JPH047217B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an NMR-CT apparatus suitable for photographing a tomographic image of a desired cross section of a subject at a predetermined timing based on the R wave of an electrocardiogram waveform. It is something.

[Background of the invention]

The gating method is generally used to take a tomographic image of the heart with an NMR-CT apparatus that is equipped with a static magnetic field generating means, a gradient magnetic field generating means, an electromagnetic wave irradiation means, and a controlling means for the gradient magnetic field. Since the R wave-to-R wave interval is not constant, even if an attempt is made to obtain a tomographic image between the R waves and the R waves after a certain period of time has elapsed since the R waves, the size of the heart at the time of each data collection is not necessarily the same. As a result, data on hearts of different sizes were collected, resulting in unclear reconstructed images (tomograms).

[Purpose of the invention]

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide an NMR-CT apparatus that can obtain a clear tomographic image of a subject (heart).

[Summary of the invention]

The present invention provides a method for obtaining a desired cross section of an object using a gate method.
In an NMR-CT device that is capable of collecting NMR image data, a specific cross section of the subject is detected with a specific gradient magnetic field applied in advance and at a predetermined timing based on the R wave of the electrocardiogram waveform by the gate method. of
a reference data collection/storage unit that collects and stores NMR image data as reference data; and a reference data collection and storage unit that collects NMR image data of the cross section to be imaged of the subject as reconstruction data at the predetermined timing while sequentially controlling a gradient magnetic field. Immediately after each data collection by the configuration data collection means and the reconstruction data collection means, NMR image data is collected on the same cross section under the same gradient magnetic field conditions as when collecting the reference data, and compared with the reference data. When the difference between both data is less than a predetermined value, it is saved as data for reconstruction in that gradient magnetic field control state,
The present invention is provided with a data comparison/judgment means for collecting reconstruction data again in the gradient magnetic field control state when the predetermined value is exceeded, thereby obtaining a clear tomographic image of the subject.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 7. Figure 1 shows NMR-CT according to the present invention.
This is a configuration diagram showing one embodiment of the device, in which 1 is a static magnetic field generation coil, 2 is an electromagnetic wave (radio wave RF) irradiation coil, 3 and 4 are gradient magnetic field generation coils, and 5 is a configuration diagram showing an embodiment of the device.
is a subject whose heart is tomographically imaged.

Further, 300 is an R wave detection circuit for detecting R waves of an electrocardiogram waveform, 301 is an RF transmission/reception control circuit, and 302
is an RF transceiver, 303 is a gradient magnetic field control circuit, 3
04 is a gradient magnetic field power supply, 305 is an operation console, and 306 is a static magnetic field power supply. 307 is a CPU that performs high-speed calculations such as image reconstruction calculations, and 308 is a CPU that controls various parts of the apparatus and performs medium- and low-speed calculations, each of which is equipped with a dedicated memory (not shown). A magnetic disk 309 stores image data, various programs, parameters, and the like.

Here, the output end of the RF transceiver 302 is connected to the coil 2, the output end of the gradient magnetic field power source 304 is connected to the coils 3 and 4, and the output end of the static magnetic field power source 306 is connected to the coil 1.

Also, an R wave detection circuit 300, an RF transmission/reception control circuit 301, a CPU 308, and a magnetic disk 309.
constitutes the main structure of the standard data collection and storage means. Furthermore, an R wave detection circuit 300 and an RF transmission/reception control circuit 3
01, the gradient magnetic field control circuit 303, the CPU 308, and the magnetic disk 309 constitute the main components of the reconstruction data collection means. Further, the R wave detection circuit 300,
RF transmission/reception control circuit 301, gradient magnetic field control circuit 3
03, the high-speed CPU 307, CPU 308, and magnetic disk 309 constitute the main components of the data comparison and determination means.

The reference data collection and storage means collects an NMR image of a specific cross section of the subject 5 at a predetermined timing based on the R wave of the electrocardiogram waveform using the gate method while applying a specific gradient magnetic field in advance. Data is collected and saved as reference data. Further, the reconstruction data collection means collects NMR image data of the cross section to be imaged of the subject 5 as reconstruction data at the predetermined timing while sequentially controlling the gradient magnetic field.
Further, the data comparison and determination means collects NMR image data on the same cross section under the same gradient magnetic field conditions as when collecting the reference data immediately after each data collection by the reconstruction data collection means, and compares it with the reference data. When the difference between both data is less than a predetermined value, it is stored as data for reconstruction in that gradient magnetic field control state, and when it exceeds the predetermined value, data for reconstruction is collected again in that gradient magnetic field control state. It is.

In the above-described apparatus, the subject 5 is positioned in a static magnetic field generated by the coil 1. Further, the subject 5 is applied with a gradient magnetic field generated by the coils 3 and 4, and is irradiated with RF by the coil 2. In this case, the gradient direction of the gradient magnetic field and the frequency of RF are determined by the gradient magnetic field control circuit 303 and the RF transmission/reception control circuit 30.
1.

Furthermore, an electrocardiogram waveform as shown in FIG.
Waves are detected and used to time data collection. That is, R waves 10 ₁ , 10 ₂ , 10 ₃ ...1
Time 11 ₁ after a fixed time delay 12 from 0 _o
At 11 ₂ , 11 ₃ . . . 11 _o , a control signal for the above-mentioned device is obtained and data is collected.

An example of data processing from collection of NMR image data to acquisition of projection data will be outlined based on FIG. 3. In this case, the gradient magnetic field is controlled by the gradient magnetic field control circuit 303, and data is collected from the RF reception coil (not shown) by the RF transmission/reception control circuit 303.
The circuit system leading to 1 performs this. Further, a high-speed CPU 307 performs calculations related to image reconstruction, such as Fourier transform, and a CPU 308 performs overall control of these operations.

In FIG. 3, it is assumed that objects 20a and 20b are located in a static magnetic field applied in a direction perpendicular to the drawing plane. In contrast, first, a gradient magnetic field 21 ₁ is applied, data is collected at a certain point in time to obtain, for example, an FID signal 22 ₁ with an illustrated waveform, and this is Fourier transformed (represented by an arrow 23) to obtain illustrated projection data 24 ₁ . can get. Next, when applying a gradient magnetic field 21 ₂ with a different gradient direction and collecting data in the same manner as described above, for example, the FID signal 22 with the illustrated waveform
₂ is obtained, and by performing Fourier transformation (arrow 23) on this, illustrated projection data 24 ₂ is obtained.
Hereafter, while changing the gradient direction of the gradient magnetic field, data was collected in the same manner as above until it rotated 360°.
The process is repeated to obtain a large number of projection data 24 ₃ to 24 _o , and image reconstruction is performed based on them.

Now, when the object to be imaged by an NMR-CT device is a moving heart, its size is
In Fig. 2, R waves 10 ₁ , 10 ₂ , 10 ₃ ...1
Each time point 1 after a certain period of time (day 12) from 0 _o
1 ₁ , 11 ₂ , 11 ₃ ...11 _o are not necessarily the same. For example, time points 11 ₃ and 11 ₄ are considered to be almost the same, but time points 11 ₁ and 11 ₂ are considered to be different. Therefore, time 11 ₁ and 1
When the image is reconstructed using the data collected in 1 ₂ , image blurring occurs.

Therefore, in the present invention, data of a specific cross section is collected in advance as reference data at a certain point in time by the reference data collection and storage means, and thereafter, the gradient direction of the gradient magnetic field is controlled by the reconstruction data collection means. Whether or not the data for reconstruction of the cross section of the object to be imaged collected during image reconstruction is to be used for image reconstruction is determined as follows. That is, the data comparison and determination means immediately after collecting each reconstruction data,
A gradient magnetic field in the same tilt direction is applied to the same cross section as when collecting the reference data, and judgment data is collected to judge whether or not the reconstruction data is accepted, and this is compared with the reference data, and the judgment data is determined. Only when the data is the same as or similar to the reference data, the reconstruction data is saved and used for image reconstruction.

In this case, the NMR-CT apparatus is capable of multi-slice measurement, and in _{FIG .}
is a specific cross section for collecting the reference data (hereinafter referred to as the reference cross section), and the cross section 30 ₂ of the heart 30 at the coordinate Z ₂ is the cross section to be imaged. All you have to do is irradiate RF with a frequency like this. That is, since the relationship between the cross-sectional coordinates (positions) Z ₁ , Z ₂ , Z _{3 .} . . and the frequencies ω ₁ , ω ₂ , ω ₃ . If RF with a frequency of ω ₁ is applied from the coil 2, data from the reference section 30 ₁ is collected, and if RF with a frequency of ω ₂ is applied, data from the target cross-section 30 ₂ is collected. In this case, the frequency control of the RF to be irradiated is performed by the RF transmission/reception control circuit 301,
This RF transmission/reception control circuit 301 is controlled by the CPU 30.
8 will do it. Note that the reference cross section 30 ₁ is also a cross section for collecting the determination data.

The operation of the apparatus of the present invention will be explained below with reference to FIG. First, an electrocardiogram waveform (see FIG. 2) is obtained from the subject 5 set as shown in FIG. 1, and an R wave, for example, an R wave ₁₀₁ is detected by the R wave detection circuit 300 (step 100). After the detection, after a certain time delay 12 (step 101) has elapsed, the gradient direction of the gradient magnetic field is directed to a specific direction, for example, the horizontal direction (hereinafter referred to as the reference direction) using the gradient magnetic field control circuit 303. Step 102), and the RF transmission/reception control circuit 301 collects NMR image data (hereinafter referred to as reference data) of the reference section ₃₀₁ with the RF frequency set to _ω1 (step 103).
The collected reference data is Fourier-transformed by the high-speed CPU 307 (step 104) to become reference projection data, and is stored in the magnetic disk 309 as the 0th data (step 105).

Next, the R wave detection circuit 300 detects an R wave, for example, R wave ₁₀₂ again (step 106), and after delay 12 (step 107), the gradient magnetic field control circuit 3
03 directs the gradient direction of the gradient magnetic field to a predetermined direction, and the RF transmission/reception control circuit 301 then directs the gradient direction of the gradient magnetic field to a predetermined direction.
The cross section to be photographed 30 ₂ with the frequency of RF as ω ₂
NMR image data (hereinafter referred to as reconstruction data) is collected (step 108). Immediately after this,
It is determined in the next steps 109 to 112 whether or not the collected reconstruction data should be saved. That is, the gradient magnetic field control circuit 303 redirects the gradient direction of the gradient magnetic field toward the reference direction (step 109), and the RF transmission/reception control circuit 301 sets the RF frequency to ω ₁ and sets the NMR image data of the reference section 30 ₁ (hereinafter referred to as (referred to as judgment data) is collected (step 110). The collected judgment data is Fourier-transformed by the high-speed CPU 307 and
As the projection data for judgment (step 111),
The CPU 307 compares this with the 0th data (reference projection data) (step 11).
2). As a result, if the difference between both data is larger than a predetermined value, the reconstruction data is discarded (step 113), and the process returns to step 117 to perform reconstruction in the same way without changing the gradient direction of the gradient magnetic field. The high-speed CPU 307 collects the data and again determines whether or not to save the data (step 106).
~112). If the difference between the two data is smaller than the predetermined value, the reconstruction data is stored in the magnetic disk 309 (step 114).

Next, the gradient direction of the gradient magnetic field is changed by the coils 3 and 4 (step 115), and step 10 is performed again.
Steps 6 to 115 are executed, and in step 116 the CPU 308 determines whether data collection and storage for all angles in the gradient direction of the gradient magnetic field has been completed.If not, the process returns to step 117 and steps 106 to 106 are executed.
Repeat step 115 and stop if completed.

As described above, the cross section 30 ₂ of the heart 30 of the subject 5
All NMR image data (first to nth reconstruction data) necessary for tomographic image reconstruction are collected and stored in the magnetic disk 309. In this case, whether or not to save the reconstruction data is determined by collecting the judgment data immediately after the data collection and comparing it with the reference data, and only if the difference between both data is smaller than a predetermined value, It is saved as data for reconstruction in the gradient direction of the gradient magnetic field. Therefore, the reconstruction data to be saved is only the reconstruction data collected when the size is the same or approximate to the specific size of the heart 30 set as reference data,
An unblurred image of the cross section 30 ₂ will be reconstructed.

In the above-mentioned embodiment, the gradient magnetic field was controlled by controlling the gradient direction of the gradient magnetic field, but the present invention is not limited to this.
For example, the ``Warp Method'' (published in 1981, ``NMR
IMAGING (Proceedings of an
International Symposium of Nuclear
Magnetic Resonance Imaging) (see pages 77 to 80) may be used. FIG. 6 is a signal waveform diagram showing the RF pulse, gradient magnetic fields G _x , G _y , G _z and NMR image data (FID signal) in the warp method. In other words, in the warp method, the gradient magnetic field G _x ,
This is a method of collecting data by applying RF pulses while applying G _y and G _z as shown in the figure. In this case, the amplitudes of the gradient magnetic fields G _x and G _y are fixed to constant values, but the amplitudes of the gradient magnetic fields G _z are changed in a predetermined order, for example, broken lines a, b, c...
Change in the order of...

FIG. 7 shows an example of the operation of the apparatus of the present invention when controlling a gradient magnetic field using the above-mentioned warp method. Note that in this example, the NMR image data collected without Fourier transformation is stored,
You may also make a comparison.

Further, in the illustrated embodiment, the case where the cross section to be imaged is the cross section 30 ₂ adjacent to the reference cross section 30 ₁ is illustrated, but it is not limited to this only, and the cross section 30 2 is adjacent to the reference cross section 30 1.
Of course, it may be _3rd grade.

〔Effect of the invention〕

As described above, according to the present invention, the saved reconstruction data is only the reconstruction data collected when the size is the same as or approximates the specific size of the subject (heart) set as reference data. This has the effect that a clear reconstructed image (tomographic image) of the subject (heart) can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an embodiment of the NMR-CT device according to the present invention, Figure 2 is a diagram showing an example of an electrocardiogram waveform, and Figure 3 is data from collecting NMR image data to obtaining projection data. A schematic explanatory diagram of a processing example,
FIG. 4 is a graph showing the relationship between the cross-sectional coordinates at which data is collected in the NMR-CT device and the frequency of irradiation RF, and FIG. 5 is a flowchart for explaining an example of the operation of the device shown in FIG. 6 and 7 are signal waveform diagrams and flowcharts for explaining another example. DESCRIPTION OF SYMBOLS 1... Static magnetic field generation coil, 2... RF irradiation coil, 3, 4... Gradient magnetic field generation coil, 5... Subject, 10 ₁ to 10 ₄ ... R wave, 12... Delay, 21
₁ , 21 ₂ ... gradient magnetic field, 22 ₁ , 22 ₂ ... FID signal,
24 ₁ , 24 ₂ ... projection data, 30 ... heart, 30 ₁
... Reference cross section, 30 ₂ ... Target cross section.

Claims (1)

[Claims] 1. Equipped with a static magnetic field generation means, a gradient magnetic field generation means, an electromagnetic wave irradiation means, and a control means for the gradient magnetic field, and performs NMR of a desired cross section of a subject using a gate method.
In an NMR-CT device capable of image data collection, a specific cross section of the subject is measured with a specific gradient magnetic field applied in advance and at a predetermined timing based on the R wave of the electrocardiogram waveform by the gate method.
a reference data collection and storage unit that collects and stores NMR image data as reference data; and a reference data collection and storage unit that collects and stores NMR image data of the cross section to be imaged of the subject as reconstruction data at the predetermined timing while sequentially controlling a gradient magnetic field. Immediately after each data collection by the configuration data collection means and the reconstruction data collection means, NMR image data is collected on the same cross section under the same gradient magnetic field conditions as when collecting the reference data, and compared with the reference data. When the difference between both data is less than a predetermined value, it is saved as data for reconstruction in that gradient magnetic field control state,
The present invention is characterized by comprising a data comparison/judgment means for collecting reconstruction data again in the gradient magnetic field control state when the predetermined value is exceeded.
NMR-CT equipment.