JPH0919411A - Magnetic resonance imaging equipment - Google Patents

Abstract

(57) Abstract: A high-precision probe such as a thermocouple can be used without affecting the image, and the temperature can be measured with high accuracy. An imager places the subject A on a movable bed 8 in order to capture a tomographic image of the subject A, and the subject A
Into the gantry 7. When the imager operates the console 1 to perform a scan, the console 1 shuts off the power supply from the power supply unit 2,
The operation of the temperature measuring device 3 is stopped. When the scan is completed, the console 1 does not output the scan signal. Therefore, power is supplied from the power supply unit 2 to the temperature measuring instrument 3 through the filter 5 that blocks the high frequency signal, and the temperature data measured by the probe 4 is changed to the temperature. It is output from the measuring device 3 to the display device 9 through the filter 5 to inform the imager of temperature information around the subject.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus for visualizing a desired tomographic plane of a subject by utilizing nuclear magnetic resonance, and more particularly to a temperature rise caused by heat generation from a gradient magnetic field generating means. The present invention relates to a magnetic resonance imaging apparatus including a temperature measuring unit for measuring.

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus processes a signal measured by utilizing a nuclear magnetic resonance phenomenon to calculate a density distribution of nuclear spins at a desired examination site in a subject,
The relaxation time distribution is measured, the measurement signal is arithmetically processed, and the image is displayed as a tomographic image of the inspection site.
A static magnetic field generating magnetic circuit that gives a uniform magnetic field to the subject, a gradient magnetic field coil that gives a gradient magnetic field, and a high-frequency pulse transmission that gives a high-frequency magnetic field to cause nuclear magnetic resonance in the atomic nuclei that make up the tissue of the subject. Means, a nuclear magnetic resonance signal detecting means for detecting a signal by the nuclear magnetic resonance, and an arithmetic means for performing an image reconstruction arithmetic operation using the nuclear magnetic resonance signal.

By the way, in recent magnetic resonance imaging apparatuses, in addition to high-speed imaging and improvement of patient throughput, it is essential to have a two-dimensional TOF angiography measuring function for measuring and imaging blood flow. .
Such angio measurement uses a sequence that adds a rephasing function (phase return function) to the gradient echo method that uses the reversal of the gradient magnetic field for spin imaging, and has a very short repetition time and a long slice thickness. This is a time-scanning imaging method, and the strength and frequency of use (duty) of the gradient magnetic field used for this method have reached several times that of conventional imaging methods.

Therefore, the current applied to the gradient magnetic field coil also increases in proportion to the gradient magnetic field used, and the problem of heat is increasing. That is, when a large current flows through the gradient magnetic field coil, heat is generated due to the resistance of the coil wire, and the temperature inside the room where the magnetic resonance imaging apparatus is arranged rises. When the gradient coil is continuously driven, the temperature of the gradient coil may rise to 100 ° C. or higher, and in such a case, the gradient coil may be burned out. Further, during the diagnosis of the subject, if the temperature in the room where the magnetic resonance imaging apparatus is placed becomes equal to or higher than the temperature at which the subject feels uncomfortable, it is necessary to stop the diagnosis to protect the patient. .

On the other hand, in a magnetic resonance imaging apparatus using a permanent magnet as a static magnetic field generating magnetic circuit, the intensity of the static magnetic field tends to change due to changes in ambient temperature. In this way, when the magnitude of the static magnetic field changes due to the influence of temperature, the gradient magnetic field generated by the gradient magnetic field coil is added to the static magnetic field so that the position corresponds to the magnitude of the magnetic field.
An error will occur in the operation of generating the resonance frequency corresponding to the position, detecting the NMR signal having this resonance frequency, and specifying the position. Since this position detection deviation causes image distortion and blurring, the magnetic resonance imaging apparatus of the permanent magnet system performs temperature control to prevent temperature changes, and keeps the magnet temperature constant at all times. ing.

As described above, in the magnetic resonance imaging apparatus, since it is necessary to measure the temperature, the temperature measuring means is usually provided in the room in which the magnetic resonance imaging apparatus is arranged, and the controller is controlled by the output of the temperature measuring means. It controls and displays the output of the temperature measuring means on the display.

[0007]

As described above, in the magnetic resonance imaging apparatus, the temperature measuring means is usually provided in the room in which the magnetic resonance imaging apparatus is arranged.
As such a temperature measuring means, conventionally, it has been considered to mainly use a sensor such as a thermocouple or a thermistor whose resistance value changes depending on the temperature.

Since such temperature sensors as thermocouples and thermistors detect temperature changes as changes in resistance value,
It is necessary to apply current to the sensor. In the magnetic resonance imaging apparatus, since such a current becomes a strong noise during imaging, such a sensor cannot be used in the magnetic resonance imaging apparatus, and the temperature control apparatus discharged to the outside from the shield room cannot be used. Non-electrical temperature sensors that measure the temperature of air or utilize pressure fluctuations due to expansion of air have been used. However, in such a non-electrical temperature measuring means, an error occurs in the measured temperature, and it is insufficient for temperature control such as protection of the gradient magnetic field coil and elimination of discomfort to the subject. Therefore, when it is necessary to measure the temperature with high accuracy, a temperature sensor such as a thermocouple or a thermistor is used although it affects the image. Furthermore, when a temperature sensor such as a thermocouple or thermistor is used, an induced current is generated in the sensor by the high-frequency magnetic field applied by the magnetic resonance imaging apparatus at the time of imaging. There was also a problem that.

The present invention has been made in view of the above circumstances, and a highly accurate probe such as a thermocouple can be used without affecting the image, and the temperature can be measured with high accuracy. An object of the present invention is to provide a magnetic resonance imaging apparatus that can be used.

[0010]

In order to achieve the above object, the magnetic resonance imaging apparatus of the present invention comprises means for applying a uniform magnetic field to a subject, means for applying a gradient magnetic field, and tissue of the subject. High-frequency pulse transmission means for applying a high-frequency magnetic field to cause nuclear magnetic resonance in the atomic nuclei of the constituent atoms, nuclear magnetic resonance signal detection means for detecting a signal by the nuclear magnetic resonance, and an image using the nuclear magnetic resonance signal In a magnetic resonance imaging apparatus having a computing unit for performing reconstruction computation, a console for instructing an imager to start execution of a scan, and a power supply unit controlled by the console, operating when the scan is stopped, and stopped when the scan is started. And a temperature measuring unit driven by the power supply unit and arranged in the magnetic resonance imaging apparatus.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic resonance imaging apparatus of the present invention is configured as described above, and when a photographer performs a scan, the console outputs a scan signal to the power supply unit and the power supply unit stops the operation. Therefore, no current is supplied to the temperature measuring means. On the other hand, when the imager does not perform the scan, the scan signal is not output from the console, and the power supply unit supplies the current to the temperature measuring unit. The temperature measuring means supplied with the current detects a temperature change at the probe position as a change in the resistance value of the probe, and the change in the resistance value is output as temperature data such as voltage to the display device or the control device of the magnetic resonance imaging apparatus. To be done.

[0012]

Embodiments of the magnetic resonance imaging apparatus of the present invention will be described below with reference to FIGS.

FIG. 1 is a basic configuration diagram of an embodiment of a magnetic resonance imaging apparatus of the present invention, in which 1 is a console for instructing the start of scan execution, 2 is a power supply unit which operates when the scan is stopped and is stopped when the scan is started 3 is a temperature measuring device, 4 is a probe for temperature measurement, 5 is a filter, 6 is a shield room, 7 is a gantry, 8 is a bed, and 9 is an indicator. The console 1 and the power supply unit 2 have an adverse effect on imaging using the magnetic resonance imaging apparatus, and are therefore installed outside the shield room 6. A filter 5 that cuts high-frequency components is installed between the temperature measuring device 3 and the power supply unit 2 at the boundary with the shield room 6. Further, a probe 4 such as a thermocouple is connected to the temperature measuring device 3,
The probe 4 is installed inside a gantry 7 located at the time of the subject A taking an image. A display device 9 for displaying the temperature data collected by the temperature measurement device 3 is installed near the console 1, and a filter 5 for cutting high frequency components is similarly provided between the temperature measurement device 3 and the display device 9. It is installed at the boundary with the shield room 6. On the other hand, although not shown, in the gantry 7, a static magnetic field generating magnetic circuit that gives a uniform magnetic field to the subject, a gradient magnetic field coil that gives a gradient magnetic field, and nuclear magnetic resonance to the atomic nuclei of the atoms constituting the tissue of the subject. A high-frequency pulse transmitting means for applying a high-frequency magnetic field to wake it up and a nuclear magnetic resonance signal detecting means for detecting a signal by the nuclear magnetic resonance are provided and controlled by a control device connected to the console 1.

FIG. 2 shows an embodiment of the power supply unit 2, which is composed of an operation coil 11, a relay 10 composed of contacts 12, and a power supply 13. Then, the scan signal from the console 1 is input to the operation coil 11, and the contact 12 of the relay 10 opens when the scan signal is received and closes when the scan signal is not received. The power supply 13 is the temperature measuring device 3
When the contact 12 is closed, a drive current is supplied to the temperature measuring device 3 when the contact 12 is closed.

On the other hand, FIG. 3 is a diagram showing an embodiment of the temperature measuring device 3 and the probe 4. The temperature measuring device 3 converts the voltage applied to the probe 4 into a voltmeter 20 and temperature data. The probe 4 is composed of a resistor 21 that changes depending on the temperature serving as a sensor portion and an electric wire 22 that transmits a power supply.

Next, the operation of the magnetic resonance imaging apparatus of this embodiment will be described. First, the imager places the subject A on the movable bed 8 and sends the subject A into the gantry 7 to capture a tomographic image of the subject A. Then, the imager executes the scan by operating the console 1. However, if the temperature measuring instrument 3 inside the shield room 6 is driven during the scanning, noise radiated by the temperature measuring instrument 3 is generated. Since the image is adversely affected, when the scan is executed, the console 1 is connected to the power supply unit 2
The scan signal is output to the relay 10, which is a constituent element of. This scan signal causes the operation coil 1 of the relay 10
A current flows through the contact 1 and the contact 12 opens. When the contact 12 opens,
The power supply 13, which is the driving power supply for the temperature measuring device 3, is released,
The temperature measuring device 3 stops operating. This temperature measuring device 3
If power is not supplied, noise is not emitted, so it does not affect the image. Then, when the scan ends, the console 1 stops outputting the scan signal, and the contact 12
Is closed, and the power supply 13 supplies power to the temperature measuring device 3.

When power is supplied to the temperature measuring device 3, FIG.
A current flows through the electric wire 22 shown in to the resistor 21 and the resistor 2
Since a voltage corresponding to the temperature is generated at both ends of 1, the voltage is measured by the voltmeter 20, and the voltage value measured by the voltmeter 20 is output to the converter 23 and converted into temperature data.
This temperature data is output to the display device 9 via the filter 5 that cuts off the high-frequency current, and the display device 9 displays this temperature data using an LED or the like to inform the imager of temperature information around the subject. Inform.

At this time, the power supply line connecting the power supply unit 2 and the temperature measuring device 3 and the line connecting the temperature measuring device 3 and the display 9 are connected to the console outside the shielded room 6 and various other devices. Since it becomes a medium for mixing the noise emitted by the inside of the shield room 6, in order to cut this noise, between the power supply unit 2 and the temperature measuring device 3 and between the temperature measuring device 3 and the display device 9, The filter 5 is installed at the boundary with the shield room 6. This filter 5
Cuts off an electric signal of a frequency component higher than the frequency of the power output from the power supply unit and the temperature data output from the temperature measuring device 3. By the action of the filter 5, noise mixed from the outside of the shield room 6 is cut.

Further, the voltmeter 20 and the converter 23 are the power source unit 2
Since it is configured to operate with the power source from the power source unit 2, when the power source unit 2 does not supply power to the temperature measuring unit 3, the voltmeter 20 and the converter 23 do not operate, and noise is not emitted. .

In the above embodiment, the temperature data output from the temperature measuring device is displayed on the display near the console. However, an alarm is sounded using this temperature data,
It is also possible to add a management mechanism such as sending air around the patient, and also to input temperature data to the console and use it for control such as stopping imaging and temperature control of the static magnetic field generating magnetic circuit. .

In the above embodiment, it is also possible to provide a means for discharging a residual current such as a transient phenomenon which occurs when the power supply unit is stopped, by means of a resistor or the like.

Further, in the above embodiment, the voltmeter 20 and the converter 23 are arranged in the shield room, but only the resistor 21 and the electric wire 22 are arranged in the shield room, and the voltmeter 2 is used.
0, the converter 23 can be arranged outside the shielded room, and in this case, since the voltmeter 20 and the converter 23 can be always supplied with power, the temperature can be measured quickly. You can

[0023]

The magnetic resonance imaging apparatus of the present invention is configured as described above, and since a highly accurate probe such as a thermocouple can be used as the temperature measuring means without affecting the image, The temperature information around the person can be accurately known, and a system that considers the habitability of the subject can be constructed.

Further, since it is possible to know the temperature information of all the heating elements existing in the shield room, such as detecting the temperature of the gradient magnetic field coil, it is possible to appropriately deal with the heat generation problem of the gradient magnetic field coil or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a magnetic resonance imaging apparatus of the present invention.

FIG. 2 is a diagram showing an example of a power supply unit of the example of FIG.

FIG. 3 is a diagram showing an embodiment of a temperature measuring device and a probe of the embodiment of FIG.

[Explanation of symbols]

 1 Console 2 Power Supply Unit 3 Temperature Measuring Instrument 4 Probe 5 Filter 6 Shield Room 7 Gantry 8 Bed 9 Display 10 Relay 11 Operating Coil 12 Contact 13 Power Supply 20 Voltmeter 21 Resistance 22 Electric Wire 23 Converter

Claims (1)

[Claims] 1. A means for applying a uniform magnetic field to a subject, a means for applying a gradient magnetic field, and a high-frequency pulse transmission for applying a high-frequency magnetic field to cause nuclear magnetic resonance in atomic nuclei of atoms constituting the tissue of the subject. In a magnetic resonance imaging apparatus having a means, a nuclear magnetic resonance signal detecting means for detecting a signal by the nuclear magnetic resonance, and an arithmetic means for performing an image reconstruction operation using the nuclear magnetic resonance signal, A console for instructing execution start, a power supply unit controlled by this console, which operates when the scan is stopped, and stops when the scan is started, and a temperature measuring unit which is driven by the power supply unit and is arranged in the magnetic resonance imaging apparatus. A magnetic resonance imaging apparatus comprising: