JPH0724306U - MRI equipment - Google Patents

Abstract

(57) [Abstract] [Object] To realize an MRI apparatus capable of detecting a temperature rise of a cable connected to an RF coil without impairing the flexibility of the cable and without using a magnetic material. . In an MRI apparatus in which a magnetic field is excited by a high frequency magnetic field in a predetermined region of a subject using a transmission coil and a magnetic resonance signal is collected from the region using a reception coil, the MRI device is connected to the reception coil or the transmission coil. A coaxial cable 10 having a heat sensitive layer 14 made of a material whose impedance changes with temperature on the outer periphery of the first conductor layer 13 and a second conductor layer 15 on the outer periphery thereof; An MRI apparatus comprising: an impedance detecting unit that detects a change in impedance of the heat-sensitive layer 14 by detecting a signal from the second conductor layer 15.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an MRI apparatus capable of detecting heat generation of a cable connected to an RF coil with the MRI apparatus.

[0002]

[Prior art]

 The MRI apparatus (magnetic resonance imaging apparatus) is an apparatus for observing a nuclear magnetic resonance (NMR) phenomenon and imaging a tomographic image of a subject. In this MRI, in order to observe the subject, a high frequency (RF) signal generated by the NMR phenomenon in the subject is detected.

In this case, when a part of the receiving coaxial cable connecting the RF coil for detection and the MR device is arranged in a loop shape, induction is caused in the looped part of the conductor layer of the coaxial cable. Electric current may flow and generate heat. The heat generated may cause burns to the subject.

[0004]

[Problems to be solved by the device]

 In order to prevent such a situation, various measures such as manuals for promoting proper operation and placement, improvement of the cable jacket, etc. have been made, but the risk of burns is not complete.

Therefore, it has been desired to realize an MRI apparatus capable of detecting the temperature of abnormal heat generation of the RF coil and the cable. However, there is a cable that can detect a temperature rise without affecting the surrounding magnetic field and sacrificing flexibility in cables that handle high frequency and high power such as MRI equipment. I didn't.

Regarding this type of temperature detection, Japanese Patent Application No. 56-68919 proposes a power cable having a temperature detection line. However, this power cable is not designed for high-frequency characteristics and cannot be used as a cable that handles high-frequency signals, such as an MRI device.

In addition, when the cables are arranged in a loop and generate heat, a portion where the cables are in contact with each other generates heat, so that the power cable including the temperature detection line has a temperature rising portion. If the position where the temperature detection line is arranged is slightly misaligned, it may not be possible to reliably detect the temperature rise.

The present invention has been made in view of the above points, and detects an increase in temperature of a cable connected to an RF coil without impairing the flexibility of the cable and without using a magnetic material. It is to realize an MRI apparatus capable of performing the above.

[0009]

[Means for Solving the Problems]

 To solve the above-mentioned problems, in a MRI apparatus that uses a transmission coil to perform magnetic resonance excitation by a high-frequency magnetic field on a predetermined region of a subject, and uses a reception coil to collect a magnetic resonance signal from the region, A coaxial cable which is connected to the coil, has a heat sensitive layer made of a material whose impedance changes with temperature on the outer periphery of the first conductor layer, and has a second conductor layer on the outer periphery thereof; An MRI apparatus including an impedance detecting means for detecting a change in impedance of the heat-sensitive layer by detecting a signal from the second conductor layer.

[0010]

[Action]

 When the temperature of a part of the coaxial cable rises, the impedance of the heat sensitive layer in that part changes. The change in impedance of the heat sensitive layer is detected by the impedance detecting means via the first conductor layer on the inner circumference and the second conductor layer on the outer circumference of the heat sensitive layer.

[0011]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a structure of a coaxial cable used in an MRI apparatus according to an embodiment of the present invention, and FIG. 2 is a configuration diagram showing a schematic configuration of a main part. In these drawings, the coaxial cable 10 has a core wire 11 in the center, an insulating layer 12 on the outer circumference of the core wire 11, a first conductor layer 13 on the outer circumference of the insulating layer 12, and a first conductor. A heat-sensitive layer 14 made of a material whose impedance changes with temperature is provided on the outer periphery of the layer 13, a second conductor layer 15 is provided on the outer periphery of the heat-sensitive layer 14, and an outer cover 16 is provided on the outer periphery of the second conductor layer 15. I have.

As the material forming the heat sensitive layer 14, various insulating materials whose impedance changes according to temperature changes can be used. For example, nylon 6, nylon 11, nylon 12, nylon 66, etc. Can be used. It is known that these materials have temperature-dependent characteristics in which the specific resistance changes linearly 1000 times or more at 40 ° C to 80 ° C.

On the other hand, the coaxial cable 10 is arranged in the transmission coil 1 in a state where one end of the core wire 11 and one end of the first conductor layer 13 are connected to the reception coil 2 for detecting the NMR signal from the test object. There is. The main body 20 of the MRI apparatus includes a control unit 21 that controls the entire operation, a transmission unit 22 that supplies the transmission coil 1 with an RF pulse for exciting spins of atomic nuclei in the subject, and a coaxial cable 10. A reception amplifier 23 that receives and amplifies a reception signal via the core wire 11 and the first conductor layer 13, a reception processing unit 24 that processes the signal amplified by the reception amplifier 23, and a first conductor of the coaxial cable 10. The impedance detector 25 is connected to the layer 13 and the second conductor layer 15 and detects an impedance change of the heat-sensitive layer 14.

The operation of the apparatus of this embodiment having the above-described configuration is as follows. The MRI apparatus shown in this embodiment starts operation according to a normal sequence. Therefore, the RF pulse supplied from the transmitter 22 causes the transmitter coil 1 to transmit an RF pulse. Then, the reception coil 2 detects the NMR signal from the subject, and the reception processing unit 24 processes the signal to display various information on a display device (not shown).

At this time, the impedance detection section 25 detects the impedance of the coaxial cable 10. If the coaxial cable for transmitting the reception signal of the reception coil 2 arranged inside the transmission coil 1 is in a normal temperature state, the impedance does not change. For example, if a part of the coaxial cable 10 is looped in the transmission coil, a standing wave is generated in that part, and a current flows in the looped conductor layer. Then, heat is generated by this current.

When such heat generation occurs, the impedance of the heat sensitive layer 14 changes. In the present embodiment, since the heat sensitive layer 14 is arranged so as to cover the entire coaxial cable 10, it is possible to detect even partial heat generation, and it is possible to compare it with the conventional temperature detection line. Even in this case, it becomes possible to reliably detect the temperature change.

When the impedance change of the heat sensitive layer 14 due to such temperature change occurs, the first conductor layer 13 and the second conductor layer 15 on the inner peripheral side and the outer peripheral side of the heat sensitive layer 14 are connected. The impedance detection unit 25 detects a change in impedance and notifies the control unit 21.

The control unit 21 that has received the notification of the impedance change executes a predetermined process according to the degree of the change. For example, when a small impedance change occurs, a warning is displayed on the display unit that the temperature rise has occurred in the coaxial cable 10, and when a large impedance change occurs to some extent, a large temperature change occurs. A warning is displayed and scanning stop processing such as stopping the transmission of RF pulses is performed.

Before the scan of the MRI apparatus is started, the correspondence between the temperature rise of the coaxial cable 10 and the impedance change of the heat-sensitive layer 14 is checked and provided in the control unit 21 as a look-up table or the like. Detailed control can be expected by executing control while referring to.

FIG. 3 is a configuration diagram showing an example of a circuit configuration of the impedance detection unit 25. In FIG. 3, the impedance detector 25 is connected to the first conductor layer 13 and the second conductor layer 15. The voltage source 25b and the detection resistor 25a are connected between the first conductor layer 13 and the second conductor layer 15. If there is no change in the impedance of the heat sensitive layer 14, the voltage generated in the resistor 25a is constant. When the impedance of the heat-sensitive layer 14 increases / decreases due to heat generation, the voltage division ratio changes accordingly, and the voltage generated in the resistor 25a decreases / increases. The detection processing unit 25c converts this voltage change into a digital signal or the like and notifies the control unit 21 of this.

Although the DC voltage is applied to the heat sensitive layer 14 to detect the DC voltage generated in the resistor 25a, the method for detecting the impedance change of the heat sensitive layer 14 is not limited to this. . For example, an AC voltage having a frequency that does not affect MRI is applied between the first conductor layer 13 and the second conductor layer 15, and the ratio of the reflected wave changes due to a partial impedance change. It is also possible to detect the partial impedance change of the thermosensitive layer 14 by detecting the ratio (SWR) of the traveling wave and the reflected wave by utilizing the property.

Further, although the description has been given by connecting the coaxial cable 10 proposed in the present embodiment to the connection between the receiving coil 2 and the main body portion 20, the coaxial cable is also connected to the transmission coil 1 and the main body portion 20. It is possible to use 10. Even when the coaxial cable 10 is used to connect the transmission coil 1 and the main body portion 20 in this way, reliable temperature detection can be performed as in the above embodiment.

As described above, by disposing a heat sensitive layer made of a material whose impedance changes with temperature on the outer circumference of the coaxial cable and a conductor layer further on the outer circumference thereof, and monitoring the impedance change of the heat sensitive layer, It becomes possible to reliably detect the temperature rise of the cable connected to the RF coil. In addition, since the heat sensitive layer and the second conductor layer are provided on the outer circumference of a normal coaxial cable, the flexibility of the cable is not impaired. Further, since no magnetic material is used, the operation of MRI is not adversely affected.

[0024]

[Effect of device]

 As described in detail above, according to the present invention, the heat sensitive layer is arranged on the outer periphery of the coaxial cable, and the second conductor layer is further arranged on the outer periphery thereof to change the impedance change of the heat sensitive layer through the conductor layers inside and outside the heat sensitive layer. By monitoring, it is possible to realize the MRI apparatus capable of reliably detecting the temperature rise of the cable connected to the RF coil without impairing the flexibility of the cable and without using the magnetic material.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a main part of an embodiment of the present invention.

FIG. 2 is a configuration diagram showing the overall configuration of an apparatus according to an embodiment of the present invention.

FIG. 3 is a configuration diagram showing a configuration of a main part of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 transmission coil 2 reception coil 10 coaxial cable 20 main body 21 control unit 22 transmission unit 23 reception amplifier 24 reception processing unit 25 impedance change detection unit

Claims (1)

[Scope of utility model registration request] 1. An MRI in which a transmission coil is used to excite magnetic resonance in a predetermined region of a subject by a high-frequency magnetic field, and a reception coil is used to collect magnetic resonance signals from the region.
In the device, connected to the receiving coil (2) or the transmitting coil (1),
A coaxial cable (1) having a heat sensitive layer (14) made of a material whose impedance changes with temperature on the outer periphery of the first conductor layer (13) and a second conductor layer (15) on the outer periphery thereof.
0) and impedance detection means (25) for detecting impedance changes of the heat sensitive layer (14) by detecting signals from the first conductor layer (13) and the second conductor layer (15). An MRI apparatus characterized by being provided.