JP3411938B2 - Electrical lead wire assembly - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention allows the passage of electromagnetic fields associated with MR processing, such as magnetic resonance (MR) radio frequency (RF) electric and magnetic fields (collectively "RF electromagnetic fields"). , An improved system for providing electrical signals generated from a subject in a diagnostic imaging process such as an MR process. More particularly, the present invention relates to a lead wire assembly for the above purposes having a conductive path consisting of a deposited film formed of metal or other conductive material. More particularly, the present invention relates to a lead wire assembly sized such that the conductive paths are substantially transparent to RF or other electromagnetic fields.

[0002]

MR imaging processing is a technique for obtaining cross-sectional images through a patient or other subject for medical diagnosis. In the MR imaging process, the patient is typically placed in a hole (bore) in the magnet and is subjected to a strong static magnetic field along the axis of the hole. A second magnetic field consisting of a series of RF pulses is created in the hole across the static magnetic field. Each RF pulse drives a nucleus in the tissue of the patient's body from a direction along the static magnetic field to a direction by the RF magnetic field. At the end of the RF pulse, the nucleus tends to return in the direction due to the static magnetic field, and an RF signal corresponding to the tissue structure is generated and received. By processing the signal resulting from the series of RF pulses, an image showing the desired cross-section through the patient can be generated.

In the MR imaging process, the ECG is measured from the subject.
Or it is often necessary to obtain other electrical signals.
For example, when imaging the patient's heart, EC from the patient
The G signal is used as a trigger signal for the MR gating process. This technique is, for example, published in November 1, 1983 in "Dynamic NMR Meas
U.S. Pat. No. 4,413,23
No. 3 is described. It is also necessary to monitor the patient's condition during the MR imaging process by extracting electrical signals representative of breathing, heartbeat or similar activity from the frail patient.

To obtain an electrical signal from a patient placed in an MR magnet, an electrode is attached to the patient and leads extending from the magnet are connected to the electrode. The leads are connected to a device such as an ECG monitor via a cable and / or optionally a preamplifier. As described above, the RF pulse necessary for the MR imaging process may induce a current in the lead wire. This current may flow through a portion of the patient's body lying between the circuit containing the leads and the electrodes.
If the impedance of the electrode / patient body interface is greater than the impedance of the leads, the patient's body adjacent the electrodes can be substantially heated. In some cases, this heating can cause significant burns to the patient.

One way to solve this problem is 199
U.S. Pat. No. 4,951,6 issued Aug. 28, 2008
No. 72 is shown. In this U.S. Patent, a lumped element in the form of a current limiting resistor is connected in series to a lead wire,
The voltage drop across the resistive element is made much larger than the voltage drop across the electrode / patient interface. However, since the lumped resistance must be a highly accurate element, it is relatively expensive. Most importantly, one or more elements or lead wires themselves are still substantially heated, and the patient is burned if the patient contacts such heated elements or lead wires.

In an alternative solution, the ECG lead wire is formed of a high impedance carbon-implanted material.
In this configuration, the resistance is evenly distributed along the length of the wire to avoid large voltage drops at specific locations, thereby preventing heat buildup at those locations. However, such materials effectively rectify the radio frequency waveform, producing a signal component that is at the same frequency as the ECG signal and that is one order of magnitude greater in amplitude. As a result, the rectified RF signal component is mistaken for an ECG signal that represents the heartbeat of the patient's heart. If the ECG signal is used to trigger the MR gating process as described above, the RF signal component will falsely trigger the process,
Generates artifacts in the MR image associated with the process.

A third solution to the problem of patient burns is to provide a protective thermal pad between the lead wire and the patient placed in the hole in the MR magnet. However, the pad is sometimes displaced from its protective position, causing the cable to contact the patient. Also, such pads cannot withstand extreme levels of heating. For example, it was found that the segment was inadvertently heated to a temperature of 700 ° F. due to the effect of the capacitance between the looped lead wire segment and the surface coil.

[0008]

SUMMARY OF THE INVENTION A signal emanating from an MR-processed object is passed through a radio frequency (RF) electromagnetic field associated with the MR process between a first position in proximity to the object and a second position identified. An electrical lead assembly is provided for transmission between. The lead wire assembly includes means for receiving a signal at a first location, a substantially lossless substrate extending from the signal receiving means to a second location, the signal receiving means and the second. A film of conductive material, such as a film of metal or metal oxide, deposited along the substrate between the locations. The film has a width and a thickness dimension, the thickness dimension being substantially smaller than the width dimension, and being substantially less than a skin depth of the conductive film material at an RF electromagnetic field at an RF frequency. small. Further, the assembly has an overlaminate material overlying the conductive film, the membrane being enclosed between the substrate and the overlaminate material.

In the preferred embodiment, the thickness dimension of the conductive film is selected to be small relative to the skin thickness in the RF field so that the film is substantially transparent to the RF field. It That is, only a negligible amount of RF energy is absorbed by the film. For example, the thickness of the membrane is chosen to be no greater than one hundredth of the skin thickness of the material used for the membrane.

In one embodiment, the lead wire assembly is so inexpensively designed that it can be disposed of after it has been used in an MR imaging process or other process. The signal receiving means in the first position has a device for easily engaging a normal electrode attached to the subject and supplying an electrical signal from the electrode to the membrane. This film forms a conductive path for signals through the RF field. The lead wire assembly has means at the second location for establishing an electrical connection between the conductive film and a conventional cable.

Accordingly, it is an object of the present invention to provide an electrical lead assembly having a conductive thin film signal path for use in close proximity to an RF field in an MR system. Another object is to sufficiently reduce MR image artifacts and heating effects associated with the use of lead wire assemblies in such environments.

Another object is to provide an electrical lead assembly in which the conductive film is almost completely transparent to the RF field. Another object is an electrical system suitable for MR systems having a uniform and high resistivity conducting path along its length to substantially reduce the flow of current through the conducting path and the resulting heating effect therein. It is to provide a lead wire assembly.

Another object is that the MR can be manufactured very cheaply.
The object is to provide a lead wire assembly that can be disposed of after being used once in a process. Another purpose is RF as described above.
It is to reduce artifacts in the MR imaging process by providing an electrical lead assembly that does not use non-metallic materials such as carbon semiconductors that rectify the signal and produce image artifacts.

These and other objects and advantages will become more readily apparent from the following description in conjunction with the accompanying drawings.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a patient 10 placed in a hole 12 in a main magnet 14 of a conventional magnetic resonance (MR) system (only the main magnet of the MR system is shown).
A pulsed RF electromagnetic field is generated in the magnet bore 12 as described above. Conventional electrodes 16 are attached to the patient and generate ECG electrical signals that result from the patient's activity, such as the heartbeat. Such a signal is also used, for example, as a trigger signal for the MR gating process as described above. Therefore, this signal must be transmitted from the electrode 16 to an electronic device 18, such as a conventional ECG monitor / trigger generator, anyway.

An electrical lead assembly 20 is provided to form a transmission path for signals through the RF field within the magnet bore 12, the lead assembly being constructed in accordance with the principles of the present invention. . The lead wire assembly 20 may extend from the electrode 16 to the monitor / generator 18, but the end of the assembly 20 opposite the electrode 16 is electrically connected to a conventional cable 22 just outside the hole 12. It has been found beneficial to extend it to the point where it is connected to. The other end of the cable 22 is connected to a preamplifier device (not shown) of the monitor / generator 18 for transmitting signals to the device. Lead wire assembly 20
Is removably connected to the cable 22 as described below in connection with FIGS. 2 and 6, or fixedly connected to the cable 22 as described below in connection with FIGS. 8 and 9. To be done.

FIG. 1 further illustrates a lead wire assembly 20 having multiple lead wires 24, each of which is electrically connected to a corresponding one of the electrodes 16 and is described below in connection with FIG. It has a coupling mechanism 26 which will be described in detail below. The assembly 20 having each of the leads 24 is a flat thin structure and is very flexible,
It is strong and durable enough for use in the environment of MR magnets.

FIG. 2 illustrates an assembly 20 having a substrate 28 of a material such as inexpensive polyester or alternatively polyamide. The length of the substrate 28 is the assembly 2
It is the same as the length of 0, which is on the order of 72 inches, but such a length is not critical to the practice of the present invention. A film of conductive material is deposited on the substrate 28 in the form of a number of traces 30. Each linear body 30
Extends from the connection pad 31 to the left (as shown in FIG. 2) along the longitudinal direction of the substrate 28 (and thus the assembly 20) to the connection pad 32. Each of the connection pads 31 and 32 beneficially has a silver ink layer printed in electrical connection with the plurality of linear bodies 30, as described below. The connection pad 32 is configured to engage with the cable 22 as described later. Coupling features 26 are crimped onto each lead 24 to make electrical contact with pads 31 (only one feature 26 is shown on lead 24 in FIG. 2).

FIG. 2 shows a large number of linear bodies 30 which are further grouped into a linear body group 34. Each group 34 corresponds to one of the lead wires 24. One linear body group 34
All the linear members of the lead wire 24 have the same connection pad 31.
And the connection mechanism 26 and the same connection pad 32. One linear body group 34
All of the linear bodies 30 of the same receive the same signal from the same electrode 16 and form an alternative transmission path for such a signal to the common connection pad 32.

Each of the coupling features 26 beneficially has a female portion of a conventional "dot snap" style connector which can be easily engaged and disengaged from a male connector element of a conventional electrode. The coupling mechanism 26 is formed of a conductive material such as non-ferrous metal or metal-filled plastic.
FIG. 2 shows a conductive film deposited on the substrate 28 in a pattern in which four linear bodies 30 are provided at intervals in each group 34. It should be noted that the number of four is not important for implementing the present invention. At a specified distance, all four filaments 30 of a group are connected to each other by a shorting bar 36. The shorting bar is also composed of a conductive film deposited on the substrate. The linear bodies are provided between the shorting bars 36 with a space therebetween. This method has only one linear body extending between the connecting pads 31 and 32, this only linear body having a width equal to the combined width of all the linear bodies 30 of the group 34. Dissipates and dissipates heat generated in the membrane filaments as a result of the action of the RF field more than the heat generated by this unique filament, as compared to what it would be assumed to have. I understood it. At the same time, by providing each shorting bar 36 as shown in FIG. 2, when a break occurs in one linear body between two adjacent shorting bars, the linear body runs along its entire length. It is not lost as a conductive path.

The aluminum-magnesium alloy is used to form the substrate 30 for forming the film filaments 30 and the shorting bars 36.
8 has been found to be particularly useful as a material deposited on. Such a material is deposited on the substrate 28, and the thickness of the linear body 30 (and the bar 36) of each film is on the order of 200 Å. This thickness is 1% of the skin thickness of the aluminum-magnesium material in the case of an electromagnetic field of RF frequency.
It is a stand.

As is well known, the skin thickness of the conductive material is
It is a linear dimension representing the depth into the material where the applied electromagnetic field decays to 37% of its value at the surface of the material for a particular electromagnetic field frequency. Since the thickness of the linear body 30 and the bar 36 of each aluminum-magnesium film is smaller than that of the skin in the case of the aluminum-magnesium material at the RF frequency, the linear body (and the bar) is formed.
Are substantially transparent to RF fields. That is,
A negligible amount of RF energy results in the conductive linear body 30.
And is only attenuated or absorbed within the membrane by the bar 36. Therefore, the lead assembly 20
The conductive film does not absorb much heat from the adjacent RF electromagnetic field. Further, the conductive film does not absorb the RF energy including the imaging information. This prevents the lead assembly from blocking the subject to be imaged. This occlusion creates artifacts in the MR image.

The electromagnetic field in the MR environment produces a difference in the electric field along the longitudinal direction of the lead wire assembly provided therein. This difference causes a current flow along the lead assembly that contributes to the generation of heat. Therefore, it is highly desirable to provide a conductive path for the lead wire assembly 20 that is composed of a wire 30 having a high resistivity that limits the flow of current as much as possible. The specific resistance of the aluminum-magnesium alloy used for the linear body 30 is 110 ohm / square, which is a sufficiently high value. The width of the linear body 30 is on the order of 0.025 inch, and the same linear body group 3
Adjacent filaments 30 within 4 are advantageously separated from each other by a distance on the order of 0.1 inches. It is useful to provide the shorting bars 36 at intervals of the order of 3 inches along each linear body group.

Conventional film deposition techniques may be used to form the linear body 30 and the shorting bar 36 on the substrate 28 with sufficient accuracy to maintain the above dimensions along the entire length of the substrate 28. I found out. To protect the metal film deposits on the substrate 28, a protective overlay 38, usually formed of polyester but thinner than the polyester substrate material, is provided over the substrate 28, the wire 30 and the shorting bar 36. And is attached to the substrate by an adhesive. Both the polyester material used for substrate 28 and the polyester material for overlay 38 may be transparent or opaque.

The overlay layer 38 includes the substrate 28 and the linear body 30.
After being provided above, the lead wire 24 is formed by forming a notch in the substrate and the overlayer and forming the slot 40 between the adjacent linear body groups 34. Slots 40 are 3-12 inches long and each lead 24
Can be separated from each other and spread, and can be attached to each electrode 16.

FIG. 2 further shows the cable 22 having a cable end 42. A large number of clamps 44 having a small insertion force are provided at the end of the cable. One clamp 44 is provided for each linear body group 34 and silver ink pad 32.
It corresponds to. With further reference to clamp 44 with reference to FIG. 6, clamp 44 is configured to collectively receive the left end of assembly 20 as shown in FIG. Each clamp 44 has a contact element 46 that is brought into electrical contact with the corresponding silver ink pad 32 when the clamp and assembly 20 are engaged. In addition, the cable 22 has a number of conductors 48, each conductor being connected to each of the contact elements 46.

FIG. 3 shows a linear body 3 having a width w and a thickness t.
0 is shown. Their width w and thickness t are on the order of 0.025 inches and 200 Angstroms, respectively, as described above. Adjacent linear bodies 30 of the same linear body group 34 are separated by a center interval s of the order of 0.1 inch. As described above, the polyester overlay 38 is provided on the linear body and the substrate 28.

4 and 5 respectively show a shorting bar 36.
And a cross-sectional view through the printed ink pad 32. FIG. 6 illustrates a clamp 44 configured to support a contact element 46 spaced from a resilient element 50.
Is shown. A portion of the end of the assembly 20 and the silver ink pad 32 thereon is provided with a contact element 46 and an elastic member 50.
Is movable into the space between, where the elastic member 50 pushes the assembly part upwards as shown in FIG.
The ink pad 32 is held in electrical contact with the contact element 46.

FIG. 7 shows a sectional view through the mechanism portion 26 and the connecting pad 31. FIG. 8 shows a modification of the present invention. In this variation, a protective outer layer of rubberized material 52 is provided on the lead wire assembly 20 shown in FIG. Also, a normal electrode clip 54 is connected to each linear body 30 of the lead wire 24 to make contact with the electrode 16. The rubberized material 52 is shown removed from the top lead 24 of FIG. 8 to show the attachment of the clip 54 to the wire 30. The silver ink pad 56 is printed on the linear body 30,
The conductive element 58 is crimped onto the pad 56 and extends outward from the pad 56. Conductor 58 is solder 62
Is joined to the conductive lead wire 60 of the clip 54. The conductor 58 and the solder 62 are supported by an end member 64 joined to the end of each lead wire 24.

FIG. 8 further illustrates one of the linear bodies 30 of the group of linear bodies 34 connected to the conductor 48 of the cable 22 with a portion of the rubberized material 52 removed. Solder 66 is used to electrically connect conductive element 68 crimped onto silver ink pad 32 in electrical contact with conductor 48. FIG. 9 shows the lead wire assembly 2
Protective rubberized material 52 around 0
It is sectional drawing which further shows.

While the preferred embodiment of the invention has been shown and described, it is to be understood that such embodiment is provided by way of example only. Many modifications, variations and substitutions will occur to those skilled in the art without departing from the spirit of the invention. For example, the lead assembly of the present invention can be used in different diagnostic imaging applications such as computed tomography (CT). In such applications, the conductive film receives X-rays, but is dimensioned to be transparent to the X-rays.

The claims are intended to cover all such modifications as fall within the spirit and scope of the invention.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention used with an MR magnet.

2 is a plan view showing the embodiment of FIG. 1 in more detail, FIG.
The intermediate layer is removed and omitted and a portion of the transparent overlaminate layer is removed to further clarify the substrate layer.

3 is a cross-sectional view taken along line 3-3 of FIG.

4 is a cross-sectional view taken along line 4-4 of FIG.

5 is a cross-sectional view taken along line 5-5 of FIG.

FIG. 6 is a view along line 6-6 of FIG.

7 is a cross-sectional view taken along line 7-7 of FIG.

FIG. 8 shows a modification of the embodiment shown in FIG. 2, in which the same intermediate part as in FIG. 2 has been removed.

9 is a cross-sectional view taken along the line 9-9 of FIG.

[Explanation of symbols]

14 Main magnet 16 electrodes 18 Monitor / Generator 20 Lead wire assembly 22 cable 24 lead wire 28 substrate 30 linear objects 34 linear bodies 36 Shorting bar 38 Upholstery

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Daniel Joseph Schaefer, No. 2824, Mainut Lane, Woksha, Wisconsin, USA (56) Reference JP-A-60-215349 (JP, A) JP Heihei 4-109933 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) A61B 5/055

Claims (15)

(57) [Claims] 1. A signal generated from an MR-processed object is passed through a radio frequency (RF) electromagnetic field associated with the MR processing between a first position in proximity to the object and a specified second position. An electrical lead assembly for transmission between, the positionable at the first position, the means for receiving the signal, and extending between the signal receiving means and the second position. A substantially lossless substrate disposed in such a manner, and a conductive material deposited along the substrate and disposed to extend between the signal receiving means and the second position. A film, the conductive film having a width dimension and a thickness dimension substantially smaller than the width dimension, the thickness dimension forming the film with respect to the RF electromagnetic field. An electrical lead assembly which is substantially smaller than the skin thickness of the. 2. The electrical conductivity of claim 1, wherein the thickness dimension of the conductive film is selected with respect to the skin thickness of the film material such that the film is substantially transparent to RF electromagnetic fields. Lead wire assembly. 3. The electrical lead wire assembly of claim 2, wherein the thickness of the conductive film is no greater than one-hundredth of the thickness of the skin of the film material. 4. The conductive film is deposited as one or more conductive linear bodies extending between the signal receiving means and the second position, each of the linear bodies having its own conductive line. The electrical lead wire assembly of claim 2 having a uniform resistivity along its length. 5. The electrical lead assembly of claim 1, wherein the assembly further comprises an overcoat material overlying the conductive film, the conductive film being surrounded between the substrate and the overcoat material. Three-dimensional. 6. A plurality of conductive linear bodies extending between the signal receiving means and the second position with a parallel interval, and a plurality of conductive linear objects at specific intervals along the longitudinal direction. The electrical lead wire assembly according to claim 1, wherein the conductive film is deposited so as to form a pattern having a shorting bar that electrically connects the linear bodies. 7. The signal receiving means detachably connects a selected one group of linear bodies of the plurality of linear bodies to an electrode connected to a subject at the first position. The electrical lead assembly according to claim 6, comprising: 8. The signal receiving means is detachably connectable to the electrode and is fixed to the substrate so as to be electrically conductive with each of the selected group of linear bodies. The electrical lead wire assembly of claim 7 having a snap connector. 9. The electrical lead assembly of claim 1, wherein the material used for the conductive film comprises a specified aluminum-magnesium alloy. 10. The substrate has a substantially flat surface, and the conductive films are arranged in parallel with each other at intervals and extend in the longitudinal direction of the substrate. The electrical lead assembly of claim 1, wherein the electrical lead assembly is deposited as a wire on the flat surface. 11. The electrical lead wire of claim 10, wherein the spacing between adjacent linear bodies is selected to be substantially greater than the width dimension of each linear body to increase heat dissipation. Assembly. 12. The plurality of linear bodies are grouped into a linear body group, and the shorting bars are arranged at a specific interval along the longitudinal direction of the linear body.
The electrical lead wire assembly of claim 11, wherein the wires of the group are electrically connected to each other. 13. A signal generated from an MR-processed subject is transmitted between a first position proximate to the subject and a specified second position through an RF field associated with the MR process. An electrical lead assembly, comprising: a conductive film extending between the first position and the second position, the conductive film being arranged to receive the signal at the first position. However, the conductive film is chosen such that its thickness dimension is small relative to the skin thickness of the material used for the film at the frequency of the RF field, such that the film is substantially resistant to the RF field. An electrical lead assembly having a non-conductive material that is transparent to, and that further supports the conductive film along its length and electrically insulates the film. 14. The conductive film is deposited as one or more conductive linear bodies on the non-conductive material.
3. The electrical lead wire assembly according to item 3. 15. An electrical lead that provides a signal to an identified second position from an electrode attached to a subject of the diagnostic imaging process at a first position through an electromagnetic radiation field associated with the diagnostic imaging process. An assembly, comprising a film of electrically conductive material arranged to extend between the first and second positions, the film having a thickness dimension in the electromagnetic radiation field. Is selected to be small relative to the skin thickness of the material forming the film at, the film being substantially transparent to electromagnetic radiation, and further non-supporting the conductive film along its length. An electrical lead assembly comprising a conductive material and means fixed to the film and the non-conductive material for supplying a signal from the electrode to the conductive film.