Surface coil system for magnetic resonance imaging

• US 4,793,356 A
• Filed: 08/14/1985
• Issued: 12/27/1988
• Est. Priority Date: 08/14/1985
• Status: Expired due to Term

• Current Assignee: Picker International, Inc. (Koninklijke Philips N.V.)
• Original Assignee: Picker International, Inc. (Koninklijke Philips N.V.)
• Inventors: Misic, George J., Orlando, Paul T., Holland, G. Neil, Hurst, Gregory C., Patrick, John L. III
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US06/765,708
• Time in Patent Office: 1,231 Days
• Field of Search: 128/653, 128/798, 128/1.3-1.5, 324/307, 324/309, 324/318, 324/322, 324/300, 343/741, 343/742
• US Class Current: 600/422
• CPC Class Codes: G01R 33/341 comprising surface coils
• CPC Class Codes: G01R 33/3628 Tuning/matching of the transmit/receive coil

Abstract

A resonance exciting coil (C) excites magnetic resonance in nuclei disposed in an image region in which a main magnetic field and transverse gradients have been produced. A flexible receiving coil (D) includes a flexible plastic sheet (40) on which one or more loops (20) are adhered to receive signals from the resonating nuclei. Velcro straps (46) strap the flexible sheet and the attached coil into close conformity with the surface of the portion of the patient to be imaged. An impedance matching or coil resonant frequency adjusting network (50) is mounted on the flexible sheet for selectively adjusting at least one of an impedance match and the peak sensitivity resonant frequency of the receiving coil. A preamplifier (52) amplifies the received signals prior to transmission on a cable (24). A selectively variable voltage source (70) applies a selectively adjustable DC bias voltage to the cable for selectively adjusting at least one of the impedance match and the LC resonant frequency of the receiving coil. The received signals are amplified by an amplifier (82) and processed by an image processor (30) to form man-readable images of the examined region of the patient for display on a video display (32) or the like.

Claims

1. A magnetic resonance imaging apparatus comprising:

a main magnetic field generating means for generating a main magnetic field longitudinally along an image region;

a gradient field means for producing magnetic field gradients across the main magnetic field in the image region;

a magnetic resonance excitation means for exciting nuclei of an object in the image region to resonate, the resonating nuclei generating radio frequency resonance signals;

a flexible coil disposed in conformity with a selected surface portion of the object for at least receiving the resonance signals;

a first variable capacitance means mounted to the flexible coil for selectively adjusting a resonant frequency thereof under control of a received resonance frequency adjusting signal;

a second variable capacitance means operatively connected with the coil for selectively adjusting an impedance match thereof under control of an impedance adjusting signal;

a common electrical conductor connected to the coil and the first and second variable capacitance means for concurrently conveying the resonance signals from the coil and resonance frequency and impedance adjusting signals to the first and second variable capacitance means;

a control means connected to the electrical conductor for applying the resonant frequency and impedance adjusting signals thereto; and

,

an image reconstruction means for reconstructing a representation of an image of resonating nuclei position and density, the image reconstruction means being operatively connected with the electrical conductor.

2. A receiving apparatus for receiving radio frequency resonance signals from resonating nuclei in a magnetic resonance apparatus, the apparatus comprising:

a radio frequency receiving coil means which is disposable in the magnetic resonance apparatus for receiving the resonance signals and including;

a first electrically conductive loop;

a second electrically conductive loop arranged concentrically with and connected electrically in parallel with the first loop such the inductance of the parallel connected loops is less than the inductance of the each of the first and second loops, the parallel connected first and second loops being configured to be disposed adjacent resonating nuclei to receive the resonance signals therefrom;

a third conductive loop arranged concentrically with the first and second loops and electrically interconnected therewith by a signal combining means which subtractively combines a current signal induced in the third loop with current signals induced in the first and second loops;

a preamplifier means operatively connected with the first and second conductive loops for amplifying the received resonance signals;

a signal processing circuit connected with the preamplifier.

3. The apparatus as set forth in claim 2 further including a capacitive network operatively connected with the conductive loops such that the conductive loops and the capacitive network form an LC resonance circuit and a resonant frequency adjusting means operatively connected with the first and second loops and the capacitive network for adjusting the LC resonance frequency thereof.

4. A receiving apparatus for receiving radio frequency resonance signals from resonating nuclei which are excited to resonance within a magnetic resonance imager, the apparatus comprising:

an electrically conductive coil which is selectively disposed in the magnetic resonance imager to receive the resonance signals;

a preamplifier means mounted on the coil and electrically connected with the coil for amplifying the received resonance signals;

a conductive lead extending from the preamplifier to a remotely located signal processing circuit for conveying the amplifier resonance signals thereto;

an adjusting means for selectively adjusting at least one of a resonant frequency of the coil and an impedance match between the coil and the preamplifier means, the adjusting means being mounted on the coil and electrically connected with the conductive lead which carries the preamplified resonance signal from the preamplifier to the remotely located signal processing circuit, the adjusting means being selectively controlled by an adjustment signal received on the conductive lead for adjusting the at least one of the resonant frequency an the impedance match; and

,

a remotely located adjustment control means for selectively applying the adjustment signal to the control lead adjacent the remotely located processing circuit such that the same control lead is utilized both to convey resonance signals from the coil to the signal processing circuit and to convey adjustment signals form the remotely located control means to the coil.

5. The apparatus as set forth in claim 4 wherein the conductive lead is a triaxialy cable which has an outer, electrically conductive sheath that is connected to a fixed ground and two inner conductors, the resonance signal being conducted as a potential across the two inner conductors;

and,

wherein the adjusting means includes a resonant frequency adjusting means and an impedance matching adjustment means, the resonance frequency adjusting means and the impedance adjusting means each being operatively connected with a different two of the sheath and two inner conductors of the triaxial cable.

6. The apparatus as set forth in claim 4 wherein the preamplifier means includes an input transistor which has a high impedance and a reactive component, the input transistor being connected with the coil such that the reactive component of the transistor affects the resonant frequency of the coil.

7. A magnetic resonance apparatus comprising:

means for exciting nuclei in a preselected resonance region to resonance such that magnetic resonance signals are generated thereby;

a receiving coil for receiving magnetic resonance signals from only a preselected subregion of the preselected region, the receiving coil including;

a first conductive loop having first and second end portions and disposed in the resonance region generally around the sub-region such that the resonance signals from the subregion and portions of the resonance region around the subregion induce a first current signal in the first conductive loop flowing with a first polarity from the first end portion to the second end portion;

a second conductive loop having first and second end portions and extending around the first conductive loop such that resonance signals primarily of the resonance region portions around the subregion induce a second current signal in the second conductive loop flowing with the first polarity from the first end portion to the second end portion;

means for interconnecting the first loop first end portion with the second loop second end portion and interconnecting the first loop second end portion with the second loop first end portion to interconnect the first and second loops in an anti-parallel relationship such that the first and second current signals are subtractively combined to produce a difference signal, whereby the resonance signals form the subregion and the resonance region portion around the subregion received by the first loop and the resonance signal primarily from the resonance region portions around the subregion received by the second loop are subtractively combined to cancel the resonance signals from the resonance region portion surrounding the subregion;

a signal processing means processing the difference signal, the signal processing means being operatively connected with the interconnecting means.