JPH04104806U - SAR monitoring device in MR equipment - Google Patents

Abstract

(57) [Summary] [Purpose] To enable direct monitoring of the amount of electromagnetic waves absorbed by patients. [Structure] A directional coupler 20 is provided in the power supply path from the RF power amplifier 8 to the RF coil 5 of the MR device 1,
Measure the coil voltage Vc, traveling wave voltage Vf, and reflected wave voltage Vr. Then, on computer 2, Psar=(Vf・Vf/50)
The absorption amount Psar of electromagnetic waves by the subject is calculated from -(Vr·Vr/50)−(Vc·Vc/Rc). Note that Rc is R
This is the coil resistance of the F coil. [Effect] Reliability can be improved because the amount of electromagnetic waves absorbed by the patient can be monitored directly and in real time. Furthermore, the restrictions on sequence programs that can be executed are minimized.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention relates to a SAR monitoring device in an MR device. The absorption amount (SAR; Specific Absorption Rate).

0002

[Conventional technology]

In MR equipment, in order to avoid negative effects on patients due to excessive SAR, Devices for monitoring are conventionally used. The SAR monitoring device in a conventional MR device cannot detect the sequence that is about to be performed. The output value of the RF power amplifier is predicted and calculated from the contents of the program. On the other hand, pre-filled The maximum allowable SAR is calculated from the patient's weight information. And said prediction The calculated output value of the RF power amplifier is compared with the maximum allowable SAR. In addition, if the predicted output value of the RF power amplifier exceeds the allowable maximum SAR, If so, do not run that sequence program.

0003

[Problem that the idea aims to solve]

The SAR monitoring device in the conventional MR device mentioned above actually monitors the This is the calculated RF power amplifier output value based on the patient's It is not the amount of absorbed electromagnetic waves itself. Therefore, calculationally, even if it is less than the maximum allowable SAR, , it cannot be confirmed whether the SAR is actually below the maximum allowable SAR. Therefore, the safety factor is It is estimated to be large.

0004 However, if the safety factor is too large, the sequence program that can be executed becomes unnecessary. There are problems with the above limitations.

[0005] Therefore, the purpose of this invention was to enable direct monitoring of the amount of electromagnetic waves absorbed by patients. An object of the present invention is to provide a SAR monitoring device for an MR device.

[0006]

[Means to solve the problem]

The SAR monitoring device of this invention connects the RF power amplifier of the MR device to the RF coil. A coil voltage measuring means for measuring the coil voltage Vc and a traveling wave voltage are provided in the power supply path. A traveling wave voltage measuring means for measuring Vf and a reflected wave voltage measuring means for measuring reflected wave voltage Vr. coil voltage Vc and traveling wave voltage V obtained by these measuring means. f, a SAR operation that calculates the amount of electromagnetic waves absorbed by the object based on the reflected wave voltage Vr. The structural feature is that a calculation means is provided.

[0007]

[Effect]

In the SAR monitoring device of this invention, the coil voltage measuring means measures the coil voltage Vc. do. Further, the traveling wave voltage measuring means measures the traveling wave voltage Vf. Also, the reflected wave The pressure measuring means measures the reflected wave voltage Vr. Then, the SAR calculation means Absorption of electromagnetic waves by the subject based on voltage Vc, traveling wave voltage Vf, and reflected wave voltage Vr Calculate the amount. The calculation formula is that the test object and the RF coil are parallel loads to the RF power amplifier. So basically, Psar=(Vf・Vf/50)−(Vr・Vr/50)−(Vc・Vc/Rc) It is. However, Psar is the absorption amount and Rc is the coil resistance.

[0008] This allows for direct monitoring of the amount of electromagnetic radiation absorbed by the patient, improving reliability. In addition, there are minimal restrictions on the sequence programs that can be executed. become.

[0009]

【Example】

This invention will be explained in more detail below with reference to embodiments shown in the figures. In addition, this However, this invention is not limited. FIG. 1 is a block diagram of an MR device including the SAR monitoring device of this invention. The computer 2 controls the overall operation based on instructions from the console 13. The sequence controller 3 performs magnetic field drive based on the stored sequence. The circuit (containing the gradient amplifier) 4 is actuated to generate a static magnet of the magnet assembly 5. Static magnetic fields and gradient magnetic fields are generated using field coils and gradient magnetic field coils. Also, the RF oscillation time 6 and generates an RF carrier. It also controls the modulation circuit 7 and controls the RF key. The carrier is modulated into an RF signal with a predetermined waveform, and the signal is output from the RF power amplifier 8 to the directional coupler. 20 to the RF coil of magnet assembly 5.

0010 The NMR signal obtained by the receiving coil of the magnet assembly 5 is sent to a preamplifier 9. is input to the phase detector 10 via the is input. The computer 2 generates an image based on the NMR signal data obtained from the AD converter 11. is reconstructed and displayed on the display device 12.

[0011] The directional coupler 20 has a coil voltage Vc, a traveling wave voltage Vf, and a reflected wave voltage Vr. is output to the second A/D converter 21.

0012 The second A/D converter 21 receives a coil voltage Vc, a traveling wave voltage Vf, and a reflected wave voltage. The pressure Vr is converted into a digital value and output to the computer 2.

[0013] The computer 2 performs SAR monitoring operations as shown in FIG. That is, in step S1, the maximum allowable SAR and the RF to be used are determined according to the patient. Coil resistance value Rc according to the coil and repetition of the scan sequence scheduled to be executed Enter time TR. In step S2, the repetition time TR is divided by a predetermined sampling period ΔT. Then, the number of sampling times N during the repetition time TR is calculated. In step S3, the coil voltage Vc and the traveling wave voltage are input from the second A/D converter 21. Read the voltage Vf and the reflected wave voltage Vr. This reading is based on the predetermined sampling This is done at a period of ΔT.

[0014] In step S4, the absorption amount Psar is calculated using the following equation. Psar=(Vf・Vf/50)−(Vr・Vr/50)−(Vc・Vc/Rc) In step S5, N Psar from the latest Psar to the N previous Psar are added. Then, divide the sum by N. As a result, the average absorption amount during the repetition time TR is Desired. In step S6, it is determined whether the average absorption amount is larger than the maximum allowable SAR. do. If it is not larger, the process returns to step S3. If it is larger, go to step S7. move on. In step S7, execution of the scan sequence is stopped.

[0015] Through the above operations, the amount of electromagnetic waves absorbed by the patient can be monitored directly and in real time. become visible. Therefore, the computer 2, the directional coupler 20, and the second A The D converter 21 constitutes a SAR monitoring device.

[0016] In addition, if there are two RF signal systems, 0° system and 90° system, monitor each system. It is necessary to conduct a visual inspection.

[0017] As another embodiment, the processing of steps S3 and S4 may be performed by an analog circuit. The following can be mentioned.

[0018]

[Effect of the idea]

According to the SAR monitoring device in the MR device of this invention, the output from the RF coil is The amount of electromagnetic waves absorbed by patients can now be monitored directly and in real time. Ru. Therefore, reliability in SAR monitoring can be improved. Also, this Therefore, the restrictions on sequence programs that can be executed are minimized, and the degree of freedom is increased. It has the effect of increasing

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a SAR monitoring device in an MR device of this invention.

FIG. 2 is a flowchart illustrating the operation of the apparatus in FIG. 1;

[Explanation of symbols]

1 MR device 2 Calculator 5 Magnet assembly 8 RF power amplifier 20 Directional coupler 21 Second AD converter

──────────────────────────────────────────────── ─── Continued from front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location 9118-2J G01N 24/04 Z

Claims (1)

[Scope of utility model registration request] 1. A power supply path from an RF power amplifier to an RF coil of an MR apparatus includes coil voltage measuring means for measuring coil voltage Vc, traveling wave voltage measuring means for measuring traveling wave voltage Vf, and reflected wave voltage. A reflected wave voltage measuring means for measuring Vr is provided, and SAR calculating means for calculating the amount of electromagnetic waves absorbed by the subject based on the coil voltage Vc, traveling wave voltage Vf, and reflected wave voltage Vr obtained by the measuring means. A SAR monitoring device in an MR device, characterized in that: