JP2011110271A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus which can expand a dynamic range when a subject is photographed with a receiving coil having a plurality of coil elements. <P>SOLUTION: In the magnetic resonance imaging apparatus, a switch 8 has eight input terminals INi (i=integer 1 to 8) and eight output terminals OUTi (i=integer 1 to 8). The switch 8 responds a control signal 10a from a central processing unit 10 and switches connection between the eight input terminals INi (i=integer 1 to 8) and the eight output terminals OUTi (i=integer 1 to 8). When magnetic resonance signals are received by the coil elements 41, 43, 45 and 47, the input terminals IN1, IN3, IN5 and IN7 of the switch 8 are switched so as to be connected respectively with the two output terminals. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus having a plurality of coil elements.

  In recent years, multi-channel receiving coils having a large number of coil elements have become widespread (see Patent Document 1). By using a multi-channel reception coil, it is possible to widen the imaging field of view and shoot. In addition, when the imaging field of view is narrow, imaging corresponding to a narrow imaging field of view can be performed by selecting a coil element located in the vicinity of the imaging region from among a large number of coil elements included in the receiving coil. Therefore, the multi-channel receiving coil can be used for photographing with a narrow field of view such as micro-imaging.

JP 2009-106480

  However, in the micro imaging imaging, the signal value of the magnetic resonance signal is larger than that in the normal imaging. Therefore, when a magnetic resonance signal collected by micro-imaging imaging is digitally converted by an AD (Analog Digital) converter, the dynamic range of the AD converter may be insufficient.

  In view of the above circumstances, an object of the present invention is to provide a magnetic resonance imaging apparatus capable of expanding a dynamic range when a subject is imaged with a receiving coil having a plurality of coil elements.

The magnetic resonance imaging apparatus of the present invention that solves the above problems
A plurality of coil elements that receive a magnetic resonance signal of a subject and generate an analog signal corresponding to the received magnetic resonance signal;
A switch that has a plurality of input terminals to which the analog signal is input and a plurality of output terminals that output the analog signal, and switches a connection between the plurality of input terminals and the plurality of output terminals;
A plurality of signal adjusting means provided corresponding to the plurality of output terminals of the switch, and amplifying or attenuating analog signals output from the plurality of output terminals;
A plurality of AD conversion means provided corresponding to the plurality of signal adjustment means, for converting analog signals output from the plurality of signal adjustment means into digital signals;
Setting means for setting the amplification amount or attenuation amount of the analog signal in the plurality of signal adjustment means;
Reconstructing means for reconstructing an image based on the digital signal;
A magnetic resonance imaging apparatus comprising:
The switch is
The plurality of analog signals input to the first input terminal of the plurality of input terminals are output from the first output terminal and the second output terminal of the plurality of output terminals. Switch the connection between the input terminal and the plurality of output terminals,
The setting means includes
Of the plurality of signal adjustment means, the amount of amplification or attenuation in the first signal adjustment means provided corresponding to the first output terminal, and the second output of the plurality of signal adjustment means. The amplification amount or attenuation amount in the second signal adjustment means provided corresponding to the terminal is set to a different value.

  In the present invention, the switch outputs an analog signal input to a first input terminal of the plurality of input terminals from a first output terminal and a second output terminal of the plurality of output terminals. As described above, the connection between the plurality of input terminals and the plurality of output terminals is switched. Therefore, even if it has a plurality of coil elements, the dynamic range can be expanded.

1 is a schematic diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention. 3 is a schematic diagram of a receiving coil 4. FIG. It is a figure which shows the connection relation of the receiving coil 4, the switch 8, and the receivers 91-98. 3 is a diagram illustrating an example of a connection pattern of a switch 8. FIG. 3 is a diagram illustrating an example of a connection pattern of a switch 8. FIG. It is a figure explaining the process of the analog signal 41a input into the receiver 91. FIG. It is a figure explaining the process of the analog signal 41a input into the two receivers 91 and 92. FIG.

  Hereinafter, although one embodiment of the present invention is described, the present invention is not limited to the following embodiment.

FIG. 1 is a schematic view of a magnetic resonance imaging apparatus according to an embodiment of the present invention.
A magnetic resonance imaging apparatus (MRI apparatus, MRI: Magnetic Resonance Imaging) 1 includes a magnetic field generator 2, a table 3, a receiving coil 4, and the like.

  The magnetic field generator 2 includes a bore 21 in which the subject 13 is accommodated, a superconducting coil 22, a gradient coil 23, and a transmission coil 24. The superconducting coil 22 forms a static magnetic field B0, the gradient coil 23 applies a gradient pulse, and the transmission coil 24 transmits an RF pulse.

  The table 3 has a cradle 31 for transporting the subject 13. The subject 13 is transported to the bore 21 by the cradle 31.

The receiving coil 4 is a multichannel coil.
FIG. 2 is a schematic diagram of the receiving coil 4.
The receiving coil 4 has a plurality of coil elements. In the present embodiment, the receiving coil 4 has eight coil elements 41 to 48. The reception coil 4 is attached to the abdomen 13 a of the subject 13. The coil elements 41 to 48 receive magnetic resonance signals from the abdomen 13a and generate analog signals 41a to 48a corresponding to the received magnetic resonance signals.

  The MRI apparatus 1 further includes a sequencer 5, a transmitter 6, a gradient magnetic field power supply 7, a switch 8, receivers 91 to 98, a central processing unit 10, an input device 11, and a display device 12.

  Under the control of the central processing unit 10, the sequencer 5 sends RF pulse information (center frequency, bandwidth, etc.) to the transmitter 6, and gradient magnetic field information (gradient magnetic field strength, etc.) to the gradient magnetic field power supply 7. send.

  The transmitter 6 drives the transmission coil 24 based on the information sent from the sequencer 5.

  The gradient magnetic field power source 7 drives the gradient coil 23 based on the information sent from the sequencer 5.

  The switch 8 switches the connection between the coil elements 41 to 48 of the reception coil 4 and the receivers 91 to 98. The specific configuration and operation of the switch 8 will be described later (see FIG. 3).

  The receivers 91 to 98 receive the magnetic resonance signal received by the receiving coil 4 via the switch 8, perform predetermined signal processing, and transmit the signal to the central processing unit 10. In this embodiment, eight receivers 91 to 98 are provided. In FIG. 1, only three receivers 91, 97, and 98 are shown for convenience of explanation.

  The central processing unit 10 summarizes the operations of each unit of the MRI apparatus 1 so as to realize various operations of the MRI apparatus 1 such as reconstructing an image based on signals received from the receivers 91 to 98. Further, the central processing unit 10 designates the control signal 10a for controlling the switching operation of the switch 8 and the attenuation amount Rg (dB: decibel) of the attenuator ATT (see FIG. 3) provided in the receivers 91 to 98. An attenuation amount designation signal 10b is generated. The central processing unit 10 is configured by, for example, a computer. The central processing unit 10 is an example of a setting unit and a reconfiguration unit in the present invention, and functions as these units by executing a predetermined program.

The input device 11 inputs various commands to the central processing unit 10 according to the operation of the operator 14. The display device 12 displays various information.
The MRI apparatus 1 is configured as described above.

Next, the receiving coil 4, the switch 8, and the receivers 91 to 98 will be described.
FIG. 3 is a diagram illustrating a connection relationship between the reception coil 4, the switch 8, and the receivers 91 to 98. As illustrated in FIG.

  The switch 8 has eight input terminals INi (i = 1 to 8) and eight output terminals OUTi (i = 1 to 8). In response to the control signal 10a from the central processing unit 10, the switch 8 has eight input terminals INi (i = 1 to 8) and eight output terminals OUTi (i = 1 to 8). Switch the connection with.

  Each of the receivers 91 to 98 includes an attenuator (signal adjusting means) ATT for attenuating an analog signal output from the output terminal of the switch 8, and an AD converter ADC for converting the analog signal output from the attenuator ATT into a digital signal. And have. The attenuation amount when the attenuator ATT attenuates the analog signal is determined by the attenuation amount designation signal 10b from the central processing unit 10.

4 and 5 are diagrams showing some examples of connection patterns of the switch 8. FIG.
4 and 5 show connection patterns of the switch 8 when the magnetic resonance signals are received by the coil elements 41, 43, 45, and 47. FIG.

  In the case of shooting where a wide dynamic range is not required for the AD converter ADC, the connection pattern shown in FIG. 4 is obtained. In FIG. 4, input terminals IN1, IN3, IN5, and IN7 are connected to output terminals OUT1, OUT3, OUT5, and OUT7, respectively. Therefore, analog signals 41a, 43a, 45a, and 47a from coil elements 41, 43, 45, and 47 are supplied to receivers 91, 93, 95, and 97, respectively.

  On the other hand, when a wide dynamic range is required for the AD converter ADC, such as for micro-imaging imaging, the connection pattern shown in FIG. 5 is switched. Input terminals IN1, IN3, IN5, and IN7 are each connected to two output terminals. For example, the input terminal IN1 is connected to the two output terminals OUT1 and OUT2. Therefore, the analog signal 41 a from the coil element 41 is supplied to the two receivers 91 and 92. Similarly, the analog signals 43a, 45a and 47a of the other coil elements 43, 45 and 47 are also supplied to the two receivers.

  Next, the operation of the switch 8 and the receivers 91 to 98 when the AD converter ADC does not require a wide dynamic range, and the switch 8 when the AD converter ADC requires a wide dynamic range. Operations of the receivers 91 to 98 will be described in order. In the following description, a case where a magnetic resonance signal is received using four coil elements 41, 43, 45, and 47 among the coil elements 41 to 48 will be described.

(1) Operation of the switch 8 and the receiver when the AD converter does not require a wide dynamic range When the AD converter does not require a wide dynamic range, the switch 8 is connected as shown in FIG. Become a pattern. Therefore, the analog signals 41a, 43a, 45a, and 47a of the coil elements 41, 43, 45, and 47 are input to the receiver, respectively.

  Next, how the analog signals 41a, 43a, 45a, and 47a input to the receivers 91, 93, 95, and 97 are processed will be described. Note that the analog signals 41a, 43a, 45a, and 47a input to the receivers 91, 93, 95, and 97 are processed in the same manner for any analog signal. The analog signal 41a input to 91 will be described (see FIG. 6).

  FIG. 6 is a diagram for explaining the processing of the analog signal 41 a input to the receiver 91.

  The attenuation amount Rg of the attenuator ATT of the receiver 91 is set to Rg = Rg1. A specific value of Rg1 is determined in advance according to the type of pulse sequence used when scanning the subject 13. The attenuator ATT attenuates the analog signal 41a input to the receiver 91 by the attenuation amount Rg1. The analog signal 41b attenuated by the attenuator ATT is converted into a digital signal 41c by the AD converter ADC. The digital signal 41c is input to the central processing unit 10 and an image is reconstructed.

(2) Operation of the switch 8 and the receiver when the AD converter requires a wide dynamic range When the AD converter requires a wide dynamic range, the switch 8 is connected as shown in FIG. Become a pattern. Therefore, the analog signals 41a, 43a, 45a, and 47a of the coil elements 41, 43, 45, and 47 are input to the two receivers, respectively.

  Next, how the analog signals 41a, 43a, 45a, and 47a input to the two receivers are processed will be described. Note that the analog signals 41a, 43a, 45a, and 47a input to the two receivers are processed in the same manner for any analog signal. The input analog signal 41a will be described for explanation (see FIG. 7).

  FIG. 7 is a diagram for explaining the processing of the analog signal 41 a input to the two receivers 91 and 92.

The attenuation amount Rg of the attenuator ATT of one of the two receivers 91 and 92 is Rg = Rg1, as in FIG. However, the attenuation amount Rg of the attenuator ATT of the other receiver 92 is set to a value that is smaller than the dynamic range of the AD converter ADC of the receiver 91. Therefore, if the attenuation amount Rg of the attenuator ATT of the other receiver is Rg = Rg2, Rg2 can be expressed by the following equation.
Rg2 = Rg1-ΔRg (1)
Here, ΔRg: a value (dB) to be expanded beyond the dynamic range of the AD converter ADC of the receiver 91

  The attenuator ATT of the receiver 91 attenuates the analog signal 41a by the attenuation amount Rg1, and the attenuated analog signal 41b is converted into the digital signal 41c by the AD converter ADC. On the other hand, the attenuator ATT of the receiver 92 attenuates the analog signal 41a by the attenuation amount Rg2, and the attenuated analog signal 42b is converted into the digital signal 42c by the AD converter ADC. FIG. 7 schematically shows the waveform of the analog signal 41 b after being attenuated by the attenuator ATT of the receiver 91 and the waveform of the analog signal 42 b after being attenuated by the attenuator ATT of the receiver 92. .

  The signal range A of the analog signals 41b and 42b is a signal range corresponding to a region near the center of the k space, and the signal range B is a signal range corresponding to a region away from the center of the k space.

  Since the analog signal 41b input to the AD converter ADC of the receiver 91 falls within the dynamic range of the AD converter ADC, the analog signal is converted into a digital value corresponding to the analog value. However, in the signal range B, since the difference in analog value is small, the quantization error becomes large.

  On the other hand, the analog signal 42b input to the AD converter ADC of the receiver 92 has an attenuation amount smaller than the analog signal 41b by ΔRg, so that a part of the analog signal protrudes from the dynamic range of the AD converter ADC. . Therefore, all the protruding portions are converted into the same digital value. However, since the signal range B in the analog signal 42b can be made larger than the signal range B in the analog signal 41b, the quantization error is reduced.

  Digital signals 41 and 42 c are input to the central processing unit 10. When the analog signals 41b and 42b are compared, the attenuation amount Rg differs by ΔRg (see equation (1)), so the central processing unit 10 converts the digital value of the received digital signal 41c to a digital value corresponding to ΔRg. Increase by value. Thereby, the difference ΔRg in the attenuation amount in the analog signal can be canceled out. Thereafter, the central processing unit 10 embeds data in the k space based on these digital signals. A procedure for filling data in the k space will be described below.

  As shown in FIG. 7, in the case of the analog signal 42b in the receiver 92, in the signal range A, there is a portion that protrudes from the dynamic range, so the protruding portion is converted to the same digital value. However, since the signal range A is a signal range corresponding to a region near the center of the k space, sufficient contrast is obtained when the region near the center of the k space is filled with the digital signal 42c from the receiver 92. I can't. Therefore, when the region near the center of the k space is filled, the digital signal 41c in the receiver 91 is used. Since the analog signal 41b of the receiver 91 has a sufficiently large analog value in the signal range A, a sufficient contrast can be obtained by using the digital signal 41c output from the receiver 91. Therefore, for the signal range A, the digital signal 41c output from the receiver 91 is used to fill the k space.

However, since the analog signal 41b in the receiver 91 has a large quantization error in the signal range B, the digital signal 41c output from the receiver 91 is used to fill a region away from the center of the k space. And sufficient spatial resolution cannot be obtained. Therefore, when filling a region away from the center of the k space, the digital signal 42c output from the receiver 92 is used. The digital signal 42c of the receiver 92 has a smaller quantization error in the signal range B than that of the digital signal 41c of the receiver 91. Therefore, sufficient spatial resolution can be obtained by using the digital signal 42c of the receiver 92. Can do. Therefore, for the signal range B, the digital signal 42c output from the receiver 92 is used to fill the k space.
In this way, data can be filled in the k space.

  In this embodiment, when a wide dynamic range is required, the switch 8 switches to a connection pattern as shown in FIG. Therefore, each of the coil elements 41, 43, 45, and 47 is connected to two receivers. For this reason, even when a magnetic resonance signal is simultaneously received by a plurality of coil elements, the apparent dynamic range of the AD converter ADC can be expanded.

  When data is embedded in the k-space, error correction may be performed using a least square method or the like for the coupling portion between the digital signals 41c and 42c.

  Further, a curve representing the relationship between the attenuation set by the central processing unit 10 and the amount by which the analog signal is actually attenuated may be created in advance and stored in the memory of the central processing unit 10. By creating this curve, even if there is a deviation between the attenuation set by the central processing unit 10 and the actual attenuation of the analog signal, the digital signal is corrected in consideration of the deviation. be able to.

  In this embodiment, the receiving coil 4 has eight coil elements 4a to 4h. However, the number of coil elements necessary for the receiving coil 4 is not necessarily limited to eight. The invention is applicable when the receiving coil 4 has two or more coil elements.

  In this embodiment, the receivers 91 to 98 have the attenuator ATT, but may include amplifiers that amplify the analog signals 41a to 48a from the coil elements 41 to 48 instead of the attenuator ATT. .

DESCRIPTION OF SYMBOLS 1 MRI apparatus 2 Magnetic field generator 3 Table 4 Reception coil 5 Sequencer 6 Transmitter 7 Gradient magnetic field power supply 8 Switch 10 Central processing unit 11 Input apparatus 12 Display apparatus 13 Subject 14 Operator 21 Bore 22 Superconducting coil 23 Gradient coil 24 Transmitting coil 31 Cradle 41 to 48 Coil element 91 to 98 Receiver

Claims (5)

A plurality of coil elements that receive a magnetic resonance signal of a subject and generate an analog signal corresponding to the received magnetic resonance signal;
A switch that has a plurality of input terminals to which the analog signal is input and a plurality of output terminals that output the analog signal, and switches a connection between the plurality of input terminals and the plurality of output terminals;
A plurality of signal adjusting means provided corresponding to the plurality of output terminals of the switch, and amplifying or attenuating analog signals output from the plurality of output terminals;
A plurality of AD conversion means provided corresponding to the plurality of signal adjustment means, for converting analog signals output from the plurality of signal adjustment means into digital signals;
Setting means for setting the amplification amount or attenuation amount of the analog signal in the plurality of signal adjustment means;
Reconstructing means for reconstructing an image based on the digital signal;
A magnetic resonance imaging apparatus comprising:
The switch is
The plurality of analog signals input to the first input terminal of the plurality of input terminals are output from the first output terminal and the second output terminal of the plurality of output terminals. Switch the connection between the input terminal and the plurality of output terminals,
The setting means includes
Of the plurality of signal adjustment means, the amount of amplification or attenuation in the first signal adjustment means provided corresponding to the first output terminal, and the second output of the plurality of signal adjustment means. A magnetic resonance imaging apparatus that sets an amplification amount or an attenuation amount in a second signal adjustment means provided corresponding to a terminal to a different value. The switch is
When it is necessary to widen the dynamic range of the AD conversion means, an analog signal input to the first input terminal of the plurality of input terminals is connected to the first output terminal and the first output terminal of the plurality of output terminals. The connection between the plurality of input terminals and the plurality of output terminals is switched so as to be output from the two output terminals,
When there is no need to increase the dynamic range of the AD conversion means, the analog signal input to the first input terminal of the plurality of input terminals is output from the first output terminal of the plurality of output terminals. The magnetic resonance imaging apparatus according to claim 1, wherein connection between the plurality of input terminals and the plurality of output terminals is switched. The first AD means of the plurality of AD conversion means converts the first analog signal output from the first signal adjustment means into a first digital signal,
The second AD means of the plurality of AD conversion means converts the second analog signal output from the second signal adjustment means into a second digital signal,
The magnetic resonance imaging apparatus according to claim 1, wherein the reconstruction unit embeds data in k-space based on the first digital signal and the second digital signal.   A curve representing the relationship between the amplification amount or attenuation amount set by the setting means and the amplification amount or attenuation amount when the analog signal is actually amplified or attenuated is stored, and based on the curve, the first The magnetic resonance imaging apparatus according to claim 3, wherein the first digital signal or the second digital signal is corrected.   5. The magnetism according to claim 1, wherein each of some of the plurality of input terminals is connected to two output terminals of the plurality of output terminals. 6. Resonance imaging device.

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