JP3485972B2 - Magnetic resonance diagnostic equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates relates to a magnetic resonance diagnosis apparatus, the method in particular applies a decoupling pulse, and ¹³
It relates to a method of observing ¹ H J-bonded to C.

[0002]

2. Description of the Related Art In recent years, magnetic resonance diagnostic devices have been widely used as medical diagnostic devices have been developed. The magnetic resonance diagnostic apparatus is an apparatus that can image not only the distribution of water in the living body but also the distribution of metabolites. By imaging metabolites, the metabolic state in the living body can be diagnosed, which may lead to early diagnosis of diseases.

In normal metabolite imaging, M shown in FIG.
RSI (Magnetic Resonance Spectroscopic Imaging)
Use a sequence. With this sequence, the distribution of spatial two-dimensional metabolites in the living body can be imaged. A spectrum as shown in FIG. 16 is obtained for each pixel, that is, for each voxel. Each peak of the spectrum corresponds to each metabolite, and the area of the peak indicates a physical quantity related to the amount of metabolite. That is, the metabolite distribution can be imaged by determining the peak area by spectral processing such as curve fitting and then generating this distribution.

In the spectroscopy of metabolites, the situation is slightly different from the above when there is a coupling with another nucleus due to spin-spin coupling or the like. For example,
FIG. 18 shows a model diagram of the ¹³ C spectrum of ethanol when data was collected in the sequence of FIG. Although seven peaks appear in FIG. 18, this does not mean that there are seven kinds of substances. Three peaks on the right side of one ¹³ C, that is, on the high frequency side, appear, and from another ¹³ C, four peaks on the low frequency side appear.
The peak of the book appears. In other words, here, although there are only two ¹³ C in the spectrum, the respective peaks are separated by the bond with ¹ H, so that the S / N is lowered.

The decoupling method is a method for solving this problem. The sequence at this time is shown in FIG. The difference from the above sequence is the presence or absence of ¹ H RF application. At the time of data collection, by applying ¹ H RF, ¹ H and ¹³
Since it is possible to break the magnetic coupling with C, there are two peaks as shown in FIG. 20, and the S / N is improved. That is,
For example, if there is a coupling such as ¹³ C and ¹ H, it is necessary to apply a decoupling pulse such as WALTZ.

In the case of such nuclide imaging, the sequence is, for example, as shown in FIG. 21, a normal MRSI sequence (FIG. 15) to which a decoupling pulse is added. However, in this case, since the decoupling pulse is applied, the SAR that regulates the amount of RF applied to the living body is specified.
(Surface Absorption Ratio) becomes a problem. An easily conceivable method for solving this problem is to reduce the power of the decoupling pulse. However, in this method, decoupling is incomplete, so S /
N No good spectrum can be obtained.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As shown above,
In a metabolite imaging method that requires a decoupling pulse, in a sequence in which the decoupling pulse is added to a normal MRSI sequence, the RF application amount increases by the amount of the decoupling pulse, so that the SAR standard is exceeded. was there. Further, the method of reducing the application amount of the decoupling pulse so as not to exceed the SAR standard has a problem that the S / N of the spectrum is deteriorated due to incomplete decoupling.

The present invention has been made to solve the above-mentioned conventional problems, and the purpose thereof is S
Another object of the present invention is to provide a magnetic resonance diagnostic apparatus capable of reducing the amount of decoupling pulse applied without degrading / N.

[0009]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention is such that when a spectrum of a specific metabolite in a living body is collected, it is chemically bound to the metabolite. In a magnetic resonance diagnostic apparatus for imaging a metabolite using a pulse sequence for decoupling and applying an RF pulse related to another metabolite, the metabolite is imaged using the pulse sequence. It is characterized by having a means for applying a decoupling pulse only when collecting data in the low frequency region on the spatial frequency when collecting the spectrum.

The invention according to claim 2 of the present application is the same as the invention according to claim 1, further comprising data of a low frequency region to which the decoupling pulse is applied and a high frequency region to which the decoupling pulse is not applied. The present invention is characterized by having a unit for periodically switching and collecting data and a unit for rearranging and reconstructing each of the collected data.

[0011]

According to the inventions of claims 1 and 2 configured as described above, the total dose of the decoupling pulse is reduced and the time average of the dose is also reduced.
It is possible to safely perform metabolite imaging by irradiating a decoupling pulse without exceeding the R standard.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a magnetic resonance diagnostic apparatus according to the first embodiment of the present invention. In the figure,
A static magnetic field magnet 1 and a gradient coil 2 and a shim coil 4 provided inside the static magnetic field magnet 1 provide a uniform static magnetic field to a subject (not shown) and a linear gradient magnetic field distribution in three directions x, y, and z orthogonal to each other in the same direction. The gradient magnetic field possessed is applied. The gradient coil 2 is driven by a gradient coil power supply 5, and the shim coil 4 is driven by a shim coil power supply 6. The probe 3 provided inside the gradient coil 2 applies a high-frequency magnetic field to the subject by being supplied with the high-frequency signal from the transmitter 7, and receives a magnetic resonance signal from the subject. The probe 3 may be used for both transmission and reception, or may be separately provided for transmission and reception. The magnetic resonance signal received by the probe 3 is detected by the receiver 8 and then transferred to the data collector 9 where it is A / D converted and then sent to the computer system 10 for data processing.

The above gradient coil power supply 5, shim coil power supply 6, receiver 8 and data collector 9 are all controlled by the sequence controller 12, and the sequence controller 1 is also included.
2 is controlled by the computer system 10. The magnetic resonance signal input from the data collection unit 9 to the computer system 10 is subjected to Fourier transform or the like, and image data of the density distribution of desired nuclei in the subject is reconstructed based on the Fourier transform. This image data is sent to the image display 13,
It is displayed as an image.

In the metabolite imaging which requires a decoupling pulse such as ¹³ C, in order to make the RF application amount as small as possible, in the present invention, the decoupling pulse is applied only in the low frequency region of the spatial frequency. , Not applied in the high frequency range. 2 and 3 show a space of spatial frequencies, that is, a so-called k space. A decoupling pulse is applied in the region a of FIG. At this time, the decoupling pulse to be applied may be a pulse train such as WALT or a continuous high frequency.

On the other hand, the decoupling pulse is not applied in the region b. In the spectrum distribution of the real space, that is, the three-dimensional space, the signal in the low frequency region of the k space becomes dominant, and the contribution of the signal in the high frequency region is small compared to this, so using the data collected by this method, If reconfigured,
There is a sufficient decoupling effect. That is, a spectrum with good S / N can be obtained.

For a method of collecting data only in a limited area of k-space, see University of Calfornia San Francisc.
o AAMaudssley et al., Society of Magnetic Resona
ncein Medicine 1991 Convention (Meeting Reprint p.186)
, Said. Since their invention does not collect data in other regions of k-space, they are susceptible to cast ringing. On the other hand, in the method of the present invention, since the data of the entire region of the k-space is collected, the influence of cast ringing is reduced.

By using this method, first, the sum of the doses of decoupling pulses can be reduced. In SAR, not only the sum of irradiation doses but also a specific time average becomes a problem. Therefore, the encoding application procedure must be changed from the conventional method. Since it is sufficient to make the time average of the irradiation amount as small as possible, when the number of points in both regions is the same, data collection in the low frequency region and data collection in the high frequency region of the spatial frequency may be alternately performed, for example. However, the number of points in the low frequency region and the number of points in the high frequency region are not necessarily the same, and in this case, the following is performed.

That is, when there are few points in the low frequency region,
First, data in the low frequency region and data in the high frequency region may be alternately collected, and then data in the high frequency region may be collected. If there are many points in the low-frequency region, they cannot be alternated, so the data acquisition method is determined from the ratio of the number of points in the low-frequency region and the number of points in the high-frequency region. For example, in the case of 2: 1, data in the low frequency region is collected twice and then data in the high frequency region is collected once. After the data is collected by such a method, the data is rearranged and reconstructed to obtain the spectrum distribution. As a result, the method of the present invention makes it possible to obtain a spectral distribution with a sufficient decoupling effect without exceeding the SAR. The above procedure is shown in the flow chart of FIG.

Here, a method of alternately collecting data of a pulse train for decoupling and a pulse train for no decoupling is shown, but the purpose is to prevent the RF application amount from exceeding the SAR standard. Therefore, it is not always necessary to take them alternately. For example, there are many combinations such as a method in which a pulse train with decoupling is continued twice and then a pulse train without decoupling pulse is applied once. The application sequence of the pulse train with the decoupling pulse and the pulse train without the decoupling pulse is designed based on the power application time of the RF pulse to be actually irradiated and the repetition time to create a sequence.

Since the method of the present invention defines the region on the k space to which the decoupling pulse is applied and the order of data collection in the k space, it does not depend on the sequence. That is, the MRSI sequence for collecting data by FID as shown in FIG. 5 or the MRSI sequence for collecting data as SE (spin echo) as shown in FIG. 6 may be used.

A second embodiment for solving the SAR problem is as follows.
This is a method of changing the application time of the decoupling pulse for each encoding. For example, as shown in FIG. 7A, the application time of the decoupling pulse (here, 0 encoding is shown) is lengthened in the low frequency region. On the other hand, as shown in FIG. 7B, the decoupling application time is shortened in the high frequency region. In the low frequency region of the k-space, the dephase due to encoding is small, so T2 * of the observed signal is long. Therefore, in order to make the decoupling effective, it is necessary to lengthen the application time of the decoupling pulse. On the other hand, in the high frequency region, since the dephase due to encoding is large, T ₂ ^{* of the} observed signal
Is short. Therefore, it is not necessary to apply the decoupling pulse for a long time, and the application time can be shortened.

If the relationship between the k-space and the application time of the decoupling pulse is set as described above and the data collection order as described in the first embodiment is adopted, the total RF application amount becomes small and the time average is also obtained. Can be made smaller.

The third embodiment is an example in which the power of the decoupling pulse is a function of time, rather than being made constant in time as in the conventional case. Basically, the power of the decoupling pulse is constant. But,
After the 90 ° RF pulse is applied, the FID is attenuated at T ₂ ^* , so not all signals contribute equally to the spectral composition.

In the FID signal of FIG. 5, the data immediately after generation becomes dominant in the spectrum generation, and as it attenuates, the contribution to the spectrum becomes smaller. That is, FI
Immediately after D is generated, sufficient decoupling is required, but the decoupling pulse may be weakened as it is attenuated.

In consideration of the above, the decoupling pulse may be made small in time. For example, a method of attenuating the power with an exponential function can be considered. At this time, the MRSI sequence is as shown in FIG.

As described above, in order to control the power of the decoupling pulse with time, in the block diagram of the magnetic resonance diagnostic apparatus of FIG. 1, the computer system 10 generates an RF drive waveform which changes with time, and the sequence controller 12 To the transmitter 7.

The fourth embodiment is a method combining the first to third embodiments. That is, the length of the application time of the decoupling pulse is determined in the k-space region, whether or not to apply the decoupling pulse is determined, and the time change of the intensity of the decoupling pulse is also added. These allow effective decoupling without exceeding the SAR standard.

In the fifth embodiment, as the decoupling method and the data collection method, the method shown in the first embodiment is used. That is, decoupling is performed only in the low-frequency region of the k space, and a pulse train for decoupling and a pulse train for no decoupling are alternately collected. After collecting the data,
Rearrange in k space. The subsequent processing is the first
Different from the embodiment described above, after the rearrangement is performed, the window function processing is performed in the k space. The state of weighting in the k space at this time is shown in FIG. As the window function, a well-known function such as exponential function, Hamming, Hanning, or Gaussian function is used. By using the window function, the connection between the high frequency region to which the decoupling pulse is applied in the k space and the low frequency region to which the decoupling pulse is applied becomes smooth. After performing this process, reconfigure,
Obtain the spectral distribution. When this processing is performed, there is no possibility of waviness and interference between voxels as in cast ringing. That is, the interference between voxels in the real space becomes smooth. A flow chart showing the procedure of the fifth embodiment is shown in FIG.

In the fifth embodiment, only the window function processing on the k-space is mentioned, but the window function processing by the exponential function on the time axis, which is usually performed by the NMR analyzer, is simultaneously performed. Is also good. The window function process in real time may be performed immediately after data collection, after the rearrangement, or after the window function process in the k space.

FIG. 11 is a diagram for explaining the sixth embodiment.
It was shown to. In this embodiment, the power of the decoupling pulse is a function of ki (i = x, y, z) as shown in this figure. The idea is the same as in the first embodiment, and a sufficient decoupling pulse is applied in the low frequency region of the k space, and the power of the decoupling pulse is reduced as the frequency advances to the high frequency region. For the data collection, for example, a method of alternately applying a pulse train that sufficiently applies the power of the decoupling pulse and a pulse train that applies a small power is used. After data collection, rearrangement is performed by rearranging in k-space.

The seventh embodiment is an application of the above method to multi-slice. The basic idea is the same as the idea of the method described above, and is based on the idea that the decoupling pulse is applied in the low frequency region of the k space and not applied in the high frequency region. Figure 12 shows the sequence.
Each slice plane (here, an example of 3 slices is shown)
The subject corresponding to is shown in FIG. As shown here, the time average of the irradiation amount of the decoupling pulse can be lowered by changing the encoding step for each slice plane. By this method, the problem of SAR can be avoided.

In the case of multi-slice MRSI, only an example in which it is combined with the first embodiment has been described, but in combination with the second embodiment, that is, the decoupling pulse is not applied in the high frequency region, the application time May be used, or may be combined with the decoupling pulse application method shown in the third to sixth embodiments.

The metabolite imaging method requiring decoupling has been described above. This nuclide is not limited to ¹ H decoupling during ¹³ C detection. For example, ¹
There is also an example of ¹³ C decoupling during H detection. In this regard, the detected and decoupled nuclei are summarized in Table 1 below.

[0034]

[Table 1] Further, in the above-mentioned sequence for explaining the application of the decoupling pulse, the sequence in which the decoupling pulse is irradiated immediately after the encode gradient magnetic field has fallen is shown, but the time of applying the RF that matches the resonance frequency of the nucleus to be detected. Therefore, the irradiation of the decoupling pulse has a greater effect of the decoupling and the S / N is also improved. Further, since the decoupling pulse is applied not before the RF irradiation of the nucleus to be detected but before the irradiation, the RF irradiation amount can be reduced. This embodiment is shown in FIG. This decoupling irradiation method can be applied to all the embodiments described in the present invention.

The metabolite imaging method requiring decoupling has been described above as a method for preventing the SAR standard from being exceeded.

[0036]

As described above, according to the present invention,
It is possible to perform metabolite imaging using a decoupling pulse without increasing the RF irradiation dose or time average value, that is, without exceeding the SAR standard.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a magnetic resonance diagnostic apparatus.

FIG. 2 is a diagram showing a region irradiated with a decoupling pulse and a region not irradiated with it in a k-space.

FIG. 3 is a diagram showing a region to be irradiated with a decoupling pulse and a region not to be irradiated in the k space.

FIG. 4 is a flow chart diagram for explaining an embodiment of the present invention.

FIG. 5 is a pulse sequence diagram for explaining an embodiment of the present invention.

FIG. 6 is a pulse sequence diagram for explaining an embodiment of the present invention.

FIG. 7A is a diagram illustrating a decoupling pulse emitted in a low frequency region on k space, and FIG. 7B is a diagram explaining a decoupling pulse emitted in a high frequency region on k space.

FIG. 8 is a diagram showing an example of a decoupling pulse for irradiation.

FIG. 9 is a diagram showing a function for weighting the collected and rearranged data on the k space.

FIG. 10 is a flowchart showing a procedure from data collection when weighting in k-space.

FIG. 11 is an explanatory diagram showing a function when the power of the decoupling pulse is changed in the k space.

FIG. 12 is a pulse sequence diagram showing irradiation of a decoupling pulse in multi-slice MRSI.

13 is a diagram showing a slice plane that is selectively excited in the sequence of FIG.

FIG. 14 is a pulse sequence diagram for explaining an example of the present invention.

FIG. 15 is a conventional MRSI pulse sequence diagram.

FIG. 16 is an explanatory diagram showing a spectral distribution obtained by an MRSI sequence.

FIG. 17 is an explanatory diagram showing data obtained in a sequence without a tecoupling pulse.

FIG. 18 is an explanatory diagram showing a spectrum obtained by the sequence of FIG.

FIG. 19 is a pulse sequence diagram for irradiating a decoupling pulse.

20 is an explanatory diagram showing a spectrum obtained by the sequence of FIG.

FIG. 21: Conventional MR irradiating a decoupling pulse
It is an SI sequence.

[Explanation of symbols]

1 Static magnetic field magnet 2 gradient coil 3 probes 4 shim coils 5 gradient coils 6 shim coil power supply 7 Transmitter 8 Receiver 9 Data collection department 10 Computer system 11 consoles 12 Sequence control unit 13 image display

Continuation of the front page (56) Reference JP-A-5-49612 (JP, A) JP-A-6-63029 (JP, A) JP-A-3-41928 (JP, A) JP-A-4-174351 (JP , A) JP 64-29747 (JP, A) JP 61-142448 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) A61B 5/055

Claims (2)

(57) [Claims] 1. When collecting a spectrum of a specific metabolite in a living body, an RF pulse relating to the other metabolite chemically bound to the metabolite is applied as a decoupling pulse to obtain another metabolite. In a magnetic resonance diagnostic apparatus that images a metabolite using a pulse sequence that suppresses the influence of the above, when collecting the spectrum of the specific metabolite, decoupling is performed only when data in a low frequency region on the spatial frequency is collected. A magnetic resonance diagnostic apparatus comprising means for applying a pulse. 2. A unit for periodically switching and collecting data in the low frequency region to which the decoupling pulse is applied and data in the high frequency region to which the decoupling pulse is not applied, and rearranging each of the collected data. 2. The magnetic resonance diagnostic apparatus according to claim 1, further comprising: