JP5709139B2 - Floating subdivided shielded cable assembly - Google Patents

Description

  The present invention relates to coaxial cables used in high RF fields where the current induced in the shield can have deleterious effects. The invention is particularly applicable to the cable when used in the high RF field used in magnetic resonance imaging, but is applicable to other cables. The present invention also includes a jacket arrangement that can be applied to conventional coaxial cables to obtain the advantageous structure described herein.

  Many coaxial cables are required to be used in the high RF fields used for MRI. These include not only receive coil arrays, but also high RF fields such as those used in pacemakers, ECG examinations, electrophysiology and EEG monitoring, and other cables that must enter the deep brain stimulation system (DBS). Including. Common mode signals or shield currents on coil cables are often induced during the transmission phase by the coil itself or by an external source such as the surrounding transmitter coil. Electrically induced current from an external source, such as the current produced by the body transfer coil, is responsible for the majority of the shield current, i.e. heat at the surface of the cable. These currents and the resulting heat can cause significant heating or burns to the patient. Common mode current also degrades image quality due to coil tuning, i.e., effects on coil coupling within the phased array coil.

  Furthermore, the generation of current at the shields of the cables in the coils, in particular the cables close to or crossing the individual coil loops of the phased array coil, is caused by the transmitter coil in the magnetic field of the MR scanner. It can interfere with the generation of the generated homogeneous RF field. This heterogeneity of the RF field can create artifacts in the resulting image.

  The advantageous use of coaxial cables having an inner axially oriented elongated conductor separated from an annular conductive shield by a dielectric material has long been known. Such coaxial cables have been used for magnetic resonance imaging as well as many other applications.

  An important safety concern associated with magnetic resonance imaging technology is burns and excessive heating from RF currents induced in electrical cables. To reduce the risk of such local burns and sunburn, MR scanner users are instructed to minimize cable-patient contact. However, such contact is unavoidable in many instances, such as when using ECG cables, surface coils or intracavity coils.

  Some commercial MR coils, such as GE Medical System magnetic resonance coils, use, for example, a patient safety module to minimize local burns and sunburn and the conduction current induced in the electrical cable. To do. This design reduces the unbalanced current on the coaxial cable.

  In addition to patient safety, this design affects radiation loss and common mode noise reduction in the coil. Similar, more serious problems exist for coils inserted into the body, such as intrarectal probes, esophageal probes and intravascular RF probes. As these instruments approach the body, the risk of causing a hot spot or burn to the patient increases. Moreover, the wavelength of the RF signal in the body is about 9 times shorter than the wavelength in the air. As a result, current induction to the short cable is possible. Thus, there is a need for an improved coaxial cable that performs effectively for its intended purpose, while at the same time causing excessive heating and burns to the undesired patient, thus creating artifacts. Reduces the generation of high currents in the shield that can interfere with the field.

  Typically, the use of a cable trap placed on the cable at regular intervals along the length of the cable reduces the effect of current generation on the shield of the coaxial cable. These act to reduce the generation of current.

  This is particularly exacerbated when the cable must be very long to accommodate various operations, such as in the system described in US Pat. Thus, medical procedures are disclosed in which the magnet is movable relative to the patient and other elements of the system. The moving magnet system allows intraoperative MRI to produce imaging more easily in neurosurgical patients, with additional applications for patients undergoing liver, chest, needle and heart surgery. In this case, the many cable traps required within the MRI coil signal transmission cable during surgery along with a cable having a very long length make the cable particularly difficult to use.

  One type of cable trap typically includes an inductor formed from a cable shield braid by wrapping the cable around a helical support so that the shield forms a helical inductor. . At one end, the copper conductor is electrically connected to the cable shield braid, and at the other end, one or more capacitors to form a tank circuit that acts to reduce unwanted shielding current on the cable Is connected in parallel with the inductor between the copper conductor and the shield.

  In the cable trap arrangement, the shield braid was continuous along the cable, forming a tank circuit defined by the shield, the copper conductor and the inductor portion of the capacitor at multiple points along its length.

  Cable traps improve coil performance by eliminating or reducing shield current along the cable shield. Although the cable trap is designed to reduce the shield current, the spiral inductor formed from the cable trap's cable shield effectively acts as an antenna to receive RF power from the transmitter coil and unexpectedly does in the cable Involved in current.

  Experiments have shown that the copper conductor contributed to the additional heat. This type of cable trap increases overall coil and cable weight and is not convenient in a surgical environment.

  The set of shield current generations is proportional to the shape of the cable. Larger surface cables produce more shielding current than smaller surface area cables. For example, a longer cable with a large diameter will generate more current than a shorter cable with a small diameter.

  The generation of the shield current is proportional to the system RF power. For example, the power from a 3.0 Tesla system is four times the power from a 1.5 Tesla system and a much higher power for systems above 7.0 Tesla, which is required for a 3.0 Tesla system The number of cable traps that will be done will be almost double compared to a 1.5T system with close spacing between the cable traps. Systems above 7.0 Tesla require more cable traps with closer spacing.

  Also, the additional length of raw cable required, when wrapped in a spiral, negatively affects the RF chain to form a cable trap.

  Many cable designs have been previously proposed as follows. Patent Document 2 (Etaler), issued to Johns Hopkins University on September 4, 2001, describes a high-frequency separation between the inner shield part and the outer conductor subdivided outer shield part so as to inhibit the induced radio frequency current. A probe coaxial cable used in MRI with an outer dielectric layer with a dielectric constant is disclosed. Thus, the disclosed arrangement connects one end of the subdivided shield to the cable shield braid and uses the free end of the subdivided shield as a quarter wave cable trap.

  Patent Document 3 (Gray), issued to Biophan technologies on October 17, 2006, describes the effect of induced voltage on a device in which the voltage compensation unit has a single-wire wiring having a balanced characteristic impedance. Disclosed is an arrangement that weakens The voltage compensation unit includes an adjustable compensation circuit connected to the wiring, the compensation circuit applying a supplemental impedance to the wiring to unbalance the characteristic impedance of the wiring and thereby the effect of the induced voltage Weaken.

  Patent Document 4 (Schulz) issued to Philips on April 17, 2008 discloses a lead used in an MRI apparatus, and the MRI apparatus has a finite-length electromagnetic coupling element that is not equal to an integral multiple of a half wavelength. An auxiliary electrical device for connecting the holding portion and the lead is provided.

  U.S. Pat. No. 5,849,028 issued to GE Healthcare on November 13, 2007 discloses a lead for use in an MRI apparatus, which has a signal-to-noise ratio more than necessary for patient safety. In order to eliminate the risk of thermal damage without compromise, the lead includes two consecutive different resistive cable elements. The second cable element connected to the patient by the first cable element has an overall resistance that increases from the normal high conductive resistance value of the patient cable to suppress antenna resonance in the second cable element. ing. The first cable element is connected to an electrode on the patient's skin to prevent electromagnetic induction current from flowing to the patient and to prevent excessive heating of the cable by electromagnetic induction. The cable element has a total resistance substantially larger than the total resistance value of the cable element.

US Pat. No. 5,735,278 US Pat. No. 6,284,971 US Patent No. 7,123,013 US Pat. No. 7,205,768 US Pat. No. 7,294,785

  One object of the present invention is to provide a cable for communicating signals in an RF field where the generation of current in the cable near the RF field is reduced.

  According to one aspect of the present invention, a shielded cable is provided, the shielded cable extending axially along the cable and an electrical connection for transmitting signals between opposite ends of the cable. And an axially extending outer shield conductor disposed to surround and surround the inner conductor structure at regular intervals, the outer shield conductor being inward from an external field. In order to shield the conductor structure, it extends continuously between opposite ends of the cable for connection to circuit ground, the inner conductor structure being electrically isolated from the outer shield conductor by a dielectric material placed between them. The shielded cable further comprises a plurality of braided or solid conductor portions each surrounding the outer shield conductor, the conductor portions being axially aligned along the cable. The conductor portions are electrically separated from each other so as to be electrically floating with respect to the other conductor portions, and the conductor portions are separated from the outer shield. Electrically separated from the outer shield conductor so as to be electrically floating relative to the conductor, the shielded cable further comprises a conductor portion and a cable jacket surrounding the outer shield conductor.

  In most cases where the conductor portion is annular, the conductor portion completely surrounds the cable, but this is not a requirement for the portion to perform the shielding action.

  In one embodiment, the conductor portion is formed from a braid, but because the foil tape interferes with the holes between the wires in the braid that can reduce the shielding effect, the conductor portion is annular or helical. Formed with wrapped non-magnetic metal foil tape. Combinations of braided and solid conductors are also possible.

  In one embodiment, the conductor portions may be spaced apart in the axial direction, i.e., one end is next adjacent so as to leave a portion of the outer shield conductor not covered by the conductor portion. It may be arranged to be spaced from the end portion to be spaced at regular intervals. However, if a high level of protection is required, the conductor portions are arranged such that the outer shield conductor is completely covered by the conductor portions, so that each end corresponds to the next adjacent conductor portion. It may be overlapped at the end. In this case, a dielectric material would be applied between the outer surface of one part and the overlapping inner surface of the next adjacent part to ensure electrical isolation. This can be formed by a wrapped tape such as Teflon tape.

  In one embodiment, a continuous envelope made of a dielectric material surrounding the outer shield conductor with which the conductor portion is engaged is provided. However, the separation of the conductor portion from the outer shield can be formed by other materials, such as a non-magnetic metal foil tape wrapped in an annular or spiral manner.

  In particular, one important feature is that the conductor portion is shaped and arranged to reduce the heat of the RF field cable, and preferably the conductor portion reduces the heat of the RF field cable of the magnetic resonance imaging system, Shaped and arranged to reduce to a temperature below that sufficient to cause harmful burns to human tissue.

  Preferably, the conductor portion for a 1.5 Tesla system or more has a length of less than a maximum of 10 inches, preferably 0.5 to 2.0 inches, which is a practical dimension for manufacturing. While ensuring that the induced current in the shield conductor and its parts is reduced to a level that enhances the operation of the cable.

  If the conductor portion is engaged around the intermediate guide layer by a cable jacket engaged over the entire structure, the above defined cable can be formed as a unitary structure. Alternatively, however, if the conductor portion is carried over an inner hollow sleeve member that engages by sliding over the cable jacket with the inner sleeve member and a second outer jacket surrounding the conductor portion, the cable Any existing conventional cable can be used to form the structure, including a coaxial cable surrounded by a jacket. This technology avoids the complete cable product and allows the use of existing cable structures as part of an inexpensive structure to be mass produced.

  In accordance with the second aspect of the present invention, there is thus provided a shield assembly for use on any existing conventional cable, the conventional cable being the main feature of the present invention. The shield assembly is made of a dielectric material and includes an inner sleeve member disposed with a hollow interior defined by the inner surface, the inner surface being coaxial cable when installed The shield assembly is further carried on the inner sleeve member so as to surround the coaxial cable when the inner sleeve member is installed. A plurality of conductor portions, each of which surrounds the inner sleeve member and is longer than the length of the inner sleeve member. Having a short length, the conductor portions are arranged at positions spaced apart in the axial direction along the inner sleeve member, the conductor portions being electrically separated from the other conductor portions, respectively; As a result, this conductor part is electrically floating with respect to the other conductor part, and the conductor part is electrically isolated from the cable, so that the conductor part is in relation to the elements of the cable. Electrically floating, the shield assembly further comprises a cable jacket surrounding the conductor portion and the inner sleeve member.

  This arrangement of the shield assembly is therefore convenient for use with any existing conventional cable, including coaxial cables, to achieve the same effect as described above.

  In accordance with a third aspect of the present invention, a method is provided for communicating a signal in an RF field, the method connecting a signal to be communicated to an elongate axially extending inner conductor or conductors. The inner conductor or the conductor has an axially extending outer shield conductor arranged at regular intervals so as to surround the inner conductor, and the inner conductor and the outer shield conductor An intervening first dielectric material is provided and a cable jacket surrounding the outer shield conductor is provided, the inner conductor and the outer shield conductor being heated to a temperature sufficient to cause harmful burns to human tissue. Arranged in an RF field of sufficient intensity and duration and of sufficient wavelength to act to generate, this method further provides heat below a temperature sufficient to cause harmful burns to human tissue by the following steps: Decrease The following steps include providing a second dielectric material disposed about the outer shield conductor, enclosing the outer surface of the second dielectric material and the outer surface of the second dielectric material. Providing a plurality of conductor portions inside the jacket, spaced apart along a cable having each conductor portion, wherein the conductor portions are each electrically isolated from the next portion. The conductor portion is electrically separated from the outer shield conductor by a second dielectric material, and the conductor portion is adapted to reduce the heat in the RF field to reduce the heat in the RF field. When acting to shield, electrical isolation from the next portion of each conductor portion prevents the generation of current along such portion.

  This method can be applied to either a single cable or a multi-conductor cable and can be used with the second aspect of the present invention of the jacket surrounding the inner sleeve member and conductor portion.

  The above method is particularly applicable when the RF field is generated by an RF transmission coil in a magnetic resonance imaging system. However, the method and cable can be used in situations where a high RF field generates otherwise harmful currents in the outer shield conductor of the coaxial cable.

  For example, the inner conductor structure and the outer shield conductor are placed in an RF field of sufficient strength and duration and of sufficient wavelength to act to generate heat to a temperature sufficient to cause harmful burns to human tissue. Multiple subdivided shield conductor portions are formed, arranged and dimensioned relative to the outer shield conductor to reduce heat to a temperature below that sufficient to cause such burns. It is done.

  Thus, the conductor portion acts to shield the outer shield conductor to reduce heat in the RF field, while electrical isolation from each other portion of the conductor portion is along that portion. Reduce the generation of current.

  In one particular embodiment, the method is used in a magnetic resonance imaging system to communicate signals from an RF receive coil. In this arrangement, the inner conductor structure includes at least one conductor connected to the RF receive coil of the magnetic resonance imaging system. The plurality of conductor portions are disposed relative to the outer shield conductor to reduce current in the cable that interferes with the uniformity of the RF transmission field and thereby causes artifacts in the image. The conductor portion acts to shield the outer shield conductor to reduce the generation of current in the cable caused by the transmitted RF field, while electrical from each other portion of the conductor portion. Separation reduces the generation of current along that portion.

  In another particular embodiment, this method is used when the RF receive coil structure has multiple receive coil portions therein. In this embodiment, the inner conductor structure includes a plurality of conductor elements each for communication with a respective one of the individual coil loops in the receive coil.

  Conductive elements, either individual single wires or multiple coaxial cables, are combined into a cable connected from the receive coil structure to the MRI system. The conductor elements are branched into individual paths at the receiver coil, each path including an outer shield conductor extending in the axial direction of the path spaced at regular intervals around the inner conductor element. A plurality of conductor portions are provided surrounding the outer shield conductor as described in.

  Preferably, the length of each conductor portion is less than λ / 4, where λ is the wavelength of the RF field, more preferably the length of each conductor portion is less than λ / 8, and λ is the wavelength of the RF field. It is.

  The method thus separates the insulator formed by the conductor portion from the outer cable braid shield having the insulator so that each portion of the subdivided shield prevents direct current on the cable braid. become. A subdivided shield produces negligible current. The smaller the subdivision, the less current is generated.

  Floating subdivided shields are different from prior art patents, especially the John Hopkins patents, where these patents accept the shield current and then attenuate the current in several ways that prevent current flow Or differ in that it reduces. This method prevents shield current from occurring on the cable shield.

  Experimental testing has shown that cable heat can be significantly reduced through the use of subdivision and floating supplemental shields as described herein. Therefore, adding a floating subdivision shield outside the first continuous shield prevents the power from the RF transmission coil from reaching the first shield, thereby providing a common in the first shield of the cable. Mode current can be prevented or reduced. A gap in the subdivided supplementary shield prevents current flow in the subdivided shield.

  The floating segmented shielded cable design can be used to reduce the heat of various cables. Applications include cables used to communicate with coils used for catheters, ECGs, deep brain stimulation (DBS), and even pacemakers benefit from the present invention to secure them to MR. Can be obtained. Any conductive wire, including a wire with an external continuous shield, can be protected by the present invention.

The arrangements described herein can provide some or all of the following features within embodiments of MRI coils:
A significant decrease in shield current in the RX cable caused by the body transmission coil, and thus a decrease in cable heat and an increase in patient safety for the patient.
Improve overall image performance with reduced shield current and improve coil tuning, coil-to-coil coupling in phased array coils, image uniformity by reducing deformation in the RFBi field, and image SNR Improved image quality.
The raw cable length is reduced by approximately 4 feet based on 3 cable traps for 1.5T, and approximately 8 feet shorter for 3T, thus reducing the overall coil and cable assembly weight.
The floating subdivision shield concept may be used with current coil designs.
Increased manufacturability due to innovative design.
The cable jacket (or cable hose) material is selected to be waterproof and can be sterilized for intraoperative coils used in clinical surgery.

This is a cost effective and more efficient way to reduce the shield current on the cable braiding. This method will increase patient safety in many applications.
The arrangement described herein can be used to replace a conventional cable trap, thus significantly reducing the total weight of the cable.

  Alternatively, this arrangement can be used with conventional cable traps that are spaced apart along the shielded cable, so that the shielded cable further reduces thermal effects and To be used with cable traps to reduce the number of cable traps required for a given length.

  In this case, the housing of the cable trap itself can be used as another one of the conductor parts, and this housing is made of non-magnetic conductor material on the inner surface so as to surround that part of the cable of the cable trap. The conductor material on the housing is separated from the other conductor parts of the cable and from the outer shield conductor inside the cable trap.

One embodiment of the invention is described in conjunction with the accompanying drawings.
1 is a schematic view of a communication cable according to the present invention having a single conductor. 1 is a schematic diagram of a communication cable according to the present invention having a plurality of conductors. It is the schematic of the shield sleeve member for communication cables by this invention. FIG. 2 is a cross-sectional view of a communication cable according to the present invention having a single conductor similar to that of FIG. 1 but including overlapping body portions. 1 is a cross-sectional view of a communication cable according to the present invention including a cable trap. FIG. 2 is a schematic diagram of an MRI system using the cable of FIG. FIG. 7 is a schematic diagram of a receive coil for the MR system of FIG. 6 including a plurality of coil loops.

  In the figures and the like, reference characters indicate corresponding parts in different figures.

  FIG. 6 schematically shows a magnetic resonance imaging system, which comprises a magnet having a hole (11), on a patient table (13), where the patient (12) has a hole ( 11). The system further includes an RF transmitter coil (14) that generates an RF field within the hole.

  The system further includes a receive coil system, generally indicated by reference numeral (15), which is located in an isocenter located within the hole and is removed from the human body in a conventional manner. Receive the generated signal. The RF control system (17) acts to control the transmitter coil (14) and receive signals from the receiving coil (15). The cable (16) must be cut in the hole on the side of the patient in order to connect to the coil assembly housed in the hole.

  FIG. 7 shows a receiving coil assembly (15), which has a plurality of receiving coil loops (15A), (15B), (15C) and (15D) in this configuration. )including. Each of these loops is connected to a signal transmission coaxial cable and control line bundle portion (16A), (16B), (16C) and (16D) so that the signal received from the loop is larger than a plurality of coaxials. It can be transmitted to the RF control system (17) via the cable and control line bundle (16). Within the receive coil assembly (15), therefore, a plurality of conductors passing through the structure forming the receive coil assembly are positioned at various locations within the receive coil assembly for coupling to individual receive coil loops. . The configuration shown is a very simple feature, and such a receiver coil assembly is extremely complex, including overlapping connections, whereby the wiring of the signal communication cable portion of the signal is routed through the configuration. It will be recognized that it is relatively complex. Each receive coil loop is connected to a respective spare amplifier (18) positioned as close as possible to the loop and its individual communication bundles.

  In a configuration such as that described in the aforementioned US Pat. No. 5,735,278, the magnet is on the table because the cable is required to accommodate the moving magnet system and is required to be cut during surgery. Move with respect to the patient, which is often necessary especially for long cables (16).

  A particular problem that arises with the MRI system described above is that any cable inside the high power RF field generated by the transmission coil can receive the induced current on the metal shield outside the cable. These are typically currents sufficient to cause unacceptable heating. In addition, the induced current is transmitted to the receiving coil, which can generate an extraneous RF field. The RF field interferes with the uniformity of the transmission field and thus creates artifacts within the image.

  This problem is of course well known and the solution typically employed is to provide so-called cable traps at spaced apart locations along the cable. The number of cable traps depends on the RF field, so that for a particular RF field, a certain spacing is required between the cable traps. Thus, in situations where the field increases due to increased power in an MRI system, or where the cable length increases and the area increases due to increased power, the cable supporting the cable trap increases in weight. However, it is difficult to handle. The cable must also support a thick insulating layer to keep the patient away from the heated conductor. All of these requirements significantly increase the weight and structure of the cable to the point where the cable becomes difficult to use.

  FIG. 1 shows the structure of the present invention, which can be used to reduce the current induced in the outer conductive shield to reduce heat and artifacts, as described above. . Thus, FIG. 1 shows a cable (21) surrounded by a dielectric layer (22) and an outer braided nonmagnetic metal shield conductor (23) and having a single inner conductor (20). Yes. In addition to these conventional components, an additional cylindrical perimeter dielectric covered by a series of regularly spaced non-magnetic metal conductor portions (25) at regularly spaced locations along the cable. A body layer (24) is provided. Around the conductor portion (25), an outer envelope (26) of conventional construction is provided. The outer envelope (26) may simply consist of a dielectric material to provide ambient protection, or may include a foamable insulating layer that reduces heat transfer.

  A cylindrical outer protective conductor (23) is continuous along the cable and can thereby be connected to circuit ground to ground the current in the conductor (23). This coaxial cable is connected to the coil so that the received signal is sent along the cable to the RF system control and shielded from RF noise effects by the continuous shield (23).

  The conductor portions (25) in the embodiment shown in FIG. 1 are spaced at regular intervals, thereby leaving a bare region (25A) between the conductor portions and the end of one conductor portion being the next adjacent conductor Axially spaced from adjacent ends of the portions.

  As described above, the conductor portion serves to shield the outer shield conductor (23) from electromagnetic induction current along its length. Thus, the outer conductor portion (25) is electrically separated from the conductor (23) by the layer (24). In order to effectively reduce the current on the braided conductor (23), the outer conductor portion (25) acts as a shield. Also, the conductor part (25) is electrically isolated from the next part and electrically isolated from the other parts, and any current generated is negligible in each conductor part and is therefore generated. The amount of heat generated is reduced.

  FIG. 2 shows an embodiment similar to that of FIG. 1, wherein a single central conductor (20) is replaced with a plurality (20A) of individual conductor elements (20B), and these coaxial cables and It consists of control lines. This of course produces an inner diameter, which is larger than the inner diameter of the cable (21), so that the cable (21A) of FIG. 2 includes a larger inner dielectric layer (22A) and an inner dielectric device ( 22A) is surrounded by a shield (23A), another dielectric layer (24), and individual conductor portions (25). The jacket (26A) surrounds the structure as described above.

  In FIG. 3, an alternative arrangement is shown, which employs a structure in which one or more individual inner conductors are surrounded by a dielectric layer, which in turn is surrounded by an outer shield layer and an outer envelope. And used with conventional cables. In the embodiment of FIG. 3, an inner sleeve member (27) is provided that carries a plurality of conductor portions (25) at spaced intervals along its length. The sleeve part and the conductor part are covered by an outer jacket (26B). The sleeve portion (27) has an inner surface (27A) which can slide over a conventional jacket as a sliding fit so as to surround the cable. This surface may be coated with a heat activated adhesive to permanently affix the sleeve to the shielded coaxial cable or wire jacket. In this way, a conventional cable can be used and its shielding effect can be supplemented by preparing the structure shown in FIG. 3 provided by an inner sleeve, a conductor portion, and an outer jacket. .

  Turning now to FIG. 4, a cross-sectional view of a structure similar to the structure of FIG. 1 including the central conductor (20), dielectric layer (22), outer shield (23), and jacket (26). It is shown in

  In this embodiment, the conductor portion (25) is supplemented by an additional conductor portion (25B) that overlaps the conductor portion (25). Thus, since the entire length of the outer shield in the conductor (23) is covered by the conductor portions (25) and (25B), there are no exposed or bare portions (25A). Outside the conductor portion (25), an insulator or dielectric layer (28) is provided, the insulator or dielectric layer (28) electrically isolating the conductor portions from each other and a common shield layer. The conductor portion (25B) is separated from the conductor portion (25) so as to be electrically separated from (23). Thus, as shown, the conductor portion (25B) has ends (25c) and (25D) that overlap the ends (25E) and (25F) of the adjacent conductor portion (25), respectively. The overlap is reduced to a negligible amount or the ends overlap almost directly with the intention that the entire shield conductor (23) is shielded by the conductor portion while minimizing the amount of conductor portion used. It will be appreciated that the location may be reduced.

  The shield conductor (23) is typically braided or can be formed from a non-magnetic metal foil wrapped in a spiral. The dielectric layer is typically an extruded jacket, but can also be formed from a wrapped tape such as a Teflon tape. Teflon tape has the advantage of being slippery and thus allowing sliding movements as needed.

  Although the dielectric layer (24) is shown as a continuous cylindrical sleeve, its function is to primarily separate the subdivided shield conductor portion (25) from the basic shield layer (23). Thus, the dielectric layer (24) can be partially formed, so that the dielectric layer (24) is directly beneath the segmented shield conductor portion in the arrangement shown in FIGS. Need only be arranged.

  Turning now to FIG. 5, an alternative arrangement is shown, which is used in conjunction with the shield arrangement described above and the conventional one used in combination to further reduce the generation of current in the shield layer. Use both cable traps.

  FIG. 5 thus shows cable portions (121) and (221), which are the structures shown in FIG. Thus, cable portions (121) and (221) include shield layers (123) and (223) that are covered by dielectric layers (124) and (224). Around this, subdivided shield conductor portions (125) and (225) are provided along with jackets (126) and (226). A cable trap (30) is disposed between these cable portions. The cable trap comprises an outer housing (31), which is fastened on the ends of the jackets (126) and (226) and acts to bridge the area between these jackets. Inside the housing (31), the jacket is stripped and the cable portion defined by the inner conductor and the shield (123) is supported by a support (in order to form a helical portion of the stripped portion of the cable. 32). This helical covering of the stripped cable portion makes the outer shield (123) a helical coil that defines the inductor. A nonmagnetic metal conductor (34) disposed inside the housing (31) is provided around the outside of the inductor. Inside the housing, a cylindrical shield layer (35) is provided. The shield layer can be formed by spray coating with a conductive nonmagnetic metal material. The shield layer (35) is maintained separate from the conductor (34) so that it is electrically isolated from the conductor (34). In general, this is accomplished by mounting a conductor on the support (32) so that the conductor is radially separated from the housing (31) and its inner layer (35) and kept at regular intervals. Will come to be. The conductor (34) is electrically attached to the shield layer (123) at one end by a solder joint (37). The other end of the conductor is provided with a capacitor (38) which is also attached to the conductor and shield by solder joints (39) and (40). Thus, the inductor defined by the wrapped shield layer and the capacitor (40) form a tank circuit, which is formed along the continuous shield layers (123) and (223). Acts to define a high impedance for currents that tend to

  The conductive layer (35) is electrically isolated from the shield (123) and electrically separated from the segmented shield conductor portions (125) and (225), so that the conductive layer (35) is It acts as another part of the conductive part surrounding the part of the cable trap between the ends of the parts (121) and (221).

  Turning now to FIG. 7, the cable (16) has the above structure formed by only the structure of FIG. 1, 2, 3, or 4 or a structure including the cable trap shown in FIG. is there. In this arrangement, the cable is a multi-conductor cable of the type shown in FIG. At the location where the cable enters the receiver coil structure (15), the cable shield material is opened and removed to expose the individual conductor portions (16A), (16B), (16C), and (16D). . These conductors are then either connected to a preamplifier for each individual coil loop or directly connected to the coil loop. A jacket or coating is provided around the external structure to prevent inadvertent electrical connections. Accordingly, each of the cable portions (16A) to (16D) is the structure itself shown in FIG. 1 or FIG.

Thus, the presence of these cable portions within the receive coil structure avoids the generation of current on the control lines or on the shield conductors of these coaxial cables.
While the thermal effect is less important in this region, the presence of current on the shield conductor will otherwise provide an external RF field at the coil portions (15A) through (15D), from the transmitter coil. Interfering with the RF field will cause artifacts. Thus, an individual cable portion reduces the current in its conductors using the same concept and arrangement by using the same concept described herein.

  Various changes may be made in my invention as described hereinabove, as well as many clearly different embodiments depart from the scope and spirit of the claims. Without departing from the spirit and scope, it is to be understood that all matter contained in the appended specification is to be interpreted solely for purposes of illustration and not in a limiting sense.

Claims (12)

Providing an MR magnet (10);
Placing a patient on a patient table (13) in the magnet;
Generating an RF field using an RF transmission coil (14);
Obtaining MR signals from the patient;
Communicating the MR signal in the RF field by connecting a signal to be communicated to an inner conductor structure (20) that extends in an elongated axial direction of a communication cable (21);
Providing a shield conductor (23) extending in the axial direction of the cable, spaced apart at regular intervals so as to surround the elongate axially extending inner conductor structure (20). Prepared,
The shield conductor extends continuously between the opposite ends of the cable and is connected to circuit ground to shield the elongate axially extending inner conductor structure (20) from an external field. ,
The inner conductor structure (20) is electrically insulated from the shield conductor by a dielectric material (22) placed therebetween;
further,
A method for obtaining a magnetic resonance image comprising providing a cable jacket (26) surrounding the shield conductor,
Said elongated inner conductor structure extending in the axial direction (20) before and carboxymethyl Rudo conductor, the arranged to the RF field generated by the RF transmission coil (14), the RF field and sufficient strength and duration Having a wavelength that acts to generate heat in the RF field to a temperature sufficient to cause harmful burns to human tissue;
The amount of heat generated is
Each surrounding the shield conductor, and to provide a shield conductor portions each have a plurality of subdivided with less than the length length of said cable,
Wherein the subdivided shield conductor portion is arranged at a position along the cable,
The subdivided shield conductor portion, so as to be electrically floating with respect to the other subdivided shield conductor portion, being electrically isolated from each the other portion, and is the fragmented A shield conductor portion is electrically separated from the shield conductor so as to float electrically relative to the shield conductor of the cable;
Reduced by
Wherein the subdivided shield conductor portion shields the shield conductor to reduce heat of the shield conductor in an RF field to a temperature sufficient to cause harmful burns to human tissue ;
Wherein the electrical isolation from other parts of the subdivided shield conductor portions each reduce the heat of the subdivided shield conductor portion of the RF field to a temperature sufficient to result in harmful burns to human tissue for, wherein the reducing the generation of current along the subdivided shield conductor portion. In a magnetic resonance imaging system, an RF receiver coil is provided, and the inner conductor structure includes at least one conductor connected to the RF receiver coil of the magnetic resonance imaging system;
Conductor portions of the multiple is to interfere with the uniformity of the RF field generated by the RF transmission method according to claim 1, thereby characterized in that to reduce the current of the cable which causes artifacts in the image . An RF receive coil structure having a plurality of receive coil loops therein is provided,
The elongate axially extending inner conductor structure comprises a plurality of inner conductor elements each for communicating with a respective one of the receive coil loops;
The inner conductor element is combined in the cable connected from the receiver coil structure;
The inner conductor element is branched into individual paths in the receiver coil structure, and each path extends in an axial direction of the path arranged to surround the inner conductor element at a predetermined interval. includes Cie Rudo conductor, before carboxymethyl Rudo conductor of the path is connected from the external noise, the circuit ground to shield the inner conductor element,
Said inner conductor element is electrically insulated from the previous carboxymethyl Rudo conductor of said path, each having a pre-carboxymethyl Rudo length shorter than the path surrounds the conductors of the path, a plurality of said path is subdivided shield conductor portion of the provision, the granular shield conductor portion is disposed at a position spaced at regular intervals in the axial direction along said path, said granular shield conductor portion, wherein as the subdivided shield conductor portion of the path is electrically floating with respect to the other subdivided shield conductor portion of said path, each electrically isolated from the other portion, said path the subdivided shield conductor portion to electrically float with respect to the front carboxymethyl Rudo conductor of said path, characterized in that it is electrically isolated from the previous carboxymethyl Rudo conductor of the path of Claim The method according to 1 or 2. The method according to the said length of the subdivided shield conductor portions of each is less than lambda / 4, lambda is any one of claims 1 to 3, characterized in that the wavelength of the RF field. Is the length of the subdivided shield conductor portions of each is less than λ / 8, λ A process according to any one of claims 1 to 4, characterized in that the wavelength of the RF field. The method according to any one of claims 1 to 5, characterized in that said subdivided shield conductor portion is annular. Wherein either subdivided shield conductor portion is formed of a nonmagnetic metal braid, or, if formed from a non-magnetic foil tape wrapped, or may be formed from a combination of a non-magnetic metal braid and a non-magnetic foil tape A method according to any one of claims 1 to 6, characterized in that The subdivided shield conductor portion, so as to leave a portion of the carboxy Rudo conductor before not covered by the granular shield conductor portion, characterized in that it is spaced axially at regular intervals 8. A method according to any one of claims 1 to 7. The subdivided shield conductor portion, as each of the ends overlap the corresponding end of the subdivided shield conductor portion adjacent the next, that is arranged, before carboxymethyl Rudo conductor the method according to any one of claims 1 to 7, characterized in that to be completely covered by the granular shield conductor portion. The method according the subdivided shield conductor portions, respectively, before carboxymethyl Rudo conductor, to one of the claims 1 to 9, characterized in that it is separated by a layer of between dielectric material. The method according to any one of claims 1 to 10 wherein the granular shield conductor portion is characterized in that disposed below the outer envelope. The subdivided shield conductor portion is carried on the sheath, covered by jacket additional external cable,
The sheath having a jacket external cables and the subdivided shield conductor portion,
11. A method according to any one of the preceding claims, wherein the method is engaged on the cable jacket.

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