JPH07246194A - Mr system - Google Patents

Abstract

PURPOSE:To enable direct monitoring of the dose of electromagnetic wave absorbed by a patient. CONSTITUTION:An SAR arithmetic unit for computing an absorbed dose of electromagnetic wave by a person being examined on the basis of a progressive wave voltage Vf, a reflected wave voltage Vr, and a coil voltage Vc that are measured by a directional coupler 20 is provided with; No.1 analog subtractor for computing (Vf-Vr), an analog adder for computing (Vf+Vr), No.1 analog multiplier for computing (Vf-Vr) (Vf+Vr), No.2 analog multiplier for computing Vc<2>, No.3 analog multiplier for computing the output of No.2 analog multiplier, Vc<2>, multiplied by the reciprocal number of a coil resistance Rc, i.e., Vc<2>/Rc, and No.2 analog subtractor for computing an absorbed dose indicator voltage Vo=(Vf-Vr)(Vf+Vr)/50-Vc<2>/Rc. Also, the system makes it possible to change over the coil resistance Rc value via a DA converter from the output of a computer 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to MR (Magnetic Res
onance) device, please refer to RF (Radio Fr)
The present invention relates to an MR device provided with SAR monitoring means for monitoring an absorption amount (SAR; Specific Absorption Rate) of an electromagnetic wave output from a coil.

[0002]

2. Description of the Related Art In an MR apparatus, in order to prevent an excessive electromagnetic wave from being absorbed by a subject, a SAR monitoring device that directly monitors the amount of electromagnetic wave absorbed by the subject is actually used.
It is proposed in Japanese Patent No. 04806. As shown in FIG. 5, in the SAR monitoring device proposed in Japanese Utility Model Laid-Open No. 4-104806, the traveling wave voltage Vf, which is the voltage of the signal wave transmitted to the RF coil C, and the signal wave reflected from the RF coil C. Of the reflected wave voltage Vr, which is the voltage of
The coil voltage Vc applied to the F coil C is actually measured, and the index P of the absorption amount is calculated by P = Vf ² / 50-Vr ² / 50-Vc ² / Rc (50Ω; line impedance, Rc; coil resistance value) To do. Then, the maximum allowable value calculated from the body weight information of the subject (patient) input in advance is monitored so that the calculated absorption index P does not exceed.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Since the SAR monitoring device proposed in Japanese Patent No. 806 can directly monitor the absorption amount of electromagnetic waves by the subject, it is more reliable than the case where the output value of the RF power amplifier is calculated from the contents of the sequence program and the absorption amount is indirectly monitored. It is possible to improve the sex. However, Japanese Utility Model Laid-Open No. 4-104806 does not consider the usability of the operator.
Therefore, the object of the present invention is to improve the usability of the SA.
An object of the present invention is to provide an MR device equipped with R monitoring means.

[0004]

According to a first aspect of the present invention, there is provided a traveling wave voltage measuring means for measuring a traveling wave voltage Vf in a power supply path from an RF power amplifier of an MR device to an RF coil, and a reflected wave. A reflected wave voltage measuring means for measuring the voltage Vr and a coil voltage measuring means for measuring the coil voltage Vc are provided, and the traveling wave voltage Vf, obtained by these measuring means,
M provided with SAR calculation means for calculating the amount of electromagnetic waves absorbed by the subject based on the reflected wave voltage Vr and the coil voltage Vc
In the R device, the SAR calculating means is
a first analog subtractor that calculates the difference (Vf−Vr) between f and the reflected wave voltage Vr; and an analog adder that calculates the sum (Vf + Vr) of the traveling wave voltage Vf and the reflected wave voltage Vr.
Second analog calculating a first analog multiplier for calculating a first product of the output of the analog subtractor and said analog adder (Vf-Vr) (Vf + Vr), the square Vc ² of the coil voltage Vc A multiplier, a third analog multiplier for calculating a product Vc ² / Rc of an output Vc ^{2 of} the second analog multiplier and an inverse of the coil resistance Rc, the first analog multiplier and the third analog multiplier. From the output of the analog multiplier, the absorption index voltage Vo = (Vf−Vr) (Vf + Vr) / 50−Vc ² /
And a second analog subtractor for calculating Rc, further comprising a coil resistance value switching means for switching the value of the coil resistance Rc according to switching of the RF coil. I will provide a.

In a second aspect, the present invention measures a traveling wave voltage measuring means for measuring a traveling wave voltage Vf and a reflected wave voltage Vr in a power supply path from an RF power amplifier of an MR device to an RF coil. The reflected wave voltage measuring means and the coil voltage measuring means for measuring the coil voltage Vc are provided, and
Traveling wave voltage Vf and reflected wave voltage V obtained by these measuring means
In the MR device provided with the SAR calculation means for calculating the absorption amount of the electromagnetic wave by the subject based on r and the coil voltage Vc, the SAR calculation means is the square of the traveling wave voltage Vf Vf ²
Of the traveling wave voltage, an analog multiplier of the reflected wave voltage Vr ² for calculating the square of the reflected voltage Vr, and an analog multiplier of the coil voltage for calculating the square of the coil voltage Vc Vc ² . And an analog multiplier for coil loss for calculating a product Vc ² / Rc of the output Vc ^{2 of} the coil voltage analog multiplier and the reciprocal of the coil resistance Rc, the traveling wave voltage analog multiplier and the reflected wave voltage analog multiplier and absorption from the output of the coil losses analog multiplier indicator voltage ^{Vo = Vf 2/50-Vr} 2/50-Vc 2 / Rc
And an analog subtractor for calculating the above. Further, there is provided an MR device including a coil resistance value switching means for switching the value of the coil resistance Rc according to switching of the RF coil.

In the MR device having the above structure, the coil resistance value switching means outputs a digital coil resistance value, and a coil resistance value converting means converts the digital coil resistance value into an analog voltage. It is preferable to have a D / A converter for inputting to the voltage analog multiplier.

[0007]

In the MR device according to the first aspect, the SAR calculation means for calculating the absorption amount of the electromagnetic wave by the subject based on the measured traveling wave voltage Vf, the reflected wave voltage Vr, and the coil voltage Vc is used as the traveling wave voltage Vf. And the reflected wave voltage Vr (Vf
-Vr), a first analog subtractor, an analog adder for calculating the sum (Vf + Vr) of the traveling wave voltage Vf and the reflected wave voltage Vr, and outputs of the first analog subtractor and the analog adder Of the coil voltage Vc and the first analog multiplier for calculating the product (Vf-Vr) (Vf + Vr) of
A second analog multiplier for calculating a power Vc ² ; a third analog multiplier for calculating a product Vc ² / Rc of an output Vc ^{2 of} the second analog multiplier and an inverse of a coil resistance Rc; From the outputs of the first analog multiplier and the third analog multiplier, the absorption index voltage Vo = (Vf−Vr) (Vf + V
constituted by the second analog subtractor for calculating a ^{r) / 50-Vc 2 /} Rc. Further, the coil resistance value switching means is provided so that the value of the coil resistance Rc can be switched according to the switching of the RF coil. As described above, since the SAR calculation means is configured by the combination of the first to third analog multipliers, the first and second analog subtractors, and the analog adder, the absorption amount index voltage Vo is acquired at high speed. It is possible to monitor the absorption amount in real time. Further, in the MR device, a plurality of RF coils having different coil resistance values are often switched and used, which can be easily dealt with. Therefore,
Usability is improved.

In the MR device according to the second aspect, the traveling wave voltage Vf, the reflected wave voltage Vr, and the coil voltage Vc which have been measured are measured.
SA for calculating the amount of electromagnetic waves absorbed by a subject based on
The R calculation means uses a traveling wave voltage analog multiplier for calculating the squared Vf ² of the traveling wave voltage Vf and a squared V of the reflected wave voltage Vr.
An analog multiplier for reflected wave voltage for calculating r ² , an analog multiplier for coil voltage for calculating square Vc ² of coil voltage Vc, an output Vc ^{2 of the} analog multiplier for coil voltage and the reciprocal of coil resistance Rc product Vc ² / and coil losses analog multiplier for calculating the Rc, the traveling wave voltage analog multiplier and the reflected wave voltage analog multiplier and absorption indices voltage V from the output of the coil losses analog multiplier
o = Vf ² / 50-Vr ² / 50-Vc ² / Rc. Further, the coil resistance value switching means is provided so that the value of the coil resistance Rc can be switched according to the switching of the RF coil. Since the SAR calculation means is configured by the combination of the analog multiplier and the analog subtractor as described above, the absorption amount index voltage Vo can be acquired at high speed and the absorption amount can be monitored in real time. Further, in the MR device, a plurality of RF coils having different coil resistance values are often switched and used, which can be easily dealt with. Therefore, usability is improved.

The coil resistance value switching means includes a coil resistance value output means for outputting a digital coil resistance value,
If the coil resistance value of the digital value is converted into an analog voltage and the D / A converter is input to the analog multiplier for the coil voltage, the coil resistance value can be freely set from a computer, which is convenient. Is improved.

[0010]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 shows an MR according to an embodiment of the present invention.
It is a block diagram of an apparatus. In this MR device 100, the magnet assembly 1 has a space portion (hole) for inserting a subject therein, and a static magnetic field for applying a constant static magnetic field to the subject so as to surround this space portion. A coil, a gradient magnetic field coil for generating a gradient magnetic field (the gradient coil includes coils for reading, phase encoding, and slice selection axes), and an RF for exciting spins of nuclei in a subject. An RF coil for applying a (high frequency) pulse, a receiving coil for detecting an NMR signal from the subject (the RF coil may also be used), and the like are arranged. Static magnetic field coil, gradient magnetic field coil, R
The F coil and the receiving coil are respectively the main magnetic field power source 2,
It is connected to the RF power amplifier 4 and further to the preamplifier 5 via the gradient magnetic field driving circuit 3 and the directional coupler 20.

The sequence storage circuit 8 operates the gradient magnetic field drive circuit 3 based on the stored data acquisition pulse sequence in accordance with a command from the computer 7 to generate a gradient magnetic field from the gradient magnetic field coil of the magnet assembly 1. At the same time, the gate modulation circuit 9 is operated to modulate the high frequency output signal of the RF oscillating circuit 10 into a pulsed signal having a predetermined timing and a predetermined envelope, which is used as an RF pulse for RF.
In addition to the power amplifier 4, the power is amplified by the RF power amplifier 4 and then applied to the RF coil of the magnet assembly 1 through the directional coupler 20 to selectively excite a target region.

The preamplifier 5 includes a magnet assembly 1
The NMR signal from the subject detected by the receiving coil is amplified and input to the phase detector 12. The phase detector 12 is
The output of the RF oscillation circuit 10 is used as a reference signal, and the preamplifier 5
The NMR signal from is phase-detected and given to the A / D converter 11. The A / D converter 11 converts the analog signal after phase detection into a digital signal and inputs it to the computer 7.
The computer 7 performs an image reconstruction operation on the digital signal from the A / D converter 11 to generate an image (proton density image) of a target area. This image is displayed on the display device 6. Further, the computer 7 is responsible for overall control such as receiving information input from the console 13.

The directional coupler 20 has a traveling wave voltage Vf, which is the voltage of the signal wave transmitted to the RF coil, and a reflected wave voltage Vr, which is the voltage of the signal wave reflected from the RF coil. , The coil voltage Vc applied to the RF coil is actually measured and output to the SAR calculator 21. That is, the directional coupler 20 is a traveling wave voltage measuring means, a reflected wave voltage measuring means, and a coil voltage measuring means. The SAR calculator 30 is an analog calculator, and is the reciprocal of the coil resistance value input from the computer 2 via the DA converter 22 by the traveling wave voltage Vf, the reflected wave voltage Vr, the coil voltage Vc, and 1 /. The absorption amount index voltage Vo is calculated from Rc. Then, this absorption amount index voltage Vo
Is output to the computer 2 via the AD converter 21.

FIG. 2 shows a circuit example of the SAR calculator 30. In the SAR calculator 30, the first analog subtractor 61 calculates a difference (Vf−Vr) between the traveling wave voltage Vf and the reflected wave voltage Vr input from the directional coupler 20, and the difference (Vf− Vr) is output to the first analog multiplier 62. The analog adder 63 adds the traveling wave voltage Vf input from the directional coupler 20 and the reflected wave voltage Vr (Vf + V).
r) is calculated, and the sum (Vf + Vr) is output to the first analog multiplier 62. First analog multiplier 62
Is a product (V) of the difference between the (Vf-Vr) and the sum (Vf + Vr).
f-Vr) (Vf + Vr) is calculated, weighted with (1/50), and (1/50) (Vf-Vr) (Vf + Vr) is output to the second subtractor 64. On the other hand, the second analog multiplier 6
5 is a coil voltage Vc input from the directional coupler 20.
Squared Vc ² is calculated and output to the third analog multiplier 66. The third analog multiplier 66 outputs the coil voltage V
c squared Vc ² and the coil resistance R given by the computer 2
The reciprocal of c (1 / Rc) is multiplied, and the product Vc ² / Rc is output to the second analog subtractor 64. Second analog subtractor 64, the absorption index voltages Vo, Vo = (1/50) ( Vf-Vr) (Vf + Vr) - (Vc 2 / Rc) is calculated by the obtained absorption index voltage Vo Calculator 2
Output to.

FIG. 3 shows a flow chart of the SAR monitoring process in the computer 7. In step S1, the operator inputs the allowable maximum value calculated based on the weight information of the subject (patient) and the coil resistance value Rc of the RF coil to be used. In step S2, 1 / Rc is given to the SAR calculator 30. In step S3, the transmission of the RF pulse is awaited. RF
If the pulse is transmitted, the process proceeds to step S4. In step S4, the absorption index voltage Vo is read from the SAR calculator 30 at a predetermined sampling cycle. In step S5, the sampled absorption index voltage Vo is accumulated to obtain a total absorption index value for the entire repetition time TR. In step S6, it is determined whether the total absorption index value is larger than the maximum allowable value. If not larger, the process proceeds to step S7. If it is larger, the process proceeds to step S8. In step S7, it is determined whether the operator has instructed to change the allowable maximum value or the coil resistance value Rc. If there is an instruction, the process returns to step S1. If no instruction is given, the process returns to step S3. In step S8, execution of the scan sequence is stopped.

According to the above MR device 100, the SAR calculator 30 is composed of a combination of three analog multipliers 62, 65 and 66, two analog subtractors 61 and 64, and one analog adder 63. Since the above configuration is adopted, the absorption amount index voltage Vo can be acquired at high speed, and the absorption amount can be monitored in real time. Further, even when a plurality of RF coils having different coil resistance values are switched and used, this can be easily dealt with. Therefore, usability is improved.

When there are two RF signal systems of 0 ° system and 90 ° system, it is preferable to perform the SAR monitoring for each system.

FIG. 4 is a circuit diagram of another SAR arithmetic unit 30 'which can replace the SAR arithmetic unit 30. This SAR
In the arithmetic unit 30 ′, the traveling wave voltage analog multiplier 5
1 is the traveling wave voltage Vf input from the directional coupler 20.
Squared Vf ² is calculated and output to the first analog subtractor 52. The reflected wave voltage analog multiplier 53 calculates the square Vr ² of the reflected wave voltage Vr input from the directional coupler 20 and outputs it to the first analog subtractor 52. First analog subtractor 52, the difference between the Vf ² and Vr ² (Vf ² -V
r ² ) is calculated and weighted with (1/50),
0) (Vf ² −Vr ² ) is output to the second subtractor 54. On the other hand, the coil voltage analog multiplier 55 calculates the square Vc ² of the coil voltage Vc input from the directional coupler 20 and outputs it to the coil loss analog multiplier 56. The coil loss analog multiplier 56 multiplies the squared voltage Vc 2 of the coil voltage Vc by the reciprocal (1 / Rc) of the coil resistance Rc given by the computer ² and calculates the product (Vc ² / R).
c) is output to the second analog subtractor 54. Second
Analog subtractor 54 of the absorption index voltages Vo, Vo = (1/50) ( Vf 2 -Vr 2) - (Vc 2 / Rc) is calculated by the obtained absorption index voltage Vo the computer 2
Output to.

Also in the MR device 100 using the SAR computing unit 30 ', four analog multipliers 51, 53, 55,
Since the SAR calculator is configured by combining 56 and the two analog subtractors 52 and 54, the absorption amount index voltage Vo can be acquired at high speed and the absorption amount can be monitored in real time.
Further, even when a plurality of RF coils having different coil resistance values are switched and used, this can be easily dealt with.
Therefore, usability is improved.

[0020]

According to the MR device of the present invention, the absorption amount of the electromagnetic wave output from the RF coil by the subject can be directly monitored in real time. Further, it is possible to easily deal with a case where a plurality of RF coils having different coil resistance values are switched and used. Therefore, the usability of the SAR monitoring function can be improved.

[Brief description of drawings]

FIG. 1 shows an M including a SAR monitoring device according to an embodiment of the present invention.
It is a block diagram of R apparatus.

FIG. 2 is a circuit diagram of a SAR calculator included in the MR device of FIG.

FIG. 3 is a flowchart illustrating the operation of the MR device in FIG.

FIG. 4 is a circuit diagram of a SAR calculator that can replace the SAR calculator of FIG.

FIG. 5 is an explanatory diagram of a relationship among a traveling wave voltage Vf, a reflected wave voltage Vr, a coil voltage Vc, and an absorption amount of an electromagnetic wave by a subject.

[Explanation of symbols]

100 MR device 1 Magnet assembly 4 RF power amplifier 20 Directional coupler 30 SAR calculator 22 D / A converter 51, 53, 55, 56, 62, 65, 66 Analog multiplier 52, 54, 61, 61 Analog subtraction Unit 63 analog adder

Claims (3)

[Claims] 1. A traveling wave voltage measuring means for measuring a traveling wave voltage Vf in a power supply path from an RF power amplifier of an MR device to an RF coil, a reflected wave voltage measuring means for measuring a reflected wave voltage Vr, and a coil voltage. A coil voltage measuring means for measuring Vc is provided, and a SAR calculating means for calculating an absorption amount of the electromagnetic wave by the subject based on the traveling wave voltage Vf, the reflected wave voltage Vr, and the coil voltage Vc obtained by the measuring means is provided. In the MR device, the SAR calculation means includes the traveling wave voltage Vf and the reflected wave voltage Vf.
A first analog subtractor for calculating a difference (Vf−Vr) between r and the sum (V) of the traveling wave voltage Vf and the reflected wave voltage Vr.
f + Vr), and the product (V) of the outputs of the analog adder and the first analog subtractor and the analog adder.
f-Vr) (first analog multiplier, a second analog multiplier, and the output Vc ² of the coil voltage analog multiplier coil for calculating the square Vc ² of the coil voltage Vc to calculate the Vf + Vr) The absorption index voltage Vo = (Vf−Vr) is calculated from the outputs of the third analog multiplier for calculating the product Vc ² / Rc of the reciprocal of the resistance Rc and the first analog multiplier and the third analog multiplier. (Vf + Vr) / 50-Vc ²
And a second analog subtractor for calculating / Rc, and further, the coil resistance Rc according to switching of the RF coil.
An MR device comprising a coil resistance value switching means for switching the value of. 2. A traveling wave voltage measuring means for measuring a traveling wave voltage Vf, a reflected wave voltage measuring means for measuring a reflected wave voltage Vr, and a coil in a power supply path from the RF power amplifier of the MR device to the RF coil. A coil voltage measuring means for measuring the voltage Vc is provided, and a SAR calculating means for calculating the absorption amount of the electromagnetic wave by the subject based on the traveling wave voltage Vf, the reflected wave voltage Vr, and the coil voltage Vc obtained by the measuring means. In the MR device provided, the SAR calculation means includes a traveling wave voltage analog multiplier for calculating a square Vf ² of the traveling wave voltage Vf, and a reflected wave voltage Vr.
An analog multiplier for the reflected wave voltage for calculating the squared Vr ² of
An analog multiplier coil voltage to calculate the square Vc ² of the coil voltage Vc, the coil losses analog multiplier for calculating the product Vc ² / Rc of the inverse of the output Vc ² and the coil resistance Rc of the coil voltage analog multiplier vessels and, absorption indices voltage from the output of the traveling-wave voltage analog multiplier and the reflected wave voltage analog multiplier and the coil loss analog multiplier ^{Vo = Vf 2/50-Vr} 2/50-Vc 2 / And an analog subtractor for calculating Rc, and further, the coil resistance Rc according to switching of the RF coil.
An MR device comprising a coil resistance value switching means for switching the value of. 3. The MR device according to claim 1 or 2, wherein the coil resistance value switching means outputs a coil resistance value of a digital value, and a coil resistance value of the digital value. Is converted into an analog voltage and inputted to the analog multiplier for coil voltage, the MR device.