Reception cable and medical image diagnostic system

Abstract

To provide a reception cable and a medical image diagnostic system capable of reducing a burden on imaging staff.SOLUTION: A reception cable 54 comprises: a coaxial cable 70; tubular shield conductors 72 which house the coaxial cable 70 and have at least one resection part 74 non-conductive at a middle part in a direction of an axis ξ; the resection parts 74; and a tubular conductor 78 which is overlapped with the respectively portions 72A and 72A of the two shield conductors 72 and 72 positioned on both of the sides of each resection part 74 and disposed around the shield conductors 72 in a direction of a diameter A of the shield conductors 72, via a gap part 76.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a receiving cable and a medical image diagnostic system, and more particularly to a technique for reducing the burden on imaging staff involved in a magnetic resonance imaging apparatus. [Background technology]

[0002] The receiving coil used in a magnetic resonance imaging (MRI) device receives signals generated in a subject. A coaxial cable is usually used as a signal line to transmit this signal. The receiving coil is placed inside the transmitting coil provided on the inner wall of the gantry and in the vicinity of the subject.

[0003] In recent years, the number of coaxial cables used to transmit received signals has increased as receiving coils have become more multi-channel. These coaxial cables are often bundled and housed in a tubular outer shield conductor (hereinafter referred to as the shield conductor) and treated as a single cable (hereinafter referred to as the receiving cable). The shield conductor is usually made of a flexible material such as a mesh conductor, and the cable can be bent and positioned within the allowable bending radius (generally about five times the diameter of the receiving cable). This improves the flexibility of receiving coil installation.

[0004] The receiving cable is connected to the receiving coil when in use. Therefore, the shielding conductor acts as an antenna when it receives electromagnetic waves of the nuclear magnetic resonance frequency emitted by the transmitting coil, and a current is induced in the shielding conductor. When a large current is induced in the shielding conductor, heat is generated at the same time, so in order to suppress this, the receiving cable may be provided with one or more baluns (BALUNs: balanced-unbalanced converters) (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 6,664,465 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the number of channels of the receiving coil is increased, the number of coaxial cables also increases, which inevitably increases the diameter and weight of the receiving cable.

[0007] In addition, when the shield conductor is regarded as a dipole antenna, the larger the diameter of the receiving cable, the larger the receiving gain. As a result, the current induced in the shield conductor by the electromagnetic waves of the nuclear magnetic resonance frequency emitted by the transmitting coil becomes larger. In the following explanation, the current induced in the shield conductor and the current induced in the receiving cable are the same.

[0008] Therefore, in order to suppress the magnitude of the current induced in a large-diameter receiving cable with a large number of channels to the same level as the current induced in a small-diameter receiving cable with a small number of channels, the large-diameter receiving cable needs to be equipped with more baluns than the small-diameter receiving cable.

[0009] That is, when the diameter of the receiving cable is increased, not only does the weight of the receiving cable increase, but the weight of the balun also increases, so that the weight of the entire receiving cable including the balun increases further.

[0010] The imaging staff must handle the transport and installation of the receiving coil, but if the weight of the receiving cable as a whole increases, the burden on the imaging staff increases.

[0011] The present invention has been made in consideration of the above circumstances, and has an object to provide a receiving cable and a medical image diagnostic system that can reduce the burden on imaging staff. [Means for solving the problem]

[0012] The receiving cable of the first aspect of the invention comprises a signal line, a tubular shielding conductor that accommodates the signal line and has at least one non-conductive cut-out portion midway in the axial direction, and a tubular conductor that overlaps the cut-out portion and a portion of each of two shielding conductors located on either side of the cut-out portion and is arranged with respect to the shielding conductor via a gap portion in the diameter direction of the shielding conductor.

[0013] According to the first aspect of the receiving cable, the cut-out portion and the tubular conductor are provided to suppress the current induced in the shield conductor and the signal line, thereby reducing the number of baluns. This reduces the overall weight of the receiving cable, thereby reducing the burden on the imaging staff.

[0014] In the receiving cable according to the second aspect of the present invention, in addition to the first aspect, the gap portion is preferably formed of a dielectric material using a thermoplastic resin having a relative dielectric constant of less than 3.5.

[0015] A receiving cable according to a third aspect of the present invention is the same as that of the second aspect, and preferably, the dielectric material is made of polytetrafluoroethylene or polyimide.

[0016] The receiving cable according to the fourth aspect of the present invention is any one of the first to third aspects, and when the axial length of the tubular conductor is 120 mm to 320 mm and the gap portion is formed by air or a dielectric with a low dielectric constant, it is preferable that the length of the gap portion in the diameter direction is 1 mm to 4 mm.

[0017] A receiving cable according to a fifth aspect of the present invention, in any one of the first to fourth aspects, preferably has a tubular sheath covering the shielding conductor, the sheath having a cut-out portion at a position corresponding to the cut-out portion, and a tubular conductor having a diameter equal to or smaller than the diameter of the sheath is disposed in the cut-out portion.

[0018] A receiving cable according to a sixth aspect of the present invention is any one of the first to fifth aspects, wherein the tubular conductor is preferably a flexible mesh member.

[0019] A receiving cable according to a seventh aspect of the present invention is, in any one of the first to sixth aspects, preferably having one end at which a coil connection portion is provided and the other end opposite the one end at which a connector is provided, and a balun is provided at a position closer to the other end than the one end.

[0020] In a receiving cable according to an eighth aspect of the present invention, in the seventh aspect, it is preferable that the balun is provided at a position within 20 cm from the other end toward the one end.

[0021] A medical image diagnostic system according to a ninth aspect of the present invention includes the receiving cable according to any one of the first to eighth aspects and a magnetic resonance imaging device. Effect of the Invention

[0022] According to the present invention, it is possible to reduce the burden on imaging staff. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a perspective view showing the appearance of a medical diagnostic system according to the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing the internal configuration of the MRI apparatus shown in FIG. [Diagram 3] FIG. 3 is a plan view of the receiving coil unit. [Figure 4] FIG. 4 is a cross-sectional view of the receiving cable. [Diagram 5] FIG. 5 is an enlarged perspective view showing the configuration of a main part of the receiving cable. [Figure 6] FIG. 6 is a graph showing current distribution in the axial direction of the shield conductor when a cutout is provided and when a cutout is not provided. [Figure 7]FIG. 7 is a graph showing current distribution in the axial direction of a coaxial cable when a tubular conductor is provided and when a tubular conductor is not provided. [Figure 8] FIG. 8 is a graph showing the relationship between the gap length of the gap portion and the absolute value of the induced current. [Figure 9] FIG. 9 is a graph showing the relationship between the axial length of the tubular conductor and the optimum gap of the gap portion. [Figure 10] FIG. 10 is an explanatory diagram of a receiving cable provided with a plurality of tubular conductors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a receiving cable and a medical diagnostic system according to the present invention will be described with reference to the accompanying drawings.

[0025] FIG. 1 is a perspective view showing the appearance of a medical image diagnostic system 10 according to an embodiment of the present invention.

[0026] As shown in Fig. 1, a medical image diagnostic system 10 of the embodiment includes a magnetic resonance imaging device (hereinafter referred to as an MRI device) 20 and a receiving cable 54 connected to a receiving coil 52. The MRI device 20 and the receiving cable 54 are an example of a magnetic resonance diagnostic device and a receiving cable of the present invention. In this specification, the configuration in which the receiving coil 52 is connected to the receiving cable 54 will be referred to as a receiving coil unit 50 and described.

[0027] The MRI apparatus 20 is installed in an examination room of an imaging diagnostic facility. In the examination room, a subject is placed on a top plate 34 of a table 32 of a bed device 30, and is then transported toward the gantry 22 of the MRI apparatus 20 by the movement of the table 32.

[0028] The MRI apparatus 20 has a gantry 22. The gantry 22 has a bore 24 which is a cylindrical imaging space, and a table 32 moves into this bore 24.

[0029] [Internal structure of MRI device] FIG. 2 is a schematic diagram showing the internal configuration of the MRI apparatus 20. As shown in FIG.

[0030] As shown in FIGS. 1 and 2, the MRI apparatus 20 of this example includes a static magnetic field generating magnet 102, a gradient magnetic field coil 104, an RF (Radio Frequency) coil (hereinafter referred to as a transmission coil) 106, and a reception coil 52.

[0031] The static magnetic field generating magnet 102 generates a uniform static magnetic field in the bore 14 in which the subject 100 is placed. The gradient magnetic field coil 104 generates a gradient magnetic field in the bore 14. The transmission coil 106 generates a high-frequency magnetic field for generating nuclear magnetic resonance signals (NMR (Nuclear Magnetic Resonance) signals) (hereinafter referred to as NMR signals) in the nuclei of atoms that constitute the tissues of the subject 100. The reception coil 52 detects the NMR signals generated from the subject 100.

[0032] The subject 100 is placed on the top plate 34 of the table 32 , and the table 32 is moved to the bore 24 so that the examination site of the subject 100 is positioned at the center of the static magnetic field of the bore 24 .

[0033] The sequencer 108 sends commands to a radio frequency magnetic field generator 110 and a gradient magnetic field power supply 112 in accordance with an imaging sequence (pulse sequence), causing them to generate a radio frequency magnetic field and a gradient magnetic field, respectively.

[0034] The generated high frequency magnetic field is applied to the subject 100 as a pulsed high frequency magnetic field (RF pulse) through the transmission coil 106. The NMR signal generated from the subject 100 is received by the reception coil 52 and detected by the receiver 114.

[0035] The gradient magnetic field coil 104 is composed of gradient magnetic field coils in three directions, X, Y, and Z, and generates gradient magnetic fields in response to signals from a gradient magnetic field power supply 112 .

[0036] The nuclear magnetic resonance frequency (detection reference frequency f0) used as the detection reference in the receiver 114 is set by the sequencer 108. The sequencer 108 controls each part so that it operates at pre-programmed timing and intensity. Among the programs, a program that describes in particular the timing and intensity of the RF pulse, gradient magnetic field, and signal reception is called a pulse sequence.

[0037] There are various known pulse sequences depending on the purpose, but a detailed description thereof will be omitted here.

[0038] The control unit 116 controls the operation of each part of the MRI apparatus 20 via the sequencer 108. The control unit 116 also receives the signal detected by the receiver 114 and performs various signal processing such as image reconstruction. The receiver 114 performs quadrature phase detection of the echo signal (NMR signal), which is an analog wave, using a set detection reference frequency f0, converts it into raw data, and then transmits it to the control unit 116. This raw data is also called an echo signal or measurement data.

[0039] The control unit 116 receives various instruction inputs from the operation unit 118 and performs overall control of each unit of the MRI apparatus 20. The control unit 116 also performs processing such as converting the echo signals in the spatial frequency domain received via the sequencer 108 into images in real space by inverse Fourier transform, thereby generating an MRI image.

[0040] The control unit 116 is realized by a general-purpose computer such as a personal computer or a microcomputer, etc. The control unit 116 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output interface, and the like.

[0041] In the control unit 116, various programs such as a control program stored in the ROM are loaded into the RAM, and the programs loaded into the RAM are executed by the CPU. This realizes the functions of each part of the MRI apparatus 20, and various arithmetic processing and control processing are executed via the input / output interface.

[0042] The operation unit 118 includes a mouse, a keyboard, and the like, and functions as a part of a GUI (Graphical User Interface) that uses a display operation window on a display (not shown) and receives input from imaging staff.

[0043] That is, the operation unit 118 functions as a GUI for the imaging staff to start and stop (including pausing) the MRI apparatus 20, select a pulse sequence, and input imaging conditions, processing conditions, and the like.

[0044] Cameras 120A and 120B may be disposed at both ends of the upper portion of the bore 24. The cameras 120A and 120B each capture an image of the subject 100 or the like.

[0045] [Receiving coil unit] FIG. 3 is a plan view of the receiving coil unit 50. As shown in FIG.

[0046] The receiving coil unit 50 of this example includes a receiving coil (torso coil in this example) 52 configured in a sheet shape, and a receiving cable 54 connected to the receiving coil 52.

[0047] The receiving coil 52 is flexible, thin and lightweight. The receiving coil 52 is a multi-channel coil, and a plurality of sub-coil channels are housed inside a bag-shaped sheet 56 that constitutes the outer cover of the receiving coil 52.

[0048] These sub-coil channels function as antennas for receiving NMR signals. The sub-coil channels are generally ring-shaped with a diameter of about 10 to 15 cm or square-shaped with each side being about 10 to 15 cm, and are arranged two-dimensionally inside sheet 56 of receiving coil 52.

[0049] Each sub-coil channel is provided with a decoupling circuit. Each decoupling circuit is provided with a voltage-driven field effect transistor (FET). The FET of each decoupling circuit is ON / OFF controlled by the drive voltage supplied from the decoupling power supply.

[0050] In the above decoupling circuit, ON / OFF switching by voltage control of an FET is shown as an example, but ON / OFF control can also be implemented using current-controlled switching of a PIN diode, or voltage-controlled switching of a MEMS (Micro Electro Mechanical Systems) device.

[0051] Each sub-coil channel is an antenna that receives NMR signals from the subject 100 and is tuned to resonate at a specific frequency. The specific frequency is determined by the nuclei (usually hydrogen nuclei) of the biological tissue to be observed and the magnetic field strength.

[0052] 3, the receiving cable 54 includes a long cable main body 60 having an axis ξ, and one balun (also called a clamp balun) 62 provided on the cable main body 60. A coil connection part 64 is provided at one end 60A of the cable main body 60, and a plug connector 66 is provided at the other end 60B of the cable main body 60.

[0053] Here, we will explain the functions (roles) of the balun 62. The balun 62 has the following two functions (first and second functions).

[0054] [First function] The first function is to cut off the mixed noise (common mode noise) propagated from the MRI system to the receiving coil 52 via the receiving cable 54, on the plug connector 66 side rather than the coil connecting portion 64.

[0055] In this case, it is preferable to place the balun 62 at a position that is not directly below the point where the irradiation coil current is at a maximum, for example, at a position within 20 cm from the other end 60B of the cable main body 60 toward one end 60A.

[0056] Thus, receiving cable 54 of this example has one end 60A where coil connection portion 64 is provided, and the other end 60B opposite end 60A where plug connector 66 is provided. One balun 62 is provided at a position closer to other end 60B than one end 60A and within 20 cm from other end 60B toward one end 60A.

[0057] By adopting such a configuration, the receiving cable 54 of this embodiment can cut common mode noise while suppressing a rise in temperature of the receiving cable 54. This makes it possible to ensure high image quality.

[0058] [Second function] The second function is to reduce noise currents induced on the receive cable 54 by RF irradiation.

[0059] The second function can suppress heat generation in the receiving cable 54. In addition, it can suppress unnecessary excitation of objects outside the field of view, thereby improving image quality degradation problems such as aliasing artifacts.

[0060] [Comparative example receiving cable] Here, a receiving cable of a comparative example will be described.

[0061] The receiving cable of the comparative example has a cable body having a diameter of 1 cm and an axial length of 1 m, and five baluns, each having a diameter of 3 cm and an axial length of 12 cm, provided at intervals.

[0062] The above dimensions include manufacturing errors that are generally considered. The same applies to dimensions in the following explanations. In addition, "0~□" indicating a range of values ​​means "0 or more, □ or less."

[0063] When five baluns are provided as in the receiving cable of the comparative example, the weight of the entire receiving cable increases, which increases the burden on the imaging staff. Also, unlike a flexible shielded conductor, the balun is made of a rigid conductor or a plastic case. Therefore, the balun part cannot be bent, and the more baluns there are, the greater the constraints on the handling work when installing the receiving coil, which increases the burden on the imaging staff.

[0064] Also, when looking at the receiving cable of the comparative example, it does not look like there are thicker parts (3 cm diameter baluns) intermittently in the axial direction of the receiving cable, but rather like there are thinner parts (1 cm diameter cable body) intermittently in the row of five baluns. In other words, it gives the impression that the diameter of the receiving cable has increased.

[0065] The reason for placing five baluns on the cable body is based on the results of a temperature rise test on the receiving cable. The temperature rise test is a test in which the temperature of the receiving cable is measured under the condition that the balun is placed directly under the point where the irradiation coil current is at its maximum (the worst heat generation condition). As a result, the five baluns were placed as above to disperse (suppress) the heat generation of the receiving cable so that the surface temperature of the receiving cable would not exceed the reference temperature.

[0066] As described above, the receiving cable of the comparative example has five baluns with large diameters, and is therefore quite heavy, which increases the burden on the imaging staff. Therefore, in order to reduce the burden on the imaging staff, it is necessary to make the diameter as small as possible and to reduce the weight of the entire receiving cable, including the cable body and baluns.

[0067] [Receiving cable of embodiment] Fig. 4 is a cross-sectional view of the receiving cable 54 of the embodiment. Fig. 5 is an enlarged perspective view of a main part of the receiving cable 54. Note that Fig. 5 shows a part of the receiving cable 54 in perspective in order to show the detailed configuration of the receiving cable 54.

[0068] As shown in Figures 4 and 5, the receiving cable 54 of this example has a coaxial cable 70. Although Figures 4 and 5 show a plurality of coaxial cables 70 corresponding to the multi-channel configuration of the receiving coil 52, the number of coaxial cables 70 is not limited to a plurality, and may be one. The coaxial cable 70 is an example of a signal line of the present invention.

[0069] The receiving cable 54 also has a tubular shield conductor 72 that houses the coaxial cable 70. The shield conductor 72 has at least one non-conductive cut-out portion 74 midway in the direction of the axis ξ. The shield conductor 72 is an example of the shield conductor of the present invention.

[0070] The receiving cable 54 also has a tubular conductor 78 disposed with a gap 76 interposed between the shield conductor 72 and the shield conductor 72 in the direction of diameter A of the shield conductor 72. The tubular conductor 78 overlaps the cutout 74 and parts 72A, 72A of the two shield conductors 72 located on both sides of the cutout 74. The parts 72A, 72A face each other in the direction of the axis ξ. The tubular conductor 78 is an example of a tubular conductor of the present invention.

[0071] Thus, the receiving cable 54 of this example includes the coaxial cable 70, the shield conductor 72 having the cutout portion 74, and the tubular conductor 78. Note that reference numeral 80 in Fig. 4 denotes a sheath. The sheath 80 is a tubular insulator that constitutes the outermost layer of the cable main body 60 (see Fig. 3).

[0072] According to the receiving cable 54 of this example, the cutout portion 74 is provided in the shield conductor 72, so that the current induced in the shield conductor 72 (induced current) can be suppressed. As a result, the temperature rise occurring in the receiving cable 54 can be suppressed.

[0073] 6 is a graph showing the current distribution in the axis ξ direction of the shield conductor when the cutout portion 74 is provided and when it is not provided. The values ​​on the vertical axis of the graph are normalized current values ​​when unit power is supplied to the transmitting coil.

[0074] When cutout 74 is provided, the induced current distribution is such that the induced current drops sharply at the "0" position on the horizontal axis where cutout 74 is located, as shown by line C in Fig. 6. In contrast, when cutout 74 is not provided, the current distribution has a peak value at the "0" position on the horizontal axis, as shown by dashed line D in Fig. 6.

[0075] As is apparent from FIG. 6, by providing the cutout portion 74 in the shield conductor 72, the current induced on the shield conductor 72 can be suppressed.

[0076] On the other hand, a current is induced in the coaxial cable 70 due to the cutout portion 74 , but this current is suppressed by the tubular conductor 78 .

[0077] FIG. 7 is a graph showing the current distribution in the direction of the axis ξ of the coaxial cable 70 when the tubular conductor 78 is provided and when it is not provided.

[0078] The current distribution when the tubular conductor 78 is provided is shown by line E in Fig. 7, and the current distribution when the tubular conductor 78 is not provided is shown by line F in Fig. 7 (note that line E is the result when the gap length described below is configured to be 2 mm). When comparing the two, at the position "0" on the horizontal axis where the tubular conductor 78 exists, the peak value of the current when the tubular conductor 78 is provided is half of the peak value when the tubular conductor 78 is not provided.

[0079] As is clear from FIG. 7, the current induced in the coaxial cable 70 can be suppressed by overlapping the cutout portion 74 with the tubular conductor 78. As a result, the temperature rise occurring in the receiving cable 54 can be suppressed. When the peak current is reduced to 1 / 2, the amount of heat generated is reduced to 1 / 4 ((1 / 2) 2 ) In addition, the current peak suppression effect at the balun attachment point is approximately 1 / 10, and it is preferable that the use of tubular conductor 78 can provide the same unwanted current suppression effect as a balun. When comparing the current peak values ​​of lines E and F in FIG. 7 with the current peak value of line D in FIG. 6, it can be seen that the current peak value of line F is greater than 1 / 10 of the current peak value of line D, while the current peak value of line E is less than 1 / 10 of the current peak value of line D.

[0080] In this way, when the receiving cable 54 of this example is adopted, the induced current can be suppressed without using a balun, so that the number of baluns 62, which account for, for example, approximately 80% of the weight of the receiving cable 54, can be significantly reduced.

[0081] As a result, the overall diameter and weight of the receiving cable 54 can be reduced, which reduces the burden on the imaging staff who handle the receiving cable 54. This will be explained in detail below.

[0082] The effect of suppressing the induced current in the coaxial cable 70 depends on the distance of the gap between the shield conductor 72 and the tubular conductor 78 in the direction of diameter A of the receiving cable 54. In the following description, the above gap is referred to as the gap portion 76, and the above distance is referred to as the gap length.

[0083] For example, when the axial length of the tubular conductor 78 is 120 mm, the gap portion 76 is filled with air, and the gap length is about 2 mm (capacitance calculated from the overlap area of ​​the shield conductor 72 and the tubular conductor 78 in the axial ξ direction of the cable main body 60 is about 10 pF) as shown by line G in the graph in FIG. 8, the induced current suppression effect is maximized. This is because a resonance system is formed near the cutout portion 74 of the shield conductor 72, as described later. Here, the gap length does not need to be strictly 2 mm, and the gap length may be changed within a range that is equal to or greater than the current peak suppression effect by the balun (the current peak value with the balun is 1 / 10 or less of the current peak value without the balun). For example, the gap range of 1.6 mm to 2.2 mm shown by the dashed line in FIG. 8 exceeds the current peak suppression effect by installing a balun, and can be used without problems in practical use.

[0084] Also, the optimum gap length at which the induced current suppression effect is optimal (maximum) tends to become smaller as the axial length of the tubular conductor 78 becomes longer, as shown by line H in the graph of FIG. 9. Here, the dashed lines above and below line H in FIG. 9 indicate the range of gap lengths at which the current suppression effect of the balun is equal to or greater than that of the balun at each axial length of the tubular conductor. For example, when the axial length of the tubular conductor 78 is 320 mm, the range of gap lengths at which the current suppression effect of the balun is exceeded is approximately 1 mm to 1.6 mm. In general, the smaller the cable diameter, the easier it is to handle, so a smaller gap length is preferred by imaging staff. In the case of the axial length of the tubular conductor 78 shown in FIG. 9 being 120 mm to 320 mm, the gap can be made smallest within a range at which the current suppression effect of the balun is equal to or greater than that of the tubular conductor 78 manufactured with a tubular conductor axial length of 320 mm and a gap length of approximately 1 mm.

[0085] The tubular conductor 78 is not merely a conductor having a shielding function, but also functions as a part of a conductor that suppresses induced currents by utilizing a resonance system.

[0086] In other words, near the cutout portion 74 of the shield conductor 72, the overlapping portion of the shield conductor 72 and the tubular conductor 78 functions as a capacitor, and the tubular conductor 78 functions as an inductor, resonating near the central frequency of the MRI device 20 (for example, 63.88 MHz when the magnetic field strength is 1.5 T).

[0087] Here, the optimal gap length shown in FIG. 9 is for the case where the gap portion 76 is filled with air, but in some cases, fixing the tubular conductor 78 to the cable main body 60 may be easier in terms of production if the gap portion 76 is formed (configured) from a dielectric.

[0088] When the gap 76 is made of a dielectric material, the inductance of the resonance system in the vicinity of the cutout 74 hardly changes, whereas the capacitance of the resonance system changes according to the relative dielectric constant of the dielectric material.

[0089] Therefore, in order to obtain the effect of suppressing the induced current, it is necessary to adjust the gap length based on the dielectric constant of the dielectric. By adjusting the gap length so that the resonance frequency when the gap portion 76 is formed of a dielectric coincides with the resonance frequency when the gap portion 76 is filled with air, it is possible to suppress the induced current induced in the coaxial cable 70 to the maximum extent. When the axial length of the tubular conductor 78 is constant and the gap portion 76 is entirely filled with a dielectric, the gap length can be adjusted to approximately the dielectric constant times the resonance frequency to coincide with the resonance frequency when the gap portion is filled with air. However, in general, the cable diameter is easier to handle if it is as thin as possible, and the cable 70 is easier to handle if the gap length is short. For this reason, it is desirable that the dielectric material filling the gap portion be a thermoplastic resin with a small dielectric constant. In particular, the dielectric material filling the gap portion 76 is preferably a material with a dielectric constant of less than 3.5. In general, a material with a dielectric constant of less than 3.5 is called a low dielectric constant material.

[0090] Furthermore, the conductivity of a dielectric (material) generally increases as the dielectric constant increases. Since the conductivity of a dielectric is a cause of heat generation, from this viewpoint as well, it is desirable for the dielectric constant of the dielectric to be as small as possible. In this example, polytetrafluoroethylene (registered trademark: Teflon) is exemplified as a dielectric with a dielectric constant of less than 3.5. However, this is not the only dielectric with a dielectric constant of less than 3.5; thermoplastic resins such as fluororesins and polyimides can also be used.

[0091] The relative dielectric constant of polytetrafluoroethylene is small, about 2.1, and the volume resistivity is also low, about 10 18 (Ω·m), which is sufficiently large to cause almost no current to flow. Therefore, a dielectric material made of polytetrafluoroethylene (for example, one formed in a sheet shape) is suitable as the dielectric material that forms the gap portion 76.

[0092] When the gap portion 76 is formed of a dielectric material made of polytetrafluoroethylene, the approximate optimum gap length when the axial length of the tubular conductor 78 is 120 mm is 1.9 mm×2.1≈4 mm.

[0093] The shorter the axial length of the tubular conductor 78, the easier it is to manufacture the tubular conductor 78. For this reason, within the axial length range of 120 mm to 320 mm, the easiest tubular conductor to manufacture is when the axial length of the tubular conductor is 120 mm and the gap portion 76 is made of a dielectric material with a low dielectric constant. When the gap portion 76 is made of a dielectric material made of polytetrafluoroethylene, the gap length is about 4 mm as described above.

[0094] In this way, when the axial length of the tubular conductor 78 is 120 mm to 320 mm and the gap portion 76 is filled with air or a dielectric made of polytetrafluoroethylene, the induced current generated in the coaxial cable 70 can be suppressed to the same extent as or better than that of a balun by setting the gap length to 1 mm to 4 mm.

[0095] The tubular conductor 78 is not limited to one with an axial length of 120 mm to 320 mm, but is preferably in the above range in consideration of ensuring the flexibility of the cable main body 60 with an axial length of 1 m to 2 m.

[0096] The dielectric is not limited to polytetrafluoroethylene, and any dielectric with a low dielectric constant can be used. For example, polyimide can be used. The dielectric constant of polyimide is also low at about 3.2, and the volume resistivity is 10 16 Since the resistance is sufficiently large (Ω·m) and almost no current flows, polyimide can also be used as the dielectric material for forming the gap portion 76.

[0097] The entire area of ​​the gap 76 may be made of a dielectric material, or only a part of the area may be made of a dielectric material. In this case, the gap 76 is formed by a dielectric material and an air layer.

[0098] The resonance near the cutout 74 of the shield conductor 72 is weaker than the resonance of the balun 62, so the amount of heat generated is small even if the cutout 74 is located close to the excitation irradiation coil. On the other hand, if the balun 62 is located close to the irradiation coil, the balun 62 generates a lot of heat.

[0099] Therefore, as described above, it is desirable to arrange the balun 62 at a position within 20 cm from the connector side (other end 60B) so as not to be disposed close to the irradiation coil, as a measure to avoid heat generation.

[0100] Furthermore, placing the heavy balun 62 near the plug connector 66 rather than near the receive coil 52 can reduce the burden on the imaging staff when attaching the receive coil 52 to the subject 100.

[0101] In addition, it is preferable to adjust the thickness of the sheath 80, the axial length of the tubular conductor 78, and the dielectric of the gap portion so that the diameter of the tubular conductor 78 is equal to or smaller than the diameter of the sheath 80 that constitutes the outermost layer of the cable body 60.

[0102] Furthermore, if the tubular conductor 78 is made of a flexible material such as a mesh conductor, it will be bendable, and from the outside it will look like a receiving cable 54 with a diameter of only about 1 cm. This reduces the burden on the imaging staff in handling the cable. This makes it possible to reduce the burden on the imaging staff.

[0103] The manufacturing methods (first and second manufacturing methods) of the receiving cable 54 will be described below.

[0104] [First manufacturing method] First, a partial range (axial length 120 to 320 mm) of the sheath 80 of the cable main body 60 is removed to provide a removed portion in the sheath 80.

[0105] Next, a cutout portion 74 is provided in the shield conductor 72 exposed through the cutout portion.

[0106] Next, the gap portion 76 is formed from a dielectric material with a low dielectric constant (for example, polytetrafluoroethylene).

[0107] Next, a tubular conductor 78 is attached to the outer periphery of the dielectric body.

[0108] Finally, a sheath having a short axial length is attached to the outer periphery of the tubular conductor 78 to cover the cut-out portion.

[0109] [Second manufacturing method] First, a partial range (axial length 120 to 320 mm) of the sheath 80 of the cable main body 60 is removed to provide a removed portion in the sheath 80.

[0110] Next, a cutout portion 74 is provided in the shield conductor 72 exposed through the cutout portion.

[0111] Next, a dielectric material with a low relative dielectric constant (eg, polytetrafluoroethylene) is attached to the inner periphery of the tubular conductor 78, and a heat shrink tube is attached to the outer periphery of the tubular conductor 78.

[0112] The tubular conductor 78 is then attached to the cutout portion of the sheath 80 .

[0113] The heat shrink tubing is then heat shrunk to secure the tubular conductor 78 around the cutout 74 .

[0114] Finally, a sheath 80 having a short axial length for covering the heat shrink tube is attached to the outer periphery of the heat shrink tube.

[0115] The heat shrink tube may also serve as the sheath 80. In that case, the step of attaching the sheath 80 can be omitted.

[0116] In this example, the receiving cable 54 is described in which one cutout portion 74 is provided in the shield conductor 72, but two or more cutout portions 74 may be provided. For example, Fig. 10 shows a receiving cable 54 in which five cutout portions 74 are provided and a tubular conductor 78 overlaps each cutout portion 74. Fig. 10 also shows a cutout portion 82 provided in the sheath 80.

[0117] In this embodiment, the torso coil is exemplified as the receiving coil 52 to which the present invention is applied, but the present invention is not limited thereto and can be applied to all receiving coils having a receiving cable. For example, the receiving cable may be built in (invisible from the outside) under the top plate 34. Even in this case, a plurality of baluns are provided (invisible from the outside) under the top plate 34 to reduce noise current induced on the receiving cable. By applying the present invention and reducing the number of these baluns, it becomes possible to utilize the space under the top plate 34 that was allocated for installing the baluns for another purpose. For example, if the vacant space is used to increase the thickness of the top plate 34, the load-bearing performance of the top plate 34 can be improved. Alternatively, the receiving performance of the MRI apparatus can be improved by effectively utilizing the vacant space under the top plate 34 to increase the number of channels of the AD converter, for example.

[0118] Although the embodiments of the receiving cable and medical image diagnostic system according to the present invention have been described above, the present invention may be improved or modified in several ways without departing from the gist of the present invention. [Explanation of symbols]

[0119] 10 Medical imaging diagnostic systems 20 MRI machine 50 Receiving coil unit 52 Receiving coil 54 Receiving cable 60 Cable body 60A one end 60B Other end 62 Balan 64 Coil connection 66 Plug Connector 70 Coaxial Cable 72 Shielded Conductor 74 Excision 76 Gap section 78 Tubular Conductor 80 Sheath 82 Deleted section

Claims

1. A signal line; a tubular shield conductor that accommodates the signal line and has at least one cut-out portion that is not conductive at a midpoint in the axial direction; a tubular conductor overlapping the cutout and a portion of each of the two shield conductors located on both sides of the cutout, the tubular conductor being disposed with a gap portion interposed between the shield conductors in a diameter direction of the shield conductors; Equipped with Receive cable.

2. the gap portion is formed of a dielectric material using a thermoplastic resin having a relative dielectric constant of less than 3.5; 2. A receiving cable as claimed in claim 1.

3. 3. The receiving cable according to claim 2, wherein the dielectric material is made of polytetrafluoroethylene or polyimide.

4. When the axial length of the tubular conductor is 120 mm to 320 mm and the gap portion is formed of air or a dielectric having a low dielectric constant, the length of the gap portion in the diameter direction is 1 mm to 4 mm. A receiving cable according to any one of claims 1 to 3.

5. a tubular sheath covering the shield conductor; the sheath has a cutout portion at a position corresponding to the excision portion, The tubular conductor having a diameter equal to or smaller than a diameter of the sheath is disposed in the cutout portion. A receiving cable according to any one of claims 1 to 3.

6. The tubular conductor is a flexible mesh member. A receiving cable according to any one of claims 1 to 3.

7. the receiving cable has one end at which a coil connection portion is provided and another end opposite to the one end at which a connector is provided, One balun is provided at a position closer to the other end than the one end. A receiving cable according to any one of claims 1 to 3.

8. The balun is provided at a position within 20 cm from the other end toward the one end.

8. A receiving cable according to claim 7.

9. A receiving cable according to any one of claims 1 to 3; A magnetic resonance imaging device; Equipped with Medical imaging diagnostic system.

Images