Inherently de-coupled sandwiched solenoidal array coil

• US 6,751,496 B2
• Filed: 08/24/2001
• Issued: 06/15/2004
• Est. Priority Date: 09/30/1999
• Status: Expired due to Term

• Current Assignee: Toshiba America MRI Incorporated (Toshiba Corporation)
• Original Assignee: Toshiba America MRI Incorporated (Toshiba Corporation)
• Inventors: Arakawa, Mitsuaki, Su, Sunyu, Kaufman, Leon
• Primary Examiner(s): Shaw, Shawna Jeannine
• Application Number:
  US09/935,705
• Publication Number:
  US 20020013526A1
• Time in Patent Office: 1,026 Days
• Field of Search: 600/422, 600/410, 324/318, 324/322
• US Class Current: 600/422
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels

Abstract

An inherently de-coupled sandwiched solenoidal array coil (SSAC) is disclosed for use in receiving nuclear magnetic resonance (NMR) radio frequency (RF) signals in both horizontal and vertical-field magnetic resonance imaging (MRI) systems. In its most basic configuration, the SSAC comprises two coaxial RF receive coils. The first coil of the array has two solenoidal (or loop) sections that are separated from one another along a common axis. The two sections are electrically connected in series but the conductors in each section are wound in opposite directions so that a current through the coil sets up a magnetic field of opposite polarity in each section. The second coil of the SSAC is disposed (“sandwiched”) between the two separated solenoidal sections of the first coil in a region where the combined opposing magnetic fields cancel to become a null. Due to the winding arrangement and geometrical symmetry, the receive coils of the array become electromagnetically “de-coupled” from one another while still maintaining their sensitivity toward receiving NMR signals. The multiple coil array arrangement also allows for selecting between a larger or smaller field-of-view (FOV) to avoid image fold-over problems without time penalty in image data acquisition. Alternative embodiments are disclosed which include unequal constituent coil diameters, unequal constituent coil windings, non-coaxial coil configurations, a three-coil quadrature detection (QD) SSAC arrangement, multiple SSAC arrangements, and optimized SSAC configurations for breast imaging in both horizontal and vertical-field MRI systems.

Claims

1. In a MRI system having multiple data acquisition channels for producing images from NMR signals emanating from a subject irradiated with an RF excitation pulse in the presence of a static polarizing magnetic field, said system having a sandwiched solenoidal array coil for receiving the NMR signals emanating from a region of interest in the subject, said sandwiched solenoidal array coil comprising a plurality of coil elements wherein at least one array coil element is a first solenoidal loop coil sandwiched between a pair of solenoidal coil sections having opposite conductor winding directions and which form a second array coil element distinct from said first coil, a method for providing field-of-view (FOV) switching without incurring substantial data fold-over artifacts or significantly increasing data acquisition time, comprising:

a) providing NMR signals received by the first solenoidal loop coil to a first data acquisition channel of the MRI system for processing;

b) providing NMR signals received by the sandwiching pair of solenoidal coil sections which form the separate second array coil element to a second data acquisition channel of the MRI system for processing;

c) during an MRI scanning sequence, acquiring and storing data from both the first and the second data acquisition channels simultaneously; and

d) after acquiring NMR signal data for producing an image, selecting between;

(i) processing NMR signal data acquired from both the first and the second data acquisition channels together to produce a large FOV image or (ii) processing NMR signal data acquired from either said first or said second data acquisition channel alone to produce a small FOV image.

2. A method for providing field-of-view (FOV) switching as set forth in claim 1, wherein the sandwiched solenoidal array coil further includes a saddle-coil element sandwiched between said pair of solenoidal coil sections and NMR signals received by the saddle-coil element are provided to a third data acquisition channel from which NMR signal data is acquired simultaneously with NMR signal data acquired from said first and second data acquisition channels and wherein, in step (d), an alternative large FOV image is selected by processing NMR signal data acquired from said third data acquisition channel together with NMR signal data acquired from said first and/or said second data acquisition channels and a small FOV image is produced by processing NMR signal data acquired only from one of said first, second or third data acquisition channel.

3. In an MRI system having multiple NMR signal data acquisition channels for producing images from NMR signals emanating from a subject irradiated with a sequence of RF excitation pulses in the presence of a static polarizing magnetic field and associated sequences of orthogonal gradients therein, said system having a plurality of sandwiched solenoidal array coils for receiving the NMR signals emanating from one or more regions of interest in the subject, said sandwiched solenoidal array coils comprising a plurality of coil elements wherein at least one coil element is a first solenoidal loop coil and at least one coil element is a split-apart solenoidal loop disposed to encompass the first solenoidal loop, a method for selectively obtaining images from different regions of interest in the subject, said method comprising the steps of:

a) providing NMR signals received by a first sandwiched solenoidal array coil, selectively located at a first region of interest on the subject, to a first data acquisition channel of the MRI system for processing;

b) providing NMR signals received by a second sandwiched solenoidal array coil, selectively located at a second region of interest on the subject, to a second data acquisition channel of the MRI system for processing; and

c) selecting between processing signal data acquired from the first data acquisition channel or the second data acquisition channel to produce an image, wherein an image produced from the first data acquisition channel covers a different region of interest than an image produced from the second data acquisition channel.

4. In an MRI system having multiple data acquisition channels for producing images from NMR signals emanating from a subject irradiated with a sequence of RF excitation pulses in the presence of a static polarizing magnetic field and associated sequences of orthogonal gradients therein, said system employing a sandwiched solenoidal array coil (SSAC) antenna apparatus for receiving the NMR signals emanating from a region of interest in the subject, said SSAC antenna apparatus comprising a plurality of antenna elements wherein at least one antenna element is a first solenoidal loop coil and at least one antenna element is a split apart solenoidal coil comprising axially separated sections wherein conductor winding directions are opposite in each of the separated sections so as to create magnetic field bucking in a region between said separate sections which encompasses at least said first loop coil antenna element, a method for selectively producing different sized FOV images from within a predetermined region of interest on said subject'"'"'s body, wherein fold-over artifacts and/or resonance frequency splitting is significantly reduced or eliminated, said method comprising the steps of:

positioning the SSAC antenna apparatus about the subject'"'"'s body over the predetermined region of interest;

during an MRI scanning sequence, simultaneously acquiring NMR signals from a plurality of individual antenna elements of the SSAC antenna apparatus, each antenna element connected to a separate data acquisition channel of the MRI apparatus; and

selectively processing NMR signal information acquired from one or more data acquisition channels to produce different sized FOV images.

5. In a MRI system having multiple data acquisition channels for producing images from NMR signals emanating from a subject irradiated with a sequence of RF excitation pulses in the presence of a static polarizing magnetic field and associated sequences of orthogonal gradients therein, said system having a sandwiched solenoidal array coil (SSAC) antenna apparatus for receiving the NMR signals emanating from a region of interest in the subject, a method for simultaneously imaging the head and neck portions of a human patient, said method comprising the steps of:

a) fitting the head and neck portions of a patient with a sandwiched solenoidal array coil antenna apparatus comprising a separated solenoidal coil element having separated coil winding portions of different diameter corresponding to respective head and neck portions of a patient, the coil winding portion corresponding to the neck of the patient having a smaller diameter and a correspondingly greater quantity of conductive windings than a coil winding portion corresponding to the head of the patient, such that magnetic fields emanating from the separated coil winding portions become a null over a region between the separated coil winding portions encompassing at least one further solenoidal loop coil element comprising the SSAC antenna apparatus;

b) orienting the patient fitted in step (a) with said sandwiched solenoidal array coil antenna apparatus within the MRI apparatus such that a primary RF magnetic field, {overscore (B)}₁, of the antenna apparatus is substantially orthogonal to a main polarizing magnetic field of the MRI apparatus; and

c) using said sandwiched solenoidal array coil antenna apparatus to receive NMR signals during an imaging operation of the MRI apparatus.

6. A method for simultaneously imaging the head and neck portions of a human patient as set forth in claim 5 wherein the coil winding portion corresponding to the neck of the patient comprises a plurality of detachable conductive windings.

7. A method for simultaneously imaging the head and neck portions of a human patient as set forth in claim 5, further comprising:

during an MRI scanning sequence, simultaneously acquiring NMR signals from said separated solenoidal coil element and from said solenoidal loop coil element, each antenna element connected to a separate data acquisition channel of the MRI apparatus; and

processing NMR signal information acquired from each data acquisition channel to produce a composite image.

8. In a MRI system having multiple data acquisition channels for producing images from NMR signals emanating from a subject irradiated with a sequence of RF excitation pulses in the presence of a static polarizing magnetic field and associated sequences of orthogonal gradients therein, said system having a sandwiched solenoidal array coil (SSAC) antenna apparatus for receiving the NMR signals emanating from a region of interest in the subject, said SSAC comprising at least one sandwiched solenoidal loop antenna element and a sandwiching second antenna element having first and second axially separated solenoidal coil sections that have current conducting windings in opposite directions, wherein said first coil section is of a larger diameter than said second coil section and wherein said second section comprises a plurality of current conducting loop winding portions that are detachably connected together, a method for simultaneously imaging head and neck portions of a human patient, comprising:

fitting the head portion of the patient with the first coil section and the sandwiched solenoidal loop antenna element of the SSAC antenna apparatus;

fitting the neck portion of the patient with a sufficient quantity of said detachably connected current conducting loop winding portions of the second coil section of the SSAC antenna apparatus to result in a nullifying of magnetic fields emanating from the axially separated first and second coil sections in a region between said first and second coil sections that encompasses the sandwiched solenoidal loop antenna element;

orienting said patient along with the SSAC antenna apparatus within the MRI apparatus such that a primary RF magnetic field corresponding to the SSAC antenna apparatus is substantially orthogonal to a main polarizing magnetic field of the MRI apparatus; and

using said sandwiched solenoidal array coil antenna apparatus to receive NMR signals during an imaging operation of the MRI apparatus.

9. A method for simultaneously imaging the head and neck portions of a human patient as set forth in claim 8 further comprising:

during an MRI scanning sequence, simultaneously acquiring NMR signals from said sandwiched solenoidal loop antenna element and said sandwiching second antenna element, each antenna element connected to a separate data acquisition channel of the MRI apparatus; and

processing NMR signal information acquired from each data acquisition channel to produce an image.