Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B11/00—Communication cables or conductors
  • H01B11/18—Coaxial cables; Analogous cables having more than one inner conductor within a common outer conductor
  • H01B11/1891—Coaxial cables; Analogous cables having more than one inner conductor within a common outer conductor comprising auxiliary conductors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
  • G01R33/3685—Means for reducing sheath currents, e.g. RF traps, baluns
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B11/00—Communication cables or conductors
  • H01B11/18—Coaxial cables; Analogous cables having more than one inner conductor within a common outer conductor
  • H01B11/1808—Construction of the conductors
  • H01B11/1813—Co-axial cables with at least one braided conductor
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
  • A61B2562/22—Arrangements of medical sensors with cables or leads; Connectors or couplings specifically adapted for medical sensors
  • A61B2562/221—Arrangements of sensors with cables or leads, e.g. cable harnesses
  • A61B2562/222—Electrical cables or leads therefor, e.g. coaxial cables or ribbon cables
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
  • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
  • A61B5/316—Modalities, i.e. specific diagnostic methods
  • A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
  • A61B5/316—Modalities, i.e. specific diagnostic methods
  • A61B5/369—Electroencephalography [EEG]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
  • G01R33/34007—Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system

Definitions

• This invention relates to coaxial cables for use in high RF fields where currents induced in the shield of the cable can have deleterious effects.
• the invention is particularly applicable to such cable when used in the high RF fields used in Magnetic Resonance Imaging but can relate to other cables.
• the invention also includes a jacket arrangement which can be applied on to a conventional coaxiai cable to obtain the advantageous construction described herein.
• coaxial cables are required to be used in the high RF fields used in MRI. These include primarily the cables to the receive coil array but also other cables that must enter the high RF field such as those used in pacemakers, ECG testing, electrophysiology and EEG monitoring, and Deep Brain Stimulation systems (DBS).
• DBS Deep Brain Stimulation systems
• Common mode signals or shield currents on coil cables are often caused by the coil itself or by an external source such as a surrounding transmit body coil during transmit phase. ElectromagneticalSy induced currents by an external source, such as those produced by the body transmit coil, are responsible for the majority of the shield current, and therefore heat, on the surface of the cable. These currents, and the resulting heat produced, can cause serious patient heating or burns. Common mode currents also degrade the image quality by affecting coil tuning, coil- to-coil coupling in phased array coils..
• coaxial cables having an inner axially oriented elongated conductor separated from an annular electrically conductive shield by a dielectric material have long been known.
• Such coaxial cables have been used in magnetic resonance imaging, as well as numerous other uses.
• important safety concerns related to magnetic resonance imaging technology are the possible burns and excessive heat due to the induced RF currents on the electrical cables.
• the users of the MR scanners are instructed to minimize patient contact with cables. Such contact, however, is unavoidable in many cases such as when using ECG cables, surface coils, or intra-cavity coils.
• some commercial MR coils such as the magnetic resonance coils of GE Medical Systems, for example, use patient safety modules. This design decreases the unbalanced currents on the coaxial cable. In addition to patient safety, this design effects reduction in radiation losses and common mode noise in the coil.
• cabie traps which are placed in the cable at spaced positions along the length of the cable. These act to reduce the generation of the current.
• One type of cable traps typically involve an inductor formed from the 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 are connected in parallel to the inductor between the copper conductor and the shield to form a tank circuit which acts to attenuate the unwanted shield current on the cable.
• the shield braid is continuous along the cable and has formed at points along its length the tank circuit defined by the inductor portion of the shield, the copper conductor, and the capacitors.
• the cable traps improve the coil performance by eliminating or reducing the shield current along the cable shield.
• the cable trap is designed to reduce the shield current, but the helical inductor formed from the cable shield of the cable trap also effectively acts as an antenna, to receive RF power from the transmit body coil and contributes unexpected current in the cable.
• the generation of the shield current is proportional to the geometry of the cable.
• a larger surface cable generates more shield current than a smaller surface area cable.
• a longer cable with a larger diameter produces more current than a shorter cable with a smaller diameter.
• the generation of the shield current is also proportional to the system RF power.
• the power from a 3.0 Tesia system will be four times the power from the 1.5 Tesla system, and much higher power for a 7.0 Tesla or higher system.
• the required number of cable traps for a 3.0 Tesla system will be approximately doubled compared to the 1.5T system, with closer spacing between cable traps.
• a 7.0 Tesla or higher system wouid require even more cable traps with closer spacing.
• US Patent 6,284,971 (Atalar) issued to Johns Hopkins University on September 4 th , 2001 discloses a co-axial cable for probes used in MRI, which has an outer dielectric layer with high dielectric constant, between inner shield portion and a segmented outer shield portion of outer conductor so as to inhibit induced radio frequency current.
• the arrangement disclosed connects the one end of a segmented shield to the cable shield braid and use the free end of the segmented shield as a VA wave cable trap.
• US Patent 7,123,013 (Gray) issued to Biophan technologies on October 17 th , 2006 discloses an arrangement in which a voltage compensation unit reduces the effects of induced voltages upon a device having a single wire line having balanced characteristic impedance.
• the voltage compensation unit includes a tuneable compensation circuit connected to the wire line which applies supplemental impedance to the wire line and causes the characteristic impedance of the wire line to become unbalanced, thereby reducing the effects of induced voltages.
• US Patent 7,205,768 (Schulz) issued to Phillips on April 17 th , 2007 discloses a lead for use in an MRI device which has an auxiliary electrical device connecting to the lead with sections with inductive coupling element of limited length not equal to integra! multiple of the half wavelength.
• US Patent 7,294,785 (Uutela) issued to GE Healthcare on November 13 th , 2007 discloses a lead for use in an MRI device where, in order to eliminate the risk of thermal injuries without compromising the signal-to-noise ratio more than what is required for patient safety, the lead comprises two successive cable elements having different resistance characteristics.
• the second cable element which is connected by the first cable element to the patient, has a total resistance increased from a normal high-conductivity resistance value of a patient cable to suppress antenna resonances in the second cable element.
• the first cable element which is connected to the electrodes on the skin of the patient, has a total resistance substantially greater than that of the second cable element to prevent electromagnetically induced currents from flowing to the patient and to prevent excessive heating of the cable by electromagnetic induction.
• a shielded cable comprising: an inner conductor construction extending axiaily along the cable and providing electrical connection for transmission of signals between opposite ends of the cable; an axiaily extending outer shield conductor disposed in spaced surrounding relationship around the inner conductor construction, the outer shield conductor extending continuously between the opposite ends of the cable for connection to a circuit ground for shielding the inner conductor construction from external fields; the inner conductor construction being electrically insulated from the outer shield conductor by dielectric material interposed between; a plurality of braid or solid conductor portions each surrounding the outer shield conductor; the conductor portions being arranged at axiaily spaced locations along the cable; the conductor portions being electrically separated each from the others such that the conductor portions float electrically relative to the other conductor portions; the conductor portions being electrically separated from the outer shield conductor such that the conductor portions float electrically relative to the outer shield conductor; and a cable jacket enclosing the conductor portions and the outer shield conductor.
• the conductor portions are formed from braid but it is often preferred that they are formed from an annular or spiral wrapped non-magnetic metal foil tape since the foil tape avoids the intervening holes between the wires in the braid which can reduce the shielding effect.
• a combination of braid and solid conductors is also possible.
• the conductor portions may be axially spaced, that is the end of one may be spaced from the adjacent end of the next, so as to leave portions of the outer shield conductor which are not covered by the conductor portions.
• the conductor portions may be arranged such that the ends of each are overlapped with corresponding ends of next adjacent conductor portions such that the outer shield conductor is wholly covered by the conductor portions.
• a dielectric material between the outer surface of one portion and the overlapping inner surface of the next adjacent portion to ensure electrical separation. This can be formed by a wrapped tape such as a TeflonTM tape.
• a continuous jacket formed of a dielectric material surrounding the outer shield conductor over which the conductor portions are engaged.
• the separation of the conductor portions from the outer shield can be formed by other material such as an annular or spiral wrapped non-magnetic metal foil tape.
• the conductor portions are shaped and arranged to reduce heating of the cable in an RF field and particularly the conductor portions are shaped and arranged to reduce heating of the cable in an RF field of a Magnetic Resonance Imaging system to a temperature less than that sufficient to cause injurious burns to human tissue.
• the conductor portions for 1.5 Tesla systems or higher have a length less than a maximum 10 inches and preferably of the order of 0.5 to 2.0 inches which is a practical dimension for manufacture while ensuring the reduction in induced current in the shielding conductor and in the portions themselves to a level which enhances the operation of the cable.
• the above defined cable can be formed as an integral construction where the conductor portions are engaged around an intermediate dielectric layer with the cable jacket engaged over the whole construction.
• the construction can be formed using any existing conventional cable, including coaxial cable enclosed by a cable jacket where the conductor portions are carried on an inner hoilow sleeve member which is engaged by sliding over the cable jacket with a second outer jacket which surrounds the inner sleeve member and the conductor portions. This technique avoids the manufacture of a complete cable and allows the use of existing cable constructions as part of the construction, which are inexpensive due to high volume manufacture.
• a shielding assembly for use on any existing conventional cable, including coaxial cable to obtain the effect of the shielded cable which is the primary feature of the invention, the shielding assembly comprising: an inner sleeve member formed of a dielectric material and arranged with a hollow interior defined by an inner surface shaped and arranged to slide over a jacket of the coaxial cable for covering the coaxial cable when installed; a plurality of conductor portions carried on the inner sleeve member so as to surround the coaxial cable when the inner sleeve member is installed; the conductor portions each surrounding the inner sleeve member and each having a length less than that of the inner sleeve member; the conductor portions being arranged at axially spaced locations along the inner sleeve member; the conductor portions being electrically separated each from the others such that the conductor portions float electrically relative to the other conductor portions; the conductor portions being electrically separated from the cable such that the conductor portions float electrically
• This arrangement of the shielding assembly thus is convenient for use with any existing conventional cable, including coaxiai cable, to obtain the same effects as described above.
• a method of communicating signals in an RF field comprising: connecting the signals to be communicated to an elongate axially extending inner conductor, or a plurality of conductors; the inner conductor, or conductors, having an axiaily extending outer shield conductor disposed in spaced surrounding relationship around the inner conductor; there being provided a first dielectric material interposed between the inner conductor and the outer shield conductor; there being provided a cable jacket surrounding the outer shield conductor; the inner conductor and the outer shield conductor being located in an RF field of sufficient intensity and time period and of a wavelength which would act to generate heat to a temperature sufficient to cause injurious burns to human tissue; and reducing the heating to a temperature less than that sufficient to cause injurious burns to human tissue by: providing a second dielectric material located around the outer shield conductor; and providing a plurality of conductor portions outside the second dielectric material and inside the jacket at spaced positions along the cable with each conductor portion surrounding an outer
• This method can be applied to either a single or multiple conductor cable, and can be used with the second aspect of this invention of the outer jacket surrounding the inner sleeve member and conductor portions.
• the above method is particularly applicable where the RF field is generated by an RF transmit coil in a Magnetic Resonance Imaging system.
• the method and the cable can be used in to the situation where a high RF field would otherwise generate deleterious currents in the outer shield conductor of a coaxial cable.
• the plurality of segment shield conductor portions are shaped, arranged and dimensioned relative to the outer shield conductor so as to reduce the heating to a temperature less than that sufficient to cause such burns.
• the conductor portions act to shield the outer shield conductor to reduce the heating thereof in the RF field while the electrical separation of the conductor portions each from the others reduces the generation of a current along the portions.
• the method is used in a Magnetic Resonance Imaging system for communication of signals from the RF receive coil.
• the inner conductor construction includes at least one conductor connected to the RF receive coil of the Magnetic Resonance Imaging system.
• the plurality of conductor portions are arranged relative to the outer shield conductor so as to reduce currents in the cable from interfering with the homogeneity of the RF transmit field and thereby causing artifacts in the image.
• the conductor portions act to shield the outer shield conductor to reduce generation of a current in the cable caused by the transmit RF field while the electrical separation of the conductor portions each from the others reduces the generation of a current along the portions.
• the method is used where the RF receive coil construction has therein a plurality of receive coii sections.
• the inner conductor construction includes a plurality of conductor elements each for communication with a respective one of the individual coil loops in the receive coil.
• the conductor elements are combined into the cabie connected from the receive coil construction to the MRl system.
• the conductor elements are branched off at the receive coil into separate paths and each path includes an axially extending outer shield conductor of the path disposed in spaced surrounding relationship around the inner conductor element and there is provided a plurality of the conductor portions as described above surrounding the outer shield conductor.
• each conductor portion is less than ⁇ /4 where ⁇ is the wavelength of the RF field and more preferably the length of each conductor portion is less than ⁇ /8 where ⁇ is the wavelength of the RF field.
• the present method thus isolates the segmented shield conductor formed by the conductor portions from the outer cable braid shield with an insulator so that each piece of the segmented shield prevents the continuous current on the cable braid.
• the segmented shield produces a negligible current; with the smaller the segment, the smaller the current produces.
• the floating segmented shield is different from the prior art patents, especially the John Hopkins patent, in that these patents accept the shield current and then try to attenuate or reduce the current by some method of blocking the current flow.
• the present method prevents the shield current from generating on the cable shield.
• Experimental testing has shown that cable heating can be significantly reduced through the use of the segmented and floating supplemental shielding as described herein.
• the addition of a floating segment shield outside the primary continuous shield can prevent or reduce the common mode current in the primary shield of the cable by preventing the power from the RF transmit coil from reaching the primary shield.
• the gaps in the segmented supplemental shield prevent the current flow in the segmented shield.
• the floating segmented shield cable design can be used to reduce the heating of a wide variety of cables. Applications include cables used for communication with coils used for catheters, ECG, Deep Brain Stimulation (DBS); and even pacemakers could benefit from this invention to make them MR safe. Any conductive electrical wires, including those with a outer continuous shield can be protected by this invention.
• the floating segmented shield concept may be used in conjunction with current coil design
• the cable jacket (or cable hose) material can be selected to be water proof and sterilized for intra-operative coils used in clinical surgery.
• the arrangement can be used with the conventional cable traps located at spaced positions along the shielded cable so that the shielded cable is used in conjunction with the cable traps to further reduce the heating effect and to reduce the number of cable traps required in a predetermined length of the cable.
• the housing of the cable trap itself can be used as another one of the conductor portions where the housing is coated on an inner surface with a non-magnetic conductive material so as to surround that portion of the cable at the cable trap, the conductive material on the housing being electrically separated from the other conductor portions of the cable and from the outer shield conductor within the cable trap.
• Figure 1 is a schematic illustration of a communication cable according to the present invention having a single conductor.
• Figure 2 is a schematic illustration of a communication cable according to the present invention having a plurality of conductors.
• Figure 3 is a schematic illustration of a shielding sleeve for a communication cable according to the present invention.
• Figure 4 is a cross sectional view of a communication cable according to the present invention having a single conductor similar to that of Figure 1 but including overlapping conductor portions.
• Figure 5 is a cross sectional view of a communication cable according to the present invention including a cable trap.
• Figure 6 is a schematic illustration of an MRI system using the cable of Figure 1.
• FIG. 7 is a schematic illustration of a receive coil for the MR system of Figure 6 including a plurality of coil loops.
• like characters of reference indicate corresponding parts in the different figures.
• Figure 6 is shown schematically a magnetic resonance imaging system which includes a magnet 10 having a bore 11 into which a patient 12 can be inserted on a patient table 13.
• the system further includes an RF transmit body coil
• the system further includes a receive coil system generally indicated at
• a RF control system 17 acts to control the transmit body coil 14 and to receive the signals from the receive coil 15.
• the cable 16 must be draped into the bore alongside the patient to connect to the received coil assembly within the bore.
• the receive coil assembly 15 which in this arrangement includes a plurality of received coil loops 15A, 15B, 15C and 15D. Each of these loops is connected to a signal transmit coaxial cable and control wire bundle portion 16A, 16B, 16C and 16D so that the received signal from that loop can be transmitted through a larger, multiple coaxial cable and control wire bundle 16 to the RF control system 17.
• each receive coil loop is connected to a respective preamplifier 18 located as dose as possible to the loops and its respective communication cable bundle.
• any cable located within the high power RF field generated by the transmit coils can receive induced currents on the external metallic shield of the cable. These are typically of such a magnitude which is sufficient to cause unacceptable heating.
• the induced currents can be communicated to the receive coil thus generating extraneous RF fields which will interfere with the homogeneity of the transmit field and thus generate artefacts within the image.
• Figure 1 a construction according to the present invention which can be used to reduce currents induced in the outer conductive shield so as to reduce heating and artefacts as described above.
• Figure 1 therefore shows a cable 21 with a single inner conductor 20 surrounded by a dielectric layer 22 and an outer braided, non-magnetic meta! shield conductor 23.
• an additional cylindrical surrounding dielectric layer 24 which is covered by a series of spaced non-magnetic metal conductor portions 25 at spaced positions along the cable.
• Around the conductor portions 25 is provided an outer jacket 26 of a conventionai construction.
• the outer jacket 26 may be simply of a dielectric material for providing surrounding protection or it may include a foam insulating layer to reduce heat transfer.
• the cylindrical outer shielding conductor 23 is continuous along the cable so that it can be connected to a circuit ground for grounding currents in the conductor 23.
• This coaxial cable is connected to the coil so that the signals received are transmitted along the cable to the RF system control and are shielded from RF noise effects by the continuous shield 23.
• the conductor portion 25 in the embodiment shown in Figure 1 are spaced so that the end of one conductor portion is axiaily spaced from the adjacent end of the next adjacent conductor portion leaving a bare area 25A between the conductor portions.
• the conductor portions act to shield the outer shielding conductor 23 from electromagneticaily induced current therealong.
• the outer conductor portion 25 is electrically separated from the conductor 23 by the layer 24.
• the outer conductor portion 25 acts as a shield to effectively reduce the current on the braided conductor 23.
• the conductor portions 25 are electrically separated each from the next and each from the others so that any current generated is negligible in each conductor portion and therefore the amount of heat created is reduced.
• Figure 2 is shown an embodiment similar to that of Figure 1 in which the single central conductor 20 is replaced by a plurality 20A of individual conductor elements 2OB, comprised of individual coaxial cables and control wires.
• This produces an internal diameter which is larger than that of the cable 21 so that the cable 21A in Figure 2 includes a larger diameter inner dielectric layer 22A, which is surrounded by the shield 23A, another dielectric layer 24, and by the individual conductor portions 25.
• a jacket 26A surrounds the structure as previously described.
• Figure 3 is shown an alternative arrangement which is used in conjunction with conventional cables utilizing the construction in which one or more individual inner conductors is surrounded by a dielectric layer which in turn is surrounded by the outer shielding layer and an outer jacket.
• an inner sleeve 27 which carries a plurality of conductor portions 25 at spaced positions along its length.
• the sleeve portion and the conductor portions are covered by an outer jacket 26B.
• the sleeve portion 27 has an inner surface 27A which can slide over the conventional jacket as a sliding fit so that the inner surface 27A surrounds the cable.
• This surface may also be coated with heat activated adhesive to permanently affix the sleeve to the jacket of the coaxial cable or wires to be shielded.
• a conventional cable can be used and can be supplemented in its shielding effect by the provision of the construction shown in Figure 3 provided by the inner sleeve, the conductor portions and the outer jacket.
• FIG 4 there is shown in cross section a construction similar to that of Figure 1 including the central conductor 20, the dielectric layer 22, the outer shield 23 and the jacket 26.
• the conductor portions 25 are supplemented by additional conductor portions 25B which overlap with the conductor portions 25.
• there are no open or bare portions 25A since the whole of the length of the outer shield in conductor 23 is covered by the conductor portions 25 and 25B.
• an insulating or dielectric layer 28 which separates the conductor portions 25B from the conductor portions 25 so that all the conductor portions are electrically separated from one another and electrically separated from the common shielding layer 23.
• each conductor portion 25B has ends 25C and 25D which overlap the ends 25E and 25F of the adjacent conductor portions 25. It will be appreciated that the overlap may be reduced to a very small amount or to where the ends are approximately directly overlying with the intention that the whole of the shielding conductor 23 shielded by the conductor portions while minimizing the amount of conductor portions utilized.
• the shielding conductor 23 is typically a braid but can be formed from helically wrapped non-magnetic metal foil.
• the dielectric layers are typically extruded jackets but also can be formed from a wrapped tape such as TeflonTM tape.
• TeflonTM tape has the advantage that it is slippery and hence allows a sliding action where required.
• the dielectric layer 24 is shown as a continuous cylindrical sleeve but it will be appreciated that it can be formed in portions since its function is primarily to separate the segmented shield conductor portions 25 from the underlying shielding layer 23 and hence the dielectric layer 24 need be located only underneath the segmented shield conductor portions in the arrangement shown in Figures 1 , 2 and 3.
• FIG 5 there is shown an alternative arrangement which utilizes both the above shielding arrangements and also the conventional cable trap which are used in combination to further reduce the generation of currents in the shielding layer.
• cable portions 121 and 221 which are of the construction shown in Figures 1 or 2.
• the cable portions 121 and 221 include a shielding layer 123 and 223 which is covered by a dielectric layer 124 and 224.
• the segmented shield conductor portions 125 and 225 together with the jackets 126 and 226.
• a cable trap 30 is located between these cable portions.
• the cable trap includes an outer housing 31 which is clamped onto the ends of the jackets 126 and 226 and acts to bridge an area between these jackets. Inside the housing 31 the jacket is stripped away and the portion of the cable defined by the inner conductor and the shield 123 is coiled around a support 32 to form a helical portion 33 of the stripped portion of cable.
• This helical wrapping of the stripped cable portion forms the outer shield 123 into a helical coil defining an inductor.
• a non-magnetic metal conductor 34 which is located inside the housing 31.
• a cylindrical shielding layer 35 On the inside of the housing is provided a cylindrical shielding layer 35.
• This shielding layer can be formed by a spray coating of a non-magnetic metallic substance which is conductive.
• the shielding layer 35 is maintained separate from the conductor 34 so as to be electrically separated therefrom. In general this is achieved by mounting the conductor on the support 32 so that it is held spaced at a radial separation from the housing 31 and its inside layer 35.
• the conductor 34 is electrically attached at one end to the shielding layer 123 by a soldered joint 37.
• a capacitor 38 which is also attached to the conductor and to the shield by a soldered joint 39, 40.
• the inductor defined by the coiled shielding layer and the capacitor 40 form a tank circuit which acts to define a high impedance to currents tending to formed aiong the continuous shielding layer 123, 223.
• the conductive layer 35 is electrically separated from the shield 123 and electrically separated from the segmented shield conductor portions 125, 225 so that it also acts as another of the conductive portions surrounding that part of the cable trap between the ends of the cable portions 121 and 221.
• the cable 16 is of the construction described above formed solely by the construction of Figures 1 , 2, 3 or 4 or including cable traps shown in Figure 5.
• the cable is a multiple conductor cable of the type shown in Figure 2.
• the cable shielding material is opened and removed to expose the individual conductor portion 16A, 16B, 16C and 16D.
• These conductors are then connected to either the pre-ampiifiers for each individual coii loop, or directly to the coil loop.
• Around the outer structure is provided a jacket or a covering to prevent inadvertent electrical connection.
• each of the cable portions 16A through 16D is itself of the construction shown in Figure 1 or Figure 2.

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• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Insulated Conductors (AREA)
• Waveguides (AREA)
• Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
• Communication Cables (AREA)
• Magnetic Resonance Imaging Apparatus (AREA)

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Cited By (12)

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• 2008
  • 2008-07-07 CA CA2636936A patent/CA2636936C/en active Active
• 2009
  • 2009-05-08 EP EP20090793731 patent/EP2311051A4/en not_active Withdrawn
  • 2009-05-08 WO PCT/CA2009/000597 patent/WO2010003215A1/en not_active Ceased
  • 2009-05-08 JP JP2011516932A patent/JP5709139B2/ja active Active

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