JP5133557B2 - MRI apparatus, RF coil, and magnetic resonance signal suppressing method - Google Patents

Description

  The present invention relates to an MRI apparatus, an RF coil, and a magnetic resonance signal suppression method. Specifically, the present invention relates to an MRI apparatus, an RF coil, and a magnetic resonance signal suppression method that transmit a saturation pulse to a region that suppresses generation of a magnetic resonance signal in a subject.

  When an object is imaged with an MRI apparatus, magnetic resonance signals from a specific region or tissue are suppressed in order to prevent aliasing artifacts or to prevent mixing of magnetic resonance signals from outside the imaging target. For this purpose, a space pre-saturation method, a selective pre-saturation method, or a magnetization transfer method is used (for example, see pages 274 to 276 of Non-Patent Document 1).

  The spatial presaturation method is a method of suppressing a magnetic resonance signal in a specific region by irradiating a saturation pulse before transmitting an RF pulse for generating a magnetic resonance signal. The selection of the region for suppressing the magnetic resonance signal is performed by applying a gradient magnetic field and transmitting an RF pulse having the resonance frequency of the region to be suppressed.

  In addition, the selective presaturation method and the magnetization transfer method irradiate a saturation pulse having a resonance frequency of a specific tissue that suppresses the magnetic resonance signal before transmitting the RF pulse for generating the magnetic resonance signal. This is a method for suppressing magnetic resonance signals from tissue.

On the other hand, in consideration of the safety of the human body, in order to suppress the Joule heat generated in the human body that is a conductor by the RF pulse, it is necessary to keep the heat absorption ratio (specific absorption rate, hereinafter referred to as SAR) per unit weight low (for example, Non-Patent Document 2, pages 1509 to 1511).
Ray. H. Hashemi, William. G. Bradbury, Jr. Written and translated by Tsuyoshi Araki, “Basic Power Text of MRI From Basic Theory to High-Speed Imaging”, Medical Science International, 1998 Toshiaki Miyaji, “Basic Course MR Series MRI Safety”, Journal of Japanese Society of Radiological Technology, 59, 12, 1508-1516, December 2003.

  In the spatial pre-saturation method, since the saturation pulse is irradiated in addition to the region that suppresses the magnetic resonance signal, the SAR increases even in the region that does not require suppression of the magnetic resonance signal. The selective pre-saturation method and the magnetization transfer method are methods for transmitting a saturation pulse of a specific frequency. Since a region for suppressing a magnetic resonance signal is not selected and transmitted in the first place, even in a region where it is not necessary to suppress the magnetic resonance signal. Becomes higher.

  In the spatial pre-saturation method, the SNR of the imaging target may further decrease due to reasons such as incomplete region selection by the gradient magnetic field.

  The present invention has been made in view of such circumstances, and irradiates a saturation pulse limited to a part of the subject to suppress the SAR in an area where the suppression of the magnetic resonance signal is unnecessary, The purpose is to prevent a decrease in SNR.

  In order to achieve the above object, an MRI apparatus of the present invention includes a first RF coil that causes a magnetic resonance phenomenon in a first region, and a magnetic field in a second region including at least a part of the first region. A second RF coil that causes a resonance phenomenon; an RF coil driving unit that drives the first RF coil; and the second RF coil, wherein the RF coil driving unit includes the first RF coil. After the first region is saturated and the second coil is driven, the magnetic resonance signal from the first region is suppressed.

  Preferably, in the MRI apparatus of the present invention, the RF coil driving unit drives the first RF coil when a gradient magnetic field is not applied and only a static magnetic field is applied.

  Preferably, in the MRI apparatus of the present invention, the RF coil driving unit drives the first RF coil when a static magnetic field and a gradient magnetic field are applied.

  Preferably, in the MRI apparatus of the present invention, the RF coil driving unit is configured such that the first RF coil and the second RF coil driving unit are based on any one of a space saturation method, a selective pre-saturation method, and a magnetization transfer method. The RF coil is driven.

  The MRI apparatus of the present invention includes an RF coil composed of two or more coils, and an RF coil driving unit capable of separately driving individual coils included in the RF coil, and the RF coil driving unit. However, a part of the coils included in the RF coil is driven, the part of the coils is caused to transmit an RF pulse for causing a magnetic resonance phenomenon in the first region, and the first region is saturated. After that, all the coils included in the RF coil are driven, and all the coils are transmitted with RF pulses for causing a magnetic resonance phenomenon in the second region including the first region. The magnetic resonance signal from the first region is suppressed.

  Preferably, in the MRI apparatus of the present invention, when the gradient magnetic field is not applied and only the static magnetic field is applied, the RF coil driving unit drives some of the coils included in the RF coil. .

  Preferably, in the MRI apparatus of the present invention, the RF coil driving unit drives some coils included in the RF coil when a static magnetic field and a gradient magnetic field are applied.

  Preferably, in the MRI apparatus of the present invention, the RF coil driving unit drives the RF coil based on any one of a space saturation method, a selective pre-saturation method, and a magnetization transfer method.

  Further, the RF coil of the present invention is different from the second RF coil that causes a magnetic resonance phenomenon in the second region, and at least a part of the RF coil is magnetic in the first region included in the second region. An RF coil for causing a resonance phenomenon, wherein an RF pulse for causing a magnetic resonance phenomenon to be generated in the second region is transmitted by the second RF coil before the magnetic resonance phenomenon in the first region. Is used to suppress the magnetic resonance signal from the first region.

  The RF coil of the present invention is an RF coil composed of two or more coils, and an RF pulse for causing a magnetic resonance phenomenon in the first region by a part of the coils included in the RF coil. After the first region is saturated, all the coils included in the RF coil transmit RF pulses for causing a magnetic resonance phenomenon in the second region including the first region. Thus, the magnetic resonance signal from the first region is suppressed, and the magnetic resonance signal is generated from the second region excluding the first region.

  The magnetic resonance signal suppression method of the present invention also includes a first RF coil that causes a magnetic resonance phenomenon in the first region and a magnetic resonance phenomenon in the second region including at least a part of the first region. A magnetic resonance signal suppression method in an MRI apparatus having a second RF coil to be generated, an RF coil driving unit that drives the first RF coil, and the second RF coil, wherein the RF coil driving unit After the first RF coil is driven and the first region is saturated, the RF coil driving unit drives the second coil, whereby the magnetic resonance signal from the first region is driven. Is suppressed.

  In addition, the magnetic resonance signal suppression method of the present invention provides a magnetic field in an MRI apparatus having an RF coil composed of two or more coils and an RF coil driving unit that can individually drive individual coils included in the RF coil. In the resonance signal suppression method, the RF coil driving unit drives a part of the coils included in the RF coil, and causes the part of the coils to generate a magnetic resonance phenomenon in the first region. After the pulse is transmitted and the first region is saturated, the RF coil driving unit drives all the coils included in the RF coil, and all the coils include the first region. By transmitting an RF pulse for generating a magnetic resonance phenomenon in the second region, the magnetic resonance signal from the first region is suppressed.

  According to the present invention, since the saturation pulse is irradiated only to a part of the subject, it is possible to suppress the SAR in the region where the suppression of the magnetic resonance signal is unnecessary and to prevent the SNR of the imaging target from being lowered. it can.

  FIG. 1 is a diagram showing an example of an MRI apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the MRI apparatus 10 includes a magnet system 11, a cradle 12, a gradient magnetic field drive unit 13, an RF coil drive unit 14, a data collection unit 15, a control unit 16, and an operator console 17.

  As shown in FIG. 1, the magnet system 11 has a substantially cylindrical inner space (bore) 111, and a cradle 12 on which the subject 30 is placed via a cushion is placed in the bore 111 by a transport unit (not shown). It is brought in. In the magnet system 11, as shown in FIG. 1, a saturation RF coil 20, a static magnetic field generation unit 112, a gradient magnetic field coil unit 113, and an RF are disposed around a magnet center (scanning center position) in the bore 111. A coil 114 is arranged. Here, the saturation RF coil 20 is an example of the first RF coil of the present invention, and the RF coil 114 is an example of the second RF coil of the present invention.

  In the present embodiment, an example of a surface coil is shown for the saturation RF coil 20, but the saturation RF coil 20 may be a coil having another shape. Moreover, although the example of a cylindrical coil is shown about RF coil 114, RF coil 114 may be a coil of other shapes.

  The static magnetic field generator 112 generates a static magnetic field in the bore 111. The direction of the static magnetic field is parallel to the body axis direction of the subject 30 in FIG. That is, the MRI apparatus 10 is a horizontal magnetic field type MRI apparatus. However, the saturation RF coil 20 of the present embodiment can also be used for a vertical magnetic field type MRI apparatus.

  The gradient magnetic field coil unit 113 generates a gradient magnetic field that gives a gradient to the strength of the static magnetic field formed by the static magnetic field generation unit 112 so that the magnetic resonance signal received by the RF coil 114 has three-dimensional position information. There are three types of gradient magnetic fields generated by the gradient magnetic field coil unit 113: a slice selection gradient magnetic field, a phase encode gradient magnetic field, and a frequency encode gradient magnetic field. Three gradient magnetic field coil units 113 correspond to these three types of gradient magnetic fields. It has a system gradient magnetic field coil.

  The gradient magnetic field drive unit 13 gives a drive signal DR1 to the gradient magnetic field coil unit 113 based on an instruction from the control unit 16 to generate a gradient magnetic field. The gradient magnetic field drive unit 13 has three systems of drive circuits (not shown) corresponding to the three systems of gradient magnetic field coils of the gradient magnetic field coil unit 113.

  The RF coil 114 excites spins of protons in the body of the subject 30 and transmits an RF pulse to generate a magnetic resonance signal and receives the magnetic resonance signal. Note that the RF coil 114 may be configured to perform only RF pulse transmission, and a reception RF coil for receiving a magnetic resonance signal may be separately provided.

  The saturation RF coil 20 transmits a saturation pulse and receives a magnetic resonance signal as described later. However, only the saturation pulse may be transmitted to the saturation RF coil 20.

  The RF coil driving unit 14 gives a driving signal DR2 to the RF coil 114 based on an instruction from the control unit 16 to generate an RF pulse for exciting the spin of protons in the body of the subject 30. Further, based on an instruction from the control unit 16, the drive signal DR3 is given to the saturation RF coil 20 to generate a saturation pulse for suppressing the magnetic resonance signal. The RF coil drive unit 14 is an example of the RF coil drive unit of the present invention.

  The data collection unit 15 takes in the magnetic resonance signal received by the RF coil 114 and outputs it to the data processing unit 171 of the operator console 17.

  The control unit 16 controls the gradient magnetic field drive unit 13 and the RF coil drive unit 14 according to a predetermined pulse sequence, and generates a drive signal DR1, a drive signal DR2, and a drive signal DR3. In addition, the control unit 16 controls the data collection unit 15.

  As shown in FIG. 1, the operator console 17 includes a data processing unit 171, an image database 172, an operation unit 173, and a display unit 174. The data processing unit 171 performs overall control of the MRI apparatus 10, image reconstruction processing, and the like. A control unit 16 is connected to the data processing unit 171 and is superordinate to the control unit 16. In addition, an image database 172, an operation unit 173, and a display unit 174 are connected to the data processing unit 171. The image database 172 is composed of, for example, a recordable / reproducible disk device or the like, and records data collected by the data collection unit 15 and reconstructed reconstructed image data. The operation unit 173 is configured with a keyboard, a mouse, and the like. The display unit 174 is configured by a graphic display or the like.

  FIG. 2 is a diagram illustrating an example of a configuration of peripheral circuits of the RF coil and the saturation RF coil. RF coil drive unit 14, data collection unit 15, control unit 16, transmission / reception switching circuit TR1, transmission / reception switching circuit TR2, low input impedance preamplifier LA1, low input impedance preamplifier LA2, and RF coil 114 and a saturation RF coil 20 are shown.

  The RF coil 114 transmits an RF pulse and receives a magnetic resonance signal generated from the subject 30. The RF coil 114 is in a resonant state when the dynamic disabling switch DS1 is enabled. That is, the RF pulse can be transmitted and the magnetic resonance signal generated from the subject 30 can be received. When the dynamic disabling switch DS1 is disabled, the RF coil 114 is not magnetically coupled to other coils. The transmission / reception switching circuit TR1 switches an electric signal path between transmission of an RF pulse and reception of a magnetic resonance signal in the RF coil 114. The transmission / reception switching circuit TR1 applies the drive signal DR2 sent from the RF coil drive unit 14 to the RF coil 114 when transmitting the RF pulse, and receives the magnetic signal received by the RF coil 114 when receiving the magnetic resonance signal. The resonance signal is sent to the low input impedance preamplifier LA1. The low input impedance preamplifier LA1 amplifies the magnetic resonance signal received by the RF coil 114 and sends the amplified signal to the reception circuit RC1 in the data collection unit 15.

  The saturation RF coil 20 transmits a saturation pulse and receives a magnetic resonance signal generated from the subject 30. The saturation RF coil 20 is in a resonant state when the dynamic disabling switch DS2 is enabled. That is, the saturation pulse can be transmitted and the magnetic resonance signal generated from the subject 30 can be received. When the dynamic disabling switch DS2 is disabled, the saturation RF coil 20 is not magnetically coupled to other coils. The transmission / reception switching circuit TR2 switches an electric signal path between transmission of a saturation pulse and reception of a magnetic resonance signal in the saturation RF coil 20. The transmission / reception switching circuit TR2 gives the drive signal DR3 sent from the RF coil drive unit 14 to the saturation RF coil 20 when transmitting a saturation pulse, and receives the magnetic resonance signal when receiving a magnetic resonance signal. The received magnetic resonance signal is sent to the low input impedance preamplifier LA2. The low input impedance preamplifier LA2 amplifies the magnetic resonance signal received by the saturation RF coil 20 and sends the amplified signal to the receiving circuit RC2 in the data collecting unit 15.

  FIG. 3 is a diagram illustrating the control bias of the switch circuit SW. The switch circuit SW in the control unit 16 disables the dynamic disabling switch DS1 from being disabled by enabling the control bias in accordance with the timing at which the RF coil 114 transmits the RF pulse and receives the magnetic resonance signal. Switch to enable. The transmission / reception switching circuit TR1 is switched from reception to transmission by enabling the control bias in accordance with the timing at which the RF coil 114 transmits the RF pulse. Similarly, the dynamic disabling switch DS2 is switched from disabled to enabled by enabling the control bias in accordance with the timing at which the saturation RF coil 20 transmits a saturation pulse and receives a magnetic resonance signal. In addition, the transmission / reception switching circuit TR2 is switched from reception to transmission by enabling the control bias in accordance with the timing at which the saturation RF coil 20 transmits a saturation pulse.

  As shown in FIG. 2, the RF coil driving unit 14 includes an RF pulse generation circuit EX1, an RF pulse amplifier RFA1, an RF pulse generation circuit EX2, and an RF pulse amplifier RFA2. The RF pulse generation circuit EX1 generates an RF pulse transmitted from the RF coil 114. The RF pulse amplifier RFA1 amplifies the RF pulse generated by the RF pulse generation circuit EX1, and sends the drive signal DR2 to the transmission / reception switching circuit TR1. The RF pulse generation circuit EX2 generates a saturation pulse transmitted from the saturation RF coil 20. The RF pulse amplifier RFA2 amplifies the saturation pulse generated by the RF pulse generation circuit EX2, and sends the drive signal DR3 to the transmission / reception switching circuit TR2.

  As shown in FIG. 2, the data collection unit 15 includes a reception circuit RC1 and a reception circuit RC2. The receiving circuit RC1 frequency-converts the magnetic resonance signal sent from the low input impedance preamplifier LA1, performs A / D conversion, and transmits the converted signal to the data processing unit 171. The receiving circuit RC2 performs frequency conversion on the magnetic resonance signal transmitted from the low input impedance preamplifier LA2, performs A / D conversion, and then transmits the converted signal to the data processing unit 171.

  When there is an RF coil dedicated to reception and the RF coil 114 is dedicated to transmission, the transmission / reception switching circuit TR1 is not necessary. The low input impedance preamplifier LA1 and the receiving circuit RC1 are connected to an RF coil dedicated to reception. Similarly, when the saturation RF coil 20 is dedicated to transmission, the transmission / reception switching circuit TR2 is unnecessary.

  FIG. 4 is a diagram illustrating different examples of the configuration of peripheral circuits of the RF coil and the saturation RF coil. RF coil drive unit 14A, data collection unit 15, control unit 16, transmission / reception switching circuit TR1, transmission / reception switching circuit TR2, low input impedance preamplifier LA1, low input impedance preamplifier LA2, and RF coil 114 and a saturation RF coil 20 are shown. 2 and 4 indicate the same components. FIG. 4 is obtained by replacing the RF coil driving unit 14 of FIG. 2 with an RF coil driving unit 14A. The data collection unit 15, the control unit 16, the transmission / reception switching circuit TR1, the transmission / reception switching circuit TR2, the low input impedance preamplifier LA1, the low input impedance preamplifier LA2, the RF coil 114, and the saturation RF coil 20 are shown in FIGS. 4 is the same.

  As shown in FIG. 4, the RF coil drive unit 14A includes an RF pulse generation circuit EX1 and an RF pulse amplifier RFA1. Unlike FIG. 2, the RF pulse generation circuit EX2 and the RF pulse amplifier RFA2 are not provided, and the drive signal generated by the RF pulse generation circuit EX1 and amplified by the RF pulse amplifier RFA1 is switched by a switch as the drive signal DR2 or the drive signal DR3. Send. However, unlike the configuration of FIG. 2, there is a limitation that the RF pulse from the RF coil 114 and the saturation pulse from the saturation RF coil 20 cannot be transmitted simultaneously. The RF coil drive unit 14A is an example of the RF coil drive unit of the present invention.

  FIG. 5 is a cross-sectional view of the RF coil, the saturation RF coil, and the subject viewed in the direction along the body axis of the subject. The saturation RF coil 20 is arranged in close contact with the subject 30, and the saturation pulse of the saturation RF coil 20 is transmitted only to the suppression region 40. After the saturation RF coil 20 transmits a saturation pulse, the RF coil 114 transmits an RF pulse for generating a magnetic resonance signal to a region including the suppression region 40. The suppression region 40 is at least part of the region included in the region irradiated with the RF pulse from the RF coil 114. Of course, the entire suppression region 40 may be included in the region irradiated with the RF pulse from the RF coil 114.

  In the first embodiment of the present invention, the magnetic resonance signal is generated from the suppression region 40 using the saturation RF coil 20 by any one of the space saturation method, the selective pre-saturation method, and the magnetization transfer method. It is suppressed.

  When suppressing the magnetic resonance signal by the spatial saturation method, for example, a saturation pulse is transmitted from the saturation RF coil 20 in an environment where only a static magnetic field is applied. The center frequency of the transmitted saturation pulse is the Larmor frequency proportional to the strength of the static magnetic field. Unlike the conventional spatial presaturation method, it is not necessary to select a region for applying a gradient magnetic field from the gradient coil unit 113 and suppressing a magnetic resonance signal. However, a gradient magnetic field is applied from the gradient coil unit 113 to irradiate the saturation pulse from the saturation RF coil 20 for the purpose of selecting only a part of the region included in the region irradiated with the saturation pulse and suppressing the magnetic resonance signal. You may do it.

  In the spatial pre-saturation method, a saturation pulse is irradiated before an RF pulse for generating a magnetic resonance signal is transmitted by the RF coil 114. However, depending on the type of the pulse sequence, it may be better to irradiate the saturation pulse continuously or intermittently with the recovery of the saturated magnetization. Therefore, if the SAR is within the limits, not only before the RF coil 114 transmits the RF pulse, but also during the reception of the magnetic resonance signal or before and after receiving the magnetic resonance signal, the saturation RF coil 20 applies the saturation pulse. You may irradiate continuously or intermittently.

  As described above, in this embodiment, the saturation pulse may be irradiated during reception of the magnetic resonance signal or before and after receiving the magnetic resonance signal. Therefore, in order to distinguish it from the spatial pre-saturation method in which a saturation pulse is transmitted before transmitting an RF pulse for generating a magnetic resonance signal, the best mode for carrying out the invention and the claims in the claims That's it.

  According to this embodiment, it is possible to irradiate the saturation pulse only to the region where the saturation RF coil 20 is in close contact with the subject 30, that is, the region where the magnetic resonance signal is desired to be suppressed. For this reason, unlike the conventional spatial presaturation method, it is possible to reduce the SAR in a region where it is not necessary to suppress the magnetic resonance signal. Further, the saturation pulse transmitted from the saturation RF coil 20 is transmitted only to the region where the saturation RF coil 20 is in close contact with the subject 30 and is not transmitted to other regions. Reduction is suppressed.

  When suppressing the magnetic resonance signal by the selective pre-saturation method, before transmitting an RF pulse for generating the magnetic resonance signal from the RF coil 114, for example, in an environment where only a static magnetic field is applied, A frequency selective saturation pulse is transmitted from the saturation RF coil 20. For example, when the purpose is to eliminate the longitudinal magnetization of fat, a saturation pulse of the resonance frequency of fat is transmitted from the saturation RF coil 20. Note that a gradient magnetic field is applied from the gradient coil unit 113 to irradiate the saturation pulse from the saturation RF coil 20 for the purpose of suppressing a magnetic resonance signal by selecting only a part of the region to be irradiated with the saturation pulse. You may do it.

  The saturation RF coil 20 can irradiate a saturation pulse only to a region that is in close contact with the subject 30, that is, a region where a magnetic resonance signal is desired to be suppressed. For this reason, unlike the conventional selective pre-saturation method, it is possible to suppress the SAR in a region where it is not necessary to suppress the magnetic resonance signal.

  When the magnetic resonance signal is suppressed by the magnetization transfer method, for example, in an environment where only a static magnetic field is applied before the RF pulse for generating the magnetic resonance signal is transmitted from the RF coil 114, the saturation signal is used. A saturation pulse for suppressing protons of protein-bound water is transmitted from the RF coil 20. The magnetization transfer method is similar to suppressing the fat magnetic resonance signal by the selective pre-saturation method, but the frequency and intensity of the saturation pulse transmitted from the saturation RF coil 20 are different from those of the selective pre-saturation method. Note that a gradient magnetic field is applied from the gradient coil unit 113 to irradiate the saturation pulse from the saturation RF coil 20 for the purpose of suppressing a magnetic resonance signal by selecting only a part of the region to be irradiated with the saturation pulse. You may do it.

  Even in the magnetization transfer method, the saturation RF coil 20 can irradiate a saturation pulse only to a region that is in close contact with the subject 30, that is, a region in which a magnetic resonance signal is desired to be suppressed. For this reason, unlike the conventional magnetization transfer method, it is possible to suppress the SAR in a region where it is not necessary to suppress the magnetic resonance signal.

  FIG. 6 is a diagram showing an RF coil and a saturation RF coil according to the second embodiment of the present invention. The point having the saturation RF coil 20 is common to the first embodiment. However, the RF coil 114 is a multi-coil and is different from the first embodiment in that the RF coil 114 is composed of coils 1141 to 1148. In the present embodiment, the saturation RF coil 20 is an example of a surface coil, but a coil having a shape other than that may be used. The RF coil 114 is an example of a coil arranged in a cylindrical shape, but may be a coil arranged in other shapes.

  FIG. 7 is a diagram illustrating an example of the configuration of peripheral circuits of the multi-coil and saturation RF coil that constitute the RF coil. An RF coil driving unit 14B, a control unit 16A, transmission / reception switching circuits TR2 to TR10, coils 1141 to 1148, and a saturation RF coil 20 are shown.

  The coils 1141 to 1148 transmit RF pulses and receive magnetic resonance signals generated from the subject 30. Coils 1141-1148 are in a resonant state when dynamic disabling switches DS3-DS10 are enabled. That is, the RF pulse can be transmitted and the magnetic resonance signal generated from the subject 30 can be received. When the dynamic disabling switches DS3 to DS10 are disabled, the coils 1141 to 1148 are not magnetically coupled to other coils. The transmission / reception switching circuits TR3 to TR10 switch electrical signal paths for transmission of RF pulses and reception of magnetic resonance signals in the coils 1141 to 1148. The transmission / reception switching circuits TR3 to TR10 give the drive signals sent from the RF coil drive unit 14 to the coils 1141 to 1148 when transmitting RF pulses, and the coils 1141 to 1148 when receiving magnetic resonance signals. The received magnetic resonance signal is sent to low input impedance preamplifiers LA3 to LA10 (not shown). The low input impedance preamplifiers LA3 to LA10 amplify the magnetic resonance signals received by the coils 1141 to 1148 and send them to receiving circuits RC3 to RC10 (not shown) in the data collection unit. Note that eight low input impedance preamplifiers LA3 to LA10 and eight receiving circuits RC3 to RC10 are provided corresponding to the coils 1141 to 1148, respectively.

  Similar to the first embodiment, the saturation RF coil 20 transmits a saturation pulse and receives a magnetic resonance signal generated from the subject 30. Also in this embodiment, similarly to the first embodiment of the present invention, the magnetic resonance signal from the suppression region 40 is suppressed by any one of the space saturation method, the selective pre-saturation method, or the magnetization transfer method.

  The RF coil driving unit 14B includes RF pulse generation circuits EX2 to EX10 and RF pulse amplifiers RFA2 to RFA10. RF pulse generation circuits EX3 to EX10 generate RF pulses transmitted from coils 1141 to 1148, respectively. The RF pulse generation circuit EX2 generates a saturation pulse transmitted from the saturation RF coil 20. The RF pulse amplifiers RFA3 to RFA10 amplify the RF pulses generated by the RF pulse generation circuits EX3 to EX10, respectively, and supply drive signals to the coils 1141 to 1148. The RF pulse amplifier RFA2 amplifies the saturation pulse generated by the RF pulse generation circuit EX2 and supplies a drive signal to the saturation RF coil 20.

  The switch circuit SW in the control unit 16A enables the dynamic disabling switches DS3 to DS10 by enabling the control bias in accordance with the timing at which the coils 1141 to 1148 transmit RF pulses and receive magnetic resonance signals. Switch from disabled to enabled. In addition, the transmission / reception switching circuits TR3 to TR10 are switched from reception to transmission by enabling the control bias in accordance with the timing at which the coils 1141 to 1148 transmit RF pulses. Similarly, the dynamic disabling switch DS2 is switched from disabled to enabled by enabling the control bias in accordance with the timing at which the saturation RF coil 20 transmits a saturation pulse and receives a magnetic resonance signal. In addition, the transmission / reception switching circuit TR2 is switched from reception to transmission by enabling the control bias in accordance with the timing at which the saturation RF coil 20 transmits a saturation pulse.

  Note that when there is an RF coil dedicated to reception and the coils 1141 to 1148 are dedicated to transmission, the transmission / reception switching circuits TR3 to TR10 are not necessary. Similarly, when the saturation RF coil 20 is dedicated to transmission, the transmission / reception switching circuit TR2 is unnecessary. Further, in the first embodiment and the second embodiment, the number of saturation RF coils 20 is one. However, when it is desired to suppress magnetic resonance signals in two or more regions, two saturation RF coils 20 are used. You may provide above.

  Further, the saturation RF coil 20 in the second embodiment is an example of the first RF coil of the present invention, the coils 1141 to 1148 are an example of the second RF coil of the present invention, and the RF coil driving unit 14B. These are examples of the RF coil drive unit of the present invention.

  FIG. 8 is a diagram illustrating an example of suppression of magnetic resonance signals by the RF coil according to the third embodiment of the present invention. The point that the RF coil 114 is a multi-coil and is composed of coils 1141 to 1148 is common to the second embodiment. However, the second embodiment is different from the second embodiment in that a saturation pulse is transmitted using some of the coils 1141 to 1148 in order to suppress the magnetic resonance signal. In addition, the suppression area | region 60 is an area | region where a magnetic resonance signal is suppressed. In this embodiment, the RF coil 114 is an example of a coil arranged in a cylindrical shape, but may be a coil arranged in other shapes.

  As described above, in this embodiment, the saturation pulse is transmitted using not all the coils 1141 to 1148 but some coils close to the region where the magnetic resonance signal is suppressed. For example, when suppressing the magnetic resonance signal in the suppression region 60 of FIG. 8, before transmitting the RF pulse for generating the magnetic resonance signal, the magnetic resonance signal is used using the coil 1143 and the coil 1144 close to the suppression region 60. A saturation pulse is transmitted to suppress this. Also in this embodiment, similarly to the first and second embodiments of the present invention, the magnetic resonance signal from the suppression region 60 is suppressed by any one of the space saturation method, the selective pre-saturation method, or the magnetization transfer method. Is done.

  Similar to the first and second embodiments, the coils 1141 to 1148 according to this embodiment can transmit a saturation pulse for suppressing a magnetic resonance signal in an environment where only a static magnetic field is applied. good. Further, for the purpose of selecting only a part of the region included in the region irradiated with the saturation pulse and suppressing the magnetic resonance signal, a gradient magnetic field may be applied from the gradient magnetic field coil unit 113 to irradiate the saturation pulse.

  FIG. 9 is a diagram illustrating an example of a configuration of a peripheral circuit of a multi-coil. An RF coil driving unit 14C, a control unit 16B, transmission / reception switching circuits TR3 to TR10, and coils 1141 to 1148 are shown. 7 and 9 indicate the same components. FIG. 9 differs from FIG. 7 in that there is no transmission / reception switching circuit TR2, saturation RF coil 20, RF pulse generation circuit EX2 and RF pulse amplifier RFA2 in the RF coil drive unit 14C. Further, the switch circuit SW in the control unit 16B is different from FIG. 7 in that no control bias is sent to the transmission / reception switching circuit TR2 for the saturation RF coil 20 and the dynamic disabling switch DS2. The transmission / reception switching circuits TR3 to TR10, the RF pulse generating circuits EX3 to EX10, the RF pulse amplifiers RFA3 to RFA10, the transmission / reception switching circuits TR3 to TR10, and the coils 1141 to 1148 are the same in FIGS.

  Similarly to the second embodiment, eight low input impedance preamplifiers LA3 to LA10 and receiving circuits RC3 to RC10 (not shown) are provided corresponding to the coils 1141 to 1148, respectively.

  FIG. 10 is a diagram illustrating the control bias sent by the switch circuit SW. The switch circuit SW in the control unit 16B enables the dynamic disabling switch DS3 by enabling the control bias in accordance with the timing at which the coils 1141 to 1148 transmit the saturation pulse and the RF pulse and receive the magnetic resonance signal. Switch DS10 from disabled to enabled. Further, the transmission / reception switching circuits TR3 to TR10 are switched from reception to transmission by enabling the control bias in accordance with the timing at which the coils 1141 to 1148 transmit the saturation pulse and the RF pulse. For example, as shown in FIG. 8, when transmitting a saturation pulse for suppressing the magnetic resonance signal from the coil 1143 and the coil 1144 to the suppression region 60, the dynamic disabling switch DS5 and the dynamic disabling switch DS6 are used. The control bias is enabled when transmitting saturation and RF pulses. The other dynamic disabling switch DS3, dynamic disabling switch DS4, and dynamic disabling switch DS7-dynamic disabling switch DS10 are enabled only when transmitting RF pulses. The control bias of the transmission / reception switching circuit TR5 and the transmission / reception switching circuit TR6 is enabled when transmitting a saturation pulse and an RF pulse. The control biases of the other transmission / reception switching circuit TR3, transmission / reception switching circuit TR4, transmission / reception switching circuit TR7-transmission / reception switching circuit TR10 are enabled only when an RF pulse is transmitted.

  Note that when there is an RF coil dedicated to reception and the coils 1141 to 1148 are dedicated to transmission, the transmission / reception switching circuits TR3 to TR10 are not necessary.

  In addition, the coils 1141 to 1148 in the third embodiment are examples of an RF coil including two or more coils of the present invention, and the RF coil driving unit 14C is an example of an RF coil driving unit of the present invention.

  As described above, according to each embodiment of the present invention, the saturation pulse is applied only to a partial region of the subject. For this reason, when suppressing a magnetic resonance signal by a space saturation method, a selective pre-saturation method, a magnetization transfer method, or the like, a region that does not require suppression of the magnetic resonance signal is not irradiated with a saturation pulse, and a region that does not need suppression SAR can be kept low.

  Further, according to each embodiment of the present invention, the region to be suppressed can be selected by irradiating the saturation pulse only to the region to suppress the magnetic resonance signal. For this reason, it is possible to prevent a reduction in the SNR of the imaging target due to incomplete selection of the region for suppressing the magnetic resonance signal.

It is a figure which shows an example of the MRI apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of a structure of the peripheral circuit of RF coil and RF coil for saturation. It is a figure which shows the control bias which switch circuit SW sends. It is a figure which shows the example from which the structure of the peripheral circuit of RF coil and RF coil for saturation differs. It is sectional drawing which looked at the RF coil, the RF coil for saturation, and the subject in the direction along the body axis of the subject. It is a figure which shows the RF coil and RF coil for saturation concerning the 2nd Embodiment of this invention. It is a figure which shows an example of a structure of the peripheral circuit of the multi-coil and RF coil for saturation which comprise RF coil. It is a figure which shows an example of suppression of the magnetic resonance signal by RF coil concerning the 3rd Embodiment of this invention. It is a figure which shows an example of a structure of the peripheral circuit of a multi coil. It is a figure which shows the control bias which switch circuit SW sends.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... MRI apparatus, 112 ... Static magnetic field generation part, 113 ... Gradient magnetic field coil part, 114 ... RF coil, 1141-1148 ... Coil, 13 ... Gradient magnetic field drive part, 14, 14A, 14B, 14C ... RF coil drive part, 20 ... RF coil for saturation

Claims (6)

An RF coil composed of two or more coils;
An RF coil driving unit capable of separately driving individual coils included in the RF coil,
The RF coil driving unit drives some coils included in the RF coil, causes the some coils to transmit an RF pulse for causing a magnetic resonance phenomenon in the first region, and the first coil. After all the regions are saturated, all the coils included in the RF coil are driven, and all the coils are caused to transmit RF pulses for causing a magnetic resonance phenomenon in the second region. An MRI apparatus in which magnetic resonance signals from the region 1 are suppressed. The MRI apparatus according to claim 1, wherein the RF coil driving unit drives a part of the coils included in the RF coil when a gradient magnetic field is not applied and only a static magnetic field is applied. The MRI apparatus according to claim 1, wherein the RF coil driving unit drives a part of the coils included in the RF coil when a static magnetic field and a gradient magnetic field are applied. 4. The RF coil driving unit according to claim 1, wherein the RF coil driving unit drives the RF coil based on any one of a space saturation method, a selective pre-saturation method, and a magnetization transfer method. MRI equipment. An RF coil composed of two or more coils,
All the coils included in the RF coil after the RF pulse for causing the magnetic resonance phenomenon to be generated in the first region is transmitted by a part of the coils included in the RF coil and the first region is saturated. By transmitting an RF pulse for causing a magnetic resonance phenomenon to occur in the second region, the magnetic resonance signal from the first region is suppressed, and the second region excluding the first region is magnetized. RF coil used to generate a resonance signal. A magnetic resonance signal suppression method in an MRI apparatus having an RF coil composed of two or more coils and an RF coil driving unit capable of separately driving individual coils included in the RF coil,
The RF coil driving unit drives a part of the coil included in the RF coil, and causes the part of the coil to transmit an RF pulse for causing a magnetic resonance phenomenon in the first region;
After the first region is saturated, the RF coil driving unit drives all the coils included in the RF coil, and causes all the coils to cause a magnetic resonance phenomenon in the second region. By sending an RF pulse,
A magnetic resonance signal suppression method in which a magnetic resonance signal from the first region is suppressed.

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