Magnetic resonance imaging apparatus and gradient coil

A magnetic resonance imaging apparatus according to an embodiment includes a gradient coil configured to generate a gradient magnetic field in an image taking space. The gradient coil includes: a first coil member formed by using a first metal that is non-magnetic; and a second coil member connected to the first coil member and formed by using a second metal that is different from the first metal and is non-magnetic.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-023692, filed on Feb. 10, 2014; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic resonance imaging apparatus and a gradient coil.

BACKGROUND

Conventionally, a magnetic resonance imaging apparatus includes a gradient coil configured to generate gradient magnetic fields in an image taking space in which a subject serving as an image taking target is placed. Generally speaking, such a gradient coil includes conductor patterns formed by using copper, as conductive members that form the coil.

DETAILED DESCRIPTION

A Magnetic Resonance Imaging (MRI) apparatus according to an embodiment includes a gradient coil configured to generate a gradient magnetic field in an image taking space. The gradient coil includes: a first coil member formed by using a first metal that is non-magnetic; and a second coil member connected to the first coil member and formed by using a second metal that is different from the first metal and is non-magnetic.

Exemplary embodiments of an MRI apparatus and a gradient coil of the present disclosure will be explained below, with reference to the accompanying drawings.

FIG. 1is a diagram of an exemplary configuration of an MRI apparatus according to an embodiment. As illustrated inFIG. 1, an MRI apparatus100includes a gantry110, a reception coil120, a gradient power source130, a transmitter140, a receiver150, a sequence controller160, a couch170, and a computer system180.

The gantry110is configured to support a magnetostatic field magnet111, a gradient coil112, and a transmission coil113that are each formed in the shape of a substantially circular cylinder, in such a manner that the central axes thereof are aligned while the gradient coil112is disposed on the inner circumferential side of the magnetostatic field magnet111, whereas the transmission coil113is disposed on the inner circumferential side of the gradient coil112. Further, the gantry110has a bore114that is formed in the shape of a circular cylinder and positioned on the inner circumferential side of the transmission coil113. An image taking space is formed on the inner circumferential side of the bore114.

The magnetostatic field magnet111is a magnet formed in the shape of a circular cylinder and is configured to generate a magnetostatic field in the image taking space, by using electric current supplied from a magnetostatic field power source (not illustrated). For example, the magnetostatic field magnet111may be a superconducting magnet including a vacuum container formed in the shape of a substantially circular cylinder and a superconducting coil immersed in a cooling liquid within the vacuum container. The magnetostatic field magnet111does not necessarily have to be a superconducting magnet and may be a permanent magnet or a normal-conducting magnet.

The gradient coil112is a coil formed in the shape of a circular cylinder and is configured to generate, inside the image taking space, gradient magnetic fields of which the intensities change along the X-, Y-, and Z-axes that are orthogonal to one another, by using an electric current supplied from the gradient power source130. For example, the gradient coil112may be an Actively Shielded Gradient Coil (ASGC) including a main coil112aand a shield coil112b. The main coil112ais configured to generate, inside the image taking space, the gradient magnetic fields of which the intensities change along the X-, Y-, and Z-axes. Further, the shield coil112bis disposed on the outer circumferential side of the main coil112aand is configured to cancel a leakage magnetic field of the main coil112a. The gradient coil112does not necessarily have to be configured with an ASGC and may not include the shield coil112b.

The transmission coil113is a coil formed in the shape of a circular cylinder and is disposed on the inside of the gradient coil112. Further, the transmission coil113is configured to generate, inside the image taking space, a radio frequency magnetic field, by using a radio frequency current supplied from the transmitter140.

The reception coil120is attached to a subject S and is configured to receive magnetic resonance signals generated from the subject S placed in the image taking space, due to an influence of the radio frequency magnetic field generated by the transmission coil113. Further, the reception coil120is configured to amplify and output the received magnetic resonance signals, by using an amplifier provided therein.

In the present embodiment, the example is explained in which the transmission coil113and the reception coil120are separate coils. However, it is also acceptable to use a coil that has both the transmitting and the receiving functions and operates for transmitting/receiving purposes. In that situation, the transmission coil113may further have the receiving function or the reception coil120may further have the transmitting function.

The gradient power source130is configured, on the basis of an instruction from the sequence controller160, to supply the electric current to the gradient coil112. For example, the gradient power source130includes a high voltage generating circuit, a gradient amplifier, and the like. The high voltage generating circuit is configured to convert an alternate current (AC) supplied from a commercial alternate current power source into a direct current (DC) having a predetermined voltage and to supply the DC to the gradient amplifier. The gradient amplifier is configured to amplify the DC supplied from the high voltage generating circuit and to supply the amplified DC to the gradient coil112.

The transmitter140is configured, on the basis of an instruction from the sequence controller160, to transmit an RF pulse to the transmission coil113. For example, the transmitter140includes, an oscillator, a phase selector, a frequency converter, an amplitude modulator, an RF amplifier, and the like. The oscillator is configured to generate the RF pulse on a resonance frequency that is unique to a targeted atom nucleus in the magnetostatic field. The phase selector is configured to select a phase of the RF pulse generated by the oscillator. The frequency converter is configured to convert the frequency of the RF pulse output from the phase selector. The amplitude modulator is configured to modulate the amplitude of the RF pulse output from the frequency modulator according to, for example, a sinc function. The RF amplifier is configured to amplify the RF pulse output from the amplitude modulator and to supply the amplified RF pulse to the transmission coil113.

The receiver150is configured to detect the magnetic resonance signals received by the reception coil120, on the basis of an instruction from the sequence controller160. Further, the receiver150is configured to generate raw data by applying an analog-to-digital conversion to the detected magnetic resonance signals and to transmit the generated raw data to the sequence controller160. For example, the receiver150includes a selector, a preamplifier, a phase detector, an A/D converter, and the like. The selector is configured to selectively receive inputs of the magnetic resonance signals output from the transmission coil113. The preamplifier is configured to amplify the magnetic resonance signals output from the selector. The phase detector is configured to detect the phase of the magnetic resonance signals output from the preamplifier. The A/D converter is configured to convert the signals output from the phase detector into digital signals.

The sequence controller160is configured, under the control of the computer system180, to perform a data acquisition process by driving the gradient power source130, the transmitter140, and the receiver150. Further, when the raw data is transmitted thereto from the receiver150as a result of the data acquisition process, the sequence controller160transmits the raw data to the computer system180.

The couch170includes a couchtop171on which the subject S is placed and is configured to move the couchtop171in up-and-down directions, front-and-back directions, and left-and-right directions. In this situation, the front direction is the direction from the couch170side toward the gantry110side along the axial direction of the magnetostatic field magnet111. The back direction is the direction from the gantry110side toward the couch170side along the axial direction of the magnetostatic field magnet111. The left direction is the direction from the axis of the magnetostatic field magnet111toward the left when the gantry110is viewed straight on, from the couch170side. The right direction is the direction from the axis of the magnetostatic field magnet111toward the right when the gantry110is viewed straight on, from the couch170side. For example, the couch170is configured to move the couchtop171on which the subject S is placed, into the image taking space formed on the inner circumferential side of the bore of the gantry110, when an image taking process is to be performed on the subject S.

The computer system180is configured to control the entirety of the MRI apparatus100. For example, the computer system180includes: an input device configured to receive various types of inputs from an operator; a sequence control processor configured to cause the sequence controller160to perform the data acquisition process on the basis of an image taking condition input by the operator; an image reconstruction processor configured to reconstruct an image on the basis of the raw data transmitted from the sequence controller160; a storage configured to store therein the reconstructed image, and the like; a display configured to display various types of information including the reconstructed image; and a main control processor configured to control operations of various functional units on the basis of an instruction from the operator.

The exemplary configuration of the MRI apparatus100according to the present embodiment has thus been explained. In the MRI apparatus100configured as described above, the gradient coil112includes the first coil member formed by using the first metal that is non-magnetic; and the second coil member connected to the first coil member and formed by using the second metal that is different from the first metal and is non-magnetic.

For example, in the present embodiment, an example will be explained in which the first metal is aluminum, whereas the second metal is copper. In other words, in the present embodiment, the gradient coil112includes: the first coil member formed by using aluminum; and the second coil member connected to the first coil member and formed by using copper.

Generally speaking, in MRI apparatuses, electrically-conductive coil members such as conductor patterns and terminals included in the gradient coil are formed by using copper, which has a high electrical conductivity. In contrast, in the MRI apparatus100according to the present embodiment, the gradient coil112is formed by using a combination of aluminum and copper. Thus, according to the present embodiment, it is possible to realize the gradient coil112that is more lightweight than when all of the electrically-conductive coil members included in a gradient coil are formed by using copper.

In the present embodiment, an example will be explained in which the first coil member is a conductor pattern that forms the coil, whereas the second coil member is a terminal that has connected thereto a power supply cable configured to supply the electric current flowing in the conductor pattern.

FIG. 2is a schematic drawing of a connection part of a conductor pattern and a terminal in the gradient coil112according to the present embodiment. For example, as illustrated inFIG. 2, the gradient coil112includes three layers of conductor patterns201to203that form the main coil112aand three layers of conductor patterns204to206that form the shield coil112b. In this situation, the gradient coil112is formed by impregnating the space in the surroundings of the conductor patterns201to203and the conductor patterns204to206with resin112c.

Further, the gradient coil112includes a terminal207connected to the conductor pattern206included in the shield coil112b. The terminal207has connected thereto a power supply cable208configured to supply the electric current flowing in the conductor pattern206. For example, to the terminal207, a terminal209provided on the power supply cable208side is attached, by using a bolt210. In this situation, the power supply cable208is provided between the gradient power source130and the gradient coil112and is configured to supply the electric current from the gradient power source130to the gradient coil112. Further, although not illustrated inFIG. 2, a terminal similar to the terminal207is connected to each of the conductor patterns201to205.

Further, each of the conductor patterns201to206is formed by using aluminum. In contrast, the terminal connected to each of the conductor patterns201to206is formed by using copper.

Generally speaking, in MRI apparatuses, conductor patterns and terminals of a gradient coil are formed by using copper, which has a high electrical conductivity. For this reason, for example, as a method for realizing a lightweight gradient coil, it is possible to form the conductor patterns and the terminals by using aluminum, which is more lightweight than copper. However, because the power supply cable connected to the gradient coil is placed in the magnetostatic field, the power supply cable vibrates due to a Lorentz force acting thereon while an electric current is flowing therethrough. Thus, there is a possibility that the terminals may be loosened by the vibration. Accordingly, it is desirable to form the terminals by using copper, which has a higher strength than aluminum.

In this regard, in the present embodiment, the conductor patterns included in the gradient coil112are formed by using aluminum, whereas the terminals connected to the conductor patterns are formed by using copper. Thus, according to the present embodiment, while ensuring the strength of the connection parts of the conductor patterns and the terminals, it is possible to realize the gradient coil112that is more lightweight than when both the conductor patterns and the terminals are formed by using copper. Further, for example, when the price of copper is higher than the price of aluminum as observed in recent years, it is possible to reduce the cost of the gradient coil112.

Further, it is predicted that an electrolytic corrosion might occur in the connection part of the conductor pattern206and the terminal207, if copper and aluminum, which are mutually-different types of metals, were simply brought into contact with each other. To cope with this situation, in the present embodiment, the connection part of the conductor pattern206and the terminal207is connected by solder, after plating of either tin or nickel is applied to the connection surface of the conductor pattern206connected to the terminal207.

Further, it is predicted that a mechanical load might be caused in the connection part of the conductor pattern206and the terminal207, due to the vibration of the power supply cable and/or the vibration of the gradient coil112itself caused by the Lorentz force. To cope with this situation, in the present embodiment, the connection part of the conductor pattern206and the terminal207is fastened by one or more screws. The number of screws used for fastening the connection part of the conductor pattern206and the terminal207may be one; however, it is desirable to use a plurality of screws in order to reduce the mechanical load caused in the sections fastened by the screws. For this reason, in the present embodiment, the connection part of the conductor pattern206and the terminal207is fastened by the plurality of screws.

The connection part of the conductor pattern206and the terminal207according to the present embodiment will be explained below further in detail. Although the connection part of the conductor pattern206and the terminal207will be explained as an example below, the other conductor patterns and the other terminals are also connected in the same manner as the conductor pattern206and the terminal207are connected together.

FIG. 3is a perspective view of an external appearance of the connection part of the conductor pattern206and the terminal207according to the present embodiment. For example, as illustrated inFIG. 3, the terminal207is formed in the shape of a substantially circular column. On one end of the terminal207, a hole207ais formed so that a bolt210used for attaching the terminal209provided on the power supply cable208side can be fitted therein. To the other end, an end of the conductor pattern206is attached.

Further, as illustrated inFIG. 3, for example, the connection part of the conductor pattern206and the terminal207is fastened by two screws211and212. In the present embodiment, the example will be explained in which the connection part of the conductor pattern206and the terminal207is fastened by the two screws; however, the connection part may be fastened by three or more screws.

FIG. 4is a perspective view of a structure of the connection part of the conductor pattern206and the terminal207according to the present embodiment. For example, as illustrated inFIG. 4, on the one end of the terminal207positioned on the side where the conductor pattern206is attached, an attachment part207bis formed in the shape of a plate that projects from the end face of the circular cylindrical shape. In this situation, two screw holes207cand207dare formed in the attachment part207b, at an interval of a length L. Further, on the one end of the conductor pattern206positioned on the side attached to the terminal207, two through holes206aand206bare formed at an interval of the length L.

Further, the screw211goes through the through hole206aformed in the conductor pattern206and is fitted into the screw hole207cformed in the attachment part207b. Further, the screw212goes through the through hole206bformed in the conductor pattern206and is fitted into the screw hole207dformed in the attachment part207b. As explained here, as a result of the screw211being fitted into the screw hole207cand the screw212being fitted into the screw hole207d, the conductor pattern206and the terminal207are fastened together.

By fastening the connection part of the conductor pattern206and the terminal207by using the plurality of screws in this manner, it is possible to reduce the load caused in the connection part. As a result, it is possible to fasten the conductor pattern206and the terminal207together more firmly.

For example, the material of which the screws211and212are made may be either copper or brass. By using the screws made of either copper or brass, it is possible to keep the electrical resistance small at the connection part of the conductor pattern206and the terminal207.

FIG. 5is a cross-sectional view of the connection part of the conductor pattern206and the terminal207according to the present embodiment. For example, as illustrated inFIG. 5, to the connection surface of the conductor pattern206connected to the terminal207, plating213of either tin or nickel is applied. Further, the connection part of the conductor pattern206and the terminal207is connected by solder214.

By applying the plating213to the connection surface of the conductor pattern206connected to the terminal207in this manner, it is possible to prevent an electrolytic corrosion that may occur at the connection part from developing. Further, by connecting the conductor pattern206and the terminal207together by the solder214, it is possible to keep the electrical resistance small at the connection part. In the present situation, the example is explained in which the plating213is applied to the connection surface on the conductor pattern206side; however, plating may further be applied to the connection surface of the terminal207connected to the conductor pattern206.

In addition, for example, plating215of either tin or nickel is also applied to the surface of the male screw thread formed on the screw211. Similarly, plating216is also applied to the surface of the male screw thread formed on the screw212. In the present situation, the example is explained in which the plating is applied to the surfaces of the male screw threads; however, for example, plating may be applied to the surfaces of the female screw threads formed in the attachment part207bof the terminal207. Further, if female screw threads are also formed in the conductor pattern206, plating may be applied to the surfaces of the female screw threads formed in the conductor pattern206. In these situations, the plating may be applied to both the surfaces of the male screw threads and the surfaces of the female screw threads. Alternatively, the plating may be applied to the surfaces of only one selected from between the male screw threads and the female screw threads.

With respect to the screws used for fastening the conductor pattern206and the terminal207together, by applying the plating to the surfaces of at least one selected from between the male screw threads and the female screw threads in this manner, it is possible to prevent the electrolytic corrosion that may occur at the male screw threads and the female screw threads from developing.

Further, for example, the plurality of screws used for fastening the connection part of the conductor pattern206and the terminal207are positioned at the interval that keeps the load on the solder214equal to or smaller than a predetermined magnitude. In this situation, to reduce the mechanical load on the solder214, it is desirable to arrange the interval L between the screw211and the screw212to be as large as possible.

However, if the interval L was arranged to be too large, a shear strain might occur at the solder214due to the difference in linear expansion coefficients between copper and aluminum, and the solder214might break. For this reason, in the present embodiment, the interval at which the plurality of screws are positioned is arranged to be such a length that keeps the magnitude of a shear stress equal to or smaller than a predetermined value, the shear stress being applied to the solder214by the shear strain occurring at the connection surface due to the difference in the linear expansion coefficients between the conductor pattern206and the terminal207.

FIG. 6is an enlarged view of the connection part of the conductor pattern206and the terminal207illustrated inFIG. 5.FIG. 6is an enlarged view of part A indicated inFIG. 5. It is generally known that copper and aluminum have mutually-different linear expansion coefficients. For this reason, if the temperature of the connection part of the conductor pattern206and the terminal207rises, the conductor pattern206and the terminal207expand with heat by mutually-different amounts. As a result, a shear force is generated by the connection surface of the conductor pattern206and the connection surface of the terminal207, and a shear strain occurs at the solder214that is positioned between the conductor pattern206and the terminal207. For example, as illustrated inFIG. 6, a difference ΔL in length occurs along the surface direction, between the surface of the solder214on the conductor pattern206side and the surface of the solder214on the terminal207side.

FIG. 7is a chart of a stress-strain curve of the solder214according to the present embodiment. For example, let us assume that the stress-strain curve of the solder214has been obtained as illustrated inFIG. 7, by performing a tensile test or the like. InFIG. 7, the vertical axis expresses a stress σ occurring at the solder214, whereas the horizontal axis expresses a strain ε occurring at the solder214. Further, σyudenotes an upper yield point, whereas εyudenotes the strain at the upper yield point σyu, and E denotes the Young's modulus. Further, σsdenotes an allowable stress calculated on the basis of the upper yield point σyuand a predetermined safety factor, whereas εs, denotes the strain corresponding to the allowable stress σs. Alternatively, the allowable stress σsmay be calculated on the basis of a tensile strength of the solder214and a safety factor.

When such a stress-strain curve has been obtained, for example, the interval L between the screw211and the screw212is set on the basis of Expression (1) presented below. In Expression (1), αCuis a linear expansion coefficient of copper, whereas αA1is a linear expansion coefficient of aluminum. Further, w denotes the thickness of the solder214, whereas G is a modulus of transverse elasticity. Further, ΔT denotes an increase in the temperature at the connection part, whereas τsdenotes an allowable shear stress that is roughly calculated on the basis of the allowable stress σs.

By setting the interval L between the screw211and the screw212in such a manner that the magnitude of the shear stress applied to the solder214is equal to or smaller than the predetermined value in this manner, it is possible to prevent the solder214from being broken by the shear force acting on the solder214. As a result, it is possible to connect the conductor pattern206and the terminal207together more firmly, while preventing the electrolytic corrosion from developing.

Further, it is generally known that an electrolytic corrosion on a conductive member made of copper or aluminum develops when the conductive member is in contact with air, due to the moisture in the air. For this reason, in the present embodiment, the connection part of the conductor pattern206and the terminal207is enclosed in resin.

FIG. 8is a drawing of surroundings of the connection part of the conductor pattern206and the terminal207in the gradient coil112according to the present embodiment. For example, as illustrated inFIG. 8, the connection part of the conductor pattern206and the terminal207is enclosed in the resin112cwith which the space in the surroundings of the conductor pattern206is impregnated. As a result, the connection part of the conductor pattern206and the terminal207is enclosed in the resin112cintegrally formed with the conductor pattern206. By arranging the connection part of the conductor pattern206and the terminal207to be enclosed in the resin in this manner, it is possible to prevent the electrolytic corrosion occurring at the connection part from developing.

Further, for example, the connection part of the conductor pattern206and the terminal207is positioned between an end face112dof the gradient coil112and the conductor pattern206. In that situation, for example, the terminal207is arranged in such a manner that at least a part thereof is disposed outside the gradient coil112. For example, as illustrated inFIG. 8, the terminal207is provided in such a manner that the end thereof positioned on the side where the terminal209provided on the power supply cable208side is attached protrudes from the end face112dof the gradient coil112.

Further, for example, the connection part of the conductor pattern206and the terminal207is covered by a barrier layer. For example, as illustrated inFIG. 8, the connection part of the conductor pattern206and the terminal207is covered by a barrier layer217configured with grass fibers wound around the connection part. By arranging the connection part of the conductor pattern206and the terminal207to be covered by the barrier layer217in this manner, even if the resin112cin the surroundings of the connection part cracks or comes off, it is possible to block the air that may otherwise enter the surroundings of the connection part. With this arrangement, even if the resin112cin the surroundings of the connection part of the conductor pattern206and the terminal207cracks or comes off, it is possible to prevent the electrolytic corrosion occurring at the connection part from developing, and it is therefore possible to prevent an electrical disconnection from occurring on the inside of the resin112c. The material of which the barrier layer217is made does not necessarily have to be glass fibers. Any other material may be used.

As explained above, in the MRI apparatus100according to the present embodiment, the gradient coil112is configured in such a manner that the conductor patterns structuring the coil are formed by using aluminum, whereas the terminals having connected thereto the power supply cables used for supplying the electric currents flowing in the conductor patterns are formed by using copper. Consequently, according to the present embodiment, it is possible to realize the gradient coil112that is more lightweight than when both the conductor patterns and the terminals are formed by using copper.

Further, according to the present embodiment, by applying the plating to the connection part of the conductor pattern206and the terminal207and enclosing the connection part in the resin, it is possible to prevent the electrolytic corrosion occurring at the connection part from developing. As a result, it is possible to keep the connection part of the conductor pattern206and the terminal207in a stable state on a long-term basis.

In the embodiment described above, the example is explained in which, in the connection part of the conductor pattern206and the terminal207, the plating is applied to the connection surface of the conductor pattern206connected to the terminal207; however, possible embodiments are not limited to this example.

For instance, it is acceptable to apply an electrically-conductive compound (grease) to the connection surface of the conductor pattern206connected to the terminal207. With this arrangement, it is possible to prevent the electrolytic corrosion occurring at the connection part from developing, similarly to the example in which the plating is applied.

Further, in the embodiment described above, the example is explained in which the mechanical load caused by the vibration of the power supply cables due to the Lorentz force is reduced by forming the terminals having connected thereto the power supply cables by using copper, which has a higher strength than aluminum; however, possible embodiments are not limited to this example.

For instance, in the embodiment described above, in the power supply cables, copper is used as a conductive member. Alternatively, for example, in the power supply cables, aluminum may be used as a conductive member. Because aluminum is more lightweight than copper, by using the power supply cables in which aluminum is used as a conductive member, it is possible to reduce the mechanical load caused by the Lorentz force.

Further, a coaxial cable may be used as any of the power supply cables. Further, a coaxial pipe that uses a pipe made of either copper or aluminum as an external conductive member may be used as any of the power supply cables. When such a coaxial pipe is used, the pipe used as the external conductive member may be more rigid than cables using electric wires. With this arrangement, it is possible to reduce the mechanical load caused by the Lorentz force.

Further, in the embodiment described above, the example is explained in which the terminal207connected to the conductor patter206of the shield coil112band the terminal209of the power supply cable208side are connected by using the bolt210; however, possible embodiments are not limited to this example.

For instance, the terminal207and the terminal209may be configured by using parts that maintain the connection state by interdigitating with each other. For example, the terminal207and the terminal209may be configured by using parts called one-touch joint or one-touch coupler. With this arrangement, it is possible to prevent loosening, which may occur when a bolt is used for connecting.

Further, in the embodiment described above, the example is explained in which the first metal is aluminum, whereas the second metal is copper; however, possible embodiments are not limited to this example.

For instance, instead of aluminum and copper, either non-magnetic stainless steel (e.g., SUS 316, SUS 304, etc.), gold, silver, platinum, tungsten, brass (alloy of copper and zinc) and the like may be used as either one of the first and the second metal. For example, the conductor patterns may be formed by using aluminum, whereas the terminals may be formed by using stainless steel, gold, silver, platinum, tungsten, or brass. Further, for example, the conductor patterns may be formed by using one selected from among aluminum, stainless steel, gold, silver, platinum, tungsten, and brass, whereas the terminals may be formed by using a metal that is selected from among copper, stainless steel, gold, silver, platinum, tungsten, and brass and that is different from the metal used for forming the conductor patterns.

Further, in the embodiment described above, the example is explained in which the conductor pattern and the terminal are formed by using the mutually-different metals; however, possible embodiments are not limited to this example.

For instance, it is acceptable to form a plurality of sections included in a single conductor pattern by using mutually-different metals. For example, a first section included in the single conductor pattern may be considered as the first coil member, whereas a second section included in the single conductor pattern may be considered as the second coil member. Further, for example, if the first coil member generates heat more frequently than the second coil member, the first metal used for forming the first coil member may be such a metal that has a higher heat resistance than the second metal used for forming the second coil member. For example, because a central section of the gradient coil112is considered to generate heat more frequently than a peripheral section of the gradient coil112, the conductor pattern in the peripheral section may be formed by using aluminum, whereas the conductor pattern in the central section may be formed by using copper, which has a higher heat resistance than aluminum.

Further, for example, when the gradient coil112is configured by combining three coils corresponding to the X-, the Y-, and the Z-axes that are orthogonal to one another, the conductor patterns in the three coils may be formed by using mutually-different metals. For example, the coil corresponding to the X-axis, which is often assigned to a read-out direction, is known to generate heat more frequently than the coil corresponding to the Y-axis and the coil corresponding to the Z-axis. For this reason, for example, as the metal forming the conductor pattern in the coil corresponding to the X-axis, a metal having a higher heat resistance than the metal forming the conductor patterns in the coils corresponding to the Y-axis and the Z-axis may be used. For example, the conductor patterns in the coils corresponding to the Y-axis and the Z-axis may be formed by using aluminum, whereas the conductor pattern in the coil corresponding to the X-axis may be formed by using copper, which has a higher heat resistance than aluminum.

Further, as explained above, when the gradient coil112is an ASGC including a main coil and a shield coil, the conductor pattern in the main coil and the conductor pattern in the shield coil may be formed by using mutually-different metals. For example, because the main coil has a larger number of windings in the conductor pattern than the shield coil does and because the main coil is positioned closer to the center of the magnetic field, the main coil is known to generate more heat than the shield coil does. For this reason, as the metal forming the conductor pattern in the main coil, a metal having a higher heat resistance than that of the conductor pattern in the shield coil may be used. For example, the conductor pattern in the shield coil may be formed by using aluminum, whereas the conductor pattern in the main coil may be formed by using copper, which has a higher heat resistance than aluminum.

In the embodiment described above, the gradient coil112includes the first coil member formed by using the first metal that is non-magnetic; and the second coil member connected to the first coil member and formed by using the second metal that is different from the first metal and is non-magnetic. In other words, according to the embodiment described above, the gradient coil112is formed by using the plurality of mutually-different metals. By forming the gradient coil112by using the plurality of mutually-different metals, it is possible to flexibly address various types of requirements for the gradient coil112.

For example, by forming one or more of the plurality of coil members included in the gradient coil112by using aluminum, it is possible to arrange the gradient coil112to be more lightweight than when all the coil members are formed by using copper. Further, for example, by forming one or more of the plurality of coil members included in the gradient coil112by using a metal that is less expensive than the one or more metals used for forming the other coil members, it is possible to lower the cost of the gradient coil112. Further, for example, by forming one or more of the plurality of coil members that are included in the gradient coil112and that generate more heat than those in the other sections of the gradient coil112, while using a metal that has a higher heat resistance than the one or more metals used for forming the other coil members, it is possible to enhance durability of the gradient coil112.

In other words, if all the coil members in the gradient coil112were formed by using mutually the same kind of metal, disadvantage characteristics of the metal might exhibit in one or more of the coil members in a concentrated manner. To cope with this situation, according to the embodiment described above, by forming one or more of the coil members while using a type of metal that is different from the one or more metals used for forming the other coil members, it is possible to complement the disadvantageous characteristics of the one or more metals used for forming the other coil members. As a result, it is possible to reduce or solve the problems that may be caused when all the coil members in the gradient coil112are formed by using mutually the same type of metal.

According to at least one aspect of the embodiments described above, it is possible to flexibly address the requirements for the gradient coil.