JPH04164435A - Rf power setting method for mri device - Google Patents

Abstract

PURPOSE:To enable easy adjustment by making convertive calculation of the RF power at the time of acquiring spectroscopic information by the use of other nuclear species on the basis of the RF power strength when image is obtained in advance using H as nuclear species. CONSTITUTION:First automatic power adjustment of <1>H is made, followed by shimming of <1>H, and then scan is made with <1>H for photographing a locational image. After ROI on the locational image is selected, the RF power is adjusted to the optimum value by the use of <31>P as another nuclear species. Then sequence is selected, and scan is conducted with <31>P for acquirement of spectroscopic information. Assume that the optimum value of the RF power after automatic adjustment of <1>H is P[W], <31>P adjustment can be obtained through convertive calculation on the basis of applicable P from the formula P'=lambdaP, where P' is the optimum value of the applicable RF power. Thus the optimum value of <31>P can be adjusted simply from the optimum value of <1>H, to ensure that the RF power is adjusted in a short time.

Description

Detailed Description of the Invention [Purpose of the Invention (Industrial Application Field) The present invention provides an MRI apparatus that uses magnetic resonance phenomena to obtain morphological information such as tomographic images of a subject and functional information such as spectroscopy. Regarding how to set the power.

(Prior Art) An MRI apparatus (magnetic resonance imaging apparatus) places a subject in a static magnetic field, and superimposes on this static magnetic field a gradient magnetic field that provides position information and an RF magnetic field that is applied in a direction perpendicular to the static magnetic field. A magnetic resonance phenomenon is generated on a specific slice plane of the subject, and after the RF magnetic field is removed, a magnetic resonance signal (MR multiplied signal) generated from the atomic nucleus of that slice plane is collected, and the slice is determined based on the collected MR multiplied signal. A surface image is created to obtain morphological information or functional information such as spectroscopy of the subject.

In this case, when imaging a specific part of the subject, scanning is performed using nuclide]) ((proton), and when obtaining functional information such as spectroscopy (hereinafter referred to as spectroscopy information), nuclide is used. 31
Scanning is performed using p. Here, the method of setting the RF power for forming the RF magnetic field is different depending on the case where the imaging is performed based on the difference in the nuclide and the case where the spectroscopy information is obtained.

Figure 11 shows a conventional method for setting the RF power of such an MRI apparatus. First, imaging is performed as in step A (1) (after tuning the coil, the IH is set in step B). Automatic power adjustment (Au
to Power Control (APC).

Next, after scanning using 1H to capture a positioning image as in step C, select an ROI (region of interest) on this image as in step D, and then select the static magnetic field B as in step E. . Perform shimming. Next, after tuning the 31p coil as in step F, adjusting the power of 31p in step G, then step H.
31p to obtain spectroscopy information. Data analysis is performed on the obtained spectroscopy information in step (3).

Here, compared to 1H, 31p cannot obtain an MR multiplied signal with significantly lower sensitivity, so it is impossible to adjust the RF power automatically as in the case of IH, so it is necessary for experts to rely on their experience. Scanning is performed after adjusting and setting the optimal value while observing the collected data.

(Problem to be solved by the invention) By the way, in the conventional method of setting RF power, l as a nuclide is
) (and when using 31p, separate adjustments are required, and the adjustment of 31p is difficult to perform even for an expert, so there is a problem that it takes time.

The present invention has been made in response to the above-mentioned problems.
It is an object of the present invention to provide a method for setting the RF power of an MRI apparatus that allows easy adjustment.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention arranges a subject in a static magnetic field and superimposes a gradient magnetic field and an excitation RF magnetic field. In the RF power setting method of an MRI apparatus that generates a magnetic resonance phenomenon in a specific region and collects the magnetic resonance signals induced by this phenomenon to obtain diagnostic information, the RF power when an image is obtained using IH as a nuclide in advance
This method is characterized by converting the RF power when obtaining spectroscopy information using other nuclides based on the power intensity.

(Function) 1) Based on the RF power intensity when scanning with () to obtain an image, convert the RF power when scanning with other nuclides such as 31p to obtain spectroscopy information. 3 from the optimal value of 1H.
The optimum value of 1p can be easily adjusted. Therefore, R
F power can be adjusted in a short time.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the configuration of an MRI apparatus used to implement the RF power setting method for an MRI apparatus according to the present invention, and 1 has a dome 1a for holding a subject 15 on a pedestal part. There are magnets around it for forming a static magnetic field2. Gradient magnetic field forming coil 3゜RF magnetic field forming coil (RF coil)
4 are arranged, each having a static magnetic field control section 5. Gradient magnetic field power supply 6
．． It is connected to the transceiver 7. Of these, RF coil 4
plays an important role of receiving MR multiplied signals generated from the subject 15 and preparing to compose an image, as well as obtaining spectroscopy information. Further, the gradient magnetic field power source 6 and the transmitter/receiver 7 constitute a scan control section and are controlled by a sequencer 8.

Reference numeral 9 denotes a computer system consisting of a CPU (Central Processing Unit), which controls the overall control operation, and when scan condition data is input from the console 10,
This condition data is stored and a control operation is performed for the sequencer 8 to cause the scan control section to sequentially execute scans. Reference numeral 11 denotes a monitor, which is composed of a CRT display or the like, and is used to display an image for positioning a desired slice plane of the subject obtained by scanning.

Reference numeral 12 denotes a bed section, on which a subject 15 is placed on a top plate 12a, and a bed control section 13 controls the bed control section 13 to adjust its height position and to move the top plate 12a to the dome 1a of the pedestal section 1. be done.

Next, a method for setting RF power using such an MRI apparatus will be described.

As shown in Figure 3, first, automatic power adjustment of the IH is performed in step A, then shimming of the IH is performed in step B, and then scanning is performed using 1H as in step C, as shown in Figure 5. Take a positioning image. Next, after selecting the ROI on the positioning image as in step D, the RF power is adjusted to the optimum value as in step E using 31p as another nuclide. Next, select the sequence as in step F, and then select 3 as in step G.
1p to obtain spectroscopy information (hereinafter referred to as MR8).

Here, if the optimum value of the RF power after the automatic power adjustment of 1) (performed in step A is P Based on this, convert it as P' = λP. λ is a coefficient that indicates the nuclide, the RF pulse used,
It is determined by the conditions of the RF coil, etc. Next, the method for determining λ will be explained.

Method for determining λ-1- ``The case where PMR3 is performed using a surface coil will be described.

(1) Surface coil structure Double identical coils of 1H and 31p are used. The circuit is shown in FIG. 6(a). L is inductance, CI + C2 is capacitor, CTICM1+
CM2 is a variable capacitor, and RY is a static magnetic field latching relay. C2 operates only when RY is on. In such a configuration, resonance frequencies fs and fp are respectively shown at 1H and 31P as shown in the following equations.

...(1) ...(2) Here, when the static magnetic field strength is 1.5T, fil = 63
．． 9 MHz, fp = 25.9 MHz, and the same coil can be tuned with two nuclides. This makes the sensitivity distribution of the 1H coil and the 31p coil the same (however, the RF
Assume that the amount of power applied is not much different between 1H and 31P)
. Also, for surface coils, variable capacitor CT
By using a trimmer with a large capacity as +CMl+CM□, double tuning of IH and 31p may be possible; in this case, the circuit becomes as shown in FIG. 6(b).

(2) Determination of the magnitude of RF power As shown in FIG. 7, it is assumed that there is a minute region S separated by a distance d from the surface coil SC.

At this time, the flip angle θ is expressed by the following equation.

θ=γB1 tp...(3)
However, γ: gyromagnetic ratio B□: Static magnetic field strength tp: RF pulse width Now, if tp is made the same for 1H and 31p, the following equations are used to excite the 1H and 31p nuclei at S in Figure 7, respectively. RF power pH (π/2) as indicated.

P, (π/2) is required. (RF pulse is π/2=
90°).

IM PH (π/2) = γMB1.1tp...
・(4) 31P P, (π/2)=γpB, tp
...(5) Here, as mentioned above, tp is the same, and B
Since 1H=BIP, the ratio of the RF powers of the IH nucleus and the 31p nucleus is expressed by the following equation.

P, (π/2) γ2 Therefore, the following formula holds true.

IH Therefore, based on the above formula ('7), p of 1H, (π/2)
It becomes possible to set pp (π/2) of 31p based on .

In actual operation, as shown in Figure 8, for example, the ROI is selected based on the axial image of the abdomen, and the 1H R
Shimming is performed after automatically adjusting the F power.

After that, in the 31p spectrum collection, R
A peak value of γP/γ; 1/2.47 is applied to the F pulse. Since there are errors in reality, 31
After setting the p power as described above, the operator adjusts the 31p power around the set value while adjusting the 31PMR8.
In some cases, this is done.

Method for determining λ-2- Next, the case where a double tune surface coil is used will be described.

(1) Structure of surface coil 1) (coil SCI as shown in FIG. 9).

31p coil SC2 is used. It is assumed that each coil is arranged concentrically and on the same plane, and each has a diameter of φ150° to φ100.

(2) Sensitivity of each surface coil Surface coil SCI as shown in FIG.

Assume that there is a minute region S separated by a distance d from SC2. At this time, the static magnetic field strength Bll of each surface coil,
BIF is expressed as follows.

However, k, k': coefficient (3) Determination of magnitude of RF power In daily usage, the target area is placed on the central axis of the surface coil. As is clear from the arrangement in Fig. 10, the multi-nuclear RF power PH (π/2), pp (
The ratio of π/2) is expressed as follows.

PM (π/2) IHBIH PP (π/2) γP BIPγP
t(1oo/2)2+a21 3/2 k' Therefore, the following equation holds true.

PP (π/2) γyo ((150/2)2+d2 + 3/2 k
'Therefore, based on the above formula (9), similarly to the above formula m, I
P, (π/2) of 31p can now be set based on PH (π/2) of H.

Note that d can be easily measured on the positioning image, and k/' can also be determined theoretically.

The information of the formula (2) or the formula α1) can be filed in advance in a storage device, and can be retrieved under the control of the CPU 9 by inputting data from the console 10 as needed. For example, as shown in FIG. 2, the 1H file 16. "Prepare file 17 for P and send RF to each
Memorize the information that gives the optimal value of power and use 9PU9
R generated from the RF pulse generator 18 under the control of
It can be configured to adjust the F power and supply it to the RF coil 4 via each amplifier 19, 20.

The amplifier 19 is for performing amplification corresponding to the APC value, and the amplifier 20 is a wideband RF amplifier.

Further, if necessary, it is also possible to use a nuclide other than 31p to prepare a file for this nuclide.

FIG. 4 shows a method of setting RF power according to another embodiment of the present invention. First, in step A, scan and image using 1H, and then in step B.
to take a positioning image. Next, in step C, ROI
A selection is made followed by automatic power adjustment within the ROI using IH in step D. Next, after performing shimming within the ROI in step E, sequence settings are performed using another nuclide, 31p, as in step F, and then the RF power is adjusted as in step G, so that Pi=λiPs
The optimum value of the RF power of 31p is determined based on +o+.

λi is a coefficient.

The setting method shown in FIG. 4 is more practical than that shown in FIG.

Note that it is also possible to set the RF power of 31p at a stage before step E, and since stable power setting can be performed, this is advantageous in reliably collecting spectroscopy information.

In this way, according to this embodiment, the 31p RF power adjustment can be omitted after the 1H RF power is automatically adjusted, so the RF power can be easily adjusted and MR3 diagnosis can be performed in a short time. It becomes like this. Therefore, even an ordinary operator can carry out the adjustment work without relying on a skilled person as in the past. This makes it possible to collect spectroscopy information with high precision. Although we have explained the case where 31p is used as a nuclide other than 1H, 13C923 is used instead of 31p.
It is optional to use other nuclides such as Na.

[Effects of the Invention] As described above, according to the present invention, the RF power of other nuclides such as 31p is calculated based on the 1H RF power intensity, making it easy to adjust the RF power. Therefore, adjustments can be made in a short time.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an MRI apparatus used to implement the RF power setting method for an MRI apparatus according to the present invention, FIG. 2 is a block diagram showing the main parts of the MRI apparatus related to the present invention, and FIG. FIG. 4 is a flowchart showing another embodiment of the invention; FIG. 5 is a display example showing a positioning image used in the embodiment of the invention; FIG. 6(a), (b) is a circuit diagram of the surface coil used in this example, Figures 7, 9, and 10 are layout diagrams of the surface coil used in this example, and Figure 8 is a diagram for explaining this example. A schematic diagram of the specific parts used;
FIG. 11 is a flowchart showing a conventional setting method. 4...RF coil, 9...CPU (computer system), 16...
・1H file, 17...31p file, 18
...RF pulse generator, 19.20...Amplifier, S
C, SCI, SC2...Surface coil. Figure 1 Pi”>iPROI (J))

Claims (2)

[Claims] (1) Placing a subject in a static magnetic field and superimposing a gradient magnetic field and an excitation RF magnetic field to generate a magnetic resonance phenomenon in a specific part of the subject and collecting magnetic resonance signals induced by this phenomenon; The R of the MRI machine that obtains diagnostic information
The F power setting method is characterized in that, based on the RF power intensity when an image is obtained using ^1H as a nuclide in advance, the RF power when obtaining spectroscopy information using another nuclide is converted. How to set the RF power of an MRI machine. (2) The RF power setting method for an MRI apparatus according to claim 1, wherein ^3^1P is used as the other nuclide.