JPH0191841A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE:To certainly pay attention to the safety of a living body even in the case of emergent diagnosis, by providing a weighing means for measuring the body wt. of an examinee in the vicinity of a region generating a static magnetic field, an exciting high frequency magnetic field and an inclined magnetic field and adjusting the output of a transmitting system by the output of said weighing means. CONSTITUTION:When an examinee P rides on a bed 6 for the purpose of diagnosis, the measured value of the body wt. of the examinee P is obtained by a body-wt. measuring scale 16 to be given to a system controller 12. When an operator sets a diagnostic condition by the console of a host computer 13, even if the power of an inclined magnetic field more than that corresponding to the body wt. of the examinee is set, an order value is adjusted by the applied power upper limit value of the exciting high frequency magnetic field to the examinee P calculated by the system controller 12 and the output of a transmitter 9 is set to a proper value. Therefore, even in the case of an unconscious examinee impossible in doctor's questions, it is prevented that an exciting high frequency magnetic field of large power of necessary quantity or more is applied and the safety of a living body can be secured.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention produces a magnetic resonance phenomenon in a specific part of a subject placed in a static magnetic field, and detects the induced magnetic resonance signal. The present invention relates to a magnetic resonance imaging apparatus capable of obtaining morphological information and functional information of the specific region, and particularly relates to a magnetic resonance imaging apparatus capable of dealing with the problem of high frequency 11 field thermal effects.

(Prior art) Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only electromagnetic waves of a specific frequency. It resonates at the angular frequency ω0 (ωa −2πν0.shiro; Larmor frequency) shown in FIG.

ωa3γHO Here, γ is the gyromagnetic ratio specific to the type of atomic nucleus,
Further, Ha is the static magnetic field strength.

An apparatus that performs biological diagnosis using the above-mentioned principle processes electromagnetic waves of the same frequency as above that are induced after the above-mentioned resonance absorption, and calculates nuclear density, longitudinal relaxation time T1. Transverse relaxation time T2. For example, slice images of a subject are obtained non-invasively as diagnostic information reflecting so-called magnetic resonance parameters such as flow and chemical shift.

Collecting diagnostic information by magnetic resonance can excite all parts of a subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical requirements for imaging images. Therefore, in an actual device, a specific slice region is excited, the position information of the region is attached, the induced magnetic resonance signals are collected, and the magnetic resonance parameters are processed through signal processing, such as the longitudinal relaxation time T1 of protons, etc. A slice image reflecting the transverse relaxation time T2 is obtained.

In this way, magnetic resonance imaging devices can provide clinically extremely useful diagnostic information, but they do not require placing a living body in a highly magnetic environment, applying a high-power high-frequency magnetic field, and applying a rapid magnetic field. Since it causes changes, the effects on living organisms are uniform.

Several studies have been conducted regarding the effects of excitation high-frequency magnetic fields on living organisms. This is called the high frequency magnetic field thermal effect. That is, 1.5 to 2. O.T.
In some magnetic field-type magnetic resonance imaging devices, the excitation high-frequency magnetic field reaches more than 10 kilowatts (amplifier output), and although this has a much lower energy density than an X-ray CT scanner, it is important to consider safety for living organisms. In this regard, several proposals have been made regarding the upper limit of the applied energy. For example, an attempt is made to suppress the absorbed energy to 1 Watt/Ka to several Watts/Ko depending on the time the device is placed in a magnetic field environment.

Specifically, when performing a whole body diagnosis on a subject with a weight of 60Ka, the energy absorbed by the subject is 300Ka.
The transmission system for the excitation high-frequency magnetic field is adjusted so that the excitation voltage is below Watts. Clinically, the surgeon asks the patient how much they weigh before making the diagnosis.
The upper limit of the excitation high-frequency magnetic field was manually set based on the body weight that was known.

Therefore, in the case of an emergency diagnosis or in the case of an unconscious patient, the above-mentioned interview may not be possible, and a high-frequency magnetic field for excitation with a higher power than necessary may be applied, which may damage the living body. There were problems in terms of safety considerations.

Furthermore, since the interview is conducted one by one for each subject, the diagnostic efficiency decreases due to the time required for the interview, which is a problem.

(Problems to be Solved by the Invention) In this way, in the conventional technology, the weight of the patient is known through an interview and measures are taken to prevent the problem of high-frequency magnetic field thermal effect, so emergency diagnosis is possible. There is a problem in terms of safety considerations for the living body in the case of an accident or in the case of an unconscious subject, and the diagnostic efficiency decreases due to the time required for the interview, which is a problem.

Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus that eliminates a decrease in diagnostic efficiency and ensures safety considerations for living organisms even in the case of emergency diagnosis or in the case of an unconscious subject. Our goal is to provide the following.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following measures are taken to solve the above problems and achieve the object. That is, in the present invention, the transmitting system transmits excitation high frequency f! to a subject placed in a static magnetic field. Inclined with 1m! A magnetic resonance imaging apparatus that applies an i-field to cause a magnetic resonance phenomenon in a specific part of the subject, and detects the induced magnetic resonance signal to obtain shape H information and functional information of the specific part, A weighing means for measuring the weight of the subject is provided near a portion where the static magnetic field, an excitation high-frequency magnetic field, and a gradient magnetic field are generated, and the output of the transmitting system is adjusted by the output of the weighing means. It is characterized by

(Function) According to this configuration, before diagnosis, the subject is guided to a site that generates a static magnetic field, an excitation high-frequency magnetic field, and a gradient magnetic field through the measuring means, but at this time, the subject's weight is measured; The value can be given to the control system, and by creating a power upper limit setting table for the excitation high-frequency magnetic field as data in advance, the excitation high-frequency magnetic field is automatically applied to the subject based on this table and the measured value. It becomes possible to adjust the applied power of the magnetic field.

(Example) An example of a magnetic resonance imaging apparatus according to the present invention will be described below with reference to FIG.

As shown in FIG. 1, the apparatus of this embodiment includes a static magnetic field magnet 1 that is made of a normal conducting magnet, a superconducting magnet, a permanent magnet, or a combination thereof that generates a static magnetic field, and a static magnetic field magnet 1 that generates a static magnetic field. a gradient magnetic field coil 2 that generates a linear gradient magnetic field along ) 3 and a cylindrical gantry 4 is mounted on the base 5.

In addition, so that the subject P can be introduced into the cylindrical diagnostic space (magnetic field generation space) 4a of the cylindrical gantry 4,
A bed 6 having a movable top plate 6a is installed on a base 5 close to the cylindrical gantry 4.

Furthermore, a static VIi field control system 7 is provided, which includes energization control for the static magnetic field magnet 1 and a refrigerant supply system in the case of a superconducting magnet. ! A source 8 is provided.

Additionally, a transmitter 9 including a high-frequency amplifier that supplies a high-frequency magnetic field for excitation to the probe 3, and a receiver 10 that receives the magnetic resonance signal detected by the probe 3, converts it into a digital signal, and outputs it. The gradient magnetic field power source 8 and the transmitter 9 are driven by a sequencer 11 in a desired sequence, and the sequencer 11 is under the control of a system controller 12.

The system controller 12 generates a drive signal that instructs the sequencer 11 on the generation form of the excitation high-frequency magnetic field and the gradient magnetic field, and also transmits the magnetic resonance signals from the receiver 10 to the host 1 to computer 13 . A hard disk magnetic storage device 14 for storing raw data from the system controller 12. It is designed to be introduced into a system including a reconstruction device 15 and the like that generates two-dimensional slice images and the like using data from the hard disk magnetic storage device 14. The shim controller 12 also generates control signals for raising and lowering the bed 6 and moving the top plate 6a.

Roughly speaking, this system controller 12 is equipped with a power upper limit setting table for the excitation high frequency vA field in advance,
The measured value of the subject P's weight is taken from the scale 16 installed on the bed 6, and the power applied to the excitation high-frequency magnetic field to the subject P is automatically adjusted based on the table and the measured value. It is supposed to be done.

The operation of this embodiment configured as above will be explained. That is, when the subject P gets on the bed 6 for diagnosis, the measured value of his/her weight is obtained by the scale 16,
is provided to the system controller 12. Then, in the system controller 12, the upper limit value of the power applied to the excitation high-frequency magnetic field to the subject P corresponding to the body weight is calculated based on the power upper limit setting table of the excitation high-frequency magnetic field held as data in advance.

Therefore, when the operator sets the diagnostic conditions using the console of the host computer 13, even if the power of the gradient magnetic field is set to be higher than that corresponding to the weight of the subject P, the system controller 12 The command value is adjusted according to the upper limit value of the applied power of the high-frequency magnetic field for excitation to the subject P, the output of the transmitter 9 is set to an appropriate value, the desired excitation procedure and data collection are performed, and the hard disk magnetic Storage device 14. A two-dimensional slice image is generated by a system including the reconstruction device 15 and the like, and can be displayed on a display (not shown).

As described above, according to this embodiment, the weight scale 16 is placed on the bed 6.
Since weight data is automatically determined when the patient P gets on the bed 6 for diagnosis, this data allows the upper limit of the power to be applied to the excitation high-frequency magnetic field to the patient P. The command value for generating a high-frequency magnetic field for excitation is adjusted, so if an emergency diagnosis occurs or if the patient is unconscious, it may be impossible to interview the patient, but even in such cases, It does not apply an excitation high-frequency magnetic field with an unnecessarily large power, and is excellent in terms of safety considerations for living organisms.

Furthermore, since it is not necessary to interview each subject one by one, the diagnostic efficiency is not reduced due to the time required for the interview, which is advantageous.

In the above example, the weight data is given to the system controller 12 and the applied power is adjusted there, but it may be done by another control system, such as the host computer 13. Further, the applied power may be set based on weight data, diagnosis time (time spent in the magnetic field space), award conditions, etc. Furthermore, instead of the example in which the weight scale 16 is provided on the bed 6, it may be provided in the vicinity of the gantry 4.

In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, in the present invention, a weighing means for measuring the body weight of a subject is provided near a site that generates a static magnetic field, a high-frequency magnetic field for excitation, and a gradient magnetic field, and the output of this weighing means is used to measure the body weight of a subject. By configuring the output of the transmission system to be adjusted, the subject is led to a site that generates a static magnetic field, an excitation high-frequency magnetic field, and a gradient magnetic field through the weighing means before diagnosis, and at this time, the subject's weight is measured. The measured value can be given to the control system, and by creating a power upper limit setting table for the excitation high frequency VII field as data in advance, the test subject can be automatically adjusted based on this table and the measured value. It is now possible to adjust the applied power of the high-frequency magnetic field for excitation to the body, thereby eliminating the drop in diagnostic efficiency and reducing the impact on the living body even in the case of an emergency diagnosis or in the case of an unconscious subject. A magnetic resonance imaging apparatus that ensures safety considerations can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention. 1... Static magnetic field magnet, 2... Gradient magnetic field coil, 3...
・Probe, 4... Cylindrical gantry, 5... Base, 6... Bed, 7... Static magnetic field control system, 8... Gradient magnetic field power supply, 9... Transmitter, 10...・Receiver, 11・
...Sequencer, 12...System controller, 1
3... Host computer, 14... Hard disk magnetic recording device, 15... Reconfiguration device. Applicant's agent Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) A transmission system applies a gradient magnetic field together with a high-frequency magnetic field for excitation to a subject placed in a static magnetic field to cause a magnetic resonance phenomenon in a specific part of the subject, and detect the induced magnetic resonance signal. In a magnetic resonance imaging apparatus that obtains morphological information and functional information of the specific region,
The weighing means for measuring the weight of the subject, the static magnetic field,
1. A magnetic resonance imaging apparatus, characterized in that the measuring means is provided near a site where a high-frequency magnetic field for excitation and a gradient magnetic field are generated, and the output of the transmission system is adjusted by the output of the measuring means. (2) The magnetic resonance imaging apparatus according to claim 1, wherein the measuring means is provided on a bed on which the subject is placed.