JP3942563B2 - High frequency coil of magnetic resonance imaging apparatus and method of manufacturing high frequency coil - Google Patents

Description

  The present invention relates to a high-frequency coil used in a magnetic resonance imaging apparatus and a method for manufacturing the high-frequency coil.

  A magnetic resonance imaging apparatus (hereinafter simply referred to as an MRI apparatus) places a subject such as a human body in a static magnetic field and has a high frequency that matches the nuclear magnetic resonance frequency of the target atom of the subject. By applying a rotating magnetic field and applying a gradient magnetic field for obtaining position information, internal information of the subject is acquired non-invasively as an image. It is known that the nuclear magnetic resonance frequency depends on the strength of the static magnetic field and the nuclide to be observed. For example, the nuclear magnetic resonance of a hydrogen atom (proton) placed in a static magnetic field having an intensity of 4.7 [T]. The frequency is approximately 200 [MHz].

  The MRI apparatus has a high frequency coil for irradiating a subject with a high frequency pulse having a nuclear magnetic resonance frequency and detecting a nuclear magnetic resonance signal from the subject. The high-frequency coil includes a saddle type, a surface coil type, a birdcage type, a TEM type, and the like, and is selected according to various conditions such as the type of subject, resonance frequency, information to be acquired, and the like.

  For example, as a birdcage coil, a coil having two ring portions that are provided coaxially and spaced apart and a plurality of elements that connect these two ring portions is known (for example, see Patent Document 1). . By adjusting the width of the element to an appropriate width, this birdcage coil suppresses the generation of eddy currents, minimizes the excitation power and increases the signal-to-noise ratio (hereinafter referred to as S / N ratio), It is characterized by increased efficiency.

  However, this birdcage coil adjusts the width of the element, but does not consider the thickness of the element, and ignores the influence of electromagnetic effects such as the skin effect at high frequencies. In the high frequency region where the nuclear magnetic resonance frequency exceeds 50 [MHz], a quasi-stationary analysis is necessary, and the skin effect and the influence of the self-inductance based thereon are factors that cannot be ignored. That is, it is known that the high-frequency current flowing through the conductor does not flow to a part exceeding a certain depth from the surface of the conductor because of the skin effect. For this reason, it is expected that the self-inductance varies depending on the thickness of the conductor, and a change in the S / N ratio due to the thickness of the coil can be considered.

Considering the use of the birdcage coil in the high frequency region as described above, there arises a problem that the S / N ratio decreases depending on the thickness of the coil.
JP-A-8-280651 (paragraphs [0020] to [0023], FIG. 2)

  An object of the present invention is to provide a high-frequency coil of a magnetic resonance imaging apparatus and a method of manufacturing a high-frequency coil that can increase the intensity of a detection signal and improve the S / N ratio.

In order to achieve the above object, the high-frequency coil of the present invention applies a gradient magnetic field to a subject placed in a 4.7 T static magnetic field, and determines the nucleus determined by the nuclide of the target atom of the subject and the strength of the static magnetic field. A magnetic resonance imaging apparatus for acquiring an image of a subject by irradiating a subject with a high frequency pulse having a magnetic resonance frequency and detecting a nuclear magnetic resonance signal corresponding to the high frequency pulse from the subject. In order to maximize the S / N ratio of the detected nuclear magnetic resonance signal, the thickness of the conductive segment formed of copper is approximately 12 times the skin depth determined by the material and the angular velocity of the high frequency pulse of 200.7 MHz . It is characterized by setting.

  Further, according to the method of manufacturing a high frequency coil of the present invention, a conductive sheet material having a target thickness of the conductive segment is prepared, a photoresist layer is provided on the sheet material, and the target of the conductive segment is determined. The photoresist layer is exposed through a mask having a shape to etch the sheet material.

Furthermore , according to the method for manufacturing a high-frequency coil of the present invention, a conductive material having the shape of the conductive segment is formed on the surface of the insulator by electroless plating, and the conductive material is grown to a target thickness by electrolytic plating. It is characterized by that.

  As described above, since the high frequency coil of the present invention has the above-described configuration and operation, the signal intensity of the nuclear magnetic resonance signal detected by the high frequency coil can be increased, and the S / N ratio can be increased. Can be improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a schematic structure of a magnetic resonance imaging apparatus 10 (MRI apparatus 10) provided with a birdcage coil 1 as a high-frequency coil according to the first embodiment of the present invention. FIG. 2 is a schematic perspective view of the birdcage coil 1. FIG. 3 is a partially enlarged view of the structure of the main part of the MRI apparatus 10. Furthermore, FIG. 4 shows a cross-sectional view taken along line IV-IV in FIG. In FIG. 4, the birdcage coil 1 is illustrated in a simplified manner for simplification of illustration.

  The MRI apparatus 10 includes a substantially cylindrical magnet 11 that functions as a static magnetic field applying unit that applies a static magnetic field having a constant strength to a rat as a subject. The diameter of the magnet 11, that is, the size of the MRI apparatus 10 can be changed as appropriate according to the type of the subject.

  A substantially cylindrical gradient coil 12 that functions as a gradient magnetic field applying unit is disposed inside the magnet 11. A power source 21 is connected to the gradient magnetic field coil 12 to generate a gradient magnetic field for giving position information to a nuclear magnetic resonance signal from an examination site of a subject. Note that a high-frequency shield, that is, a Faraday shield 13 is attached to the inside of the gradient magnetic field coil 12.

  The birdcage coil 1 is disposed further inside the gradient magnetic field coil 12. The birdcage coil 1 is connected to a power source 22 for irradiating a subject with a high frequency pulse and an amplification circuit 23 for amplifying a nuclear magnetic resonance signal detected from the subject.

  As shown in FIG. 2, the birdcage coil 1 has two ring members 2, 2 made of conductive members provided coaxially with each other and spaced apart by a predetermined distance. Between the two ring members 2, 2, a plurality (eight in this embodiment) of substantially rectangular film-like conductive segments 4 are provided. A fixed gap is formed in each connection portion where each conductive segment 4 faces the ring member 2, and a capacitance 6 is provided in each gap. The capacitance 6 is fixed by soldering or the like.

  The MRI apparatus 10 includes a computer 24, a monitor 25, and a table 26. The computer 24 functions as signal processing means for processing the nuclear magnetic resonance signal amplified through the amplifier circuit 23 to generate an image of the subject, and includes two power sources 21 and 22, an amplifier circuit 23, and a table 26. Control.

  The monitor 25 functions as a display unit that displays an image of the subject generated by the computer 24. Further, the table 26 slides in the axial direction of the birdcage coil 1 with the subject placed thereon, and the subject is inserted toward the center of the birdcage coil 1.

  When acquiring an image of a subject by the MRI apparatus 10 configured as described above, first, a static magnetic field is applied to the subject by the magnet 11, and a gradient magnetic field is applied by the gradient magnetic field coil 12. Then, a high frequency pulse having a nuclear magnetic resonance frequency determined by the static magnetic field strength and the nuclide of the subject's target atom is given to the subject via the birdcage coil 1, and a nuclear magnetic resonance signal corresponding to the high frequency pulse is given from the subject. To detect. Further, the detected nuclear magnetic resonance signal is amplified and processed by the computer 24 to obtain an image of the subject. The acquired image is displayed via the monitor 25.

  In order to acquire an image of a subject (phantom image) with a high S / N ratio by the MRI apparatus 10 described above, it is generally effective to reduce the resistance value of the plurality of conductive segments 4 of the birdcage coil 1. It is considered. That is, it is considered effective to increase the cross-sectional area of the conductive segment 4.

  However, according to the Maxwell equation, it is known that the high-frequency current flowing through the conductive segment 4 does not flow to a part exceeding a certain depth from the surface of the conductive segment 4, and a phenomenon called skin effect exists. .

That is, when ω is the angular velocity of the high frequency pulse, σ is the electrical conductivity, and μ is the magnetic permeability.
δ = [2 / (ω × σ × μ)] ^1/2
It is known that the current density is remarkably reduced when the depth is exceeded. This σ is generally called the skin depth.

  The meaning of this equation means that the fluctuating current does not flow beyond a certain depth of the conductive segment 4, and does not mean that the equivalent series resistance is higher in the thick conductor than in the thin conductor. Rather, the resistance value at a certain thickness or more is the same, and the resistance value is not improved even if an unnecessarily thick conductor is used. That is, the birdcage coil 1 of the present embodiment is considered. For example, if the thickness of the conductive segment 4 is equal to or greater than a certain thickness, the S / N ratio should be interpreted as being substantially constant.

On the other hand, for example, the self-inductance of a conductor having a radius a and a length l is described by the sum of internal inductance and external inductance as follows: However, mu is the magnetic permeability of the conductor, mu ₀ is the permeability of vacuum, a _s is the skin depth of the conductor.

  The first item in the above equation is the internal inductance when the skin effect is taken into consideration, and the second item is the external inductance. This equation means that as the radius a increases, both the external inductance and the internal inductance decrease. In other words, it indicates that the thicker the thickness, the smaller the self-inductance. It is considered that the S / N ratio is larger when the self-inductance is larger, suggesting that the S / N ratio decreases if the conductive segment is thicker. That is, when considered together with the above-described equivalent series resistance, it suggests that there exists a certain optimum value for the thickness of the conductive segment.

Further, it is known that in a region exceeding the skin depth, although no fluctuation current flows, it is affected by the fluctuation of the magnetic field and there is a hysteresis loss . It is known that a copper material generally used as the material of the conductive segment 4 has a very small hysteresis loss , and this loss is generally ignored in many cases. However, there is no doubt that there is a loss, but the S / N ratio decreases when a thick conductor is used.

  In view of the above, it is understood that the optimum value of the thickness of the conductive segment 4 of the birdcage coil 1 described above is not easily predicted and needs to be obtained by experiment. Conventionally, there has been no report that has been investigated in detail regarding the relationship between the conductor thickness and the S / N ratio.

  Therefore, the inventors of the present application changed the thickness of the conductive segment in various ways, measured the signal intensity of the nuclear magnetic resonance signal detected from the subject in each case, and conducted an experiment to obtain the optimum value of the thickness of the conductive segment. went.

  In the experiment, an experimental coil was formed by winding a strip-shaped conductive segment having a thickness of 1 [cm] around a tubular insulating object having a diameter of 2 [cm] and a length of 3 [cm]. The signal intensity of the nuclear magnetic resonance signal obtained from this coil was measured. The results are shown graphically in FIG.

  At this time, a sample filled with a 0.1 [%] concentration copper sulfate aqueous solution was inserted into the coil, magnetic field inhomogeneity was removed as much as possible by shimming operation, and then the cut image of the sample was spin-echoed. Was obtained every 2 [mm]. Then, the signal intensity is indicated by a value obtained by integrating the signal intensity of each pixel of 3 slices (corresponding to a signal of 6 [mm] width) in which the maximum luminance is obtained. The coil has a capacitance (1) necessary for tuning at a frequency to be measured (in this case, 200.7 [MHz] which is the nuclear magnetic resonance frequency of proton in a static magnetic field of 4.7 [T]). −30 [pF]) was attached. In addition, a balance-unbalance converter (balun) was inserted to prevent the effects of unbalanced current.

  As is clear from the experimental results shown in FIG. 5, it was confirmed that there was a peak of signal intensity and there was an optimum thickness that maximized the signal intensity. Here, the optimum thickness was 60 [μm]. That is, it has been found that the S / N ratio is improved by designing the conductive segment to a thickness that maximizes the signal intensity.

  In the above-described experiment, the optimum thickness of the conductive segment was obtained from the S / N ratio of the phantom image acquired using the MRI apparatus, but the S / N ratio was maximized even by the method of directly obtaining the magnetic field strength of the coil. The optimum thickness of the conductive segment can be estimated. In this case, the magnetic field strength in the coil generated by exciting a high-frequency current in the coil is measured by a magnetic sensor. As the magnetic sensor, a sensor that can measure a high-frequency magnetic field in the vicinity of the resonance frequency and has little AC coupling is desirable. As a corresponding sensor, for example, there is a magnetic field measurement sensor using a micro shield loop. The point with the maximum magnetic field strength has the maximum S / N ratio. By inserting this sensor into the coil and measuring the magnetic field strength, the maximum S / N ratio point can be estimated from the magnetic field strength.

  Hereinafter, a method for adjusting the conductive segment of the coil to an optimum thickness will be described.

  First, a coil shape suitable for the purpose of inspection is selected. For example, when blood flow measurement such as arteriole spin labeling is performed, it is desirable that a uniform high-frequency magnetic field be applied to the entire subject, and it is preferable to use a birdcage coil. Further, if it is desired to obtain a local anatomical image with high resolution, it is preferable to select a surface coil capable of obtaining a high S / N ratio.

  Next, the size of the coil and the width of the conductive segment are determined according to the size of the subject. In this determination, the size of the coil and the width of the conductive segment are determined so that the volume of the subject is closely packed with respect to the internal volume of the coil. The thickness of the conductive segment is about the skin depth at the nuclear magnetic resonance frequency used. Then, the capacitance necessary for tuning the coil at the nuclear magnetic resonance frequency is obtained, and the S / N ratio of the coil is obtained by actually obtaining a phantom image using the coil or measuring the magnetic field strength of the coil.

  Then, the thickness of the conductive segment is gradually increased from the initial value, and the capacitance of the capacitor is changed in accordance with the inductance value of this thickness to obtain the S / N ratio of the coil. This operation is repeated to determine the thickness of the conductive segment that maximizes the S / N ratio.

  Hereinafter, the procedure for determining the thickness of the conductive segment in the birdcage coil will be specifically described.

  First, the length of the conductive segment of the birdcage coil and the diameter of the ring member are determined from the size of the subject. In this determination, the filling factor is determined to be maximized so that the volume of the subject is closely packed with respect to the internal volume of the birdcage coil. For example, when observing the head of a rat that is an experimental animal, the diameter of the ring member is 38 [mm] and the length of the conductive segment is 40 [mm]. The initial value of the width of the conductive segment is approximately the same as the segment interval. Although it is desirable that the number of conductive segments is as large as possible, it is set to 16 or 32 in consideration of adjustment of the tuning capacitor. The skin depth at the resonance frequency used is used as the initial value of the thickness of the conductive segment. Then, the capacitance required to tune the birdcage coil at the nuclear magnetic resonance frequency is obtained, and the S / N ratio of the birdcage coil is obtained by actually obtaining a phantom image or measuring the magnetic field strength.

  Then, the thickness of the conductive segment is increased from the initial value, and the capacitance of the capacitor is changed in accordance with the inductance value of this thickness to obtain the S / N ratio of the birdcage coil. This operation is repeated to determine the thickness of the conductive segment that maximizes the S / N ratio.

  In addition, although it is common to use comparatively cheap copper for the electrically-conductive member which comprises the birdcage coil 1 demonstrated by embodiment mentioned above, other metal materials, such as silver and gold | metal | money, are used. May be. The conductive segment 4 may be manufactured by cutting a metal member into a desired size and pasting it with an adhesive or the like. However, the conductive segment 4 may be manufactured using a tape-like metal member with an adhesive attached in advance. Also good.

  In addition, the metal member is not limited to a plate shape, and a pipe shape can also be used. In this case, the thickness of the pipe may be set to a value that maximizes the intensity of the nuclear magnetic resonance signal.

  FIG. 6 shows a surface coil 30 as a high-frequency coil according to the second embodiment of the present invention. The conductive segment 31 of the surface coil 30 is formed in an annular shape, but may be formed in a square shape such as a quadrangular shape, a triangular shape, or a hexagonal shape.

  Also in this embodiment, the thickness of the conductive segment 31 is set to a thickness that maximizes the intensity of the nuclear magnetic resonance signal detected via the surface coil 30. Moreover, the conductive segment 31 may cut out a metal plate or metal foil, or may use a pipe-shaped material. When a pipe is used, the thickness thereof is regarded as the thickness of the conductive segment 31. The metal member may be cut out to a desired size and then pasted with an adhesive or the like. Alternatively, the metal member may be produced using a tape-shaped metal member with an adhesive beforehand. When the thickness of the conductive segment 31 is relatively thick, the surface coil 30 can be formed by itself using only a metal member. However, when the thickness is relatively thin and it is difficult to stand by itself, it is fixed to a support member (not shown). You may do it. In this case, the shape of the support member can be arbitrarily selected, and can be processed into a shape along the shape of the subject. That is, the surface coil 30 can be brought close to the subject, and the S / N ratio can be further improved.

  FIG. 7 shows a saddle coil 40 as a high-frequency coil according to the third embodiment of the present invention. Similarly to the conductive segments 4 and 31 of the coils of the first and second embodiments described above, the intensity of the nuclear magnetic resonance signal detected from the subject is maximized in the conductive segment 41 of the saddle coil 40 as well. Set to thickness. As a result, the same effects as those of the first and second embodiments described above can be obtained.

  FIG. 8 is an operation explanatory diagram for explaining a method of manufacturing the conductive segments 4, 31, and 41 of the first to third embodiments described above. Here, the case where a conductive segment is formed by a photographic method and an etching method will be described.

  In the MRI apparatus having a static magnetic field strength of 4.7 [T], when the nuclear magnetic resonance frequency of proton is 200 [MHz] and a copper material is used for the conductive segment, according to the present invention, the thickness of the conductive segment is It becomes several tens of μm. Therefore, a manufacturing method using a combination of a photographic method and an etching method can be used for the conductive segment of the present invention.

  As a preferred material, an example (FIG. 8a) using, for example, copper-clad polyimide in which a conductive copper sheet 52 is bonded to an insulating sheet 51 is shown. The thickness of the copper sheet 52 is about the thickness of the target conductive segment.

  First, as shown in FIG. 8B, a photosensitive photoresist tape 53 is applied to the surface of the copper sheet 52. Photoresist can be applied by spin coating, but when copper-clad polyimide is used, it is preferable to use a photoresist tape such as ORDYL TR400 manufactured by Tokyo Ohka Co.

  Then, as shown in FIG. 8C, a mask 54 having a pattern that does not transmit light is superimposed on the upper surface of the photoresist tape 53, and a predetermined amount of light depending on the photoresist tape 53 is exposed to irradiate light. The photoresist tape 53 is removed into an arbitrary shape by development by chemical modification of the site subjected to the treatment (FIG. 8d).

  Further, as shown in FIG. 8E, the copper sheet 52 is partially etched by immersing it in a copper etching solution with the photoresist tape 53 removed in an arbitrary shape, and a desired copper pattern is formed. Is done.

  Since exposure and development are preferably performed on a planar material, the exposure and development are performed by this method. Although the copper pattern is flat, it is developed by directly exposing the three-dimensional part by applying a sprayed photoresist (spray coating method) and a rotary exposure device using laser light. Thus, a three-dimensional copper pattern can be directly formed.

  When the copper pattern is produced in a flat shape, it can be attached to a fixing member such as plastic, or can be placed on the measurement object as it is in a state having towability.

  In addition, a method of forming a conductive segment on the surface of an insulator such as plastic by using a plating method is conceivable. A technique for forming a metal pattern on the surface of an insulator by plating is a well-known technique.

  As a method of applying a metal to the surface of an insulator such as a synthetic resin body (plastic), a known electroless plating method can be applied. That is, after roughening the surface of the insulator by etching using a wet method (such as a method of immersing in an alkaline solution such as NaOH) or a dry method (such as a method using plasma etching), a known plating containing lead or platinum is used. After applying a catalyst (for example, palladium chloride) to the surface, the catalyst metal is deposited on the surface by an accelerator (accelerating liquid), and then infiltrated into a known metal plating bath (copper plating or silver plating bath) for insulation. This is a technique of applying metal to the surface.

  In general, since the metal film obtained by electroless plating is thin, electrolytic plating is used to grow the conductive segment to a desired thickness. As the electrolytic plating method, a known electrolytic plating method can be applied. For example, in the case of copper plating, a copper sulfate plating bath, a copper cyanide plating bath, and in the case of silver plating, a cyan alkali bath or a non-cyan bath (for example, Daiwa Kasei Dyne Silver) can be used.

  In the example of the birdcage coil 1 shown in FIG. 2, after thinly and entirely copper-plating the plastic surface by electroless plating, the copper plating is patterned with a laser beam or the like, and then electroplating. , And grow to a desired thickness (thickness at which the nuclear magnetic resonance signal detected by the birdcage coil 1 is maximized).

  Further, in electroless plating, a catalyst is required, and a conductive segment having an arbitrary shape can be formed by a method of controlling the catalyst applied to the plastic surface. According to this method, it is possible to form a conductive segment pattern on the inner circumference of the cylinder, and it is also possible to easily form a shielded birdcage coil by covering the outer circumference with a metal foil as a shield. is there.

The following four methods can be applied to the patterning of the conductive segment in manufacturing the coil by such a plating method.
(1) A method in which, after applying a catalyst, patterning is performed by forming a film that does not grow plating on the catalyst surface, electroless plating is grown, and then an electrolytic plating layer is grown.
(2) After applying the catalyst, the whole is electrolessly plated, a film (resist layer) that resists etching is formed on the surface, the resist layer is patterned, the electroless plating layer is etched, and then electrolysis is performed. Method of plating.
(3) A method of performing electroplating after patterning the electroless plating layer directly by laser ablation or the like after electroless plating of the whole after applying the catalyst.
(4) A method of etching the electroless plating layer and the electroplating layer after applying the catalyst, electrolessly plating the whole, electroplating, forming a resist layer on the surface and patterning the resist layer.

In addition, the method of forming a film that does not grow plating and a film that resists etching is almost the same, and the following method can be applied.
(1) By a silk printing method or a dispenser coating method, a polyimide film (for example, Semicofine manufactured by Toray), a water-soluble polymer material or a hydrolyzable polymer material (for example, polyvinyl alcohol, polylactic acid, etc .; A method of applying a molecular material film) according to a pattern.
(2) A method in which a polyimide film or a polymer material film is applied to the entire surface by a dip method or a spray coating method, and then unnecessary portions are removed by a laser ablation method.
(3) The photosensitive resist is applied to the entire surface by dipping or spray coating, and then the photosensitive resist is patterned by photolithography using a projection exposure apparatus having a focal length of laser light or depth. Method.

  As described above, according to the present invention, the thickness of the conductive segment of the high-frequency coil is set to a thickness that maximizes the intensity of the nuclear magnetic resonance signal detected through the high-frequency coil. The S / N ratio of the image could be improved.

  In addition, according to the present invention, since the thickness of the conductive segment is formed to be about several tens of μm, the conductive segment can be formed using a photographic method or an etching method, unlike a conventional method for manufacturing a conductive segment. For this reason, a device suitable for a relatively small subject, for example, a small part such as a human finger, joint, ankle, or wrist can be provided, and can be suitably applied to imaging of animals as described in the present embodiment.

  In addition, since the conductive segment can be formed in a film shape, the shape of the high-frequency coil can be formed in a shape along the shape of the subject, the conductive segment can be brought closer to the subject, and the S / N ratio can be further improved. it can.

  Furthermore, since the conductive segment of the present invention can be created using photolithography technology, the positional accuracy between each conductive member can be increased on the micron order, and application to a finer subject is expected, and FDTD Applications that can realize coil design based on simulation results such as (Finite Difference Time Domain) method (time domain difference method) with high accuracy are also expected.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, you may delete some components from all the components shown by embodiment mentioned above. Furthermore, you may combine the component covering different embodiment suitably.

The figure which shows schematic structure of the MRI apparatus provided with the birdcage coil which concerns on 1st Embodiment of this invention. The perspective view which shows the schematic structure of the birdcage coil integrated in the MRI apparatus of FIG. The partial expanded sectional view which expands and shows partially the structure of the principal part of the MRI apparatus of FIG. Sectional drawing cut | disconnected by line segment IV-IV of FIG. The graph which shows the experimental result for investigating the relationship between the thickness of the conductive segment of a high frequency coil, and signal strength. The schematic perspective view which shows the surface coil which concerns on 2nd Embodiment of this invention. The schematic perspective view which shows the saddle type coil which concerns on 3rd Embodiment of this invention. Operation | movement explanatory drawing for demonstrating the manufacturing method of an electroconductive segment.

Explanation of symbols

1 ... Birdcage coil,
2 ... Ring member,
4, 31, 41 ... conductive segment,
6 ... Capacitance,
10 ... MRI equipment,
11 ... Magnet,
12 ... gradient coil,
13 ... Faraday shield,
21, 22 ... power supply,
23. Amplifier circuit,
24 ... Calculator,
25. Monitor,
26 ... table,
30 ... Surface coil,
40: saddle type coil.

Claims (2)

Applying a gradient magnetic field to a subject placed in a 4.7 T static magnetic field, irradiating the subject with a radio frequency pulse having a nuclear magnetic resonance frequency determined by the nuclide of the subject's target atom and the strength of the static magnetic field, A high-frequency coil used in a magnetic resonance imaging apparatus for acquiring an image of a subject by detecting a nuclear magnetic resonance signal corresponding to the high-frequency pulse from the subject,
In order to maximize the S / N ratio of the detected nuclear magnetic resonance signal, the thickness of the conductive segment formed of copper is set to approximately 12 times the skin depth determined by the material and the angular velocity of the high frequency pulse of 200.7 MHz. A high-frequency coil characterized by A method of manufacturing the high-frequency coil according to claim 1,
Prepare a conductive sheet material having a target thickness of the conductive segment,
A photoresist layer is provided on this sheet material,
Exposing the photoresist layer through a mask having a target shape of the conductive segment;
A method for producing a high-frequency coil, comprising etching the sheet material.

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