JPH04212329A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To provide the magnetic resonance imaging device which selects only the coil assemblies taking part in photographing among plural pieces of the coil assemblies and can activate the assembly. CONSTITUTION:The entire part of the photographing visual field of a patient is divided to plural regions and the coil assemblies 1 to 1 are provided in each of the respective regions. The respective assemblies 1 are constituted of a signal receiving coil 6 and a variable capacitor 8, and pin diodes 5 are disposed between the assemblies. The on-off of the pin diodes 5 are controlled by prescribed sequence to control the activation and passivation of the respective coil assemblies 1. Only the coil assemblies by as much as the min. required number taking part in signal reception are activated.

Description

[Detailed description of the invention]

0001

[Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus that has a plurality of receiving coils and selects a receiving coil to be activated in accordance with a region to be imaged of a subject to obtain an MRI image.

0003

[Prior Art] In recent years, magnetic resonance imaging devices (hereinafter referred to as MRI devices) have been equipped with multiple receiving coils, and only the coils necessary for imaging are activated in order to improve the S/N ratio. a method of receiving an NMR signal by
In other words, efforts are being made to develop a multi-coil system.

[0004] Conventionally, in such a multi-coil type MRI apparatus, an operator selects and activates a receiving coil placed at a position corresponding to the part of the subject to be imaged before the examination, and the MRI image is I was getting .

[0005]

However, with such conventional devices, the region to be imaged is limited, and therefore multi-slice imaging, which collects a large number of cross-sectional signals in a short period of time, cannot be performed.

On the other hand, if multiple receiving coils are activated at the same time, receiving coils that are not involved in imaging will be activated, and this will generate noise. There was a problem in that the S/N ratio deteriorated compared to MRI images obtained with a limited number of receiving coils.

[0007] The present invention has been made to solve such conventional problems, and its purpose is to select and activate only those involved in imaging out of a plurality of coil assemblies. The object of the present invention is to provide a magnetic resonance imaging device that can perform the following tasks.

[0008]

[Structure of the invention]

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention activates a coil assembly installed near a subject, thereby removing NM from a region to be imaged.
In a magnetic resonance imaging apparatus that detects an R signal to obtain an imaging signal, a plurality of coil assemblies are installed to divide the entire imaging field of the subject, and a storage means for storing an activation order of each coil assembly; , and coil selection means for activating each coil assembly in the stored order.

0010

[Operation] With the above-described structure, first, the order is set in advance to select a single coil assembly or the minimum necessary number of coil assemblies to be activated from among the plurality of installed coil assemblies.

[0011]The coil selection means outputs an activation command signal to each coil assembly in this order, and controls the received NMR signal to be taken in.

As a result, it becomes possible to take a tomographic image at high speed while switching the receiving coil, thereby shortening the taking time.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of a receiving system in a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) to which the present invention is applied.

As shown in the figure, the reception system according to the present embodiment includes a plurality of coil assemblies 1 to 1 for detecting NMR signals from a region to be imaged of a subject (not shown), and
An MRI system 2 that centrally controls gradient magnetic fields, RF pulses, a receiving section, etc. in the RI device, and sets the activation order of the coil assemblies 1 to 1;
A coil selection unit 3 that activates each coil assembly 1-1 according to the order set in the system 2, and a signal that captures and outputs an NMR signal received by the activated one of each coil assembly 1-1. It has a selection section 4.

When the coil assemblies 1 to 1 receive an activation command signal from the coil selection unit 3, the PIN diode 5 conducts the command signal as a bias voltage.
It has a receiving coil 6 that receives an NMR signal from the subject when the PIN diode 5 becomes conductive, and the received resonance signal is sent to the signal selection unit 4 via a coaxial cable 7.
is being supplied to. Further, numerals 8 to 8 are choke coils, and numerals 9 to 9 are variable capacitors for tuning.

The MRI system 2 integrally controls a host CPU 10 positioned as the control center of the MRI apparatus, gradient magnetic fields, RF pulses, a receiving section, etc., and in particular,
It includes a system controller 11 that generates a reception timing signal in synchronization with the NMR signal.

The coil selection unit 3 has a memory 21 in which the activation order of each coil assembly 1 to 1 is stored in advance, and sends out the order data stored in the memory 21 when a reception timing signal is given from the system controller 11. A CPU 12, a register 14 that outputs an activation command signal to each coil assembly 1 to 1 based on this order data, and an AND signal of this activation command signal and the reception timing signal output from the system controller 11. AND circuits 15 to 15, and when the AND signal is given, the corresponding PI of the coil assembly 1
A driver 16 that applies a bias voltage to the N diode 5
~16.

The signal selection unit 4 selects the NMR signal from the activated coil assembly 1 by the signal from the register 14.
An analog switch 17 that takes in only the signal, preamplifiers 18 to 18 that are provided for each coil assembly 1 to 1 and amplifies the NMR signal that has passed through the analog switch 17, and adds the signals amplified by each preamplifier 18 to 18. It has an summing amplifier 19 that outputs the summing signal.

Next, the operation of this embodiment will be explained.

Now, two coil assemblies 1 are prepared, and the receiving coils 6 (6a, 6b) are disposed facing each other near the sides of the subject's head 20, as shown in FIG. Next, an example will be described in which tomographic images as shown by the broken line in the figure are taken in the order of (a) to (f).

FIG. 3 is a time chart showing the operation of each device at this time. When an RF pulse is applied to the subject's head 20 as shown in FIG. occurs (Fig. 3(B)).

Further, the memory 21 of the coil selection unit 3 shown in FIG. 1 stores order data for alternately activating the first receiving coil 6a and the second receiving coil 6b shown in FIG. Therefore, shift register 1 shown in Figure 1
4 is alternately switched between the first receiving coil 6a side and the second receiving coil 6b side each time the reception timing signal (FIG. 3(C)) from the system controller 11 arrives (FIG. 3(D)). )).

Therefore, when the first reception timing signal arrives from the system controller 11, an AND signal is first output from the AND circuit 15 corresponding to the first reception coil 6a, and a bias voltage is output from the corresponding driver 16. be done. As a result, the bias voltage that has passed through the choke coil 8 is applied to both ends of the PIN diode 5 of the coil assembly 1 including the first receiving coil 6a, so that the PIN diode 5 becomes conductive.

As a result, the NMR signal received by the receiving coil 6a is conducted to the analog switch 17 of the signal selection section 4 via the coaxial cable 7. At this time, the analog switch 17 is activated by the command from the register 14.
Since the first channel connected to the receiving coil 6a is turned on (FIG. 3 (G)), the NMR signal received by the coil 6a passes through the analog switch 17, is amplified by the preamplifier 18, and then added. The signal is supplied to the amplifier 19.

Next, the system controllers 11 to 2
When the second reception timing signal arrives, the output of the register 14 is changed from the first reception coil 6a side to the second reception timing signal.
Since the second receiving coil 6b side is switched to the second receiving coil 6b side, an AND signal is output from the AND circuit 15 corresponding to the second receiving coil 6b.

Thereafter, the corresponding coil assembly 1 is activated (FIG. 3(F)), so that the signal selection section 4 is supplied with the NMR signal received by the second receiving coil 6b. Then, in the analog switch 17, the second channel becomes conductive in order to conduct this NMR signal (
In FIG. 3(H)), the NMR signals are amplified by the preamplifier 18, then added by the summing amplifier 19, and sent to the subsequent process.

Thereafter, each time a reception timing pulse arrives, the coil assemblies 1 to 1 to be activated are switched in the same procedure, and NMR signals are obtained alternately from each reception coil 6a, 6b.

In this manner, when tomographic images of the subject's head 20 shown in FIG. 2 are taken alternately from both sides, the first receiving coil 6a and the second receiving coil 6b are activated alternately. This can be achieved by doing this.

In this way, in this embodiment, a plurality of receiving coils 6 are installed, and the NMR signal is obtained by switching the receiving coils 6 to be activated at a predetermined timing.

[0030] Therefore, multi-slice imaging is possible, and a large number of tomographic images can be obtained in a short time.

Furthermore, since only the receiving coil 6 involved in reception is activated and all other receiving coils 6 are not activated, the generated noise can be reduced and the S/N ratio can be significantly improved.

[0032] In this embodiment, an example is shown in which two receiving coils are disposed on both sides of the subject's head 20, but the present invention is not limited to this. A plurality of receiving coils may be arranged at the bottom.

Further, in this embodiment, the output of the register 14 is switched using the reception timing signal oscillated from the system controller 11 as a trigger, but when generating a transmission pulse, the transmission RF
It is customary to send a gating signal to protect against the strong power of the pulse, and this gating signal may also be used as a trigger for switching the output of the register 14.

Furthermore, even if there is no gating signal, the receiving coil will generate a strong signal corresponding to the transmitted RF pulse, and this signal may be used as a trigger for switching the output of the register 14.

FIG. 4 is a block diagram showing a second embodiment of the present invention. In this figure, the same components as those in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted.

As shown in FIG. 4, each coil assembly 1
A parallel resonant circuit constituted by a capacitor 30 and a coil 31 is connected to the PIN diode 5 provided at .about.1. That is, one end of the coil 31 is connected to the output side of the PIN diode 5, and the other end is connected to the variable capacitor 9 side. Further, since the connection point between the coil 31 and the variable capacitor 9 and the input terminal of the PIN diode 5 are connected via the capacitor 30, when the PIN diode 5 is conductive, the coil 31 and the capacitor 30 form a parallel resonant circuit. is formed.

In the first embodiment described above, the system controller 11 of the MRI system 2 outputs the reception timing signal in synchronization with the received NMR signal, but in this example, the system controller 11 outputs the reception timing signal in synchronization with the RF pulse applied to the subject. outputs a gate signal. The receiver control circuit 35 supplies this gate signal to the buffer amplifier 34, and the buffer amplifier 34
This gate signal is amplified and supplied to the coil selection unit 3.

Further, each output terminal of the register 14 is connected to the inverters 33 to 33, and this output side is connected to the OR circuits 32 to 33.
32. Further, the other ends of the OR circuits 32 to 32 are connected to the output end of the buffer amplifier 34, and are supplied with a gate signal. The output terminals of the OR circuits 32 to 32 are connected to the driver 16.

Next, the operation of the first embodiment will be explained with reference to the time chart shown in FIG.

[0040] Here, similar to the first embodiment described above,
Two coil assemblies 1 are prepared, and this receiving coil 6
(6a to 6b) are disposed opposite to each other near the sides of the subject's head 20 as shown in FIG. Next, the side for photographing the tomographic images indicated by the broken line in the figure in the order of (a) to (f) will be explained.

Now, when the RF pulse shown in FIG. 5(A) is applied, an NMR signal is generated with a slight delay (FIG. 5(B)). The memory 21 of the coil selection unit 3 shown in FIG. 4 also stores the first receiving coil 6a and the second receiving coil shown in FIG.
The shift register 14 shown in FIG.
The output of
It is alternately switched between the a side and the second receiving coil 6b side (FIG. 5(D)).

Therefore, when the first gate signal arrives from the system controller 11, the first receiving coil 6
Since an "on" signal is output to the inverter 33 corresponding to a, one input terminal of the OR circuit 32 becomes "off". Since the gate signal (FIG. 5C) from the buffer amplifier 34 is input to the input terminal of the OR circuit 32, when the gate signal turns off, both inputs of the OR circuit 32 turn off, and the driver No signal is output to 16.

Therefore, the PIN diode 5 corresponding to the first receiving coil 6a becomes non-conductive until the next gate signal is output (FIG. 5(E)). As a result, the receiving coil 6a and the variable capacitor 9 are connected via the capacitor 30, so that the NMR signal received by the receiving coil 6a is amplified by the preamplifier 18 and sent to the summing amplifier 19.

Next, when the next gate signal is output from the system controller 11, the gate signal is input to one input terminal of the OR circuit 32 corresponding to the receiving coil 6a, so the output of the OR circuit 32 becomes "on". ”, and the PIN diode 5 becomes conductive. As a result, in the coil assembly 1 including the first receiving coil 6a, a parallel resonant circuit is formed by the capacitor 30 and the coil 31, so that the NMR signal received by the first receiving coil 6a is blocked.

On the other hand, at this time, the output of the shift register 14 is switched to the second receiving coil 6b, so the PIN diode 5 corresponding to the second receiving coil 6b becomes non-conductive in the same manner (see FIG. 5). (F)). Therefore, the NMR signal received by the receiving coil 6b is captured. Since the above operation is repeated every time a gate signal is applied, the NMR signal is alternately received by the first receiving coil 6a and the second receiving coil 6b. As a result, the cross sections of the subject's head 20 shown in FIG.
c)...(f) Photographs can be taken in the following order.

[0046] In this way, in the second embodiment, the PIN
When the diode 5 is in a conductive state, the capacitor 30 and the coil 31 form a parallel resonant circuit to cut off the circuit, and when the PIN diode 5 is in a non-conductive state, the NMR signal is taken in through the capacitor 30. There is. Therefore, compared to the first embodiment described above, since the PIN diode 5 receives the NMR signal when it is not conductive, it is possible to prevent the signal-to-noise ratio of the NMR signal from decreasing due to the conduction resistance of the PIN diode 5.

In the first and second embodiments described above, the coil assemblies 1 to 1 are used only for reception, but it goes without saying that they may also be used as coils for transmission and reception.

[0048]

As explained above, in the present invention, when an order is set to select the minimum necessary number of coils to be activated from among a plurality of coil assemblies, each coil assembly is activated in accordance with this order. Becomes activated.

Therefore, even in the case of a multi-coil system in which a plurality of receiving coils are installed, it is possible to image the subject using multi-slices, and the imaging time can be significantly shortened.

Further, only the minimum necessary number of coil assemblies involved in reception are always activated, and the other coils are not in operation. Therefore, the effects of reducing noise components and significantly improving the S/N ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the photographing position of the subject's head.

FIG. 3 is a time chart showing the operation of the first embodiment.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a time chart showing the operation of the second embodiment.

[Explanation of symbols]

1-1 Coil assembly 2 MRI system 3 Coil selection unit 4 Signal selection section 5~5 PIN diode 6～6 Receiving coil 9~9 Variable capacitor 11 System controller 12 CPU 14 Shift register 15-15 AND circuit 17 Analog switch 20 Subject's head 21 Memory 30 Capacitor 31 Coil 32 OR circuit 33 Inverter

Claims (10)

[Claims] 1. A magnetic resonance imaging apparatus in which a coil assembly installed near a subject is activated, thereby detecting an NMR signal from a region to be imaged to obtain an imaging signal, wherein the coil assembly is placed near a subject. A plurality of coil assemblies are installed to divide the entire imaging field of view of a person, and the coil assembly includes a storage means for storing the activation order of each of the coil assemblies, and a coil selection means for activating each coil assembly in the stored order. A magnetic resonance imaging device featuring: 2. The magnetic resonance imaging apparatus according to claim 1, wherein the plurality of coil assemblies are two coil assemblies disposed facing each other with the subject in between. 3. The magnetic resonance imaging apparatus according to claim 1, wherein the plurality of coil assemblies are arranged in parallel on one side of the subject. 4. The coil assembly includes a receiving coil that receives an NMR signal from a site to be imaged, a variable capacitor that can adjust the reception frequency of the receiving coil, and a variable capacitor that is disposed between the receiving coil and the variable capacitor. 2. The magnetic resonance imaging apparatus according to claim 1, further comprising at least a PIN diode which is conductive when a bias voltage is applied. 5. The coil selection means includes a first controller that outputs a reception timing signal synchronized with generation of an NMR signal, a second controller that reads activation order data of the coil assembly from the storage means, and a second controller that reads activation order data of the coil assembly from the storage means; 5. The magnetic resonance imaging apparatus according to claim 4, further comprising biasing means for supplying a bias voltage to the PIN diode based on a received timing signal and activation order data. 6. The magnetic resonance imaging apparatus according to claim 5, wherein said bias means is comprised of a register and an AND gate circuit. 7. The coil assembly includes a receiving coil that receives an NMR signal from a region to be imaged, a variable capacitor that can adjust the receiving frequency of the receiving coil, and a variable capacitor that is disposed between the receiving coil and the variable capacitor. PIN
The magnetic resonance imaging apparatus according to claim 1, comprising a diode and a parallel resonant circuit connected in parallel with the PIN diode. 8. The coil selection means includes: a first controller that outputs a gate signal synchronized with the output of the RF pulse; a second controller that reads activation order data of the coil sections from the storage means; 8. The magnetic resonance imaging apparatus of claim 7, further comprising biasing means for applying a bias voltage to PIN diodes of said coil assembly that do not receive an NMR signal based on the signal and activation order data. 9. The magnetic resonance imaging apparatus according to claim 8, wherein the bias means is comprised of a resistor and a plurality of OR gates. 10. The magnetic resonance imaging apparatus according to claim 1, wherein the coil assembly receives an NMR signal and outputs an RF pulse toward the subject.