JPH02209130A - High frequency output adjustment method - Google Patents

Abstract

PURPOSE:To exactly set the condition of a high frequency output such as a 90 deg. pulse or 180 pulse and to obtain an exact signal by setting slice thickness tick so as to include the whole uniform area of a maximum high frequency coil when the inclination angle of a spin system magnetic moment is adjusted to a prescribed value. CONSTITUTION:In a nuclear magnetic resonance imaging device 1, an inclined magnetic field generation coil 2 to generate an inclined magnetic field for obtaining the position information of a part, where a magnetic resonance signal is induced, and a high frequency coil 3 as a transmission/reception system to radiate a rotary high frequency magnetic field and to detect the induced magnetic resonance signal are provided. When an MR signal is obtained to set the high frequency output of the 90 deg. pulse and 180 deg. pulse, slice width S is set thick by adjusting a Z-axis inclined magnetic field, which is a magnetic field for slice, in advance so that the sensitivity of the maximum high frequency coil becomes the uniform area. Accordingly, even when a slice position is dislocated by breating motion, etc., for a part to be checked like the chest, the high frequency output of the 90 deg. pulse and 180 deg. pulse to induce a magnetic resonance phenomenon can be exactly adjusted and an exact tomographic picture can be obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to nuclear magnetic resonance (NMR).
It is related to a magnetic resonance imaging method that applies the phenomenon of magnetic resonance (magnetic resonance), in particular, by changing the transmission pulse power used to generate an excitation rotating magnetic field according to the attributes of the subject, the inclination angle of the spin-based magnetic moment can be adjusted to a predetermined value. This invention relates to a high frequency output adjustment method for adjusting the output value.

(Prior Art) Nuclear magnetic resonance is a phenomenon in which atomic nuclei placed in a magnetic field resonate and absorb electromagnetic wave energy of a specific wavelength, and then emit this energy as electromagnetic waves. Devices that utilize this phenomenon to diagnose living organisms use the above-mentioned atomic nuclei, especially
Electromagnetic waves emitted from protons (hereinafter referred to as MR multiplied signals).

) is detected, the detected MR signal is processed, and the atomic nucleus (proton) density, longitudinal relaxation time T1, transverse relaxation time T2,
Diagnostic information such as a tomographic image of the subject reflecting information such as flow and chemical shift can be obtained.

By the way, in order to detect MR multiplied signals from protons using such a nuclear magnetic resonance phenomenon, an excitation rotating magnetic field generated by a 901' pulse and a high frequency pulse called 180° is used to It is necessary to selectively excite the measurement site so that the angle of inclination of the proton spin magnetic moment at the measurement site is set to a predetermined value. Here, the 90'' pulse has the function of causing magnetic resonance absorption and rotating the magnetic moment of the spin of an atomic nucleus by 90 degrees from a direction parallel to the direction of the static magnetic field in which the subject is placed until it rises perpendicularly. Furthermore, the 180° pulse has the function of causing magnetic resonance absorption and rotating the magnetic moment of the spin of the atomic nucleus by 180@ from a direction parallel to the direction of the static magnetic field in which the subject is placed. .

For these 90' pulses and 180° pulses, it is necessary to set conditions such as the pulse size in advance before detecting the MR multiplied signal from the measurement site. However, when setting the conditions for this high-frequency pulse, the stray capacity Q, which is an electrical characteristic, changes depending on attributes such as the shape of the subject.
``Pulse 180'' Hals conditions are off,
The angle of inclination of the spin magnetic moment differs from the set value. As a result, the obtained signals vary depending on the attributes of the subject. In particular, when the measurement site is the pleura,
Due to respiratory movements, the pleura swings back and forth in the body, and the diaphragm moves up and down in the direction of the body height, causing the slice position to shift relative to the area to be measured.
The conditions for the 90″ pulse or the 180′ pulse are deviated, and furthermore, spin phase changes occur during data collection.
There is a problem in that the obtained MR multiplied signal strength changes.

(Problems to be Solved by the Invention) As described above, when obtaining a tomographic image of the pleural region using nuclear magnetic resonance, the 90° pulse or The condition settings for the high-frequency output of the 180@pulse will shift the relative slice position, so the conditions for the 90" or 180" pulse will shift, and the angle of inclination of the magnetic moment of the spin will differ from the set value. There is a problem in that it is difficult to obtain accurate signals.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-frequency output adjustment method that allows accurate setting of high-frequency output conditions for 90° pulses or 180'' pulses and obtains accurate signals.

[Configuration of the Invention (Means for Solving the Problems) The present invention detects magnetic resonance signals induced from a subject placed in a static magnetic field to obtain morphological information or functional information of a detected region. In a high-frequency output adjustment method that adjusts the inclination angle of the spin-based magnetic moment to a predetermined value by changing the transmitted pulse power used to generate an excitation rotating magnetic field according to the attributes of the subject, This high frequency output adjustment method is characterized in that the slice thickness when adjusting the inclination angle of the moment to a predetermined value is set thick so as to include the entire uniform region of the maximum high frequency coil.

(Function) In the high-frequency output adjustment method of the present invention, the slice thickness when adjusting the inclination angle of the spin-based magnetic moment to a predetermined value is set thick so as to include the entire uniform region of the maximum high-frequency coil. When obtaining the MR multiplied signal to set the output, the high frequency coil is selectively excited in the entire region where the sensitivity is uniform, and in order to obtain the MR multiplied signal only from this region, the area to be examined is made like the pleura. Even if the slice position is shifted due to respiratory motion or the like, the high frequency output of the 90° pulse and 180' pulse that excites the magnetic resonance phenomenon can be adjusted accurately, and an accurate tomographic image can be obtained.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a schematic diagram showing the configuration of a nuclear magnetic resonance imaging apparatus used in an example of the present invention. As shown in Figure 1, this device (1) includes a gradient magnetic field generating coil (2) for generating a gradient magnetic field for obtaining positional information of a site where a magnetic resonance signal is induced, and a rotating high-frequency magnetic field for emitting a magnetic field. It also has a high frequency coil (3) which is a transmission/reception system for detecting the induced magnetic resonance signals. This gradient magnetic field generating coil (2) generates a gradient magnetic field about the Z-axis, which is the axis in the height direction of the subject (P), and the X-axis and Y-axis, which are perpendicular to the Z-axis, respectively. X-axis gradient magnetic field generation coil (2a), Y-axis gradient magnetic field generation coil (2b)
), and a Z-axis gradient magnetic field generating coil (2C).

Each gradient magnetic field generating coil (2a), (2b), (2C) generates an X-axis gradient magnetic field, a Y-axis gradient magnetic field, and a Z-axis gradient magnetic field (not shown).
Each power supply for the axial gradient magnetic field is connected to supply a current for generating a magnetic field. Furthermore, as will be described later, the high-frequency coils (3) are placed above and below the subject (P) at positions corresponding to the position of the pleura of the subject (P), and are transmitters that supply high-frequency pulses. The device is connected to a receiver to receive the MR multiplied signal induced in the device and the site to be measured.

Furthermore, this device (1) includes a sequencer for implementing each gradient magnetic field and a pulse sequence of high-frequency pulses of 90° pulses and 180° pulses, and each power source, transmitter,
It also includes a computer system that controls the receiver and sequencer and performs signal processing of the detected signals. The signals processed by this computer system are displayed on a display or the like. This device (1) also includes a static magnetic field coil (not shown) that generates a static magnetic field in the Z-axis direction toward the subject (P), and a power source (not shown) that supplies current to this static magnetic field coil. Be prepared.

Next, the high frequency output adjustment method of this embodiment will be explained using the imaging apparatus having the above-described configuration. First, as shown in Figure 2, when obtaining the MR multiplied signal for setting the high frequency output of 90'' pulse and 180 @ pulse,
By adjusting the two-axis gradient magnetic field, which is the magnetic field for slicing, in advance, the slice width S, which is the shaded area in Figure 1, is adjusted so that the maximum high-frequency coil sensitivity is uniform. Set it thicker than the adjustment method. Under these conditions, the slicing gradient magnetic field shown in FIG. 3(a) was applied, and 9011 pulses and 180° pulses were applied to the high-frequency coil as shown in FIG. 3(b).
Detect the induced MR multiplied signal, adjust the size of each pulse to maximize the MR multiplied signal, and set the conditions for each pulse so that the angle of inclination of the spin-based magnetic moment becomes a predetermined value. do.

When setting these conditions, for example, the block diagram shown in FIG. 4 can be used as a circuit system that can automatically set the conditions for each pulse.

That is, this circuit system includes transmission pulse control means (10
), a transmitter (11), and a receiver (12). This transmission pulse control means (lO) is configured mainly of, for example, a central processing unit, and controls the transmission pulse power used for generating the excitation rotating magnetic field by the high-frequency coil (3) according to the attributes of the subject. By changing the
This is to set the angle of inclination of the spin-based magnetic moment to a predetermined value. For example, while receiving the MR multiplied signal induced in the measurement site via a high-frequency coil, while changing the transmitted pulse power within a predetermined range, determine the transmission pulse power value that maximizes the received MR multiplied signal peak value. Based on this value, the transmission pulse power when taking a tomographic image of the subject is automatically set.

Further, the transmitter (11) is connected to a high frequency coil (3) that emits each pulse. This transmitter (11) includes an oscillating means (13) for outputting a continuous wave, a modulating means (14) for modulating the continuous wave from the oscillating means (13), and a modulating means (14) for modulating the continuous wave from the oscillating means (13).
14), a selection means (15) for selecting and setting the amplitude and pulse width of the pulse wave for modulating the continuous wave, and a power controller (APC) (1B) for varying the transmission pulse power by controlling the transmission pulse control means (lO). ), this A
A first amplification means (radio frequency amplifier) (17), a second amplification means (drive amplifier) (18), and a third amplification means (final amplifier) that amplify the output of the PC (1B), respectively.
(19), an impedance matching means (20) for performing impedance matching, and a tuning means (21) for tuning with the high frequency coil (3).

Further, the receiving section (12) is connected to a high frequency coil (3) that receives the MR multiplied signal induced by this pulse.

When a common high-frequency coil (3) is used for both high-frequency pulse emission and MR multiplied signal reception, it is necessary to separate the transmitting section (11) and receiving section (12) using an isolator or the like. In addition, in the high-frequency output adjustment method of this embodiment, since the slice thickness is set thick so as to include the entire uniform area of the maximum high-frequency coil, the MR multiplied signal intensity at the time of setting the conditions for each pulse is signal strength.

Therefore, in this receiving section (12), it is necessary to lower the gain of the amplifier or provide an appropriate attenuator to lower the MR signal level to receive an appropriate MR multiplied signal. For example, in order to lower the gain of the amplifier, as shown in Figure 5(a), the gain of the first stage amplifier (22) on the high frequency coil side should be made variable, and when setting the output, this gain should be adjusted. In order to lower the MR signal level or to lower the MR signal level, the first stage amplifier (22
) and the second stage amplifier (23) can be provided with an attenuator (24). The operation of this circuit system will be explained. The transmission pulse power setting, which is performed prior to imaging the subject, is done manually by the operator.
After coarse adjustment of the 90@pulse condition and the 180@pulse condition in advance, a 90@pulse and a 180° pulse are applied from the transmitter (11) to the high frequency coil (3) based on a control signal from the transmission control means (10). By doing so, an excitation rotating magnetic field is applied from the high-frequency coil (3) to the measurement site.The MR multiplied signal from the measurement site is received by the reception unit (12) via the high-frequency coil (3), and the transmission pulse is controlled. It is input into means (10).

The transmission pulse control means (lO) holds the input MR multiplied signal peak value. After this, the attenuator in APC (1B) is varied to change the transmission pulse power, and the MR multiplied signal at different transmission pulse powers is received in the same way as described above.
Holds the MR multiplied signal peak value.

Multiple MRs collected by changing the transmission pulse power in this way
Based on the multiplication signal, the transmission pulse control means (10) controls the transmission pulse power when the MR multiplication signal peak value is maximum, that is, A
Recognize the control state of the attenuator in PC(1B). Thereby, the transmission pulse power is set according to the attributes of the subject. In other words, the conditions for the 90° pulse and the 180' pulse are appropriately set according to the attributes of the subject, and the inclination angles of the spin-based magnetic moments are adjusted to predetermined values of 90° and 180°.

Moreover, in the case of this embodiment, the slice width is further increased to include the maximum sensitivity/uniform area of the high frequency coil.
The received MR double signal intensity increases, and due to respiratory movements such as the thoracoabdominal region, the change in relative slice position becomes smaller than the slice thickness, and the change in MR double signal intensity becomes smaller, making it more accurate. Each pulse condition can be set.

In the above embodiment, when changing the transmission pulse power,
Although a power controller (APC) (1B) was used, there is no selection means (for selecting and setting the amplitude and pulse width of the pulse wave).
15), various modifications such as changing the amplitude and changing the transmission pulse power can be performed.

In addition, the characteristics of the high-frequency coil that sends the transmission pulse (size of uniform region, efficiency of rotating magnetic field generation, etc.) and the 9
The transmission pulse power values of 0° pulse and 180@pulse, etc., as well as the gain of the amplifier and the amount of attenuation of the attenuator in the receiving section (12), etc. can be stored in advance in the computer j system or the like.

Further, in the above embodiment, the maximum value of the MR multiplied signal generated by the 90' pulse-180° pulse sequence was used, but t
A method using the minimum value of the MR multiplied signal obtained when only the aO° pulse is used can also be used.

[Effects of the Invention] As described above, according to the present invention, 90″ pulse or 18″ pulse
It is possible to provide a high frequency output adjustment method that can accurately set the conditions for high frequency output of 0'' pulses and obtain accurate signals.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a magnetic resonance imaging apparatus used in an embodiment of the present invention, FIG. 2 is a characteristic diagram for explaining the present invention in detail, and FIG. FIG. 3(b) is a graph showing the gradient magnetic field for slicing, FIG. 3(b) is a graph showing the pulse sequence in this example, FIG. 4 is a block diagram showing the system circuit used in this example, FIG. 5(a) and FIG. FIG. 5(b) is a circuit diagram showing the main parts of the receiving section in the circuit used in this embodiment. l...Magnetic resonance imaging device, 2...Gradient magnetic field generation coil, 3...High frequency coil lO...Transmission pulse control means 11...Transmission means, 12...Reception means

Claims (1)

[Claims] Prior to detecting magnetic resonance signals induced from a subject placed in a static magnetic field to obtain morphological or functional information of the detected region, transmit pulse power used to generate an excitation rotating magnetic field is applied to the subject. In a high-frequency output adjustment method that adjusts the inclination angle of the spin-based magnetic moment to a predetermined value by changing it according to the attribute, the slice thickness when adjusting the inclination angle of the spin-based magnetic moment to a predetermined value is set to the maximum high-frequency A high frequency output adjustment method characterized by setting the thickness to include the entire uniform area of a coil.