JP5288693B2 - Magnetic resonance imaging apparatus and high-frequency coil unit - Google Patents

Description

  The present invention acquires a magnetic resonance signal generated by applying a gradient magnetic field and a high-frequency pulse to a subject in a static magnetic field, and uses the acquired magnetic resonance signal to reconstruct an image of the subject. The present invention relates to an imaging (MRI: Magnetic Resonance Imaging) apparatus and a high-frequency coil unit, and more particularly to a magnetic resonance imaging apparatus and a high-frequency coil unit having a plurality of surface coils for receiving a magnetic resonance signal.

  Conventionally, a magnetic resonance imaging apparatus is used as a monitoring apparatus in a medical field. The magnetic resonance imaging apparatus forms gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions with a gradient magnetic field coil in an imaging region of a subject set inside a cylindrical static magnetic field magnet that forms a static magnetic field, and RF. A radio frequency (RF) signal is transmitted from a (Radio Frequency) coil to magnetically resonate nuclear spins in the subject, and the subject is utilized using a nuclear magnetic resonance (NMR) signal generated by excitation. This is an apparatus for reconstructing the MR image.

  In this magnetic resonance imaging apparatus, a technique has been devised in which surface coils for receiving NMR signals are arranged in a region of interest of a plurality of subjects and imaged at a higher speed than before. This technique is also called parallel imaging.

  FIG. 15 is a diagram illustrating an example in which a plurality of surface coils are arranged around the abdomen of a subject in parallel imaging using a conventional magnetic resonance imaging apparatus.

  As shown in FIG. 15, when imaging the entire abdomen of the subject P, usually, a plurality of surface coils 1 are arranged so as to surround the subject P, and the magnetic resonance imaging apparatus uses each surface coil 1. An NMR signal can be acquired from the entire abdomen. And the magnetic resonance imaging apparatus can acquire an image with sufficient sensitivity for every imaging region by arranging a plurality of surface coils 1 appropriately according to the imaging region. FIG. 15 is a diagram illustrating an example in which reception signals from six surface coils 1 are received by six reception channels 2.

  In parallel imaging, it is said that the data collection time can be shortened to one-th of the number of coils arranged in the encoding direction at the time of image data collection. When the axial cross section of the body part in FIG. 15 is imaged, if the encoding direction is the x direction, since the three surface coils are arranged, it can be said that the data collection time is about 1/3.

  Such parallel imaging technology has been further developed in recent years, and the number of surface coils and the number of reception channels of the system tend to increase more and more in order to enable faster imaging with less distortion. For example, at present, even a magnetic resonance imaging apparatus having a relatively small number of surface coil coils has been commercialized with 4 reception channels and a maximum of 32 channels.

  However, on the other hand, since it is necessary to arrange a surface coil for each imaging region, there is a problem that the number of surface coils increases. Further, every time the subject or the imaging region changes, the user needs to replace the surface coil corresponding to the imaging region. For this reason, it is necessary for the user to prepare a large number of dedicated surface coils corresponding to the imaging region, and the replacement of the surface coils is a very troublesome operation for users such as doctors and technicians in the field.

  In general, in a magnetic resonance imaging apparatus, the number of reception channels needs to be able to correspond to the maximum number of coils when the most surface coils are used in the imaging region. Therefore, if the number of reception coils of the magnetic resonance imaging apparatus is small even if there are only a large number of surface coils, the number of surface coils that can be used simultaneously is limited, and signals from a wide area of the subject body part are transmitted by each surface coil. There is a problem that it cannot be covered.

  Therefore, a magnetic circuit is configured so that a combination of surface coils used for reception can be mode-selected by providing a switch circuit and a synthesis circuit (Matrix) for a plurality of surface coils arranged in the X-axis direction perpendicular to the body axis of the subject. A resonance imaging apparatus has been proposed (see, for example, Patent Document 1). In a magnetic resonance imaging apparatus provided with this switch circuit and synthesis circuit, parallel imaging with fewer channels than the number of surface coils is achieved by synthesizing received signals from an appropriate number of surface coils by selecting the surface coil mode. Is possible. Patent Document 1 proposes a switch circuit that can output a reception signal received by a maximum of eight surface coils as a single reception signal.

  FIG. 16 is a conceptual diagram showing an example in which reception signals from a plurality of surface coils can be synthesized by a synthesis / switch circuit in parallel imaging by a conventional magnetic resonance imaging apparatus.

  As shown in FIG. 16, when the six surface coils 1 are arranged around the abdomen of the subject P, two synthesis circuits 3 are provided. Then, if each of the combining circuits 3 is configured so that reception signals from three different surface coils 1 can be combined and output as one reception signal, the reception signals from the six surface coils 1 are converted into two reception channels 2. Can be received.

  Further, a distribution / combination circuit may be provided to synthesize a plurality of types of reception signals from the respective surface coils so that the reception signals can be mode-selected (for example, see Non-Patent Document 1).

  FIG. 17 is a diagram showing sensitivity distributions of three surface coils of interest among six surface coils arranged around the abdomen of the subject in parallel imaging using a conventional magnetic resonance imaging apparatus, and FIG. FIG. 18 is a circuit configuration diagram of a distribution / synthesis circuit for synthesizing received signals from a surface coil of interest in the conventional magnetic resonance imaging apparatus shown in FIG. 17.

  A plurality of modes for synthesizing received signals from the three surface coils L, M, and R having the sensitivity distribution 4 as shown in FIG. 17 can be set. For example, as shown in FIG. 18, the distribution / synthesis circuit 5 is configured using a 0 ° -180 ° hybrid circuit 6 and a 0 ° -90 ° hybrid circuit 7. A signal obtained by synthesizing two input signals is output from the 0 ° output side of the 0 ° -180 ° hybrid circuit 6, and the phases of the two input signals are shifted from each other by 180 ° from the 180 ° output side. A composite signal is output. The 0 ° -90 ° hybrid circuit 7 outputs a signal obtained by synthesizing two input signals from the 0 ° output side, and the 90 ° output side shifts the phases of the two input signals by 90 °. A synthesized signal of the processed signals is output.

  Specifically, a 0 ° -180 ° hybrid circuit 6 is provided on the output side of the surface coil L and the surface coil R, and 0 ° is provided on the 180 ° output side of the 0 ° -180 ° hybrid circuit 6 and the output side of the surface coil M. A -90 ° hybrid circuit 7 is provided. Further, the signal output from the 0 ° output side channel of the 0 ° -180 ° hybrid circuit 6 is the signal B, and the signal output from the 0 ° output side channel of the 0 ° -90 ° hybrid circuit 7 is the signal C, A signal output from the 90 ° output side channel of the 0 ° -90 ° hybrid circuit 7 is a signal A.

  Then, the signal B is a signal obtained by synthesizing (adding) the reception signal from the surface coil L and the reception signal from the surface coil R. The signal A corresponds to a received signal from a so-called QD (quadrature detection) surface coil in which the surface coil M is arranged as a loop type surface coil on the 8-shaped surface coil composed of the surface coil L and the surface coil R. QD signal. Further, the signal C becomes an Anti-QD signal corresponding to a signal obtained by canceling the QD signal.

  In the QD surface coil, it is known that the signal to noise ratio (SNR) can be improved by taking the sum of the received signal from the loop type surface coil and the received signal from the 8-shaped surface coil by shifting the phase by 90 °. ing. Therefore, a 0 ° -90 ° hybrid circuit is used for synthesizing the signal from the surface coil M corresponding to the loop type surface coil and the surface coil L forming the 8-shaped surface coil and the 180 ° shift composite signal of the surface coil R. 7 is used.

  19 is a diagram showing a sensitivity distribution 4 formed by the surface coils L, M, and R when the output signal A from the conventional distribution / synthesis circuit 5 shown in FIG. 18 is selected as a reception signal. FIG. 21 is a diagram showing a sensitivity distribution 4 formed by the surface coils L, M, and R when the mode is selected using the output signal C from the conventional distribution / synthesis circuit 5 shown in FIG. 18 as a reception signal. It is a figure which shows the sensitivity distribution 4 formed by each surface coil L, M, R when the output signal B from the conventional distribution / synthesis circuit 5 shown in FIG.

  As shown in FIGS. 19, 20, and 21, if a mode can be selected by synthesizing reception signals from the surface coils L, M, and R, a combination of common surface coils L, M, and R A plurality of different sensitivity regions 4 can be formed without replacing the surface coils L, M, and R. For this reason, three image patterns reconstructed by each received signal can be obtained. In addition, a reception signal used for imaging can be selected according to the number of reception channels provided in the reception system of the magnetic resonance imaging apparatus.

  For example, when six surface coils 1 are provided as shown in FIG. 17, the three surface coils 1 facing the three surface coils L, M, and R are similar to the distribution / synthesis circuit 5 shown in FIG. A distribution / synthesis circuit is provided. If the output signals corresponding to the signals A, B, and C are the signal A ′, the signal B ′, and the signal C ′, the signal A and the signal A when the number of reception channels provided in the reception system is two channels. A ′ can be selected as the received signal. Since the QD signal has a wide sensitivity region, it is possible to image a wide region even if there are only two reception channels.

  Further, when the number of reception channels provided in the reception system is 4, the signals A, B, A ′, and B ′ are received. When the number of reception channels is 6, the signals A, B, Signal C, signal A ′, signal B ′, and signal C ′ can be used for imaging as received signals. In this way, the imaging speed can be increased according to the number of reception channels.

As described above, in recent magnetic resonance imaging apparatuses, the reception signals from the respective surface coils are used so that parallel imaging can be performed even if there is a relationship of N ≧ M between the reception channel number M and the coil number N of the surface coil. A switch circuit for selecting or synthesizing is provided.
JP 2003-334177 A "Mode Matrix-A Generalized Signal Combiner For Parallel Imaging Arrays" A. Reykowski, M. Blasche, 2004 Proceedings On CD-ROM, International Society for Magnetic Resonance in Medicine, Twelfth scientific meeting, Kyoto, Japan 15-21 May 2004, pp1587 .

  However, when the number of surface coils is further increased in the conventional magnetic resonance imaging apparatus, the circuit configuration of the switch circuit becomes complicated and the circuit board increases when the switch circuit performs everything from selection of received signals to synthesis. Problems such as an increase in power consumption and difficulty in ensuring quality arise.

  In recent years, a magnetic resonance imaging apparatus has been devised in which a large number of surface coils are arranged not only in the XY plane direction perpendicular to the body axis of the subject but also in the body axis direction so that a wider range of imaging can be performed. . In such a magnetic resonance imaging apparatus, if the number of reception channels in the body axis direction is small, signals from a wide region of the subject body cannot be covered even though there are many surface coils. On the other hand, if the received signal in the body axis direction is selected by the switch circuit, there is a problem that the circuit becomes complicated as described above as the number of surface coils increases.

  The present invention has been made to cope with such a conventional situation. Even when the number of surface coils is increased and arranged in the body axis direction, less reception is achieved without complicating the circuit configuration. An object of the present invention is to provide a magnetic resonance imaging apparatus and a high-frequency coil unit capable of realizing a wide imaging region with a channel.

In order to achieve the above object, a high-frequency coil unit according to the present invention distributes a plurality of surface coils arranged in the body axis direction of a subject and received signals from the plurality of surface coils in the body axis direction. Distributing and synthesizing means for generating a new received signal by synthesizing , wherein the plurality of surface coils include a first surface coil, a second surface coil, a third surface coil, and a fourth surface coil. The distribution synthesis means includes a first 0 ° -180 ° hybrid circuit provided on the output side of the first surface coil and the second surface coil, the third surface coil, and the fourth surface coil. The second 0 ° -180 ° hybrid circuit provided on the output side of the first, the 0 ° output side of the first 0 ° -180 ° hybrid circuit, and the 0 ° output of the second 0 ° -180 ° hybrid circuit On the side Provided on the 180 ° output side of the first 0 ° -180 ° hybrid circuit and the 180 ° output side of the second 0 ° -180 ° hybrid circuit. And a fourth 0 ° -180 ° hybrid circuit .

  In the magnetic resonance imaging apparatus and the high-frequency coil unit according to the present invention, even if the number of surface coils is increased and arranged in the body axis direction, it is wide with fewer receiving channels without complicating the circuit configuration. An imaging area can be realized.

  Embodiments of a magnetic resonance imaging apparatus and a high-frequency coil unit according to the present invention will be described with reference to the accompanying drawings.

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

  The magnetic resonance imaging apparatus 10 includes a gantry 11 and a control system 12. The gantry 11 is configured by providing a cylindrical gradient magnetic field coil unit 14 and a cylindrical transmission high-frequency coil 15 coaxially inside a cylindrical static magnetic field magnet 13. A bed 16 is provided inside the transmission high-frequency coil 15, and the subject P is set on the bed 16. In addition, a receiving high-frequency coil 17 is provided in the imaging region of the subject P. The control system 12 includes a gradient coil drive circuit 18, a transmission unit 19, a reception unit 20, a data collection unit 21, a computer 22, a console 23, a display 24, a synthesis / switch circuit 25, and a sequence controller 26. A high frequency coil unit can also be formed by unitizing all or part of the synthesis / switch circuit 25 as a part of the reception high frequency coil 17.

  The static magnetic field magnet 13 has a function of uniformly applying a static magnetic field to the subject P set in the imaging region. The gradient magnetic field coil unit 14 includes an X-axis direction gradient magnetic field coil, a Y-axis direction gradient magnetic field coil, and a Z-axis direction gradient magnetic field coil (not shown), and in accordance with a drive signal from the gradient magnetic field coil drive circuit 18, respectively. , Has a function of forming gradient magnetic fields Gx, Gy, Gz whose magnetic field intensity linearly changes in the Z-axis direction in the imaging region. The transmission high-frequency coil 15 has a function of transmitting a high-frequency signal to the subject P arranged in the imaging region in accordance with the high-frequency pulse received from the transmission unit 19.

  The reception high-frequency coil 17 includes a plurality of surface coils, a function of receiving a magnetic resonance signal generated by a high-frequency signal applied from the transmission high-frequency coil 15 into the subject P, and an electric signal of the received magnetic resonance signal. As a function of outputting to the synthesis / switch circuit 25. The synthesizing / switching circuit 25 has a function of inputting a reception signal from each surface coil of the reception high-frequency coil 17, synthesizing and selecting the input reception signal, and giving the output signal to the reception unit 20 as a reception signal.

  The gradient coil driving circuit 18 drives the X axis direction gradient coil, the Y axis direction gradient coil, and the Z axis direction gradient coil of the gradient coil unit 14 according to a control signal (sequence) received from the sequence controller 26. And a desired gradient magnetic field Gx, Gy, Gz is formed in the imaging region.

  The transmission unit 19 has a function of applying a high frequency signal toward the subject P by applying a high frequency pulse to the transmission high frequency coil 15 in accordance with a control signal (sequence) received from the sequence controller 26. The receiving unit 20 has a plurality of receiving channels, and a function to amplify and detect the received signal received from the synthesis / switch circuit 25 through each receiving channel and then give it to the data collecting unit 21 under the control of the sequence controller 26 Have

  The data collection unit 21 has a function of collecting a magnetic resonance signal received as a reception signal from the reception unit 20 via each reception channel under the control of the sequence controller 26, performing A / D conversion, and then supplying the magnetic resonance signal to the computer 22. . The computer 22 is controlled by a control signal from the console 23, performs an image reconstruction process on the magnetic resonance signal acquired from the data collection unit 21, and generates the image data of the subject P. The generated image data is displayed on the display 24. It has the function to display by giving to.

  FIG. 2 is a configuration diagram of the reception high-frequency coil 17 and the synthesis / switch circuit 25 of the magnetic resonance imaging apparatus 10 shown in FIG.

  As shown in FIG. 2, the reception high-frequency coil 17 includes a plurality of surface coils 30. A desired number N of surface coils 30 are arranged at desired positions in the body axis direction of the subject P and in the direction perpendicular to the body axis. At this time, at least two surface coils 30 shifted from each other in the body axis direction of the subject P are provided. Normally, the body axis direction of the subject P is the Z axis.

  The synthesis / switch circuit 25 can be configured by connecting a distribution / synthesis circuit 31 and a switch circuit 32. The distribution / combination circuit 31 receives N reception signals from the N surface coils 30 and generates and generates N reception signals by distributing and combining the received signals. A function of outputting the received signals to the switch circuit 32. That is, the synthesis / switch circuit 25 has a function of generating a desired reception signal from the reception signals from the surface coils 30 according to an arbitrary method. The composition / switch circuit 25 is configured by a passive circuit that does not require a drive power supply, thereby saving power. Further, if the distribution / synthesis characteristics of the distribution / synthesis circuit 31 are configured to be represented by an N × N matrix having a determinant whose value is not 0, that is, represented by a matrix having an inverse matrix, The received signal from each surface coil 30 can be effectively used without being discarded.

  The switch circuit 32 selects M reception signals satisfying N ≧ M from the N reception signals received from the distribution / combination circuit 31, and selects the M reception signals of the M channels provided in the reception unit 20. It has a function of outputting to the receiver 33. That is, the switch circuit 32 has a function of selectively switching the N received signals received from the distribution / combination circuit 31 in a modal manner in accordance with the number M of reception channels in the reception unit 20.

  Accordingly, the circuit configuration of the distribution / synthesis circuit 31 is determined depending on the number N and the arrangement of the surface coils 30. On the other hand, the switch circuit 32 can be arbitrarily designed so that M received signals can be selected. Therefore, if a high-frequency coil unit is formed by the plurality of surface coils 30 and the corresponding distribution / combination circuit 31, a high-frequency coil unit with a desired number of coils N can be easily replaced according to the purpose of diagnosis. . Further, if the distribution / synthesis circuit 31 is configured by a passive circuit that does not require a driving power supply, the circuit configuration of the high-frequency coil unit can be simplified.

  FIG. 3 is a diagram illustrating a configuration example of the distribution / combination circuit 31 illustrated in FIG. 2.

  As shown in FIG. 3, the distribution / synthesis circuit 31 can be configured by a 0 ° -180 ° hybrid circuit 40 which is an example of a passive circuit. FIG. 3 shows a case where the number of surface coils 30 is N = 2, and a 0 ° -180 ° hybrid circuit 40 is provided on the output side of the two surface coils C1, C2 shifted in the body axis direction of the subject P. Then, from the 0 ° side of the 0 ° -180 ° hybrid circuit 40, a signal A1 obtained by adding the reception signals from the surface coils C1 and C2 is output as a reception signal. Further, from the 180 ° side of the 0 ° -180 ° hybrid circuit 40, the received signal from the surface coils C1 and C2 is shifted by 180 ° from each other, and then added to obtain a signal A2 obtained as a received signal. The

  FIG. 4 is a diagram showing sensitivity distributions formed by the surface coils C1 and C2 when the mode selection is performed using the output signal A1 from the 0 ° side of the 0 ° -180 ° hybrid circuit 40 shown in FIG. FIG. 5 is a diagram showing a sensitivity distribution formed by the surface coils C1 and C2 when the mode selection is performed using the output signal A2 from the 180 ° side of the 0 ° -180 ° hybrid circuit 40 shown in FIG. 3 as a reception signal. is there.

  As shown in FIGS. 4 and 5, the surface coils C1, C2 can be selected by synthesizing received signals from the two surface coils C1, C2 using the 0 ° -180 ° hybrid circuit 40 so that the modes can be selected. It is possible to form two sensitivity regions 50 without replacing. As a result, the reception signal used for imaging can be selected according to the number of reception channels provided in the reception unit 20 of the magnetic resonance imaging apparatus 10. Moreover, since the surface coil 30 for acquiring two types of received signals can be shared, an increase in the number of surface coils can be suppressed.

  However, the number of surface coils 30 is not limited to two, and an arbitrary number N of surface coils 30 corresponding to the diagnosis can be arranged around the subject P. Therefore, as described above, the distribution / synthesis circuit 31 also has a circuit configuration corresponding to the number N of the surface coils 30.

  FIG. 6 is a diagram showing an example in which four surface coils 30 are arranged on the back surface of the subject P as the receiving high-frequency coil 17 of the magnetic resonance imaging apparatus 10 shown in FIG.

  As shown in FIG. 6, if four surface coils C11, C12, C13, and C14 are arranged on the back surface of the subject P in the body axis direction, reception data useful for diagnosis can be collected in the imaging region. FIG. 6 shows an example in which four surface coils C11, C12, C13, C14 are arranged on the back surface of the subject P. However, the surface P is not limited to the back surface of the subject P, and four or more surface coils 30 are provided on the subject P. In many cases, it is possible to collect received data suitable for diagnosis if it is arranged around the.

  FIG. 7 is a diagram showing a configuration example of the distribution / synthesis circuit 31 when four surface coils C11, C12, C13, and C14 are used as the reception high-frequency coil 17 of the magnetic resonance imaging apparatus 10 shown in FIG.

  As shown in FIG. 7, when the four surface coils C11, C12, C13, and C14 are used as the reception high-frequency coil 17, the distribution / synthesis circuit 31 is configured by using four 0 ° -180 ° hybrid circuits 40. can do. That is, a common (first) 0 ° -180 ° hybrid circuit 40 is provided on the output side of the surface coil C11 and the surface coil C12. Also, a common (second) 0 ° -180 ° hybrid circuit 40 is provided on the output side of the surface coil C13 and the surface coil C14.

  Next, the 0 ° -180 ° hybrid provided on the output side of the 0 ° -180 ° hybrid circuit 40 provided on the output side of the surface coil C11 and the surface coil C12, and the 0 ° -180 ° hybrid provided on the output side of the surface coil C13 and the surface coil C14. A common (third) 0 ° -180 ° hybrid circuit 40 is provided on the 0 ° output side of the circuit 40. Also, the 180 ° output side of the 0 ° -180 ° hybrid circuit 40 provided on the output side of the surface coil C11 and the surface coil C12, and the 0 ° -180 ° hybrid circuit provided on the output side of the surface coil C13 and the surface coil C14. A common (fourth) 0 ° -180 ° hybrid circuit 40 is provided on the 40 ° 180 ° output side.

  The output signal from the 0 ° output side of the third 0 ° -180 ° hybrid circuit 40 is B1, the output signal from the 180 ° side is B2, and the 0 ° output of the fourth 0 ° -180 ° hybrid circuit 40 is 0. The output signal from the side is B3, and the output signal from the 180 ° side is B4. If it does so, it will become possible to form a different sensitivity field 50 by four modes using four surface coils C11, C12, C13, and C14, and to obtain a received signal.

  FIG. 8 is a diagram showing a phase profile when the output signals B1, B2, B3, and B4 output from the distribution / combination circuit 31 shown in FIG. 7 are received signals. FIG. 9 is a diagram showing the distribution / composition shown in FIG. FIG. 10 is a diagram showing a sensitivity distribution formed by the surface coils C11, C12, C13, and C14 when the output signal B1 output from the synthesis circuit 31 is selected as a received signal, and FIG. 10 is a distribution / synthesis shown in FIG. FIG. 11 is a diagram showing a sensitivity distribution formed by the surface coils C11, C12, C13, and C14 when the output signal B2 output from the circuit 31 is selected as a reception signal, and FIG. 11 is a distribution / synthesis circuit shown in FIG. The sensitivity distribution formed by the surface coils C11, C12, C13, and C14 when the mode is selected with the output signal B3 output from 31 as the received signal. FIG. 12 shows sensitivity distributions formed by the surface coils C11, C12, C13, and C14 when the mode is selected with the output signal B4 output from the distribution / synthesis circuit 31 shown in FIG. 7 as a reception signal. FIG.

  As shown in FIGS. 8, 9, 10, 11, and 12, the received signals from the four surface coils C11, C12, C13, and C14 are divided into four 0 ° -180 ° hybrid circuits 40. By distributing and synthesizing by the synthesizing circuit 31, it is possible to switch the four sensitivity regions 50 that can be switched modally and to output each received signal to the receiving unit 20. For this reason, even when the number of coils N = 4 of the surface coil 30, the reception signal used for imaging is used according to the number M of reception channels provided in the receiver 20, as in the case of the number N = 2 of coils. Can be switched. Then, it is possible to reconstruct a large number of patterns using a smaller number of reception channels and surface coils 30.

  The arrangement of the plurality of surface coils 30 may be performed not only in the body axis direction but also in a direction perpendicular to the body axis (XY direction when the body axis is the Z-axis direction). Further, the distribution / combination of the received signals by the combining / distributing circuit may be performed on the received signals obtained from the plurality of surface coils 30 arranged in the direction perpendicular to the body axis.

  For example, the surface coil 30 for the head of the subject P can be configured by including a plurality of surface coil units configured by arranging three surface coils 30 in the XY direction when the body axis is the Z-axis direction. .

  FIG. 13 is a diagram illustrating an arrangement example of each surface coil 30 when a plurality of surface coils 30 are used for the head of the subject P as the reception high-frequency coil 17 of the magnetic resonance imaging apparatus 10 illustrated in FIG. 1. is there.

  As shown in FIG. 13, a pair of surface coil units 60 configured by arranging three surface coils CL, CM, and CR in the XY directions are arranged on the front side (Anterior) side and the rear side (Posterior) side of the subject P. Further, two pairs of the pair of surface coil units 60 are arranged by shifting in the body axis direction. In other words, the surface coil unit 60 is arranged in the body axis direction shifted to the front side and the back side of the subject P, respectively.

  A distribution / combination circuit 61 for the non-body axis direction is connected to the output side of each surface coil unit 60 constituted by three surface coils CL, CM, CR. Since each surface coil unit 60 has three outputs from the surface coils CL, CM, CR, the input channel and the output channel of the distribution / synthesis circuit 61 for the non-body axis direction are also set to 3. That is, the distribution / combination characteristics of the distribution / combination circuit 61 for the non-body axis direction can be represented by a 3 × 3 matrix.

  The non-body-axis direction distribution / synthesis circuit 61 is configured using a 0 ° -90 ° hybrid circuit and a 0 ° -180 ° hybrid circuit 40, for example, in the same manner as the conventional distribution / synthesis circuit 5 shown in FIG. be able to. If the distribution / synthesis circuit 61 for the non-body axis direction is configured in the same manner as the conventional distribution / synthesis circuit 5 shown in FIG. 18, the reception signals L, M, and R from the three surface coils CL, CM, and CR are 3 Two received signals A, B, and C are generated.

  In this case, the received signal A is a QD signal corresponding to a received signal from a QD surface coil in which a surface coil CM is arranged as a loop type surface coil on an 8-shaped surface coil composed of a surface coil CL and a surface coil CR. Become. Further, the reception signal B becomes a reception signal L + R obtained by adding the reception signal L from the surface coil CL and the reception signal R from the surface coil CR, and the reception signal C becomes an Anti-QD signal obtained by canceling the QD signal. However, the non-body axis direction distribution / combination circuit 61 may have a circuit configuration other than the circuit configuration shown in FIG.

  The four surfaces provided in the body axis direction (Z-axis direction) on the front side and the rear side of the subject P head by the signal distribution / synthesis operation of the non-body axis direction distribution / synthesis circuit 61. Twelve received signals are generated from the twelve received signals output from the coil unit 60. Here, the reception signals A, B, and C output from the two non-body-axis direction distribution / combination circuits 61 on the front side of the head are the reception signals AA, AB, and AC, respectively. The reception signals A, B, and C output from the non-body axis direction distribution / synthesis circuit 61 are referred to as reception signals PA, PB, and PC, respectively.

  On the output side of the distribution / synthesis circuit 61 for the non-body axis direction, a distribution / synthesis circuit 31 for distributing and synthesizing received signals from the surface coils CL, CM, and CR further shifted in the body axis direction is provided. . This distribution / combination circuit 31 can be configured using, for example, a 0 ° -180 ° hybrid circuit 40. FIG. 13 shows an example in which the received signals from the surface coils CL, CM, CR shifted in the body axis direction are individually input to the six 0 ° -180 ° hybrid circuits 40, respectively.

  That is, the two received signals AA obtained by the non-body axis direction distribution / synthesis circuit 61 from the surface coils CL, CM, CR shifted in the body axis direction are input to the common 0 ° -180 ° hybrid circuit 40. Is done. Similarly, the two received signals AB, AC, PA, PB, and PC are also input to the common 0 ° -180 ° hybrid circuit 40, respectively. Then, the 0 ° side outputs of the respective 0 ° -180 ° hybrid circuits 40 are received signals AA0, AB0, AC0, PA0 obtained by adding two received signals AA, AB, AC, PA, PB, PC, respectively. PB0 and PC0. In addition, the 180 ° -side outputs of the respective 0 ° -180 ° hybrid circuits 40 are received signals obtained by adding the two received signals AA, AB, AC, PA, PB, and PC after shifting the phase by 180 °. AA1, AB1, AC1, PA1, PB1, and PC1.

  As a result, twelve received signals obtained by forming the sensitivity areas 50 having different patterns that can be switched modally from the twelve surface coils 30 are generated. A switch circuit 32 is provided on the output side of the reception signal generated by the distribution / synthesis circuit 61 and the distribution / synthesis circuit 31 for the non-body axis direction. In the switch circuit 32, an arbitrary received signal can be selectively switched from the twelve received signals and provided to the receiving unit 20 at the subsequent stage.

  Therefore, for example, when the number M of reception channels provided in the reception unit 20 is 4, the reception signals AA0, AB0, PA0, and PB0 can be selected as reception signals. Further, when the number M of reception channels is 8, the reception signals AA0, AA1, AB0, AB1, PA0, PA1, PB0, and PB1 are reception signals. When the reception channel number M is 12, all reception signals AA0 , AA1, AB0, AB1, AC0, AC1, PA0, PA1, PB0, PB1, PC0, and PC1 can be selected as received signals, respectively. That is, when the number M of reception channels is large, the magnetic resonance imaging apparatus 10 can be configured so that faster parallel imaging can be performed.

  In the example of FIG. 13, the received signal from the surface coil 30 shifted in the direction perpendicular to the body axis is distributed and synthesized by the distribution / combination circuit 61 for the non-body axis direction, and then the surface coil shifted in the body axis direction. The distribution / synthesis circuit 31 is configured to distribute and synthesize the reception signal corresponding to the reception signal from 30, but conversely, the distribution / synthesis circuit 31 receives the reception signal from the surface coil 30 shifted in the body axis direction. After distribution / combination, the distribution / combination circuit 61 for non-body axis direction may be configured to distribute / combine reception signals corresponding to reception signals from the surface coil 30 shifted in the direction perpendicular to the body axis. Good. In other words, the non-body axis direction distribution / synthesis circuit 61 may be provided on the output side of the distribution / synthesis circuit 31.

  Further, as in the example of FIG. 13, distribution and synthesis of reception signals in the body axis direction do not have to be performed on all the surface coils 30 arranged in the non-body axis direction. That is, in the example of FIG. 13, the received signals AA0, AA1, AB0, AB1, AC0, AC1 from the surface coil 30 arranged on the front (Anterior) side are targeted for distribution and synthesis, and on the rear (Posterior) side. Reception signals PA0, PA1, PB0, PB1, PC0, and PC1 from the arranged surface coil 30 are subject to another distribution and synthesis.

  Thus, only the received signals from a part of the surface coil 30 arranged in the non-body axis direction according to the diagnostic purpose can be targeted for distribution and synthesis. Therefore, only the reception signal from the front side coil 30 or the rear side coil 30 may be subject to distribution and synthesis. Conversely, distribution synthesis may be performed between the reception signals from the front and rear surface coils 30. Further, when a large number of surface coils 30 are arranged in the non-body axis direction, a plurality of groups of reception signals to be distributed may be formed.

  Incidentally, as described above, the received signals from the surface coils 30 can be distributed / combined in the distribution / combination circuit 31, but each of the surface coils 30 or any part thereof can be used individually. There may be cases where it is important to image a narrow area with high sensitivity. Therefore, a switch is provided on the output side of each surface coil 30, and the output destination of each surface coil 30 is routed to the receiving unit 20 via the distribution / combination circuit 31 without passing through the distribution / combination circuit 31. It can be configured to be able to switch to a route toward the receiving unit 20.

  FIG. 14 is a diagram showing an example in which four surface coils 30 are provided as the receiving high-frequency coil 17 of the magnetic resonance imaging apparatus 10 shown in FIG. 1, and switches are provided on the output side of each surface coil 30.

  As shown in FIG. 14, a switch 70 is provided on the output side of the surface coils C 11, C 12, C 13, C 14, a path for guiding the received signal to the distribution / synthesis circuit 31, and a switch circuit without going through the distribution / synthesis circuit 31. 32 and a route leading to the receiving unit 20 can be selected. Also, a switch 71 is provided on the input side of the switch circuit 32 in the subsequent stage, the path of the received signal guided to the switch circuit 32 via the distribution / combination circuit 31, and the switch circuit without passing through the distribution / synthesis circuit 31. The path of the received signal led to 32 can be selected. With this configuration, the surface coil 30 can be used alone by switching the switch 70, or parallel imaging can be performed using a plurality of surface coils 30.

  Next, the operation and action of the magnetic resonance imaging apparatus 10 will be described.

  First, the surface coil 30 necessary for diagnosis is arranged in advance at a predetermined position. The surface coil 30 can be arranged even if the number of coils N is equal to or greater than the number M of reception channels in the reception unit 20. For example, if more C11, C12, C13, C14 for the fuselage shown in FIG. 6 and surface coils CL, CM, CR for the head shown in FIG. 30 replacement work can be reduced.

  Next, the subject P is set on the bed 16, and the static magnetic field is uniformly applied to the subject P set in the imaging region by the static magnetic field magnet 13. Further, a sequence defining a predetermined scanning condition is read from the storage device in the computer 22 to the sequence controller 26 by operating the console 23. At this time, the surface coil 30 used for scanning is determined according to the sequence set by the user, and the sensitivity region 50 formed by the surface coil 30 and the mode of the received signal used for imaging are selected. The mode selected is preferentially and selectively received from the sensitivity region 50, which is more important for diagnosis, according to the magnitude relationship between the number M of reception channels of the receiving unit 20 and the number N of coils of the surface coil 30. An appropriate mode as received by the unit 20 is set.

  Then, the sequence controller 26 gives control signals to the gradient coil drive circuit 18, the transmission unit 19, the reception unit 20, and the data collection unit 21 according to the read sequence. Then, the gradient magnetic field coil drive circuit 18 sends drive signals to the X-axis direction gradient magnetic field coil, the Y-axis direction gradient magnetic field coil, and the Z-axis direction gradient magnetic field coil of the gradient magnetic field coil unit 14 according to the control signal received from the sequence controller 26. Thus, desired gradient magnetic fields Gx, Gy, and Gz whose magnetic field strengths linearly change in the X-axis, Y-axis, and Z-axis directions are formed in the imaging region.

  With the static magnetic field and the gradient magnetic field applied to the subject P as described above, the transmission unit 19 applies a high-frequency pulse to the transmission high-frequency coil 15 according to the control signal received from the sequence controller 26. The transmission high-frequency coil 15 transmits a high-frequency signal to the subject P arranged in the imaging region in accordance with the high-frequency pulse received from the transmission unit 19. Therefore, a magnetic resonance signal is generated in the subject P, and the generated magnetic resonance signal is received by the plurality of surface coils 30 used as the receiving high-frequency coil 17.

  The magnetic resonance signals received by the surface coils 30 are converted into electrical signals and output to the synthesis / switch circuit 25 as reception signals. When the plurality of surface coils 30 are arranged side by side only in the body axis direction as shown in FIGS. 3 and 7, the reception signal output from the surface coil 30 is input to the distribution / synthesis circuit 31. . The distribution / combination circuit 31 generates a reception signal corresponding to the desired sensitivity region 50 and outputs the received signal to the switch circuit 32 provided at the subsequent stage of the distribution / synthesis circuit 31. At this time, when the distribution / combination circuit 31 is configured by a passive circuit like the 0 ° -180 ° hybrid circuit 40, an increase in power consumption in the distribution / combination circuit 31 is suppressed.

  When a plurality of surface coils 30 are arranged not only in the body axis direction but also in the direction perpendicular to the body axis as shown in FIG. 18, the magnetic resonance signals received by the surface coil 30 are temporarily And output to the distribution / combination circuit 61 for the non-body axis direction. The distribution / combination circuit 61 for the non-body axis direction distributes and combines the reception signals from the plurality of surface coils 30 arranged in the non-body axis direction. Then, a reception signal such as a QD signal is generated and output to the distribution / combination circuit 31 for the body axis direction.

  Then, in the distribution / combination circuit 31 for the body axis direction, reception signals from the plurality of surface coils 30 arranged shifted in the body axis direction are distributed and combined to generate a new reception signal. The generated reception signal is output from the distribution / synthesis circuit 31 for the body axis direction to the switch circuit 32.

  In addition, when the switch 70 and the switch 71 are provided in the distribution / combination circuit 31 and the switch circuit 32, respectively, a received signal from one surface coil 30 is operated from another surface coil 30 by the operation of the switch 70 and the switch 71. It is also possible to guide to the switch circuit 32 alone without being combined with the received signal.

  In this way, the reception signal output from the surface coil 30 is distributed and combined by the distribution / combination circuit 31 and then guided to the switch circuit 32. In the switch circuit 32, the number of reception signals corresponding to the number M of reception channels provided in the reception unit 20 is selected. That is, when the surface coil 30 having the number of coils N is used, N reception signals are guided to the switch circuit 32, and the reception signals having the number M of reception channels are selected by the switch circuit 32 and are given to the reception unit 20. It is done.

  Therefore, the reception signal selected by the switch circuit 32 is input to the reception channel of the reception unit 20. Under the control of the sequence controller 26, each received signal is amplified and detected by the receiving unit 20 and then sent to the data collecting unit 21. As a result, the received signal is collected in the data collecting unit 21. In the data collection unit 21, A / D conversion of the collected reception signal is executed, and the reception signal after A / D conversion is sent to the computer 22.

  When the user gives an image display instruction from the console 23, the computer 22 executes image reconstruction processing on the received signal input from the data collection unit 21. Since the reception signals from each surface coil 30 are usually subjected to image reconstruction processing independently, the number of images corresponding to the number of reception signals to be subjected to surface coil 30, reception channels, and image reconstruction processing is reconstructed. . Each reconstructed image is synthesized into one image by an image synthesis process such as a process of taking a root of square sum in the computer 22. Further, image processing necessary for parallel imaging such as unfolding processing is appropriately executed.

  Then, the image data obtained by such reconstruction and synthesis is given to the display 24 and displayed. For this reason, the user can refer to a diagnostic image with higher SNR and higher speed by parallel imaging using a plurality of surface coils 30.

  According to the magnetic resonance imaging apparatus 10, the received data processing method in the magnetic resonance imaging apparatus 10 and the high frequency coil as described above, the reception signals from the plurality of surface coils 30 arranged in the body axis direction of the subject P are distributed. Can be synthesized. Accordingly, even when the number of reception channels of the magnetic resonance imaging apparatus 10 is small, it is possible to expand the range of mode selection for parallel imaging in all the X, Y, and Z directions. As a result, even if the number of surface coils 30 increases in the body axis direction, a wide imaging region can be realized with a simpler circuit configuration and fewer reception channels. It is particularly suitable for imaging a wide region in the body axis direction using the magnetic resonance imaging apparatus 10 in which a plurality of surface coils 30 are arranged in the body axis direction.

  Further, by providing the distribution / synthesis circuit 31 separately from the switch circuit 32, the circuit configuration of the synthesis / switch circuit 25 can be simplified. Furthermore, since the distribution / synthesis circuit 31 can be a passive circuit, the synthesis / switch circuit 25 as a whole can save power.

  If the distribution / combination circuit 31 for the body axis direction is configured by arranging only the 0 ° -180 ° hybrid circuits 40 in a hierarchical manner without using the 0 ° -90 ° hybrid circuit, the distribution / synthesis circuit 31 can be arranged in the body axis direction. In addition, a distribution / synthesis circuit 31 suitable for synthesis of reception signals from the surface coil 30 can be configured. That is, if the distribution / combination circuit 31 is configured using only the 0 ° -180 ° hybrid circuit 40, the noise components included in the received signals from the surface coils 30 arranged in a plurality of planes are not correlated. Therefore, an increase in noise components in the received signal to be synthesized can be suppressed.

  Further, if the switch 70 is provided so that the reception signal from each surface coil 30 can be supplied to the receiving unit 20 without being distributed / combined by the distribution / combination circuit 31, each surface coil 30 can be used alone. It is possible to respond to the need to image a narrow area with high sensitivity.

1 is a configuration diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention. FIG. 2 is a configuration diagram of a reception high-frequency coil and a synthesis / switch circuit of the magnetic resonance imaging apparatus shown in FIG. 1. FIG. 3 is a diagram showing a configuration example of a distribution / synthesis circuit shown in FIG. 2. The figure which shows the sensitivity distribution formed by each surface coil when the mode selection is carried out using the output signal from the 0 degree side of the 0 degree-180 degree hybrid circuit shown in FIG. 3 as a reception signal. The figure which shows the sensitivity distribution formed by each surface coil when the output signal from the 180 degree side of the 0 degree-180 degree hybrid circuit shown in FIG. 3 is selected as a reception signal. The figure which shows the example which has arrange | positioned four surface coils in the back surface of a subject as a high frequency coil for reception of the magnetic resonance imaging apparatus shown in FIG. FIG. 3 is a diagram showing a configuration example of a distribution / combination circuit when four surface coils are used as the reception high-frequency coil of the magnetic resonance imaging apparatus shown in FIG. 1. FIG. 8 is a diagram showing a phase profile when output signals output from the distribution / combination circuit shown in FIG. 7 are received signals. The figure which shows the sensitivity distribution formed by each surface coil when the mode is selected by using the output signal B1 output from the distribution / synthesis circuit shown in FIG. 7 as a reception signal. The figure which shows the sensitivity distribution formed by each surface coil when the mode is selected by using the output signal B2 output from the distribution / synthesis circuit shown in FIG. 7 as a reception signal. The figure which shows the sensitivity distribution formed by each surface coil when the mode selection is carried out using the output signal B3 output from the distribution / synthesis circuit shown in FIG. 7 as a reception signal. The figure which shows the sensitivity distribution formed by each surface coil when the mode is selected by using the output signal B4 output from the distribution / synthesis circuit shown in FIG. 7 as a reception signal. The figure which shows the example of arrangement | positioning of each surface coil in the case of using a several surface coil for the head of a subject as a high frequency coil for reception of the magnetic resonance imaging apparatus shown in FIG. The figure which shows the example which provided four surface coils as a high frequency coil for reception of the magnetic resonance imaging apparatus shown in FIG. 1, and provided the switch on the output side of each surface coil. The figure which shows the example which has arrange | positioned several surface coils in the circumference | surroundings of the abdomen of a subject in the parallel imaging by the conventional magnetic resonance imaging apparatus. The conceptual diagram which shows the example comprised so that the received signal from several surface coils can be synthesize | combined by a synthetic | combination and switch circuit in the parallel imaging by the conventional magnetic resonance imaging apparatus. The figure which shows the sensitivity distribution of the 3 surface coils to which attention is paid among the 6 surface coils arrange | positioned around the abdominal part of the subject in the parallel imaging by the conventional magnetic resonance imaging apparatus. FIG. 18 is a circuit configuration diagram of a distribution / synthesis circuit for synthesizing reception signals from a surface coil of interest in the conventional magnetic resonance imaging apparatus shown in FIG. 17. The figure which shows the sensitivity distribution formed by each surface coil when the output signal A from the conventional distribution / synthesis circuit shown in FIG. 18 is selected as a reception signal. The figure which shows the sensitivity distribution formed by each surface coil when the output signal B from the conventional distribution / synthesis circuit shown in FIG. 18 is selected as a reception signal. The figure which shows the sensitivity distribution formed by each surface coil when the output signal C from the conventional distribution / synthesis circuit shown in FIG. 18 is selected as a reception signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Magnetic resonance imaging apparatus 11 Gantry 12 Control system 13 Static magnetic field magnet 14 Gradient magnetic field coil unit 15 High frequency coil 16 for transmission 16 High frequency coil 18 for reception Gradient magnetic field coil drive circuit 19 Transmitter 20 Receiving part 21 Data collection part 22 Computer 23 Console 24 Display 25 Synthesis switch circuit 26 Sequence controller 30 Surface coil 31 Distribution synthesis circuit 32 Switch circuit 33 Receiver 40 0 ° -180 ° hybrid circuit 50 Sensitivity region 60 Surface coil unit 61 Distribution synthesis circuit 70 for non-body axis direction switch P subject

Claims (8)

A plurality of surface coils arranged in the body axis direction of the subject;
A distribution and synthesis means for generating a new reception signal by distributing and combining the reception signals from the plurality of surface coils in the body axis direction;
Have
The plurality of surface coils include a first surface coil, a second surface coil, a third surface coil, and a fourth surface coil;
The distribution / synthesizing means includes a first 0 ° -180 ° hybrid circuit provided on the output side of the first surface coil and the second surface coil, and outputs of the third surface coil and the fourth surface coil. A second 0 ° -180 ° hybrid circuit provided on the side, a 0 ° output side of the first 0 ° -180 ° hybrid circuit, and a 0 ° output side of the second 0 ° -180 ° hybrid circuit A third 0 ° -180 ° hybrid circuit provided; a 180 ° output side of the first 0 ° -180 ° hybrid circuit; and a 180 ° output side of the second 0 ° -180 ° hybrid circuit. A fourth 0 ° -180 ° hybrid circuit;
RF coil unit, characterized in that it comprises a. 2. The distribution / synthesis unit is configured such that distribution / synthesis characteristics are represented by a matrix having an inverse matrix of N × N where N is the number of coils of the plurality of surface coils. The high frequency coil unit described. The high-frequency coil unit according to claim 1, wherein the distribution / synthesis unit includes only a 0 ° -180 ° hybrid circuit as a passive circuit. 2. A path changeover switch for switching the reception signals output from the plurality of surface coils to a path that passes through the distribution / combination means and a path that does not pass through the distribution / synthesis means. High frequency coil unit. Signal generating means for generating a magnetic resonance signal by applying a gradient magnetic field and a high frequency pulse to a subject in a static magnetic field;
A plurality of surface coils arranged in the body axis direction of the subject and receiving the magnetic resonance signal;
A distribution and synthesis means for generating a new reception signal by distributing and synthesizing reception signals input from the plurality of surface coils in the body axis direction;
A switch for selecting the number of received signals corresponding to the number of received channels from the new received signals generated in the distribution and combining means;
A receiver for acquiring a received signal selected by the switch;
An image reconstruction unit for reconstructing an image of the subject from a reception signal acquired in the reception unit;
Have
The plurality of surface coils include a first surface coil, a second surface coil, a third surface coil, and a fourth surface coil;
The distribution / synthesizing means includes a first 0 ° -180 ° hybrid circuit provided on the output side of the first surface coil and the second surface coil, and outputs of the third surface coil and the fourth surface coil. A second 0 ° -180 ° hybrid circuit provided on the side, a 0 ° output side of the first 0 ° -180 ° hybrid circuit, and a 0 ° output side of the second 0 ° -180 ° hybrid circuit A third 0 ° -180 ° hybrid circuit provided; a 180 ° output side of the first 0 ° -180 ° hybrid circuit; and a 180 ° output side of the second 0 ° -180 ° hybrid circuit. A fourth 0 ° -180 ° hybrid circuit,
Magnetic resonance imaging apparatus characterized by. Said dividing and combining means, according to claim, characterized in that the dispensing synthesized characteristic matrix having an inverse matrix of N × N is configured as represented when the number of coils of the plurality of surface coils and N 5 The magnetic resonance imaging apparatus described. 6. The magnetic resonance imaging apparatus according to claim 5 , wherein the distribution / synthesis unit includes only a 0 ° -180 ° hybrid circuit as a passive circuit. Claim the reception signals outputted from said plurality of surface coils, wherein a route via a distribution synthesizing means, characterized in that a second switch for switching to the path which does not pass through the distributing and combining means 5 The magnetic resonance imaging apparatus described.

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