The plurality of generated cardiac temporal images correspond to changes in cardiac dynamics.

(Example) A magnetic resonance imaging apparatus according to an example of the present invention will be described below.

As shown in Fig. 1, the magnet assembly capable of accommodating the subject P therein includes a static magnetic field magnet made of a permanent magnet, a normal conducting magnet, a superconducting magnet, or a combination thereof. (A shim coil for static magnetic field correction may be added.) 1 and a gradient for generating gradient magnetic fields in the X, Y, and Z axes directions to give position information to the induced site of the magnetic resonance signal. It has a magnetic field generating coil 2 and a probe 3 consisting of a coil that is a transmitting and receiving system for transmitting a high frequency magnetic field for excitation (RF pulses such as 90° pulses and 180° pulses) and detecting the induced magnetic resonance signals. are doing.

Here, the subject P places a certain part CP of the heart at approximately the center of the static magnetic field uniform space of the static magnetic field magnet 1 in order to slice the heart, and the probe 3 is placed at the certain part CP of the heart. Use something that can cover the area.

In the case of the superconducting system, there is a static magnetic field control system 4 which includes refrigerant supply control and mainly controls the energization of the static magnetic field power source, and an X-axis, Y-axis, and Z-axis gradient magnetic field power source 5, 6, and 7. It is equipped with

Furthermore, the signals from the transmitter 8, which provides power for generating a high-frequency magnetic field to the probe 3, and the receiving coil of the probe 3 are amplified to the extent that they can be applied to subsequent processing, and the outputs are subjected to phase detection in the real and imaginary parts, respectively. The receiver 9 converts this phase detection output into a digital signal and outputs an A/D conversion output.

It also includes a sequencer 10 that performs a data collection sequence regarding protons. Then, the raw data from the receiver 9 is taken into the computer system 11, where it is reconstructed into slice images of, for example, 256 matrices using, for example, a two-dimensional Fourier transform method, and then displayed on the display system 12. ing. This display system 12 is capable of holding a large number of images, and is also capable of high-speed cyclic display (cinematic display) of the large number of held images.

The present device also includes an electrocardiograph 13 that generates a signal synchronized with an electrocardiogram waveform. This electrocardiograph 1
3 consists of an induction electrode 13a applied to the subject P and a synchronization signal generation section 13b, and from this synchronization signal generation section 13b, the R wave-R wave is multi-divided, and generally in the case of R wave-R wave 800 msec. It is divided into n=16 and the division interval Δt is set to 50 msec. A synchronizing signal is generated at this division interval Δt, and is applied to the computer system 11 as a data collection signal.

With the apparatus configuration as described above, the method of this embodiment is performed as follows. That is, as shown in FIG. 2, a synchronization signal based on the electrocardiograph of the subject P is given from the electrocardiograph 13 to the computer system 11, and the computer system 11 generates a data collection signal based on this synchronization signal. Sequencer 10
give to

That is, in FIG. 2, with the period between the first heartbeat and the second heartbeat as one data collection cycle, a synchronization signal is generated every Δt with the R wave as a reference, and the computer system 11 responds to this synchronization signal. A data acquisition signal is provided to the sequencer 10. As a result, the sequencer 10 executes a data collection sequence to drive the transmitter 8 and the X-axis, Y-axis, and Z-axis gradient magnetic field power supplies 5, 6, and 7, and generates a predetermined magnetic field using the probe 3 and the gradient magnetic field coil 2. is generated to excite the slice site SI, and the induced magnetic resonance signal is detected by the probe 3 and receiver 9 and provided to the computer system 11.

Therefore, during the period between the first heartbeat and the second heartbeat, Δt
The time phase is different for each (the first time phase for the first heartbeat,
The second time phase, the third time phase, the fourth time phase, etc.
Regarding the heartbeat, the n+1th time phase, the n+2th time phase, the nth time phase,
+3rd time phase, n+4th time phase, . . . ) first line data is collected. By repeating this for example 256 times, which corresponds to the number of image matrices, 256 lines of data to generate the first temporal image have been collected, and 256 lines to generate the second temporal image have been collected. data has been collected,
256 lines of data to generate the third temporal image have been collected. Collection of 256 lines of data to generate the fourth temporal image has been completed.

Then, the computer system 11 reconstructs the first time phase image, the second time phase image, the third time phase image, the fourth time phase image, and so on, and provides the reconstructed images to the display system 12, where the first time phase image, the second time phase image, etc. , the third time phase image, the fourth time phase image, and so on are displayed as cine images.

According to the method described above, the early diastolic phase,
It is possible to obtain data groups at predetermined intervals from the peak, end stage, and systole, and by selecting data for each time phase to generate multiple time phase images, which are displayed in cine, it is possible to respond to changes in cardiac dynamics. The result is a good representation of the changes in the image of the SI of the same part of the heart.

Furthermore, even if the R-wave-to-R wave interval in the data collection cycle fluctuates, one piece of data for each time phase is collected in units of two adjacent heartbeats, so there may be differences in the data group. Each time phase data corresponds to the dynamics of the heart. Then,
Even if the R wave-to-R wave interval varies greatly depending on the subject, the plurality of generated cardiac time phase images correspond to changes in cardiac dynamics.

Fig. 3 shows another embodiment of the present invention; in Fig. 2, data was collected for the same region SI, whereas in Fig. 3, data was collected for the first time phase of the first heartbeat. In this case, the slice site SI1 is set, the slice site SI2 is set at the second time phase, the slice site SI3 is set at the third time phase, and the slice site SI4 is set at the fourth time phase, and data collection for this slice site SI4 is performed at the n+3th heartbeat of the second heartbeat. The process is performed up to the time phase, and the slice site SI5 is set at the n+4th time phase.

According to this method, multiple time phase images regarding the same site SI4 and sites SI1 and SI having different time phases are obtained.
2, SI3, and SI5 images can be obtained, resulting in improved image collection per unit time, which is advantageous in terms of imaging efficiency.

In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, the present invention includes a static magnetic field generating means, a gradient magnetic field generating means, a high frequency magnetic field generating means, and a magnetic resonance signal detecting means, and each magnetic field generated by each of these means is applied to a subject. a main body that performs magnetic resonance excitation on a desired imaging region of the subject and collects magnetic resonance signals from the imaging region; an electrocardiographic synchronization signal generation unit that generates an R wave of a specific heartbeat in the form at predetermined intervals from the specific heartbeat to the next heartbeat, and repeatedly executes this operation every two heartbeats; , a magnetic resonance signal acquisition section that collects magnetic resonance signals from the imaging region for each synchronization signal from the electrocardiogram synchronization signal generation section; an image generation section that generates a plurality of images with different time phases by performing reconstruction processing on the selected magnetic resonance signal group; For example, when the imaging target is the heart, the image display unit is equipped with an image display section for displaying images, and therefore, if the imaging target is the heart, predetermined intervals between two heartbeats from the beginning of the diastole, the peak, the end of the diastole, and the systole of the heart. By selecting data for each time phase to generate a plurality of time phase images and displaying them in cine mode, dynamic changes in the heart can be well expressed.

Furthermore, since one piece of data for each time phase is collected in units of two adjacent heartbeats, even if the R-wave to R-wave interval fluctuates greatly during repeated data collection, the data in the data group Each time phase data therein corresponds to the dynamics of the heart. Therefore, even if the R wave-R wave interval varies greatly,
The plurality of generated cardiac temporal images correspond to changes in cardiac dynamics.

Therefore, according to the present invention, changes in cardiac dynamics can be detected by
It is possible to provide a magnetic resonance imaging apparatus that allows an observer to understand the present invention well.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the magnetic resonance imaging device of the present invention, FIG. 2 is a diagram showing an example of a heartbeat synchronized magnetic resonance cardiac imaging method using the device of the same embodiment, and FIG. A diagram showing another example of the heart rate synchronized magnetic resonance cardiac imaging method using the device of the same embodiment, FIG. 4 is a diagram showing a conventional example, and FIG. 5 is a diagram showing changes in cardiac dynamics in relation to electrocardiographic waveforms. It is a diagram. 1... Static magnetic field magnet, 2... Gradient magnetic field coil, 3
... Probe, 4 ... Static magnetic field control system, 5, 6, 7
... Gradient magnetic field power supply, 8 ... Transmitter, 9 ... Receiver, 10 ... Sequencer, 11 ... Computer system, 1 ... Display system, 13 ... Electrocardiograph.

Claims (1)

[Scope of Claims] 1. A device comprising a static magnetic field generating means, a gradient magnetic field generating means, a high frequency magnetic field generating means, and a magnetic resonance signal detecting means, and by applying each magnetic field generated by each of these means to the subject. A main body that performs magnetic resonance excitation on a desired imaging region of the examiner and collects magnetic resonance signals from the imaging region; an electrocardiogram synchronization signal generation unit that generates the electrocardiogram synchronization signal at predetermined intervals from the specific heartbeat to the next heartbeat based on the wave, and repeatedly executes this operation every two heartbeats, and the electrocardiogram synchronization signal a magnetic resonance signal collection unit that collects magnetic resonance signals from the imaging region for each synchronization signal from the generation unit; a magnetic resonance signal collection unit that selects the magnetic resonance signals collected by the magnetic resonance signal collection unit in accordance with the collection order of each cycle; an image generation unit that generates multiple images with different time phases by performing reconstruction processing on the selected magnetic resonance signal group; and an image display unit that displays the multiple images generated by the image generation unit. , A magnetic resonance imaging apparatus comprising: