JP2007263621A - Coil for magnetic resonance detection and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily manufacture a coil for magnetic resonance detection capable of stably achieving satisfactory magnetic characteristics. <P>SOLUTION: A circumferential wall of the coil 10 for magnetic resonance detection is constituted of a main body layer 20 and a covering layer 22 covering its surface. High-purity aluminum is used for the main body layer 20, and a diamagnetic material such as gold which negates the magnetic susceptibility of aluminum is used for the covering layer 22. The covering layer 22 may be easily formed on the main body layer 20 by means such as vapor deposition and plating. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic resonance detecting coil used for NMR and the like and a method for manufacturing the same.

  In general, magnetic resonance detection such as NMR is performed by irradiating a sample inserted inside a substantially cylindrical magnetic resonance detection coil with a high-frequency pulse, and then outputting a magnetic resonance signal emitted from the sample after a certain period of time. A means such as picking up with the magnetic resonance probe is taken. Further, since the magnetic resonance signal is weak, in order to increase the detection sensitivity, a cooling pipe is provided in the magnetic resonance probe and a refrigerant such as helium is allowed to flow through the cooling pipe, whereby the magnetic resonance detection coil It has also been carried out to reduce thermal noise by cooling to a very low temperature.

  Conventionally, as a coil suitable for such magnetic resonance detection, Patent Document 1 proposes an RF coil for an NMR probe formed by a plate material in which both the front and back surfaces of an inner layer are covered with an outer layer. In this RF coil, as the material constituting the outer layer, high-purity aluminum having excellent specific resistance characteristics (characteristic that the specific resistance is low in magnetic field dependency) is used particularly in a cryogenic state, while the inner layer is configured. As the material to be used, a material having a magnetic susceptibility opposite to the magnetic susceptibility of aluminum constituting the outer layer, such as copper, that is, a diamagnetic material is used.

According to this configuration, by using high-purity aluminum for the outer layer, the specific resistance of the coil can be kept sufficiently small even in an environment where a strong magnetic field is formed at a very low temperature, and at the same time, By using a magnetic material, it is possible to cancel the magnetic susceptibility of the aluminum by using its diamagnetism, thereby further increasing the accuracy of detection of magnetic resonance.
JP 2002-162455 A

  In the coil described in Patent Document 1, the surface of high-purity aluminum constituting the outer layer is easily oxidized, and the formation of the oxide film may adversely affect good magnetic properties.

  In addition, as a means for forming this coil, Patent Document 1 describes a method of integrating an aluminum plate and a copper plate by hot pressing in the same manner as normal plywood molding, but compared with normal plywood. Since the production volume of the magnetic resonance detection coil is extremely low and the plate thickness is very small, it is difficult to produce such a coil at a low cost using the hot press.

  In view of such circumstances, the present invention provides a magnetic resonance detection coil capable of stably obtaining good magnetic characteristics, and more preferably, a magnetic resonance detection coil that can be easily manufactured. And it aims at providing the manufacturing method.

  As means for solving the above-mentioned problems, the present invention provides a magnetic resonance detection coil having a substantially cylindrical peripheral wall and forming a space into which a sample is inserted, and the peripheral wall is made of aluminum. And a covering layer covering the surface of the main body layer, and the covering layer is made of a diamagnetic material having a magnetic susceptibility opposite to that of aluminum forming the main body layer. .

  According to this configuration, the magnetic susceptibility of the aluminum constituting the main body layer is canceled out by the diamagnetic material constituting the covering layer, so that the magnetic susceptibility of the coil itself is effectively reduced and a highly accurate magnetic resonance experiment is performed. It can be carried out. In addition, since the coating layer is formed so as to cover the surface of the main body layer made of aluminum, the surface of the main body layer is prevented from being exposed to the atmosphere, and an aluminum oxide film is formed on the surface. It is possible to effectively prevent the influence of the magnetic characteristics due to the formation of the oxide film.

  Furthermore, if the volume ratio of the main body layer and the covering layer is set so that the magnetic susceptibility of the aluminum constituting the main body layer and the magnetic susceptibility of the diamagnetic material constituting the covering layer are offset, better magnetic properties It becomes possible to realize the characteristics.

  As the diamagnetic material constituting the coating layer, for example, silver, copper, beryllium, and the like can be used. In particular, gold has high diamagnetism, and an excellent magnetic susceptibility canceling effect is obtained while suppressing the volume ratio. It is possible.

  The coil for magnetic resonance detection using gold includes a coating step in which a coating layer is formed by vapor deposition or gold plating on the surface of aluminum constituting the main body layer, and before or after the coating step. It can be easily manufactured by a method including a coil forming step of forming the main body layer into a cylindrical shape.

  In particular, when gold is deposited in the coating step, the setting of the deposition time cancels out the susceptibility of the aluminum constituting the main body layer and the diamagnetic material constituting the coating layer. The volume ratio of the main body layer and the coating layer can be obtained accurately and easily.

  As described above, according to the present invention, by coating the surface of the main body layer made of aluminum with the coating layer made of the diamagnetic material, excellent magnetic properties can be obtained, and the surface of the main body layer is made of aluminum. Thus, it is possible to effectively prevent the oxide film from being formed and to prevent the oxide film from affecting the magnetic characteristics.

  A preferred embodiment of the present invention will be described with reference to FIGS.

  FIG. 2A shows an outline of an NMR (nuclear magnetic resonance) apparatus according to this embodiment. This apparatus includes a container 30 that contains a refrigerant such as liquid helium, and a superconducting coil 32 is contained in the refrigerant in the container 30. The superconducting coil 32 is obtained by winding a superconducting wire in a cylindrical shape around a vertical axis, and the container 30 is also formed in a donut shape so as to cover the coil 32 from the radially inner side. That is, an inner space 34 extending in the vertical direction is formed at the center of the container 30. An NMR probe 36 is inserted into the inner space 34.

  The NMR probe 36 has an electrode portion 38 and a cylindrical probe main body 40 connected to the electrode portion 38, and the probe main body 40 is inserted into the inner space 34 from below.

  As shown in FIG. 2 (b), the probe body 40 has an inner tube 42 arranged on the inner side in the radial direction and an outer tube 44 arranged on the outer side in the radial direction. The tubes 42 and 44 are made of a nonmagnetic material such as quartz glass that does not affect the magnetic field. A sample insertion space 46 is secured inside the inner tube 42, while the magnetic resonance detection coil (NMR detection coil 10 in this embodiment) has a diameter between the tubes 42 and 44. The structure is sandwiched between the inside and outside of the direction.

  As shown in FIG. 1 (a), the NMR detection coil 10 is formed by rolling a thin metal plate to form a substantially cylindrical peripheral wall. It has a pair of skirt parts 14 divided in the circumferential direction. The skirt portion 14 and the cylindrical portion 12 are connected to each other via a connecting portion 16, and a sample space 18 opened laterally is secured between the connecting portions 16. The skirt portions 14 are connected to a power source (not shown) via the electrode portion 38, and the NMR detection coil 10 is cooled to a very low temperature by a cooling pipe (not shown) disposed in the probe. It has come to be.

  In the present invention, any specific coil shape can be set as appropriate according to the frequency of the high frequency pulse used for magnetic resonance detection and other specifications. For example, the present invention can be suitably applied to a coil having a shape described in Patent Document 1.

  As a feature of the NMR detection coil 10 according to this embodiment, the plate material constituting the peripheral wall covers the main body layer 20 and the surface of the main body layer 20 from both the front and back sides as shown in FIG. The coating layer 22 is constituted.

  The main body layer 20 is made of high purity aluminum. This high-purity aluminum exhibits excellent specific resistance characteristics particularly in a cryogenic state, and maintains a low resistivity regardless of the change of the magnetic field in the cryogenic state. For example, compared to copper, the specific resistance of copper increases significantly as the magnetic field increases. It has the characteristic to maintain, and the characteristic becomes more remarkable as the purity is higher.

  Therefore, in the present invention, the higher the purity of the aluminum used for the main body layer 20 is, the better in terms of characteristics. However, considering the cost, a 99.99% purity level that is relatively easily available is sufficient. It is.

On the other hand, the covering layer 22 plays a role of canceling out the magnetic susceptibility of the high-purity aluminum. From this relationship, the covering layer 22 has a magnetic susceptibility of the high-purity aluminum (+21 at a temperature of 300K). A diamagnetic material having a magnetic susceptibility with a sign (minus) opposite to × 10 ⁻⁶ ) is used.

  The coating layer 22 may be made of any material as long as it has a property of canceling the magnetic susceptibility of the high-purity aluminum. For example, silver, copper, and beryllium can be applied, but gold is particularly preferable. This gold has the following advantages:

1) Particularly strong diamagnetism. For example, at a temperature of 300 K, the magnetic susceptibility of copper is −9.8 × 10 ⁻⁶ and the magnetic susceptibility of silver is −24 × 10 ⁻⁶ , whereas the magnetic susceptibility of gold is −34 × 10 ⁻⁶ . Therefore, it is possible to effectively cancel the magnetic susceptibility of the high-purity aluminum while keeping the volume ratio with respect to the high-purity aluminum constituting the main body layer 20 small. Now, assuming that the thicknesses of the layers 20 and 22 are sufficiently smaller than the coil diameter and the volume ratio of the layers 20 and 22 is equal to the thickness ratio of the layers, The total thickness of the covering layer 22 may be about 2/3 of the aluminum main body layer 20, and the covering layer 22 on one side may be 1/3 the thickness of the main body layer 20. When used at an extremely low temperature, it is necessary to consider the magnetic susceptibility at that temperature, but in any case, the gold layer thickness can be set smaller than that of silver or copper.

  However, in the present invention, the volume ratio of the coating layer 22 to the main body layer 20 may not be set accurately so as to cancel the magnetic susceptibility, and at least the absolute value of the magnetic susceptibility can be reduced. It is sufficient that the layer thickness is set.

  2) The coating layer 22 can be easily formed. Specifically, the coating layer 22 can be formed on both surfaces of the main body layer 20 by a very general method such as gold vapor deposition or gold plating. In particular, when vapor deposition is employed, a desired layer thickness can be obtained accurately and easily by managing the vapor deposition time.

  When actually forming the coil, after performing the coating layer forming step of forming the coating layer 22 on both the front and back surfaces of the main body layer 20, the layers 20 and 22 are molded into a cylindrical shape (coil shape). The coil forming step may be performed, or conversely, the main body layer 20 may be formed into a cylindrical shape, and then the covering layer 22 may be laminated on both the front and back surfaces.

  Note that, on the end face of the completed coil (for example, the upper end face 11 of the NMR detection coil 10 shown in FIG. 1A and the edge face 13 surrounding the side opening), the aluminum constituting the main body layer 20 is slightly present. Although it will be exposed, the exposed area is extremely small, so there is no effect on magnetism, and the effects of the present invention can be fully exerted. Further, the main body layer 20 exposed at the end face can be covered with the covering layer 22 in the same manner as the other faces.

  Conversely, the covering layer 22 does not necessarily have to be formed so as to cover the entire surface of the main body layer 20 and may have a structure in which the main body layer 20 is partially exposed. However, if the covering layer 22 is formed so as to cover the entire front and back surfaces of the main body layer 20, a higher magnetic susceptibility canceling effect can be obtained, and an oxide film can be formed on the surface of the main body layer 20 made of aluminum. There is an advantage that it is possible to more effectively suppress the fluctuation of the magnetic characteristics due to the formation of the oxide film more reliably.

  In manufacturing the NMR detection coil 10 as shown in FIGS. 1A and 1B, the following steps are executed.

1) Body layer forming step As a metal thin plate constituting the body layer 20, an aluminum foil having a thickness of 30 μm made of 99.99% aluminum is prepared. It is sufficient that this foil finally has a size of about 50 mm square. However, the foil is made of a thin plate material with a predetermined shape (for example, a coil shown in FIG. In the case of cutting out the shape of the metal sheet, it is preferable to prepare a sheet having a size of about 100 mm square with a margin in the size of the metal thin plate.

2) Coating layer forming step Gold is vapor-deposited on both the front and back surfaces of the aluminum foil to form the coating layer 22. As a pretreatment, the front and back surfaces of the foil are worn by about 5 μm by sputtering or the like in order to remove oxide films and deposits (organic matter in the air, etc.) formed on the surface of the aluminum foil. As a result, the thickness of the aluminum foil is 30 μm−5 μm × 2 = 20 μm. Since the ratio of the absolute value of the magnetic susceptibility of the high-purity aluminum constituting the aluminum foil and the absolute value of the magnetic susceptibility of the gold constituting the coating layer 22 is about 2: 3, A coating layer 22 having a thickness of about 6.7 μm (about 13.3 μm on both sides) is formed on both the front and back surfaces of the main body layer 20. The thickness of the coating layer 22 can be accurately and easily realized by managing the gold deposition time.

  In order to cancel out the magnetic susceptibility of the high-purity aluminum and the magnetic susceptibility of gold, it is necessary to accurately set the volume ratio of the two, but the thickness of each layer is constant, and the thickness dimension is Since the curvature of the layer (that is, the coil diameter) is sufficiently small, it can be sufficiently approximated by the layer thickness ratio.

3) Coil forming step The plate material on which the main body layer 20 and the covering layer 22 are laminated is rolled into a cylindrical shape as shown in FIG. 1A to form a magnetic resonance detecting coil 10, as shown in FIG. 2B. The inner tube 42 and the outer tube 44 are sandwiched.

  The following various metal rings were wound around a part of the sample as a simulation coil, and the magnetic field strength distribution in the axial direction was measured. Specifically, in the NMR apparatus, the superconducting coil is adjusted so that the magnetic field strength is uniform in the axial direction before the simulation coil is inserted, and then various coils are inserted to measure the magnetic field strength. I tried to do it.

  Metal ring 1 (Example): Both front and back surfaces of an aluminum main body layer having a thickness of 30 μm are covered with a gold coating layer having a thickness of 10 μm.

  Metal ring 2 (Example): The front and back surfaces of an aluminum main body layer having a thickness of 100 μm are covered with a copper coating layer having a thickness of 30 μm.

  Metal ring 3 (comparative example): Only a copper plate having a thickness of 100 μm.

  The result is shown in FIG. In the figure, curves L1, L2, and L3 indicate the characteristics of the metal rings 1, 2, and 3, respectively.

  As indicated by the curve L3 (dashed line) in the figure, in the metal ring 3, the diamagnetism of copper appears in the magnetic intensity distribution as it is, and a significant magnetic field distortion is generated on the negative side. Compared with this metal ring 3, in the metal ring 2, the diamagnetism of copper and the magnetism of aluminum cancel each other, and the magnetic field distortion is effectively reduced as shown by the curve L2 (broken line). According to the metal ring 1 corresponding to the embodiment, the magnetic field distortion can be further effectively reduced as shown by the curve L1.

(A) is a perspective view of the NMR detection coil which concerns on embodiment of this invention, (b) is sectional drawing which shows the structure of the board | plate material which comprises the coil. (A) is a cross-sectional front view of an NMR apparatus including the NMR detection coil, and (b) is a cross-sectional plan view showing an internal structure of an NMR probe incorporated in the apparatus. It is a graph which shows magnetic field strength distribution of the coil for magnetic resonance detection formed with various materials.

Explanation of symbols

10 Coil for NMR detection 20 Body layer 22 Covering layer

Claims (5)

  In a magnetic resonance detection coil having a substantially cylindrical peripheral wall and forming a space into which a sample is inserted, a main body layer made of aluminum and a coating layer covering the surface of the main body layer The coil for magnetic resonance detection is characterized in that the coating layer is made of a diamagnetic material having a magnetic susceptibility opposite to the magnetic susceptibility of aluminum forming the main body layer.   2. The magnetic resonance detection coil according to claim 1, wherein the volume of the main body layer and the coating layer is such that the magnetic susceptibility of aluminum constituting the main body layer and the susceptibility of the diamagnetic material constituting the coating layer are offset. A coil for magnetic resonance detection, characterized in that a ratio is set.   The magnetic resonance detection coil according to claim 1 or 2, wherein the coating layer is made of gold.   A method for manufacturing the magnetic resonance detecting coil according to claim 3, wherein a coating layer is formed by depositing gold on the surface of aluminum constituting the main body layer or by gold plating, and the coating step. A coil forming step of forming the main body layer into a cylindrical shape before or after the step of manufacturing the magnetic resonance detecting coil.   5. The method for manufacturing a magnetic resonance detecting coil according to claim 4, wherein the covering step is to deposit gold on the surface of the main body layer, and to form the magnetic susceptibility of the aluminum constituting the main body layer and the covering layer. A method for manufacturing a magnetic resonance detecting coil, characterized in that the gold deposition time is set so that a volume ratio of a main body layer and a coating layer is obtained so that a magnetic susceptibility of a diamagnetic material to be canceled out.

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