JP4891692B2 - Multi-coil, MR apparatus using the same, and RF transmission / reception method - Google Patents

Description

  The present invention relates to an MR apparatus for performing magnetic resonance imaging and magnetic resonance spectroscopy, and more particularly to a multi-coil, an MR apparatus using the same, and an RF transmission / reception method.

  MRI (Magnetic Resonance Imaging) and MRS (Magnetic Resonance Spectroscopy) give a static magnetic field with a uniform intensity to the examination area and generate RF radio waves (high-frequency radio waves) polarized in a plane perpendicular to the direction of the static magnetic field. It is a device that receives the RF radio waves emitted from the nuclei that are irradiated and excited thereby, and processes the signals. Hereinafter, MRI and MRS are collectively referred to as “MR apparatus”.

  In an MR apparatus, an RF coil is used to fulfill the function of an antenna that transmits RF radio waves and receives high-frequency signals. Among the transmitting RF coils, those in which the sensitivity region has a substantially uniform magnetic field are particularly called volume RF coils or volume coils. Of the receiving RF coils, those placed near the portion where an image is to be taken are particularly called a surface RF coil or a surface coil. Hereinafter, the RF coil is simply referred to as “coil”.

  For example, Patent Document 1 discloses an MR apparatus, and Patent Documents 2 and 3 disclose coils.

The “magnetic resonance imaging apparatus” of Patent Document 1 aims to make it possible to take a diagnostic image necessary for a treatment while monitoring the temperature of a treatment site in a minimally invasive thermotherapy. The control system controls the temperature measurement in parallel with the morphological image capture, and displays the morphological or functional MRI image and the information indicating the temperature of a specific part alternately or simultaneously on the display. It is.
With this device, the surgeon can observe the treatment process while monitoring the temperature.

The “high-frequency coil and magnetic resonance examination apparatus using the same” disclosed in Patent Document 2 is intended to be able to apply or receive a high-frequency magnetic field only to a clinically required imaging region. As shown in FIG. An RF coil in which three ring-shaped conductor portions 51 to 53 divided by 58 to 60 are coupled by linear conductors 54 to 57, and diodes 61 to 64, 65 are connected to the ring 52 and the linear conductor. -68 are connected in series, and the power supply to this is controlled to select a part to be used as a reception and / or irradiation RF coil.
With this apparatus, it is possible to eliminate dangers such as heat generation of the subject due to application of a high-frequency magnetic field to unnecessary portions, burns of the subject or operator, electric shock, and the like.

As shown in FIG. 12, the “volume coil for MR apparatus” of Patent Document 3 is configured by arranging elongated elements 71 at intervals in the circumferential direction, and each element 71 resonates with the frequency of a high-frequency radio wave. It functions as a transmission / reception antenna for high-frequency radio waves.
Hereinafter, this MR apparatus volume coil is called a patch antenna coil and is abbreviated as a PAAC coil.

JP 2001-170022 A, “Magnetic Resonance Imaging Device” Japanese Patent Application Laid-Open No. 9-201346, “High-frequency coil and magnetic resonance inspection apparatus using the same” Japanese Patent Application Laid-Open No. 2006-149518, “Volume Coil for MR Device”

In an MR apparatus, a gradient magnetic field for slice selection is applied to a subject (living body) placed in a magnetic field, and high-frequency power at a frequency at which spins resonate with the magnetic field strength at the position where the slice to be imaged exists. When the spin is generated after the spin is excited and the transmission of the high frequency power is stopped, the high frequency signal generated by the spin is detected to acquire an image.
In such an MR apparatus, the above-described coil is used to irradiate high-frequency power and detect a high-frequency signal.

  In recent years, in order to improve the performance of MR apparatuses, development of ultra-high magnetic field MR apparatuses with increased magnetic field strength has been underway. In this ultra-high magnetic field MR apparatus, it is necessary to increase the frequency of the high-frequency power transmitted to excite spin (spin resonance frequency) in proportion to the magnetic field strength, resulting in the following problems.

At the time of spin excitation, an RF radio wave (high frequency radio wave) is irradiated to the subject, and heat generation is generated in the subject based on the dielectric characteristics of the subject. Due to this heat generation, the temperature of the subject such as a human body rises, and if the temperature exceeds an allowable temperature (for example, 40 ° C.), the subject may be adversely affected. Therefore, in order to avoid invasion to the subject, it is necessary to suppress this heat generation to a certain value or less.
Further, in the ultrahigh magnetic field MR apparatus having a high spin resonance frequency, the loss inside the subject, which is a dielectric, increases in proportion to the frequency, which is particularly problematic.
However, in the MR apparatus, when the transmission power of the RF radio wave is limited, the transmission time of the RF radio wave becomes extremely short. As a result, the drawing range, the drawing depth, the drawing method, and the like are limited, and high-precision inspection cannot be performed. There was a point.

  In order to solve this problem, the apparatus of Patent Document 1 captures a diagnostic image necessary for treatment while monitoring the temperature of the treatment site. However, this means can monitor the temperature, but cannot suppress the temperature rise.

  In the apparatus of Patent Document 2, the same coil can be switched to an irradiation coil made of a long resonator, an irradiation coil made of a short resonator, and a saddle type surface coil. However, with this means, it is difficult to uniformly irradiate near the boundary of the short resonator, and there is a problem that it is necessary to use an irradiation coil composed of a long resonator for photographing this portion.

  Furthermore, the coil of Patent Document 2 is a birdcage type, and when a control current is supplied to the diode for switching the coil and a direct current flows through the element, the static magnetic field is disturbed and the image distortion associated therewith is disturbed. There was a problem that occurred.

  Further, the PAAC coil of Patent Document 3 requires a diode with a high withstand voltage because a high voltage (for example, about 2000 V) acts on the diode of the blocking circuit connected to the end of the element 71, and therefore the response speed of the diode is high. There was a problem that a fast diode could not be applied.

The present invention has been developed to solve the above-described problems. That is, a first object of the present invention is to provide a multi-coil capable of irradiating a subject with high-frequency radio waves and detecting a high-frequency signal from the subject while suppressing an increase in temperature of the subject, and an MR apparatus and an RF using the same. It is to provide a transmission / reception method.
A second object of the present invention is to capture an image with a high S / N ratio with little disturbance of the static magnetic field applied to the subject, and to increase the SAR (Specific Absorption Rate). An object of the present invention is to provide a multi-coil that can be reduced, an MR apparatus using the same, and an RF transmission / reception method.
Furthermore, a third object of the present invention is that a blocking circuit for switching between tuning and non-tuning of the coil can be constituted by a diode having a low withstand voltage, thereby increasing the response speed at the time of switching. An object is to provide a coil, an MR apparatus using the same, and an RF transmission / reception method.

According to the present invention, it has a plurality of partial coils divided in the axial direction so as to surround different positions of the subject,
Each partial coil is composed of a plurality of elements arranged at intervals in the circumferential direction and elongated in the axial direction,
Each element is arranged in a staggered manner with the elements and ends of adjacent partial coils overlapping in the axial direction and spaced apart in the circumferential direction .
Furthermore, a cylindrical shield housing that surrounds the subject and blocks radio waves,
A blocking circuit that tunes or detunes the partial coil to the resonance frequency of the spin of the measurement nuclide,
The partial coil is attached to the inside of the shield housing;
A multi-coil is provided in which the blocking circuit is attached to the outside of the shield housing .

  According to a preferred embodiment of the present invention, each element is a conductive member that resonates at the same frequency and functions as a transmitting / receiving antenna for high-frequency radio waves.

  The blocking circuit is connected to a position near the electrical center of the element and ground, in which the high-frequency voltage distribution on the element exceeds 0 and is sufficiently smaller than the withstand voltage of the diode.

  Preferably, the blocking circuit includes a quarter wavelength circuit whose output end is connected to the element, and a diode connected between the input end of the quarter wavelength circuit and the ground.

Further, according to the present invention, it has a plurality of partial coils divided in the axial direction so as to surround different positions of the subject, and each partial coil is arranged at intervals in the circumferential direction and is elongated in the axial direction. Each element consists of a cylindrical shield housing that surrounds the subject and blocks radio waves, with the elements and ends of adjacent partial coils overlapping in the axial direction and arranged in a staggered manner in the circumferential direction. And a blocking circuit that tunes or detunes the partial coil to the resonance frequency of the spin of the measurement nuclide, the partial coil is mounted inside the shield housing, and the blocking circuit is mounted outside the shield housing A multi-coil,
A plurality of coaxial cables for independently supplying high-frequency radio waves to each of the partial coils;
There is provided an MR apparatus comprising a tuning control device that tunes only a single or some partial coils and detunes other partial coils.

Furthermore, according to the present invention, a plurality of partial coils divided in the axial direction so as to surround different positions of the subject are provided, and each partial coil is arranged at intervals in the circumferential direction and is elongated in the axial direction. Each element comprises a multi-coil in which elements and ends of adjacent partial coils overlap in the axial direction and are arranged in a staggered manner in the circumferential direction.
Only one or some partial coils are tuned, other partial coils are untuned, only a part of the subject is irradiated with high-frequency radio waves, and high-frequency signals are detected from that part ,
An axially overlapping portion of two adjacent partial coils is positioned so as to surround a desired position of the subject, two adjacent partial coils are alternately tuned, and the others are untuned. An RF transmission / reception method is provided.

According to the apparatus and method of the present invention described above, since the plurality of partial coils constituting the multi-coil are divided in the axial direction so as to surround different positions of the subject, only a single or a partial coil is included. And the other partial coils are detuned, so that the nontuned portion can be cooled while photographing the tuned portion.
That is, since the high-frequency radio wave is not irradiated to the non-tuned portion, the high-frequency signal can be detected from the subject in the tuning portion by irradiating only the tuning portion with the high-frequency radio wave while cooling this portion by natural heat dissipation or a biological function. .

  In addition, since the elements constituting the partial coil are arranged in a staggered manner in the axial direction with the elements of the adjacent partial coil overlapped with each other in the circumferential direction, they are evenly arranged near the boundary between the adjacent partial coils. Irradiation is possible.

  In addition, since the partial coil is attached to the inside of the shield housing and the blocking circuit is attached to the outside of the shield housing, the shield housing can be operated even if the current is changed by operating the blocking circuit outside the shield housing. There is little disturbance of the static magnetic field added to the subject located inside.

  Furthermore, since the subject (living body) in the non-synchronized part that is not irradiated with the high-frequency radio wave hardly generates heat, the noise from the non-synchronized part can be reduced and an image with a high S / N ratio can be taken. (Specific absorption rate) can be reduced.

  In addition, since the blocking circuit is connected to the position near the electrical center of the element whose high-frequency voltage distribution exceeds 0 and is sufficiently smaller than the withstand voltage of the diode and the ground, a blocking circuit for switching between tuning and non-tuning of the coil is provided. A diode having a low withstand voltage (for example, less than 100 V) can be used, and thereby the response speed at the time of switching can be increased.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is an overall configuration diagram of an MR apparatus according to the present invention. In this figure, the MR apparatus 10 of the present invention includes a magnet 12, a gradient coil 14, a coaxial cable 16, a tuning control device 18, and a multi-coil 20.
The magnet 12 generates a spatially and temporally uniform static magnetic field with respect to the subject 1 in the Z direction in the figure, and a normal conducting electromagnet, a superconducting electromagnet, a permanent magnet or the like is used. The subject 1 is a living body, for example, and is a human head in this example.
The gradient coil 14 generates a gradient magnetic field in the static magnetic field direction (Z direction), and uses, for example, a Maxwell coil. The gradient coil 14 is controlled by the gradient coil control device 15 and controls the measurement position of the subject 1 in the Z direction.

The multi-coil 20 of the present invention irradiates the subject 1 with high-frequency radio waves and detects a high-frequency signal from the subject 1.
The coaxial cable 16 connects the transmitter 17 and the multicoil 20, and supplies a predetermined high frequency radio wave from the transmitter 17 to the multicoil 20. The high frequency radio wave is preferably an ultra short wave of 30 MHz to 300 MHz, for example.

The tuning control device 18 is connected to the multi-coil 20 via the control signal line 18a, and has a function of tuning or non-tuning the multi-coil 20. A signal received by the multicoil 20 is received by the coaxial cable 16.
Here, “tuning” means a state in which the multi-coil 20 resonates at the spin resonance frequency of the measurement nuclide and functions as a transmission / reception antenna for high-frequency radio waves. Detuning means that the multi-coil 20 does not resonate at the spin frequency of the measurement nuclide and does not function as a transmission / reception antenna for high-frequency radio waves.
Hereinafter, tuning, tuning, and resonance, and non-tuning, detune, and non-resonance are used in the same meaning.

  The gradient coil control device 15, the transmitter 17, and the tuning control device 18 described above are connected to and controlled by the MR system control device 19, respectively.

  With the above-described configuration, the MR apparatus 10 according to the present invention can be used as MRI (magnetic resonance imaging) or MRS (magnetic resonance spectroscopy).

2A and 2B are schematic views of the multi-coil of the present invention, where FIG. 2A is a side view and FIG. 2B is an end view.
As shown in FIG. 2A, the multi-coil 20 of the present invention includes a plurality of partial coils 22 (22A) divided in the axial direction (Z direction) so as to surround different positions of the subject 1 (see FIG. 1). , 22B, 22C). In this example, there are three divisions, but it may be two divisions or four or more divisions.
As shown in FIG. 2B, a plurality (eight in this example) of elements 23 constituting each of the partial coils 22A, 22B, and 22C are arranged in a staggered manner at a constant interval in the circumferential direction. .

Each partial coil 22 includes a plurality of elements 23 that are arranged at intervals in the circumferential direction and are elongated in the axial direction.
In addition, each element 23 is arranged in a staggered manner in such a manner that the end portions of the elements 23 of the adjacent partial coils overlap in the axial direction and are spaced apart in the circumferential direction. Hereinafter, a portion overlapping with an adjacent element is referred to as an overlapping portion 23a, and a portion not overlapping is referred to as a single portion 23b.

  With this configuration, the elements 23 constituting the partial coil are arranged in a staggered manner with the elements 23 and ends of the adjacent partial coils overlapping in the axial direction and spaced apart in the circumferential direction. Uniform irradiation is possible even in the vicinity.

In this figure, the multi-coil 20 of the present invention further includes a hollow cylindrical shield housing 30 that surrounds the subject and blocks radio waves. The shield housing 30 is an integral hollow cylindrical member in this example, but may be divided to suppress eddy currents.
The shield housing 30 is made of a conductive material, and a copper foil, a copper plate, a copper-clad plastic plate, or the like can be used. The surface is coated with an insulator such as a fluororesin or a glass epoxy resin as necessary.
The shield housing 30 may be a perforated plate or a wire mesh as long as it can block radio waves.

Each partial coil 22 described above is attached to the inside of the shield housing 30.
The coaxial cable 16 includes a plurality of coaxial cables 16A, 16B, and 16C, and independently supplies high-frequency radio waves to the partial coils 22A, 22B, and 22C.
Furthermore, in the present invention, the tuning controller 18 is adapted to tune only a single or some partial coils and detune other partial coils.

Using the MR apparatus 10 of the present invention described above, in the RF transmission method of the present invention, only a single or some partial coils are tuned and the other partial coils are untuned.
For example, at least one of the plurality of partial coils 22 (for example, 22B) is positioned so as to surround a desired position of the subject 1, only that partial coil is tuned, and the other partial coils are untuned.
By this method, the non-synchronized part can be cooled while photographing the synchronized part.

Further, the overlapping portion (overlap portion 23a) in the axial direction of two adjacent partial coils (for example, 22A and 22B) is positioned so as to surround a desired position of the subject 1, and the two adjacent partial coils are alternately tuned. And make others untuned.
By this method, it is possible to photograph alternately while irradiating a desired position (overlapping portion 23a) alternately with two partial coils. In this case, since the part surrounded by the two partial coils is also heated only half of the entire imaging time, most of the subject 1 can be suppressed to a low temperature.

  FIG. 3 is a perspective view of the element shown by cutting a part thereof. In this figure, the element 23 electrically connects the radiation portion 24a disposed inside the shield housing 30, the adjustment portion 24b disposed outside the shield housing 30, and the radiation plate 24a and the adjustment plate 24b. It is composed of a conductive portion 24c. The radiation part 24a, the adjustment part 24b, and the conductive part 24c are integrated in this example, but may be separate. In this figure, reference numeral 25 denotes an insulating support.

The element 23 resonates with the frequency of the high-frequency radio wave as a whole, and the shape (width, thickness, length) is set so as to function as a transmission / reception antenna for the high-frequency radio wave. In particular, the tuning frequency can be easily adjusted by adjusting the length of the adjusting plate 24b. The tuning frequency can also be adjusted by inserting a capacitor between the adjusting plate 24b and the shield housing 30.
In addition, the element 23 of this invention is not limited to this structure, For example, you may comprise only with the radiation board 24a.

In this figure, the coaxial cable 16 (16A, 16B, 16C) is connected to a position near the center of the element 24 (that is, the radiating portion 24a), and its shield coating is connected to the shield housing 30.
The coaxial cable 16 needs to be connected to at least one of the plurality of elements 24 constituting each partial coil 22. That is, by supplying a high-frequency radio wave to at least one of the plurality of elements 23 constituting the single partial coil 22, all elements constituting the coil can be excited.

However, it is preferable that the two coaxial cables 16 are connected to two elements that are different from each other by 90 degrees in the circumferential direction among a plurality of elements constituting a single partial coil, and are separately supplied by the two cables.
With this configuration, each partial coil can be used as a quadrature coil (circularly polarized coil) that inputs electromagnetic waves having different phases by 90 ° and detects changes in the magnetic field along two axes (X axis and Y axis). it can.

In FIG. 3, the multicoil 20 of the present invention further includes a blocking circuit 40. The blocking circuit 40 has a function of tuning the partial coil 20 to a high frequency radio wave or detuning it.
The blocking circuit 40 is attached to the outside of the shield housing 30.
With this configuration, even if the current of the blocking circuit 40 is changed outside the shield housing 30, disturbance of the static magnetic field added to the subject 1 located inside the shield housing 30 can be prevented.

  FIG. 4 is a circuit diagram of the blocking circuit. As shown in this figure, the blocking circuit 40 has an output end 41 connected to the element 23 and the ground (shield housing 30), and a quarter wavelength circuit 42 connected to an input end 43 of the quarter wavelength circuit 42. And a diode 44.

Hereinafter, the operation of the blocking circuit will be described.
In a state without the blocking circuit 40, the partial coil 22 (and the element 23 constituting the partial coil 22) resonates at a frequency to be used, and signals can be transmitted and received.
The blocking circuit 40 has a configuration in which a quarter wavelength circuit 42 constituted by two capacitors C and one inductor L1 is terminated by one diode D (diode 44).
When the diode 44 is OFF (the voltage of the control signal is less than or equal to zero), the impedance of the diode is high. Therefore, the impedance of the blocking circuit 40 viewed from the RF feeding point (output terminal 41) is zero (0), and the RF feeding point is The coil 22 is short-circuited to the ground plane (shield housing 30), and the coil 22 is in a non-resonant state (blocking state) at the frequency used.
When the diode 44 is ON (the voltage of the control signal is positive), the impedance of the diode 44 is zero, and the impedance of the blocking circuit 40 viewed from the RF feeding point 41 is infinite, which is the same as the state without the blocking circuit. The coil 22 is in a resonance state.
In this figure, the inductor L2 has a sufficiently high impedance at the frequency of the RF signal and has a function of preventing the RF signal from being mixed into the control signal input.

  With the configuration described above, the relationship between the control signal of the blocking circuit and the resonance state of the coil is as shown in Table 1.

FIG. 5 is a schematic diagram showing the voltage distribution and current distribution on the element.
As described above, the element 23 of the present invention as a whole resonates at the spin resonance frequency of the measurement nuclide and functions as a high-frequency radio wave transmitting / receiving antenna. This antenna is a half-wave dipole antenna. As shown in this figure, the voltage near the center is low and the voltage at the end is high.
When the high-frequency radio wave is an ultrashort wave of, for example, 30 MHz to 300 MHz, this voltage distribution is only less than 100 V, for example, at the central portion, but exceeds 2000 V at the end portion. Therefore, when the blocking circuit 40 is connected to the end of the element 23, a high voltage exceeding 2000V may act on the blocking circuit 40.

As shown in FIG. 3, in the present invention, the blocking circuit 40 is connected to the position near the center of the element 23 and the ground. The position near the center of the element 23, that is, the connection point, is set to a position where the voltage exceeds 0 and is sufficiently smaller than the withstand voltage (for example, 100 V) of the diode 44 in the voltage distribution on the element.
The blocking circuit 40 is preferably provided for each element 23, but a part of the elements 23 can be configured without a blocking circuit as long as tuning / non-tuning can be controlled as a whole.

The coaxial cable 16 is also preferably set at a position where the voltage exceeds 0 and is sufficiently smaller than the withstand voltage of the diode in the voltage distribution on the element.
When both the coaxial cable 16 and the blocking circuit 40 are connected to the same element, they may be connected to the same portion of the element 23 as shown in FIG.
Hereinafter, the multi-coil of the present invention described above is referred to as a multi-patch antenna coil, and is simply referred to as a multi-PAAC coil or simply a multi-coil.

As described above, in order to solve the problems of the prior art, the present invention uses a multi-coil 20 (multi-PAAC coil) configured by a plurality of partial coils 22 divided in the axial direction. The multi-coil 22 can be used as a transmission-only coil, a reception-only coil, and a transmission / reception coil (transmission / reception coil).
When transmitting high-frequency power, only a specific partial coil among the plurality of partial coils 22 is driven, and the other partial coils are not resonated at the frequency to be used (block state). By doing so, the portion of the subject 1 to which the high frequency power is irradiated is limited, and the loss inside the subject and the heat generation based thereon are suppressed. Further, since the high frequency power is transmitted only around the range where the spin is excited, the transmission power is reduced.
Furthermore, since power is irradiated only around the slice where the spin is to be excited, heat generation within the subject is limited to the power irradiation portion, and no heat is generated in other portions. As a result, the overall SAR (specific absorption rate) decreases.

When acquiring an MR image, the spins on any XY plane of the subject 1 placed inside the partial coil 22 are excited. The high frequency power is transmitted using any of the partial coils 22A, 22B, and 22C including the plane, and the other partial coils are not operated by the blocking circuit 40.
With this configuration, the irradiation range of the high-frequency power for exciting the spin can be narrowed, and the required power can be reduced and the SAR (specific absorption rate) can be reduced. Further, when operating as a receiving coil, the observation range of the partial coil 22 becomes the observation range of the entire coil, and therefore, it is difficult to receive noise such as thermal noise generated from a portion of the subject other than the observation range. Therefore, the S / N can be improved as compared with the conventional coil.
In other words, in the present invention, the partial coils 22 other than one partial coil containing the slice to be excited by spin are blocked (in a non-tuned state), and only a specific partial coil is set in an operating state (tuned state). , Solving the problem.

FIG. 6 is a diagram showing one of the partial coils developed on a plane. In this figure, the shield housing 30 is shown as an independent rectangle, but it may be a houndstooth arrangement, a polygon like a puzzle, or the whole.
In this example, one partial coil 22 is composed of 8 elements, and actually 8 elements arranged in a cylindrical shape are shown expanded on a plane. However, as long as the inside of the subject has a substantially uniform magnetic field. The number of elements may be increased or decreased.

  In this example, two coaxial cables 16 are connected to two elements 23 that are 90 degrees different in the circumferential direction, and high-frequency radio waves are separately supplied by the two coaxial cables 16, and a quadrature coil (circular polarization coil) ) Can be used.

  When the above-described multi-coil 20 of the present invention is used as a transmission / reception coil (transmitting / receiving coil), the coil 22 must always be in a resonance state. Therefore, the diode is always ON and the control signal is always positive.

FIG. 7 shows an embodiment in which the multi-coil of the present invention is used as a transmission / reception coil. (A) is an arrangement of each partial coil, (B) is a connection diagram of an MR system and a control signal generator, and (C) is an observation. It is a control signal figure of a field and each partial coil.
In this figure, coil 1, coil 2, and coil 3 correspond to the partial coils 22A, 22B, and 22C described above. The control signal generator corresponds to the tuning control device 18 described above.
In this case, the relationship between the control signal of the blocking circuit and the tuning state of the coil is as shown in Table 2.

In this example, the multi-coil 20 is used as a transmission / reception coil, and at least one of a plurality of partial coils constituting the multi-coil is tuned and then received by the partial coil while being tuned.
By performing this for each partial coil, the entire imaging can be performed while suppressing heat generation.

FIG. 8 is a reference example using a transmit-only coil and a receive-only coil. (A) is a configuration diagram of the receive-only coil, (B) is a connection diagram of the MR system and a control signal generator, and (C) is a transmit circuit. It is a control signal diagram of a dedicated coil and a receive-only coil.
In this figure, the transmission-only coil is, for example, the partial coil 22 described above. The control signal generator corresponds to the tuning control device 18 described above.
When the multi-coil 20 of the present invention is used as a transmit-only coil, it is necessary to install a receive-only coil inside the coil and control both coils.

FIG. 8A is a configuration diagram of a normal loop coil used as a receive-only coil.
In this figure, the receive-only coil 3 includes four capacitors C and a loop-shaped element 2 and is configured to resonate at the same frequency of high-frequency radio waves.
In this figure, when the control signal becomes a positive voltage and the diode D is turned on, the capacitor C and the inductor L1 resonate, the impedance of the loop element 2 increases, and the reception-only coil 3 enters the non-resonant state. .

  With the above-described configuration, the relationship between the control signal of the receive-only coil and the resonance state of the coil is as shown in Table 3.

  Table 4 shows a summary of the relationship between each control signal (blocking circuit and receive-only coil) and the resonance state of each coil.

In this case, as shown in FIG. 8C, transmission by the transmission-only coil (CH1) and reception by the reception-only coil 3 (CH2) can be performed alternately.
That is, the multi-coil 20 is used as a transmission-dedicated coil, the reception-dedicated coil 3 is installed inside the multi-coil 20, and at least one of the plurality of partial coils is tuned, and then the partial coil is untuned for reception. By receiving with the dedicated coil 3, the entire imaging can be performed while suppressing heat generation.

FIG. 9 shows an embodiment in which the multi-coil of the present invention is used as a transmission-dedicated coil. (A) is an arrangement of each partial coil and reception-dedicated coil. (B) is a connection diagram of the MR system and a control signal generator. (C) is a control signal diagram of an observation area, each partial coil, and a reception-only coil.
In this figure, coil 1, coil 2, and coil 3 correspond to the partial coils 22A, 22B, and 22C described above. The control signal generator corresponds to the tuning control device 18 described above.
When the multi-coil 20 of the present invention is used as the transmission-only coil and the loop coil is used as the reception-only coil 3, the relationship between each control signal (blocking circuit and reception-only coil) and the tuning state of each coil is shown in Table 5. It becomes like this.

(Imaging and advantages of the present invention)
10A and 10B are explanatory diagrams showing the merits of the present invention, where FIG. 10A is a relational diagram of partial coils, regions, and cross sections, FIG. 10B is high-frequency transmission power, FIG. 10C is a gradient coil signal, and FIG. Signal (high-frequency image signal).
In this figure, coil 1, coil 2, and coil 3 correspond to the above-described partial coils 22A, 22B, and 22C, respectively.

The advantages of the present invention will be described using the fast spin echo method as an example of the imaging method.
In the Fast Spin Echo (FastSpinEcho), as shown in FIGS. 10B, 10C, and 10D, a pulse (90 ° pulse) for exciting the 90 ° spin flip angle is transmitted once, and a specific cross section is transmitted. Excites the Spin. Thereafter, a 180 ° pulse is transmitted, and then a required current is supplied to the gradient coil to obtain 1 line of K-space.
Further, the operation after the transmission of the 180 ° pulse is repeated a required number of times (for example, 64 to 512 times) to obtain a signal on the entire surface of the K-space, and this is subjected to Fourier transform to obtain an actual image on that surface.

The frequency of the high frequency power transmitted here corresponds to the selected cross section.
In the figure, in order to image the cross section 1, high-frequency power corresponding to the cross section 1 is transmitted to the coil 1 and an image signal is received from the coil 1.
In order to image the cross section 2, transmission and reception are performed using the coil 2.

As described above, according to the present invention, only the coil to which the cross-section to be imaged belongs is excited, so there is no need to transmit high-frequency power to the entire subject.
Accordingly, the transmission power is reduced according to the number of divisions of the coil (3 in the example), and the heat generation in the subject is reduced.
The 90 ° pulse has a peak power of several hundred watts and a transmission time of several tens to several hundreds of microseconds. The 180 ° pulse has the same peak power as several kW, and the time is the same as the 90 ° pulse.

In addition, the multi-coil 20 of the present invention has an advantage that a static magnetic field is hardly distorted because a diode control current flows outside the shield housing 30.
Conventionally, tuning / untuning control by supplying a current to a control diode (for example, 44 in FIG. 4) has been a problem common to MR coils because static magnetic field distortion occurs.
In the multi-coil of the present invention, this problem is essentially solved by attaching the control diode 44 to the outside of the shield housing 30.

As described above, according to the apparatus and method of the present invention, the plurality of partial coils 22 constituting the multi-coil 20 are divided in the axial direction so as to surround different positions of the subject (living body). By tuning only one or some of the partial coils 22 and detuning the other partial coils, it is possible to cool the non-tuned portion while photographing the tuned portion.
That is, since the high-frequency radio wave is not irradiated to the non-tuned portion, the high-frequency signal can be detected from the subject in the tuning portion by irradiating only the tuning portion with the high-frequency radio wave while cooling this portion by natural heat dissipation or a biological function .

  Further, each element 23 constituting the partial coil 22 is arranged in a staggered manner in such a manner that the elements and ends of the adjacent partial coils overlap in the axial direction and are spaced apart in the circumferential direction. Even irradiation is possible.

  Further, even if the partial coil 22 is attached to the inside of the shield housing 30 and the blocking circuit 40 is attached to the outside of the shield housing 30, the current of the blocking circuit 40 can be changed outside the shield housing 30. The disturbance of the static magnetic field added to the subject located inside the shield housing is small.

  Further, since the subject in the non-synchronized part that is not irradiated with the high-frequency radio wave hardly generates heat, it is possible to take an image with a high S / N ratio by reducing noise from the non-synchronized part, and SAR (specific absorption rate). ) Can be reduced.

  Further, since the blocking circuit 40 is connected to the position near the electrical center of the element where the high-frequency voltage distribution on the element exceeds 0 and is sufficiently smaller than the withstand voltage of the diode, and to the ground, switching between tuning and non-tuning of the coil is performed. The blocking circuit can be composed of a diode having a low withstand voltage (for example, 100 V or less), and thereby the response speed at the time of switching can be increased.

  It should be noted that the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist of the present invention.

1 is an overall configuration diagram of an MR apparatus according to the present invention. It is a schematic diagram of the multi-coil of this invention. It is a perspective view of the element which cut and shows a part. It is a circuit diagram of a blocking circuit. It is a schematic diagram which shows the voltage distribution and current distribution on an element. It is a figure which expands and shows one of the partial coils on a plane. It is an Example which uses the multi-coil of this invention as a transmission / reception coil. This is a reference example using a transmission-only coil and a reception-only coil. It is an Example which uses the multi-coil of this invention as a coil only for transmission. It is explanatory drawing which shows the merit of this invention. FIG. 6 is a schematic diagram of a coil of Patent Document 2. It is a schematic diagram of the coil of patent document 3. FIG.

Explanation of symbols

1 subject (living body), 2 loop element, 3 receive coil,
10 MR devices, 12 magnets,
14 gradient coil, 15 gradient coil controller,
16, 16A, 16B, 16C coaxial cable,
17 transmitter, 18 tuning controller, 19 MR system controller,
20 Multi-coil (multi-PAAC coil),
22, 22A, 22B, 22C partial coil,
23 elements, 23a overlapping part, 23b single part,
24a radiation part, 24b adjustment part, 24c conductive part,
30 shield housing, 40 blocking circuit,
41 output terminal, 42 1/4 wavelength circuit, 44 diode

Claims (6)

Having a plurality of partial coils divided in the axial direction so as to surround different positions of the subject;
Each partial coil is composed of a plurality of elements arranged at intervals in the circumferential direction and elongated in the axial direction,
Each element is arranged in a staggered manner with the elements and ends of adjacent partial coils overlapping in the axial direction and spaced apart in the circumferential direction .
Furthermore, a cylindrical shield housing that surrounds the subject and blocks radio waves,
A blocking circuit that tunes or detunes the partial coil to the resonance frequency of the spin of the measurement nuclide,
The partial coil is attached to the inside of the shield housing;
The multi-coil according to claim 1, wherein the blocking circuit is attached to the outside of the shield housing .   The multi-coil according to claim 1, wherein each element is a conductive member that resonates at the same frequency and functions as a transmission / reception antenna for high-frequency radio waves. The blocking circuit is a multi according to claim 1, a high frequency voltage distribution on the element is connected to the electrical center position near the ground sufficiently small elements than exceeded and the diode having a withstand voltage of 0, it is characterized by coil. The blocking circuit is a quarter wavelength circuit having an output connected to the element, consisting of a diode connected between the between the input terminal and the grounding of the quarter-wave circuit, it in claim 1, wherein The multi-coil described. It has a plurality of partial coils divided in the axial direction so as to surround different positions of the subject, each partial coil is composed of a plurality of elements that are arranged at intervals in the circumferential direction and elongated in the axial direction. The adjacent partial coil elements and ends overlap in the axial direction and are arranged in a staggered manner in the circumferential direction. The cylindrical shield housing surrounds the subject and blocks radio waves, and the partial coil is measured. A blocking circuit that tunes or detunes to the resonance frequency of the spin of the nuclide, wherein the partial coil is attached to the inside of the shield housing, and the blocking circuit is a multi-coil attached to the outside of the shield housing ;
A plurality of coaxial cables for independently supplying high-frequency radio waves to each of the partial coils;
An MR apparatus comprising: a tuning control device that tunes only a single or some partial coils and detunes other partial coils. It has a plurality of partial coils divided in the axial direction so as to surround different positions of the subject, each partial coil is composed of a plurality of elements that are arranged at intervals in the circumferential direction and elongated in the axial direction. , Comprising the multi-coil in which the elements and ends of the adjacent partial coils overlap in the axial direction and are arranged in a staggered manner in the circumferential direction;
Only one or some partial coils are tuned, other partial coils are untuned, only a part of the subject is irradiated with high-frequency radio waves, and high-frequency signals are detected from that part ,
An axially overlapping portion of two adjacent partial coils is positioned so as to surround a desired position of the subject, two adjacent partial coils are alternately tuned, and the others are untuned. RF transmission / reception method.

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