JPH0919413A - Subject body weight measuring method for mri, mri device, and table device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily measure the body weight of a subject with an MRI device by driving a cradle mounted with the subject with prescribed force, and obtaining the weight of the testee based on the force and the friction coefficient of the cradle at the time of the image pickup of the subject via magnetic resonance. SOLUTION: The friction coefficient is measured before the start of the normal operation of an MRI device, and the friction coefficient data between a support base and a cradle 22 is written in a table 35. When the start of an arithmetic process section 32 is instructed, an instruction for driving the cradle 22 is generated by the arithmetic process section 32, and an instruction for generating fixed force (f) is given to a motor 42 from a drive controller 33. The position of the cradle 22 is detected by a sensor 43 and reported to an acceleration detection section 34 while the cradle 22 is driven, the acceleration of the cradle 22 is obtained via secondary differentiation, the total mass of the cradle 22 and the subject based on the friction coefficient and the driving force (f), and the mass of the subject is calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the weight of an object used in a magnetic resonance imaging (MRI) apparatus, an MRI apparatus capable of measuring the weight, and a table apparatus suitable for weight measurement.

[0002]

2. Description of the Related Art An MRI apparatus uses a nuclear magnetic resonance phenomenon to measure a nuclear spin density distribution, a relaxation time distribution, and the like at a desired inspection site in a subject, and uses the measured data to determine a cross section of the subject. An image is displayed.

A nuclear spin of a subject placed in a uniform and strong static magnetic field generator precesses around a direction of the static magnetic field at a frequency (Larmor frequency) determined by the strength of the static magnetic field. Therefore, when a high frequency pulse having a frequency equal to this Larmor frequency is irradiated from the transmission coil, spins are excited and a transition is made to a high energy state. This is called a nuclear magnetic resonance phenomenon. When the irradiation of the high frequency pulse is terminated, the spin returns to the original low energy state with a time constant corresponding to each state, and at this time, the electromagnetic wave is irradiated to the outside. This is detected by the high frequency receiving coil tuned to the frequency. At this time, a triaxial gradient magnetic field is applied to the static magnetic field space for the purpose of adding position information to the space. As a result, position information in space can be captured as frequency information.

In this case, since the irradiated high frequency pulse is absorbed by the subject, it is preferable that the strength of the high frequency pulse (transmission power of electromagnetic waves) depends on the weight of the subject. That is, by adjusting the transmission power of the electromagnetic wave according to the body weight, the absorption amount (SAR: Specific Absorption Rate) of the electromagnetic wave by the subject can be kept within an appropriate range.

Therefore, in the conventional case, a general scale is placed near the MRI apparatus to measure the weight before the examination by the MRI apparatus. Alternatively, a value measured in advance or a value self-reported by the subject itself has been used.

Then, the procedure is such that the operator inputs such a value from a key input device of the console or the like. The MRI apparatus recognizes the value of the body weight of the subject inputted in this way, and the intensity of the high frequency pulse (transmission power)
To determine the operating state.

In this case, since the weight of the subject is required to determine the strength of the high frequency pulse, a message is displayed so that the operator does not forget to input the value of the weight, or the operator does not forget to enter the weight value. In the case of input, the setting was made so that the irradiation of high frequency pulses was not started.

[0008]

However, in order to make the MRI apparatus recognize the weight value as described above,
There was a problem of burdening the operator such as weight measurement and key input. Further, it is not possible for the MRI apparatus side to recognize whether the input value is correct, and there is a possibility that an error may occur in the contents of self-declaration or key input.

In order to solve such a problem, it is technically possible to connect a weight scale capable of electrically outputting the measurement result to the MRI apparatus or to incorporate the weight scale on the table on which the subject is placed. Is considered to be. However, in either case, there is a problem that the configuration of the device and the processing contents become complicated.

The present invention has been made in view of the above points, and a first object thereof is to realize a weight measuring method capable of easily measuring the weight of a subject in an MRI apparatus.

A second object of the present invention is to realize an MRI apparatus capable of easily measuring the weight of a subject. Another object of the present invention is to realize a table device capable of easily measuring the weight of a subject.

[0012]

[Means for Solving the Problems] The inventor of the present application, as a result of earnest research to improve the problem of measuring the weight of the subject in the conventional MRI, has found that the weight of the subject when moving the subject on the cradle is reduced. The present invention has been completed by newly discovering a method for performing measurement.

That is, the present invention, which is means for solving the problems, is basically as described in the following (1) to (5). (1) A first aspect of the invention for solving the above-mentioned problems is to drive a cradle on which a subject is placed with a predetermined force when magnetic resonance imaging is performed on the subject, and calculate the predetermined force and the friction coefficient of the cradle. MRI characterized by using the weight of the subject
Is a method for measuring the body weight of a subject.

In the first aspect of the invention, the weight of the subject is obtained from the predetermined force for driving the cradle and the friction coefficient of the cradle. Therefore, the weight of the subject is measured when the cradle is moved.

By doing so, since the weight can be measured when the subject is placed on the cradle and moved, a weight measuring method which can easily measure the weight of the subject in the MRI apparatus is provided. realizable.

(2) A second invention for solving the above-mentioned problem is an MRI apparatus for magnetic resonance imaging by driving a cradle on which a subject is placed by driving means, wherein the driving means causes the cradle to have a predetermined force. The MRI apparatus is characterized in that it is provided with a control means that is driven by the above-mentioned method and uses the predetermined force and the friction coefficient of the cradle to obtain the weight of the subject.

In the present invention, the cradle is driven by the driving means with a predetermined force, and the weight of the subject is obtained from the predetermined force and the friction coefficient of the cradle. By doing so, the weight measurement can be executed when the subject is placed on the cradle and moved, so that the MRI apparatus capable of easily measuring the weight of the subject can be realized.

(3) A third invention for solving the above-mentioned problems is an MRI apparatus for magnetic resonance imaging by driving a cradle on which a subject is placed by a drive means, and a drive for driving the cradle by force f. Means, a position detecting means for detecting a position when the cradle is driven, and an acceleration a of the cradle obtained from a change in the position per unit time detected by the position detecting means, and a force f, an acceleration a, and a dynamic friction of the cradle. The MRI apparatus is provided with a control means for obtaining the mass m2 of the subject from the coefficient b and the mass m1 of the cradle.

In the present invention, the acceleration a of the cradle is obtained from the change in the position per unit time detected by the position detecting means, and the control means is obtained from the force f, the acceleration a, the coefficient of dynamic friction b of the cradle and the mass m1 of the cradle. Is the mass of the object m2 (m2 = (f / (a + bg))-m
1) is required. Note that g is the acceleration of gravity.

By doing so, the weight of the subject can be measured when the subject is placed on the cradle and moved, so that the weight of the subject can be easily measured.
The device can be realized.

(4) A fourth invention for solving the above problems is an MRI apparatus for magnetic resonance imaging by driving a cradle on which a subject is placed by a driving means, and a drive for driving the cradle by a force f. Means and the force f for driving the cradle by the driving means are gradually increased from a small value, and the force f'when the cradle starts to move, the static friction coefficient c of the cradle and the mass m1 of the cradle to the mass m of the subject.
And a control means for determining 2
I device.

In the present invention, the force f for driving the cradle by the drive means is gradually increased from a small value, and the force f'when the cradle starts to move, the static friction coefficient c of the cradle, and the mass m1 of the cradle are used as the target. Mass of sample m2
(M2 = (f '/ cg) -m1) is obtained. G
Is the gravitational acceleration.

In this way, the weight of the subject can be measured when the subject is placed on the cradle and moved, so that the weight of the subject can be easily measured.
The device can be realized.

(5) A fifth invention for solving the above problems is a table device for driving a cradle on which a subject is placed by a driving means, wherein the driving means drives the cradle with a predetermined force. A table device comprising control means for determining the weight of a subject using a predetermined force and a friction coefficient of a cradle.

In the present invention, the cradle is driven by the driving means with a predetermined force, and the weight of the object is determined from the predetermined force and the friction coefficient of the cradle. By doing so, the weight measurement can be performed when the subject is placed on the cradle and moved, so that it is possible to realize a table device that can easily measure the weight of the subject.

Further, the weight measuring method which is the processing procedure in the above-mentioned third invention and fourth invention is also included in the scope of the invention. In each of the above inventions, the mass of the subject is determined, and this mass is treated as the weight of the subject.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a flow chart showing the procedure of a method for measuring an object weight of MRI of the present invention.
Further, FIG. 2 is a configuration diagram showing a configuration of a main part of the MRI apparatus required to realize the method for measuring the weight of the subject.
Then, FIG. 3 is a configuration diagram showing main parts of mechanical components of the MRI apparatus.

First, the configuration of the MRI apparatus will be described with reference to FIGS. 2 and 3, and then the operation will be described with reference to FIG.
As shown in FIG. 3, the MRI apparatus as a whole is composed of a magnet unit 10 and a table 20, and an operator console (not shown) is electrically connected thereto.
The cradle 22 is configured to enter the bore of the cylindrical hole of the magnet unit 10, and a drive mechanism (not shown) is provided between the support base 21 and the cradle 22. Then, the subject 23 placed on the cradle 22 is moved into the magnet 10 and the MRI is performed.
The image diagnosis is performed.

The electrical structure of the MRI apparatus is as shown in FIG. Control unit 30 is cradle 2
It is a control means for controlling the driving of the table 2 and is arranged near the table 20. The communication control unit is a data communication control means for communicating various instructions with an external operator console.

The arithmetic processing section 32 is a processing means for determining the masses of the cradle and the subject by giving instructions when driving the cradle 22 and referring to various data. Drive control unit 33
Is a control means for performing drive control by instructing the value of the force at the time of driving based on the instruction from the arithmetic processing unit 32.

The acceleration detecting section 34 is a detecting means for detecting the acceleration of the cradle 22 by referring to the position detection result from the position detecting sensor described later. The table 35 is a data holding unit that holds various data such as the friction coefficient of the cradle 22.

The controller 41 is drive control means for receiving a command from the drive control section 33 and generating a signal for driving the motor. In addition, the motor 42 is the controller 4
1 is a motor that receives a driving signal from the motor 1 to generate a predetermined force. The broken line from the motor 42 in FIG. 2 indicates the transmission of force from the motor. Sensor 43 is cradle 2
2 is a sensor that detects the position 2 and notifies the acceleration detection unit 34 of the detected position. The broken line from the cradle 22 to the sensor 43 in FIG. 2 indicates that the position is detected. The controller 41 and the motor 42 form a driving unit.

The procedure for measuring the weight of the subject by the MRI apparatus configured as described above is as follows. MRI
The friction coefficient was measured before the normal use of the device, and the friction coefficient between the support base 21 and the cradle 22 (hereinafter,
Data of the friction coefficient of the cradle 22) is written in the table 35. The coefficient of friction includes a dynamic coefficient of friction and a static coefficient of friction, but the term “friction coefficient” is considered to include both.

When an operation start instruction is given from the operator console or the like, the communication control unit 31 which receives the start instruction from the operator console or the like gives the operation processing unit 32 an instruction to start. Here, the arithmetic processing unit 32 executes the analysis of the instruction (step 1 in FIG. 1). As a result, the electrical state and mechanical position of each unit are set to the instruction execution waiting state.

At the time when the analysis of the instruction is completed, or after the elapse of a fixed time sufficient to complete the analysis of the instruction,
The arithmetic processing unit 32 gives an instruction for driving the cradle 22 to the drive control unit 32. The drive control unit 32 has a constant force f
Is given to the controller 41. As a result, the controller 41 generates the voltage / current necessary for the motor 42 to generate the predetermined force f and supplies the voltage / current to the motor 42. In this way, the cradle 22 is driven with a predetermined force f (step 2 in FIG. 1).

When the rotation of the motor 42 is transmitted to the cradle via a reduction mechanism for reducing the number of rotations at a predetermined reduction ratio (gear ratio), the cradle 22 is set in consideration of the reduction ratio. So that it can be driven with a predetermined force f,
Any of the arithmetic processing unit 32 to the controller 41 issues a command according to the reduction ratio. In this case, it is conceivable to store data on the reduction ratio in the table 35. Even in the case where the rotation speed is changed in this way, as long as the cradle can be driven with a predetermined force f, it has no effect on the detection of acceleration and various calculations to be described later.

While the cradle 22 is being driven in this manner, the position of the cradle 22 is detected by the sensor 43 and the acceleration detector 34 is notified (step 3 in FIG. 1). The position of the cradle 22 in this case may be an absolute position, a relative position, or a movement amount. Since the notification of this position is for detecting the acceleration which will be described later, the notification of the position is performed twice or more.

Therefore, the acceleration detecting section 34 uses the sensor 43.
The second-order differentiation is performed with reference to the position data from and the time when this data was obtained, and the acceleration a of the cradle 22 is calculated.
Is calculated (step 4 in FIG. 1). Then, the acceleration a thus obtained is notified to the arithmetic processing unit 32.

Here, in general, the mass of a moving object is m,
When the acceleration of the moving object is a, the force for driving the moving object is f, and the dynamic friction coefficient of the moving object is b, the equation f = m (a + bg) (1) holds. Here, g is the gravitational acceleration.

Therefore, the arithmetic processing unit 32 uses the acceleration a notified from the acceleration detecting unit 34, the force f for driving the cradle 22, and the dynamic friction coefficient b stored in the table 35 to obtain the following equation (2). Perform an operation. m = f / (a + bg) (2) In this way, the acceleration a is obtained from the moving position of the cradle 22 and the calculation is performed using the friction coefficient b and the driving force f. The total mass m with the sample can be determined (step 5 in FIG. 1).

Then, when the data of the mass m1 of the cradle 22 is held in the table 35, the subtraction is performed in the arithmetic processing unit 32 to calculate the mass m2 of the subject (m2 = m-m1).
).

The total mass m of the cradle 22 and the test object 23 thus obtained or the mass m of the test object 23
The arithmetic processing unit 32 notifies 2 to the communication control unit 31 (see FIG. 1).
Step b).

Then, the communication control section 31 notifies the operator console (not shown) of the mass m2 of the subject 23. As a result, the scan planning unit of the operator console can recognize the weight based on the mass of the subject 23 and properly determine the strength of the high frequency pulse.

Further, since such weight measurement is performed within the time when the subject 23 on the cradle 22 is moved into the magnet unit 10, the time only for weight measurement becomes unnecessary, and The inspection time will also be shortened. And since there is no need for manual input, mistakes during input will not occur.

Further, the sensor 43 for detecting the position of the cradle 22 and the driving means for driving the cradle 22 with a predetermined force are originally included in the MRI apparatus, and therefore no additional mechanical element is required. Is.

In the above processing procedure, the mass a may be obtained by obtaining several accelerations at different timings during the acceleration instead of obtaining the acceleration a only once. In this case, the obtained acceleration a should be completely the same if no error occurs, but if different values are obtained as a result of the arithmetic processing, averaging processing may be performed. Further, it is also possible to exclude the ones having a large difference from the plurality of values and then perform the averaging.

In the above case, the description has been made on the assumption that the dynamic friction coefficient b is constant, but the above-mentioned b is caused by the frictional force generated by the rotating shaft of the motor 42, the speed reducing mechanism, or the like.
There may be cases where the value cannot be regarded as constant. In such a case, a coefficient and a relational expression capable of correcting the dynamic friction coefficient b in accordance with the rotation speed of the motor 42 are stored in the table 35, and the arithmetic processing unit 32 performs the arithmetic processing while correcting the b. It is also possible to execute.

Next, referring to the flowchart of FIG.
Another example of the procedure of the method of measuring the subject weight of RI will be described.
When executing the processing of FIG. 4, M shown in FIG.
It is possible to use the RI device as it is, and
It is also possible to use an MRI apparatus having a configuration in which the sensor 43 and the acceleration detection unit 34 are removed from the MRI apparatus of FIG. Here, the processing procedure will be described with reference to the MRI apparatus in FIG.

When an operation start instruction is given from the operator console or the like, the communication control section 31 which receives the start instruction from the operator console gives a start instruction to the arithmetic processing section 32. Here, the arithmetic processing unit 32 executes the analysis of the instruction (step 1 in FIG. 4). As a result, the electrical state and mechanical position of each part are set to the initial state.

At the time when the analysis of the instruction is completed, or after the elapse of a fixed time sufficient to complete the analysis of the instruction,
The arithmetic processing unit 32 gives an instruction for driving the cradle 22 to the drive control unit 32.

Here, the drive control unit 32 gives the controller 41 an instruction to gradually increase the force f from a small value. As a result, the controller 41 generates the voltage / current necessary for the motor 42 to generate a force that changes in response to the above-described command, and supplies the voltage / current to the motor 42.

In this way, the cradle 22 is driven by the gradually changing force f (step 2 in FIG. 4). When the rotation of the motor 42 is passed through a reduction mechanism having a predetermined reduction ratio, one of the arithmetic processing unit 32 to the controller 41 changes the reduction ratio so that the cradle 22 can be driven with a predetermined force f. A command corresponding to the force f is issued to the motor 42. That is, a command is given so that the motor 42 outputs a force according to the reduction ratio and the desired force f. In this case, it is conceivable to store data on the reduction ratio in the table 35.

In this way, a force f that gradually changes is applied to the cradle 22, and when the cradle 22 starts to move from a stationary state, the sensor 43 causes the cradle 22 to move.
And detects the movement of the and notifies the control unit 30. The arithmetic processing unit 32 in the control unit 30 holds the force when the cradle 22 starts moving as f ′. Or cradle 22
The drive control unit 33 notifies the arithmetic processing unit 32 of the force f ′ at the start of the movement.

The gradually changing force f may be a continuous change or a stepwise change.
Here, in general, when the mass of an object is m, the force for driving the object is gradually increased, and the force when the object starts to move is f ′, and the coefficient of static friction of the object is c, The formula f ′ = m · cg (3) holds. Here, g is the gravitational acceleration.

Therefore, in the arithmetic processing section 32, the cradle 2
Using the force f ′ at which 2 starts to move and the static friction coefficient c stored in the table 35, the calculation of the following equation (4) is executed. m = f '/ cg (4) In this way, the total mass m of the cradle 22 and the subject is calculated by performing the calculation using the force f'when the cradle 22 starts to move and the friction coefficient c. Can be obtained (step 3 in FIG. 4).

Then, when the data of the mass m1 of the cradle 22 is held in the table 35, the subtraction is carried out by the arithmetic processing unit 32 so that the mass m2 of the object (m2 = m-m1).
).

The arithmetic processing unit 32 notifies the communication control unit 31 of the total mass m of the cradle 22 and the subject 23 thus obtained or m2 of the subject 23 (step 4 in FIG. 1).

Then, the communication controller 31 notifies the operator console (not shown) of the mass m2 of the subject 23. As a result, the scan planning unit of the operator console or the like can recognize the weight based on the mass of the subject 23 and appropriately determine the strength of the high frequency pulse.

Further, since such weight measurement is performed within the time when the subject 23 on the cradle 22 is moved into the magnet unit 10, the time only for weight measurement is unnecessary, and The inspection time will also be shortened. And since there is no need for manual input, mistakes during input will not occur.

In the example described with reference to the processing procedure of FIG. 1 and the processing procedure of FIG. 4, the dynamic friction coefficient b and the static friction coefficient c are measured in advance and stored in the table 35. It was When the data is stored in advance in this way, it is also possible to periodically perform calibration as calibration. Further, instead of storing it in advance, it is possible to newly detect the friction coefficient each time the device is started up.

In the case of this calibration or new detection, the same process as the process shown in FIG. 1 or 4 described above is executed without placing the subject on the cradle 22. In this case,
Since the value of the mass m is equal to the already known m1, the friction coefficient can be accurately obtained. Therefore, the friction coefficient thus obtained may be written in the table 35.

Further, in the above description, the body weight of the subject is measured in the MRI apparatus, but it is possible to use it in all table apparatuses using a cradle other than the MRI apparatus. Therefore, a table device capable of measuring the weight is also within the scope of the present invention.

Here, the MRI apparatus for adjusting the output of electromagnetic waves using the weight measured as described above will be briefly described. In the MRI apparatus, the amount of electromagnetic waves output from the RF coil absorbed by the subject (SAR: Specif
The SAR monitoring device for monitoring the ic absorption rate) is provided, and the SAR device adjusts the output of the electromagnetic wave using the value of the weight of the subject.

The operation of this SAR monitoring device is as follows. The SAR monitor predictively calculates the output value of the RF power amplifier from the contents of the sequence program to be executed. On the other hand, the maximum allowable SAR is calculated from the body weight information of the subject that has been input in advance. Then, the predicted output value of the RF power amplifier and the allowable maximum S
Comparing AR.

If the predicted output value of the RF power amplifier exceeds the maximum allowable SAR, the sequence program is not executed. By controlling in this way, the amount of electromagnetic waves absorbed by the subject can be kept within an appropriate range.

By the way, in the SAR monitoring device as described above, what is actually monitored is the calculated output value (input value to the RF coil) of the RF power amplifier based on the sequence program. It is not the amount of electromagnetic waves absorbed by the sample (or the actual output from the RF coil) itself.

That is, a reflected wave may be generated due to a difference in impedance of the RF coil or a power feeding cable, and the output value of the RF power amplifier is not all output from the RF coil due to the influence of the reflected wave. Absent.

Therefore, the maximum permissible S calculated as described above
It is also possible that the AR does not match the actual maximum allowed SAR. For this reason, the safety factor may be overestimated. If the safety factor is too large,
The sequence programs that can be executed will be restricted more than necessary.

Therefore, the absorption amount of the electromagnetic wave (R
A SAR monitoring device that can directly monitor the actual output from the F coil is desirable. As such a SAR monitoring device that can directly monitor the absorption amount of electromagnetic waves, the inventor of the present application filed Japanese Patent Application No. It has already been proposed as No. 8227.

FIG. 5 shows an MRI including the SAR monitoring device.
It is a block diagram of an apparatus. In FIG. 5, the control unit 3
0 controls the whole operation based on the instruction from the console 63. The sequence controller 53 operates a magnetic field drive circuit (including a gradient amplifier) 54 based on the stored sequence to generate a static magnetic field and a gradient magnetic field with the static magnetic field coil and the gradient magnetic field coil of the magnet unit 10. . It also controls the RF oscillation circuit 56 to generate an RF carrier. In addition, the modulation circuit 57 is controlled to modulate the RF carrier into an RF signal having a predetermined waveform, and an RF power amplifier 58 is provided.
From the RF of the magnet unit 10 via the directional coupler 70.
Add to the coil.

The NMR signal obtained by the receiving coil of the magnet unit 10 is passed through the preamplifier 59 to the phase detector 60.
To the control unit 30 via the AD converter 61.
Is input to

The control unit 30 controls the N obtained from the AD converter 61.
An image is reconstructed based on the MR signal data and displayed on the display device 62. The directional coupler 60 receives the coil voltage Vc, the traveling wave voltage Vf, and the reflected wave voltage Vr from the second voltage.
Output to the A / D converter 71.

The second A / D converter 71 has a coil voltage V
c, the traveling wave voltage Vf, and the reflected wave voltage Vr are converted into digital values and output to the control unit 30. Control unit 30
Performs SAR monitoring operation as shown in the flowchart of FIG.

That is, in step S1, the maximum allowable SAR according to the subject, the coil resistance value Rc according to the RF coil to be used, and the repetition time TR of the scan sequence to be executed are input.

In step S2, the repetition time TR is
Divide by a predetermined sampling period ΔT, and repeat time T
Calculate the number of sampling times N between R. Step S3
Then, from the second A / D converter 71 to the coil voltage Vc,
The traveling wave voltage Vf and the reflected wave voltage Vr are read. This reading is performed at a predetermined sampling period ΔT.

At step S4, the absorption amount Psar is calculated by the following equation. Psar = (Vf · Vf / 50)-(Vr · Vr / 50)-
(Vc · Vc / Rc) In step S5, N Psars from the latest Psar to the Nth previous Psar are added, and the sum is divided by N. Thus, the average amount of absorption during the repeating time TR can be obtained.

At step S6, it is determined whether the average absorption amount is larger than the maximum allowable SAR. If not, the process returns to step S3. If so, step S
Go to 7.

In step S7, execution of the scan sequence is stopped. In the above operation, the electric power actually output from the RF coil is measured by measuring the traveling wave voltage and the reflected wave voltage. Since the electric power actually output from the RF coil is approximately equal to the amount of electromagnetic waves absorbed by the subject, the amount of electromagnetic waves absorbed by the subject can be monitored directly and in real time. Therefore, the control unit 30, the directional coupler 70, and the second A
The / D converter 71 constitutes a SAR monitoring device.

If there are two RF signal systems, the 0 ° system and the 90 ° system, it is necessary to monitor each system. It is also possible to perform the processing of steps S3 and S4 by an analog circuit.

According to this SAR monitoring device, the amount of electromagnetic waves output from the RF coil absorbed by the subject is
By eliminating the influence of reflected waves, it becomes possible to monitor directly and in real time. Therefore, it is possible to improve reliability in SAR monitoring of the MRI apparatus.

Therefore, the value of the body weight obtained by the above-described method and apparatus for measuring the weight of the subject is used for this SAR monitoring device, so that the amount of electromagnetic wave absorbed by the subject is properly determined. Can be kept within a range.

As described in detail above, the cradle is driven with a predetermined force, and the mass of the subject is obtained by using the predetermined force and the friction coefficient of the cradle during the driving.
Since the body weight can be measured when the subject is placed on the cradle and moved, it is possible to realize the body weight measuring method and the body weight measuring MRI apparatus capable of easily measuring the body weight of the subject in the MRI apparatus. become.

Further, the cradle is driven by a force f, the acceleration a of the cradle is obtained from the change of the position per unit time, and the mass of the subject is calculated from the force f, the acceleration a, the dynamic friction coefficient b of the cradle and the mass of the cradle. Since the weight measurement can be performed when the subject is placed on the cradle and moved by executing the calculation for obtaining m2, a weight measurement method that can easily measure the weight of the subject in the MRI apparatus, and It becomes possible to realize an MRI apparatus capable of measuring weight.

Then, the force f for driving the cradle is gradually increased from a small value, and the force m'when the cradle starts moving, the static friction coefficient c of the cradle and the mass of the cradle are used to obtain the mass m2 of the subject. By performing the calculation, the weight can be measured when the subject is placed on the cradle and moved, so that the weight measurement method and the weight can be easily measured in the MRI apparatus. MRI device can be realized.

Further, the cradle is driven by a predetermined force, and the mass of the test object is obtained by using the predetermined force and the friction coefficient of the cradle at the time of driving, so that the test object is placed on the cradle and moved. Since the weight can be measured when the table is measured, a table device capable of measuring the weight can be realized.

[0086]

As described above in detail, according to the invention in which the cradle is driven by a predetermined force and the weight of the test object is obtained by using the predetermined force and the friction coefficient of the cradle, Since the body weight can be measured when the body is placed on the cradle and moved, it is possible to realize a body weight measuring method capable of easily measuring the body weight of the subject in the MRI apparatus.

According to the invention in which the cradle is driven by a predetermined force and the weight of the subject is determined by using the predetermined force and the friction coefficient of the cradle, the subject is placed on the cradle and moved. Since the body weight can be measured at that time, it is possible to realize the MRI apparatus that can easily measure the body weight of the subject.

Further, the cradle is driven by a force f, and the acceleration a of the cradle is obtained from the change of the position per unit time. According to the invention for determining m2, the weight can be measured when the subject is placed on the cradle and moved, so that the MRI apparatus capable of easily measuring the weight of the subject can be realized.

Then, the force f for driving the cradle is gradually increased from a small value to obtain the mass m2 of the subject from the force f'when the cradle starts moving, the static friction coefficient c of the cradle and the mass m1 of the cradle. According to the invention, since the body weight can be measured when the subject is placed on the cradle and moved, an MRI apparatus capable of easily measuring the body weight of the subject can be realized.

Further, according to the invention in which the cradle is driven with a predetermined force and the mass of the subject is determined by using the predetermined force and the friction coefficient of the cradle during the driving, the subject is placed on the cradle. Since the weight can be measured when moving the table, a table device capable of measuring the weight can be realized.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a principle processing procedure of a method for measuring an object weight of MRI of the present invention.

FIG. 2 is a configuration diagram showing a configuration of an example of an embodiment of an MRI apparatus of the present invention.

FIG. 3 is a configuration diagram showing an external configuration of an example of an embodiment of an MRI apparatus of the present invention.

FIG. 4 is a flowchart showing another example of the processing procedure of the MRI subject weight measuring method of the present invention.

FIG. 5 is a configuration diagram showing an example of an embodiment of an MRI apparatus of the present invention.

FIG. 6 is a flowchart showing an example of a processing procedure for obtaining an electromagnetic wave absorption amount in MRI of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 magnet part 20 table 21 support stand 22 cradle 23 subject 30 control part 31 communication control part 32 arithmetic processing part 33 drive control part 34 acceleration detection part 35 table 41 controller 42 motor 43 sensor

Claims (5)

[Claims] 1. When magnetic resonance imaging is performed on a subject, a cradle on which the subject is placed is driven with a predetermined force, and the weight of the subject is determined using the predetermined force and the friction coefficient of the cradle. A method for measuring the body weight of a subject, which is characterized by MRI. 2. An MRI apparatus for performing magnetic resonance imaging by driving a cradle on which a subject is placed by a drive means, wherein the drive means drives the cradle with a predetermined force, and the predetermined force and the friction coefficient of the cradle. An MRI apparatus comprising: a control unit that obtains the weight of a subject by using. 3. An MRI apparatus for performing magnetic resonance imaging by driving a cradle on which a subject is placed by driving means, wherein the driving means drives the cradle by force f and the position when the cradle is driven is detected. The position of the cradle is calculated from the position detecting means and the position change per unit time detected by the position detecting means, and the force f, the acceleration a, the coefficient of dynamic friction b of the cradle and the mass m of the cradle are calculated.
An MRI apparatus comprising: a control unit that determines the mass m2 of the subject from 1. 4. An MRI apparatus for performing magnetic resonance imaging by driving a cradle on which a subject is placed by a driving means, the driving means driving the cradle by force f, and the force f driving the cradle by the driving means. A control means for gradually increasing the value from a small value to a force f'when the cradle starts to move, a static friction coefficient c of the cradle, and a mass m2 of the subject from the mass m1 of the cradle. MRI device. 5. A table device for driving a cradle on which a subject is placed by a driving means, wherein the driving means drives the cradle with a predetermined force, and the predetermined force and the friction coefficient of the cradle are used to move the object. A table device comprising control means for determining the weight of a sample.