Magnetic resonance imaging apparatus, receiving coil and method of manufacturing the coil

A magnetic resonance imaging apparatus is provided, characterized by: one pair of static magnetic field generating means disposed sandwiching a space in which a test object is placed; magnetic field generating means configured to apply a high-frequency magnetic field and a gradient magnetic field to the test object placed in the static magnetic field; and receiving means configured to receive a nuclear magnetic resonance signal generated from the test object, and characterized in that: the receiving means includes a receiving coil having a predetermined coil pattern and capable of being shaped into a cylinder; the receiving coil includes flexible parts and rigid parts alternately disposed along the circumference direction when shaped into the cylinder; and the flexible parts include a flexible substrate on which a portion of the predetermined coil pattern is mounted and a air-bubbles-containing resin section for covering the both surfaces of the flexible substrate.

TECHNICAL FIELD

The present invention relates to an RF receiving coil used in a magnetic resonance imaging apparatus (MRI apparatus) and, more particularly, to a flexible receiving coil that can be closely fitted to a test object and a method for manufacturing the receiving coil.

BACKGROUND ART

An MRI apparatus arranges a test object in a uniform static magnetic field space, applies a high-frequency magnetic field and a gradient magnetic field to the test object according to a predetermined pulse sequence, and causes a nuclear spin in a certain cross section of the test object to magnetically resonate. Then, the MRI apparatus detects the resulted nuclear magnetic resonance signal, reconstructs the detected signal into an image using two- or three-dimensional Fourier transform or the like, and displays tomographic images.

MRI apparatuses are classified into horizontal magnetic field apparatuses and vertical magnetic field apparatuses depending on the direction of the static magnetic field. In any of the magnetic field apparatuses, a magnetic resonance signal is detected using an RF receiving coil disposed in proximity to the test object. The RF receiving coil needs to be disposed in the direction in which the magnetic resonance signal (magnetic field) perpendicular to the direction of the static magnetic field is detected. Accordingly, the configuration of the receiving coil varies depending on the direction of the static magnetic field.

In a horizontal magnetic field apparatus, by using a tunnel-shaped magnet, a static magnetic field is generated in the same direction as the center axis of the tunnel, and a test object is positioned in the static magnetic field such that the body axis of the test object is along the direction of the static magnetic field. Accordingly, the RF receiving coil needs to be disposed in the direction in which a magnetic field perpendicular to the body axis of the test object is detected, so a saddle-shaped coil or a loop coil to be disposed on the surface of the test object is often used for the RF receiving coil.

On the other hand, in a vertical magnetic field apparatus, two magnets are disposed in the vertical direction, a static magnetic field is generated in the vertical direction between the magnets, and a test object is positioned in the static magnetic field such that the body axis of the test object is perpendicular to the direction of the static magnetic field. Accordingly, the RF receiving coil can be disposed along the direction in which a magnetic field in the body axis direction of the test object is detected, so, conventionally, a solenoid coil wound around the circumference of the test object was often used. Also, a technique of using together two coils the magnetic field directions of which are perpendicular to each other to perform QD (Quadrature Detection) combining in order to improve the sensitivity. In the vertical magnetic field apparatus, in addition to the solenoid coil for detecting the magnetic field in the body axis direction, a saddle-shaped coil for detecting a magnetic field in the body width direction can be used together to perform QD combining.

The sensitivity and SN ratio of the RF receiving coil of the MRI apparatus improve more as the distance to the test object decreases more. Accordingly, the shape of the receiving coil is desirably determined so as to follow the shape of the test object depending on the size and shape of the test object so that an air gap between the test object and the RF receiving coil pattern is as small as possible. Conventionally, various RF receiving coils for accommodating the directions of static magnetic fields and the sizes and shapes of test objects have been invented. However, many of them are fabricated by winding a coil pattern around a bobbin that is made of a resin and is poor in flexibility.

In order to improve this problem, Patent Document 1 describes that both flexible and rigid, nonconductive support members for supporting an RF receiving coil pattern are used, in which flexible parts and rigid parts are alternately connected to each other in the circumference direction into a cylindrical shape. This facilitates the RF receiving coil to be wound around and closely fitted to the test object.

Also, the cylindrical-shaped RF receiving coil described in Patent Document 1 includes connector sections for connecting and disconnecting the coil pattern. When the connector sections are connected, two coil systems (solenoid coil and saddle-shaped coil) that have magnetic field components perpendicular to the static magnetic field direction and perpendicular to each other can be formed. The intersection part of the two coil systems is formed as rigid part to limit the flexibility of deformation, and the coil members of the intersection part are separated from each other by the distance of at least 5 mm. This separation prevents the two coil systems from being electromagnetically coupled.

Also, by determining the lengths of the flexible parts and rigid parts appropriately depending on the area of the test object is to be imaged, the RF receiving coil having a good reception sensitivity and a wide uniform reception area was achieved.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The flexible parts of the RF receiving coil of Patent Document 1 have a coil pattern formed on a flexible sheet made of a resin. Accordingly, as the diameter of the test object increases and the size of the RF receiving coil increases, the weight of the resin sheet increases. Furthermore, when the thickness of the resin sheet is increased in order to increase the reliability of the flexible parts against bending, the weight of the resin sheet further increases. The weight increase of the RF receiving coil increases a load on the test object. Also, the weight increase of the RF receiving coil makes its handling difficult for a operator who fits the RF receiving coil to the test object.

Furthermore, since the RF receiving coil of Patent Document 1 cannot be used with the coil pattern exposed on the resin sheet, the RF receiving coil in use may need to be, for example, entirely covered with a leather cover. Using the cover increases the weight of the RF receiving coil. Also, as the size of the RF receiving coil increases, the size of the cover increases, which in turn increases the weight of the entire RF receiving coil.

It is an object of the present invention to provide a receiving coil to be wound around a test object, the receiving coil being lightweight and flexible.

Means for Solving the Problems

In order to achieve the above object, according to a first aspect of the invention, an MRI apparatus is provided as follows. The MRI apparatus includes: one pair of static magnetic field generating means disposed sandwiching a space in which a test object is placed; magnetic field generating means configured to apply a high-frequency magnetic field and a gradient magnetic field to the test object placed in the static magnetic field; and receiving means configured to receive a nuclear magnetic resonance signal generated from the test object. The receiving means includes a receiving coil having a predetermined coil pattern and capable of being shaped into a cylinder.

The receiving coil includes flexible parts and rigid parts alternately disposed along the circumference direction when shaped into the cylinder. The flexible parts include a flexible substrate on which a portion of the predetermined coil pattern is mounted and a air-bubbles-containing resin section for covering the both surfaces of the flexible substrate. Using the air-bubbles-containing resin section in this way achieves the windability, light weight and ease in handling of the receiving coil.

For example, the above-described rigid parts include a rigid substrate on which a portion of the predetermined coil pattern is mounted and a case for containing the rigid substrate. For example, fitting sections are formed on the edge of the air-bubbles-containing resin section, the shape of the fitting sections being such that the fitting sections fit to the edge of the case. The fitting sections can be fitted to the case to connect the edges of the flexible parts and the rigid parts. The coil patterns of the rigid substrate and the flexible substrate are electrically connected at the edge at which the flexible parts and the rigid parts are connected. Thus, the rigid substrate and the flexible substrate can be alternately disposed to achieve the predetermined coil pattern.

Also, the thickness of a portion of the air-bubbles-containing resin section positioned on the inner circumference surface side of the flexible parts when shaped into the cylinder can be thinner than a portion of the air-bubbles-containing resin section positioned on the outer circumference surface side. This allows the coil pattern of the flexible substrate to be disposed close to the test object.

Grooves in the direction parallel to the body axis of the test object can be provided in the portion of the air-bubbles-containing resin section positioned on the outer circumference surface side when shaped into the cylinder. Providing the grooves can limit the bending position of the flexible parts to the locations of the grooves. Also, in the portion of the air-bubbles-containing resin section positioned on the inner circumference surface side grooves in the direction parallel to the body axis of the test object can be provided at the positions corresponding to the positions of the grooves on the outer circumference surface side. This allows the receiving coil to bend with a small curvature radius at limited bending positions and to be also applicable to a small-diameter test object. The grooves in the portion of the air-bubbles-containing resin section on the outer circumference surface side can be deeper than the grooves in the portion of the air-bubbles-containing resin section on the inner circumference surface side.

The flexible parts can include a frame embedded in a predetermined area of the portion of the air-bubbles-containing resin section positioned on the outer circumference surface side when shaped into the cylinder. The shape of the frame is such that the longitudinal direction of the frame is along the body axis direction of the test object. Alternatively, two or more frames can be arranged and secured along the body axis direction of the test object. This can limit the bending direction of the flexible parts to the direction perpendicular to the body axis, which allows the receiving coil to be easily wound around the test object and easily handled.

The inside of the frame may not be covered with the air-bubbles-containing resin section and can function as a window through which the flexible substrate is exposed. Electrical circuit components can be mounted on the flexible substrate within the window. This allows the electrical circuit components to be tuned or replaced through the window. Also, a lid for covering the window can be secured to the frame.

Elastic members can be disposed between the fitting sections of the air-bubbles-containing resin section and the case. This can prevent the air-bubbles-containing resin section from being damaged. Elastic members can be disposed between the lid and the air-bubbles-containing resin section also at the positions at which the lid is secured. This allows the lid to be rigidly secured to the frame and the air-bubbles-containing resin in which the frame is embedded.

If the receiving coil is a coil to be wound around the body of the test object, the coil can have notches at the positions corresponding to the armpits of the test object when shaped into the cylinder. Thus, the receiving coil can cover the test object to upper chest and upper back.

Also, the receiving coil can include: a belt-shaped member in which the flexible parts and the rigid parts are alternately disposed; and first and second connecting sections disposed to one end and the other end of the belt-shaped member, respectively, to connect the both ends. As guide members for aligning the first and second connecting sections, one or more guide protrusions can be provided to one of the first and second connecting sections, and guide holes to be engaged with the guide protrusions can be provided to the other. Also, as fitting members for fitting the first connecting section to the second connecting section, one or more first fitting sections and second fitting sections that fit the first fitting sections can be provided. In this case, the one or more guide members and the one or more fitting members can be disposed in alignment. This allows the connecting sections to be difficult to be disconnected by an external force.

The coil pattern of the flexible parts can be divided into two or more portions by one or more slits. The divided coil patterns are electrically connected by capacitors having a predetermined capacitance. The capacitance of the capacitors are considered electrically short-circuited at a frequency of nuclear magnetic resonance signal, and considered electrically open at a frequency of eddy current. This can suppress the generation of eddy current on the coil pattern.

According to a second aspect of the invention, a receiving coil, capable of being shaped into a cylinder, for a magnetic resonance imaging apparatus is provided. The receiving coil includes flexible parts and rigid parts alternately disposed along the circumference direction when shaped into the cylinder. The flexible parts include a flexible substrate on which a portion of the predetermined coil pattern is mounted and a air-bubbles-containing resin section for covering the both surfaces of the flexible substrate.

According to a third aspect of the invention, a method for manufacturing a receiving coil is provided as follows. Flexible parts in which both surfaces of a flexible substrate are covered with an air-bubbles-containing resin section the shape of which corresponds to a predetermined mold is made by disposing a air-bubbles-containing resin member on the both surfaces of the flexible substrate and heating them in the mold to press and heat-seal the air-bubbles-containing resin member, the flexible substrate including a portion of a predetermined coil pattern. The flexible parts and rigid parts including a substrate on which a portion of the predetermined coil pattern is formed are alternately connected to form a shape that can be shaped into a cylinder. Also, grooves to limit the bending position of the flexible parts, spaces for embedding the frames, and the positions of the windows for accessing an internal component to replace the component or tune its characteristic can be individually configured by adjusting the shape of the mold.

According to a fourth aspect of the invention, a receiving coil is provided as follows. The receiving coil is used for a magnetic resonance imaging apparatus, and includes: a belt-shaped member having a predetermined coil pattern; and first and second connecting sections disposed to one end and the other end of the belt-shaped member, respectively, to connect the both ends. As guide members for aligning the first and second connecting sections, one or more guide protrusions are provided to one of the first and second connecting sections, and guide holes to be engaged with the guide protrusions are provided to the other. Also, as fitting members for fitting the first connecting section to the second connecting section, one or more first fitting sections and second fitting sections that fit the first fitting sections are provided. The one or more guide members and the one or more fitting members are disposed in alignment. This allows the connecting sections to be difficult to be disconnected by an external force.

According to a fifth aspect of the invention, a receiving coil is provided as follows. The receiving coil is used for a magnetic resonance imaging apparatus, and has a coil pattern mounted on a substrate, and the coil pattern is divided into two or more portions by one or more slits. The divided coil patterns are electrically connected by capacitors having a predetermined capacitance. The capacitance of the capacitors are set to be considered electrically short-circuited at a frequency of nuclear magnetic resonance signal, and considered electrically open at a frequency of eddy current. This can reduce eddy current generated on the coil pattern, thereby reducing the influence of magnetic field generated by the eddy current on the test object, and preventing the image quality from degrading even when the coil pattern is close to the test object. In totality, the image quality can be improved.

Advantage of the Invention

According to the invention, a receiving coil to be wound around a test object can be provided, the receiving coil being lightweight and flexible.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention are described below in detail with reference to the drawings.

First Embodiment

First, an entire configuration of an MRI apparatus according to a first embodiment is described with reference to a perspective view and a block diagram shown inFIGS. 1 and 2, respectively. As shown inFIG. 1, the MRI apparatus includes a main body200and a bed70. The main body200includes an imaging space10in which a test object103is imaged. The bed70carries the test object103into the imaging space10.

The main body200includes an upper main body202disposed on the upper side of the imaging space10, an lower main body203disposed on the lower side of the imaging space10, and an supporting post204for coupling the upper and lower main bodies202and203. As shown inFIG. 2, each of the upper and lower main bodies202and203includes a magnet201, and includes a shim coil212, a gradient magnetic field coil206and an RF radiation coil207disposed in order on the test object103side of the magnet201.

The pair of magnets201generate a static magnetic field in the imaging space10and may be a permanent magnet, a normal conducting magnet or a super conducting magnet. The shim coil212is a coil that generates a magnetic field for correcting the static magnetic field to improve the static magnetic field uniformity. As shown inFIG. 2, the shim coil212is connected to a shim power supply213that supplies a predetermined shim current.

In order to add location information to a nuclear magnetic resonance signal and for other purposes, the gradient magnetic field coil206generates in the imaging space10a gradient magnetic field relating to directions of orthogonal three axes (x-, y- and z-axes) of the imaging space10. As shown inFIG. 2, the gradient magnetic field coil206is connected to a gradient magnetic field power supply211that supplies a predetermined gradient magnetic field current.

As shown inFIG. 2, the RF radiation coil207is connected to an RF power amplifier208and an RF pulse generator209. The RF pulse generator209generates an RF signal with a predetermined frequency that is amplified by the RF power amplifier208and provided to the RF radiation coil207. Then, the RF radiation coil207generates a high-frequency magnetic field that excites the nuclear magnetization of the test object103.

An RF receiving coil500is disposed in proximity to the test object103in the imaging space10. The RF receiving coil500according to the embodiment can be wound around the test object103and has a shape that closely fits the test object103.

The RF receiving coil500receives the nuclear magnetic resonance signal generated from the test object103and converts the received signal into an electrical signal. As shown inFIG. 3, the RF receiving coil500according to the embodiment includes a solenoid coil216-1for detecting a magnetic field in the direction parallel to the body axis and a saddle-shaped coil216-2for detecting a magnetic field in the body width direction.FIG. 3schematically illustrates the shapes of the solenoid coil216-1and the saddle-shaped coil216-2when the RF receiving coil500is wound around the test object103. For each of the solenoid coil216-1and the saddle-shaped coil216-2,FIG. 4shows the shape of the coil and the direction of current that flows when a magnetic field shown by an arrow is applied.

As shown inFIG. 2, the RF receiving coil500includes preamplifiers217-1and217-2for amplifying the signals received by the solenoid coil216-1and the saddle-shaped coil216-2, respectively. The preamplifiers217-1and217-2are connected to receivers218-1and218-2, respectively, for detecting the amplified received signals.

The receivers218-1and218-2are connected to a calculator219that performs image reconstruction and the like on the received signals. The reconstructed images are displayed on a display220connected to the calculator219and also stored in a storage medium221.

Also, as shown inFIG. 2, the MRI apparatus includes a sequencer210. The sequencer210controls the operation of the RF pulse generator209, the receivers218-1and218-2, the gradient magnetic field power supply211, the shim power supply213and the magnet201(when it is a normal conducting magnet) to perform an imaging pulse sequence of irradiating the test object103with a gradient magnetic field and a high-frequency magnetic field pulse at a predetermined timing, and receiving a generated nuclear magnetic resonance signal at a predetermined timing.

As shown inFIG. 1, the bed70includes a top plate71for carrying the test object103and a bed chassis72. The bed chassis72includes an actuator for actuating the top plate71to a table top205on the top surface of the lower main body203. The test object103, around which the RF receiving coil500is wound, is put on the top plate71and carried onto the table top205to be positioned in the imaging space10.

The structure of the RF receiving coil500is described below in detail.

As shown inFIG. 5(a), the RF receiving coil500has a strip-shaped structure in which five rigid parts505,506,507,508,509and four flexible parts501,502,503,504are alternately disposed and connected. Each of the five rigid parts505,506,507,508,509includes a rigid substrate on which a predetermined conductive traces are formed.

Each of the four flexible parts501,502,503,504includes a flexible substrate on which a predetermined conductive traces are formed. In connecting sections between the rigid parts and the flexible parts, the internal rigid substrates and the internal flexible substrates are mechanically and electrically connected to configure a coil pattern of the solenoid coil216-1and the saddle-shaped coil216-2, as shown inFIG. 5(b).

The first rigid part505located at one edge includes a first connector section510at that edge, and the fifth rigid part509located at the other edge includes a second connector section511at that edge. The first and second connector sections510and511are formed so as to fit with each other. As shown inFIG. 6, when the first connector section510is not fitted with the second connector section511, the RF receiving coil500is strip-shaped and then can be inserted between the test object103and the top plate71of the bed70.

With the RF receiving coil500inserted in this way, fitting the first connector section510with the second connector section511allows the RF receiving coil500to be wound around and closely fitted to the test object103as shown inFIG. 3.

Next, a structure and manufacturing procedure of the first to fourth flexible parts501to504is described. Since the flexible parts501to504have the same structure, the flexible part501is described here with reference toFIGS. 7 to 10.

As shown inFIG. 7, a perspective view, the flexible part501includes a flexible substrate601on which conductive traces are formed, the both surfaces of which are covered with an air-bubbles-containing resin602such as foam material. In order to connect the flexible part501to the adjacent rigid parts505,506, fitting sections81are formed of the air-bubbles-containing resin602at connecter edges80. In the fitting sections81, holes82passing through the air-bubbles-containing resin602and the flexible substrate601are provided. Also in the connecter edges80, the edges of the flexible substrate601are exposed. The exposed edges of the flexible substrate601are electrically and mechanically connected to a rigid substrate603of the rigid parts505and506.

Also, the air-bubbles-containing resin602is thinly provided on the side of the surface facing to the test object103(body surface side) of the flexible substrate601, and is thickly provided on the outer side (outer circumference side when wound around the test object103) of the flexible substrate601. This allows the conductive traces of the flexible substrate601to be located closer to the test object103.

As shown inFIGS. 7 and 8, in the surface of the outer circumference side of the air-bubbles-containing resin602, two more grooves85are provided along the body axis direction of the test object103. With the grooves85provided, when the RF receiving coil500is bent, the flexible part501bends at the grooves85.

This allows the flexible part501to bend only at the grooves85. The flexible substrate601bends at the positions outside the areas on which electrical circuit components91such as tuning capacitor are mounted, which can protect the electrical circuit components91.

Preferably, the depth of the grooves85is determined so that the remaining thickness after subtracting the depth of the groove85from the thickness of the air-bubbles-containing resin602is equal to or less than the thickness of the rigid parts505to509and is also more than about 15 mm. This allows the flexible parts501to504to be flexible while maintaining their strength.

Also, two or more windows83are provided on the air-bubbles-containing resin602to expose portions of the flexible substrate601. On the portions of the flexible substrate601exposed through the windows83, the electrical circuit components91such as tuning capacitor are mounted as shown in an enlarged perspective view inFIG. 9.

Then, an operator can adjust or replace the electrical circuit components91through the windows83.

As shown inFIGS. 7 and 9, rigid frames608are embedded in the periphery of the windows83. As shown inFIG. 10(a), the frames608are secured to the flexible substrate601by screws610, and then, the frames608and the screws610are integrally thermoformed and embedded in the air-bubbles-containing resin602. Also, as shown inFIGS. 10(a),11(a) and11(b), rigid lids607are secured to the frames608by screws605. The screw holes of the lids607are covered by resin caps606after the screws605are secured. Since the frames608and the lids607are secured to the flexible substrate601in this way, the flexible part501does not bend at the windows83as shown inFIG. 10(b), even when the flexible part501bends at any position other than the grooves85. This allows the electrical circuit components91secured in the windows83to be protected.

Also, as shown inFIG. 10(a), rubber packings700are disposed between the top surface of the air-bubbles-containing resin602integrally formed on the top surface of the frames608and the bottom surface of the lids607. The disposed rubber packings700allows the lids607to be rigidly secured to the frames608and the air-bubbles-containing resin602integrally formed on the frames608, increasing the strength of the frames608. Accordingly, even when the flexible part501bends at any position other than the grooves85as shown inFIG. 10(b), the electrical circuit components91can be protected.

Also, as seen fromFIG. 7, in the embodiment, the shape of the frames608is such that the longitudinal direction of the frames608is along the body axis direction of the test object103, and/or the two or more frames608are arranged in the body axis direction. This allows the shape of the flexible part501to be such that the flexible part501is easy to bend in the circumference direction of the test object103and is difficult to bend in the body axis direction. Limiting the bending direction of the flexible part501to the circumference direction allows the RF receiving coil to be easily wound around and easily fitted to the test object103.

As shown inFIGS. 12(a-1) and12(a-2), the flexible substrate601is configured by sticking first and second conductive plate layers601-3and601-7to both surfaces of a base film601-5made of a resin using adhesive layers601-4and601-6. As shown inFIG. 12(a-2), the first and second conductive plate layers601-3and601-7are electrically connected via through holes601-10at the edges of the flexible substrate601.

As shown inFIG. 12(a-1), the first and second conductive plate layers601-3and601-7are formed with four parallel traces. As apparent fromFIG. 5, the conductive traces formed on the flexible parts501,502,503,504are two parallel conductive traces forming a part of the solenoid coil216-1and two parallel conductive traces forming a part of the saddle-shaped coil216-2. These conductive traces are formed with the four parallel traces shown inFIG. 12(a-1). Note that the shape of the trace of the second conductive plate layer601-7is the same as that of the first conductive plate layer601-3.

The four parallel traces of the first and second conductive plate layers601-3and601-7are divided by areas corresponding to the windows83, and mounting areas86for mounting the electrical circuit components91are provided at the divided edges. The first and second conductive plate layers601-3and601-7are electrically connected via the through holes601-10also at the mounting areas86. Frame securing holes87for securing the frames608with the screws610are provided on the base film601-5around the windows83.

As shown inFIG. 12(a-2), the first and second conductive plate layers601-3and601-7are covered with cover film layers601-1and601-9via adhesive layers601-2and601-8except the mounting areas86. This increases the electrical reliability.

As shown inFIG. 12(a-1), openings84and through holes92are provided in portions of the base film601-5in which the first and second conductive plate layers601-3and601-7are not disposed. As shown inFIG. 7, the air-bubbles-containing resin602is not disposed on the openings84to save the weight of the flexible part501. On the other hand, the through holes92are provided for the purpose of increasing the degree of adhesion of the air-bubbles-containing resin602of the surface of the outer circumference side and the air-bubbles-containing resin602of the surface of the body surface side.

Slits601aare provided in the traces of the conductive plate layers601-3and601-7. As shown inFIG. 13(a), the conductive plate layers601-3and601-7divided by the slits601are electrically connected by capacitors802-1to802-8having a large capacitance.

Specifically, these capacitors (for example, 1000 pF) are considered electrically short-circuited at a high frequency (for example, 50 MHz) of nuclear magnetic resonance signal, and are considered electrically open at a low frequency. When the capacitors802-1, etc. are disposed in this way, the conductive plate layers601-3, etc. become equivalent to the circuit shown inFIG. 13(b), in which a high-frequency nuclear magnetic resonance signal can flow in the conductive plate layer601-3as in the case without the slits601a, but a low-frequency eddy current cannot flow across the slits601a. This can suppress the generation of the eddy current without interfering with receiving the nuclear magnetic resonance signal.

Since the receiving coil500is flexible, it is fitted to the test object103. So, when eddy current is generated in the conductor of the receiving coil500, the magnetic field generated by the eddy current interferes with the magnetization of the test object103. This may cause, for example, the image to be partially darkened, degrading the image quality. In the embodiment, the slits601aand the capacitor802-1, etc. can prevent eddy current from being generated in the conductor of the receiving coil.

As an example of the base film601-5, polyimid film with a thickness of 25 μm may be used. As an example of the conductive plate layers601-3and601-7, a copper plate with a thickness of 35 μm may be used.

The air-bubbles-containing resin602may be any resin containing many air bubbles therein. As an example, a foamable resin may be used. As an example of the foamable resin, polyethylene, polyuretane, boron or rubber sponge may be used. As an example of method for foaming, chemical foaming method may be used. The apparent density of the air-bubbles-containing resin602is desirably equal to or less than 0.1 g/cm3.

Next, a procedure for manufacturing the flexible part501is described. First, the conductive plate layers601-3and601-7having a predetermined shape are stuck to both surfaces of the base film using the adhesive layers601-4and601-6. Then, the through holes601-10are provided, and the conductive plate layers601-3and601-7are connected. Then, the cover film layers601-1and601-9are stuck to the conductive plate layers601-3and601-7using the adhesive layers601-2and601-8except the mounting areas86.

The fitting section through holes82, the openings84, the frame securing holes87and the through holes91are provided in the base film601-5. At this time, the flexible substrate601is completed.

Next, the frames608and bases609are disposed on the outer circumference surface side and the body surface side of the flexible substrate601, respectively, and secured with the screws610as shown inFIGS. 14(a) and14(b). Then, on both surfaces of the flexible substrate601, a resin sheet that is the material of the air-bubbles-containing resin602is disposed. Then, the flexible substrate601is heated in a mold having a predetermined shape. This causes the resin sheet to foam to be the air-bubbles-containing resin602and be shaped into the shape shown inFIG. 7. Through the windows83, the electrical circuit components91are mounted on the mounting areas86. Then, the rubber packings700are disposed on the top surface of the air-bubbles-containing resin602that is integrated with the top surface of the frames608. Then the lids607are secured with the screws605. Caps606are attached to the screw holes. At this time, the flexible part501is completed.

Next, a configuration and manufacturing procedure of the rigid parts505-509is described.

The rigid parts505,506,507,508,509have a structure in which the rigid substrate603as shown inFIG. 12(b-1) is disposed in a rigid resin case604. For the rigid parts506,507,508, the outer shape of the resin case604is a rectangular parallelopiped as shown inFIG. 15. The resin case604of the rigid part505includes the first connector510at the edge as shown inFIG. 16(a). The resin case604of the rigid part509includes the second connector511having the shape as shown inFIG. 16(b) at the edge. The first connector510fits the second connector511.

As shown inFIG. 12(b-2), the rigid substrate603is configured by securing conductive plate layers603-1and603-2to both surfaces of a substrate603-5made of a rigid material (e.g., glass epoxy resin) using adhesive layers603-4and603-6. The conductive plate layers603-1and603-2are connected via through holes603-3. Traces of the conductive plate layers603-1and603-2includes traces for forming the solenoid coil216-1and traces for forming the saddle-shaped coil216-2. The conductive plate layer603-1forming the saddle-shaped coil216-2includes connecting sections131ato131f. The conductive plate layer603-1forming the solenoid coil216-1includes connecting sections132ato132d. By connecting these connecting sections in an appropriate combination using bridge-like connecting components (not shown), the coil patterns of the rigid parts505to509can be formed.

Also, by connecting the connecting sections131a,131band131cand connecting the connecting sections131d,131eand131f, the coil patterns of the saddle-shaped coil216-2of the rigid part505can be formed. Also, by connecting the connecting sections132aand132band connecting the connecting sections132cand132d, the coil patterns of the solenoid coil216-1of the rigid part505can be formed. For the rigid part507, the coil pattern of the saddle-shaped coil216-2is formed by connecting the connecting sections131a,131band131cand connecting the connecting sections131d,131eand131f, and a noncontact crossing section of the 2-turn solenoid coil216-1is formed by diagonally connecting the connecting sections132aand132dand diagonally connecting the connecting sections132band132c.

Since the rigid substrate603is used in each of the rigid parts505to509, the solenoid coil216-1and the saddle-shaped coil216-2can intersect with a predetermined distance (a few millimeters) maintained therebetween by using bridge-like connecting component. This separation can prevent the two coil systems from being electromagnetically coupled.

Also, as shown inFIG. 12(b-1), slits603aare formed in the conductive plate layer603-1. As in the case shown inFIG. 13(a), capacitors having a large capacitance are disposed on the slits603aand prevent eddy current from being generated.

As shown inFIG. 5(b), receiving cables512are connected to the solenoid coil216-1and the saddle-shaped coil216-2of the rigid part505for outputting received signals from the coils. The receiving cables512are lead out from the rigid part505through the flexible part501, as shown inFIG. 5(b).

When manufacturing the rigid parts505, etc., the conductive plate layers603-1and603-2having a predetermined pattern are stuck to both sides or one side of the substrate603-5using the adhesive layers603-4and603-6, then through holes603-10are formed to connect the both conductive plate layers603-1and603-2, as shown inFIGS. 12(b-1) and12(b-2). Then, an electrical circuit component such as a capacitor and decoupler is mounted as appropriate.

The rigid substrate603is disposed in the resin case604as shown inFIG. 17. The case604is divided into an outer circumference surface side member604-1and a body surface side member604-2. As shown inFIG. 18(a), the rigid substrate603is secured in the body surface side member604-2using screws171. The outer circumference surface side member604-1and the body surface side member604-2include protrusions604-3and604-4, respectively, that fit the fitting sections81of the adjacent flexible part504, etc. by being inserted into the holes82of the fitting sections81. The protrusions604-4of the body surface side member604-2are fitted to the fitting sections81of the flexible part504, etc. The edge of the rigid substrate603is soldered to the edge of the flexible substrate601to electrically connect the coil patterns. Then, the outer circumference surface side member604-1is put over the rigid substrate603. Then, the protrusions604-3are fitted to the fitting sections81and secured with the screws605. At this time, the rigid parts505to509can be made and also connected to the adjacent flexible parts501to504.

Note that, as shown inFIG. 18(a), rubber packings172are disposed in a fitting section at which the edge of the resin case604is fitted to the air-bubbles-containing resin602of the flexible parts501to504. This rubber packings172can prevent the air-bubbles-containing resin602from being damaged at the fitting section with the resin case604even when the flexible part501or the like bends at any position other than the grooves85as shown inFIG. 18(b).

Next, the shape of the connector sections is described.

In the embodiment shown inFIG. 16(b), the first connector section510of the rigid part505and the second connector section511of the rigid part509are detachably engaged to shape the RF receiving coil500into a cylinder to be wound around the test object103and to connect each of the coil38patterns of the solenoid coil216-1and the saddle-shaped coil216-2.

As shown inFIG. 16(a), guide pins515-1and515-2are provided in the first connector section510, and guide holes151-1and151-2are provided in the second connector section511. By engaging the guide pins in the guide holes, the first connector section510and the second connector section511can be disposed at the position at which they can be connected. In the first connector section510, four female connectors514-1to514-4are disposed aligned with the guide pins515-1and515-2. In the second connector section511, male connectors (not shown) that fit these female connectors are disposed. Thus, the first connector section510can be fitted to the second connector section511by fitting the female connectors514-1to514-4to the male connectors while being aligned by the guide pins. Also, the first connector section510can be released from the second connector section511by operating levers513-1and513-2provided in the second connector section511.

Advantageously, the connector sections510and511shown inFIGS. 16(a) and16(b) can be connected rigidly because the guide pins515-1and515-2and the connectors514-1to514-4are disposed in alignment. Specifically, as shown inFIG. 19(a), even when an external force is applied in the direction shown by an arrow, the position181of the guide pins515-1and515-2and the position182of the connectors514-1to514-4are in alignment, the point of which can be used as supporting point for supporting the external force, rigidly connecting the connector sections510and511while preventing them from being displaced. On the other hand, as an comparison example, as shown inFIG. 19(b), when the position181of the guide pins515-1and515-2is not aligned with the position182of the connectors514-1to514-4, the supporting point is the position182of the connector514-1, then the external force is obliquely applied to the guide pins515-1and515-2. So, the guide pins515-1and515-2are easily displaced from the guide holes151-1and151-2, then the external force cannot be supported. In this case, the connection is not so rigid as that shown inFIG. 19(a).

As described above, in the embodiment, the RF receiving coil500to be wound around the test object103has a structure in which the flexible parts and the rigid parts are alternately disposed and the flexible substrate in each of the flexible parts is covered with the air-bubbles-containing resin602. This structure achieves the flexibility, light weight and ease in handling of the RF receiving coil500, which reduces the stress on the test object, and also allows the operator to easily fit the RF receiving coil500to the test object. Furthermore, the RF receiving coil500can be closely fitted to the test object, which can increase the received signal level to improve the image quality.

Also, providing the grooves85in the flexible parts501to504can limit the bending position to the locations of the grooves85, which can protect the electrical circuit components91mounted on the flexible parts from stress due to bending. Also, providing the frames608in the mounting areas of the electrical circuit components91in the flexible parts501to504can protects the electrical circuit components91from stress due to bending even when the flexible parts bend at any position other than the grooves85.

The shape of the frames608is such that the longitudinal direction of the frames608is along the body axis direction, and/or the two or more frames608are arranged in the body axis direction. This allows the structure of the flexible part to be such that the flexible part is difficult to bend in the body axis direction and is easy to bend in the body circumference direction. This limitation on the bending direction provides the RF receiving coil that can be easily wound around the body and easily handled.

Also, providing the windows83in the air-bubbles-containing resin602and mounting the electrical circuit components91on the flexible substrate601exposed through the windows83allow tuning or the like to be performed on the electrical circuit components91while the flexible substrate601is covered with the air-bubbles-containing resin. Also, in use, the lids607are attached to the windows83, which prevents the test object103or the operator from directly touching the flexible substrate601or the mounted components.

Further, in the embodiment, as shown inFIGS. 18(a) and18(b), in the fitting section of the flexible part and the rigid part, the rubber packings172are disposed between the rigid case604and the air-bubbles-containing resin602. This allows the air-bubbles-containing resin602to be less likely damaged and more durable when the flexible part bends.

Also, disposing the guide pins515-1and515-2and the connectors514-1to514-4in alignment in the connector sections allows the RF receiving coil to be difficult to be disconnected by an external force.

Second Embodiment

As a second embodiment, an RF receiving coil that can be fitted to the test object103when the test object103is a smaller body is described. The basic configuration of this RF receiving coil is similar to that of the RF receiving coil of the first embodiment except some differences. One difference is that, as shown inFIGS. 20,21(a) and21(b), the width (length in the body axis direction) of the RF receiving coil is decreased to form notches191at the positions corresponding to the armpits of the test object103. Another difference is that, as shown inFIG. 22, the grooves83are formed not only in the outer circumference surface side but also in the body surface side of the flexible parts501to504. The positions of the grooves83on the body surface side correspond to those on the outer circumference surface side.

Since the notches191are provided at the positions corresponding to the armpits of the test object103, the RF receiving coil, when wound around the test object103, can cover the test object103to near the neck in a portion of the body other than the side portions (that is, the front and back portions of the body), as shown inFIG. 21(b).

Also, providing the grooves85on the both sides allows the RF receiving coil to more largely bend and to be shaped into a cylinder having a smaller curvature radius. Accordingly, the RF receiving coil can be closely fitted to the test object103having a smaller girth.

The remaining configuration and manufacturing method are the same as those of the first embodiment and will not be further explained.